In computer networking and telecommunications, packet switching is a communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path.
Packet switching was invented by Donald Davies and Paul Baran in the early 1960s. Some people claim that Leonard Kleinrock also invented packet switching, but Davies contested this prior to his death and pointed out that Kleinrock's research was actually in queueing theory, which is a key theoretical underpinning to packet switching. Kleinrock's published works nowhere mention breaking a user's message up into segments, and sending the segments through the network separately, which was the key innovation in Baran's and Davies' work.
A packet is a block of user data together with necessary address and administration information attached, to allow the network to deliver the data to the correct destination. One data connection will usually carry a stream of packets of data that will not necessarily be all routed the same way over the physical network.
Analogous to a physical packet sent through the post with the address written on the outside, this provides the information the network (the postal service) needs to get the packet to the correct destination.
Packets are routed to their destination through the most expedient route (as determined by some routing algorithm). Not all packets travelling between the same two hosts, even those from a single message, will necessarily follow the same route.
The destination computer reassembles the packets into their appropriate sequence. Packet switching is used to optimize the use of the bandwidth available in a network and to minimise the latency. Ethernet, X.25 and Frame relay are international standard layer 2 packet switching networks. Compare with ATM which uses cell relay instead of packet switching.
Notably, the Internet is a packet-switched network, running the Internet Protocol layer 3 protocol over a variety of other network technologies. Newer mobile phone technologies such as GPRS and i-mode also employ packet switching.
- Paul Baran, On Distributed Communications
- Paul Baran, On Distributed Communications Networks (IEEE Transactions on Communications Systems, March 1964)
- Leonard Kleinrock, Information Flow in Large Communication Nets, (MIT, Cambridge, May 31, 1961) Proposal for a Ph.D. Thesis
- Leonard Kleinrock, Communication Nets: Stochastic Message Flow and Design (McGraw-Hill, 1964)
- Katie Hafner, Where Wizards Stay Up Late (Simon and Schuster, 1996)