8/8/2019 DSS unit 1

1/63

BASICS OFBASICS OF

TELECOMMUNICATIONSTELECOMMUNICATIONS

By

Manojkumar S.B

Lecturer, Dept of E&C

B.G.S.I.T B.G.Nagara

8/8/2019 DSS unit 1

2/63

2

Information

Information

Communication TechnologyCommunication TechnologyComputerComputer

TechnologyTechnology

To collect, store, process, search,

retrieve, and present electronic

information to meet the needs of

various kinds of users, e.g., computer

hardware & software, PDAs, printers,groupware, smart cards.

What is Information?

To deliver, disseminate, exchange,

transmit, and receive electronic

information in local, regional or global

contexts, e.g., networks, fax machines,

cell phones, email, satellites, GPS,Internet, telephony, .

8/8/2019 DSS unit 1

3/63

3

COMPUTER SYSTEMS

REDEFINEDComputer systems used to be defined as:

Computer systems are now redefined as:

hardware

hardware

networks

networkssoftware

softwarehardware

hardware

software

software+

+ +

8/8/2019 DSS unit 1

4/63

DEFINITION

Telecommunications means to changeinformation

into electric signals for remote transmission and

switching.

Telecommunication is the assisted transmission of

signals over a distance for the purpose of

communication.

Telecommunication: communication at adistance.

8/8/2019 DSS unit 1

5/63

The World ofConnectivity

Wired or wireless communications links offer

several options for information andcommunications.

Source: The McGraw-Hill Companies,Inc. 1999

8/8/2019 DSS unit 1

6/63

Figure 1.4 Categories of physical topology

Physical topology

physical topology: design or layout of the network

8/8/2019 DSS unit 1

7/63

TELECOM NETWORK TOPOLOGIES

Star

Network

Mesh

Network

Tree

Network

Bus Network

Ring

Network

8/8/2019 DSS unit 1

8/63

MESH NETWORKS: Point to point dedicated link between

any two nodes Elimination of traffic problem

Provides security and privacy of data

Robust

Not Scalable Interface problem Good reliability

Usage of the links is low

The network is not economic

This type of network is only usedwhen there are extremely high

requirements for reliability

8/8/2019 DSS unit 1

9/63

Mesh

A fully connected mesh topology (five devices)

1

2

3

4

5

Example: telephone regional

offices

Advantages: no traffic problems Robust. No link failure no

effect on others. Privacy security Easy to detect the

abnormal situation.

Disadvantages: Amount of cables, i/o

ports Efficiency and

effectiveness Space Cost

8/8/2019 DSS unit 1

10/63

STAR NETWORKS: Each node is connected to the central

controller.

It does not allow direct traffic between

devices. Robust, provided the controller

remains active

Scalable

It is the basis of the ordinarily used

telephone network structure. Oneswitching center is configured, which

enables the calls among subscribers.

The reliability of star network is lower

than the overall meshed network, but

the star network is much more

economic than the overall meshed

network.

8/8/2019 DSS unit 1

11/63

Star

A star topology connecting four stations

Less expensive. One

link and I/o portconnecting to the

hub. No direct

traffic between

two devices.

Advantages: Easy to install Less cables Maintain: add,

move, delete Robustness

Disadvantages; Hub is too

important The hub

represents a

single source of

failure

8/8/2019 DSS unit 1

12/63

8/8/2019 DSS unit 1

13/63

Bus

A bus topology connecting three stations

Multipoint

Advantages: Easy to install Less cables

Disadvantages: Hard to detect fault isolation. Bus cable is too important

8/8/2019 DSS unit 1

14/63

RING NETWORKS:

Each device has a dedicated point to pointconnection only to the two devices on eitherside of it.

No broadcasting of data.

