1.1 LAN Switching
1.1.8 Two switching methods

There are two switching modes that can be selected to forward a frame through a switch. The latency of each of these switching modes depends on how the switch forwards the frames. The faster the switch mode the smaller the latency in the switch. To accomplish faster frame forwarding the switch takes less time to check for errors. The trade off is less error checking which can lead to a higher number of re-transmissions.

There are two ways to forward frames through a switch:

  • Store and Forward - the entire frame is received before any forwarding takes place. The destination and/or the source addresses are read and filters are applied before the frame is forwarded. Latency occurs while the frame is being received; the latency is greater with larger frames because the entire frame takes longer to read. Error detection is high because of the time available to the switch to check for errors while waiting for the entire frame to be received.
  • Cut-through (Fast Forward) - the switch reads the destination MAC address and begins forwarding the frame before it is completely received. This mode decreases the latency of the transmission and has poor error detection.
Web Links
Cisco Connection Online
Cisco Documentation
Networking Tutorial Articles
Search Cisco