Basic Telecoms

7/29/2019 Basic Telecoms

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Basic Telecom Course

CONTEN

Transmission Lines Basic

Analogue and Digital Signal

ISDN Basic

Circuit switch system Vs Packet switchedsystem

GSM Network Overview

ADSL Network

1


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Transmission Lines Basic

Telecommunications means:

The electronic transmission of alltypes of information audio, video,

voice, graphics, pictures, animation

from a location to another over acommunications link.


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Basic Elements of a Telecommunication System

Transmitter

Receiver

TransmitterSource

Destination

Channel


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Telecommunications Channels

Transmission lines - carrier is electrical energy - channelisnormally copper cable

Optical fibers - carrier is electromagnetic energy at lightfrequencies - channel is the optical fiber cable

Radio waves - carrier is electromagnetic energy at radio

frequencies - channel is free space between transmitting Antennaand receiving Antenna.


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Transmission Media

Transmission Medium

Physical path between transmitter and receiver

Guided Media

Waves are guided along a solid medium

E.g., copper twisted pair, copper coaxial cable, optical fiber

Unguided Media

Provides means of transmission but does not guide

electromagnetic signals

Usually referred to as wireless transmission

E.g., atmosphere, outer space


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Copper transmission line

Coaxial cable - this is called an unbalanced line ( has one

conductor grounded or exposed to the outside elements

in greater magnitude than the other conductor.)

Twisted Pair Cable- this is called a balanced line (each

line has equal impedance relative to ground or itssurroundings)

Guided Media

Fiber optic Transmission Line

Unguided MediaElectromagnetic waves, called wir eless transmission


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PSTN Architecture, Lines and Trunks

PBX

PBX

Telephone

Telephone

Individualuserstations,Linens orExt

ResidentialServices

CPE Local Loop Backbone,or CoreNetwork

LocalExchangeTrunks

Subs Line

Subs Line

InterexchangeTrunks

Local

Exchanges

TandemTrunks

International GatewayFor routing calls betweencountries

Toll/Transit Switchfor routing calls to orfrom other cities

Tandem/Junction Excfor routing calls between localExc within the city


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Local Exchange

Main Exchange

Main Exchange

Main Exchange

Subs

SubsSubs

Subs

Cell Tower

Mobile Exchange

International

Exchange

Cell

Phone Box

Telephone

Poles

River

PayphoneBox

Payphone

Fiber Optic

Cables

Local Ex. Is connected to

all the phones in a small

geographical area

Signal leaves your house

to a telephone box outside

From the Local & Mobile

Exs. Calls are routed to

the main Ex.

Cell phone calls travel to

the cell tower & from

there, on to a mobile ex.


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Local Exchane

Main Exchange

Subs

SubsSubs

Subs

Phone Box

Telephone

PolesRiver

International

Exchange

International

Exchange

Undersea

Cable

Satellite

To Other

Countries

The Calls are sent to the other

countries via undersea cables or

satellite systems


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Analog Signals and Digital Signal

A continuously varying electromagnetic wave that may be

propagated over a variety of media, depending on frequency

Examples of media:

Copper wire media (twisted pair and coaxial cable)

Fiber optic cable

Atmosphere or space propagation

Analog signals can propagate analog and digital data


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Analog and Digital Transmission

Analog Transmission


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Digital Signals

A sequence of voltage pulses that may be transmitted over a copper wire medium

Generally cheaper than analog signaling

Less susceptible to noise interference

Suffer more from attenuation

Digital signals can propagate analog and digital data


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ISDN Basic

What is ISDN?

Integrated Service Digital Network,

A system of digital phone connections, which allow

voice and data to be transmitted simultaneously

using end-to-end digital connectivity.


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Integrated Service Digital Networks

ISDN - is a digital telephone service which

provides fast, accurate voice & data transmissionover existing copper telephone wiring.

ISDN based on a number of fundamental building blocks.

First, there are two types of ISDN

"channels" or communication paths:


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B-channel The Bearer ("B") channel is a 64 kbps channel

This channel can be used for video, data, voice, ormultimedia calls.

D-channel The Delta ("D") channel can be either a 16 kbps or 64

kbps channel

Mainly this channel is used for communications (or

"signaling") between switching equipment in the ISDNnetwork & the ISDN equipment at your location.


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These channels are delivered to the user in one of two pre-defined

configurations:

Basic Rate Interface (BRI)

BRI is the ISDN service used to connect to the Internet. BRI connectionsupports two channels B and D over a standard phone line. often called"2B+D".

