[ntp:questions] 1Gb/s network issues - was: Re: OT: GPS18x LVC failure

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Mon Oct 12 10:00:04 UTC 2009


"Unruh" <unruh-spam at physics.ubc.ca> wrote in message 
news:QsBAm.47742$Db2.29202 at edtnps83...
[]
> Actually those Gb ethernet switches seems to have some really bad and 
> variable
> latencies. My system, before they installed Gb switches, had a 
> consistant
> roundtrip of 140 usec and gave better than 20usec jitter (with 100Mb 
> switches). Since those new switches
> were installed things have gone to hell-- variable roundtrips ( 140usec, 
> 300usec
> and up to 1 sec roundtrip) and much much worse jitter. NOt sure where 
> the problem
> is, but it sure is terrible.
> Doing a plot of roundtrip vs offset it is definitely one way delay.

Most interesting, Bill.  Mine is a relatively cheap and cheerful device 
from Netgear (GS608):

  http://www.netgear.co.uk/ethernet_network_switch_gs605.php

so whether being very simple and unmanaged is likely to mean that it's 
performance is better or worse I leave to speculation or measurement!

Thanks Hal for his comments: the test (resulting in 110 - 140 microseconds 
jitter) was using the network controllers built into the PCs.  The 
stratum-1 source had a 2 - 2.5 microseconds jitter.

Cheers,
David 




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