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Broad Band Technologies for high
speed data communications
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•
•
•
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Plain old telephone service (POTS)
Integrated Services for Digital Network (ISDN)
Digital subscriber line (DSL)
Cable Modem Technology
Satellites Technology
Cellular Communication Technology
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Plain old telephone service (POTS)

The Public Switched Telephone Network
– Worldwide
– A call may cross many telephone company
boundaries

Also Known as POTS
– Plain old telephone service
– “Old” “Uninteresting”
3
The Basic Telephone System
•POTS is the plain old telephone system that
connects most homes and small businesses
•POTS lines were designed to transmit the human
voice, which has a bandwidth less than 4000 Hz
•A telephone conversation requires two channels,
each occupying 4000 Hz
4
The Basic Telephone System (continued)
5
Plain old telephone service (POTS)
• Ordinary telephone systems are often referred to as
POTS (plain old telephone service)
• Normally, each subscriber is connected to the central
office by a single twisted pair of wires
• The wires are twisted to reduce crosstalk
• Future developments include the inclusion of fiberoptic connections direct to the subscriber for greater
bandwidth.
The Basic Telephone System (continued)
7
POTS advantages and disadvantages
• Advantages
–
–
–
–
Available everywhere
Reliable connectivity
Low cost
Easy setup
• Disadvantages
–
–
–
–
Only one session per circuit
FCC limited transmission speed at 53 Kbps
Most circuits will only reach 44 Kbps due to line noise
Analog transmissions only
‫‪ISDN‬‬
‫‪Integrated Services Digital Network‬‬
‫•‬
‫•‬
‫•‬
‫•‬
‫شبكات الخدمات الرقمية المتكاملة‬
‫توحيد الشبكات كلها في شبكة رقمية واحدة حيث يتم النقل عليها بشكل‬
‫رقمي (صوت‪ ,‬صورة‪)...,Data ,‬‬
‫كانت البداية عام ‪ 1984‬حيث أصدرت ‪ CCITT‬سلسلة معايير ‪standards‬‬
‫سميت بسلسلة ‪ )I series( I‬من (‪)I 100I 400‬‬
‫ثم أصدرت مجموعة أكثر كماالً عام ‪ 1988‬هي (‪)I 500, I 600‬‬
‫‪Basic Rate ISDN‬‬
‫• ‪ 3‬أقنية مختلفة‪:‬‬
‫– قناتي ‪ B‬بسعة ‪ 64 Kb/s‬لكل منهما (‪ )B channel‬وهي اختصار‬
‫لـ ‪(Bearer‬الناقل)‬
‫– قناة ‪ D‬بسعة ‪ 16 Kb/s‬أو ‪ )D channel( 64 Kb/s‬وهي‬
‫اختصار لـ ‪Delta‬‬
‫• لذلك تدعى ‪ Basic Rate‬أيضا ً بـ ‪2B+D‬‬
‫‪B‬القناتين‬
‫• يمكن نقل جميع أنواع الخدمات على كل من القناتين ‪B‬‬
‫• يمكن مثالً استخدام قناة للصوت ‪ voice‬وأخرى للمعطيات‬
‫‪data‬‬
‫• كما يمكن أيضا ً ضم القناتين معا ً للحصول على وصلة بسعة‬
‫‪128 Kb/s‬‬
‫‪D‬القناة‬
‫• تستخدم للتحكم بالقناتين ‪B‬‬
‫إقامة اتصال‬
‫– ‪Call setup‬‬
‫إشارة ورود مكالمة‬
‫– ‪Ringing‬‬
‫– ‪ Status indication‬معرفة الحالة‬
‫• يمكن استخدام هذه القناة لنقل معطيات ‪( data‬وليس ‪ )voice‬ولكن بسعات‬
