I have two customers with Cisco 4321 ISR routers. We have exactly the same problem with both customers.
There is (not always) one-way voice for outgoing calls. The other party does not understand the internal subscriber. The other direction works. It is not a single telephone but a problem covering the whole area. We could already find out that the Cisco 4321 routers are responsible in some direction. Both customers exchanged Cisco 2900 routers for these 4321 routers. After the problem could not be solved quickly, the old 2900 routers were installed again. The problem disappeared immediately!
I already found in the release notes and a blog that the 4000 routers use a different RTP port range. For this reason we have adapted the RTP ports in the "voice service voip" accordingly. But also without success. We also have updated IOS Image to the latest 16.x Release. CUCM is also on latest 11.5.x.
Here is the setup:
ISDN BRI -> ISR 4321 -> H323 -> CUCM 11.5 -> IP Phone
ISDN PRI E1 -> ISR 4321 -> H323 -> CUCM 11.5 -> IP Phone
Problem exist in IP Phone to PSTN. External callers did not hear RTP.
Has anyone seen this issue? How can we troubleshoot this? We can exclude the network infrastructure that everything has already been moved to a subnet (without success). There are also no firewalls included.
Any help is welcome!
Thanks a lot!
the strange thing is that some calls work and some calls not. Same calling and called party.
This installations work for over more than 6 years without any problem. After the change of the Voice Gateways (ISR Router), we have the problems. So packets from phone to gateway are OK.
The second call leg to PSTN is a PRI.
Did you ever fix this ? I have the same one way voice problem going from H.323 or SIP to ISDN (BRI) when a 4351 is upgraded from 15.5-2.S6 to 16.9.4. have ended up downgrading back and two way voice then works fine. SIP to SIP through the same router works fine across both versions of IOS.