Overview of telecommunications
means for the GTS
LI Xiang
Telecommunication Division, NMC, China
E-mail: lixiang@cma.gov.cn
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1. Leased circuits
Data Communications Equipment:
Converting the digital signals to the signals
more suitable for transmission
DTE
DCE
Data Terminal Equipment:
- acting as sources or sinks
for data communication link
- Terminal/Computer
DCE
DTE
Leased circuit:
• point-to-point dedicated data
transmission circuit between two
points
• leased by an organization from a
telecommunication service provider
• permanently open connection
• medium: copper wire, optical fiber,...
• signals: analog, digital
1.1 Analogue Circuits
DTE
At the source
- digital to analogue conversion
- modulate
At the destination
- Demodulate
- analogue to digital conversion
Phone
PC +
Communication
Software
Modem
- a analogue connection
- analogue signals
Line
Modem
 A digital connection, consisting of
- a Transmit Data line
- a Receive Data line
- many hardware handshaking
control lines.
Features of analogue circuits

Dedicated voice-grade circuit

Using existing telephone cable network to provide a fixed and
transparent connection between two points in the voice frequency
band 300 - 3400 Hz

Supporting low-speed data communication

Typical date rates over analogue circuits are: 300, 1200, 2400, 9600,
14.4k, 19.2k, 28.8kbps

Low costs
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1.2 Digital circuits
• source encoding/decoding
• channel coding/decoding
• synchronization
Digital
Modem
PC +
Communication
Software
circuit
Modem
- a digital connection
- digital baseband signals
Computer +
Communication
Software
Features of digital circuits

High quality communication links

providing a fixed and transparent connection
between two points

terminated by a digital interface

supporting high-speed data communication: 64Kbps
– 155Mbps
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1.3 Examples of use of Leased Circuits (1)
Beijing – Moscow GTS link
Physical link
- analogue circuit
Physical Layer
- V.34
Data Link Layer
- Link Access Procedure
Balanced (LAPB)
Network Layer
- X.25 Packet Layer
Protocol (PLP)
1.3 Examples of use of Leased Circuits (2)
Beijing – Offenbach GTS link
Physical link
- digital circuit
Physical Layer
- V.35
Data Link Layer
- Link Access Procedure
Balanced (LAPB)
Network Layer
- X.25 Packet Layer
Protocol (PLP)
1.3 Examples of use of Leased Circuits (3)
Using TCP/IP protocol to exchange data over a leased circuit
2. Frame Relay


A protocol standard for sending information,
which is divided into frames or packets, over a
wide area network.
A fast and efficient packet-switching technology





A Frame-Relay network doesn't perform error detection
The intelligent network devices connected to a FrameRelay network are responsible for the error correction
and frame formatting
Frame Relay typically operates at 56 Kbps to
1.544 Mbps.
Frame Relay is protocol independent, it can
process traffic from different networking
protocols like IP, IPX, and SNA.
Multiple logical connections can be established
over a single physical connection
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Concept of Frame Relay communicate
A
Frame
Relay
Network
router
T
H
T
FR data packet
-Translating existing data
communications protocols for
transmission over a Frame-Relay
network
- Routing the data across the
network to another frame router or
other Frame-Relay compatible
device
- Handling many types of
protocols, including LAN protocols
- Each router supports one of
many physical data interfaces and
can provide several user ports.
PVC
FR data
packet
- Frame Relay sends
information in packets
called frames through a
shared Frame-Relay
network.
- A frame contains all
the information
necessary to route it to
the correct destination
H
B
router
DLCI: Data-Link Connection identifier, represents the address of the frame
and corresponds to a PVC.
C/R: Command/Response Field Bit, designates whether the frame is a
command or response.
EA: Extension Bit, can be used for expanding the number of possible
addresses.
DE: Discard Eligibility Indicator, provides the network a signal to determine
which frame to discard. When there is a congestion on the line, in order to
free the line, the network will discard frames with a DE value of 1 before
discarding other frames.
FECN: Forward Explicit Congestion Notification. If FECN is changed to 1 as
a frame is sent downstream toward the destination location when congestion
occurs during data transmission.
BECN: Backward Explicit Congestion Notification. If BECN is changed to 1
as a frame traveling back toward the source of data transmission on a path
where congestion is occurring.
FCS: Frame Check Sequence
CIR



Committed Information Rate
Instead of being allocated a fixed
amount of bandwidth, Frame-Relay
services offer a CIR at which data is
transmitted.
If traffic and the service agreement
allow, data can burst above the
committed rate.
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PVC

Permanent Virtual Circuits

A PVC is a dedicated connection through the shared Frame-Relay network
replacing a dedicated end to-end line.
A PVC is needed for each site in the network. But in a Frame Relay network,
the bandwidth is shared among multiple users. So any single site can
communicate with any other single site without the need for multiple
dedicated lines.
PVCs function via a Local Management Interface (LMI), which provides
control procedures. The control procedures function in three ways:






link integrity verification initiated by the user device
network status report giving details of all PVCs
network notification of whether a PVC's status changes from active to inactive
Data-Link Connections (DLCs) are PVCs pre-configured by both sides of
the connection. The DLC identifier (DLCI) is used as the logical address for
frame-layer multiplexing.
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Examples of use of Frame Relay service
KDDI
Frame Relay
Port 256K
Router
Sun
Port 192K
CIR 32K
Sun
JMA
Router
CMA
CNC
Frame Relay
CIR 32K
KT
Frame Relay
Router
Sun
Port 128K
KMA
3. Introduction to VSAT,and
satellite based DVB, DAB
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3. 1 Introduction to VSAT





Very Small Aperture Terminal
Self-contained hub station
Unbalanced traffic in outroute and
inroute
The utilization rate of VSAT network
improved with the increase of remote
terminals
Support of broadcast
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Types of VSAT network



Star network: mostly adopted by data
communications network.
Full mesh network: mostly adopted by
telephony communications network.
Hybrid architecture: applied to
integrated services network
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Generally, VSAT systems operate in the
Ku-band and C-band frequencies.