‫صغيرة‬
‫• البروتوكول المستخدم في القناة ‪ D‬هو بروتوكول من طبقة ‪ Data Link‬ويسمى بـ‬
‫‪)Link Access Protocol, D-channel( LAPD‬‬
‫‪LAPD‬العنونة في البروتوكول‬
‫• يمكن ربط ‪ 8‬أجهزة مختلفة على خط ‪ISDN‬‬
‫• يوجد حقل جزئي في حقل العنوان ‪ LAPD‬لعنونة هذه األجهزة‪:‬‬
‫– يسمى هذا الحقل الجزئي بـ (‪Terminal Endpoint Identifier)TEI‬‬
‫– يعنون ‪ TEI‬الجهاز الطرفي النهائي‬
‫• هناك حقل جزئي آخر في حقل العنوان ‪ LAPD‬يدعى)‪(SAPI‬‬
‫‪Service Access Point Identifier‬‬
‫– يستخدم لمعرفة البروتوكول الموجود في الطبقة األعلى والذي يستخدم البروتوكول ‪LAPD‬‬
‫(مثالً ‪ X25‬أو ‪)frame relay‬‬
‫• الزوج (‪ )SAPI, TEI‬هو زوج وحيد على خط ‪ ISDN‬المستثمر وهو يعرف‬
‫محادثة عن طريق ‪ D-channel‬بين أحد األجهزة والمقسم‬
‫‪Encoding‬الترميز‬
‫• يتم استخدام الترميز الرباعي‬
‫• يدعى هذا الترميز بـ ‪2B1Q‬‬
‫• يقوم باستبدال خانتين "‪ "bits‬بترميز رباعي واحد يدعى‬
‫"‪”quat‬‬
‫‪Encoding‬مثال على الترميز‬
‫‪• E = (69)10 = (01 00 01 01)2‬‬
‫تجهيزات الـ ‪ISDN‬‬
‫(‪)ISDN Equipments‬‬
‫‪ ISDN‬هو جهاز رقمي ولكنه ال يعمل على ‪• TE1 :Terminal Equipment type 1‬‬
‫‪ 2B1Q‬إلى الترميز ‪ AMI‬هو جهاز يحول من الترميز ‪• NT1 :Network Termination 1‬‬
‫‪ ISDN‬يتصل على‪TE1‬وبالعكس مما يجعل‬
‫تجهيزات الـ ‪ISDN‬‬
‫(‪)ISDN Equipments‬‬
‫عرف الـ ‪ standard‬نقاط مرجعية ‪ reference points‬هي‪:‬‬
‫‪ :V‬السلك الواصل بين المأخذ ‪(U connector‬البريز) و‪ switch‬ويكون الترميز هنا هو ‪2B1Q‬‬
‫‪ :U‬السلك الواصل بين المأخذ (البريز) و ‪ NT1‬ويكون الترميز هنا هو ‪2B1Q‬‬
‫‪ :S/T‬السلك الواصل بين ‪ NT1‬و ‪ TE1‬ويكون الترميز هنا هو ‪AMI‬‬
‫تجهيزات الـ ‪ISDN‬‬
‫(‪)ISDN Equipments‬‬
‫يمكن أن يكون لدينا جهاز تماثلي ‪ TE2‬والذي البد من وصله مع محول ‪Terminal ( TA‬‬
‫‪ )Adaptor‬ليتم تحويل اإلشارة إلى إشارة رقمية ثم نقوم بوصلها إلى ‪ NT1‬حتى نستطيع‬
‫التعامل مع ‪ISDN‬‬
‫لألجهزة ثالثة أنواع هي‪:‬‬
‫•تماثلي‬
‫•رقمي ال يتعامل مع ‪ISDN‬‬
‫•رقمي ويتعامل مع ‪ISDN‬‬
‫(نصله مع ‪ TA‬ثم ‪)NT1‬‬
‫(نصله مع ‪)NT1‬‬
‫(نصله مباشرة فال يكون لدينا الجزء ‪)S/T‬‬
Cable Modem Technology
• For millions of people, television brings news,
entertainment and educational programs into
their homes. Many people get their TV signal
from cable television (CATV) because cable TV
provides a clearer picture and more channels.
• Many people who have cable TV can now get
a high-speed connection to the Internet from
their cable provider.
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Cable Modem Technology
• In a cable TV system, each channel is given a
6-MHz slice of the cable's available bandwidth
and then sent down the cable to your house.
The cable TV system can carry hundreds of
megahertz of signals.
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Cable Modem Technology
• Internet can use the same cables because the
cable modem system puts downstream data
(data sent from the Internet to an individual
computer) into a 6-MHz channel.
