RE: Wierd metro WiFi problem

How many wireless hops away?  Why is it variable?  Are you doing mesh
routing?  

Please explain this topology -- I think its going to be important in
troubleshooting.


> -----Original Message-----
> From: [email protected] 
> [mailto:[email protected]] On Behalf Of Tyler 
> van Houwelingen
> Sent: Thursday, January 26, 2006 12:50 PM
> To: SeattleWireless Talk List
> Subject: Re: Wierd metro WiFi problem
> 
> 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
> > >
> > >
> > > _______________________________________________
> > > Talk mailing list
> > > [email protected]
> > > http://seattlewireless.net/mailman/listinfo/talk
> > >
> >
> >
> > _______________________________________________
> > Talk mailing list
> > [email protected]
> > http://seattlewireless.net/mailman/listinfo/talk
> >
> _______________________________________________
> Talk mailing list
> [email protected]
> http://seattlewireless.net/mailman/listinfo/talk
> 
> 
> _______________________________________________
> Talk mailing list
> [email protected]
> http://seattlewireless.net/mailman/listinfo/talk
> 
_______________________________________________
Talk mailing list
[email protected]
http://seattlewireless.net/mailman/listinfo/talk