There are two main types of switches and they use different methods to process frames: store-and-forward and cut-through.  While neither is “right” or “wrong,” an understanding of the two will enable you to determine which is best for your particular application.  Let’s discuss the main differences between these two types.

• A Store-and-Forward approach results in a device design that works like a LAN bridge.  The entire incoming frame is captured, an address lookup occurs to resolve the outgoing port, a Cyclic Redundancy Check (CRC) is performed on the Frame Check Sequence (FCS) to validate the frame, and the frame is sent to the proper port.  Because of the full buffering, this technique provides higher levels of error detection since corrupt frames can be detected and discarded, while valid frames are processed, queued and transmitted. Most software-based packet switches are of the store-and-forward variety
• Cut-Through switches start selection and frame transmission well before the entire frame is received. A cut-through switch will reduce the amount of introduced time latency because the switch begins transmitting the frame to the receiving port as soon as the destination address is decoded (usually within the first 20-30 bytes of the frame). This will also include corrupt frames since the error checking of a cut-through switch is severely limited. Most of these switches are hardware-state machines that have a high level of sophistication at the electronics layer, resulting in a higher price per port.  Since the frames are forwarded from the transmitting port to the receiving port immediately upon the decoding of the destination address, very little processing is required after opening the port.

Some switches utilize both processes. They begin with cut-through switching and, through CRCs, they monitor the number of errors that occur.  When that number reaches a certain point (a threshold) they become store-and-forward switches.  They remain so until the number of errors declines, then they change back to cut-through.  This type of switching is called threshold detection or adaptive switching.