Table of Contents
Switching Modes
Switching modes are used for routing packets in different ways. Different sections of a frame are recognized in switching mode. Layer 2 switches are responsible for data transmission on the data link layer, as well as error checking on transmitted and received frames. The MAC address is used by layer 2 switches to forward packets.
Elements of the frame are preamble, destination MAC address, source MAC address, user’s data, and FCS
Switching modes are divided into three categories:
- Store-and-forward
- Cut-through
- Fragment-free
1. Store-and-forward
The term “store-and-forward” refers to a mechanism in which intermediate nodes save incoming frames and then check for defects before passing packets to the next node. The layer 2 switch waits until the complete frame has been received before making a decision.
When the switch receives the complete frame, it stores it in the switch buffer memory. This is referred to as “storing the frame.”
After the frame has been saved, it is verified for errors. The message is discarded if there is a mistake, else it is passed to the next node.
The CRC (Cyclic Redundancy Check) technique is used to check for faults in the received frame using a number of bits. The store-and-forward strategy offers a high level of security because the erroneous frames will not harm the target network. Because it does not forward colliding frames, store-and-forward switches are extremely reliable
2. Cut-through Switching
Cut-through switching is a method of forwarding packets when the target address has been determined rather than waiting for the whole frame to arrive. When the frame is received, the switch examines the first six bytes of the frame after the preamble, then looks up the destination in the switching table to determine the outgoing interface port, and then passes the frame to the destination.
Because the switch does not wait for the complete frame to be received before transferring packets to the destination, it has a low latency rate. It doesn’t have any kind of error-checking mechanism. As a result, the errors can be conveyed to the receiver with or without errors.
Cut-through switching has a short wait time since it forwards packets as soon as the target MAC address is identified. Collisions are not detected in this technique, thus if frames collide, they will be sent as well.
3. Fragment-free Switching
Fragment-free switching is a more advanced Cut-through Switching approach. Fragment-free switching is a technique for providing error-free transmission by reading at least 64 bytes of a frame before forwarding it to the next node. It combines the speed of Cut-through Switching with the functionality of error checking. This approach examines the 64 bytes of the ethernet frame that contain addressing information.
If a collision is found within the first 64 bytes of a frame, the frame will not be transmitted any further.
