01/04/2014

Computers Data Communication and Networks PDF


Data Communication and Networks notes


Local Area Network (LAN): A LAN is a data communication network, which connects many computers of workstations (computer terminal, printer etc.) and permits exchange of data and information among themselves, within a localised area, typically confined to a building, or a cluster of buildings.

LAN topology: A network topology refers to the physical layout of the network in which all the devices are connected. This includes all the hardware that makes up the network. The points of connection to the network by the stations are called Nodes or link stations. There are several types of typographical design and strategies used to implement LAN. The majority of these are based on three types of topologies: Star, Bus and Ring

Star Topology: In this topology, a number of stations are connected directly to a central station or controller. Communications on the connecting links between the stations and the central station of a star topography can be bi-directional and are point-to-point. 

Bus Topology: All stations are connected to a single communication line. This single communication line is referred to as a bus.

Ring Topology: Local area networks that have each station attached to an adjacent station using point-to-point links form a physical ring. Each station attached and active to the ring regenerates the information frame, and then re-transmits the information frame on the ring. The ring itself is logically circular and the information travels in one direction.

Wide Area Network: A Wide Area Network, or WAN, is a network that links separate geographical locations. A WAN can be a public system such as the Public Switched Telephone Network (the PSTN) or one of the various packet switched services provided by the public telecommunication authorities. WANs can also use most other types of circuit including satellite networks, ISDN, Value Added Networks (VANs/ VADs).

The main distinguishing feature between a WAN and LAN is that the LAN is under the complete control of the organisation which owns it, whereas the WAN needs the involvement of another authority like the telephone company.

Network/ File server system: For sharing data in a LAN, users stores files on a file server. A file server is a central node (Computer in the network) that stores data files where all users can access them.

Client/ Server system: Any local area network could be considered as client/ server system, since the workstation (clients) requests services such as data, programme files, or printing from server. A client/ server (C/S) has three distinct components, each focussing on a specific job: a database server, a client application and a network.

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