Lecture1 by Dr. M. G. Sharma, PhD, IIT Kharagpur Dean Telecom Aegis School of Telecom Email:[email protected] Introduction to Voice, Data and Computer Communications.

Lecture1by Dr. M. G. Sharma, PhD, IIT KharagpurDean Telecom Aegis School of Telecom

Email:[email protected]

Introduction to Voice, Data and Computer

Communications

Aegis School of Telecommunication www.aegisedu.org/telecomsystemsI.htm

Aegis School of Telecommunication

www.aegisedu.org/telecomsystemsI.htm

Information & Communication Generation and transfer of

information is critical to today’s businesses and social life

Flow of information both mirror and shape organizational structures

Networks are the enabling technology for this process



The “Manager’s Dilemma”

Technology is necessary for competitiveness

Cost of technology has decreased Reliance on technology has

increased Number of choices have increased Choices are both more difficult and

more important



Events in History 1837 - Telegraph is invented 1876 - Telephone is patented (Alexander Graham Bell) 1877 - Bell company is formed 1885 - AT&T is founded 1951 - Long distance direct-dialing 1970 - MCI is allowed to provide long distance service 1984 - Breakup of AT&T; start of cellular phone service 1996 - Telecommunications Competition and

Deregulation Act - deregulates U.S. telephone system Refer to telecom history PPT on Telecom Systems I

course page



Telecommunication

Telephone/ Telecommunication network. Engineered to deliver real-time voice. Also world-wide. Low delay but more expensive. Users identified but telephone number Uses

electricity to transmit messages Speed of electricity dramatically extends reach

Sound waves: ~670 mph Electricity: ~186,000 (speed of light)

Bandwidth= information-carrying capacity of a channel



The original invention

Telephone was patented by G. Bell in 1876



The handset

Electro-magneticspeaker

Carbon powdermicrophone(now replacedby electronicallyamplified device)



The voice channel

50 V



The voice channel

50 V

Inductive loaded lines for improving

long distance transmission



Voice Communication

Connection Oriented Communication Connection establishment : Signaling Connection usage : Conversation Connection termination : Signaling

Additional signaling during conversation Billing Escape for call transfer Interrupt for incoming call while in conversation Escape for switching between calls

Calling Line Identification



The Telephone Network

In 1878, the Bell Telephone company opened its first switching office (in New Haven, CT).

Each user would connect to the local switching office. When a user wanted to make a call,

s/he rang to the office, and would be manually connected to the other end.



The Telephone Network

For one telephone to be able to talk with another telephone, a direct connection between the two telephones was needed. Within one year, cities were covered

with a wild jumble of wires!



The Telephone Network (cont’d)

To allow for long-distance calls, switching offices (switches) were connected .

Several connections can go through inter-switch trunks simultaneously.

At some point, there were too many connections between switching offices!



Thus, a second-level hierarchy was added.

The current telephone system has five levels of hierarchy.

The Telephone Network (cont’d)



Computer Network

Provide access to local and remote resources.

Collection of interconnected end systems: Computing devices (mainframes,

workstations, PCs, palm tops) Peripherals (printers, scanners,

terminals).



Data Communication

Adding storage overcomes time constraints

Store-and-forward communication E-mail, voice mail, facsimile, file

transfer, WWW



Business Information Requirements Voice Data Image Video



Voice Outside Services

Public telephone Networks Local National

Private On site

Private Branch Exchange (PBX) On premise switching facility Interconnects telephone with public telephone system

Off Site Centrex – provides same service but equipment

located at telephone office



Analog Voice Communication Primarily used for transmission of human

voice (telephony) Microphone captures voice vibrations,

converts them to waves than can be expressed through variations of voltage

Examples Telephone (3000Hz) Hi-Fi Sound (15,000Hz; approximate range of

human ear) Compact Disc (20,000Hz for each of two

channels)



Digital Voice Communication For good representation, must sample

amplitude at a rate of at least twice the maximum frequency

Measured in samples per second, or smp/sec Telephone quality: 8000smp/sec, each

sample using 8 bits 8 bits * 8000smp/sec = 64kbps to transmit

CD audio quality: 44000smp/sec, each sample using 16 bits 16 bits * 44000smp/sec = 1.41mbps to transmit

clearly



Converting Images

Break image up into small units More units means more detail Units called pixels

Use photocell to read each unit, assign value

How can we represent those units electrically?

