What is Circuit Switching – Diagram, Advantages & Disadvantages

For transmission of data from sender to receiver, communication links are to be established. In a simple computer network, only one link connecting the sender and receiver would be sufficient. But for larger networks, there will exist more than one route between the sender and receiver. In such a case, the network switching methods helps in establishing a proper connection between the communication terminals. The information is switched between different links. There are four switching techniques available for digital data like circuit switching, packet switching, message switching, and cell switching. These methods are chosen based on their efficiency and bandwidth requirements.

What is Circuit Switching?

This method of switching establishes a dedicated communication path between the sender and receiver. Here the link is established in physical form between two stations present in the network. The link will be established, maintained and terminated for each communication session. The most common example of circuit switching is the Analog telephone network.

This method of switching provides a constant bit delay and fixed data rate channel between the sender and receiver. The full channel capacity is dedicated for the duration of a connection. When data is to be transferred from sender to receiver, firstly the sender sends a request to the switching station for the establishment of a connection. The receiver replies with an acknowledgment. After receiving the acknowledgment signal the sender starts the data transmission. This switching is commonly used for voice circuits. The public switched telephone network, Datakit, B channel of ISDN, Optical mesh network, etc are some of the examples of circuit-switched networks.

Circuit Switching Diagram

In this type of switching, there is a set of switches connected with physical links. Here once the dedicated path is established between the sender and receiver, it stays the same until one of the users terminates the connection. Fixed data is transmitted and this type of switching is highly used to transfer voice data. The network consists of the switching offices with permanent links between them. Whenever is connection requested the communication links are dedicated to the terminals forming the transmission route. This dedicated link is maintained until the connection is terminated. Other users will be able to use this link only when it is terminated by the sender or receiver.

There are three phases in the establishment of a circuit switching network. They are – circuit establishment, Data transfer and circuit disconnect.

 Circuit Establishment

This is the circuit setup phase. Here the link is established between the sender and receiver. When a connection has to be established between station A and station B, station A sends a connection request to node 1 through a dedicated link between station A and node1. Then node1 sends the request to all the nodes connected to it. The request is forwarded among the nodes finally forming a route to the Station B. Based on its status station B sends the acknowledgment if it is not busy. Thus a dedicated communication link will be established between Station A and Station B.

 Data Transfer

All the internal connections in the communication link are duplex. Before starting communication the resources to be used are reserved for that link. Some of such resources are switch buffers, switch processing time, switch Input/output ports. In this method, crossbar switches are commonly used. After the establishment of the link, data will be transmitted continuously with a fixed data rate for both the sender and receiver. In this switching method, the data is not packetized.

 Circuit Disconnect

The dedicated path established between the sender and receiver will be maintained for the entire duration of communication until it is terminated by either of the users. After the termination of the network, a notification signal is propagated to all the nodes in the link to release the reserved resources.

Differences Between Circuit Switching and Packet Switching

• In-circuit switching, data is transmitted continuously between the sender and receiver. Whereas in packet switching the data is packetized and sent independently over a shared network.
• When the connection is maintained in the circuit switching no other user can access that link, even when no data is been transmitted. Thus circuit switching provides high-quality service.
• In packet switching the bandwidth is shared by the users. Thus, the quality of the service is low in packet switching.
• Unlike circuit switching, the path is not reserved in the packet switching network. Packet switching supports store and forward transmission.
• No physical path is established for the packet switching network.
• Packet switching is more efficient compared to circuit switching.
• Packet switching infrastructure is less complicated compared to circuit switching.

Advantages and Disadvantages

Some of the advantages of circuit switching are as follows –

• It uses a fixed bandwidth.
• A dedicated communication channel increases the quality of communication.
• Data is transmitted with a fixed data rate.
• No waiting time at switches.
• Suitable for long continuous communication.

Some of the disadvantages of circuit switching are as follows-

• A dedicated connection makes it impossible to transmit other data even if the channel is free.
• Resources are not utilized fully.
• The time required to establish the physical link between the two stations is too long.
• As a dedicated path has to be established for each connection, circuit switching is more expensive.
• Even if there is no transfer of data, the link is still maintained until it is terminated by users. By this channel remains ideal for a long time thereby making circuit switching inefficient.
• Dedicated channels require more bandwidth.

The telecommunication network is the collection of terminals and nodes. Circuit switching is a method of establishing a telecommunication channel between two network nodes. Each terminal in a network has a unique address. It is very similar to the early Analog telephone network. With the advances in technology, new digital methods of communication are being introduced.

The first telephone switch was operated in New Haven Connecticut in January 1878. Over the years the switching technology has changed drastically but the basic function has remained the same. What are the three phases in the implementation of the circuit switching method?