Switching

When a user accesses the internet or another computer network outside their immediate location, messages are sent through the network of transmission media. This technique of transferring the information from one computer network to another network is known as switching.
Switching in a computer network is achieved by using switches. A switch is a small hardware device which is used to join multiple computers together with one local area network (LAN).
Network switches operate at layer 2 (Data link layer) in the OSI model.
Switching is transparent to the user and does not require any configuration in the home network.
Switches are used to forward the packets based on MAC addresses.
A Switch is used to transfer the data only to the device that has been addressed. It verifies the destination address to route the packet appropriately.
It is operated in full duplex mode.
Packet collision is minimum as it directly communicates between source and destination.
It does not broadcast the message as it works with limited bandwidth.

Why is Switching Concept required?

Switching concept is developed because of the following reasons:

Bandwidth: It is defined as the maximum transfer rate of a cable. It is a very critical and expensive resource. Therefore, switching techniques are used for the effective utilization of the bandwidth of a network.
Collision: Collision is the effect that occurs when more than one device transmits the message over the same physical media, and they collide with each other. To overcome this problem, switching technology is implemented so that packets do not collide with each other.

Switch increases the bandwidth of the network.
It reduces the workload on individual PCs as it sends the information to only that device which has been addressed.
It increases the overall performance of the network by reducing the traffic on the network.
There will be less frame collision as switch creates the collision domain for each connection.

A Switch is more expensive than network bridges.
A Switch cannot determine the network connectivity issues easily.
Proper designing and configuration of the switch are required to handle multicast packets.

The layer 2 switches are used for transmitting the data on the data link layer, and it also performs error checking on transmitted and received frames.
The layer 2 switches forward the packets with the help of MAC address.
Different modes are used for forwarding the packets known as Switching modes.
In switching mode, Different parts of a frame are recognized. The frame consists of several parts such as preamble, destination MAC address, source MAC address, user's data, FCS.

There are three types of switching modes:

Store-and-forward is a technique in which the intermediate nodes store the received frame and then check for errors before forwarding the packets to the next node.
The layer 2 switch waits until the entire frame has received. On receiving the entire frame, switch store the frame into the switch buffer memory. This process is known as storing the frame.
When the frame is stored, then the frame is checked for the errors. If any error found, the message is discarded otherwise the message is forwarded to the next node. This process is known as forwarding the frame.
CRC (Cyclic Redundancy Check) technique is implemented that uses a number of bits to check for the errors on the received frame.
The store-and-forward technique ensures a high level of security as the destination network will not be affected by the corrupted frames.
Store-and-forward switches are highly reliable as it does not forward the collided frames.

Cut-through switching is a technique in which the switch forwards the packets after the destination address has been identified without waiting for the entire frame to be received.
Once the frame is received, it checks the first six bytes of the frame following the preamble, the switch checks the destination in the switching table to determine the outgoing interface port, and forwards the frame to the destination.
It has low latency rate as the switch does not wait for the entire frame to be received before sending the packets to the destination.
It has no error checking technique. Therefore, the errors can be sent with or without errors to the receiver.
A Cut-through switching technique has low wait time as it forwards the packets as soon as it identifies the destination MAC address.
In this technique, collision is not detected, if frames have collided will also be forwarded.

A Fragment-free switching is an advanced technique of the Cut-through Switching.
A Fragment-free switching is a technique that reads atleast 64 bytes of a frame before forwarding to the next node to provide the error-free transmission.
It combines the speed of Cut-through Switching with the error checking functionality.
This technique checks the 64 bytes of the ethernet frame where addressing information is available.
A collision is detected within 64 bytes of the frame, the frames which are collided will not be forwarded further.

Store-and-forward Switching	Cut-through Switching
Store-and-forward Switching is a technique that waits until the entire frame is received.	Cut-through Switching is a technique that checks the first 6 bytes following the preamble to identify the destination address.
It performs error checking functionality. If any error is found in the frame, the frame will be discarded otherwise forwarded to the next node.	It does not perform any error checking. The frame with or without errors will be forwarded.
It has high latency rate as it waits for the entire frame to be received before forwarding to the next node.	It has low latency rate as it checks only six bytes of the frame to determine the destination address.
It is highly reliable as it forwards only error-free packets.	It is less reliable as compared to Store-and-forward technique as it forwards error prone packets as well.
It has a high wait time as it waits for the entire frame to be received before taking any forwarding decisions.	It has low wait time as cut-through switches do not store the whole frame or packets.

In large networks, there can be multiple paths from sender to receiver. The switching technique will decide the best route for data transmission.

Switching technique is used to connect the systems for making one-to-one communication.

Classification Of Switching Techniques