Flow routing is a network routing technology that takes variations in the flow of data into account to increase routing efficiency. The increased efficiency helps avoid excessive latency and jitter for streaming data, such as VoIP (voice over IP) or video.
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Rather than routing individual packets, a flow router observes and evaluates flows to gather statistics, including source, destination, amount of traffic "in flight," and stream duration. A flow is a single meaningful end-to-end activity over the network. This evaluation permits the router to prioritize traffic, deliver on quality of service (QoS) requirements, and keep flows from consuming more than some pre-allotted portion of network resources.
A flow router evaluates traffic flows in real time, based on an ID, route, time of receipt and rate of flow, to keep streaming traffic moving as quickly as possible. By contrast, conventional (Layer 3) IP routing does not differentiate between packets. Conventional routing uses a best-effort technique to ensure delivery of incoming traffic to the proper destination on a packet-by-packet basis, and is not sensitive to timing and data rate requirements for streaming data such as voice, video, multimedia and IPTV.
Industry analysts indicate that high-end conventional routers can achieve many of the same advantages touted for flow routing using ancillary queuing, deep-packet inspection, rate shaping and policing, and selective packet discard methods. Nevertheless, flow routing's unique ability to accommodate streaming data types makes it interesting and potentially valuable, especially for networks where such data consumes an appreciable portion of overall bandwidth and resources.
Dr. Lawrence G. Roberts (founder of Anagran and one of the creators of the ARPANET), developed Anagran's flow-based router over a period of seven years at that company and his previous start-up, Caspian.