[asterisk-users] Dropped Calls / Maximum Retries Exceeded / No Reply to Our Critical Packet

[Lincoln King-Cliby]

Hi All,

I've looked through the archives and tried several variations in Google, and I haven't found anything on-point... So I'm hoping someone here may be able to help this relative Asterisk neophyte shed some light on an issue:

I have a box running Asterisk 1.4.22 in our lab with several Cisco 7961G phones and an AEX804E card (4 FXO, hardware echo cancellation).

The server and all phones are on the same subnet (10.2.0.x/255.255.255.0) of the local LAN with no NAT, routing, firewall, etc., etc. between the server and the phones.

Periodically I'm seeing calls placed from the 7961s through anything on the PBX that requires digit entry (the Auto Attendant, Voicemail, etc.) 'randomly' drop; extension-to-extension calls extension-to-PSTN, and PSTN-to-extension calls never have any issues whatsoever. Nor have I been able to duplicate the issues hopping around auto attendants on an inbound PSTN call.

When the call drops, the phone still thinks that it is connected, but the audio path is cut off and something similar to the following is dumped to the console

-- <SIP/1103-b71184e0> Playing 'vm-password' (language 'en')
[Oct 28 14:23:07] WARNING[9423]: chan_sip.c:1958 retrans_pkt: Maximum retries exceeded on transmission 0016c82d-5455002d-2155dfac-8901da83 at 10.2.0.224 for seqno 102 (Critical Response) -- See doc/sip-retransmit.txt.
[Oct 28 14:23:07] WARNING[9423]: chan_sip.c:1980 retrans_pkt: Hanging up call 0016c82d-5455002d-2155dfac-8901da83 at 10.2.0.224 - no reply to our critical packet (see doc/sip-retransmit.txt).

All of the results Google has turned up, and the doc/sip-retransmit.txt file point to problems with things in the middle of the path between the server and the phone (NAT, firewall, "SIP middle box", proxy) that simply don't exist in the configuration that we're using.

I suspect it's an issue with the way the Cisco phones are dealing with DTMF to Asterisk or Asterisk dealing with the DTMF from Cisco but that's where I go off into unknown territory. (FWIW, until the call drops everything works fine, pressing a button triggers the desired action, and audio quality is fantastic)

I've rolled the firmware on the phones up and down with no noticeable change, and I also upgraded to Asterisk 1.4.22 version of Asterisk (I had been running 1.4.21.2, and there are fewer dropped calls with .22 but it's still way too often to be acceptable)

Any suggestions are greatly appreciated, but please be explicit... short of editing the configuration files and "make install" my Asterisk experience is rather limited.

Thanks in advance,

Lincoln

--
Lincoln King-Cliby, CTS
Applications Engineer
ControlWorks Consulting, LLC
http://www.thecontrolworks.com/