Scalable

8/8/2019 DSS unit 1

15/63

Ring

A ring topology connecting six stations

Point to point with 2 devices

on both sides

Advantages: Easy to install Maintain: add move

delete Fault isolation

Disadvantages: Unidirectional traffic

8/8/2019 DSS unit 1

16/63

TREE NETWORKS:

At present widely used in CATV distributionnetworks and private network (e.g. militarynetworks).

8/8/2019 DSS unit 1

17/63

Hybrid

A hybrid topology: a star backbone with three bus networks

8/8/2019 DSS unit 1

18/63

BASIC STRUCTURE OF TELECOM LOCAL

NETWORK

PBX

End office

PBX

To toll end

office

Branchoffice

Tandem

End office

PBXBranch

office

To toll end

office

Single Tandem Office Network Multiple-Tandem Office Network.

8/8/2019 DSS unit 1

19/63

NATIONAL TELECOMMUNICATIONSNETWORK

Primary Center (Local Network/Primary TrunkSwitching Centers)

Secondary Center (Trunk network/Regional

Tandem Switching Centers)

Tertiary Center (National TandemExchanges/Tertiary Trunk Switching Centers)

8/8/2019 DSS unit 1

20/63

THE PSTN HIERARCHY

Since 96 in Finland all the exchanges of PSTN have

been digital However, there exists still analog phones

Natural connection to the modern PSTN is the ISDN-interface

Country-level

County-level

City-level

8/8/2019 DSS unit 1

21/63

EXAMPLE: PSTN NETWORK OPERATOR INTWO TOWNS

PBX: Private Branch Exchange

MUX: multiplexer

RLL: Radio in the Local Loop

NMC: Network Maintenance

Center

X.25

OSS: Operations Support

SystemATM

A PCM-link

Note that by dial-up

networkingpart

of local exchange capacity

is allocated for another

operator

8/8/2019 DSS unit 1

22/63

Figure Representative telephone Network Hierarchy

8/8/2019 DSS unit 1

23/63

TERMINOLOGY:

North American

1Customers Loop

2 Central Office3 End Office4 Class 5 Office

Inter Office Trunk5 Junctor

6 Toll Office7 Toll Network

British

1 Local Network/Access

Network2 Exchange

3 Local Exchange

4 Junction

5 Trunk

6 Trunk exchange7 Trunk Network

8/8/2019 DSS unit 1

24/63

REGULATIONS:

Different countries have used differentmethods to regulate the telecommunicationbusiness. In most countries thetelecommunication monopoly has been

controlled by state ownership like BSNL inIndia.

8/8/2019 DSS unit 1

25/63

STANDARDS:

International Communications Union (ITU)

The work of ITU is carried out through two main bodies:

1) The ITU Telecommunication Sector (ITU-T)

Its duties include the study of technical questions,operating methods and tariffs for telephony, telegraphyand data communications

2) The ITU Radio Communication Sector (ITU-R)

It studies all technical and operating questions relatingto radio communications including point to pointcommunications, mobile services and broadcasting.Associated with it is the International Frequency

Registration Board (IFRB), which regulates theassignment of radio frequencies to prevent interferencebetween different transmissions

8/8/2019 DSS unit 1

26/63

A digital exchange (NortelDMS-100) used by an operator to

offer local and long distance services

http://en.wikipedia.org/wiki/Nortelhttp://en.wikipedia.org/wiki/DMS-100http://en.wikipedia.org/wiki/DMS-100http://en.wikipedia.org/wiki/Nortel

8/8/2019 DSS unit 1

27/63

8/8/2019 DSS unit 1

28/63

TELECOMMUNICATIONSTRANSMISSION

8/8/2019 DSS unit 1

29/63

COMMUNICATION NETWORK

Telecommunication

Network

8/8/2019 DSS unit 1

30/63

COMMUNICATION

Main purpose of communication is to transferinformation from a source to a recipient via achannel or medium.

Basic block diagram of a communicationsystem:

Source Transmitter Receiver RecipientChannel

8/8/2019 DSS unit 1

31/63

A COMMUNICATIONS MODEL

8/8/2019 DSS unit 1

32/63

8/8/2019 DSS unit 1

33/63

Generally, Digital signal must be discrete in time

and amplitude. Analog signal,contrarily,is

continuous in amplitude.

