Tag: Circuit Switching PDF

Circuit Switching in Networking | Switching

Switching in Computer Networks-


The process of moving the data packets towards their destination by forwarding them from one port to the other port is called as switching.


Switching Techniques-


Various switching techniques are-



  1. Circuit Switching
  2. Message Switching
  3. Packet Switching


In this article, we will discuss about Circuit Switching.


Circuit Switching-


This switching technique operates in the following three phases-

  1. Establishing a circuit
  2. Transferring the data
  3. Disconnecting the circuit


1. Establishing A Circuit-


In this phase,

  • A circuit is established between the two ends.
  • Circuit provides a dedicated path for data to travel from one to the other end.
  • Resources are reserved at intermediate switches which are used during the transmission.
  • The intermediate switches are connected by the physical links.



2. Transferring The Data-


After the circuit is established,

  • The entire data travels over the dedicated path from one end to the other end.


3. Disconnecting The Circuit-


After the data transfer is completed,

  • The circuit is torn down i.e. disconnected.


Total Time-


Total time taken to transmit a message in circuit switched network

= Connection set up time + Transmission delay + Propagation delay + Tear down time



  • Transmission delay = Message size / Bandwidth
  • Propagation delay = (Number of hops on way x Distance between 2 hops) / Propagation speed


Also Read- Packet Switching




Circuit switching has the following advantages-

  • A well defined and dedicated path exists for the data to travel.
  • There is no header overhead.
  • There is no waiting time at any switch and the data is transmitted without any delay.
  • Data always reaches the other end in order.
  • No re ordering is required.




Circuit switching has the following disadvantages-

  • The channel is blocked for two ends only.
  • It is inefficient in terms of utilization of system resources.
  • The time required for establishing the circuit between the two ends is too long.
  • Dedicated channels require more bandwidth.
  • It is more expensive than other switching techniques.
  • Routing decisions can not be changed once the circuit is established.


Important Notes-


  • Circuit switching is implemented at physical layer.
  • Circuit switching is now outdated.






Consider all links in the network use TDM with 24 slots and have a data rate of 1.536 Mbps. Assume that host A takes 500 msec to establish an end to end circuit with host B before begin to transmit the file. If the file is 512 kilobytes, then how much time will it take to send the file from host A to host B?





  • Total bandwidth = 1.536 Mbps
  • Bandwidth is shared among 24 slots
  • Connection set up time = 500 msec
  • File size = 512 KB


Calculating Bandwidth Per User-


Total bandwidth = Number of users x Bandwidth per user

So, Bandwidth per user

= Total bandwidth / Number of users

= 1.536 Mbps / 24

= 0.064 Mbps

= 64 Kbps


Calculating Transmission Delay-


Transmission delay (Tt)

= File size / Bandwidth

= 512 KB / 64 Kbps

=  (512 x 210 x 8 bits) / (64 x 103 bits per sec)

= 65.536 sec

= 65536 msec


Calculating Time Required To Send File-


Time taken to send a file in circuit switched network

= Connection set up time + Transmission delay

= 500 msec + 65536 msec

= 66036 sec

= 66.036 msec


To gain better understanding about Circuit Switching,

Watch this Video Lecture


Next Article- Message Switching


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