Report of work experience in Public
Telecommunication Corporation
Prepared by
Abdullah Al-Marwani
D‫ا‬erar Al-salahy
Emad Al-hasany
Mohammed Abdulwahab Al-Gahmi
Mojahed moaid
Omair Yousef Al-Jaadi
Supervised By
Dr. Jameel Sultan
Communication Engineering Department
Sana'a Community Collage
Sana'a
2021
List of abbreviation ................................................................................................................................................... V
List of figures .......................................................................................................................................................... XIV
List of tables ........................................................................................................................................................... XVI
CHAPTER 1.................................................................................................................................................................. 1
INTRODUCTION .......................................................................................................................................................... 1
1.1Introduction ...................................................................................................................................................... 1
1.2Training Background ......................................................................................................................................... 3
1.2.1Public Telecommunication Corporation. ................................................................................................... 3
1.2.2Services of PTC ........................................................................................................................................... 3
1.3Training Statement ........................................................................................................................................... 4
1.4Training Objectives ........................................................................................................................................... 4
1.5Training Limitations........................................................................................................................................... 4
CHAPTER 2.................................................................................................................................................................. 5
LITRTURE REVIEW ...................................................................................................................................................... 5
2.1.
Introduction ............................................................................................................................................... 5
2.2.
Microwave Department in Public Telecommunication Corporation. ........................................................ 5
-
Introduction ............................................................................................................................................... 5
-
Microwave communication systems ......................................................................................................... 5
-
Emergence of MW Communication ........................................................................................................... 5
-
Fundamental Parameters in MW Link ....................................................................................................... 5
-
digital microwave equipment .................................................................................................................... 5
-
Modulation Schemes Used in Digital Microwave Communication............................................................ 5
-
Diversity in Microwave Links...................................................................................................................... 5
-
Microwave antenna ................................................................................................................................... 5
-
Antenna Installation ................................................................................................................................... 5
-
Adjusting Antenna...................................................................................................................................... 5
-
Advantages of Microwaves & Disadvantages of Microwaves ................................................................... 5
-
Applications of Microwaves ....................................................................................................................... 5
2.3.
Optical Transmission (SDH) in Public Telecommunication Corporation. ................................................... 6
-
Introduction To SDH ................................................................................................................................... 6
-
Plesiochronous Digital Hierarchy (PDH) ..................................................................................................... 6
-
Limitations of PDH Network....................................................................................................................... 6
I
-
PDH multiplexing........................................................................................................................................ 6
-
Synchronization of Digital Signals SDH....................................................................................................... 6
-
Basic SDH Signal ......................................................................................................................................... 6
-
SDH Advantages ......................................................................................................................................... 6
-
SDH multiplexing ........................................................................................................................................ 6
-
PDH vs SDH | Difference between PDH and SDH ...................................................................................... 6
-
Transmission Hierarchies ........................................................................................................................... 6
-
The components of SDH............................................................................................................................. 6
-
SDH Protection Technologies ..................................................................................................................... 6
-
SDH network topologies and structures .................................................................................................... 6
2.4.
Switching network. .................................................................................................................................... 7
-
Introduction ............................................................................................................................................... 7
-
Switching system hierarchy ....................................................................................................................... 7
-
Classification of Switching Systems............................................................................................................ 7
-
Basics of a Switching System ...................................................................................................................... 7
-
Electronic Exchanges .................................................................................................................................. 7
-
The Advantages of Electronic Exchanges Switching Techniques ............................................................... 7
2.5.
Switching Technology (NGN) in Public Telecommunication Corporation. ................................................ 7
-
Introduction of Next Generation Networking (NGN)................................................................................. 7
-
TDM Service Architectures......................................................................................................................... 7
-
NGN Network Architecture and Network Elements .................................................................................. 7
-
Benefits of a Next Generation Services Architecture ................................................................................ 7
-
Characteristics of NGN in contrast with TDM. ........................................................................................... 7
-
NGN Technology Operation. ...................................................................................................................... 7
-
How does PSTN work with NGN ................................................................................................................ 7
-
Application of NGN .................................................................................................................................... 7
-
Advantages and disadvantages of NGN ..................................................................................................... 7
CHAPTER 3.................................................................................................................................................................. 8
PROJECT METHODOLOGY .......................................................................................................................................... 8
3.1. Introduction .................................................................................................................................................... 8
3.2. Training plan.................................................................................................................................................... 8
CHAPTER 4.................................................................................................................................................................. 9
II
ANALYZING & DISCUSSION ........................................................................................................................................ 9
4.1.
4.1.1.
Introduction ............................................................................................................................................... 9
Training Reports ..................................................................................................................................... 9
Title: Microwave Department in Public Telecommunication Corporation at Operating and Maintenance
General Department. ...........................................................................................................................................11
-
Introduction ............................................................................................................................................... 5
-
Microwave communication systems ......................................................................................................... 5
-
Emergence of MW Communication ........................................................................................................... 5
-
Fundamental Parameters in MW Link ....................................................................................................... 5
-
digital microwave equipment .................................................................................................................... 5
-
Modulation Schemes Used in Digital Microwave Communication............................................................ 5
-
Diversity in Microwave Links...................................................................................................................... 5
-
Microwave antenna ................................................................................................................................... 5
-
Antenna Installation ................................................................................................................................... 5
-
Adjusting Antenna...................................................................................................................................... 5
-
Advantages of Microwaves & Disadvantages of Microwaves ................................................................... 5
-
Applications of Microwaves ....................................................................................................................... 5
Title: Training in Public Telecommunication Corporation, at Operating and Maintenance General Department.
(Optical Transmission (SDH).................................................................................................................................34
-
Introduction To SDH ................................................................................................................................... 6
-
Plesiochronous Digital Hierarchy (PDH) ..................................................................................................... 6
-
Limitations of PDH Network....................................................................................................................... 6
-
PDH multiplexing........................................................................................................................................ 6
-
Synchronization of Digital Signals SDH....................................................................................................... 6
-
Basic SDH Signal ......................................................................................................................................... 6
-
SDH Advantages ......................................................................................................................................... 6
-
SDH multiplexing ........................................................................................................................................ 6
-
PDH vs SDH | Difference between PDH and SDH ...................................................................................... 6
-
Transmission Hierarchies ........................................................................................................................... 6
-
The components of SDH............................................................................................................................. 6
-
SDH Protection Technologies ..................................................................................................................... 6
-
SDH network topologies and structures .................................................................................................... 6
III
Title: Training in Public Telecommunication Corporation, at Operating and Maintenance General Department.
(switching network PSTN) ....................................................................................................................................53
-
Introduction ............................................................................................................................................... 7
-
Switching system hierarchy ....................................................................................................................... 7
-
Classification of Switching Systems............................................................................................................ 7
-
Basics of a Switching System ...................................................................................................................... 7
-
Electronic Exchanges .................................................................................................................................. 7
-
The Advantages of Electronic Exchanges Switching Techniques ............................................................... 7
Title: Training in Public Telecommunication Corporation, at Operating and Maintenance General Department.
..............................................................................................................................................................................79
-
Introduction of Next Generation Networking (NGN)................................................................................. 7
-
TDM Service Architectures......................................................................................................................... 7
-
NGN Network Architecture and Network Elements .................................................................................. 7
-
Benefits of a Next Generation Services Architecture ................................................................................ 7
-
Characteristics of NGN in contrast with TDM. ........................................................................................... 7
-
NGN Technology Operation. ...................................................................................................................... 7
-
How does PSTN work with NGN ................................................................................................................ 7
-
Application of NGN .................................................................................................................................... 7
-
Advantages and disadvantages of NGN ..................................................................................................... 7
Chapter 5 ..................................................................................................................................................................90
Difficulties and Facilitates ........................................................................................................................................90
5.1Introduction ....................................................................................................................................................90
5.2 Difficulties ......................................................................................................................................................90
5.2.1 Academic Difficulties ...............................................................................................................................90
5.2.2 Difficulties during filed visit.....................................................................................................................90
5.3 Facilities..........................................................................................................................................................91
5.3.1 Academic Facilities ..................................................................................................................................91
5.3.2 Facilities during filed visit ........................................................................................................................91
Certificates of Training Course .............................................................................................................................91
IV
List of abbreviation
AT&T
American Telephone & Telegraph
MSC
mobile switching center
BS
base station
MS
Mobile station
PSTN
public switched telephone network
AMPS
Advance mobile phone system
WWWW
World-Wide Wireless Web
DAWN
Dynamic ad-hoc Wireless Networks
WMAN
Wireless Metropolitan Area Networks
WPAN
Wireless Personal Area Network
UMTS
Universal Mobile Telecommunication system
CDMA
code division multiple access
V
TDMA
time division multiple access
TG
Telecom Generations
AMTS
advanced mobile telephone system
MTS
mobile telephone system
OLT
offending land mobile telephone
PTT
push to talk
IMTS
improved mobile telephone service
PALM
Public Automated Land Mobile
VHF
Very high frequency
TACS
total access communication system
NMT
Nordic mobile telephone
GSM
Global System for Mobile communications
VI
GPRS
General packet radio service
SGSN
The Serving GPRS Support Node
GGSN
The Gateway GPRS Support Node
GMSC
gateway MSC
CS
Coding Schemes
VMSC
visited MSC
PCS
Personal Communication Services
WAP
wireless application Protocol
HSCSD
high speed circuit switched data,
MLS
Mobile location service
ETSI
the European Telecommunications Standards Institute
ME
Mobile Equipment
SIM
subscriber identity module
BSS
Base Station Subsystem
BSC
base station controller
BTS
base transceiver stations
HLR
Home location register
VII
VLR
Visitor location register
AuC
Authentication center database
EIR
Equipment identity register database
MAP
Mobile application part
TIA
Telecom Industry Association
MMS
Multimedia message services
EDGE
Enhanced Data Rates for GSM Evolution
GMSK
Gaussian minimum-shift keying
HSCSD
High-Speed Circuit-Switched Data
SMS
short message service
8- PSK
8- phase shift keying
W-CDMA
Wideband CDMA
IMT-2000
International Mobile Telecommunications-2000
OHG
Operator Harmonization Group
G3G
Global Third Generation
UE
User Equipment
UTRAN
UMTS Terrestrial Radio Access Network
RNC
Radio Network Controller
TDD
Time Division Duplex
FDD
frequency Division Duplex
VIII
HSPA
High-Speed Packet Access
MIMO
Multiple Input Multiple Output
HSDSCH
High Speed Downlink Shared Channel
QoS
Quality of service
H-ARQ
Hybrid Automatic Repeat Request
LTE
Long Term Evolution
HSOPA
High Speed OFDM
RTT
Round Trip Time
ITU
International Telecommunication Union
TD-SCDMA
Time Division Synchronous CDMA
DS- CDMA
Direct-Sequence Code Division Multiple Access
OFDMA
Orthogonal Frequency Division Multiple Access
SAE
System Architecture Evolution
IX
EPC
Evolved Packet Core
UEs
User Equipment
eNodeB
evolved Node B base stations
E-UTRA
Evolved Universal Terrestrial Radio Access
MME
The Mobility Management Entity
SGW
The Serving Gateway
PGW
The Packet Data Network Gateway
HSS
The Home Subscriber Server
ANDSF
Access Network Discovery and Selection Function
ePDG
The Evolved Packet Data Gateway
PLMN
providers Public Land Mobile Network
PCRF
The Policy and Charging Rules Function
CRF
the Charging Rules Function
IMT Advanced
International Mobile Telecommunications Advanced
HDTV
High Definition Television
X
WiMAX
World Interoperability for Microwave Access
LAN
Local area network
IJNGN
International Journal of Next-Generation Networks
ISD
Inter Site Distance
CA
Carrier Aggregation
PAPR
Peak to Average Power Ratio
SC-FDMA
single carrier FDMA
TSP
Telecom Service Providers
RF
Radio Frequency
SNR
Signal to Noise Ratio
LOS
Line of sight
3rd Generation Partnership Project
3GPP
XI
IS-95
Interim Standard 95
RLP
radio link protocol
Internet service provider
ISP
Value added service providers
VASP
enhanced GPRS
EGPRS
Future Public Land Mobile Telecommunication System
FPLMTS
Universal Wireless Communications
UWC136
Adaptive Multi-Rate
AMR
Algebraic Code Exited Linear Prediction
ACELP
Mobile Telephony system D
MTD
Wireline Common Carriers
WCCs
Radio Common Carriers
RCCs
ES
expanded spectrum
XII
Adaptive Modulation and Coding
AMC
HARQ
Hybrid Automatic Request
XIII
List of figures
Figure 4.2.1. Electromagnetic spectrum ...................................................................................................................... 12
Figure 4.2.2. Radio Frequency spectrum ..................................................................................................................... 12
Figure 4.2.3. Microwave radio relay link ....................................................................................................................... 14
Figure 4.2.4. A type Line of Sight (LOS) of a MW link ................................................................................................... 16
Figure 4.2.5 Transverse electromagnetic wave ............................................................................................................ 18
Figure 4.2.6 Microwave ODU in 1+0 Configuration with Antenna ............................................................................... 20
Figure 4.2.9. Basic horn antenna ................................................................................................................................... 22
Figure 4.2.10. A wave-guide will act as an inefficient radiator ...................................................................................... 23
Figure 4.2.11. Types of horn Antenna............................................................................................................................ 23
Figure 4.2.12. Dimensions of a horn .............................................................................................................................. 24
Figure 4.2.13. A Parabolic Dish ...................................................................................................................................... 25
Figure 4.2.14 Setting the antenna using north angle.................................................................................................... 27
Figure 4.2.15Elevation angle......................................................................................................................................... 27
Figure 4.2.16 Vertical Polarizations .............................................................................................................................. 28
Figure 4.2.17Horizontal polarization ............................................................................................................................ 28
Figure 4.2.19 networks properties................................................................................................................................ 30
Figure 4.2.20 Adjusting antenna ................................................................................................................................... 30
Figure .4.2.21 setting antenna line of sight .................................................................................................................. 31
Figure 4.3.1 PDH multiplexing by steps, showing add/drop function .......................................................................... 36
Figure 4.3.2 PDH level hierarchy used in North America .............................................................................................. 37
Figure 4.3.3. depicts PDH levels used in Europe ........................................................................................................... 38
Figure 4.3.4 SDH multiplexing ....................................................................................................................................... 40
Figure 4.3.4. Schematic diagram of hybrid communications networks ....................................................................... 43
Figure 4.3.5: block diagram of Regenerator ................................................................................................................ 43
Figure 4.3.6: block diagram of Terminal multiplexers .................................................................................................. 43
Figure 4.3.7: block diagram of Add/drop multiplexers ................................................................................................. 44
Figure 4.3.8: block diagram of Digital cross-connects .................................................................................................. 44
Figure 4.3.9: Line protection ......................................................................................................................................... 45
Figure 4.3.10: Unidirectional Ring Protection ............................................................................................................... 46
Figure 4.3.11: Bidirectional Ring Protection ................................................................................................................. 47
Figure 4.3.12: Sub-network connection protection ...................................................................................................... 47
XIV
Figure 4.3.13: A chain network with 1+1 protection .................................................................................................... 48
Figure 4.3.14: Ring network implemented using add and drop multiplexers. ............................................................. 49
Figure 4.3.15: The principle of Mesh network topology............................................................................................... 50
Figure 4.3.16: Star network........................................................................................................................................... 50
Figure 4.3.16: Tree network .......................................................................................................................................... 51
Figure 4.4.1 Public Switched Telephone Network (PSTN) ............................................................................................ 55
Figure 4.4.2 Point to point connection ......................................................................................................................... 56
Figure 4.4.3 switching system ....................................................................................................................................... 56
Figure 4.4.4 Switching system hierarchy ...................................................................................................................... 58
Figure 4.4.5 Subscriber Loop Systems .......................................................................................................................... 59
Figure 4.4.6 Local Loop ................................................................................................................................................. 60
Figure 4.4.7 Classification of Switching Systems........................................................................................................... 61
Figure 4.4.8 Switching network .................................................................................................................................... 63
Figure 4.4.9 The block diagram of the switching system .............................................................................................. 64
Figure 4.4.10: Block Schematic diagram of electronic exchanges ................................................................................ 67
Figure 4.4.11 Common control subsystem ................................................................................................................... 69
Figure 4.4.12 Circuit switching ...................................................................................................................................... 71
Figure 4.4.13 Pattern of Message switching ................................................................................................................. 72
Figure 4.4.14 A) A typical packet format. b) Packet switching network ....................................................................... 73
Figure 4.4.16 connection switching types..................................................................................................................... 74
Figure 4.4.17 Transfer modes and connection types.................................................................................................... 74
Figure 4.4.118 Time division space switch model......................................................................................................... 76
Figure 4.5.1 TDM Service Architectures–The Four Key Functions of Class 4/5 Digital Switch ..................................... 81
Figure 4.5.2 NGN layers architecture ............................................................................................................................ 83
Figure 4.5.3 NGN network architecture and network elements .................................................................................. 83
Figure 4.5.4 NGN network overall architecture ............................................................................................................ 85
Figure 4.5.6 The interconnecting between MGW and MGC/SS ................................................................................... 87
Figure 4.5.7 NGN Layers ................................................................................................................................................ 87
XV
List of tables
Table (3.1) Shows Training Table. ................................................................................................................................... 8
Table 4.5.1. Comparing between TDM and NGN technologies. ................................................................................... 86
XVI
CHAPTER 1
INTRODUCTION
1.1Introduction
Work experience is the part of an educational program that provides a student with an opportunity to
participate in, observe or learn about the performance of tasks and responsibilities related to an
occupation or career in the workplace.
