switching............(Circuit switching)

Friends,
This article is about circuit switching which is a type of switching.In previous article switching we discussed about switching and major type names.In this article we will discuss first type of switching i,e circuit switching.
Circuit switching:-
In a circuit switched network a dedicated circuit must first connected.Once the circuit has been "nailed up" ,transmission can begin.When the transmission is complete then the circuit is released for next transmission.ex. telephone switching is circuit switching.



Understand the concept by taking an example:-
let us make a call.When we dial a telephone number,then telephone company search its database to determine which circuit should be used to deliver the call.If it is a log distance call,the switch know it must connect to another telephone company office,where a switch called a tandem.Tandem use a circuit that connect it to another office.This process is continue untill there are circuit connected from orginator to the destination.
These circuit cannot be used further for any other call,this is dedicated to call untill call is complete.Once the call is complete,circuit can be released and used for another call.
A circuit switch network consist of set of switches connected by physical links,in which each link is divided into n channels.
There are three phases in circuit switching:-
1.Set up phase.
2.Data transfer phase
3. Tear down phase.
Set up phase:-When a system needs to communicate with another system b then a system a send request to system b for connection that must be accepted by all the switches as well as b itself.a circuit or channel defined the dedicated path.

Data transfer phase:-After the dedicated path made of connected circuit is established and data can be tranfered.

Tear down phase:-After all the data have been transfered,the circuits are tear down means released for another commuication.

some important points to be considered:-
1. circuit switching takes place at physical layer.
2. Before starting communication resources should be reserved which are needed during communication.These resources such as channel ,switch buffers,switch processing time ,input output ports must remains dedicated during entire duration of data transfer untill tear down phase arised.
3. The data should be sent in a flow from source to destination.
4.There is no addressing involve during data transfer.

Advantage of circuit switching:-
1.It is well suited for long elastic channels.
2.It is simple and not require extra facility.

Disadvantage of circuit switching:-
1. Delay in setting up a connection.
2. Resource remain allocated during full length of communication untill channel is released.this is wastage of channel capacity.
Friends,next type of switching is message switching which we will discuss in next article.
Thanks......stay in touch.