Primary Rate Interface (PRI)

ISDN PRI service is used primarily by large organizations with intensivecommunications needs. This PRI connection supports 30 64kbps

European- (23 64 kbps) American B-channels and one 64 kbps D-channel

(30B+D , 23B+D) over a high speed (T1 or E1) circuit.


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Circuit Switching

Circuit switching Dedicated communications path between two stations

E.g., public telephone network ( Plain Old Telephone System- POTS)Phases of Circuit Switching

Circuit establishment

An end to end circuit is established through switching nodes

Information Transfer ( call progress and transfer)

Information transmitted through the network

Data may be analog voice, digitized voice, or binary data

Circuit disconnect

Circuit is terminated

Each node de-allocates dedicated resources


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Circuit Switched

Telephone

Telephone

Switch 1 Switch 2

Switch 3 Switch 4

Three phases of circuit switched:- Establish,

- Transfer,- Disconnect

To establish aconnection:Must haveswitching Capacity& Channel Capacity

Must haveintelligenceto workoutrouting

SubsLoop Trunk


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Packet Switching

computer2

computer2

D C B A

Packet switching Message is broken into a series of packets Each node determines next leg of transmission for each

packet


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Packet Switching Advantages

Line efficiency is greater

Many packets over time can dynamically share the

same node to node link

Packet-switching networks can carry out data-rate

conversion

Two stations with different data rates can

exchange information

Unlike circuit-switching networks that block callswhen traffic is heavy, packet-switching still accepts

packets, but with increased delivery delay

Priorities can be used


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Disadvantages of Packet Switching

Each packet switching node introduces a delay

Overall packet delay can vary substantially

This is referred to as jitter

Caused by differing packet sizes, routes taken

and varying delay in the switchesEach packet requires overhead information

Includes destination and sequencing

information

Reduces communication capacity

More processing required at each node


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Comparison between packet switching networks and circuit switching networks

Circuit Switching

Dedicated transmission path

Continuous transmission

No storage of data/messages

Same path for duration of

connectionCall setup required

Overload may block call

Busy signal if called busy

Fixed bandwidth transmission

Charging by minute

Packet Switching

No dedicated path

Transmission of packets

Packets may be stored

Each packet may take

different routeNo call setup needed

Overload increases packetdelay

No busy signal

dynamic use of bandwidth

Charging by packet


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Leased Line

Leased Line (Private Line or Dedicated Line)

Point-to-point connection

Always on

Lower cost per minute than dial-up service Must be provisioned (set up)


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GSM GSM stands for

Global System for Mobiletelecommunications.

Cell Structure the coverage area of an operator is divided

into cells

A cell is the area that one or more transmitterscan cover


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Introduction

Types of Cells

Different types of cells are used depending ofthe population density in a country

Macrocells

Microcells Selective or sectorized cells

Umbrella cells

Nano-cells

Pico-cells


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Cell Types

Macrocells

Large cells for remote and separate populated areas

Can be larger than 3 to 35 km

Microcells

Used for densely populated areas by splitting theexisting cell into smaller cells

May be as small as .1 to 1 km

Pico-cells

smaller version of microcells

Covers approximately .01 to 1 km


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Cell Types cont.

Nano-cells

Smaller and smaller segments Covers .01 to .001 km

Umbrella Cells Covers several micro-cells to solve the problem of

overabundance of handovers among the different smallneighboring cells

When the speed ofis too high, the is handed off toumbrella cell


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GSM Architecture

A GSM networks consists of

several functional entities

SIM

Mobile TE Um Abis ABSSNSS

MSC

BSC

BTS

ME

HLR VLR AuC EIRPSTN


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Cellular System Architecture

MSC MSC

HLR

VLR

HLR

VLRTo otherMSCs

PSTNPSTN


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Each cell is served by a base station (BS)

Each BS is connected to a mobile switchingcenter (MSC) through fixed links

Each MSC is connected to other MSCs andPSTN


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Each MSC is a local switching exchange thathandles switching of mobile user from one basestation to another

Locating the current cell of a mobile user Home Location Register (HLR): database recording

the current location of each mobile that belongs tothe MSC

Visitor Location Register (VLR): database recording

the cell ofvisiting

mobiles

Interfacing with other MSCs and PSTN



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One channel in each cell is set aside for signalinginformation between BS and mobiles

