Switching
In large networks, there may be more than one paths exist for transmitting data from sender to receiver.The process of selecting a best path for sending the data from sender to receiver is known as Switching. Switching in a computer network is achieved by using a small hardware device that is called switch which is used to join multiple computers together with one Local Area Network.
The process of moving the data packets towards their destination by forwarding them from one port to the other port is called as switching.
To reduce the collision between packets we use switching. Packet Collision in minimum as it directly communicates between source to destination.
It increases the overall performance of the network by reducing the traffic on the network.
Switching Techniques
Switching technique is used to connect the systems for making one-to one communication. There are various following techniques are available which are given below :
Circuit Switching
Circuit switching is a method of implementing a telecommunication network in which two network nodes establish a dedicated path.In Circuit switching a complete end-to-end path must exist before the communication takes place.
In Circuit switching technique a dedicated path is established between sender and receiver before starting the transmission of packets. and that dedicated path will remain to exist until the connection is terminated.
When any user wants to send the data it may be in the form of voice, video, etc. then it sends a request signal if the path is exist then receiver sends back an acknowledgement to the sender to ensure the availability of the dedicated path. After receiving the acknowledgment, dedicated path transfers the data.
Circuit switching technique is used in public telephone network. It is used for voice transmission.
Communication by using circuit switching has 3 phases :
- Connection Establishment (Circuit Establishment) : In this phase a circuit (Path) is established between one node to another node. Circuit provides a full dedicated path to travel the data from source to destination.
- Data Transfer : After the connection establishment the entire data are sent through dedicated path (circuit)from source to destination.
- Connection Termination : After the completion the process of sending data the circuit is disconnected means the connection between two nodes has terminated.
Total time taken to transmit a message in circuit switched network
= Connection set up time + Transmission Time + Propagation Time + Tear down time
Advantages
- Before transmit the data a full dedicated path is established to travel the data.
- Data is transmitted without any delay because there is no waiting time at any switch.
- Receiver always receives the data in the order. in order.
- No re ordering is required.
Disadvantages
- The set up required time ( for connection establishment) is too long.
- Dedicated channels require more bandwidth.
- It is more expensive than other switching techniques.
- Routing decisions (The path between two nodes) can not be changed once the circuit is established.
Space Division Switches :
In space division switching, a dedicated path is established between the source and destination for the entire period of transmission.
Space Division Switching can be achieved by using crossbar switch. A crossbar switch is a metallic crosspoint or semiconductor gate that can be enabled or disabled by a control unit. This requires separate physical path for each signal connection.
Time Division Switches
The incoming and outgoing signals when received and re-transmitted in a different time slot, is know as Time Division Switching.
In the Time Division switching, sampled values of speech signals are transferred at fixed intervals.The Time Division Switching may be analog or digital.
Time Division Switching uses time-division multiplexing to achieve switching means different ongoing connections can use same switching path but in different time interval.There are two popular methods for Time Division Switching namely Time Slot Interchange (TSI) and the TDM bus.
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