ip phone 786 request ack sip message missing

[muazam ali]

Dear All,

I have installed CUCM version 11.5 and registered 2 ip phones 8865 model, when i am calling to both phones on LAN calls are going fine but when calling from WAN calls are ringing on phones but can not gets answered while pressing answer button several times.

i have collected the logs from phone in both scenarios i have notices in not working scenario there is no "SIP    768    Request: ACK sip:xxxx@x.x.x.x:5060;transport=tcp | " message

but in working scenario i am getting the message in logs.

does any one know what can be possible issue here?

[hsood]

Hi,

Is there any device in the path monitoring the SIP traffic or it could be possible for a device that limits the MTU size?

I have seen it occur when any device strips off the ACK message as it did not fit the MTU size criteria.

You can always gather packet captures from both the phones and confirm that if the packet left the calling phone for  SIP ACK  message and was dropped somewhere down the whole path.

https://supportforums.cisco.com/docs/DOC-11735

Please rate and mark correct if helpful.

Regards,

Hitesh

[muazam ali]

Hi Hitesh,

I did open up a TAC case and send logs to TAC below is their analysis.

Analysis:

CUCM send 6 times OK message to phone but never received a ACK from phone and after that CM send BYE to phone. As you can see from below packet capture, OK message from CUCM is not reaching to the phone. This is getting blocked in between the network. Firewall blocking this OK message and not sending to Phone.

do you still believe that MTU can be the issue? there are firewalls but as per network team firewalls are only in routing mode not blocking any thing.

[hsood]

Hi Mauzam,

As already mentioned by TAC , there is something in the network which is causing the issue.

I have seen this occur with MTU size being greater in size and the packets go as fragmented and the firewall drops it.

I will recommend to have the Firewall team from TAC be involved and they can probe this further and recommend the solution for you.

Regards,

Hitesh

[muazam ali]

Hi Hitesh, Problem resolved, network had SIP Inspection turned on that is why call was not going through, after unchecking the sip inspection on firewall calls started going through.

[hsood]

Hi Mauzam,

Glad to know that firewall team was able to correct the issue.

Please mark the post as resolved in case you do not have any further queries.

Regards,

Hitesh

[muazam ali]

Hi Hitesh, ip phones are now able to make and receive calls but when i am dialing from jabber to ip phone i am facing the same issue but when i am calling from ip phone to jabber call is working fine. what do you suggest to check on firewall side or do u think it is some configuration issue

[hsood]

Hi Muazam,

Since , SIP inspection is disabled and there is no issue in SIP IP phone to SIP IP phone call, I am assuming that it could be an issue with the routing since the jabber phone would take  a data IP of your machine which might not be allowed again on the firewall.

Would recommend to check the firewall inside interface captures again to check this out.

Regards,

Hitesh

[muazam ali]

Hi Hitesh,

i would like to see local contacts not LDAP contacts on IP phone, do i need to manually add every number or it can configured to automatically ?