Switching Study Notes for GATE & Computer Science Engineering Exams

By Mukesh Kumar|Updated : December 3rd, 2021

The following approaches useful when there are multiple devices in the network. 

  • Install a point-to-point connection between each pair of devices, but it is impractical and wasteful approach when applied to very large network.
  • For large network, we can go for switching. A switched network consists of a series of interlinked nodes, called switches.


  • Switch switches within the subnet called as switching.
  • In switching, packets are transferred from source to destination using MAC address.
  • Switching is done within the same network.
Types of Switching:

Circuit Switching:

  • Circuit switching was designed for voice communication.
  • In a telephone conversation e.g., Once a circuit is established, it remains connected for the duration of the session.
  • It creates a direct physical connection between two devices such as phones or computers.
  • In Circuit Switching a dedicated link is established across the sender and the receiver which is maintained for the entire duration of the conversation.
  • In circuit switching the routing, the decision is made when the path is set up across the given network.
  • After the link has been set in between the sender and the receiver then the information is forwarded continuously over the provided link.
  • Communication via circuit switching involves three phases: Circuit Establishment, Data Transfer, and Circuit Disconnect.
  • Connection path must be established before data transmission begins. Nodes must have switching capacity and channel capacity to establish the connection
  • Space Division Switching: Separates the path in the circuit from each other spatially.
  • Time Division Switching: Uses time-division multiplexing to achieve switching.
Advantages of circuit switching
  • Guaranteed bandwidth
  • A reliable communication channel between hosts
  • Low per-packet overhead: No IP (and TCP/UDP) header on each packet

Disadvantages of Circuit Switching

  • Less suited to data and other non-voice transmissions.
  • A circuit switched link creates the equivalent of a single cable between two devices and thereby assumes a single data rate for both devices. This assumption limits the flexibility and usefulness of a circuit switched connection.
  • Once a circuit has been established, that circuit is the path taken by all parts of the transmission, whether or not it remains the most efficient or available.
  • Circuit switching sees all transmissions as equal. Any request is granted to whatever link is available. But often with data transmission, we want to be able to prioritise.

Packet Switching

  • To overcome the disadvantages of circuit switch. Packet switching concept came into the picture.
  • In a packet switched network, data are transmitted in discrete units of potentially variable length blocks called packets.
  • Each packet contains not only data but also a header with control information (such as priority codes and source and destination address).
  • A packet contains three major fields:  The header, the message, and redundancy check bits.
  • The packets are sent over the network node to node.
  • At each node, the packet is stored briefly, then routed according to the information in its header.
  • There are two popular approaches to packet switching.
    • Datagram
    • Virtual circuit


Datagram Approach:

  • Each packet is treated independently from all others.
  • It is also called connection-less packet switching.
  • Each packet treated independently.
  • Packets can take any practical route in the network.
  • Packets may arrive out of order. Packets may go missing.
  • Routers in the internet are packet switches that operate in datagram mode.
Virtual Circuit Approach:
  • Sender divides the data into packets
  • Store-and-forward transmission: Multiple packets may arrive at once
  • A single route is chosen between sender and receiver at the beginning of the session.
  • Network can provide sequencing and error control.
  • When the data are sent, all packets of the transmission travel one after another along that route.
  • We can implement it into two formats:
    • Switched Virtual Circuit (SVC)
    • Permanent Virtual Circuit (PVC)

Switched Virtual Circuit:

  • This SVC format is comparable conceptually to dial-up lines in circuit switching.
  • Here, a virtual circuit is created whenever it is needed and exists only for the duration of the specific exchange.
Permanent Virtual Circuit: 
  • The PVC format is comparable to leased lines in circuit switching.
  • In this method, the same virtual circuit is provided between two users on a continuous basis.
  • The circuit is dedicated to specific users. No one else can use it and because it is always in place, it can be used without connection establishment and connection termination.

Message Switching

  • It is also known as store and forward.
  • In this mechanism, a node receives a message, stores it, until the appropriate route is free, and then send it along.
  • Store and forward is considered a switching technique because there is no direct link between the sender and receiver of a transmission.
  • A message is delivered to the node along one path, then rerouted along with another to its destination.
  • In message switching, the messages are stored and relayed from secondary storage (disk), while in packet switching the packets are stored and forwarded from primary storage (RAM).
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