Work experience is intended to help graduated students for the transition to the world of work or further
education and training. The community becomes the classroom where students gain knowledge and
experience about the workplace and are provided with a frame of reference to review or revise their
career goals. Work experience provides students with an opportunity to apply classroom learning in a
context outside of college and to bring back to the classroom new perspectives about their learning.
Through work experience students will have the opportunity to observe and practise generic
employability skills required in the workplace and, in some cases, to practise technical skills relating to
specific occupations.
Work experience is often offered between the second and final years of an undergraduate degree course,
especially in the science, engineering and computing fields. Courses of this nature are often called
sandwich courses, with the work experience year itself known as the sandwich year. During this time,
the students on work placement have the opportunity to use the skills and knowledge gained in their four
years, and see how they are applied to real world problems. This offers them useful insights for their
final year and prepares them for the job market once their course has finished. Some companies sponsor
students in their final year at university with the promise of a job at the end of the course. This is an
incentive for the student to perform well during the placement as it helps with two otherwise unwelcome
stresses the lack of money in the final year, and finding a job when the University course ends.
Workplace experience will complement your academic studies by providing another way of learning
outside the classroom. It will also provide you with crucial knowledge, skills and personal attributes that
employers look for.
1
A degree alone is not enough. Employers are looking for more than just technical skills and knowledge
of a degree discipline. They particularly value skills such as communication, team-working and problem
solving. Job applicants who can demonstrate that they have developed these skills will have a real
advantage."
There are many benefits of work experience and we list them below
-
It provides a different perspective and a context for academic learning, an opportunity to put
theory into practice.
-
It helps you develop ideas for final year projects, if such are part of your degree.
-
It offers opportunity to earn (sometimes – note that work experience can also be unpaid) and
hence reduce debt.
-
It will enhance employability by:
• Helping you work on a whole range of employment skills, from learning about and adapting
to workplace culture to time management and teamwork.
• Offering you the opportunity to network
• In some cases, rehiring you after graduating.
-
It will help you develop your chosen career but giving you a chance to see how different aspects
of it work, for example you may get the opportunity to see how marketing works differently
from sales.
-
It will help you develop personally.
Practical training means studying which takes place in a company or business, offering the student the
opportunity to adapt what she or he has learned in practice and develop professionally. Since practical
training is part of the student's studies, it must be well-planned and supervised.
In this training courses are going to show the knowledge that we gain from to field study at PTC.
2
1.2Training Background
1.2.1Public Telecommunication Corporation.
Public Telecommunication Corporation (PTC) is a public corporation of an economic nature which is
fully owned by government established in 1981. (PTC) enjoys a financial and administrative
independence, and subject to the provisions of Law No. (20) for the year 1981 and provisions of Law
No (38) for the year 1991 of Telecom law. PTC is working under supervision of Ministry
of Telecommunication and Information Technology.
PTC was established by Republican Decree No. (20) for the year 1981, as the responsible body for
achieving overall government objectives in telecommunication sector, through executing responsibilities
and purposes assigned in the provisions of its creation law and the Basic Law of Telecom starting in
1982.
After Yemen Unity in May 22nd 1990, Public Telecom Corporation in Sana’a was fully merged with
Authority of Telecom in Aden to become (PTC) Public Telecom. Corporation, which is responsible on
providing all Telecom. services and implementation of telecom projects in all Yemeni governorates.
PTC is considered as one of the most important service providers and successful leader in Yemen,
according to many surveys (questionnaires and public opinion) that conducted by a many official and
civil organization, including SABA news agency and September 26 newspaper. PTC has been awarded
the first and second position for best corporations in terms of excellency in providing services to the
public through the years 2004 and 2005
1.2.2Services of PTC
PTC mainly provides telecommunication and technology services to all citizens of society in both rural
and urban areas, to ensure the right of every citizen (individual, groups or sectors ) to get the benefits of
updated telecommunication and technology services with high quality, which (PTC) has undertaken
since its inception to meet those requirements, and keep up with these developments, and to respond the
needs of customers, and bearing in mind that “to achieve this” is the main objective through which
(PTC) reinforce its position and identity, especially in a world where telecommunications role is
strongly growing. (PTC) achieves that through an integrated package of activities and services,
including the following:
▪
Wired telephony services (fixed telephone).
▪
wireless telephony Services for rural areas.
▪
International telecommunications services.
▪
CDMA Mobile technology services.
3
▪
Various Internet services.
▪
Networking and data transmission services.
▪
Training and special qualifying courses and, expanding technological awareness.
▪
I.T Services and projects.
1.3Training Statement
Training Field is going to achieve the requirement of the Work Experience in block three fourth year.
1.4Training Objectives
The training courses are going to include three objects as following:
1. to have enough knowledge about the devices that use in PTC
2. to get knowledge about PTC services
3. To participate in recognizing and analyzing the development needs of the field.
1.5Training Limitations
Time Limitation
The Training is done from 2019/12/16_ 15/1/2020.
Place Limitation
The Training done in Public Telecommunication Corporation, at Operating and Maintenance General
Department.
4
CHAPTER 2
LITRTURE REVIEW
2.1. Introduction
This chapter is containing the background theory of the Training and pilot study.
2.2. Microwave Department in Public Telecommunication Corporation.
Major: Telecommunication Engineering
Field Training: Microwave Department.
Trainer: Yousf Nasar
Outcomes:
-
Introduction
-
Microwave communication systems
-
Emergence of MW Communication
-
Fundamental Parameters in MW Link
-
digital microwave equipment
-
Modulation Schemes Used in Digital Microwave Communication
-
Diversity in Microwave Links
-
Microwave antenna
-
Antenna Installation
-
Adjusting Antenna
-
Advantages of Microwaves & Disadvantages of Microwaves
-
Applications of Microwaves
5
2.3.Optical Transmission (SDH) in Public Telecommunication Corporation.
Major: Telecommunication Engineering
Field Training: Optical Transmission (SDH).
Trainer: Ali kraba
Outcomes:
- Introduction To SDH
- Plesiochronous Digital Hierarchy (PDH)
- Limitations of PDH Network
- PDH multiplexing
- Synchronization of Digital Signals SDH
- Basic SDH Signal
- SDH Advantages
- SDH multiplexing
- PDH vs SDH | Difference between PDH and SDH
- Transmission Hierarchies
- The components of SDH
- SDH Protection Technologies
- SDH network topologies and structures
6
2.4.Switching network.
Major: Telecommunication Engineering
Field Training: PSTN network
Trainer: Abdolqaui AL-kharasani
Outcomes:
-
Introduction
-
Switching system hierarchy
-
Classification of Switching Systems
-
Basics of a Switching System
-
Electronic Exchanges
-
The Advantages of Electronic Exchanges Switching Techniques
2.5.
Switching Technology (NGN) in Public Telecommunication Corporation.
Major: Telecommunication Engineering
Field Training: Switching Technology (NGN)
Trainer: hassan al-shithaly
Outcomes:
-
Introduction of Next Generation Networking (NGN).
-
TDM Service Architectures
-
NGN Network Architecture and Network Elements
-
Benefits of a Next Generation Services Architecture
-
Characteristics of NGN in contrast with TDM.
-
NGN Technology Operation.
-
How does PSTN work with NGN
-
Application of NGN
-
Advantages and disadvantages of NGN
7
CHAPTER 3
PROJECT METHODOLOGY
3.1. Introduction
This chapter contains the plan of procedures that are going to achieve the objectives. To give a detailed
explanation to show the steps which was followed to carry out the study such as Training plan,
framework, branch study, time table.
3.2. Training plan
The plan of the Training is shown in the following table (3.1). It explains the components of each
chapter with the final result of each chapter and the period that spent in training.
Table (3.1) Shows Training Table.
Step
Time
Essential plan First week
Background
Second week
Review
Training
Descriptions
Final result
- Define training background.
- Define the background.
- Define training statement.
- Define Problem statement.
- Define training limitation.
- Define the objectives.
- Define training objective.
- Define the limitation.
- Collect training data and topics.
Finding the required information
- Collecting information and other studies and data about the training.
Second week
Timetable
- Making timetable.
Planning
Analysis
- Making training plan.
Third week
Training reports
Making training reports
8
CHAPTER 4
ANALYZING & DISCUSSION
4.1. Introduction
In this chapter, analyze the collected data from the training field in department of operation and
maintenance, in some majors like: microwave transmission at the PTC, optical transmission, switching
technology like NGN, TDM and telephone networks.
4.1.1. Training Reports
The data will be analyzed from the knowledge that have gained with the engineers in the Public
Telecommunication Corporation. It contains five reports, microwave transmission at the PTC, optical
transmission, switching technology like NGN, TDM and telephone networks.
9
TRAINIG REPORT
Sana'a Community College
HPE Division
Report one
TCET Department
Microwave transmission
Don by
Abdullah Al-Marwani
Dherar Al-salahy
Emad Al-hasany
Mohammed Abdulwahab Al-Gahmi
Mojahed moaidh
Omair Yousef Al-Jaadi
Supervised By
Dr. Jameel Sultan
Communication Engineering Department
Sana'a Community Collage
Sana'a
10
2021
Title: Microwave Department in Public Telecommunication Corporation at Operating and
Maintenance General Department.
Major: Telecommunication Engineering
Field Training: Microwave Department.
Trainer: Yousf Nasar
Outcomes:
1. Introduction
2. Microwave communication systems
3. Emergence of MW Communication
4. Fundamental Parameters in MW Link
5. digital microwave equipment
6. Modulation Schemes Used in Digital Microwave Communication
7. Diversity in Microwave Links
8. Microwave antenna
9. Antenna Installation
10. Adjusting Antenna
11. Advantages of Microwaves & Disadvantages of Microwaves
12.Applications of Microwaves
11
4.2.Microwave transmission
1.
INTRODUCTION
Microwaves are electromagnetic waves (EM) in the frequency range from 300MHz up to 300GHz,
which corresponds to wavelengths from 1mm to 1m (Pozar, 2005). They are part of radio waves, which
are having frequencies in the range 104 to 1011 Hz as shown in the frequency spectrum of Figures 4.2.1
and radio frequency spectrum of Figure 4.2.1 below.
Figure 4.2.1. Electromagnetic spectrum
Figure 4.2.2. Radio Frequency spectrum
From the radio frequency spectrum of Figure 4.2.2 it is evident that microwave covers ultra-high
frequency (UHF) through super-high frequency (SHF) band.Microwave frequencies in the UHF band
are used for Terrestrial TV, Satellite communication, surveillance radar, WiFi (2.4GHz band), WiPAN
(e.g. Bluetooth, ZigBee), DECT, ultra-wide band (UWB) radio and navigational aids, whereas the one in
the SHF band are used for airborne radar, microwave links, WiFi (5.8GHz band), Satellite
communication. Additional to the communication-related applications, microwave frequency are also
used for other applications, which inter alia, include industrial, science and medical uses; for example,
2.450GHz is used in domestic microwave ovens, 915MHz to 2.450GHz is used for industrial heating
applications, such as grain drying, manufacturing of wood and paper products, and material curing, and
last, but not least, 915MHz to 2.450GHz is also used in medical applications, such as diathermy, which
is the electrically induced heat or the use of high-frequency electromagnetic currents as a form of
physical or occupational therapy and in surgical procedures that include hyperthermia or localized
heating of tumours.
12
Most of these non-communication-based applications are predominantly based on frequencies around
2.4GHz, hence the band of frequencies around 2.4GHz is referred to as Industrial, Scientific and
Medical (ISM) band.
Microwave frequencies are usually sub-divided into small frequency bands, which are designated as
follows:
Table 4.2.1 Microwave frequency band designators
2.
Band designator
Frequency (GHz)
L
1–2
S
2–4
C
4–8
X
8 – 12
Ku
12 – 18
K
18 –27
Ka
27 – 40
MICROWAVE COMMUNICATION SYSTEMS
Microwave systems are broadband terrestrial line-of-sight radio systems. They are commonly used by
telecommunication companies (telecoms) as backhaul to provide wideband fixed point-to-point radio
communication links for distances up to about 50 km, which offer major trunk channels for long
distance communication to carry voice, data and video traffic. In addition to backhaul application,
microwave systems are also used for radio local loop to provide broadband wireless access (BWA); that
is, they are used as radio access technology (RAT). A typical example of RAT is the Worldwide
Interoperability for Microwave Access (WiMAX), which is RAT that is based on IEEE 802.16
standards for broadband wireless access networks. They operate in the frequency range from 1 GHz to
about 30 GHz. Though their bandwidth is less compared to that of optical fiber, microwave systems
have major advantages over cabling systems. These advantages include, inter alia:
-
-Freedom from land acquisition rights; that is, acquisition of rights to lay cabling or repair
cabling, and have permanent access to repeater. The use of radio links, that require only the
acquisition of the transmitter/receiver station, removes this requirement. It also simplifies the
maintenance and repair of the link.
