Overview of telecommunications means for the GTS

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1

Overview of telecommunications
means for the GTS

LI Xiang

Telecommunication Division, NMC, China

E
-
mail: lixiang@cma.gov.cn

1. Leased circuits

DTE

D
ata
T
erminal
E
quipment:


-

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


D
ata
C
ommunications
E
quipment:

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

Modem

Phone

Line

Modem

DTE

At the source

-

digital to analogue conversion

-

modulate

At 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

Modem

Digital

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 circuit

Physical Layer

-

V.34

Data Link Layer



-

Link Access Procedure


Balanced (LAPB)

Network Layer



-

X.25 Packet Layer


Protocol (PLP)

Physical link

-

digital circuit

Physical 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

B

router

H

T

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
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.

Examples of use of Frame Relay service

CNC

Frame Relay

KDDI

Frame Relay

CIR 32K

Router

Router

Port 256K

Port 192K

CMA

KT

Frame Relay

JMA

Router

Port 128K

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
inroute


The utilization rate of VSAT network
improved 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

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 and
Ulan Bato)r


Data broadcasting system


Covered regional, provincial ,city and county level weather centers

SWAN


two
-
way system


One outbound
channel: 512kbps


Eight inbound
channels:
8*128kbps


Remotes to Hub:
ftp


Hub to Remotes:
multicast

SWAN

CMA

s PCVSAT data broadcasting network


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

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

27

What a end user needs?

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,
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

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
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.

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