Re: Wierd metro WiFi problem

If you are adding latency with wireless hops, are the wireless hops on 
different frequencies? If they are all on the same frequency and indoors 
in the same room, you are probably interfering with yourself. Try 
configuring the wireless "hops" on different frequencies, where 
necessary connecting the radios together with Ethernet crossover cables. 
Also, either configure the transmit power levels very low or attenuate 
the transmitter power levels down with long, small-diameter cables so 
you aren't blasting the receivers and perhaps introducing receive 
errors. Using wireless hops seems a rather unpredictable way of 
introducing testing latency. Maybe someone can suggest a simpler, 
non-wireless method.
                                                                                                                                       
jack


Tyler van Houwelingen wrote:

> casey, we are setting MTU to 1500 and RWIN to 256960.  This gives us 
> the best results.  TCPOptimizer is a nice free tool for this.
>
> The latency is being injected by wireless hops.  We are not seeing 
> retransmissions and it is not interference as we we have replicated it 
> exactly across 2.4, 5Ghz as well as 4.9GHz licensed 802.11a.  The more 
> hops we are away essentially, the worse it always gets, independant of 
> traffic on the network, etc.  We have tried this with Alvarion, 
> Proxim, Meru and off the shelf Linksys gear.
>
> Is there anyway to run a "speed test" with UDP traffic?
>
> tyler
>
>
> ----- Original Message ----- From: "Casey Halverson" 
> <[email protected]>
> To: "SeattleWireless Talk List" <[email protected]>
> Sent: Thursday, January 26, 2006 1:03 PM
> Subject: RE: Wierd metro WiFi problem
>
>
> What are you using for distribution between your 400 AP's and your edge
> router?
>
> I would also check the error counters on your serial interfaces (T1), as
> well as interface status.  Sporadic errors can cause packet loss at
> random times, which can send you on wild goose chases such as this one.
>
> I have actually seen a number of issues on multiplex T1's were one T
> will go down, and a loop is thrown back, making the router think the
> interface is up, and ultimately trying to multiplex over it.  This can
> cause sporadic packet loss.  I'd highly suggest you contact your
> provider to see if this problem can be diagnosed.
>
> If this is honest to god latency (as opposed to latency caused by packet
> drops and retransmits), you will see a direct correlation between
> latency and download speed.  Your TCP windows are probably set way too
> low.  I know you are using some tools to set these windows, but could
> you please tell us what settings you are using?
>
>
>
>> -----Original Message-----
>> From: [email protected]
>> [mailto:[email protected]] On Behalf Of Tyler
>> van Houwelingen
>> Sent: Thursday, January 26, 2006 11:57 AM
>> To: SeattleWireless Talk List
>> Subject: Re: Wierd metro WiFi problem
>>
>> Agreed, unfortunately this does not appear to be the case.
>> We can use the same interfaces and make the download speed
>> change simply by increasing the latency between.  We look at
>> the switches, routers, etc and there are no errors on the ports.
>>
>> a hypothesis of the problem is that maybe with an upload, the
>> latency and wireless hops are at the beginning of the link,
>> causing any retransmissions to be immediate.  with a
>> download, the latency and hops are at the end, potentially
>> causing retransmissions.  We dont however, detect any retransmissions.
>>
>> ty
>>
>>
>>
>> ----- Original Message -----
>> From: "Jack Unger" <[email protected]>
>> To: "SeattleWireless Talk List" <[email protected]>
>> Sent: Thursday, January 26, 2006 12:50 PM
>> Subject: Re: Wierd metro WiFi problem
>>
>>
>> > Could be a router Ethernet port speed-mismatch issue.
>> >                                                        jack
>> >
>> > Tyler van Houwelingen wrote:
>> >
>> >> I am contacting the best wireless minds I know to help
>> with a bizarre
>> >> issue that has us stumped.
>> >>  Situation:
>> >> - We have 4 bonded T1 lines currently for our backbone,
>> running a large
>> >> (400 AP) metro WiFi network.
>> >> - When connecting directly into the backbone router, we
>> get 6M down, 6M
>> >> up as expected.
>> >> - However, when we begin to add a little latency between a
>> testing PC and
>> >> the backbone connection, the upload speed stays the same, but the
>> >> download gets hammered.  With 10ms of average latency from
>> the metro WiFi
>> >> network side, the speed drops to 2M down and 5M up.  At
>> 40ms, it is
>> >> around 800k/5M.
>> >> - The wireless communications are more than fine as we get
>> 8M/8M back to
>> >> our headquarters from anywhere in the metro WiFi network.
>> The problems
>> >> only come from testing into the Internet.  We get the same
>> goofy results
>> >> when we disconnect the city network completely and just
>> add latency in
>> >> the lab.
>> >> - We have run all the DrTCP (MTU, RWIN) like tricks which
>> provides some
>> >> improvement, but not much.
>> >>  Why would this additional latency kill the downloads so
>> much?  I suspect
>> >> the problem is with our backbone provider (Expedius) or
>> some limitation
>> >> of metro WiFi that worries me.  In our other metro WiFi
>> network, we do
>> >> not see this, but they all use a different backbone
>> provider (AT&T).
>> >>  Any suggestions to debug/fix this would be very much appreciated.
>> >>  tyler
>> >>  Tyler van Houwelingen
>> >> Founder and CEO
>> >> Azulstar Networks, Inc.
>> >> 1051 Jackson, Grand Haven, MI 49417
>> >> 1117 Rio Rancho Blvd 13, Rio Rancho, NM 87124
>> >> 1-877-AZULSTAR
>> >> www.azulstar.com <http://www.azulstar.com>
>> >>
>> >>
>> >>
>> --------------------------------------------------------------
>> ----------
>> >
>> > -- > Jack Unger - President, Ask-Wi.Com, Inc.
>> > Serving the License-Free Wireless Industry Since 1993
>> > Author of the WISP Handbook - "Deploying License-Free Wireless WANs"
>> > True Vendor-Neutral WISP Consulting-Training-Troubleshooting
>> > [email protected]  (818) 227-4220  http://www.ask-wi.com
>> >
>> >
>> > _______________________________________________
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>> > [email protected]
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>> >
>>
>>
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-- 
Jack Unger - President, Ask-Wi.Com, Inc.
Serving the License-Free Wireless Industry Since 1993
Author of the WISP Handbook - "Deploying License-Free Wireless WANs"
True Vendor-Neutral WISP Consulting-Training-Troubleshooting
[email protected]  (818) 227-4220  http://www.ask-wi.com



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