Ku-band system

Smaller sizes of VSAT antennas at remotes




0.6 ~ 2.4 m antenna
Abundant in frequency resource
Existing the propagation problems caused by rain
C-band system

Larger sizes of VSAT antennas at remotes



1.8 ~ 2.4 m antenna
Most C-band frequency resource already used
Existing the interference problem between
adjacent channels because of the congestion of
channels
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Model of a transmission channel from
one terminal to another (VSAT)
satellite
earth station
PROCESSING
DEMOD
MOD
earth station
IF/RF
RF/IF
SATELLITE
PROCESSING
NETWORK
STATION / TERMINAL
INTERFACE
STATION / TERMINAL
INTERFACE
USER
TERMINAL
DEMOD
USER
TERMINAL
CMA’s VSAT system

Communication Satellite




Satellite: AsiaSat II
Frequency Band: Ku-band
Coverage: China and some other Asia countries adjacent to China
Consisting of three parts

Satellite telephony network




Satellite Wide Area network




One hub, about 350 remotes
Full mesh network
Covered regional, provincial and city level weather centers
One hub, about 350 remotes
Star network
Covered regional, provincial and city level weather centers
PCVSAT broadcasting system



One hub, over 2000 remotes (including the remotes installed in Pyongyang and
Ulan Bato)r
Data broadcasting system
Covered regional, provincial ,city and county level weather centers
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SWAN
Regional Centers
National network center
VSAT
VSAT
Control
Control
Center
Center
SWAN
Server
two-way system
 One outbound
channel: 512kbps
 Eight inbound
channels:
8*128kbps
 Remotes to Hub:
ftp
 Hub to Remotes:
multicast

PBX
TCP/IP
CHINAPAC
Provincial
centers
National operational
centers
City bureau
CMA’s Intranet
CMA’s PCVSAT data broadcasting network
PCVSAT data
broadcasting
network
LNB
Multiplex

PC Card
PCVSAT broadcasting system
One way system
 Broadcasting rates: 2Mbps
 Supporting 256 logical channels, the typical logical
channel rate is 64kbps
 Authorization and management centralized at hub

3.2 Introduction to DVB

DVB: international standard for digital
video broadcasting

Based on ISO 13818 MPEG-2 coding
and multiplexing specifications
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Types of DVB standards

DVB-S


DVB-C


DVB-S satellite transmission standard, based on QPSK, is
now the de-facto world satellite transmission standard for
digital TV applications
cable delivery mechanism, is closely related to DVB-S, and
is based around 64-QAM, although higher order modulation
schemes are also supported.
DVB-T

Based on COFDM (Coded Orthogonal Frequency Divisional
Multiplexing) and QPSK, 16 QAM and 64 QAM modulation, it
is the most sophisticated and flexible digital terrestrial
transmission system available today.
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Concept of DVB Signal Generation
MPEG 2
digital
compression
coder
Digital compression
signals
modulator
Digital signals
multiplexer
Analog audio
and video
signals
analogdigital
converter
DVB
digital signals
Data Server
digital broadcasting
or
digitization TV program
broadcasting
amplifier
video signal
What a end user needs?
Satellite dish
PC
DVB card
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Why DVB?










Smaller VSAT antenna
Secure transmission with entitlement control
Higher data rates, 256Kpbs – 58Mbps
Support for Multi-protocol Encapsulation (MPE) of IP
data
Multiplexing of up to 8192 streams
Integration of data with video and audio
Co-existence between multiple DVB steams
Multicast enabled
Ease of implementation & upgrade
Open architecture
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3.3 Introduction to DAB




DAB: Digital audio broadcasting
Based on two techniques

Musicam
 is a digital compression system based on MPEG technology
 makes the signal down to 10 times lighter
 provides an CD-like quality of sounds
 enables the association of data to the audio programmes (title, CD cover,
author of the song)

Digicast
 eliminates traditional reception problems (distortion, interferences, etc.) by
spreading signals in time on several frequencies. The information that are
broadcast separately remain linked by encoding.
 eliminates interferences ; propagation echoes become an advantage by
enforcing the reception quality including in more complex areas.
 is able to send independently audio Streams (ex : Musicam) and Packet
Datas (ex : NPAD)
Operating via multiplexes. Each multiplex is composed of programmes and
associated services. A sole transmitter can broadcast several programmes. The
output can be up to 1.5 Mbps.
Supporting Datacasting
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DATACASTING : DATA BROADCASTING VIA DAB
Procedures on data sending and receiving

At the sending end,



User’s data files being sent to the local uplink site of the DAB
services provider, such as WorldSpace, via FTP or other means.
The services provider‘s scheduler at the uplink site
automatically picks up the data and places it into the
defined bin at which point it is sent up to the satellite.
At the receiving end,


A PC-adaptor, connected to a satellite digital receiver and a PC
transforms the receiver into a one-way satellite modem that can
receive data at the rate up to 128 kbps.
The delivered files are stored in the end user's designated
directory on the hard drive.
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Why DAB?

Wide coverage



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
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DAB services: almost all over the world
Datacasting: Africa and Asia
Lower transmission costs for broadcasters :
US$10 per MB
Smaller antenna
Wide choice of equipments at receiving ends
Higher data rates


Broadcasting rate: up to 1.5Mpbs
Receiving rate: up to 128kbps
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Thank you
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