Overview of Telecom Network

For circulation to Trainees only

Overview of Telecom

Network


Outline of Lecture

What is Telecom?

Concepts and Definitions

Overview of Telecom Network

PSTN

Internet/Data Network

Cellular Telephone Networks

NGN

Transmission & Systems in Telecom


What is Telecom ?

Telecommunication is the assisted

transmission of signals over a distance for the

purpose of communication.

It is the technology of transferring information

over a distance.


Information

1. Information can be of several type:

Audio Telephone

Text - Telegraph , email, SMS

Pictures Picture attachments

Video Clipping over internet

Data ATM to bank.

2. The same telecom technology/service cannot

communicate all the types of information.


Telecom scenario

Growing subscriber base.

New services and technologies.

More focus on wireless & internet.

Government wants more development in rural areas.

Decreasing Prices.

Increasing demand for bandwidth.


OVERVIEW OF TELECOM NETWORK

There are three networking approaches for a telecom

network infrastructure.

Circuit-switched,

Internet / Data Network and

Cellular mobile,

Finally, all these architectures are migrating towards a

common IP network infrastructure called Next

Generation Network (NGN).


CIRCUIT-SWITCHED NETWORKS &

DIGITAL SWITCHING SYSTEMS

Public Switched

Telephone Network(PSTN)


Concepts & Definitions

Telecommunications is the transfer of information from a

transmitter to a receiver over a distance.

A telecommunication network is required to transmit

messages between any of its users (who are usually

called customers or subscribers), and the messages may

be conveyed by signals that are either digital or

analogue.

Telecommunication system - enable the transmission

of information over public or private networks (voice,

data, graphics, video)



Definitions:

Transmitter: originates information transfer

Receiver: receives the transferred information

Circuit: a communications path between transmitter and

receiver over an established medium

Link: a two-point segment of an end-to-end circuit



Definitions (contd)

Switch: a device that establishes, maintains, and

changes connections over circuits

Line: a single physical connection between a user

and a switch

Trunks: the physical connection between switches

Channel: a channel is a division in a transmission

medium so that it can be used to send multiple

streams of information, a circuit can contain

multiple channels



Definitions (contd)

Bit : The binary digit or bit is a unit of information transfer.

Byte : a collection of 8 bits

Signal : It is electrical, electronic or optical representation of data, which can be sent over a communication medium. Stated in mathematical terms, a signal is merely a function of the data. Signals can be either analogue or digital.

Symbols : In communications, the analog signal shape, by pre-agreed convention, stands for a certain number of bits and is called a symbol.



Definitions (contd)

Baud : Symbols transmitted per second is known as baud.

Modulation : The shaping of a signal to convey information is known as modulation.

Network : A network is a collection of transmitters, receivers and transceivers that communicate with each other.

Multiplexing : combining a defined integral number of input signals (called tributaries).



Definitions (contd)

Modems (modulation/demodulation) : Changes signals from analog to digital and back to analog.

Spectrum -range of frequencies Bandwidth -width of the spectrum Bandwidth Alternatives : Bandwidth is the

frequency range of a telecommunications network. Determines the channels maximum transmission rate. Measured in bits per second (bps) or baud.

Narrow-band : Low-speed transmission. Broadband : High-speed transmission.


ANALOG SIGNAL

Continuous Waveform

Analog signals are continuous-valued;

Voice Communications and video


DIGITAL SIGNAL DISCRETE WAVEFORM i.e. depicted as discontinuous

TWO DISCRETE STATES:

1-BIT & 0-BIT

ON / OFF PULSE (Each pulse (on/off) is known as a

bit)USES MODEM TO TRANSLATE ANALOG TO

DIGITAL, DIGITAL TO ANALOG


Advantages of Digital Transmission

The signal is exact

Signals can be checked for errors

Noise/interference are easily filtered out

A variety of services can be offered over one line

Higher bandwidth is possible with data

compression


Network Elements of PSTN

A telecommunication network may therefore be

considered as a system consisting of four basic network

elements:

Station apparatus

Transmission

Switching

Signaling


Network Elements


Station apparatus

Station Apparatus are the transmitters and receivers:

Telephones

Answering Machines

Facsimile Machines

Most are combined transmitters and receivers


TRANSMISSION

Transmission is the conveyance of signals from one

place to another.