13
-
Ease of communication over difficult terrain. Some terrains make cable laying extremely
difficult and expensive, even if the land acquisition cost is negligible.
-
Wider bandwidths, which are required for broadband signals like television signals and for
provision of large number of telephone channels.
A basic microwave link consists of a transmitting station (Tx), one or more relay stations or repeaters
(RPT), and a receiving station (Rx), as shown in Figure 4.2.3.
Figure 4.2.3. Microwave radio relay link
At the transmitting station the signal to be transmitted (i.e. baseband signal) is first processed (i.e.
encoded) before it is used to modulate an intermediate carrier of 70 MHz (or 140 MHz). The modulated
signal is then up-converted to the allocated microwave frequency and amplified before being fed to the
antenna for radiation.
The repeater or relay station is added at the obstacle point or other suitable place to provide LoS or at
50 km intervals to boost the power of the signal so that it can go a longer distance. There are two types
of repeater: passive and active repeater. Passive is like a beam diverter to make the beam surpass
obstacle using back-to-back parabolic antennas connected by a section of a waveguide, and they do not
have any amplifying device. Active repeater includes an amplifier to boost the signal strength and others
also have frequency translation circuits to change the frequency of the signal before retransmitting it.
The former active repeater, which does not have frequency translation circuit, is referred to as RF direct
relay station, while the latter is called a regenerative relay station. At the receiving station the signal is
down-converted to 70 MHz (or 140 MHz) before it is demodulated to recover the baseband signal. To
radiate or receive the radio waves, the microwave system uses directional high gain parabolic dish
antennas. The old microwave systems were analogue: using analogue modulation and frequency
14
division multiplexing (FDM); however, nowadays microwave systems are digital. These digital
microwave systems use digital modulation schemes which include M-array modulation schemes, such
as quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM): 16-QAM or higherQAM, and multicarrier modulation schemes such as orthogonal frequency division multiplexing
(OFDM) for the newer BWA microwave systems and time division multiplexing (TDM).
3.
Emergence of MW Communication
With the 21st century, it can be said that the world has closer means. In this age we can talk, chat, meet,
greet people and our friends from every part and corner of the world within a click. The click can be
over the cell phone for having a talk or over the keyboard or mouse of a computer to have an online chat
with our near and dear ones. It is possible only because of the technology called microwave
communication. Internet usage in modern life is very essential job and with it even the remotest of areas
are connected. Cell phone is the most dominating technology in terms of consumption and revenue and
it is emerging day by day with due credit to MW communication. Security systems are also advancing
with the help of MW link.
Satellite communication, data communication, bio-medical engineering and cellular networks are the
main domains for MW communication. Due to following advantages microwave communication is
emerging day by day
-
Large bandwidth Line of sight propagation
-
Antenna size reduction
-
Can accommodate large number of channels
-
Less Power requirement especially in case of repeaters
-
Environmentally Stable
4.
Fundamental Parameters in MW Link
Line of Sight (LOS)
For any point-to-point radio communication; the general setup requires Microwave antennas to be
placed in a high position so that there are no obstacles in between. This direct link is usually referred as
Line of Sight (LOS). It is very important to find out a visible path between sites before establishing
those links. Now a day, LOS and other parameters are designed in special RF virtual instruments.
Moreover, only seeing a visible path does not always confirm that LOS will give a sufficient level of
15
signal, it should satisfy other parameter such as the terrain for wave propagation. Figure 4.2.4. shows a
Line of Sight (LOS) where one microwave antenna has a direct link to another antenna placed at far end.
Figure 4.2.4. A type Line of Sight (LOS) of a MW link
Free Space Loss
When a signal is spread from an antenna, it gets weaker with the distance and this phenomenon is
generally referred as Free Space Loss (FSL). The FSL calculations only look at the loss of the path only
and do not contain any factors relating to the transmitter power, antenna gains or receiver sensitivity
level. These factors are normally addressed when designing a link budget and are used within radio and
wireless survey tools. A model of link budget is shown in Appendix A.
Fresnel Zone
When LOS is measured, it should be kept in mind that only a visible position of link does not confirm
that link will provide enough RSL. The clearance area from one site to another would also need the
strongest signal beam to have an obstacle free propagation of signal. The strongest signals are often
accounted within an angular sphere often termed as Fresnel Zone. In it is said that, to make a line of
sight; the main beam has to be clear about 60% in the 1st Fresnel Zone.
There are some other parameters in microwave link which are significant in design phase of link
establishment.
-
Antenna Gain
-
Multi-path Reflections
-
Precipitation loss
-
Fading
16
-
Link budget calculation
-
Atmospheric Refraction
5.
DIGITAL MICROWAVE EQUIPMENT
Digital microwave equipment can be classified based on multiplexing method used (i.e. PDH or SDH),
capacity, or structure. However, the most commonly used method to classify microwave equipment is
based on the structure as follows:
-
All-indoor microwave
-
All-outdoor microwave
-
Split microwave
All-indoor Microwave
The all-indoor microwave, also called big microwave, has all its units; that is, radio frequency RF unit
(RFU), Signal Processing Unit (SPU) and Multiplexer residing indoor, and it is only the antenna that is
outdoor. Compared to other types, it is having a high transmission capacity, though that comes at a price
of high costs. It is suitable for backbone line transmission or backhaul.
All-outdoor Microwave
The all-outdoor microwave has all its units residing outdoor. It is easy to install, saves equipment room
space; however, it can be easily damaged.
Split Microwave
Consists of both indoor unit (IDU) and outdoor unit (ODU), which are connected using intermediate
frequency (IF) cable. The cable carries IF service signals, communication control signals and power to
the ODU. Though it is easy to install, split microwave has a low capacity.
6.
Modulation Schemes Used in Digital Microwave Communication
The baseband signal cannot be directly transmitted over microwave radio channels but must be
converted into frequency band signal in order to implement microwave transmission. Generally, the
digital baseband signal is the service signal to be transmitted. After the digital baseband signal
is modulated into the IF signal, it still cannot be directly transmitted over the air link but must be
converted once more into the signal of a higher frequency.
By the parameters used to modulate the carrier signal with the digital baseband signal, there can be
various modulation methods
17
1- ASK (Amplitude Shift Keying): Use the digital baseband signal to change the carrier
amplitude.
2- FSK (Frequency Shift Keying): Use the digital baseband signal to change the carrier
frequency.
3- PSK (Phase Shift Keying): Use the digital baseband signal to change the carrier phase.
4- QAM (Quadrature Amplitude Modulation): Use the digital baseband signal to change the
carrier phase and amplitude.
PROPAGATION
Microwave systems are wireless system; therefore, the information is transmitted in the form of
electromagnetic waves through the space from the transmitting antenna connected to the transmitter
to the receiving antenna that is connected to the receiver.
Electromagnetic Waves
Electromagnetic waves can be described as energy that radiates from a source or as oscillations that
propagate through the free space with a velocity of light (3 108 m/s).
These oscillations are perpendicular to the direction of propagation; hence the electromagnetic waves
are said to be transverse (TEM). Their simplest form is called plane waves. Electromagnetic wave
consists of an electric field E and magnetic field H that are at right angles with each other. These two
waves oscillate in phase with each other and are perpendicular to the direction of propagation (that is,
the direction of propagation is at right angle with both electrical and magnetic field). This setup also
applies after the wave has been radiated, as shown in Figure 4.2.5.
Figure 4.2.5 Transverse electromagnetic wave
The formulation of the fields of the electromagnetic waves is governed by Gauss laws, Faraday’s
law, and Ampère’s law. Gauss law describes the electric and magnetic flux vectors. Faraday’s law
states that a time varying magnetic field acts as a source of electric field. Ampère’s law states that a
time varying electric field acts as a source of magnetic field. Thus when either field is changing with
time, a field of the other kind is induced in the adjacent regions of space. This electromagnetic
disturbance, which consists of time- varying electric and magnetic fields can propagate through space
from one region to another even when there is no matter in the intervening region.Maxwell built on
18
the theoretical knowledge developed by Gauss, Faraday, Ampère, and other scientists and came up
with Maxwell equations which describe the inter- relationship between the electromagnetic fields and
fluxes in any media and their spatial variations; that is, how the electromagnetic fields are generated
and altered by each other and by charges and current.
7.
Diversity in Microwave Links
In terrestrial microwave links, a diversity scheme refers to a method for improving the reliability of a
message signal by using two or more communication channels with different characteristics.
Diversity
plays
an
important
role
in
combatting fading and co-channel
interference and
avoiding error bursts. It is based on the fact that individual channels experience different levels of
fading and interference. Multiple versions of the same signal may be transmitted and/or received and
combined in the receiver. Alternatively, a redundant forward error correction code may be added and
different parts of the message transmitted over different channels. Diversity techniques may exploit
the multipath propagation, resulting in a diversity gain, often measured in decibels. The following
classes of diversity schemes are typical in Terrestrial Microwave Links:
•
Frequency diversity: The signal is transmitted using several frequency channels or spread
over a wide spectrum that is affected by frequency-selective fading. Microwave radio
links often use several active radio channels plus one protection channel for automatic use by
any faded channel. This is known as N+1 protection
•
Space diversity: The signal is transmitted over several different propagation paths. In the case
of wired transmission, this can be achieved by transmitting via multiple wires. In the case of
wireless transmission, it can be achieved by antenna diversity using multiple transmitter
antennas (transmit diversity) and/or multiple receiving antennas (reception diversity).
•
Polarization diversity: Multiple versions of a signal are transmitted and received via antennas
with different polarization. A diversity combining technique is applied on the receiver side.
The design goal is to maintain the link uptime to be as near to 100% as high as possible. In order to
achieve such reliability, there are various redundancy method that have been implemented over the
years.
Particular attention has been paid to protect against problems with radio chain. Much of the radio
equipment is located outdoors, often mounted directly to the back of the antenna. Outdoor Unit
(ODU) failures could take a long time, even days to repair/replace, as time climbs are needed to
19
access the gear. To prevent this situation, one needs to implement a back-up scheme to keep the link
up and running during the time of repair.
•
Unprotected: Microwave links where there is no diversity or protection are classified as
Unprotected and also as 1+0. There is one set of equipment installed, and no diversity or
backup
Figure 4.2.6 Microwave ODU in 1+0 Configuration with Antenna
•
Hot Standby: Two sets of microwave equipment (ODUs, or active radios) are installed
generally connected to the same antenna, tuned to the same frequency channel. One is
“powered down” or in standby mode, generally with the receiver active but transmitter
muted. If the active unit fails, it is powered down and the standby unit is activated. Hot
Standby is abbreviated as HSB, and is often used in 1+1 configurations (one active, one
standby). Other resilient configurations are 1+1 SD (Space Diversity, using separate antennas,
one ODU on each) and 1+1 FD (Frequency Diversity)
Figure 4.2.7Two Microwave ODUs in 1+1 HSB
20
The other non-resilient configuration is 2+0 which has two ODUs connected to a single antenna via a
coupler. The hardware configuration is identical to 1+1 FD, but the ODUs carry separate signals to
increase the overall capacity.
Figure 4.2.82+0 configuration with Coupler and Antenna
Microwave tower: The towers are used in microwave system to support antenna or in some cases,
reflectors, design of microwave antenna tower depends upon the following factors: a) The number of routes
b) Space diversity requirements
c) Future expansion (especially VHF/VHF/SPUR)
d) Antenna heights
e) Other loads like lights, transmission line etc.
All towers fall in two general categories, namely self-supporting type and guyed type. Selfsupporting towers are costly but occupy small areas whereas guyed type though cheaper larger area
for the guys. For design of a tower information regarding types and sizes of antennas transmission
line, wind velocity etc. is required to be supplied.
MICROWAVE ANTENNAS
Since microwave systems are wireless systems, they rely on antennas to launch waves into space and
to intercept waves from space. Antennas that are used by microwave systems include wire antennas:
dipole and helical; aperture antennas: reflectors, horn and lens; printed antennas: patch (or
microstrip) and printed versions of wire antennas, and other antennas such as solid-state arrays and
slot antennas.
Antennas are transducers that are designed for maximum radiation, and they possess reciprocity,
which is the property that makes them to be interchangeable between transmit (or launching of waves
21
into space) and receive (or intercepting of waves from space). For any antenna system operation to be
efficient, the transmitting antenna and the receiving antenna must have the same polarization, signal
being transmitted or received must be within the bandwidth of the antennas used, and if the antennas
are directional, the two antennas must be aligned so that they point directly to each other. The latter
two help to minimize polarization mismatch losses that result from polarization mismatch between
the transmitting and the receiving antenna, and pointing losses that occur when the transmitting
antenna is not pointing directly to the receiving antenna.
Types of microwave antenna
There are two main types of antenna that are used in microwave links. They are:
1-
A horn-reflector antenna
2-
A parabolic dish antenna
Horn-reflector antenna
A horn antenna is nothing more than a flared wave-guide as shown in Figure 1. The horn exhibits
gain and directivity, however its performance is improved more by using it in combination with a
parabolic reflector.
An open-ended wave-guide is an inefficient radiator of energy due to the impedance mismatch at
the mouth, it can be improved by simply flaring the end of the waveguide. Flaring of the wave-guide
ends creates a horn antenna as shown in Figure .9 .4.2
Figure 4.2.9. Basic horn antenna
Horn antennas have excellent gain and directivity. The longer the horn, the greater its gain and
directivity. Different kinds of horn antennas can be created by flaring the end of the wave-guide in
different ways for example flaring in one dimension creates a sectoral horn
e.g. horns flared in the E or H planes. Flaring the wave guide in each dimension produces a
pyramidal horn e.g. horns flared in both E and H planes. If a circular wave-guide is used the flare
22
produces a conical horn. These are shown in Figure 4.2.10.(a to d)
Figure 4.2.10. A wave-guide will act as an inefficient radiator
Figure 4.2.11. Types of horn Antenna
23
Figure 4.2.12. Dimensions of a horn
The important dimensions of the horn antenna are
- Horn length
- Aperture area
- Flare angle
The length of a typical horn is usually 2 to 15 wavelengths at the operating frequency. The longer
horns though more difficult to mount and work with provide higher gain and better directivity. The
aperture area is the area of the rectangle formed by the opening of the horn and is simply the product
of the height and width of the horn. The greater this area, the higher the gain and directivity.
The flare angle also affects gain and directivity. Typical flare angles vary from about 200 to 500.
Increasing the flare angle increases the aperture area. For a given size of aperture area
decreasing the length increases the flare angle as shown in Figure 4.2.12.
Each of these dimensions is adjusted to achieve the desired design objective. An important aspect of a
microwave antenna is its bandwidth. Most antennas have a narrow bandwidth because they are
resonant at only a single frequency. Their dimensions determine the frequency of operation. Bandwidth
is an important consideration at microwave frequencies because the spectrum transmitted on the
microwave carrier is usually wide so that a considerable amount of information can be carried. Horn
antennas have relatively large bandwidth. Horns are essentially non-resonant or periodic which means
they will operate over a wide frequency range.
