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Lecture1 by Dr. M. G. Sharma, PhD, IIT Kharagpur Dean Telecom Aegis School of Telecom Introduction to Voice, Data and Computer Communications.

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Presentation on theme: "Lecture1 by Dr. M. G. Sharma, PhD, IIT Kharagpur Dean Telecom Aegis School of Telecom Introduction to Voice, Data and Computer Communications."— Presentation transcript:

1 Lecture1 by Dr. M. G. Sharma, PhD, IIT Kharagpur Dean Telecom Aegis School of Telecom Introduction to Voice, Data and Computer Communications Aegis School of Telecommunication

2 Aegis School of Telecommunication Information & Communication Generation and transfer of information is critical to todays businesses and social life Flow of information both mirror and shape organizational structures Networks are the enabling technology for this process

3 Aegis School of Telecommunication The Managers 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

4 Aegis School of Telecommunication 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

5 Aegis School of Telecommunication 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

6 Aegis School of Telecommunication The original invention Telephone was patented by G. Bell in 1876

7 Aegis School of Telecommunication The handset Electro-magnetic speaker Carbon powder microphone (now replaced by electronically amplified device)

8 Aegis School of Telecommunication The voice channel 50 V

9 Aegis School of Telecommunication The voice channel 50 V Inductive loaded lines for improving long distance transmission

10 Aegis School of Telecommunication 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

11 Aegis School of Telecommunication 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.

12 Aegis School of Telecommunication 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!

13 Aegis School of Telecommunication The Telephone Network (contd) 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!

14 Aegis School of Telecommunication Thus, a second-level hierarchy was added. The current telephone system has five levels of hierarchy. The Telephone Network (contd)

15 Aegis School of Telecommunication 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).

16 Aegis School of Telecommunication Data Communication Adding storage overcomes time constraints Store-and-forward communication E-mail, voice mail, facsimile, file transfer, WWW

17 Aegis School of Telecommunication Business Information Requirements Voice Data Image Video

18 Aegis School of Telecommunication 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

19 Aegis School of Telecommunication 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)

20 Aegis School of Telecommunication 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

21 Aegis School of Telecommunication 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

22 Aegis School of Telecommunication 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-users satisfaction

23 Aegis School of Telecommunication 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

24 Aegis School of Telecommunication 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

25 Aegis School of Telecommunication 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

26 Aegis School of Telecommunication 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?

27 Aegis School of Telecommunication Data Represented by finite alphabet, ex: text Transmitting a page of text 8by 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

28 Aegis School of Telecommunication Transmission of Information Transmission and transmission media e.g. twisted pair, fiber, wireless, coax Communication Techniques encoding, interface, protocols Transmission efficiency multiplexing, compression

29 Aegis School of Telecommunication 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

30 Aegis School of Telecommunication Communications Tasks Transmission system utilization Addressing InterfacingRouting Signal generationRecovery SynchronizationMessage formatting Exchange managementSecurity Error detection and correction Network management Flow control

31 Aegis School of Telecommunication Simplified Communications Model - Diagram

32 Aegis School of Telecommunication Simplified Data Communications Model

33 Aegis School of Telecommunication 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)

34 Aegis School of Telecommunication 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)

35 Aegis School of Telecommunication Circuit Switching Dedicated communications path established for the duration of the conversation e.g. telephone network

36 Aegis School of Telecommunication 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

37 Aegis School of Telecommunication 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

38 Aegis School of Telecommunication 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)

39 Aegis School of Telecommunication 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

40 Aegis School of Telecommunication LAN Configurations Switched Switched Ethernet May be single or multiple switches ATM LAN Fibre Channel Wireless Mobility Ease of installation

41 Aegis School of Telecommunication Metropolitan Area Networks MAN Middle ground between LAN and WAN Private or public network High speed Large area

42 Aegis School of Telecommunication Networking Configuration

43 Aegis School of Telecommunication Communications Software TCP/IP Distributed Applications Client/Server Architectures & Intranets

44 Aegis School of Telecommunication Management Issues Doing Business on the Internet Network Management Network Security

45 Aegis School of Telecommunication Communications Standards Importance Process Organizations

46 Aegis School of Telecommunication 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)

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