# Circuit Switching in Computer Network

• Difficulty Level : Medium
• Last Updated : 13 Jun, 2022

In circuit switching network resources (bandwidth) are divided into pieces and bit delay is constant during a connection. The dedicated path/circuit established between sender and receiver provides a guaranteed data rate. Data can be transmitted without any delays once the circuit is established.

Telephone system network is one of the example of Circuit switching. TDM (Time Division Multiplexing) and FDM (Frequency Division Multiplexing) are two methods of multiplexing multiple signals into a single carrier.

• Frequency Division Multiplexing : Divides into multiple bands
Frequency Division Multiplexing or FDM is used when multiple data signals are combined for simultaneous transmission via a shared communication medium.It is a technique by which the total bandwidth is divided into a series of non-overlapping frequency sub-bands,where each sub-band carry different signal. Practical use in radio spectrum & optical fibre to share multiple independent signals.

• Time Division Multiplexing : Divides into frames
Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line. TDM is used for long-distance communication links and bears heavy data traffic loads from end user.
Time division multiplexing (TDM) is also known as a digital circuit switched.

It has the following advantages :

1. The main advantage of circuit switching is that a committed transmission channel is established between the computers which give a guaranteed data rate.
2. In-circuit switching, there is no delay in data flow because of the dedicated transmission path.

It has the following disadvantages :

1. It takes a long time to establish a connection.
2. More bandwidth is required in setting up dedicated channels.
3. It cannot be used to transmit any other data even if the channel is free as the connection is dedicated to circuit switching.

Formulas in Circuit Switching :

```Transmission rate = Link Rate or Bit rate /
no. of slots = R/h bps
Transmission time = size of file /
transmission rate
= x / (R/h) = (x*h)/R second
Total time to send packet to destination =
Transmission time + circuit setup time ```

Question on Circuit switching –

Example 1 : How long it takes to send a file of ‘x bits’ from host A to host B over a circuit switched network that uses TDM with ‘h slots’ and have a bit rate of ‘R Mbps’, circuit establish time is k seconds.Find total time?

Explanation :
Transmission rate = Link Rate or Bit rate / no. of slots = R/h bps
Transmission time = size of file/ transmission rate = x / (R/h) = (x*h)/R

Total time = transmission time + circuit setup time = (x*h)/R secs + k secs

Example 2 : If a link transmits F frames/sec and each slot has B bits then find the transmission rate?

Explanation :
Since it is not mention how many slots in each frame we take one frame has one slot.
The transmission rate is the amount of data sent in 1 second.
Transmission rate = F * B bits/sec

To know the difference between Circuit Switching and Packet Switching refer – Difference b/w Circuit switch & packet switch

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