Wisdom of Helios

Packet Switching & Circuit Switching

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There are mainly two methodologies for transmitting data over the computer network – 1. Packet Switching  and   2. Circuit Switching.

Packet Switching :

A digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packet.

In packet-switching, the packets are sent towards the destination irrespective of each other. Each packet has to find its own route to the destination. There is no predetermined path; the decision as to which node to hop to in the next step is taken only when a node is reached. Each packet finds its way using the information it carries, such as the source and destination IP addresses.

If a packet switch does not have enough resources, it sends a Connect Reject and the Connection Establishment Fails.


Advantage of Packet Switching:

More efficient use of overall network bandwidth due to flexibility in routing the smaller packets over shared links. Packet switching networks are often cheaper to build as less equipment is needed given this ability to share.

Another benefit of packet switching is known as “pipelining”.

Disadvantage of Packet Switching:

Longer delays in receiving messages due to the time required to package and route packets. For many applications, delays are not long enough to be significant, but for high-performance applications like real-time video, additional data compression and QoS technology is often required to achieve the required performance levels.

Potential for network security risks due to the use of shared physical links. Protocols and other related elements on packet switching networks must designed with the appropriate security precautions.

Circuit Switching :

Circuit-switched is a type of network in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection.

Ordinary voice phone service is circuit-switched. The telephone company reserves a specific physical path to the number you are calling for the duration of your call. During that time, no one else can use the physical lines involved.

Traditional PSTN phone system uses circuit switching while VoIP uses packet switching.

  Difference Between Packet and Circuit Switching :

Packet Switching Circuit Switching
Variable rate data stream(packed) over a shared connection Constant rate data stream(packed) over some dedicated connection
characterized by a fee per unit of information. characterized by a fee per time unit of connection time, even when no data is transferred
Low reliable , subject to congestion Highly reliable

There are 2 modes of Packet switching –

  1. Connectionless Packet Switching  /  Datagram Switching.
  2. Connection Oriented Packet Switching  /  Virtual Circuit Switching.

Connectionless Packet Switching  /  Datagram Switching :

Transmission of packets are made on Per-Packet basis.

  1. Each packet routes individually.
  2. Packets may route in different paths and sometimes may be out of order.
  3. Each packet contains the complete addressing of their routed paths sometimes of sequence number of the packet.
  4. The packets may arrive at the destination machine in an order different from the transmission order.
  5. Routers in Connectionless switching network maintain a simple but long routing table that contains two columns  – Destination Address and Output Port.

Example : Ethernet , IP , UDP.

Connection Oriented Packet Switching  /  Virtual Circuit Switching :

Transmission of packets are made on Per-Packet basis.

  1. Transmission of packets from a source machine to a destination machine is done on a per source‐destination pair basis, meaning that all packets from the same source going to the same destination are transmitted over the same routes and through the same routers
  2. Different packet reached their destination in order.
  3. Having almost constant delay in packet transmission .
  4. The packets include a connection identifier rather than address information. This identifier is changed every time when the packet is transmitted. Address information is only transferred to each node during a connection set-up phase, when the route to the destination is discovered and an entry is added to the switching table in each network node through which the connection passes

Example : X.25 , Frame Relay

VCI (Virtual Circuit Identifier) are local to each switch or link.

1)  more VC can be assigned 

2)  searching for an unused VCI is simple 

The format of the Virtual Circuit Switching Table has four columns  –  Input Port    Input VCI    Output Port    Output VCI    


Advantages of  Virtual Circuit Switching :

Shorter headers are required for VC (VCI is shorter than full network address: VCI may have a length of 1 or 2 bytes, while Full IP address has length of 4 bytes for IPv4 and 12 bytes of IPv6).

Faster because no routing is done (VCI list is shorter and all packets are made to follow each other along  the same path by simply looking up the VC table) .

Resources are set up in advance for the VC (reserve buffers and some bandwidth at each switch) .

Disadvantages of  Virtual Circuit Switching :

When a failure occurs, all virtual circuits must be set up again.

Author: Munir

I'm good for nothing

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