Horn antennas are used by themselves in many applications but many times higher gain and
directivity is desirable. This can easily be obtained by using a horn in conjunction with a parabolic
reflector.
24
Parabolic reflector
The parabolic reflector antenna is one of the most wide spread of all the microwave antennas and is
the type that normally comes to mind when thinking of microwaves systems. This type of antenna
derives its operation from optics and is possible because microwaves are in transition region between
ordinary radio waves and infrared/visible light. The parabolic reflector antenna (often called a
dish antenna).
The dish is not actually an antenna but serves a reflector. It must be driven by a radiating
element at the focal length. This radiating element could be a dipole or a horn radiator. A parabola is
a mathematical curve such that its reflection property causes an incoming beam of parallel rays to
focus to one point. Conversely radiated waves from a point signal placed at the focal point are
reflected by the surface to form parallel rays in the outgoing beam. Thus, a parabolic antenna can be
employed as a transmitter and receiving device.
The parabolic reflector may take many forms. The larger the reflector with respect to the wave-length
the narrower the beam width.
A typical dish antenna with a paraboloid shape is shown in Figure 4.2.13.
Figure 4.2.13. A Parabolic Dish
A key dimension of the parabola above is a line drawn from its center at point Z to a point on the
axis labeled F which is the focal point. The ends of the parabola could extend outwardly for an
infinite distance but usually they are limited. The limits are shown by the dashed vertical line with
the end points labeled X and Y. The distance between the focal point and the parabola and the
vertical dashed line is a constant value, for example in the Figure 4.2.13.
25
the distance represented by the sum of the lines FA to AB and FC to CD are equal. This effect
causes a parabolic shaped surface to collimate electromagnetic waves into a narrow beam of
electrons. Placing an antenna at the focal point F will cause it to radiate waves from the parabola in
parallel lines. If used as a receiver, the parabola will pick up the electromagnetic waves into a narrow
beam of electrons. Placing an antenna at the focal point F will cause it to radiate waves from the
parabola in parallel lines. If used as a receiver, the parabola will pick up the electromagnetic waves
and reflect them to the antenna located at the focal length.
Polarization
Antennas radiate electromagnetic waves, which consists of an electric field and magnetic field that
are at right angles with each other. These two waves oscillate in phase with each other and are
perpendicular to the direction of propagation (that is, the direction of propagation is at right angle
with both electrical and magnetic field).
The magnetic field always surrounds the current carrying conductor, so it is always perpendicular
to it, while electric field is always parallel to the current carrying conductor. Thus, electric and
magnetic field are at right angles with each other. This setup also applies after the wave has been
radiated (i.e. left the antenna)
The polarization of the wave is determined by the electric field; for example, if the electric
intensity vectors are vertical, the wave is said to be vertically polarized, and if they are horizontal, the
wave is said to be horizontal polarized. Since the direction of the electric field is always parallel to
the radiating conductor, it can be said that the direction of polarization is the same as the direction of
the antenna. Thus, vertical antennas radiate vertical polarized waves, horizontal antennas radiate
horizontal polarized waves and helical (helix or spiral) antennas radiate circular polarized waves. The
energy in the circular polarized waves is divided equally between the horizontal and vertical
components, thus making it possible for the circular polarized wave to be received by both horizontal
and vertical polarized antennas.
On the receiver, it is important to have the antenna to be of the same orientation as the transmitting
antenna (that is, both horizontal, or both vertical), and when using the helical antennas, it is important
to make sure that both antennas have the same thread orientation (that is, both clockwise, or both
counter-clockwise), otherwise the received signal will be significantly reduced due to polarization
mismatch.
8.
Antenna Installation
There many techniques to setup the microwave antenna but most useful way is to start identify the
north and the turn left of right as deal with the one of is in the other side to be line of sight and also
26
by sitting the elevation angle of the antenna as need to be line of sight.
Figure 4.2.14 Setting the antenna using north angle
Figure 4.2.15Elevation angle
Microwave Polarization
There are two type of polarization that could be setup the antenna to transmission over the
microwave link.
27
- Vertical polarization
Figure 4.2.16 Vertical Polarizations
- Horizontal polarization
Figure 4.2.17Horizontal polarization
28
Software Installation
To configure the microwave site, it should be connected to the indoor microwave remotely or
ethernet as shown in this figure4.2.18.
Figure 4.2.18 Configure the antenna in indoor
If the configuration is remotely the far site should be configuring first and then the near sit then
configures. First step:
- Is to modify the IP address.
- Log in authentication should be entered.
- Modify the ID microwave site.
- Then go configuration choose link configuration. After that selecting the modulation mode.
Second step: For Microwave Link Planning, the software package can be configured with the
characteristics of your required radio links like.
- Transmit Power
- Frequency
- Antenna Gain
- Receiver Sensitivity
- Antenna heights
- System losses
29
Figure 4.2.19 networks properties
Adjusting Antenna
The strengths of electromagnetic waves transmitted by an antenna are different in different
directions. Adjusting antenna is aligning the major lobes of two antenna with each other. Make a
multimeter 20 V test cable whose on one end is a BNC connector. Use the multimeter to measure the
voltage of the port. Adjust the azimuth of the local antenna. Slowly rotate the antenna around the pole
in a large range in the horizontal direction until a small voltage value is displayed on the multimeter.
Fasten the nuts on the fine adjusting bolt when the value displayed on the multimeter reaches the
maximum.
Fasten the local antenna when the receive level is the maximum within the scan range.
Figure 4.2.20 Adjusting antenna
30
Figure .4.2.21 setting antenna line of sight
11. Advantages and disadvantages of microwave
Advantages
There are many advantages of Microwaves such as the following:
• Supports larger bandwidth and hence more information is transmitted. For this reason,
microwaves are used for point-to-point communications.
• More antenna gain is possible.
• Higher data rates are transmitted as the bandwidth is more.
• Antenna size gets reduced, as the frequencies are higher.
• Low power consumption as the signals are of higher frequencies.
• Effect of fading gets reduced by using line of sight propagation.
• Provides effective reflection area in the radar systems.
• Satellite and terrestrial communications with high capacities are possible.
• Low-cost miniature microwave components can be developed.
• Effective spectrum usage with wide variety of applications in all available frequency ranges of
operation.
Disadvantages
There are a few disadvantages of Microwaves such as the following:
•
Cost of equipment or installation cost is high.
•
They are hefty and occupy more space.
•
Electromagnetic interference may occur.
31
•
Variations in dielectric properties with temperatures may occur.
•
Inherent inefficiency of electric power.
12. Applications of Microwaves
There are a wide variety of applications for Microwaves, which are not possible for other radiations.
They are:
•
For long distance telephone calls
•
WIMAX operations
•
Outdoor broadcasting transmissions
•
Broadcast auxiliary services
•
Remote pickup unit
•
Studio/transmitter link
•
Direct Broadcast Satellite (DBS)
•
Personal Communication Systems (PCSs)
•
Wireless Local Area Networks (WLANs)
•
Cellular Video (CV) systems
•
Automobile collision avoidance system
32
Sana'a Community College
HPE Division
TRAINIG REPORT
TCET Department
Report two
Optical transmission
Don by
Abdullah Al-Marwani
Dherar Al-salahy
Emad Al-hasany
Mohammed Abdulwahab Al-Gahmi
Mojahed moaidh
Omair Yousef Al-Jaadi
Supervised By
Dr. Jameel Sultan
Communication Engineering Department
Sana'a Community Collage
Sana'a
33
2021
Microwave Report 3
Title: Training in Public Telecommunication Corporation, at Operating and
Maintenance General Department. (Optical Transmission (SDH)
Major: Telecommunication Engineering
Field Training: Optical Transmission (SDH).
Trainer: Ali kraba
Outcomes:
1. Introduction To SDH
2. Plesiochronous Digital Hierarchy (PDH)
3. Limitations of PDH Network
4. PDH multiplexing
5. Synchronization of Digital Signals SDH
6. Basic SDH Signal
7. SDH Advantages
8. SDH multiplexing
9. PDH vs SDH | Difference between PDH and SDH
10. Transmission Hierarchies
11. The components of SDH
12. SDH Protection Technologies
13. SDH network topologies and structures
34
4.3.Optical transmission (SDH)
1. Introduction To SDH
SDH (Synchronous Digital Hierarchy) is a standard for telecommunications transport formulated by
the International Telecommunication Union (ITU), previously called the Consultative Committee
International Telegraph and Telephone (CCITT).
SDH was first introduced into the telecommunications network in 1992 and has been deployed at
rapid rates since then. It’s deployed at all levels of the network infrastructure, including the access
network and the long-distance trunk network. It’s based on overlaying a synchronous multiplexed
signal onto a light stream transmitted over fiber optic cable. SDH is also defined for use on radio
relay links, satellite links, and at electrical interfaces between equipment.
The comprehensive SDH standard is expected to provide the transport infrastructure for worldwide
telecommunications for at least the next two or three decades.The increased configuration flexibility
and
bandwidth
availability
of
SDH
provides
significant
advantages
over
the
older
telecommunications system. These advantages include:
-
A reduction in the amount of equipment and an increase in network reliability.
-
The provision of overhead and payload bytes – the overhead bytes permitting management of
the payload bytes on an individual basis and facilitating centralized fault sectionalization.
-
The definition of a synchronous multiplexing format for carrying lower-level digital signals
(such as 2 Mbit/s, 34 Mbit/s, 140 Mbit/s) which greatly simplifies the interface to digital
switches, digital cross-connects, and add-drop multiplexers.
-
The availability of a set of generic standards, which enable multi-vendor interoperability.
-
The definition of a flexible architecture capable of accommodating future applications, with a
variety of transmission rates.
In brief, SDH defines synchronous transport modules (STMs) for the fiber-optic based transmission
hierarchy.
Background
Before SDH, the first generations of fiber-optic systems in the public telephone network used
proprietary architectures, equipment line codes, multiplexing formats, and maintenance procedures.
The users of this equipment wanted standards so they could mix and match equipment from different
suppliers.
35
The task of creating such a standard was taken up in 1984 by the Exchange Carriers Standards
Association (ECSA) in the U.S. to establish a standard for connecting one fiber system to another. In
the late stages of the development, the CCITT became involved so that a single international standard
might be developed for fiber interconnect between telephone networks of different countries. The
resulting international standard is known as Synchronous Digital Hierarchy (SDH).
2. Plesiochronous Digital Hierarchy (PDH)
To correctly understand the concepts and details of SDH, it’s important to be clear about the meaning
of Synchronous, Plesiochronous and Asynchronous.
Traditionally, digital transmission systems and hierarchies have been based on multiplexing signals
which are plesiochronous (running at almost the same speed). Also, various parts of the world use
different hierarchies which lead to problems of international interworking; for example, between
those countries using 1.544 Mbit/s systems (U.S.A. and Japan) and those using the 2.048 Mbit/s
system.
To recover a 64 kbit/s channel from a 140 Mbit/s PDH signal, it’s necessary to demultiplex the
signal all the way down to the 2 Mbit/s level before the location of the 64 kbit/s channel can be
identified. PDH requires “steps” (140-34, 34-8, 8-2 demultiplex; 2-8, 8-34, 34-140 multiplex) to drop
out or add an individual speech or data channel
(see Figure 4.3.1). This is due to the bit-stuffing used at each level.
140 Mbit/s
140 Mbit/s
140-34 DEMUX
34-140 MUX
34-8 DEMUX
8-34 MUX
8 Mbit/s
8 Mbit/s
8-2 DEMUX
2-8 MUX
2 Mbit/s
Figure 4.3.1 PDH multiplexing by steps, showing add/drop function
3. Limitations of PDH Network
The main limitations of PDH are:
-
Inability to identify individual channels in a higher-order bit stream.
36
-
Insufficient capacity for network management;
-
Most PDH network management is proprietary.
-
There’s no standardized definition of PDH bit rates greater than 140 Mbit/s.
-
There are different hierarchies in use around the world. Specialized interface equipment is
required to interwork the two hierarchies.
4. PDH multiplexing
In PDH, digital multiplexer's inputs (bit streams) are of same bit rate and are derived from different
clocks from different oscillators. Each will differ within tolerance of few clock periods. Hence it is
called plesiochronous. Bit Interleaving is used in PDH to combine digital signals.
Figure 4.3.2 PDH level hierarchy used in North America
In PDH there are two main standards i.e., 30 channel one used in Europe and 24 channel one used
in North America/Japan. Basic rate is 64 Kbps in North America (designated as DS0) and in Europe
(designated as E0). Rates derived from 2.048 Mbps basic rate including bit stuffing in 30 channel
case are mentioned below.
2.048 x 4 gives 8.448 Mbps (120 channels)
8.448 x 4 gives 34.368 Mbps (480 channels)
34.368 x 4 gives 139.264 Mbps (1920 channels)
139.264 x 4 gives 564.992 Mbps (7680 channels)
37
Figure 4.3.3. depicts PDH levels used in Europe
The figure- 4.3.2 depicts PDH level hierarchy used in North America while figure-4.3.3. depicts
PDH levels used in Europe. Rates derived from 1.544 Mbps basic rate including bit stuffing in 24
channel case are mentioned below.
1.544 x 4 gives 6.312 Mbps (96 channels)
6.312 x 7 gives 44.736 Mbps (672 channels)
44.736 x 6 gives 274.16 Mbps (4032 channels)
44.736 x 3 gives 139.264 Mbps
44.736 x 12 gives 564.992 Mbps
Table4.3.1. The table below mentions PDH rates used in Japan.
Level
data rate in Japan
0
0.064 Mbps
1
1.544 Mbps
2
6.312 Mbps
3
32.064 Mbps
38
5. Synchronization of Digital hieracy SDH
In a set of Synchronous signals, the digital transitions in the signals occur at exactly the same rate.
There may however be a phase difference between the transitions of the two signals, and this would
lie within specified limits. These phase differences may be due to propagation time delays, or lowfrequency wander introduced in the transmission network. In a synchronous network, all the clocks
are traceable to one Stratum 1 Primary Reference Clock (PRC). The accuracy of the PRC is better
than ±1 in 1011 and is derived from a cesium atomic standard.
If two digital signals are Plesiochronous, their transitions occur at “almost” the same rate, with any
variation being constrained within tight limits. These limits are set down in ITU-T recommendation.
For example, if two networks need to interwork, their clocks may be derived from two different
PRCs. Although these clocks are extremely accurate, there’s a small frequency difference between
one clock and the other. This is known as a plesiochronous difference.
In the case of Asynchronous signals, the transitions of the signals don’t nec essarily occur at the
same nominal rate. Asynchronous, in this case, means that the difference between two clocks is much
greater than a plesiochronous difference. For example, if two clocks are derived from free-running
quartz oscillators, they could be described as asynchronous.
6. Basic SDH Signal
The basic format of an SDH signal allows it to carry many different services in its Virtual Container
(VC) because it is bandwidth-flexible. This capability allows for such things as the transmission of
high-speed packet-switched services, ATM, contribution video, and distribution video. However,
SDH still permits transport and networking at the 2 Mbit/s, 34 Mbit/s, and 140 Mbit/s levels,
accommodating the existing digital hierarchy signals. In addition, SDH supports the transport of
signals based on the 1.5 Mbit/s hierarchy.
