Circuit Switching And Packet Switching

Switching :

Two different switching techniques are used by the network :

1. circuit switching
2. packet switching.

1. Circuit Switching:

• It is made of a set of switches connected by physical links in which each link is divided in n-channels.

• Circuit Switching takes place at Physical layer .

• The resources needed to reserved during the setup phase and remain dedicated for the entire duration of data transfer until the data transmission complete.

• There is no addressing involved during data transfer.

• Ex- Telephone lines.

                                             Circuit Switching

2. Packet Switching :

• In packet switching data split into small units called packets.
• each packet is containing a header information and data.

Packet switching is further two types:

1.  Datagram Packet Switching
2. Virtual Circuit Packet Switching 

1. Datagram  Packet Switching : 

• In a datagram network each packet is treated independently of others.

• It is connection-less switching.

• Destination address is unchanged at each intermediate device.

• The delay between packets is not uniform.

• Packets may arrived at receiver out of order.

• Store and forward type of technique.

• Datagram switching is normally done at Network Layer

• IP  uses Datagram based packet switching.

                                                        Datagram Packet Switching 

2. Virtual Circuit Packet Switching(VC) :

• VC switching is connection-oriented packet switching.

• A logical connection is establish between sender and receiver before data transfer starts.

• Connection established using signalling protocol.

• Signaling protocol first identify end to end path between sender and receiver.once a path is identified all packets follow the same path.

• This path is not reserved for this session alone multiple session can share the links in same path.

• After identify packet switches allocate VC IDs or label to uniquely identify each connection.

• The labels only have local significance at each intermediate switch, not having end-end significance.

• Packets are switched using these labels.

• At each intermediate device look at incoming label and link, based on this identify suitable outgoing link and label by consulting to a local virtual circuit table.

• After completion of data transfer labels are drooped from VC table.

• It is implemented at the Data link layer.

• VC based switching is very useful in switched WAN for fast switching.

• Ex- X.25,Frame-Relay, ATM and MPLS . 

                                     Virtual Circuit Packet Switching