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A network is set of devices connect to each other with the help of some communication medium either word or nodes A nodes can be computer printer or any other device capable of sending or reviving data generated by other nodes on the network. the communication called as communication channel.

TOPOLOGY:-  topology is the physical and logical lay out of a network topology of a network is generation representation of the relationship of all the links and linking devices (nodes) two each other .two type of relationship are possible

(1) PEAR TO PEAR:- in this all the devices shared the link equally -ring’s, mesh,

(1) primary/secondary :-when one device control traffic and other most transmute through it -star and tree .

  • mesh:-all nodes are directly connected to each other .

for this connection amount of cable required .

ADVANTAGE :-lode balance each connection own carries load.

  1. Robustness if one link become unstable if does not effect other system .
  2. security is high as all the device have p ravel link .fault identification and fault isolation is easy that is the traffic  can be routed to divided speared link .


(1) amount of cable recurred is more .

(2) number of parts ( LAN card) recurred is also more.

(3) installation of every computer and reconfiguration is difficult .

(4) cost is high due to amount of cable cards.

BUS TOPOLOGY:- in the bus topology all the device are the connected control cable as back bone or bus. each work station is connected to next in point to point pear . i f one work station is goes fault. All work station may be effected because  all the workstation share the same cable.


(1) use is small network .

(2)less amount of cable is required.

(3) connection are simple.


(1) use is small network.

(2) as all the computer share the same cable the performance of the network . when number of computer are increased beyond the limit.

(3) fault identification is difficult.

(4) A fault made stop all the transmission.

(5) As the length of the cable increase.

(…………………………………..make the figure of bus topology………………………………………………………………)


in the ring topology all the device are connected to one and other in sane or a close loop so the each device is connected directly to two other device one each side . data is transmitted around ring in one direction each station passes the data to the next till it record the destination.


(1) easy to install and modifying in the network

(2) fault installation is easy.

(3) unlike bus topology there is no single is lost.


(1) Adding and removing of computers dis loop the entire network.

(2)A breaking a ring can stop the entire network.

(3)fault finding is difficult.

(4) expenses when compare to another network.

(……………………………..make figure of ring topology………………………………………………………)


star topology is use a central switch/hub though which all the component are connected nodes communicate across the network by passing the data though the central hub the central hub make all the routing decisions.


(1) installation and configuration is easy

(2) less expanses then compare to mesh.

(3) fault finding is easy .

(4) failure of a single computer effected the other .

(5) support multiple cable type .


(1) failure of the central hub break the whole network done.

(2) Amount of cabling required is more there fore cost is high.


tree topology is a logical extension of the bus topology and could be describe as a multiple inter connected bus network.


(1) Installation and configure is easy.

(2) Less expenses with compare to mess

(3) For finding is easy.

(4) Support multiple cable such as  UTS.


(1) If  primary hub is fail all connection is failure .

(2) Amount of cable require is more.


Cellular topology device area being service into cell in wireless media. Each point transmit in certain geographical area called as cell. Each cell represent a person the total network in cellular topology . The device are present and communicate . There are central hub measures responsible for routing  data accesses the network.


(1) The hub maintenance point to point to link with the device therefore soothing easy.

(2) Hub to hub all traffic is comparable but allow simple fault isolation


(1)When hub fails there is loss of all services.


                                                                             OS I:- (OPEN SYSTEM INTERCONNECTION)___________________________

Open System Interconnection allows any two different system to communicate regardless  of their underline architecture the purpose of OSI modal is to  open communications between different system without requiring changes to the logic of underline software or hardware.

OSI modal is built of seven layers. All the layers make thought as different sub-group having different and function. similar function are grouped together ti form a layer the lower layer provides services ti the upper layer hiding all the internal details of implementations. At every layer a healer  is appended but a better link layer tailor  is also appended.header and taller are the control information either of the beginning of data or at the end of the data.

The header appended at one layer is chopped off (removed)of the corresponding counter parts layer.


it coordinate the functions required to translate a bit stream over a physical medium.

(1) physical characteristics of interfaces and media:-it defines the type of transmission medium (cat-5,coaxial, fiber optical …)

(2) Representation of bits:-the bit most be encoded in to the singles.

(3) data rate or transmission rate :- number of bit send par second (Mbps,gbps).

(4)Synchronization of bits:-the sender or receiver  clock most be synchronization.

(5) line configuration :- the physical layer is concern with the connection of devices with two medium (point to point or multi point.)

(6) physical topology:-the physical layer define how the nodes are physically connected to make a network(bus,ring,star,mesh…)

(7)Transmission mode :-the physical layer also define the direction of transmission.


(2) DATA LINK LAYER:- It is responsible for note to node delivery .DDL provide the services to the network layer. the row data coming form the physical layer is converted in to frame. this is done to ensure that the transmission of data is error free. convert the bit in to the frame is tedious process.


(1) Framing:- The DLL divides the stream of bits from a network layer into manageable and transmittable  data units called as frame.

(2) Physical Addressing:- If the frames are to be distributed to different stream on a network . The DLL adds the header to defines total physical address of the sender and receiver.

The rate cost which the sender and receiver will transmit or receive the data.

(4) Access Control:- When two or more devices are connected to the same LAN . It is necessary to determine which device is get the control of the links.

(5) Error Control:-  Mechanism  to defect and re transmit the damaged of losses frame error control achieve by adding a trailer at end of the frame.

(3) NETWORK LAYER:- Network layer is responsible for source to destination delivery of a packet possibly across multiple networks network layer insure that each packet gets from it point of origin to its final destination.

Following functions are….

(1) Logical address means the IP Address of sender and receiver so that if there is any change in physical address logical address is not effected.

(2) Routing:- When independent networks or links are connected to create inter network ie network of networks, the connecting devices called as route or switch . Route the packet to the find destination through the best available path.

(3) TRANSPORT LAYER:-Transport layer is responsible for source to destination delivery of the entire message. Transport layer ensure that the whole message arrives intact and in order, the transport layer ensure that the whole message arrives three steps. connection released the function . Services point addressing computer often run several programs of the same time communication is not between one computer to another computer but it is from one specifier program to another specific program in another computer . The transport layer those program by a number called as part number and port address.

(4) SESSION LAYER:- Session layer is the dialog controller . It establish maintains , and synchronizes the interaction among communicating system

Session layer are following functions:-

(i) It allows two system to enter into a dialog . It allows the communication between two processes to take place in either half duplex or full duplex.

(ii) Synchronization:- The session layer allows the process to at check point into the string of data .so that it crash sources the data can be re-downloaded from the last check point.

(6) PRESENTATION LAYER:- Presentation layer concerned with the syntax and semantics of the information exchanges between two system.

Functions are:-

(i)Translation:- The presentation layer at the sender changes the information from its sender dependent format into a common format. The presentation layer at the receiving machine changes the common format into its receiver dependent format.

(ii)Encryption:-To carry sensitive information the sender transformation original information to another form and send the resulting message our the network .The decryption reverse the original process to transform the message back to its original form.

(iii) Compression:- Compression reduces no of bits contained in the information . Data compression becomes particularly important in the transmission of multimedia.

(7) APPLICATION LAYER:- The application layer enables the user whether human or software to access the network. It provides user interfaces and support for services such as electronic mail, x500, directory services , share data management network vertical terminal.






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