BW )(: Weird cyclical lag pinging access point

[Lloyd Cohen]

Peter Ferne wrote:
> We've just got a new ADSL2 connection in the Jiva office which works 
> fine over wired ethernet but is behaving very strangely on the 
> wireless. There's a ten to thirty second lag before a page loads. Once 
> it starts loading it's very quick (c.12Mbps) but the horrendous 
> latency is a killer.
>
> As I said this only happens when connecting wirelessly. It's a 
> Speedtouch (536 IIRC) wireless router and when I ping it I get the 
> following cyclical pattern:
>
> PING 192.168.1.254 (192.168.1.254): 56 data bytes
> 1361.759
>  372.038
>    1.954
>    1.768
> 1055.497
> 1360.370
>  363.406
>    1.112
>    1.210
> 1354.161
>  361.835
>    2.917
>    1.314
> 1054.297
>  369.234
>    1.593
>    1.291
> 1053.876
> 1357.369
>  371.639
>    1.319
>    1.246
>
> If I ping it on a wired connection I get a steady c. 1ms ping time.
>
> Given that it's only a few feet away with a clear line of sight does 
> anybody have any idea what might cause such *huge* variation in ping 
> times over the course of a few seconds (c. 20s for the output above)?

To me this looks suspiciously un-varied.  It repeats every 4-5s, 
suggesting to me that there's an issue in the data layer.  Remember that 
a ping uses the transport layer, which queues packets up and passes them 
to the data layer (wireless protocols, CSMA/CD etc) for transmission.  
Those ping times suggest a flaw at this level where communications are 
dropping and take between 2 and 3 seconds to begin talking again.  
Packets sit in the transport queue while this renegotiation occurs, then 
flow through, after which things are fine for a couple of seconds.  Then 
the data link drops, and renegotiation must be completed once again...

> I've had Be tech support on the phone and they got me to turn off a 
> few checks by telnetting into the router:
>
> {Administrator}=>firewall config tcpchecks=none
> {Administrator}=>firewall config udpchecks=disabled
> {Administrator}=>dsd config state=disabled
> {Administrator}=>ids config state=disabled
> {Administrator}=>ids config trace=disabled
> {Administrator}=>saveall
> {Administrator}=>exit
>
> and to try switching to a different channel (although iStumbler shows 
> no conflicting networks on nearby channels) neither of which seem to 
> have had any affect at all.

You haven't said whether you've used more than one client - this could 
be an issue with your laptop, or as you'd probably know about it if it 
were broken more likely a conflict between the way it's hardware and 
that within the router speak wireless protocol.

Or perhaps you get the same results with any client regardless of 
hardware, singling out the AP as needing returning/a call out.

Either way, updating drivers and flashing the AP with the most 
up-to-date firmware is about all you can do without getting it replaced, 
or replacing it yourself.

Does the Speedtouch thing have an ADSL input, or is the ADSL modem 
seperate?  If you can, I'd dump the thing for a Linksys WRT54GL 
ethernet/wireless router running latest OpenWRT Kamikaze.  In any 
environment where the connection is heavily used by multiple people, a 
combination of the traffic shaping/QoS within a new linux kernel 
together with the customisations OpenWRT use to take advantage of these 
features quickly make the thing worth it's £40 pricetag.

--
Lloyd Cohen
BristolWireless Infrastructure

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