Analog signal

Digital signal

8/8/2019 DSS unit 1

34/63

Analog signal

Continuous waveform

Passes through communications medium

Used for voice communications

Digital signal

o Discrete waveform

o Transmits data coded into two discrete states as 1-bits and 0-bits

o Used for data communications

Modemo Translates computers digital signals into analog and vice

versa

8/8/2019 DSS unit 1

35/63

Bandwidth

8/8/2019 DSS unit 1

36/63

Bandwidth

21 Frequency (Hz)

Bandwidth

channel bandwidth: The bandwidth of a channel (medium) is definedto be the range of frequencies that the medium can

support. Bandwidth is measured in HzWith each transmission medium, there is afrequency range of electromagnetic waves that canbe transmitted:Twisted pair cable: 0 to 109 Hz (Bandwidth : 109

Hz)Coax cable: 0 to 1010 Hz (Bandwidth : 1010 Hz)

ANY CHANNEL/MEDIUM CAN BE VIEWED

8/8/2019 DSS unit 1

37/63

ANY CHANNEL/MEDIUM CAN BE VIEWEDAS A FILTER.

ch

an

ne

l

DIFFERENT SERVICES REQUIRE

8/8/2019 DSS unit 1

38/63

DIFFERENT SERVICES REQUIREDIFFERENT RATES

10k 1M 100M

GraphicsGraphicsCADCAD

FaxFax

Inter-LAN/PBX communicationsInter-LAN/PBX communications

VideoVideo

TV/HDTVTV/HDTV

Video conf.Video conf.

BroadcastingBroadcasting

TelephonyTelephony

Da

ta

Vid

eo

Vo

ice

bitrate

serv

ice

8/8/2019 DSS unit 1

39/63

Types of informationVoice, data, video, music, email etc.

Types of communication systemsPublic Switched Telephone Network(voice,fax,modem)Satellite systemsRadio,TV broadcasting

Cellular phonesComputer networks (LANs, WANs, WLANs)Radars

8/8/2019 DSS unit 1

40/63

dB IN COMMUNICATIONS

The db (decibel) is a relative unit of measurement

commonly used in communications for providing areference for input and output levels. Power gain or loss.

Decibels are used to specify measured andcalculated values in audio systems, microwave system gain calculations,

satellite system link-budget analysis, antenna powergain, light-budget calculations and in many othercommunication system measurements

In each case the dB value is calculated with respect to astandard or specified reference.

8/8/2019 DSS unit 1

41/63

POWER LEVELS

8/8/2019 DSS unit 1

42/63

Definition s of dBm and dBw

8/8/2019 DSS unit 1

43/63

8/8/2019 DSS unit 1

44/63

TELEPHONY

The telephone is connected to Public switchedtelecommunications network (PSTN) for local,national , and international voicecommunications

The same connections can carry data andimage information (television)

The connection to the PSTN may be via localexchange carriers (LEC)

End-users, nodes, and connectivities

8/8/2019 DSS unit 1

45/63

8/8/2019 DSS unit 1

46/63

8/8/2019 DSS unit 1

47/63

NORMAL SIGNAL FLOW

8/8/2019 DSS unit 1

48/63

TRANSMISSION SYSTEM

Two-Wire versus Four-Wire All subscriber loops in the telephone network are

implemented with a signal pair of wires

Both directions of transmission

Conversations are superimposed on the wirepair

Two directions of longer distances are separated

Two-Wire-to-Four-Wire Conversion

Basic conversion function is provided by hybridcircuits

Impedance matching is important

Impedance mismatch causes echo

8/8/2019 DSS unit 1

49/63

8/8/2019 DSS unit 1

50/63

8/8/2019 DSS unit 1

51/63

MULTIPLEXING

Trunks between central offices carry hundreds of

Conversations Cant run thick bundles!

