Cut-through is a packet-switching method, where the switch forwards a packet as soon as the destination address is processed without waiting for the entire packet to be received. The next packet is sent as soon as the previous one has been verified as reaching the recipient without waiting for the complete transmission of the previous packet.
Working :
In cut-through switching, whenever a packet arrives at the switching device, data transmission is started as soon as the destination address is processed. The switch performs a look–up operation in the address table to check whether the destination address is valid or not. If the address is valid and the outgoing link is available then the switching device immediately transmits the frame to the destination port.
Switch use Cyclic Redundancy Check (CRC) on incoming packets for error detection and marks corrupted frame EOF field as invalid. It relies on the destination devices for error handling of the corrupted data. The destination devices detect the invalid flag and drop the frame.
Types :
Primarily Cut-through switching is characterized into two types:
1. Rapid Frame Forwarding :
- Switch forwards the frame as soon as it has looked up the destination MAC address of the frame in its MAC address table. It does not wait to receive the rest of the frame.
- It has low latency and high data transfer speed.
- It has a high error rate because frames with errors are forwarded to other segments.
2. Fragment Free :
- Switch waits for the collision window (64 bytes) to pass before forwarding the frame. It checks the data field to ensure no fragmentation has occurred.
- It has a comparatively lesser data transfer speed.
- It has a low error rate because it monitors the integrity of each frame while forwarding.
Advantages :
-
Low- latency –
Switching device does not wait for the entire packet to arrive for transmission which reduces the latency (time required to process the data) to pass through the switch. -
High speed –
Low latency leads to higher transfer speeds i.e. speed at which data packets are transmitted. -
Less storage requirement –
Switching devices do not require storing of data packets which reduces the internal storage requirement.
Disadvantage :
-
Integrity issues –
Switches forward corrupted frames since they don’t wait to check if the checksum at the end of each frame is valid or not.
Uses :
- Fiber channel communication
- SCSI traffic transmission
- ATM networks
- InfiniBand networks
- Bitcoin