Packet switching

Packet switching breaks a message into small units, each carrying its own addressing information, and sends them into a network whose links are shared by many conversations at once. Each packet is forwarded hop by hop, packets from the same message may take different routes, and the receiver puts them back in order. The internet and every IP network work this way. Some packet-switched technologies, such as MPLS, set up virtual circuits so that packets for a flow follow a predetermined path while still sharing the underlying links.

The contrast is with circuit switching, in which a dedicated path is reserved for the whole of a session, as in the traditional telephone network. A circuit gives constant capacity and predictable delay but wastes that capacity when nobody is speaking. Packet switching uses links far more efficiently, and it can route around a failed link, but because packets compete for the same links, latency and jitter vary with load. That is why real-time services such as voice over IP rely on quality of service to prioritise their packets.

Exam relevance: questions in this area tend to ask which switching method fits a requirement. Candidates are expected to link dedicated, predictable capacity with circuit switching, and shared, efficient but variable delivery with packet switching.