7. SDH Advantages
The primary reason for the creation of SDH was to provide a long-term solution for an optical
midspan meet between operators; that is, to allow equipment from different vendors to communicate
with each other. This ability is referred to as multi-vendor interworking and allows one SDHcompatible network element to communicate with another, and to replace several network elements,
which may have previously existed solely for interface purposes.
The second major advantage of SDH is the fact that it’s synchronous. Currently, most fiber and
multiplex systems are plesiochronous. This means that the timing may vary from equipment to
39
equipment because they are synchronized from different network clocks. In order to multiplex this
type of signal, a process known as bit-stuffing is used. Bit-stuffing adds extra bits to bring all input
signals up to some common bit-rate, there by requiring multi-stage multiplexing and demultiplexing.
Because SDH is synchronous, it allows single-stage multiplexing and demultiplexing. This singlestage multiplexing eliminates hardware complexity, thus decreasing the cost of equipment while
improving signal quality.
In plesiochronous networks, an entire signal had to be demultiplexed in order to access a particular
channel; then the non-accessed channels had to be re-multiplexed back together in order to be sent
further along the network to their proper destination. In SDH format, only those channels that are
required at a particular point are demultiplexed, thereby eliminating the need for back-to-back
multiplexing. In other words, SDH makes individual channels “visible” and they can easily be added
and dropped.
8. SDH multiplexing
In SDH, digital multiplexer's inputs are of same bit rate and are derived from common clock, hence
are in phase. Hence it is synchronous.
Figure 4.3.4 SDH multiplexing
40
9. PDH vs SDH | Difference between PDH and SDH
Following table compares PDH vs SDH with respect to various parameters and mention difference
between PDH and SDH in the form of table below.
PDH
SDH
Plesiochronous Digital Hierarchy
Synchronous Digital Hierarchy
In PDH, reference clock is not synchronized
In SDH, Reference clock is synchronized
throughout the network.
throughout the network.
There is no synchronization between payload
There is synchronization between payload and
and frame.
frame.
PDH system has different frame structures at
SDH system has consistent frame structures
different hierarchy levels.
throughout the hierarchy.
Physical cross-connections are provided on
Digital cross-connections are provided at
the same level in PDH.
different signal levels in SDH.
In SDH, rates are derived from basic rate of
In PDH, rates are derived from basic rate of
155.52 Mbps. The maximum up to 40 Gbps
1.544 Mbps. The maximum capacity is about
rates
566 Mbps.
mentioned.
There is no universal standard for PDH.
Universal standard exists for SDH.
PDH is incompatible with other signals such
SDH is compatible with other signals such as
as ATM, FDDI, DQDB etc.
ATM, FDDI, DQDB etc.
41
can
be
derived
from
basic
rate
Multipling method used in PDH is complex.
Multipling method used in SDH is simple.
Implementation cost of PDH is lower.
Implementation cost of SDH is higher.
10. Transmission Hierarchies
Following ANSI’s development of the SONET standard, the ITU-T under- took to define a standard
that would address interworking between the 2048 kbit/s and 1554 kbit/s transmission hierarchies.
That effort culminated in 1989 with ITU-T’s publication of the Synchronous Digital Hierarchy
(SDH) standards.
Tables 4.3.2 and 4.3.3 compare the Non-synchronous and Synchronous transmission hierarchies
Table 4.3.2. Non- Synchronous, PDH Hierarchy
Signal
Digital Bit Rate
Channels
E0
64 kbit/s
One 64 kbit/s
E1
2.048 Mbit/s
32 E0
E2
8.448 Mbit/s
128 E0
E3
34.368 Mbit/s
16 E1
E4
139.264 Mbit/s
64 E1
Table 4.3.3. SDH Hierarchy
Bit Rate
51.84 Mbit/s
155.52 Mbit/s
622.08 Mbit/s
2488.32 Mbit/s
9953.28 Mbit/s
39813.12 Mbit/s
Abbreviated
51 Mbit/s
155 Mbit/s
622 Mbit/s
2.4 Gbit/s
10 Gbit/s
40 Gbit/s
SDH
SDH Capacity
STM-0
STM-1
STM-4
STM-16
STM-64
STM-256
21 E1
63 E1 or 1 E4
252 E1 or 4 E4
1008 E1 or 16 E4
4032 E1 or 64 E4
16128 E1 or 256 E4
STM = Synchronous Transport Module
11. The components of SDH
The schematic diagram in Figure 4 shows an SDH ring structure with various tributaries. The mixture
of different applications is typical of the data transported by SDH. Synchronous networks must be
able to transmit plesiochronous signals and be able to handle future services, such as ATM.
42
Current SDH networks consist of four NE types. The topology (that is the ring or mesh structure)
is governed by the requirements of the network provider.
Figure 4.3.4. Schematic diagram of hybrid communications networks
Regenerator
Regenerators, as the name implies, regenerate the clock and amplitude relationships for incoming
data signals that have been attenuated and distorted by dispersion. They derive their clock signals
from the incoming data stream. Messages are received by extracting various 64 kbps channels (for
example, service channels E1 and F1) from the regenerator section overhead (RSOH) and then can be
sent also using these channels.
Figure 4.3.5: block diagram of Regenerator
Terminal multiplexers
Terminal multiplexers are used to combine plesiochronous and synchronous input signals into
higher-bit-rate STM-N signals.
Figure 4.3.6: block diagram of Terminal multiplexers
43
Add/drop multiplexers
Plesiochronous and lower-bit-rate synchronous signals can be extracted from or inserted into highspeed SDH bit streams using add/drop multiplexers (ADMs). This feature enables ring structure
setup, which, in the event of a fault, can automatically back up path switching using elements in the
ring.
Figure 4.3.7: block diagram of Add/drop multiplexers
Digital cross-connects
Digital cross-connects (DXC) offer the broadest functionality such as mapping PDH tributary signals
into virtual containers and switching various containers up to and including VC-4.
Figure 4.3.8: block diagram of Digital cross-connects
12. SDH Protection Technologies
1) Line Protection
Three schemes are common for protection in line channels: one-plus-one, one-to
one, and one-to-many:
-
One-Plus-One 1+1 : In this scheme, there are normally two lines: one working line and one
protection line. Both lines are active all the time. The sending multiplexer sends the same data
on both lines; the receiver multiplexer monitors the line and chooses the one with the better
44
quality. If one of the lines fails, it loses its signal, and, of course, the other line is selected at
the receiver. Although the failure recovery for this scheme is instantaneous, the scheme is
inefficient because two times the bandwidth is required.
-
One-to-One: In this scheme, which looks like the one-plus-one scheme, there is also one
working line and one protection line. However, the data are normally sent on the working line
until it fails. At this time, the receiver, using the reverse channel, informs the sender to use the
protection line instead. Obviously, the failure recovery is slower than that of the one-plusscheme, but this scheme is more efficient because the protection line can be used for data
transfer when it is not used to replace the working line.
-
One-to-Many n+m : This scheme is similar to the one-to-one scheme except that there is only
one protection line for many working lines. When a failure occurs in one of the working lines,
the protection line takes control until the failed line is repaired. It is not as secure as the oneto-one scheme because if more than one working line fails at the same time, the protection
line can replace only one of them.
Figure 4.3.9: Line protection
45
Ring Protection
SDH rings can be used in either a unidirectional or a bidirectional configuration. In each case, we can
add extra rings to make the network self-healing, capable of self-recovery from line failure.
Unidirectional Path Switching Ring (UPSR): is a unidirectional network with two rings: one ring
used as the working ring and the other as the protection ring. The idea is similar to the one-plus-one
APS scheme we discussed in a linear network. The same signal flows through both rings, one
clockwise and the other counterclockwise. A node receives two copies of the electrical signals at the
path layer, compares them, and chooses the one with the better quality. If part of a ring between two
ADMs fails, the other ring still can guarantee the continuation of data flow. UPSR, like the one-plusone scheme, has fast failure recovery, but it is not efficient because we need to have two rings that do
the job of one. Half of the bandwidth is wasted.
Figure 4.3.10: Unidirectional Ring Protection
Bidirectional Line Switching Ring (BLSR): In BLSR, communication is bidirectional, which
means that we need two rings for working lines. We also need two rings for protection lines. This
means BLSR uses four rings. The operation, however, is similar to the one-to-one APS scheme. If a
working ring in one direction between two nodes fails, the receiving node can use the reverse ring to
inform the upstream node in the failed direction to use the protection ring.
46
Figure 4.3.11: Bidirectional Ring Protection
3) Sub-Network Connection Protection (SNCP)
SNCP uses the 1+1 protection mode. Traffics are simultaneously sent on both the working and
protection sub-network connection. When the working sub-network connection fails, or when its
performance deteriorates to a certain level, at the receiving end of the sub-network connection, the
signal from the protection subnetwork connection is selected according to the preference selection
rule. Switching usually takes the unidirectional switching mode, thus it needs no APS protocol.
Figure 4.3.12: Sub-network connection protection
47
13. SDH network topologies and structures
SDH network as all other transmission networks has several different basic network topologies. When
designing a network, the things affecting the choice of the topology to be used are the network application,
the complexity of the network, the wanted reliability, geographical aspects and the current network in use.
The structure of network is also affected if there is a need for unidirectional, bi-directional or broadcast
network structure. In the unidirectional structure the signal is transmitted only into one direction via one
SDH network element. Distribution of video could be one application for the use of this type of coupling. In
the bi-directional structure there are bi-directional cross-connects in the SDH network elements. Bidirectional structure is used for needs of telephony and communications. In the broadcast structure the
incoming virtual container is coupled in SDH network element into several outgoing virtual containers. For
example, The Finnish broadcasting company Yleisradio uses this structure as a part of its network.
Chain network
The chain network is formed out of several consecutive network elements. Add and drop multiplexers can be
used to take the tributary unit signal out from the network. Tributary unit signals can be added alike.
Branching of the STM-1 level signals is done with the cross-connects.
Advantages:
-
Economical to build.
-
Easy to operate, administrate and maintain.
Disadvantages:
-
Traffics are difficult to protect.
Ring network
Figure 4.3.13: A chain network with 1+1 protection
The inherent protection feature is typical for the ring networks. Error in transmission medium or in node
does not cut the traffic in bi-directional ring networks. This type of protection requires that the capacity of
transmission is doubled in the case of error situations.
48
Advantages:
-
High survivability.
-
- High reliability.
Disadvantages:
-
To implement self-healing ability, the nodes must be configured using very complex methods.
-
Difficult to maintain.
Figure 4.3.14: Ring network implemented using add and drop multiplexers.
Mesh network
There are plenty of physical connections between the SDH network elements in network structured using
mesh topology. The situation can be so radical that there are connections between every network element.
This means that there is innumerable way to do the switching using mesh network solution and the
network done like this has a very reliable and large capacity. This complexity makes it very hard to manage
especially when it comes to synchronization.
Advantages:
-
No traffic bottleneck problem exists.
-
High reliability.
Disadvantages:
-
Complicated.
-
Costly.
-
Difficult to maintain.
49
Star Network
Figure 4.3.15: The principle of Mesh network topology.
In a star network there is a central node to which the other nodes are directly connected. There are no direct
links between other nodes.
Star network is mainly used in access networks or rural telephone networks in which nodes are scattered
here and there and the traffics are not important.
Figure 4.3.16: Star network
Advantages:
-
Have the capability of managing the bandwidth comprehensively and flexibly.
Disadvantages:
-
There is a potential bottleneck of the bandwidth at the central node.
-
An equipment failure of the central node may cause a breakdown of the entire network. 3
Tree network
A tree network can be considered as a combination of the chain and star topologies.Tree network is mostly
used for broadcasted services like CATV.
Advantages:
-
Advantage of the Tree Networks are similar to those of Chain and Star Networks.
Disadvantages:
-
Not suitable for bidirectional traffics.
50
Figure 4.3.16: Tree network
51
Sana'a Community College
HPE Division
TRAINIG REPORT
TCET Department
Report three
Switching Network
Don by
Abdullah Al-Marwani
Dherar Al-salahy
Emad Al-hasany
Mohammed Abdulwahab Al-Gahmi
Mojahed moaidh
Omair Yousef Al-Jaadi
Supervised By
Dr. Jameel Sultan
Communication Engineering Department
Sana'a Community Collage
Sana'a
52
2021
Title: Training in Public Telecommunication Corporation, at Operating and
Maintenance General Department. (switching network PSTN)
switching network(PSTN).
Major: Telecommunication Engineering
Field Training: PSTN network
Trainer: Abdolqaui AL-kharasani
Outcomes:
1. Introduction
2. Switching system hierarchy
3. Classification of Switching Systems
4. Basics of a Switching System
5. Electronic Exchanges
6. The Advantages of Electronic Exchanges Switching Techniques
53
4.4.Introduction of switching network
1. Introduction
The world has undergone many changes since the evolution of man.
For instance, the exchange of
information was initially in the form of signs and sounds. This transitioned to the language and script form
with advanced inventions. The communication from one place to another which called for distance between
individuals was carried through letters; sent by pigeons and between two groups through drum beats or
semaphores. Men used to travel long distances to pass on messages. Today ‘s world is more an age of
communication. The advancement of communication techniques has increased the speed with which the
transfer of information takes place. This development has not been an easy process. At the onset of the
invention of communication systems, the invention and usage of telephony was the most important one. The
way the telephone systems evolved from a basic system into an essential multi- purpose friendly gadget
today, leaves one and all astonished knowing the innovations made out of the meagre resources available in
those days.
The exchange of information between two or many individuals is called Communication. The word
tele is a Greek word which means distance. Hence, Telecommunication means the exchange of information
between two distant places. Telecommunications represent the transfer of information, from an entity at one
place to an entity at another place, whereas the information can be in the form of data, voice or symbol. The
entities can be human beings, computers, facsimile machines, telegraphy machines, phones or so on. In
telephone conversation, the one who initiates the call is referred to as the Calling Subscriber and the one for
whom the call is destined is the Called Subscriber. In other cases of information transfer, the communicating
entities are known as Source and Destination, respectively.
In March 1876, Alexander Graham Bell invented and demonstrated his telephone set and the
possibility of long-distance voice communication. He demonstrated the point-to-point communication, in
which a calling subscriber chooses the appropriate link to establish connection with the called subscriber.
This system also requires some mode of Signaling to alert the called subscriber about the incoming call and
a signal to indicate the calling subscriber, when the called subscriber is busy on another call.
Public switched telephone networks are communication systems that are available to the public to allow
users to interconnect communication devices. Public telephone networks within countries and regions are
standard integrated systems of transmission and switching facilities, signaling processors, and associated
operations support systems that allow communication devices to communicate with each other when they
operate. Figure 1.1 shows a basic overview of the Public Switched Telephone Network (PSTN) as deployed
in a typical metropolitan area. PSTN customers connect to the end-office (EO) for telecommunications
services. The EO processes the customer service request locally or passes it off to the appropriate end or
54
tandem office. As Different levels of switches interconnect the parts of the PSTN system, lower-level
switches are used to connect end-users (telephones) directly to other end-users in a specific geographic area.
Higher-level switches are used to interconnect lower-level switches.
