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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.

Lack of flexibility: Circuit switching is not flexible as it only allows one type of communication at a time, such as voice or data. This can limit the ability of users to perform multiple tasks simultaneously.

Limited mobility: Circuit switching is not well-suited for mobile devices or nodes that move frequently, as it requires the establishment of a dedicated communication path. This can result in communication disruptions or dropped calls.

Limited capacity: Circuit switching can have limited capacity as it requires the establishment of a dedicated communication path between two nodes. This can limit the number of simultaneous communications that can occur.

High setup time: Circuit switching requires a significant setup time to establish the dedicated communication path between two nodes. This can result in delays in initiating communication.

No prioritization: Circuit switching does not provide any mechanism for prioritizing certain types of traffic over others. This can result in delays or poor performance for time-critical applications, such as voice or video.

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.
3. Reliability: Circuit switching provides a high level of reliability since the dedicated communication path is reserved for the entire duration of the communication. This ensures that the data will be transmitted without any loss or corruption.
4. Quality of service: Circuit switching provides a guaranteed quality of service, which means that the network can prioritize certain types of traffic, such as voice and video, over other types of traffic, such as email and web browsing.
5. Security: Circuit switching provides a higher level of security compared to packet switching since the dedicated communication path is only accessible to the two communicating parties. This can help prevent unauthorized access and data breaches.
6. Ease of management: Circuit switching is relatively easy to manage since the communication path is pre-established and dedicated to a specific communication. This can help simplify network management and reduce the risk of errors.
7. Compatibility: Circuit switching is compatible with a wide range of devices and protocols, which means that it can be used with different types of networks and applications. This makes it a versatile technology for various industries and use cases.

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.
4. Limited Flexibility: Circuit switching is not flexible as it requires a dedicated circuit between the communicating devices. The circuit cannot be used Waste of Resources for any other purpose until the communication is complete, which limits the flexibility of the network.
5. Waste of Resources: Circuit switching reserves the bandwidth and network resources for the duration of the communication, even if there is no data being transmitted. This results in the wastage of resources and inefficient use of the network.
6. Expensive: Circuit switching is an expensive technology as it requires dedicated communication paths, which can be costly to set up and maintain. This makes it less feasible for small-scale networks and applications.
7. Susceptible to Failure: Circuit switching is susceptible to failure as it relies on a dedicated communication path. If the path fails, the entire communication is disrupted. This makes it less reliable than other networking technologies, such as packet switching.
8. Not suitable for bursty traffic: Circuit switching is not suitable for bursty traffic, where data is transmitted intermittently at irregular intervals. This is because a dedicated circuit needs to be established for each communication, which can result in delays and inefficient use of resources.

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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