Cisco ISR4321 - ISDN PRI and SIP TRUNK issue

[fpiccinin]

Hi all,

we are experiencing an issue with a cisco ISR4321 (running isr4400-universalk9.16.06.05.SPA.bin).

The voice gateway is used to connect an ISDN PRI trunk (from provider) to a CUCM Cluster using a SIP trunk configuration.

on inbound calls from ISDN carrier to ISR4321, the isdn q931 debug displays this error:

Dec 10 13:24:51.218: ISDN Se0/1/0:15 **ERROR**: Ux_BadMsg: Invalid Message for call state 7, call id 0x4703, call ref 0x8915, event 0x8A
Dec 10 13:24:51.218: ISDN **ERROR**: Module-l3_sdl_u Function-Ux_BadMsg Error-Source ID = 400 Event = 8A

In that case SIP session vs CUCM is correctly setup but the ISDN caller still hear the ringing tone and does not receive the connect.

If we use H323 protocol between the ISR4321 and the CUCM the error disappears and all the inbound call are connected without issues.

Thanks

Francesco

[Nithin Eluvathingal]

A quick question, is there a firewall between CUCM and gateway. If yes check SIP settings on firewall. 

[fpiccinin]

Hi Nighin,

thanks for your feedback.

I confirm that a firewall is present but we check sip configuration and logs and we haven't seen any drop.

After some test, I discovered that the "connection-reuse" command, under sip-ua was causing the issue.

If sip-ua / connection-reuse is presente, the gateway send 200 OK to CUCM using a different port from 5060. For this reason CUCM 200 does not receive the 200 OK and after 3 retransmission from the GW CUCM send a 503 "Service Unavailable".

Removing the "connection-reuse" seems to fix the issue.

Gateway start sending 200 OK to UDP 5060 destination port and now is accepted from CUCM.

You can have a look on the attached traces.

connection-reuse-KO.pcap

(packets 5-9) the gw send 200 OK to CUCM using these dest UDP ports:

21285
21302
21323
21374
21414

CUCM does not accept it and, as on packet 10, it replies with a 503.

connection-reuse-OK.pcap

packet 5 200 OK is sent from gw to CUCM using UDP dest port 5060.

CUCM reply then correctly using a 200 OK.

These behaviour was unexpected since connection-reuse should be used just to force sip-ua running on the gw to use 5060 as source and dest port for SIP signaling.

Could this be related to an ios bug?

Thanks

Regards

Francesco