[cisco-voip] R: TCP ZeroWindow

[Wes Sisk]

Remote device was introduced by
CSCsc06953    Delayed cut-through on low bandwidth pipes with shared lines

Note this was specifically related to phones over low bandwith links.  
It is also related to concurrent signaling to multiple devices (i.e. 
shared lines).

How many phones are in this remote site?  Do you use shared lines in 
this site?  What differences do you observe between this site and the 
other remote sites?

Is the 0 window coming from the phone or from the CM?  If it really is 0 
window then no more data can be passed over the tcp session until window 
becomes available.  Do you have concurrent packet capture from CM side 
and phone side?  Do both show the same window?  We've seen issues with 
window size when using NAT or TCP proxy.

It may be time for a TAC case for more formal engagement and detailed 
analysis.

/Wes

On Friday, May 21, 2010 6:19:32 PM, Mauro Celli <mauro.celli at 2000net.it> 
wrote:
> I have analyzed the problem better.
> his is my situation:
> One remote cucm 6.1 (3Gb memory,2gb free/cached) connected with cisco 2811 10Mbit mcr xds, and five sites connected with cisco 877 dsl (300k mcr) . 
> All work over mpls.
> Four of the sites work correctly.
> In fifth site,if the phone is in iddle, it send and receive keepalaive correctly.
> If i press on phone down button (to show latest calls) and exit and i repeat for some times,
>  it send some skinny message (why??? is the exit button???) and after some packets,it receive an ack with 0 window (ttl ok).
> No syslog lines on cucm.
> Now it continue to  exchanges skinny keepalive.
> Now if i press line button,the phone exchanges skinny packet and keepalive with cucm but it hung.
> During the hung,it continue to  exchanges skinny packet and keepalive.
> In the phone log,i see nothing until it auto-reboot with a tcp timeout.
> In cucm syslog,i see the phone unregistered and re-registered.
> If i check “remote device” in phone configuration, i continue to see 0-window and same packets in the same situation
> but the phone not hung and work correctly.
> In this situation the problem is introduced very very very less frequently.
> The line seem to work correctly,same situation with and without qos.
> Switch are all catalyst and the lan work correctly.
> >From cisco site i see that  “remote device” is for slow skinny response,not for hunging phone...
> And why in other four sites same phone with same firmware works correctly?
> Thanks
> ________________________________________
> Da: Wes Sisk [wsisk at cisco.com]
> Inviato: venerdì 21 maggio 2010 20.12
> A: Mauro Celli
> Cc: cisco-voip at puck.nether.net
> Oggetto: Re: [cisco-voip] TCP ZeroWindow
>
> If you see 0 window you must be looking at packet capture.
>
> In the IP TTL for the 0 window packets, are the TTL consistent with other frames in the stream?  This would confirm the 0 window is coming from CM and not some interim device such as a firewall or inspection device.
>
> Beyond that the only reason I have seen 0 window from CM is byproduct of a memory leak on the CM server.  Do you see indication of increased VMRss or file descriptors on CM when this happens?
>
> /Wes
>
> On Friday, May 21, 2010 11:19:45 AM, Mauro Celli <mauro.celli at 2000net.it><mailto:mauro.celli at 2000net.it> wrote:
> Hi,
> my remote cucm 6.1 ,sometimes send a TCP ZeroWindow packet and my phone stop responding for some times (30sec or 30mins) reboot and reconnect.
> If i check “remote device” in phone configuration no TCP ZeroWindow appear and phone work well.
> >From another site all is ok.
> I have checked my line with download,flood etc.. and it’s ok, no lost packet…
> Why?
> Thans
>
> Cordiali saluti
> Mauro Celli (work in progress...)
> Site: www.2000net.it<http://www.2000net.it/>
> 13011 Borgosesia (VC) Italy
> Via XXV Aprile,41
> Tel.   0163.209111
> Fax.  0163 .209301
> Supporto tecnico: 0163 .209561
> Email: mauro.celli at 2000net.it<mailto:mauro.celli at 2000net.it>
>
> [cid:part1.03020000.09040707 at cisco.com]
>
>
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