Chapter 2- Physical Layer

• Wired transmission (Copper Core, Glass Core)
• Wireless transmission (electromagnetic spectrum)
• Asynchronous Communication
• ISDN, ATM
• Cellular Radio
• Switching Techniques issues

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Computer Networks

Asynchronous Communication

• in telecommunications, 
• asynchronous communication is transmission of data, generally without the use of an external clock signal,
• where data can be transmitted intermittently rather than in a steady stream.
• timing required to recover data from the communication 
• Definition
• Transmitter and receiver do not explicitly coordinate each data transmission.
• Transmitter can wait long for transmission. (keyboard).
• Means no explicit info about where data bit begin and end

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WCB/McGraw-Hill

© The McGraw-Hill Companies, Inc., 1998

ISDN: Integrated Services Digital Network

• (ISDN) is a set of communication standards for simultaneous digital transmission

of voice, video, data, and other network services over the traditional circuits of the PSTN

public switched telephone network in telecommunications, 

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ISDN: Integrated Services Digital Network

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•  PSTN is the world’s collection of interconnected voice-oriented public telephone networks
• called circuit-switched telephone network.

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ATM

• Asynchronous transfer mode (ATM) is a switching technique used by telecommunication networks
• it uses asynchronous time-division multiplexing to encode data into small, fixed-sized cells.
• This is different from Ethernet or internet
• Uses fixed length packets called cells,
• Achieves fast speed by avoiding flow control and error checking.

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Cellular Radio

• cellular network or mobile network is a communication network where the last link is wireless
• network is distributed over land areas called "cells“
• each cell served by at least one fixed-location transceiver
•  cell sites cell sites or base transceiver stations. (BTS-BSS)
• cell with the network coverage which can be used for transmission of voice, data, and other types of content.

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personal communications systems 

in which the mobile receiver switches 

frequencies automatically as it passes 

from one cell to another

Cellular Radio

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ISD (International Subscriber Dialling) stands for International calls, STD (Subscriber's Trunk Dialling) for Inter-state calls and PCO (Public Call Office) for local calls

Functionalities of Physical layer

• “responsible for moving individual bits from one node to next node”
• Transmission Media
• Types of encoding
• Data rate (nr. of bits sent/second)
• Synchronization of bits
• Line configuration (point to point / multiport)
• Types of topologies (mesh, star bus, ring)
• Transmission mode (Simplex, Duplex-Half/full)

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End of session (Ch-2, Physical layer)

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Thanks.

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Self exercise

Q- what is Switching? Describe Circuit switching, message switching, packet switching