PACMAN example



Image Quality Issues More pixels=better quality More compression=reduced quality

“Lossy” gives from 10:1 to 20:1 compression “Lossless” gives less than 5:1

Less compression=reduced speed of transfer

Choices in imaging technology, conversion, and communication all affect end-user’s satisfaction



Image Examples include pictures, medical

imaging Digital Angiography

1 MB per image x 20 images x 8 bits/byte=160 million bits

Time to transmit over 56kbps line 160Mb/56,000bps = 2857.14 sec

Compression techniques Lossy – allows a loss of information Problems for medical images where detail is

important



Video Communication

Sequences of images over time Same concept as image, but with

the dimension of time added Significantly higher bandwidth

requirements in order to send images (frames) quickly enough

Similarity of adjacent frames allows for high compression rates



Video Ex: TV, teleconference Black and White TV Signal

Frame resolution = 360 pixels by 280 pixels

At 30 frames /sec Each pixel can represent 256 shades of

gray therefore takes 8 bits for each pixel

(360pixels x 280 pixels) x 30 frames/sec x 8 bits/pixel = 24, 192, 000 bits



Data Communication

In this context, we mean data stored on computers

Already digital, so no conversion necessary

Bandwidth usually affects speed, but not quality

Examples?



Data Represented by finite alphabet, ex: text Transmitting a page of text 8”by 11” with 1

inch margins Each letter represented by a byte = 8 bits Double spaced page has 3 lines per inch

9in x 3lines/in = 27 lines per page Typically 10 char/inch

6in x 10 char/in = 60 char/line 60 char/line x 27 lines/page = 1,620 char/page x 8

bits /char = 12,960 bits/page To send a page over 56,000 bps line

12,960bits/56,000bps=.23 sec



Transmission of Information Transmission and transmission

media e.g. twisted pair, fiber, wireless, coax

Communication Techniques encoding, interface, protocols

Transmission efficiency multiplexing, compression



A Communications Model Source

generates data to be transmitted Transmitter

Converts data into transmittable signals Transmission System

Carries data Receiver

Converts received signal into data Destination

Takes incoming data



Communications Tasks

Transmission system utilization

Addressing

Interfacing Routing

Signal generation Recovery

Synchronization Message formatting

Exchange management Security

Error detection and correction

Network management

Flow control



Simplified Communications Model - Diagram



Simplified Data Communications Model



Networking Point to point communication not

usually practical Devices are too far apart Large set of devices would need

impractical number of connections Solution is a communications

network Wide Area Network (WAN) Local Area Network (LAN)



Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier

circuits Alternative technologies

Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM)



Circuit Switching Dedicated communications path

established for the duration of the conversation

e.g. telephone network



Packet Switching Data sent out of sequence Small chunks (packets) of data at a

time Packets passed from node to node

between source and destination Used for terminal to computer and

computer to computer communications

Frame Relay, ATM



Frame Relay Packet switching systems have

large overheads to compensate for errors

Modern systems are more reliable Errors can be caught in end system Most overhead for error control is

stripped out



Asynchronous Transfer Mode ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Constant data rate using packet

switching technique (Anything from 10Mbps to Gbps)



Local Area Networks Smaller scope

Building or small campus Usually owned by same

organization as attached devices Data rates much higher Usually broadcast systems Now some switched systems and

ATM are being introduced



LAN Configurations Switched

Switched Ethernet May be single or multiple switches

ATM LAN Fibre Channel

Wireless Mobility Ease of installation



Metropolitan Area Networks MAN Middle ground between LAN and

WAN Private or public network High speed Large area



Networking Configuration



Communications Software TCP/IP Distributed Applications Client/Server Architectures &

Intranets



Management Issues Doing Business on the Internet Network Management Network Security



Communications Standards Importance Process Organizations



Assignments Read the Data Transmission before coming

to class Give detail presentation on Indian Telecom

History three days Give Presentation on Telecommunication

Standards one week Give a presentation on Telcom Network

structure of BSNL (Land line and Mobile), RIL, TATA Telecom and Touch Tele, Air Tel, Idea (time one month)

Lecture1 by Dr. M. G. Sharma, PhD, IIT Kharagpur Dean Telecom Aegis School of Telecom Email:[email protected] Introduction to Voice, Data and Computer Communications.

Documents

telephone office slide

telephone network contd

channel slide

www slide

page slide

process slide

important slide

telephone number