Fragment free cut-through
From Free net encyclopedia
Fragment-free switching is suitable for backbone applications in a congested network, or when connections are allocated to a number of users. This is typically done with Ethernet frames. The switching device checks the source and destination MAC address of a frame, and sends the frame to the port corresponding to the destination.
The frames are sent through the switch as a continuous flow of data--the transmit and receive rates are always the same. Because of this, fragment-free switching cannot pass packets to higher speed networks, for example, to forward packets from a 10 Mbit/s to a 100 Mbit/s Ethernet network. Therefore, if you opt for fragment-free switching, you cannot make direct connections to higher speed networks from that port.
Fragment-free switching offers a compromise between cut through (which offers the fastest possible forwarding at the expense of any error checking) and store-and-forward (which offers maximum error checking at the expense of latency), to provide an average latency of approximately 60 µs and sufficient error checking to eliminate most common errors.
Fragment-free switching checks that there are no collisions within the first 64 bytes of the packet--the minimum valid message size required by the IEEE 802.3 specification. This guarantees that message fragments less than 64 bytes (runts) are not forwarded to other network segments. Runts are typically the result of collision fragments.