Figure 4.4.1 Public Switched Telephone Network (PSTN)
Switches within the PSTN send control messages to each other, usually through a separate controlsignaling network called signaling system number 7 (SS7). The SS7 network is composed of signaling
transfer points (STPs) and service control point (SCP) databases. A STP is used to route packets of control
messages through the network. SCP’s are databases that are used by the network to process or reroute calls
through the network (such as 800 number toll free call routing). SS7 also provides for the newer features
such as incoming call identification and automatic call rerouting used by some service companies that
provide 24/7, worldwide dial-in support.
Need for Switching Exchanges
The point-to-point connection for establishing communication requires the telephone sets to be linked using
wires. If the number of telephone sets or the subscribers present is low in number, the type of connection
will be a little complex. However, if this number is high or moderate, then the connections will lead to a
mess. To understand the complication, let us consider a network of 5 subscribers. The following figure
shows a point-to-point connection for five subscribers (telephone sets):
55
Figure 4.4.2 Point to point connection
In the point-to-point connection, for n entities, we need n(n-1)/2 links. All these links form a network.
Networks with point-to-point links among all the entities are known as Fully Connected Networks. The
number of links required in a fully connected network becomes very large even with moderate values of n.
Hence, a system of switching the networks is needed in-between these subscribers. Alexander Graham
Bell recommended the Switching between the subscribers using a switching office that maintains the
telephone connections.
Switching Systems
This network connection cannot be simply made with telephone sets and bunch of wires, but a good system
is required to make or break a connection. This system is known as the Switching System or the Switching
Office or the Exchange. With the introduction of the switching system, the subscribers instead of getting
connected directly to one another, are connected to a switching office and then to the required subscriber.
The following figure will help you understand the switching system.
Figure 4.4.3 switching system
Switching systems are assemblies of equipment that setup, maintain, and disconnect connections between
multiple communication lines. Switching systems are often classified by the type of network they are part of
(e.g., packet or circuit switched) and by the methods that are used to control the switches. The term “switch”
is sometimes used as a short name for switching system. Public telephone switching systems have many
56
switches within their network. A typical switch can handle up to 10,000 communication lines each. Early
switches used mechanical levers (crossbars) to interconnect lines.
Modern switches use computer systems to dynamically setup, maintain, and disconnect
communication paths through one or more switches. True computer-based switching came about through the
introduction of the electronic switching systems (ESS’s). ESS EOs did not require a physical connection
between incoming and outgoing circuits. Paths between the circuits consisted of temporary memory
locations that allowed for the temporary storage of traffic. For an ESS system, a computer controls the
assignment, storage, and retrieval of memory locations so that a portion of an incoming line (time slot) could
be stored in temporary memory and retrieved for insertion to an outgoing line. This is called a time slot
interchange (TSI) memory matrix. The switch control system maps specific time slots on an incoming
communication line (e.g., DS3) to specific time slots on an outgoing communication line. The public
telephone network switching system architecture typically uses a distributed switching system that has a
hierarchy structure of switching levels. The use of distributed switching systems allows calls in the same
geographic area to be connected to each other by the nearest switching system. Centralized switching
systems require that all calls be connected through a single switch, even if the switch was located a long
distance away from the callers. The use of distributed network architecture PSTN systems also allows for
reduced call processing requirements at each switch. Using a multilevel hierarchy structure for switching
systems (such as local switched interconnected by long distance switches) allows switching to occur at lower
levels of switching unless the telephone call must pass between multiple switches. At that point, the call is
passed up to a higher-level switch for transfer to more distant locations.
In conjunction with distributed network architecture which is arranged in the hierarchy of serving offices.
The offices are buildings where the switching equipment is located and they are so coordinated to effectively
transition traffic through the network. The equipment office closest to the subscriber is called the “end
central office”. This central office is unique to a given NNX or exchange number for a given community so
that the only way to terminate a phone call to a specific customer is through his serving end central office.
Multiple end central offices are then connected to local tandems that facilitate connections between all other
local and central offices in that community. For calls outside the local tandem serving area, area tandems are
employed and basically are best represented by area codes or NPAs for the dialing plans served by that
telephone company. Then, if the concentration of traffic is large enough, a company may employ regional
tandems as well. Regional tandems would be the interface point between other serving telephone companies
for the purposes of connection and cross-connection to the other telephone companies.
Tandems can be duplicated to insure fault-tolerant routing of telephone calls. A telephone number and a
specific telephone are served by only one end central office. Should there be equipment fault at that end
57
central office serving that telephone customer he will lose all of his services until the matter is corrected.
This telephone hierarchy should be integrated with a third complete paragraph starting with public telephone
switching systems used and office telephone switches.
2. Switching system hierarchy
Figure shows the switching system hierarchy
‫ ـــ‬International gateway: These offices have access to international gateway offices in other
countries. They also provide international operator assistance.
Figure 4.4.4 Switching system hierarchy
58
Subscriber Loop Systems
In a general telephone network, every subscriber has two dedicated lines connecting to the nearest switching
exchange, which are called the Loop lines of that subscriber. The laying of lines to the subscriber premises
from the exchange office is called Cabling. As it is difficult to run cables from each subscriber‘s premises to
the exchange, large cables are used through which the drop wires (subscriber lines) are taken to a distribution
point. The drop wires are connected to wire pairs distribution point, in the cables. Such distribution cables
from nearby geographical area are connected at a same feeder point where they connected to branch feeder
cables which in turn, are connected to the main feeder cable. This whole process can be understood with the
help of the following figure.
Figure 4.4.5 Subscriber Loop Systems
The subscriber cable pairs from the exchange will also terminate at MDF through main feeder cables that
carry large number of wire pairs. These subscriber pairs and exchange pairs are interconnected at the MDF
using jumpers, which makes MDF to provide flexible mechanism for reallocating cable pairs and subscriber
numbers. This means a subscriber who shifts to a different location though in the same exchange area, can be
allowed to use the same number using appropriate jumper, while his old drop wires can be used by another
subscriber with a new number. The local loop is the connection (wireless or wired) between a customer’s
telephone or data equipment and a LEC or other telephone service provider. Traditionally, the local loop
59
(also called “outside plant” or the “last mile”) has been composed of copper wires that extend from the EO
switch. The EO is the last switching office in the telephone network that connects customers to the telephone
network. The EO switch cables meet the copper (or other types of lines) at the main distribution frame
(MDF). The MDF is a wiring rack that allows technicians to splice the local loop lines with the lines from
the switching system. Local loop lines leave the MDF in bundles (possibly thousands of wires in each
bundle) and arrive in other junction points such as local distribution frames (LDF). The LDF allows the
connection of the final connection (the “drop”) to the business or residence. At the entry to the customer’s
location, there is often a network termination (NT) device that isolates the telephone network from the
wiring inside the customers building.
Figure 1.2 depicts a traditional local loop distribution system. This diagram shows a central office (CO)
building that contains an EO switch. The EO switch is connected to the MDF splice box. The MDF connects
the switch to bundles of cables in the “outside plant” distribution network. These bundles of cables
periodically are connected to local distribution frames (LDFs). The LDFs allow connection of the final cable
(called the “drop”) that connects to the house or building. A NT block isolates the inside wiring from the
telephone system. Twisted pair wiring is usually looped through the home or building to provide several
telephone connection points, or jacks, so telephones can connect to the telephone system.
Figure 4.4.6 Local Loop
3. Classification of Switching Systems
In the early stages of telecommunication systems, the process and stages of switching, played an
important to make or break connections. At the initial stages, the switching systems were operated
manually. These systems were later automated. Figure 4.4.7 shows how the switching systems were
classified.
60
Figure 4.4.7 Classification of Switching Systems
The switching systems in the early stages were operated manually. The connections were made by the
operators at the telephone exchanges in order to establish a connection. To minimize the disadvantages of
manual operation, automatic switching systems were introduced. The Automatic switching systems are
classified as the following:
1. Electromechanical Switching Systems - Here, mechanical switches are electrically operated.
2. Electronic Switching Systems – Here, the usage of electronic components such as diodes,
transistors and ICs are used for the switching purposes.
Electromechanical Switching Systems
The Electromechanical switching systems are a combination of mechanical and electrical switching types.
The electrical circuits and the mechanical relays are deployed in them. The Electromechanical switching
systems are further classified into the following.
1. Step-by-step: The Step-by-step switching system is also called the Strowger switching system after
its inventor A B Strowger. The control functions in a Strowger system are performed by circuits
associated with the switching elements in the system.
2. Crossbar: The Crossbar switching systems have hard-wired control subsystems which use relays and
latches. These subsystems have limited capability and it is virtually impossible to modify them to
provide additional functionalities.
Electronic Switching Systems
The Electronic Switching systems are operated with the help of a processor or a computer which control the
switching timings. The instructions are programmed and stored on a processor or computer that control the
operations. This method of storing the programs on a processor or computer is called the Stored Program
Control (SPC) technology. New facilities can be added to a SPC system by changing the control program.
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The switching scheme used by the electronic switching systems may be either Space Division Switching or
Time Division Switching.
•
Space division switching, a dedicated path is established between the calling and the called
subscribers for the entire duration of the call.
•
Time division switching, sampled values of speech signals are transferred at fixed intervals.
The time division switching may be analog or digital. In analog switching, the sampled voltage
levels are transmitted as they are. However, in binary switching, they are binary coded and
transmitted. If the coded values are transferred during the same time interval from input to
output, the technique is called Space Switching. If the values are stored and transferred to the
output at a time interval, the technique is called Time Switching. A time division digital switch
may also be designed by using a combination of space and time switching techniques.
3. Basics of a Switching System
In this section, we will learn about the different components and terms used in switching systems.
•
Inlets and Outlets: The set of input circuits of an exchange are called Inlets and the set of output
circuits are called the Outlets. The primary function of a switching system is to establish an electrical
path between a given inlet-outlet pair. Usually, N indicates the inlets and the outlets are indicated by
M. So, a switching network has N inlets and M outlets.
•
Switching Matrix: The hardware used to establish connection between inlets and outlets is called the
Switching Matrix or the Switching Network. This switching network is the group of connections
formed in the process of connecting inlets and outlets. Hence, it is different from the
telecommunication network mentioned above.
•
Types of Connections: There are four types of connections that can be established in a
telecommunication network. The connections are as follows:
1. Local call connection between two subscribers in the system.
2. Outgoing call connection between a subscriber and an outgoing trunk.
3. Incoming call connection between an incoming trunk and a local subscriber.
4. Transit call connection between an incoming trunk and an outgoing trunk.
•
Folded Network: When the number of inlets is equal to the number of outlets for a switching
network, such a network is called the Symmetric Network, which means N=M. A network where the
outlets are connected to the inlets, is called the Folded Network. In a Folded Network, the N number
of inlets which come as outlets are again folded back to the inlets. Nevertheless, the switching
network provides connections to the inlets and outlets as per the requirement. As one connection can
be given to one line per time, only N/2 connections are established for N inlets of a folded network.
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Such a network can be called as Non-blocking network. In a non- blocking network, as long as the
called subscriber is free, a calling subscriber will be able to establish a connection to the called
subscriber. The inlet and outlet connections if used in an Inter-exchange transmission such that
the exchange does not support connection between local subscribers, then it is called the
Transit Exchange. A switching network of such kind is called the Non-folded network. This is
shown in the following figure:
Figure 4.4.8 Switching network
•
Blocking Network: If there are no switching paths free in the network, the call requested will be
denied, where the subscriber is said to be blocked and the network is called the Blocking Network. In
a blocking network, the number of simultaneous switching paths is less than the maximum number
of simultaneous conversations that can take place. The probability that a user may get blocked is
called the Blocking Probability. A good design should ensure low blocking probability.
•
Traffic: The product of the calling rate and the average holding time is defined as the Traffic
Intensity. The continuous sixty-minute period during which the traffic intensity is high is the Busy
Hour. When the traffic exceeds the limit to which the switching system is designed, a subscriber
experiences blocking.
•
Erlag: The traffic in a telecommunication network is measured by an internationally accepted unit of
traffic intensity known as Erlang (E). A switching resource is said to carry one Erlang of traffic if it
is continuously occupied through a given period of observation.
Elements of a Switching System
Though there are different kinds of switching systems from manual to automatic, a few basic elements play
an essential role for the functioning of a switching system. Along with the switching network, there are
different sub systems such as control sub system, signaling system, trunk and subscriber line interfaces,
distributor units, operator console, juncture circuits, essential for the operation of the whole switching
system.
Switching System
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In this section, we will understand the structure of the switching system. We will also understand how the
different elements work in it. Figure 2.1 shows the block diagram of the switching system given below show
the essential elements of a switching system.
Figure 4.4.9 The block diagram of the switching system
The diagram shown above contains different blocks of the switching system. The blocks are discussed
below.
•
Switching Network: It provides the switching paths between the called subscribers and the calling
subscribers.
•
Control Subsystem: This is the critical part of the switching system, which actively establishes the
switching paths, by identifying the inlet and outlet lines and interpreting the signaling information
received on these lines. This control subsystem, controls the making and breaking of the connection
by sensing the signal transfer on the lines. The control sub system sends out signaling information to
the subscriber and other exchanges connected to the outgoing trunks.
•
Signaling: The signaling formats and requirements for the subscriber, the trunks and the sub systems
differ significantly. Accordingly, a switching system provides for three different forms of
signaling:
1. Subscriber loop signaling
2. Interexchange signaling
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3. Intra-exchange or register signaling
A switching system is composed of elements that perform switching, control and signaling functions.
•
Trunk Interface: The Trunk lines used for connections between the switching systems, are
terminated at this port. The Trunk interface is the point where the trunk lines are connected to the
system.
•
Subscriber Line Interface: The Subscriber lines used for connections between the subscribers and
the switching systems are terminated at this port. The subscriber line interface is the point where the
lines from the subscribers are connected to the system.
•
Line Scanning Unit: The line scanning unit senses and obtains the signaling information from the
respective lines. The information obtained from these lines are given to the control sub system to
identify the inlets and outlets.
•
Distributor Units: The distributor units are used for distributing or sending out the signaling
information on the respective lines. The distribution of information through the trunk lines, is done
through the distribution units
•
Operator Console: The operator console permits interaction with the switching system for
maintenance and administrative purposes.
•
Service Circuit Interface: The service circuit interface provides interaction between circuits for
maintenance and testing purposes.
•
Junctures: The Junctures is a junction that provides a folded connection for the local subscribers and
the service circuits. If the called subscriber and the calling subscriber both are local, then the folded
connection helps in making the connection to a local call, whereas the trunk lines will not be in use.
•
Direct and Indirect: The switching systems are of the following two types:
1. Direct Control Switching System: The Switching systems where the control sub systems
form an integral part of the network are called the Direct Control Switching systems. For
example, the Strowger switching system.
2. Indirect Control Switching System: The Switching system in which the control sub
system is present outside the switching network is called the Indirect Control Switching
system or the Common Control Switching system or the Register Control switching
system. The examples of this system include Crossbar switching system, Electronic
switching system or Stored Program Control method of switching systems.