Instead, send many calls on the same wiremultiplexing

Analog multiplexing (Frequency Division Multiplexing) bandlimit call to 4 KHz and frequency shift onto higher

bandwidth trunk

Obsolete

Digital multiplexing

first convert voice to samples 1 sample = 8 bits of voice

8000 samples/sec => call = 64 Kbps

8/8/2019 DSS unit 1

52/63

DIGITAL MULTIPLEXING

Time division multiplexing trunk carries bits at a faster bit rate than inputs

n input streams, each with a 1-byte buffer

output interleaves samples

need to serve all inputs in the time it takes onesample to arrive

=> output runs n times faster than input

overhead bits mark end of frame

8/8/2019 DSS unit 1

53/63

TIME DIVISION MULTIPLEXING (TDM)

The process by which many voice signals are

arranged in different Time Slots according to

certain rules and transmit along a single bearer.

DCD A C B AB

A

B

D

A

B

C

D

C

8/8/2019 DSS unit 1

54/63

TIME DIVISION MULTIPLEXING (3)

Multiplexing T1 streams into higher carriers.

8/8/2019 DSS unit 1

55/63

T T T

T T T

8/8/2019 DSS unit 1

56/63

8/8/2019 DSS unit 1

57/63

PCM PRIMARY GROUP FORMAT

The PCM primary group system is the basic system for

digital multiplexing.

Its primary frame structure contains 32 time slots.

TS1-15 &TS17- 31are used for Voice Channels,TS0 is normally used for Frame Synchronization.

TS16 is used as a Signaling Time Slot.

Each time slot has 8 bits.

Each multi-frame is composed by 16 single frames

8/8/2019 DSS unit 1

58/63

0 1 15 16 17 30 31

FRAME

32 TS, 256 bits, 125s,

0 1 2 1 4 15

MULTI-FRAME

16 Frames, 2ms, 4096 bits

a b c d a b c d

1 0 0 1 1 0 1 1

1 1 A1 1 1 1 1 1

0 0 0 0 1 A2 1 1 d0 d1 d2 d3 d4 d5 d6 d7

TS0 MULTIFRAME: MULTIFRAME SYNCRONIZATION

TS0: FRAME:FRAME SYNCRONIZATION

TS1TS15 & TS17 TS31 :VOICE CHANNELS

TS 16: FRAME: SIGNALING INFORMATION

8/8/2019 DSS unit 1

59/63

FEATURES OF PCM30/32

Sampling Rate 8000Hz

Frame Period 125 s

Width per TS 3.9 s

Multi - Frame period 125 s*16=2ms

Bits/ Sample Value 8 bits

Bits/ Frame 32*8bits=256bitsBits/ Multi-frame 256*16=4096bits

TS / Frame 32TS

TS / Multi-frame 32*16=512TS

Channel rate 64kb/s

Channel rate = 8k * 8 bits= 64kbits/per secSingle Frame Rate 2Mb/s

64Kb/s * 32 = 2048Kb/s 2Mb/s

8/8/2019 DSS unit 1

60/63

LINK TECHNOLOGY

Many in use today twisted pair

coax cable

terrestrial microwave

satellite microwave optical fiber

Increasing amount of bandwidth and cost perfoot

Popular Fiber

satellite

8/8/2019 DSS unit 1

61/63

OPTICAL FIBER LINK

Wonderful stuff! lots of capacity

nearly error free

very little attenuation

hard to tap

A long thin strand of very pure glass

8/8/2019 DSS unit 1

62/63

SATELLITES LINK

Long distances at high bandwidth

Geosynchronous 36,000 km in the sky

up-down propagation delay of 250 ms

bad for interactive communication

slots in space limited

Non-geosynchronous (Low Earth Orbit) appear to move in the sky

need more of them

handoff is complicated

e.g. Iridium

8/8/2019 DSS unit 1

63/63