What Is Cut-Through Switching?

Cut-through switching is a data transfer technique that sends a packet before the prior packet has finished sending, a method that has both advantages and disadvantages. The main benefit to cut-through switching is that latency — the amount of time it takes to process data — is decreased and transfer speeds are better. At the same time, the data are quickly sent one after another, so there is no way to check for quality, and the sender’s side will often send corrupted data just to push them along. Another version of this switching technique, called fragment-free, reduces the chances that corrupted data will transfer, but it also decreases transfer speed.

When a network sends information packets, it will send one packet, the network will ensure the packet is finished and complete, and then the next packet will be sent. With cut-through switching, the second packet will be sent before the first packet is finished. That next packet normally is sent as soon as the first one has been verified as reaching the recipient.

Latency refers to how long it takes for each packet to be read and verified. Long latency means transfer speeds must slow down with normal transmission techniques because, until a packet is verified, another packet will not send. Cut-through switching bypasses this issue, so packet sending is often much faster than with other methods.

A major problem with cut-through switching comes from how the packets are sent. When a packet is sent, the other side of the transmission normally will check each packet for quality and consistency; this occurs at the end of the transfer process. The cut-through method sends the packets so quickly that there is no time for quality checks, so there is no guarantee that the packets will work once transferred. Corrupted and unusable data also will send, and because it bypasses the quality check, the recipient will not notice the corrupted packets until the transfer is finished.

To improve quality and to reduce the chances of the network sending corrupted packets, there is a version of cut-through switching known as fragment-free. Instead of checking for quality on the recipient’s side, this ensures a quality check is applied to the sender’s side, and corrupted packets should not send. The quality check is only partial, though, so there is still a chance that poor packets will get through the transmission, and this tends to slow down the transmission below normal cut-through speeds.