Circuit Switching in Computer Network

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.

drawbacks:

Inefficient use of resources: Circuit switching requires the establishment of a dedicated communication path between two nodes, which means that the resources along that path, such as bandwidth and switch ports, are reserved for the duration of the communication. This can result in inefficient use of resources, as the resources may remain unused during periods of low or no communication.

Limited scalability: Circuit switching is not well-suited for large-scale networks with many nodes, as it requires a dedicated communication path between each pair of nodes. This can result in a high degree of complexity and difficulty in managing the network.

Vulnerability to failures: Circuit switching relies on a dedicated communication path, which can make the network vulnerable to failures, such as cable cuts or switch failures. In the event of a failure, the communication path must be re-established, which can result in delays or loss of data.

Delay and latency: Circuit switching requires the establishment of a dedicated communication path, which can result in delay and latency in establishing the path and transmitting data. This can impact the real-time performance of applications, such as voice and video.

High cost: Circuit switching requires the reservation of resources, which can result in a high cost, particularly in large-scale networks. This can make circuit switching less practical for some applications.

Advantages of Circuit Switching:
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.

Disadvantages of Circuit Switching:
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 – 
These questions will help you understand 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

References : 
https://en.wikipedia.org/wiki/Circuit_switching
https://en.wikipedia.org/wiki/Frequency-division_multiplexing

This article is contributed by Shaurya Uppal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks. 

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