Signals may be audio, video, or data

Transmission systems include:

Open Wire

Copper wire cable (Twisted Wires)

Co-axial Cable

Microwave radio (terrestrial and satellite)

Fiber optic cable

Other wireless


TRANSMISSION

Open wire


TRANSMISSION (contd) The network is composed of transmission media linked at physical locations (central offices, carrier units, etc.)

Originally each line ran all the way back to the C.O.

Called a home run architecture

Circuit cards linked the transmission media

Access Lines Circuit

Ports

Toll Trunk

IXC Switch


TRANSMISSION (contd)

Modern networks use multiplexing, the sharing of a transmission medium by multiple signals

Frequency (analog) & Time-division (digital) muxing

Multiple channels on a single circuit

Node architecture has replaced the home run

Circuit Digital Line DLC Ports

Carrier Units

Toll Trunk Splice point

Access Lines DLC IXC Switch

DLC


Transmission Modes

Performance can be measured by the mode of the

connection.

Simplex transmission, messages can be

carried in only one direction.

Half-duplex, messages can be carried in

both directions just not simultaneously.

Full-duplex, messages can be carried in

both directions simultaneously.


SWITCHING

Telephones introduced in late-1800s. Initially each telephone was directly

connected to another site. This led to an explosion of direct connections

(n*(n-1)/2) This lead to the need to switch the connections.

Switch


SWITCHING

Switches establish, maintain, and change connectivity

between circuits

The earliest telephone exchanges used switchboards

worked by operators. The manual exchange was unique

among switching systems, since a single switch (i.e., the

operator) could make a connection to any of several

thousand lines by inserting a plug in a jack within arms

reach.

A modern electronic exchange performs basic actions

very rapidly, so it can be controlled by a single central

digital processor.


SWITCHING

Switches used to be electro-mechanical in nature; most

are now digital

Digital switches are simply computers that make logical

routing decisions to connect circuits to complete calls

When a call is dialed, the end-office switch decides

whether it can handle the call or if it needs to pass it up

the hierarchy

Each switch in succession makes the decision to pass it

up or down the hierarchy until it reaches the end-office

that can complete the call


SIGNALING

In order for the network to function properly, the various

components and elements must have the ability to signal

each other to indicate status and condition.

Signaling can be either:

In-band: takes place over the same physical path as

the conversation and occupy the same channel

Out-of-band: takes place over a separate channel or

physical path as the conversation


SIGNALING

Signaling performs several functions:

Supervising: monitoring the status of a line

or circuit to see if it is busy, idle or requesting

service; and performing diagnostics

Alerting: indicates a specific condition such

as the arrival of an incoming call (ringing),

off-hook status (alert tone), busy signal, etc.

Addressing: transmitting routing, billing and

destination information


SIGNALING MODELS

Point-to-Point Signaling Point-to-Point signaling model is used to establish

and release connections between two end-points. The is the most common model of signaling. Not only is this model popular, it is also very

simple to implement. Point-to-MultiPoint (PMP) Signaling

Point-to-MultiPoint signaling model is used to establish and release connections between a root and multiple end-points.

This form of signaling is mainly used for multicasting or broadcasting applications (e.g., distant learning).


SIGNALING

Basic Phases of a Call



Phase 1- When a customer trying to make call he will lift

the receiver. This intern will activate the telephone exchange

and immediately dial tone will be fed from the exchange to

indicate that exchange is waiting for the dialing digits.

Phase 2- Customer starts dialing. Normally this dialing

period is variable and usually around 10 seconds.

Phase 3- When customer dials the complete B number (call

number) the originating exchange will decide the route that

has to be activated and send the B number details in an

agreed protocol to the terminating exchange. The time taken

for this phase too is variable but maybe limited to the

maximum of one or two seconds.