Mobile-to-BS: location, call setup for outgoing,

response to incoming BS-to-Mobile: cell identity, call setup for

incoming, location updating



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The Network & Switching Subsystem

The switching system (SS) is responsible for performing call processingand subscriber-related functions. The switching system includes the following

functional units:home location register (HLR)The HLR is a database used for storage andmanagement of subscriptions. it stores permanent data about subscribers, including asubscriber's service profile, location information, and activity status.

buys a subscription from one of the PCS operators, he or she is registered in theHLR of that operator

Mobile Services Switching Center (MSC) - MSC performs the telephonyswitching functions of the system

controls calls to and from other telephone and data systems

also performs such functions as toll ticketing, network interfacing, commonchannel signaling, and others.

Visitor location register (VLR) -VLR is a database that contains temporaryinformation about subscribers that is needed by the MSC in order to service visitingsubscribers.

The VLR is always integrated with the MSC. When a mobile station roams into a new MSCarea, the VLR connected to that MSC will request data about the mobile station from the HLR.Later, if the mobile station makes a call, the VLR will have the information needed for callsetup without having to interrogate the HLR each time.


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Authentication center (AUC) -A unit called the AUC provides

authentication and encryption parameters that verify the user's identity andensure the confidentiality of each call.

The AUC protects network operators from different types of fraudfound in today's cellular world.

Equipment identity register (EIR) - The EIR is a database that containsinformation about the identity of mobile equipment that prevents calls fromstolen, unauthorized, or defective mobile stations

The AUC and EIR are implemented as stand-alone nodes or as acombined AUC/EIR node.

The Network & Switching Subsystem Cont.


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Base Station System (BSS)

All radio-related functions are performed in the BSS, which consists of base station

controllers (BSCs) and the base transceiver stations(BTSs)

BSC - The BSC provides all the control functions and physical links between the MSC

and BTS.

It is a high-capacity switch that provides functions such as handover, cell configuration data,

and control of radio frequency (RF) power levels in base transceiver stations. A number of

BSCs are served by an MSC.

BTS - The BTS handles the radio interface to the mobile station. The BTS is the radio

equipment (transceivers and antennas) needed to service each cell in the network. A

group of BTSs are controlled by a BSC.


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ADSL

Asymmetric Digital Subscriber Line (ADSL)


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Heres What You Will Learn About ADSL!

What is it?

What are the benefits?

How fast is it?

How does it work?

What can I use it for?


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What is ADSL?

ADSL is a latest broadband

communication technology

that creates high-speed

access to the Internet and

remote networks using thephone lines that are already

present in your home.

ADSL is an asymmetr ic comm unicat ion techno logy designed

for resident ia l users; i t is no t suitable for businesses.

Note


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What are the benefits of ADSL?

You can talk on the phone and use the Internet at

the same time on a single phone line

You can connect to the Internet at up to 140 times

faster than analog modems

Your connection to the Internet is always on

Your home has its own dedicated connection

Your connection is highly reliability

Your connection is highly secure

Si lt C ti


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Simultaneous Connections

Talk on the phone and surf the Internet at the same time on the

same phone line!

You do not have to disable call waiting to connect to the Internet.

Even if the power goes out, you will still be able to make phone

calls. Unlike cable modems, your connection speed will not be affected by

how much bandwidth your neighbors use.

ADSL Reliability


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Always On

Because the information is transmitted separately from

the voice/fax calls, your Internet connection can stay on

all the time.

No more logging on and off

No more busy signals

No more waiting

just open your browser and go!


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ADSL Security

The dedicated connection that ADSL uses

provides more security than cable.

Cable modem users share bandwidth with theirneighbors. Information traveling across the

network is easier to snoop.


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ADSL modem


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DSLAM

To interconnect multiple ADSL users a Digital Subscriber Line Access Multiplexer

(DSLAM) is used

DSLAM is used at the telephone central office that separates the data signals

from the telephone line


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What can I use ADSL for?

Faster downloads of anything digital

CD-quality audio

Graphics-rich websites

Faster and better multimedia

High-speed multiplayer games


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Types of DSL

ADSLAsymmetric DSL

R-ADSL Rate Adaptive DSL

HDSL High Bit Rate DSL

SDSL Single Line DSL

VDSL Very High Bit Rate DSL


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ADSL Summary

ADSL provides a new way to use existing phone

lines.

Its faster!

Its always on!

Voice and data on one line at the same time!

ADSL is the bestway to get online!

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