Hi Bob, On Wednesday, 21 October 2020, Bob kb8tq <kb...@n1k.org> wrote:
> *Networking* hardware is the issue ….. > Undeniably so, but to what extent? > If you have fully symmetric delays, then there is no need for 1588. NTP > will > do just fine. Lab results and years of production deployment tell me otherwise. Hardware timestamps are the key. NTP *with hardware timestamps on both server and client* will do just fine, yes. > Unfortunately as even home networking hardware loads up, > ( = lots of traffic in only one direction) this may not be the case. When > things > *do* go asymmetric, then you *do* need 1588 compatible switches. > > Quantify "lots". My argument is that the uncertainty of software-generated timestamps can outweigh that of a network that isn't loaded up to choking point e.g. little to no buffering. Home traffic tends to be bursty, with occasional constant load and yes asymmetric. But your PTP device is not sitting on your ISP link, neither of them will, and unless your host running PTP is sitting on a saturated link, it really is not as bad as it may seem. Even cheap switches these days are non-blocking, so unless you have lots of multicast, PTP hosts on your network will not be critically affected by other traffic. Yes, they are store and forward, but it's about selecting packets in a band with minimum transit latency or, say, mode. The band has to be wide enough to catch at least one packet per second. With a rate of say 32 msg/sec chances of catching lucky packets increase. I can't normally take results out of my work lab unfortunately, but I think I might just drop a "home" switch in there and put some application traffic through it for a proper test. I know what difference a PTP transparent clock switch makes, but even without one, it really is "not that bad". Numbers or it didn't happen, so I'll ad that to my to-do list. Cheers, Wojciech -- - Wojciech Owczarek _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.