# Computer Network | Circuit Switching

In circuit switching network resources (bandwidth) is 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 the one of 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 fiber 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.

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.
Transmission rate is amount of data send in 1 second.
Transmission rate = F * B bits/sec

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