Editing Packet switching (section)

==Connectionless and connection-oriented modes==
Packet switching may be classified into [[connectionless]] packet switching, also known as [[datagram]] switching, and [[connection-oriented]] packet switching, also known as [[virtual circuit]] switching. Examples of connectionless systems are Ethernet, IP, and the [[User Datagram Protocol]] (UDP). Connection-oriented systems include X.25, [[Frame Relay]], [[Multiprotocol Label Switching]] (MPLS), and TCP.

In connectionless mode each packet is labeled with a destination address, source address, and port numbers. It may also be labeled with the sequence number of the packet. This information eliminates the need for a pre-established path to help the packet find its way to its destination, but means that more information is needed in the packet header, which is therefore larger. The packets are routed individually, sometimes taking different paths resulting in [[out-of-order delivery]]. At the destination, the original message may be reassembled in the correct order, based on the packet sequence numbers. Thus a [[virtual circuit]] carrying a [[byte stream]] is provided to the application by a [[transport layer]] protocol, although the network only provides a connectionless [[network layer]] service.

Connection-oriented transmission requires a setup phase to establish the parameters of communication before any packet is transferred. The [[signaling (telecommunications)|signaling]] protocols used for setup allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated. The packets transferred may include a connection identifier rather than address information and the packet header can be smaller, as it only needs to contain this code and any information, such as length, timestamp, or sequence number, which is different for different packets. In this case, address information is only transferred to each node during the connection setup phase, when the route to the destination is discovered and an entry is added to the switching table in each network node through which the connection passes. When a connection identifier is used, routing a packet requires the node to look up the connection identifier in a table.{{citation needed|date=April 2021}}

Connection-oriented transport layer protocols such as TCP provide a connection-oriented service by using an underlying connectionless network. In this case, the end-to-end principle dictates that the end nodes, not the network itself, are responsible for the connection-oriented behavior.