• On the cable, the Internet data looks just like a
TV channel. So Internet downstream data
takes up the same amount of cable space as
any single TV channel.
• Downstream data = download
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Cable Modem Technology
• Upstream data (information sent from an the
user back to the Internet)-- requires just 2
MHz, since the assumption is that most
people download more than they upload.
• Upstream data = Upload
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Cable Modem Technology
• Putting both upstream and downstream data on
the cable television system requires two types of
equipment:
– a cable modem on the customer end
– a cable modem termination system (CMTS) at the
cable provider's end.
• Between these two types of equipment, all the
computer networking, security and management
of Internet access over cable television is put into
place.
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Cable Modem Technology
• Inside the Cable Modem
• Cable modems can be
– internal or
– external to the computer.
– part of a set-top cable box, requiring that only a
keyboard and mouse be added for Internet access.
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Cable Modem Technology
• Inside the Cable Modem
• Regardless of their outward appearance, all
cable modems contain certain key
components:
– A tuner
– A demodulator
– A modulator
– A media access control (MAC) device
– A microprocessor.
25
Cable Modem Technology
• Inside the Cable Modem
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Cable Modem Technology
• Inside the Cable Modem: Tuner
• The tuner connects to the cable outlet,
sometimes with the addition of a splitter that
separates the Internet data channel from
normal CATV programming. Since the Internet
data comes through an otherwise unused
cable channel, the tuner simply receives the
modulated digital signal and passes it to the
demodulator.
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Cable Modem Technology
• Inside the Cable Modem: Demodulator
• Demodulator converts a radio-frequency
signal into a simple signal that can be
processed by the analog-to-digital (A/D)
converter.
• The A/D converter converts the signal into a
series of digital 1s and 0s.
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Cable Modem Technology
• Inside the Cable Modem: Modulator
• modulator is used to convert the digital
computer network data into radio-frequency
signals for transmission and consists of three
parts:
– A section to insert information used for error
correction on the receiving end
– A QAM modulator
– A digital-to-analog (D/A) converter.
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Cable Modem Technology
• Inside the Cable Modem: MAC
• The MAC sits between the upstream and
downstream portions of the cable modem,
and acts as the interface between the
hardware and software portions of the various
network protocols.
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Cable Modem Technology
• Inside the Cable Modem: Microprocessor
• The microprocessor's job depends somewhat
on whether the cable modem is designed to
be part of a larger computer system or to
provide Internet access with no additional
computer support.
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Cable Modem Technology
• Cable Modem Termination System (CMTS)
• The CMTS takes the traffic coming in from a
group of customers on a single channel and
routes it to an Internet service provider (ISP) for
connection to the Internet.
• A CMTS will enable as many as 1,000 users to
connect to the Internet through a single 6-MHz
channel. Since a single channel is capable of 30 to
40 megabits per second (Mbps) of total
throughput.
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CMTS
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Pros and Cons to Cable Modem
Technology
• As new users are connected to the channel
the performance decreases. It is possible that,
in times of heavy usage with many connected
users, performance will be far below the
theoretical maximums.
• The good news is that this particular
performance issue can be resolved by the
cable company adding a new channel and
splitting the base of users.
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Pros and Cons to Cable Modem
Technology
• Another benefit of the cable modem for
Internet access is that, unlike ADSL, its
performance doesn't depend on distance from
the central cable office.
