[ntp:questions] Garmin 18 LVC: whether to fudge
janspam.ceuleers at skynet.be
Wed Feb 11 20:13:03 UTC 2009
Brian Utterback wrote:
> Decreased bandwidth means increased latency. The two are related.
Only indirectly so.
There are at least two components to the higher latency on the ADSL
uplink as compared to the downlink. A minor component is the fact that
the lower bitrate means that equal-sized packets are in flight longer on
the uplink than they are on the downlink.
The main component is however that there is a transmit queue in the CPE
that packets take a while to get through before actually being sent up
the link, particularly under load. So this component is not only
dominant, it is also variable with upstream load.
One way to get around that is to set up multiple transmit queues for
different flows, perhaps based on TOS marking. This way, NTP packets,
when suitably marked, can be made to bypass the transmit queue for
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