Re: occasional 1.5 second latency on a particular Sun Ray

From: John Doe (john.doe_at_jasspa.com)
Date: 03/30/04 

Date: Tue, 30 Mar 2004 01:20:33 +0100

CJT wrote:
> I've got three Sun Rays scattered around my house, and am
> quite happy with their performance, but I have noticed that
> the one in one of my rooms experiences high latency at
> random times.
>
> It doesn't happen very often (on average about twice per
> day) but the curious thing is that the latency reported
> by utcapture is always nearly the same -- it's always in
> the range 1502-1505 ms. Some days it doesn't happen at all,
> and on other days it has happened as many as four times.
> I don't think I've ever been sitting at the affected
> device during an incident, so I don't know whether there's
> anything perceptible when it happens.
>
> The time of day when it happens seems to be random, and not
> correlated with any cron activity or any other load on the
> system or the individual Ray. And it only affects ONE of
> the Rays, which are all on the same server and (dedicated)
> subnet. I have confirmed that they are all running the same
> firmware version (even though I don't know how they could
> be otherwise, given the automatic firmware update of the Sun
> Ray system).
>
> When I swap the offending Ray with one of the others, the
> problem stays in the room rather than following the Ray,
> which suggests a cabling problem, but I've carefully checked
> the punch-downs on the keystones and can't detect a problem,
> and have tried switching drop cables. Plus, millions of
> packets can be exchanged without any indication of a problem
> between incidents (I often use them to play music, which
> results in lots of packets being transferred).
>
> Switching ports on my ethernet switch has no effect.
>
> I've also considered the possibility that the surge protector
> in that room may have been generating RF, and tried removing
> it -- no change. I'm not aware of anything else along the cable
> run that might be generating noise. In fact, for much of its
> length, the implicated cable runs parallel to one to another
> room which does not exhibit the problem. I do not know whether
> the AC outlet in the affected room is on the same side of the
> AC line as the others, but doubt that should make a difference
> (has anybody ever seen a ground loop or ground imbalance affect
> a Sun Ray?). One thing that suggests some sort of interference
> is that the errors sometimes appear in burst pairs close
> together in time (i.e. a high latency will be detected by
> utcapture followed by another a few seconds later -- e.g. the
> two most recent ones on my screen right now happened yesterday
> at 9:42:29 and 9:42:44, both about 28 hours ago).
>
> It's more an annoyance than anything, since I've never actually
> seen that Ray malfunction as a result, but the consistency of
> the length of the latency suggests to me that it's something
> that could be solved if I could identify it precisely. It's
> annoying enough I may just run another cable the next time the
> attic is cool enough to spend some time up there, but I'd hate
> to do that and still have the annoyance.
>
> Does anybody have any suggestions?
>

Had a similar problem with one of my Rays - turned out
it was a bad Ethernet cable. Swapped it out with a new
one and was fine. Also took me a while to figure out
as was fine most of the time - in the end I tested by
temporarily directly connecting the Ray to the hub
with a long new cable to actually confirm that the
existing wiring was at fault. Once confirmed then
I under took the task of replacing the faulty
cable properly.

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