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Satellite Microwave Transmission
• Similar to terrestrial microwave except the
signal travels from a ground station on earth
to a satellite and back to another ground
station
• Can also transmit signals from one satellite to
another
• Satellites can be classified by how far out into
orbit each one is (LEO, MEO, GEO, and HEO)
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
36
Satellite Microwave Transmission
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
37
Satellite Microwave Transmission
• LEO (Low-Earth-Orbit) – 100 to 1000 miles out
– Used for wireless e-mail, special mobile telephones, pagers,
spying, videoconferencing
• MEO (Middle-Earth-Orbit) – 1000 to 22,300 miles
– Used for GPS (global positioning systems) and government
• GEO (Geosynchronous-Earth-Orbit) – 22,300 miles
– Always over the same position on Earth (and always over the
equator)
– Used for weather, television, government operations
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
38
Satellite Microwave Transmission
• HEO (Highly Elliptical Earth orbit) – satellite
follows an elliptical orbit
– Used by the military for spying and by scientific
organizations for photographing celestial bodies
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
39
Satellite Microwave Transmission
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
40
Satellite Microwave Transmission
• Satellite microwave can also be classified by
its configuration:
– Bulk carrier configuration
– Multiplexed configuration
– Single-user Earth station configuration (e.g., VSAT)
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
41
Satellite Microwave Transmission
Data Communications and Computer Networks: A Business User's Approach, Fifth Edition
42
Cellular Wireless Networks
Cellular Network Organization
• Multiple low power transmitters
– 100w or less
• Area divided into cells
– Each with own antenna
– Each with own range of frequencies
– Served by base station
• Transmitter, receiver, control unit
– Adjacent cells on different frequencies to avoid
crosstalk
Shape of Cells
• Square
– Width d cell has four neighbors at distance d and four at distance
2
– Better if all adjacent
antennas equidistant
• Simplifies choosing and switching to new antenna
• Hexagon
– Provides equidistant antennas
– Radius defined as radius of circum-circle
• Distance from center to vertex equals length of side
– Distance between centers of cells radius R is
– Not always precise hexagons
• Topographical limitations
• Local signal propagation conditions
• Location of antennas
R
3
d
Cellular Geometries
Frequency Reuse
• Power of base transceiver controlled
–
–
–
–
–
Allow communications within cell on given frequency
Limit escaping power to adjacent cells
Allow re-use of frequencies in nearby cells
Use same frequency for multiple conversations
10 – 50 frequencies per cell
• E.g.
–
–
–
–
N cells all using same number of frequencies
K total number of frequencies used in systems
Each cell has K/N frequencies
Advanced Mobile Phone Service (AMPS) K=395, N=7 giving 57
frequencies per cell on average
Operation of Cellular Systems
• Base station (BS) at center of each cell
– Antenna, controller, transceivers
• Controller handles call process
– Number of mobile units may in use at a time
• BS connected to mobile telecommunications switching office
(MTSO)
– One MTSO serves multiple BS
– MTSO to BS link by wire or wireless
• MTSO:
– Connects calls between mobile units and from mobile to fixed
telecommunications network
– Assigns voice channel
– Performs handoffs
– Monitors calls (billing)
• Fully automated
Overview of Cellular System
Channels
• Control channels
– Setting up and maintaining calls
– Establish relationship between mobile unit and
nearest BS
• Traffic channels
– Carry voice and data
Typical Call in
Single MTSO Area (2)
• Call accepted
–
–
–
–
–
Mobile unit recognizes number on set up channel
Responds to BS which sends response to MTSO
MTSO sets up circuit between calling and called BSs
MTSO selects available traffic channel within cells and notifies BSs
BSs notify mobile unit of channel
• Ongoing call
– Voice/data exchanged through respective BSs and MTSO
• Handoff
– Mobile unit moves out of range of cell into range of another cell
– Traffic channel changes to one assigned to new BS
• Without interruption of service to user
Call Stages
Other Functions
• Call blocking
– During mobile-initiated call stage, if all traffic channels busy, mobile tries again
– After number of fails, busy tone returned
• Call termination
– User hangs up
– MTSO informed
– Traffic channels at two BSs released
• Call drop
– BS cannot maintain required signal strength
– Traffic channel dropped and MTSO informed
• Calls to/from fixed and remote mobile subscriber
–
–
–
–
MTSO connects to PSTN
MTSO can connect mobile user and fixed subscriber via PSTN
MTSO can connect to remote MTSO via PSTN or via dedicated lines
Can connect mobile user in its area and remote mobile user
Call Sequence
1. Subscriber initiates call by keying in number and presses
send
2. MTSO validates telephone number and checks user
authorized to place call
• Some service providers require a PIN to counter theft
3. MTSO issues message to user's phone indicating traffic
channels to use
4. MTSO sends ringing signal to called party
• All operations, 2 through 4, occur within 10 s of initiating call
5. When called party answers, MTSO establishes circuit and
initiates billing information
6. When one party hangs up MTSO releases circuit, frees radio
channels, and completes billing information