A packet switch is a switching node in a data transmission network which is using packets (as opposed to circuit-switching). They are connected to a number of physical network links in the overall network, and take packets in from one network interface, and send them out on another, as the packets moves from the source host to the destination.
All packet switches contain at least two major types of functionality:
- the handling of user traffic through the packet switch, which is called forwarding
- path selection, the computation of routing tables/data (by routing protocols/algorithms), which is usually called by the short name routing
The latter term can be confused with 'router', the name for a packet switch which operates at the internetworking layer in a protocol stack; too few words, too many distinct concepts!
The first packet switches were minicomputers provided with serial line interfaces (since synchronous serial lines the only data transmission technology available for the first packet data networks), such as the Interface Message Processors of the ARPANET.
The early generations of routers, used in the first decades of the Internet, were similar, but could use interfaces to the various local area network technologies (e.g. Ethernet). Only the very earliest used minicomputers; systems based on microprocessors were the usual for a long period thereafter.
More recently, very high speed packet switches use custom hardware.