Why is latency (ping time) higher for lower speed ADSL services?
We observe empirically that the lower speed an ADSL service happens to be, the higher the time recorded for a ‘ping’ test (or other measures of round trip latency) on the service. We believe that some of this latency is a function of interleaving settings in the Telstra exchange DSL equipment, but some (relatively!) simple mathematics demonstrates that most of it can be explained simply by the physics of the situation. Obviously a lower line speed -does- mean that a packet takes longer to transit a network link than it would do at a higher speed – because a slower ADSL service is, well, slower (!) – but how much does this affect things, and is it consistent with observations in the real world on the Telstra xDSL network? Lets take a test case, and ‘work the numbers’: A 64 byte ping packet is sent from a customer site to a router attached directly to our Telstra interconnect point in a capital city, and back again to the customer, with a resulting observed ‘ping time’ Even at a minimum