•
Strowger Switching System: The first ever automatic telephone switching was developed by Almon
B Strowger. As the operator at the Manual telephone exchange was the wife of his competitor
and was diverting all the business, Strowger thought of developing a switching system, which does
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not require an operator. This led to the invention of the automatic switching system developed by
Strowger. The Strowger Switching system is also called the step-by-step switching system as the
connections are established in a step-by-step manner.
•
Automatic Switching System: The Manual Switching system requires an operator who after
receiving a request, places a call. Here, the operator is the sole in-charge for establishing or releasing
the connections. The privacy of the calls and the details of the called and the calling subscribers are
at stake. Overcoming the disadvantages of Manual Switching systems, the Automatic Switching
systems come with the following advantages:
1. Language barriers will not affect the request for connection.
2. Higher degree of privacy is maintained.
3. Faster establishment and release of calls is done.
4. Number of calls made in a given period can be increased.
5. Calls can be made irrespective of the load on the system or the time of the day.
6. Electronic Exchanges
Initially the electronic exchanges used the transistor a switching element. But with further technological
advancements, integrated circuits took over. The controls in this system are computer controlled. These
advanced systems usually comprise four major blocks as shown in Fig. 4.4.10.
1. Connection unit (Interface Unit)
2. Switching networks
3. Control unit
4. Maintenance unit
Let us discuss the functions of these units in brief:
•
Connection Unit: Interface block shown in Fig.7.17 represents the connection unit. It performs the
job of providing interface between subscribers and the switching networks. On the one end, the
subscriber lines are connected to the connection unit while the other end is connected to the
switching network. The connection unit is also connected to the control unit, which monitors all the
actions of the exchange. The major functions of the connection unit are:
1. Providing battery supply to subscriber lines.
2. Converting analog speech signals received from callers in to digital form.
3. Feeding various tones to subscriber (dial, busy, ringing tone etc.).
4. Play recorded announcements.
•
Switching Network: It is the largest sub-system in size comprising many electronic switches
performing routing of call from one interface unit to another, i.e. it carries out the function of
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establishing connection between calling and called subscriber.
This switching facilitates
transmission of speech signal between the two points. It is controlled by a control unit.
Figure 4.4.10: Block Schematic diagram of electronic exchanges
•
Control Unit: The entire system is controlled by this centralized unit. It monitors and controls all the
activities of the exchange. It is basically an electronic controller in the form of microprocessor,
microcontroller, microcomputer or advance computer. With the advances in technology, the capacity
of controllers has improved and along with monitoring the switching operations, it can handle many
more other functions that the subscribers demand. Mostly, the control unit operates on the principle
of Stored Programmer Control, commonly termed as SPC. In this scheme, all the switching
procedures to set up a call are already stored in the memory files known as programmer modules.
The processor handling the call accesses this programmer and executes it. The main functions of the
control unit are:
1. Call set up: This includes monitoring of subscriber lines through connecting unit to detect
new calls, releasing subscriber lines after call completion, and receiving and transmitting the
dialed digits.
2. Making and Breaking the call: Issuing the instruction to switching networks to connect the
calling subscriber to the called subscriber and disconnecting it after call completion.
3. Supervision: This covers identification of type of subscriber; detection of error condition;
confirming the fault and determining its location; and controlling alarm circuits.
4. Charging: This cover handling the subscribers accounts; counting the number of metered
charges; registering the duration of each call and charging it as per the type of the call i.e.,
Local, STD, ISD.
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Modern electronic exchanges working with computer control can handle many additional features
like
1.
Push button dialing: DTMF dialing which increases the speed of number dialing.
2.
Conference call:
A subscriber can set up connection with more than one subscriber
simultaneously to conduct a conference on telephone.
3.
Call waiting: By this facility subscriber can receive another call even if already one call is in
progress.
4.
Call transfer: Subscriber can receive the telephone call on any other predecided telephone
number automatically.
5.
Announcements: Any type of pre-recorded announcements can be played on subscriber lines
in electronic exchanges. e.g., this route is busy or this number is changed etc.
6.
Caller ID: The telephone number of calling subscriber is displayed on the called subscriber’s
telephone.
7.
Detailed billing: The record of time, date and duration of the calls made by the subscriber can
be made available.
8.
Dynamic Lock: Telephone can be barred for outgoing calls such as STD, ISD or even local
calls by dialing a code.
•
Maintenance Unit: This is also known as Operation and Maintenance Centre (OMC). It performs
the important functions of monitoring the working of all the units; watching subscribers’ meters and
store metered information for generating the bills; and management of traffic data.
5. The Advantages of Electronic Exchanges are:
1. The electronic exchange allows handling of analog as well as digital signals. This improves speed
and quality of data transmission as well as allows facilities like Internet Connectivity.
2. It requires less maintenance since there are no mechanical or electromechanical switches.
3. Since there are no physical wire links involved, the installation and maintenance of these exchanges
is cost and time effective.
4. Capacity of these exchanges can be easily expanded since only electronic switching boards need to
be added which do not occupy large space.
5. Possibility of using time division switching reduces the physical space and hardware involved.
Common Control Subsystem
In order to avoid the complication and to make it easier for a subscriber to place a call, two main ideas were
implemented by the Common Control Sub system. The ideas are listed below:
1. The routing of the call should be done by the exchange, but not by the numbers dialed.
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2. A unique Identification Number should be allotted to the subscriber. The UIN contains the number
of the exchange of the subscriber and the number indicating the line of the subscriber.
The above ideas helped solve the problem associated with the placement of calls. These two solve the
problem and make the work simple. Wherever the calling subscriber calls from, the call is directed to the
particular called subscriber, in a particular network. The routing of this call is taken care by the exchange
itself. Hence, the uniform numbering scheme identifies the subscriber based on the aspects described below.
Exchange Identifier + Subscriber Line Identifier
This is a combination of STD (Subscriber Trunk Dialing) code and the subscriber ‘s number; consider this as
the physical line address. Every user is assigned a logical number irrespective of the physical line number.
An Address translation mechanism translates the logical address to actual physical address for connection
establishment. The call processing takes place independent of the switching network. A Director system is
employed in the common control sub system. As soon as the translated digits are transmitted, the Director is
free to process another call and is not involved in maintaining the circuit for the conversation. The figure
below shows the diagram of the Common Control Subsystem, which contains Call Processing Sub system,
Charging Circuits, Operation Control, Maintenance Control and Event Monitor.
Figure 4.4.11 Common control subsystem
The above block diagram is a simple indication of the common control switching system. The control
functions in a switching system can be categorized as the following.
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1) Event Monitoring: Event monitoring section of the control subsystem monitors the events occurring
outside the exchange at
the
line
units, trunk junctures and
inter
exchange
signaling
and sender/receiver units. The events at the line units are - call request and call release. The control
of relays to establish connection to the required line is an event at the junctures. There is control of
relays between the exchanges for connection and also for signaling the required tones both to the
sender and receiver circuits at the inter exchange. This event monitoring may be distributed.
2) Call Processing: The call processing units contain digit receiver and storage register, which receive
and store the dialing number from the calling party. The units also contain the initial and final
translators. The Initial translator is the Office Code translator that determines the route for the call
through the network or charging method or rate. The Final translator is the Subscriber Code
translator which determines the line unit to which a call must be connected and category of the
called line. The Register Sender transfers the route digit and dialed digit using proper signaling,
depending on the requirements of the destination exchange.
3) Charging: This is related to the charges levied on the calls made. It depends upon the type of
subscriber and the service of the subscriber. For example, some services like emergency lines or fault
repairs are free of charge; a few commercial services also may offer charge- free services.
4) Operation and Maintenance: The control and operation of the switching network with two main
techniques known as Map-in-memory and Map-in-network.
1. Map-in-Memory: The path in this technique is determined by marking the switching elements at
different stages in accordance with a set of binary data defining the path, whereas the control unit
supplies the data. At this stage, the command for the actual connection of the path is given. This
Map-in-memory technique is present in Stored Program Control.
2. Map-in-Network: In this technique, the Path finding may be carried out at the level of common
control unit, where it marks the inlet and outlet to be connected and the actual path is determined
by the switching network. This Map-in-Network technique is common in Crossbar exchanges
using markers for control.
The administration and maintenance of a switching system, involves activities such as laying the new
subscriber lines and trunks into service, modifying subscriber service entitlements and changing routing
plans based on the network status, which are performed with the coordination of control systems.
Maintenance personnel do the maintenance activities such as supervision for proper functioning,
performing tests and making measurements for different line parameters.
Switching Techniques
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In this chapter, we will discuss the switching techniques in Telecommunication Switching Systems and
Networks. In large networks, there may be more than one path for transmitting data from the sender to
the receiver. Selecting a path that data must take out of the available options can be understood as Switching.
The information may be switched while it travels between various communication channels. There are three
typical switching techniques available for digital traffic. They are:
1) Circuit Switching
2) Message Switching
3) Packet Switching
Let us now see how these techniques work.
Circuit Switching
In Circuit switching, two nodes communicate with each other over a dedicated communication
path. In this, a circuit is established to transfer the data. These circuits may be permanent or temporary.
Applications that use circuit switching may have to go through three phases. The different phases are:
1. Establishing a circuit
2. Transferring the data
3. Disconnecting the circuit
Figure 4.4.12 shows the pattern of Circuit switching.
Figure 4.4.12 Circuit switching
Circuit switching was designed for voice applications. Telephone is the best suitable example of circuit
switching. Before a user can make a call, a virtual path between the called subscriber and the calling
subscriber is established over the network. The drawbacks of circuit switching are:
1. The waiting time lasts long, and there is no data transfer.
2. Each connection has a dedicated path, and this gets expensive. When connected systems do
not use the channel, it is kept idle. The circuit pattern is made once the connection is
established, using the dedicated path which is intended for data transfer, in the circuit
switching. The telephone system is a common example of Circuit Switching technique.
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Message Switching
In message switching, the whole message is treated as a data unit. The data is transferred in its entire
circuitry. A switch working on message switching, first receives the whole message and buffers it until there
are resources available to transfer it to the next hop. If the next hop is not having enough resource to
accommodate large size message, the message is stored and the switch waits.
Figure 4.4.13 shows the pattern of Message switching.
Figure 4.4.13 Pattern of Message switching
In this technique, the data is stored and forwarded. The technique is also called the Store- and- Forward
technique. This technique was considered a substitute to circuit switching. But the transmission delay that
followed the end-to-end delay of message transmission added to the propagation delay and slowed down the
entire process. Message switching has the following drawbacks:
1. Every switch in the transit path needs enough storage to accommodate the entire message.
2. Because of the waiting included until resources are available, message switching is very slow.
3. Message switching was not a solution for streaming media and real -time applications.
The data packets are accepted even when the network is busy; this slows down the delivery. Hence, this is
not recommended for real time applications like voice and video.
Packet Switching
The packet switching technique is derived from message switching where the message is broken down into
smaller chunks called Packets. The header of each packet contains the switching information which is then
transmitted independently. The header contains details such as
node
source,
destination and
intermediate
address information. The intermediate networking devices can store small size packets and don‘t
take many resources either on the carrier path or in the internal memory of switches. Individual routing of
packets is done where a total set of packets need not be sent in the same route. As the data is split,
bandwidth is reduced. This switching is used
for performing data rate conversion.
Figure 4.4.14 shows the pattern of Packet switching.
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Figure 4.4.14 A) A typical packet format. b) Packet switching network
The line efficiency of packet switching can be enhanced by multiplexing the packets from multiple
applications over the carrier. The internet which uses this packet switching enables the user to differentiate
data streams based on priorities. Depending upon the priority list, these packets are forwarded after storing
to provide quality of service. The packet switching technique was proved to be an efficient technique and is
being widely used in both voice and data transfer. The transmission resources are allocated using different
techniques such as Statistical Multiplexing or Dynamic Bandwidth allocation.
The figure 4.4.15 illustrates the connection switching types.
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Figure 4.4.16 connection switching types
In addition, the figure 4.4.17 summarizes the transfer modes and connection types
Figure 4.4.17 Transfer modes and connection types
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Statistical Multiplexing
Statistical multiplexing is a communication link sharing technique, which is used in packet switching. The
shared linking is variable in statistical multiplexing, whereas it is fixed in TDM or FDM. This is a strategic
application for maximizing the utilization of bandwidth. This can increase the efficiency of network, as well.
By allocating the bandwidth for channels with valid data packets, statistical multiplexing technique
combines the input traffic to maximize channel efficiency. Each stream is divided into packets, and delivered
on a first-come, first-served basis. The increase in priority levels allow to allocate more bandwidth. The time
slots are taken care not to be wasted in the statistical multiplexing whereas they are wasted in time division
multiplexing.
Time Division Multiplexing
When the transmission of data or signals is done in digital means, using the limited number of resources
available, then the Time Division Multiplexing is used for the transmission of such data. Multiplexing is the
process in communication, which merges two or more signals at its input into a single output, which when
de-multiplexed, offers all those signals separately as they were. The Multiplexers are broadly classified as
Analog and Digital, where the Time Division Multiplexing comes under Digital Multiplexing. There are two
types of TDM called as Synchronous and Asynchronous TDM discussed as following:
1) Time Division Space Switching
Time division switches may also employ space division switching techniques, whereas an
appropriate mixture of both time and space division switching is advantageous in various
circumstances. A Time division space switch takes outputs of several time-division switches (say,
TSI switches) which are then given as inputs to space division switches. This means that one of the
two similar outputs produced by a TDM switch, can be selected by space switch to deliver to another
output path which reduces the number of Cross-points. The model of time division space switch is as
shown in figure2.20 below.
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Figure 4.4.118 Time division space switch model
The interchange of time slots is not possible in time division switching, as the incoming time slot
transfers the data to its dedicated output time slot only. Hence, time multiplexed switches do not
provide full availability. A time multiplexed Time Division Space Switch can be configured around
a space array, which has M input horizontals and N output verticals. If both inputs and outputs are
equal, M=N the switch leads to non-blocking. If inputs are greater than outputs; for concentrating
switch we have M>N and if the outputs are higher, the switch expands gathering one more
connection. In every time slot, one logic gate per vertical if M>N, or one logic per horizontal if M<N
is enabled for one-to-one connections. In every time slot, up to N or M samples are switched
simultaneously. Because of the parallel transfer of N or M data samples in each time slot, a large
number of channels can be multiplexed per input line. If along with multiplexing for N control
memory modules, full availability has to be achieved, one should opt for time division time
multiplexing technique.
2) Time Division Time Switching
The main advantage of time division time multiplexing technique is that, unlike time division
space switching, it allows time slot interchange (TSI) of sample values. In TSI, a speech sample input
during a time slot may be sent to the output during a different time slot, which implies a delay
between reception and transmission of a sample. The rate at which the time slot clock runs is 125-μ
sec. The time slot counter increments by one, at the end of each clock pulse, the contents of which
provide location addresses for data memory and control memory. The input sample is read at the
beginning of the slot and it is clocked at the end of the clock pulse. Because of the storage action, the
sample is delayed at least by a single time slot in passing from the input to the output, even if there is
no time slot interchange. A TSI which can be expanding or concentrating, has different number of
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time slots per frame at input and output also. For an expanding switch, the output bit rate is
higher, whereas for a concentrating switch, the input bit rate is higher. The handling of input and
output subscribers in this technique can be done in four ways, such as serial-in/serial-out, parallelin/parallel-out, serial-in/parallel-out, parallel-in/serial-out.
