On 12/24/2011 8:11 PM, Dave Hart wrote: > On Sat, Dec 24, 2011 at 18:18, unruh <[email protected]> wrote: >> On 2011-12-24, David J Taylor <[email protected]> wrote: >>> - one Netbook PC worked very well on a LAN connection (about 1 ms steady >>> jitter). However, when moving to a Wi-Fi connection after a power-down >>> reboot, the reported jitter gradually built up over about a 30 minute >>> period, ending up with a 5 ms peak, later decaying to a value between 1.3 >>> and 2.5 ms. The offset also appeared to have spikes which because much >>> worse after about 30 minutes. >> >> I would expect wifi to be much worse than a lan for jitter. The signal >> has to be converted, broadcast, reconverted and then sent on down the >> lan. That all takes time, and can have aproblem with dropped bits, >> retransmission, etc. > > Retransmission is the killer issue for NTP performance over 802.11. > For practical interop with software developed on wired networks, WiFi > equipment detects packet loss and triggers retransmission invisibly to > higher layers. I suspect NTP would do better if the 802.11 layer > differentiated its handling of UDP 53 and 123 :) Where dropping DNS > queries has an awful impact on user experience, it would be preferable > for NTP compared to introducing the extra delay and thereby jitter. > I'd love to see more DNS over TCP, so that perhaps one day layer 2 > wireless networks will do better letting UDP drop rather than > retransmit at layer 2.
No you don't want to do DNS over TCP if you can avoid it. It would be a major hit on the resolver servers and with the kind of high volume that you get as mobile devices make increasing use of such networks. You want WiFi to drop UDP packets if they are lost rather than attempting to retransmit them. Danny _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
