Occasional Dead Air VoIP Calls Toshiba CIX 40 using Cisco 2811

[brett.stone]

I have a reoccuring issue with our Toshiba CIX 40 Phone System where extension to extension VoIP calls occasionally result in dead air (no speach path, just no sound/no voice/dead air heard on both sides upon connection of the call).  When the issue occurs, the phones will ring on both sides and the LCD will show connected and the timer will start counting the seconds that the call is connected, but you can't hear the caller on either side.  We have had them hang up and re-dial but in almost all cases the same problem occurs; in rare others it will connect and voice path is restored only for the issue to reoccer a few minutes later.

I have tried everything I know Cisco wise to restore the voice path including rebooting the router/switch, clearing arp tables, shutting/no shutting  tunnels, and rebooting the IP phones themselves but nothing ever seems to work.  The only way we are able to restore the voice path when this issue occurs is to go in to the Toshiba CIX itself and hit the reset button on the Toshiba IP Card.  Once I hit the reset button on the IP card, every IP phone connected to that IP Card (32 phones) is knocked offline as the IP card resets.  While this instantly fixes the problem it interrupts 31 other phones for the 2 minutes it takes for the IP card to reset and for the phones to reconnect so this obviously is not very preferable to do.

I have seen this problem occur over and over again for years now.  Most of the time it will be weeks/months of perfect VoIP service until one day out of the blue a certain extension will get the dead air issue.  In some cases I have been able to determine that a brief drop in Internet connectivity occured shortly before the dead air issue was reported so I have a theory that the RTP stream gets jibbered up somehow when the connectivity is lost under some circumstances (certainly not every time connectivity is lost).  I have spoken to Toshiba over and over about this issue for years now and Toshiba blames my equipment (Cisco 2811 on the host side) and I blame Toshiba and we obviously aren't getting anywhere.  What I know for certain is that hitting the reset button on the Toshiba IP card instantly fixes the problem every single time without fail and no Cisco command in a router that I have been able to find has been able to restore connectivity. 

I talked to another Cisco Guru that I know about this issue last week and he said he has heard of similar VoIP issues with other types of systems.  If I understood him correctly he said that in some instances an RTP stream may get interrrupted somehow and when it does the PBX/CIX phone system begins to send the media stream to where the phone was connected prior to the stream being interrupted rather than its new place after interruption was restored thus resulting in dead air in the VoIP Call.  This may explain why hitting the reset button on the IP card fixes the issue as it forces the PBX/CIX to reset all media streams on that IP Card thus fixing the problem.  He reccomended getting an SBC device to help manage the IP connectivity at the gateway but I obviously don't want to overcomplicate this issue if I don't have to.

This issue seems to be relatively intermittant and unpredictable.  Are there any Cisco commands that I may be missing that can help jumpstart/reset the media stream after it gets interrupted? I already have QOS DSCP 46 matching and traffic shaping enabled and this is a dedicated VoIP network with no data traffic whatsoever.

Any ideas?  Below is the revision of the 2811 that I am using to host the VoIP traffic on the HDQ end.  The remote end uses a number of different types of Ciscos such as the Cisco 877 or the Cisco 861.

ROM: System Bootstrap, Version 12.4(13r)T5, RELEASE SOFTWARE (fc1)

System returned to ROM by power-on
System image file is "flash:c2800nm-advsecurityk9-mz.150-1.m3.bin"
Last reload type: Normal Reload

Thank you in advance!

[paolo bevilacqua]

If the problem is fixed by resetting the PBX, seek a solution with that vendor.

[brett.stone]

Unfortunately I have been seeking a solution with the vendor Toshiba for multiple years but no matter what I say, thier automatic answer is "your network is to blame".  I am 110% positive everything is set up correctly within the Cisco and the system works perfectly fine for weeks/months on end until randomly out of the blue we will get a dead air issue.  Even though I have told Toshiba 1000 times that the only thing that can fix this issue is resetting the CIX IP Card, they insist it is network related and my equipment is to blame.  I don't know how they can honestly overlook the fact that the only thing that fixes the issue is resetting the CIX IP Card, then tell me my network is to blame?  They are so clueless it isn't even funny and I'm not sure what else I can tell them so I am doing my due diligence and posting in a Cisco forumn about the issue just in case someone else out there has encountered a similar issue. 

Any ideas?

[brett.stone]

I just wanted to follow up with a solution in case anyone ever has a similar problem with Toshiba's & Ciscos.  This was in fact a Toshiba issue and the Cisco was not to blame.  In a nutshell, we have major bandwidth issues at our location and had to use the g729a codec instead of g711 codec since we had very little bandwidth at our disposal.  The Toshiba call routing table was using g711 settings instead of g729a settings which mucked up the phone system and caused all sorts of grief with dead air issues that would come and go.  The very first thing Toshiba will every do is blame the customers equipment and it took me almost 3 years and several hundred phone calls/emails to convince Toshiba that this is not a customer issue and this was in fact a Toshiba issue.  I had to escalate and escalate and just when I thought I couldn't escalate any higher I had to escalate again until I finally found a Toshiba tech who believed me.  So in summary, if you truly believe your equipment is not to blame and you have information to back up your cause, do not let the vendor tell you that the problem is your equipment.  You may have to play the "its not me its you" game but being persistant will eventually turn up a solution.