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

 

where-

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

 

Also Read- Packet Switching

 

Advantages-

 

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.

 

Disadvantages-

 

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• Circuit switching is now outdated.

 

PRACTICE PROBLEM BASED ON CIRCUIT SWITCHING TECHNIQUE-

 

Problem-

 

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?

 

Solution-

 

Given-

• 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 (T_t)

= 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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