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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.
Forwarding is the process used by a bridge, switch, or router to move a frame or packet from an input to an appropriate output port. Bridges and switches operate at layer 2 and handle frames. Routers operate at layer 3 and handle datagrams (packets).
The usual process is to store-and-forward packets, meaning that a packet must be fully received in memory before it is forwarded. But cut-through forwarding improves performance. Basically, the forwarding device looks at the forwarding address even before the packet is fully received and immediately begins to forward the packet.
The forwarding process in routers involves a table lookup to determine how a packet should be forwarded. Removing this step by using new label-switching techniques can improve performance. A label is a piece of information added to a packet at the edge of the network that identifies a specific network path through the network. By reading the label, devices in the network can immediately forward a packet without making routing decisions. Refer to "Label Switching" for more information.
Network nodes that implement the differentiated services enhancements to IP use a special field in the IP header to select a per-hop behavior (PHB) as the specific forwarding treatment for packets. Refer to "Differentiated Services (Diff-Serv)" for more information.
Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.