Phase 4- When the terminating exchange finds the B

customer is free it will send ringing current to the B

customer and send Ring Back Tone to the A customer (A

is the originating customer). This period is a variable and

can go up even to two minutes until the B customer

answers. If B customer does not answer within two

minutes (can be programmed) A customer will be

disconnected.



Phase 5- When the B customer answers the terminating

exchange will remove Ring Back Tone and ringing current

and inform the answer condition to the originating

exchange. Normally this will take around 100-200ms and

generally is variable within millisecond periods.

Phase 6- A and B customers speaking. Without their

knowledge they will follow the following phases


Public Circuit Switched Network


INTERNET AND DATA NETWORK (PSPDN)


What Is the Internet?

Internet is the network of networks i.e. a global network which make WWW (world wide web).

An Internet: A network of networks of computer hosts able to seamlessly communicate - usually through the Internet Protocol (IP) and services


Birth of the Net

The Internet grew out of an experiment in the

1960s by the U.S. Department of Defense. The

DoD wanted to create a computer network that

would continue to function in the event of a

disaster, such as a nuclear war. If part of the

network was damaged or destroyed, the rest of

the system still had to work. That network was

ARPANET, (Advanced Research Projects

Agency Network) which linked U.S. scientific

and academic researchers. It was the

forerunner of today's Internet.


Internet Milestones

Originally called ARPANET, the Internet began as a military-academic network

1969

Worldwide: Over

1 billion Internet

users

2007 1990

Commercial

access to the

Internet begins

ARPANET splits:

Milnet - for military Internet - academic, education

and research purposes only

1983

NSF Net

created as US

Internet

backbone

1986

Government

funding of the

backbone ends

1994


The Internet

Client

Connection Using TCP/IP Protocol

Internet

Server

Text, Audio, Video,

and Graphics Data


Internet Services

Internet

Electronic Mail (e-mail)

World Wide Web (WWW)

Chat

Internet News

File Transfer Protocol (FTP)


CELLULAR TELEPHONE NETWORKS (PLMN)


CELLULAR TELEPHONE NETWORKS

The public land mobile networks (PLMN) use a landline component that employs many of the basic principles of landline telephony, either based on circuit or packet techniques.

However, they require additional functionality to enable radio connections to be made to mobile phones and to keep track of where the network users are located.

Just as major change is reshaping fixed, or landline, telephone networks, so, too, is massive change being seen in mobile networks with third-generation networks now being widely introduced.


Evolution of Wireless Technology

1st Generation

2nd Generation

Generation 2+

4th Generation

1990

1995

2010

Analog

AMPS, TACS, JTACS

Digital (Speech)

GSM, IS-95, PDC

3rd Generation 2000

Digital, Multimedia-

Capable

IMT-2000

Broadband Wireless

Digital (Speech + data)

EDGE, GPRS, IS-95 B,C

1980


GENERATIONS OF CELLULAR SYSTEMS

FIRST-GENERATION SYSTEMS

SECOND-GENERATION SYSTEMS

SECOND-AND-A-HALF GENERATION SYSTEMS

THIRD-GENERATION SYSTEMS



1979-80 Came the first Cellular Mobile

system such as:

AMPS ( Advance Mobile Phone Service),USA

:800 MHz Band

NMT ( Nordic Mobile Telephony ), Sweden,

Denmark 450 Mhz, & 900 MHz

TACS ( Total Access Communication System),

UK 900 MHz

These were analog in Nature and known as First

Generation System


THE MOBILE SYSTEMS WORKING DURING EARLY 1980s

WERE INCOMPATIBLE & RESULTED IN MOBILE PHONES

DESIGNED FOR ONE SYSTEM COULD NOT BE USED WITH

OTHER SYSTEM.

IN 1982 CEPT (CONFEDERATION OF EUROPEAN POSTS &

TELECOMMUNICATION ) SET UP A COMMITTEE.

