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Dropped Calls "Temporary Failure"

All –

A client of mine is experiencing the most frustrating condition with their new AVVID phone solution. They are dropping about 20% or their calls. I have read all the references in the professional forum about calls dropping and it seems to be a tough problem to solve via postings and we are often referred to TAC. So first I should say TAC is well involved. I suppose the purpose for my posting is to have other talented eyes on the problem.

The configuration is simple:

· An Ethernet Voice VLAN with 25 phones (model 7940)

· 3640 with an HDVM + 1MFT-T1 gateway (routing data and voice vlans and terminating their PRI PSTN interface)

· IOS 12.2.8T4

· Call Manager 3.1.3

The client makes and receives about 300 calls per day. Of these 20-30 will drop. DBUG of ISDN Q931 reveals a received (RX) cause code of 0x82a9 for all of these dropped calls. More inbound calls drop than outbound calls but other than that there is no obvious pattern to the calling. The translation of the cause code indicates that this is a problem with the local carrier switch and that it’s a “temporary failure” of service. Call detail reports and system traces also support the debug cause code as the reason for the disconnect.

In spite of the indications that this is a carrier issue, we have replaced all gateway components except the 3640 chassis and upgraded IOS to 12.2.8T4 with no success. Call manager and Windows components have been patched to the latest revs. The T1 PRI tests clean, no CRC, framing or in/output errors seen.

We have referred this to the carrier (Worldcomm… no jokes please) and they can’t seem to isolate a problem in their network. TAC agrees that this is a carrier issue; I second that motion. Can anybody chime in and or answer the following for me:

1. Are Q931 cause codes universal? Should the carrier be able to see the cause code they are transmitting to me and understand it/track it down?

2. Has anyone else experienced anything similar?

3. How would you further troubleshoot this?

4. Is there any chance this could be caused by our network and only appear to be a carrier issue?

We are about to fire the carrier, but it will be at least 4 weeks before we can get another T1 pulled in from SBC. God forbid the call dropping follows to the new carrier.

- Bob Evans

CCIE 7998

1 REPLY
Cisco Employee

Re: Dropped Calls "Temporary Failure"

Hi Bob,

1. Yes, Q931 causes code are universal. Yes, the carrier should be able to see it and track it down.

2. Personally not, but it is not an uncommon issue from Telco.

3/4. If the router did receive inbound q931 with cause code of 0x29, then it is the carrier who sent it.

-ben

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