Flow (computer networking)

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 service) to a single destination (another computer host, multicast group, broadcast domain, process, or class of service). 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 to form a multiplexed stream (e.g. A1, B7, C9, A2, C10, A3), a form of statistical multiplexing since the link is shared as required.

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

Conceptual description

Data flow can be conceptualized similar to the water flow model used to conceptualize electrical flow in circuit theory. Channels can be thought of as pipes, with packets being small objects inserted into the water stream. This visualization can help to understand bottlenecks, queuing, and help understand the unique requirements of tailored systems.

Utility for network administration

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 .

See also

• Flow control
• Flow network in graph theory
• Stream (computing)
• Telecommunication connection