77
TRAINIG REPORT
Sana'a Community College
Report four
HPE Division
TCET Department
NGN
Don by
Abdullah Al-Marwani
Dherar Al-salahy
Emad Al-hasany
Mohammed Abdulwahab Al-Gahmi
Mojahed moaidh
Omair Yousef Al-Jaadi
Supervised By
Dr. Jameel Sultan
Communication Engineering Department
Sana'a Community Collage
Sana'a
78
2021
Microwave Report 3
Title: Training in Public Telecommunication Corporation, at Operating and
Maintenance General Department.
(Switching Technology (NGN) in Public Telecommunication Corporation)
Major: Telecommunication Engineering
Field Training: Switching Technology (NGN)
Trainer: Hassan al-shithaly
Outcomes:
1. Introduction of Next Generation Networking (NGN).
2. TDM Service Architectures
3. NGN Network Architecture
4. Network Elements
5. Benefits of a Next Generation Services Architecture
6. Characteristics of NGN in contrast with TDM.
7. NGN Technology Operation.
8. How does PSTN work with NGN
9. Application of NGN
10. Advantages and disadvantages of NGN
79
4.5.
Next Generation Network
1. Introduction
Telecommunication Next Generation Network NGN is a converged network aims to provide a multitude of
services over a single integrated network infrastructure, rather than multiple separated and overlay networks,
as have existed for decades. NGN designing have brought unique challenges in how to design and
dimensioning the NGN to meet the uncertain market demands of the new bandwidth hungry services with a
minimum cost. Building any NGN telecom network should pass through the three main phases, Network
Planning, Designing, and Network Innovation with the new value-added services VAS. This paper will
present a precisely method based on mathematics criteria to calculate the essential resources and
equipment’s needed for NGN deployment in its’ three different phases. This method aims to reduce the
capital expenditure (CAPEX) by determining the optimal quantities of the equipment’s that meet the highly
required grade of services. Innovating the network with a high usability new NGN VAS services is very
important phase of the network that enrich the life with the introduced services, attract and increase the
subscriber’s loyalty and the ARPU.
Telecommunication Next Generation Network NGN is a packet-switched network providing a range
of telecommunications services, which uses transport technologies for several bandwidths and classes of
services, in which service-related functions are independent of the underlying transport technologies. NGN
covers multiple networks and layers. It is a means of providing services across a range of technologies
giving users consistent and ubiquitous service provision, and unrestricted access to different service
providers, with supporting general mobility. NGN provides a single platform and integrate
the existing
separated voice and data networks into a simpler and more flexible network based on IP protocols. The aim
of the telecom operators (fixed and mobile) in the whole world is to migrate their networks to NGN in order
to benefit from the NGN features as well as to avoid the drawbacks coming from their legacy networks,
beside other financial factors such as reducing the capital expenditure (CAPEX) and the operation
expenditure (OPEX).
2. TDM Service Architectures
At the core of traditional circuit-switched voice service networks were the Class 4/5 switch (referred to as
C5 switch in the rest of this document). C5 switches were monolithic devices built from the ground up on
proprietary hardware and software components much like a mainframe computer. All of the functions
necessary to run the service logic and connect to the network were built into these switches (Figure 1). These
functions fell into one of four categories:
1. Service Logic.
2. Signaling and Call Control.
80
3. Network Interfaces.
4. Media Processing
Figure 4.5.1 TDM Service Architectures–The Four Key Functions of Class 4/5 Digital Switch
3. Next Generation Network Architecture
Next Generation Network architecture is designed to be the infrastructure of the future telecommunication
networks and services, and meet the new requirements due to emerging of number of services and
applications (Broadband, IPTV, Multimedia …..etc). Standards organization such as ITU and ETSI , are the
primary workers for designing NGN architecture. TISPAN The technical committee for Telecommunication
and Internet converged Services and Protocols for Advanced Networking continues the working on NGN
architecture specification till today. TISPAN specification is known as TISPAN NGN R1[15]. It was
composed by the leading telecom vendors and operators, to fulfill services providers requirements.
The architecture highlight of TISPAN R1 can be summarized as following:
1. PSTN emulation subsystem to support legacy PSTN services over NGN.
2. An independent access technology.
3. Support Session initial protocol (SIP) and non-SIP based applications.
4. IP Multimedia Subsystem (IMS) supporting SIP based applications.
5. Road map for fixed/mobile convergence.
6. Adaptable with other standards development organizations.
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The overall NGN architecture is summarized in the below three layers:
A. Access Network Layer: The access network layer consists of different types of equipment’s that
help the end user to interconnect with the NGN such as: Multi-Service Access Nodes (MSAN) which
able to deliver different services including telephony, high speed internet access and video services
using the same copper pair. Different Access Gate Ways (AGWs) will be installed in the customers
campuses for access to NGN. It also supports the access to narrow band services.
B. Edge/Core Network Layer: Edge/Core network uses label switching technology MPLS with the
ability to set up connection-oriented paths over a connectionless IP. This part of NGN network
includes: Ethernet Service Switch (ESS), Service Routers (SR) and Routing Management (RM).
C. Control Layer: The control layer controls all the calls and bearer in the network. It consists of:
-
Soft Switch (SS) is the telephony signaling and control platform. Soft switch contains four functional
blocks:
• Residential Gateway Controller (RGC).
• Call and Session
• Subscription
• Media
Controller (CSC).
Location
Gateway
Server (SLS).
Controller (MGC).
Media Gateway (MG) is the equipment that converts the voice traffic from TDM into VoIP. MG
offers services such as: VoIP Termination, VoIP Trucking, TDM to Primary Rate Interface (PRI)
grooming, and Private Branch Exchange (PBX) Access. Management Center is the management
application converging all management elements from VoIP subsystem and OSP (Open System
Platform). It gives centralized access from single server to all Graphic User Interfaces GUIs that used
by operation application. Based on the above architecture, different solutions for network design and
migration from PSTN to NGN can be deployed. At the first step of migration NGN will based on
soft switch solution that can separate the call control from bearer and services platform.
Figure 4.5.2 shows NGN layers architecture.
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Figure 4.5.2 NGN layers architecture
4. Network Elements
NGN network has many elements that build the network architecture as shown in figure 4.5.3
Figure 4.5.3 NGN network architecture and network elements
NGN network elements are discussed as following:
1) Packet based networks
a) Trend is to use IP based networks over various transport possibilities (ATM, SDH, WDM…).
b) In addition, IP based networks must offer guarantees of Quality of Service (QoS) regarding the
real time characteristics of voice, video and multimedia.
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2) Access Gateways
a) Allows the connection of subscriber lines to the packet network.
b) Converts the traffic flows of analogue access (Pots) or 2 Mb/s access devices into packets.
c) Provides subscriber access to NGN network and services.
3) Trunking Gateways
a) Allows interworking between classical TDM telephony network and Packet-based NGN
networks.
b) Converts TDM circuits/ trunks (64kbps) flows into data packets, and vice versa.
4) Softswitch/MGC
a) referred to as the Call Agent or Media Gateway Controller (MGC).
b) Provides the “service delivery control” within the network, in charge of Call Control and
handling of Media Gateways control (Access and/or Trucking) via H.248 protocol.
c) Performs signaling gateway functionality or uses a signaling gateway for interworking with
PSTN N7 signaling network.
d) Provides connection to Intelligent Network /applications servers to offer the same services as
those available to TDM subscribers.
5) Application Server (AS)
A unit that supports service execution, e.g. to control Call Servers and NGN special resources (e.g.
media server, message server).
6) H.248 Protocol
a) Known also as MEGACO: standard protocol, defined by ITU-T, for signaling and session
management needed during a communication between a media gateway, and the media gateway
controller managing it.
b) H.248/MEGACO allows to set up, keep, and terminate calls between multiple endpoints as
between telephone subscribers using the TDM.
7) Session Initiation Protocol SIP
Session Initiation Protocol SIP in order to handle call establishment, maintenance and termination
from packet mode terminals.
8) signaling Gateway (SG)
a) A unit that provides signaling conversion between the NGN and the other networks (e.g. STP in
SS7).
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b) ENUM – Electronic NUMbering: Protocol that allows to establish a correspondence between the
traditional telephone numbering (E.164 ) and the network addresses related to the packet mode
networks ( RFC 2916 "E.164 number and DNS" IETF).
Figure 4.5.4 shows NGN network overall architecture.
Figure 4.5.4 NGN network overall architecture
5. Benefits of a Next Generation Services Architecture
The move to this pure-IP services infrastructure can help service providers to reach their goal of increasing
revenues while lowering infrastructure costs, shortening the payback on their investment as we will see in
business case model scenarios coming up. NGN networks have finally emerged to support a single set of
technologies that can support multiple services. The basic guiding principle of NGN network design and
usage is reuse. This flexible, efficient and innovation-friendly infrastructure model is a sharp departure from
the monolithic stovepipe model, and provides much greater opportunities; it enables and simplifies service
application adaptations, customizations and extensions, and lets the services infrastructure simultaneously
and economically support multiple services and markets. And we can all now focus on a singular “services
architecture” as opposed to what we referred to as multiple “service architectures” in TDM networks. There
are many benefits of NGN technology as following:
1) Increase the granularity and power processing distribution of the Network.
o Low density interconnection.
o Signaling, Media and IN capabilities distributed or concentrated depending on carrier needs.
2) One Network
o Reduction planning and engineering time.
o Reduction maintenance and operation costs.
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3) Transport
o Eliminate the need of internal E1.
o Reduction bandwidth needed.
o Reduction maintenance and operation costs.
4) Organization
o UTStarcom solution implemented in a common platform allow to focus on services instead of
networks
5) Less network nodes and links due to the higher capacity of systems (one order of magnitude).
6) Same capillarity at access level due to identical customer location.
7) Topological connectivity higher for high-capacity nodes and paths for security.
8) High protection level and diversity paths/sources in all high-capacity systems, both at functional and
physical levels
6. Characteristics of NGN in Contrast with TDM
Characteristics that make NGN better than TDM are depicted in the following table.
Table 4.5.1. Comparing between TDM and NGN technologies.
7. NGN Technology Operation
NGN technology operation. NGN is divided into four layers: access layer, network layer, control layer and
service layer. NGN bases on packet switching transmission. Each layer does many functions and those layers
contact with others by using protocols. SIP, H.232, MGWC, and H.242 are the most important protocols in
NGN. Figure (4.4) depicts the layers of NGN.
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1- Access media layer: allows end points to connect to the telecommunication network and can be
accessed be any technique such as; (POTS, ISDN, GSM/UMTS, HFC, LMDS, ADSL, etc).
2- Network layer: ensures the format adaptation of user information coming from the access layer to be
sent onto the control layer. In addition, network layer combines the MGW equipment. The function
of MGW is to adapt user data to the backbone network based on packet switching using IP.
3- Control layer The MGC that is located in control layer. It is used to handling and control the MGW
control layer. Figure (4.5.6) depicts the way of communicating between MGC and MGWs via H.248.
Figure 4.5.6 The interconnecting between MGW and MGC/SS
4- Application layer: contains the servers that NGN can provide to the users. As shown in the
figure (4.5.7). It is open interfaces with interconnection with the control layer.
Figure 4.5.7 NGN Layers
Operating Systems of NGN
NGN operating system is softswitch Linux and windows server. MG's operating system is windows server.
8. How Does PSTN Work with NGN
There are two solutions for this issue that are:
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1- First solution, Alcatel Company Upgrade: It makes upgrade for the PSTN by replacing the central
switch in every city via MGWs. Then MGWs are connected to the MGCs. There are twenty-four
MGWs and two MGCs. This solution will be stopped in 2018 as it is still in the primary plan but the
PTC cannot execute the project until nowadays. The fault of this solution is, the network will face
problem in accommodating with the new techniques in the future.
2- Second solution, ZTE Company Softswitch(SS) can be connected to the MGWs by MPLS such in
Al-Tehrair Central. On the other hands’ SS can be connected directly to the MGWs as occurred in
PTC. The aim of MPLS is to move the packet through transmission network with minimum delay.
Because NGN is fast technology, the MPLS is the suitable technique solution to work with NGN.
Then the MG is the intermediate between the PSTN and the SS. There are two SS and MGWs. One
of the SS and MGW is located in the Sana's PTC and the another one is in Sana'a A1. The advantage
of this solution is that supporting the new techniques in the future like IMS and LTE.
9. Application of NGN
The various applications of NGN are explained below:
-
Voice Telephone services
-
Multimedia services
-
Data services
-
Push to talk over NGN (PoN)
-
Content delivery services
-
Global mobility services
-
Virtual Private Services (VPNs)
-
Broadcasting/Multicast services
-
e- commerce and m- commerce
-
Session Controller based Internet services
-
Third party/OSA based services
-
3D Imaging
-
Machine to Machine communication
-
Data Augmentation
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10. Advantages and disadvantages of NGN
Advantages of NGN NGN makes use of the best of both the worlds i.e. flexibility, efficiency &
innovativeness of IP and QoS, Security, Reliability, Customer-friendly features of proven PSTN. Besides
this it has following advantages:
-
It generates additional revenue streams for new IP/Ethernet services.
-
It fulfils customer’s demand for high bandwidth, Ethernet/ IP solutions.
-
It diminishes expertise in legacy.
-
It gives End of Life/ End of Service vendor notification.
-
Users can choose multiple service providers to take maximum advantage of competitive offers but
may get single bill.
Disadvantages of NGN Though having huge advantages and applications, NGN is having some major
loopholes which are stated as follows:
-
Migration complexities
-
Not all legacy services can be replaced with new alternatives
-
Not all existing infrastructure can be shut down
-
Regulatory restrictions for critical services
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Chapter 5
Difficulties and Facilitates
5.1Introduction
This chapter contains the difficulties and facilities that are faced during the training. It includes the
Academic difficulties and facilities. Also, field difficulties and facilities.
5.2 Difficulties
Difficulties that faced during the training are:
5.2.1 Academic Difficulties
The academic difficulties that faced training are:
1. Current Situation in Yemen.
2. Our knowledge was not good because most of information was new about us we have not studied before.
3. The researchers did not have knowledge about NGN Technology.
5. No Electricity and No Internet.
5.2.2 Difficulties during filed visit
The field difficulties that faced training are:
1. Facing difficult in getting the permission to enter the Public Telecommunication Corporation.
2. Engineers sometime busy.
3. Because the war it was difficult to visit some site with the engineers.
4. The trainer in PTC is so busy because of over work.
6. Transport cost.
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5.3 Facilities
Facilities that help during training are:
5.3.1 Academic Facilities
Academic facilities that facilitate the training which are:
1. Getting helping in choosing the topic of the training by D/ Jamal.
2. Correcting the information of the document.
3. Easley contact with the supervisor.
5.3.2 Facilities during filed visit
Field facilities that facilitate the training are:
1. Engineers were helpful with us and work hard to help us in our training.
2. Engineers give us references and notes about the devices.
3. We have gotten good chance to practice what they train us.
Certificates of Training Course
Attachment
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