Question

what is Switching and types of switching ? Three methods of switching with diagrams.? The Structure of a Switch?

Answer 1

Switching:

The mechanism for exchange of information between different computer networks and network segments is called switching in Networking. On the other words we can say that any type signal or data element directing or Switching toward a particular hardware address or hardware pieces.

Types:

There are basically three types of switching methods are made available. Out of three methods, circuit switching and packet switching are commonly used but the message switching has been opposed out in the general communication procedure but is still used in the networking application.

1) Circuit Switching: In circuit switching the routing decision is made when the path is set up across the given network. After the link has been sets in between the sender and the receiver then the information is forwarded continuously over the provided link.
2) Packet Switching: The major advantage of Packet switching is that they they are used for performing data rate conversion. When traversing the network switches, routers or the other network nodes then the packets are buffered in the queue, resulting in variable delay and throughput depending on the network’s capacity and the traffic load on network.
3) Message Switching: In case of Message Switching it is not necessary to established a dedicated path in between any two communication devices. Here each message is treated as an independent unit and includes its own destination source address by its own. Each complete message is then transmitted from one device to another through internetwork.

There are three types of switching methods; the store-and-forward method, the fragment-free method, and the cut-through method.

1.The store-and-forward switching method:

In this method, the switch does not start the internal frame processing until the complete frame is received. After receiving the entire frame, switch verifies whether the received frame is in the good state or not. If the received frame is in the good state, only then the switch processes it. If the received frame is not in the good state, the switch discards it.

To know the condition of a frame, the switch uses the FCS (frame check sequence) field of the frame. The FCS field contains a value known as the CRC value. The CRC value allows any receiving device to know whether the frame is exactly same as the source packed it or it has been damaged in the middle.

After creating a frame, the sender or source device runs the CRC (Cyclic Redundancy Check) algorithm on it. The value produced by this algorithm is known as the CRC value. The CRC value is stored in the FCS field of the frame. The frame is the last layer of data packing. After storing the CRC value, the sender node loads that frame in the media.

Upon receiving this frame, the receiver or destination device runs the CRC algorithm on the frame and compares the result with the CRC value stored in the FCS field of the frame. If both the result and the CRC value match, the frame is considered in the good state. If both values do not match, the frame is considered as the damaged frame.

2.The cut-through switching method:

In this method, the switch starts the frame processing as soon as it reads the destination MAC address of the frame. Ethernet frame stores destination MAC address in the third field.

To start the frame processing, a switch only needs the destination MAC address. Since the destination MAC address occurs very early in the Ethernet frame, a switch can start the frame processing before it receives all the bits of the frame.

Just after reading the destination address, it checks the CAM table and based on the match it starts the forwarding of the frame (even though the frame may still be coming into the switch).This method, before forwarding a frame, does not check its condition. This reduces the latency, but it also propagates errors. From all three switching methods, this is the fastest method of switching. But it provides speed at the price of having forwarded some frame that contains errors.

3.The fragment-free switching method

In this method, the switch starts the frame processing after reading the first 64 bytes of the frame. 64 bytes is the minimum legal size of an Ethernet frame. An Ethernet frame that is smaller than 64 bytes is known as the runt frame. A runt frame is a corrupt frame.This method reduces the number of Ethernet runt frames that are being switched.

Basically, the fragment-free switching method is the modified version of the cut-through switching method. Sometimes it is also known as the modified cut-through or runtless switching method.