Flow (computer networking)

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For other uses, see flow.

In a Packet Switching network, a packet flow or traffic flow is a sequence of packets from one particular source (e.g. a computer host, process or class of services) to a single destination (another computer host, a multicast group, a broadcast domain, a process or a class of services). As they are sent over successive data links towards their destination, the packets from one flow (e.g. A1, A2, A3) will be intermingled with packets from other flows also traversing the network (e.g. A1, B7, C9, A2, C10, A3), since packet mode switching is a form of statistical multiplexing.

The term flow is often used synonymously to a multiplex channel or a path in a network.

The concept is important, since it may be that packets from one flow need to be handled differently from others, by means of separate queues in switches, routers and network adapters, to achieve traffic shaping, fair queueing or Quality of Service. It is also a concept used in network analysers or packet tracing.

Applied to Internet routers, a flow may be a host-to-host communication path, or a socket-to-socket communication identified by a unique combination of source and destination addresses and port numbers, together with transport protocol (either UDP or TCP). In the TCP case, a flow may be a virtual circuit, also known as a virtual connection or a byte stream.

In packet switches, the flow may be identified by IEEE 802.1Q Virtual LAN tagging in Ethernet networks, or by a Label Switched Path in MPLS tag switching .

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