1

Overview of telecommunications means for the GTS

LI XiangTelecommunication Division, NMC, China

E-mail: lixiang@cma.gov.cn

1. Leased circuits

DTE

Data Terminal Equipment: - acting as sources or sinks for data communication link - Terminal/Computer

DCE 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

Data Communications Equipment:Converting the digital signals to the signals more suitable for transmission

A digital connection, consisting of- a Transmit Data line- a Receive Data line - many hardware handshaking control lines.

1.1 Analogue Circuits

PC +Communication

Software

ModemPhone

Line Modem

DTE

At the source - digital to analogue conversion- modulateAt the destination - Demodulate - analogue to digital conversion

- a analogue connection- analogue signals

4

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

- a digital connection- digital baseband signals

1.2 Digital circuits

PC +

Communication

Software

Computer +Communication

Software

Modem ModemDigital

circuit

• source encoding/decoding• channel coding/decoding• synchronization

6

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

Features of digital circuits

1.3 Examples of use of Leased Circuits (1)

Beijing – Moscow GTS link

Physical link - analogue circuitPhysical Layer- V.34Data Link Layer - Link Access Procedure Balanced (LAPB) Network Layer - X.25 Packet Layer Protocol (PLP)

Physical link- digital circuitPhysical Layer - V.35 Data Link Layer - Link Access Procedure Balanced (LAPB) Network Layer - X.25 Packet Layer Protocol (PLP)

Beijing – Offenbach GTS link

1.3 Examples of use of Leased Circuits (2)

1.3 Examples of use of Leased Circuits (3)

Using TCP/IP protocol to exchange data over a leased circuit

10

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 Frame-

Relay 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

Concept of Frame Relay communicate

A router

Frame Relay

Network

Frame Relay

Network

B router

HT

FR data packet

H

T

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

-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

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

13

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.

14

PVC

Permanent Virtual Circuits A PVC is a dedicated connection through the shared Frame-Relay network r

eplacing 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.

Examples of use of Frame Relay service

CNCFrame Relay

KDDI Frame Relay

CIR 32K

Router

Router

Sun

Port 256K Port 192K

CMA

Sun

KT Frame Relay

JMA

Router

Port 128KSun

KMA

CIR 32K

16

3. Introduction to VSAT,and satellite based DVB, DAB

17

3. 1 Introduction to VSAT

Very Small Aperture Terminal Self-contained hub station Unbalanced traffic in outroute and inrout

e The utilization rate of VSAT network imp

roved with the increase of remote terminals

Support of broadcast

18

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

19

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

satellite

RF/IF DEMOD PROCESSING

STATION / TERMINALINTERFACE

TERMINAL

DEMOD IF/RFPROCESSING MOD

STATION / TERMINALINTERFACE

TERMINAL

SATELLITE NETWORK

earth stati onearth stati on

USERUSER

Model of a transmission channel from one terminal to another (VSAT)

21

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

One hub, about 350 remotes Full mesh network Covered regional, provincial and city level weather centers

Satellite Wide Area network 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 an

d Ulan Bato)r Data broadcasting system Covered regional, provincial ,city and county level weather centers

VSAT Control Center

VSAT Control Center

PBX

Server

TCP/IPCHINAPAC

Regional Centers

Provincialcenters

City bureau

National network center

CMA’s Intranet

National operationalcenters

SWANtwo-way systemOne outbound

channel: 512kbpsEight inbound

channels: 8*128kbps

Remotes to Hub: ftp

Hub to Remotes: multicast

SWAN

MultiplexPC Card

LNB

PCVSAT databroadcasting network

CMA’s PCVSAT data broadcasting network

PCVSAT broadcasting systemOne way systemBroadcasting rates: 2MbpsSupporting 256 logical channels, the typical logical

channel rate is 64kbpsAuthorization and management centralized at hub

24

3.2 Introduction to DVB

DVB: international standard for digital video broadcasting

Based on ISO 13818 MPEG-2 coding and multiplexing specifications

25

Types of DVB standards

DVB-S DVB-S satellite transmission standard, based on QPSK, is

now the de-facto world satellite transmission standard for digital TV applications

DVB-C 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.

Concept of DVB Signal Generation

analog-digital

converter

MPEG 2digital

compressioncoder

Analog audioand video

signals

mu

ltiple

xe

r

mo

du

lato

r

amplifier

broadcasting

Digital signals Digital compressionsignals

DVBdigital signals

video signal

Data Server

digital broadcastingor

digitization TV program

27

What a end user needs?

Satellite dish

PC DVB card

28

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

29

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, aut

hor 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

DATACASTING : DATA BROADCASTING VIA DAB

31

Procedures on data sending and receiving

At the sending end, User’s data files being sent to the local uplink site of the DAB ser

vices provider, such as WorldSpace, via FTP or other means. The services provider‘s scheduler at the uplink site auto

matically 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 t

ransforms 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.

32

Why DAB?

Wide coverage 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

33

Thank you