David J Taylor wrote: > For those without wide-bandwidth academic connections - those folks on > cable or ADSL - how good is an "equal split round trip" assumption?
I calculated this for my case once (3840 kbit/s down and 512 kbit/s up). The difference in transmission time due only to the different bitrates was about 1.2ms in my case. This is however only the best case, because it assumes that the uplink is not saturated. If it is, and if you are able to prioritise your upstream NTP packets over all other traffic, then you need to add half of the transmission latency of the average upstream packet to the above 1.2ms. To give you some idea, assuming that the uplink is saturated due to a file upload (i.e. MTU-sized packets), this brings the difference in latency to 14.4ms (including the above 1.2ms). If you cannot control upstream priority queuing, then the upstream latency depends on the total size of your upstream queue, which may add several MTU-sized packet transmission times to the difference (in my case, 26.5ms times three plus 1.2ms). This is then really the worst case, because it assumes that the downlink is not saturated so that there is no queueing on the ISP's side. Cheers, Jan _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