THIS COMMITTEE WAS KNOWN AS GROUP SPECIAL

MOBILE (GSM) & LATER KNOWN AS GLOBAL

SYSTEM FOR MOBILE COMMUNICATIONS.

IN 1989 THE RESPONSIBILITY FOR FRAMING SPECS FOR

GSM WAS PASSED FROM CEPT TO ETSI (EUROPEAN

TELECOMMUNICATION STANDARD INSTITUTE) .



During 1990 many digital mobile standards were

introduced in different regions/ countries

DAMPS ( Digital Advance Mobile Phone

Service), USA: 800 Mhz.

GSM ( Global System for Mobile

Communications), EUROPE: 900/1800 MHz.

CDMA ( Code Division Multiple Access )

These are known as 2nd Generation System (voice & Data SMS)



For introduction of data transfer capability on

the Mobile ,additional Hardware was

introduced in GSM systems, known as GPRS (

General Packet Radio Service ) . These are

being referred as 2.5 Generation System

Data rate supported 64 kbps-144 kbps

ENHANCED DATA RATE FOR GSM EVOLUTION

EDGE-384 KBPS



Now a Global Standard IMT-2000

(International Mobile Telecom.-2000) is

proposed which encapsulate all the existing

networks and different access technologies to

provide any time and any where type of

communication in very near future and known

as 3rd Generation standard.

Supports 2Mbps



EVOLUTION TO IMT-2000/3G

GSM GPRS EDGE

PDC

CdmaOne

TDMA

IS-136

TDMA/

GPRS

TDMA/

EDGE

Cdma 2000 WCDMA

IMT-2000

CAPABLE SYSTEMS

2000 EVOLVED 2G

64-115 Kbps

TODAY 2G

9.6/14.4Kbps

3G

115-384 Kbps &384-2 Mbps


Communication - Mobile


Uplink and Downlink frequencies

Cell To Mobile Down Link

Mobile to Cell Up Link

935-960 Mhz

1805-1880 Mhz

890-915 Mhz

1710-1785 Mhz

BTS


Multiple Access Techniques


GSM Network Architecture

l

MS

BTS

BTS

BTS

BTS BTS

BTS

BTS

BTS

BSC

BSC

PSTN

VLR

TRAU HLR

EIR

OMC

SMSC

BC

AUC

VMSC

MSC

A

SMSC : Short Message Service Center

VMSC : Voice Mail Service Center

BC : Billing Center

OMC : Operations and Maintenance Center


GSM Network Architecture

BTS : Base Transceiver Station

BSC : Base Station Controller

MS : Mobile Station

TRAU : Trans-coder Rate Adaptation Unit

MSC : Mobile Switching Center

HLR : Home Location Register

VLR : Visiting Location Register

AUC : Authentication Centre

EIR : Equipment Identity Register

SMSC : Short Message Service Center

VMSC : Voice Mail Service Center

BC : Billing Center

OMC : Operations and Maintenance Center


One network for everything

Today Tomorrow

Telephone

network

Mobile radio

network

IP-Network

Multimedia Access - Advantages:

Easy to handle Reliable Mobile

Internet

Transition to NGN: Third wave


Wireless

Gateways

Internet

POTS

Integrated

Services

Over IP

Evolving towards All IP Communications

Next Generation Networks (NGN) Present Day Networks

Next Generation Networks Technology


NEXT GENERATION NETWORKS

It is a packet-based network that can use

multiple transport network technologies.

The transport network has QoS capabilities.

Service-related functions are separated from the

transport technologies.

The access and core networks are clearly

separated so that users can have a choice about

who delivers the services.

Generalized mobility is supported so that users

can have ubiquitous access to services.


Transmission &

Systems


ROLE OF TRANSMISSION SYSTEM

Transmission is the process of transporting

information between end points of a system or

network. The end-to-end communication distance

is often very long and there are many electrical

systems on the line.


Elements of a Transmission System


Transport Network by Geography


Conclusion

There are unprecedented developments

happening in

Access

Core

Transport

Client Devices

Convergence at every level


16-Feb-12

Documents

Overview of Telecom Network