Flow

In a packet switching network, packet flow or a data traffic flow is a sequence of packets from a source computer to a destination, which may be another host, a multicast group, or a broadcast domain. As packets traverse successive communication 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). This represents a form of statistical multiplexing because 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

Packet flow can be described as being 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 analyzers or in 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 (for example, 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

• Data flow (software engineering)
• Data stream
• Flow control
• Flow network in graph theory
• Stream (computing)
• Telecommunication connection
• Traffic flow

References

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