Sorry,
The first sentence should read:
The SYMPTOM of the problem is RF noise and high latency however the
SOURCE of the problem could be either on the wired side of your network
or on the wireless side.
Sheeeeshh.... looks I need a professional proofreader to look over my
shoulder all the tyme.... oooppps... time.
j
Jack Unger wrote:
David,
Let me add more details than in my previous post -
The SYMPTOMS of the problem is RF noise and high latency however the
SOURCE of the problem could be either on the wireled side of your
network or on the wireless side.
(SOURCE on wired, SYMPTOMS on wireless)
On the wired side, a virus infection could be generating abnormal
traffic levels and that traffic could be using up all the timeslots on
your wireless network. This gets much worse if your wireless network is
already running near capacity or interfering with itself or being
interfered with by another network. A packet sniffer on your
wired/Ethernet network should give you a good idea if the wired network
traffic pattern is normal or is abnormally congested and flooding your
wireless network.
(SOURCE on wireless, SYMPTOMS on wireless)
On the wireless side, interference from your own or other network(s)
could also be using up all your wireless timeslots and slowing
throughput. I see you are using 5 channels in the 2.4 band therefore
some channels are overlapping other channels. To eliminate
self-interference be sure that these overlapping-channel APs are not
capable of being heard by and interfering with any other APs. This may
require a network re-design where you add more AP locations but lower
the AP antennas so the signals don't carry far enough to hit your other
APs. Reducing your use of omni antennas and using sector antennas
instead, may give you enough AP-to-AP isolation to allow you to avoid
adding new AP locations. Use all the tricks in the book (including cross
polarization) to keep your APs from interfering with each other.
Once you're sure that there are no wireless self-interference problems
AND that the problem SOURCE isn't on your wired network, it's time to
get out the trusty spectrum analyzer and attempt to identify the
signature of the off-network interference source (or sources), then use
triangulatio to track that source (or sources) to their physical
location(s) and talk with the other network operator about frequency and
polarization coordination to minimize interference with each other.
Call me if you would like to talk some more about these points.
jack
Jack Unger wrote:
Lots of possible causes (self-interference, interference from other
networks, too high an oversubscription/traffic level, etc.) but I'd
suggest pulling the AP packet-retransmit percentage statistics and
manually creating a bar graph with APs across the bottom and retrans
percent on the vertical (Y) axis. Any APs that are running above about
10% or 15% are having RF problems. If all the problem APs are below
10% then it is likely that the latency problem is
Ethernet-traffic-level related and not an RF/interference problem.
If it turns out to be a non-RF problem, is your network switched (with
no MAC-layer filtering or protection from abnormally high traffic
levels) or routed? Also, is per-client bandwidth-management in place
and working?
jack
David E. Smith wrote:
Okay, Scriv and I are stumped on this one.
Over the last couple of weeks, we've started seeing some very odd
oddness on a few of our 2.4GHz POPs. Not all, just some. Here's what
appears to be happening:
A couple times a day, usually during business hours, something somewhere
generates a massive amount of noise. Connections which report an RF
noise of -90 start showing noise levels of -60 (or worse in some cases),
as reported by our StarOS access point. If it really is RF noise, it's
very broad, as it's simultaneously hitting five or six POPs, some
several miles away, but all at the same time.
The towers are all running StarOS on Mikrotik RouterBoard hardware, with
a mix of Orinoco and Prism cards, some with amps, some not. Some have
sectored antennas (180 degrees), some have omnis. Between them, the
towers cover just about the entire 2.4 spectrum (obviously, one channel
per access point, but we're using at least channels 1, 4, 6, 8, and 11).
Those towers are basically identical to several other towers that aren't
affected.
The other really really weird part is the crazy latency. Pings to the
APs themselves are reliable, and our backhaul links (5.3 and 5.8 GHz)
don't seem to be affected. And pings to our end-customers don't seem to
get lost, they just take their sweet time getting there. While "the
event" is happening, I've seen pings that take in excess of twenty
seconds to complete their round trip.
64 bytes from 10.232.175.130: icmp_seq=7 ttl=62 time=27239 ms
(I think that's my record. In that particular test, there were no
packets lost, they just took a very long time to get there.)
I've checked or replaced just about everything I can think of in our
network that might cause something like this, and frankly, I'm stumped.
I don't think it's a network problem (traffic bursts or similar) because
of the weird bursts of RF noise. But that'd have to be one helluva burst
of noise to do what it's doing - affecting every channel across ten
miles at once.
I can go into more detail on any part of the network if you like, though
I think all the likely-relevant details are covered here.
Help!
David Smith
MVN.net
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Jack Unger ([EMAIL PROTECTED]) - President, Ask-Wi.Com, Inc.
Serving the License-Free Wireless Industry Since 1993
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