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Don't Bump Up the BandwidthThe real killer for client-server apps over the wide area is network latency. Here's where it comes from: Propagation delay is an unavoidable factor related to the physics of transmission, including the speed of electrons along a cable or light waves in a fiber. Propagation delay depends on t he length of a connection. For example, a 5,000-kilometer circuit incurs at least 60 milliseconds of round-trip delay, regardless of bandwidth. Satellite links exhibit propagation delay of about 500 milliseconds. Insertion delay results from the mismatch between a fast LAN link and a slow WAN link that forces a packet to wait in a queue until it can be transmitted at the slower speed. Queuing delay is added when shared networks are congested and routers and other gear buffer packets in queues until outbound links are available. Since queuing delays typically occur during traffic peaks, shared networks often exhibit variable latency. Processing delay is added as network gear like switches and routers shunt data from input to output ports. In general, private lines and circuit-switched services have minimal processing delays since they don't use additional connection equipment. Cell-switched services add slightly more, while packet-switc hed services add the most. [ Home ]
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