UCM6510 doesn't send SIP 200 OK, what happen


Hi guys
I have a UCM6510 works as Call-Center and office phone also. Maximum concurrent calls is about 20~25 (all types)

We receive about 1000 - 1500 calls a day from our customers. But 10% is failed call.
Most of failed call in which customer can not hear anything. UCM6510 IP is And the SIP Provider server IP is

I am using network troubleshooting tool on UCM6510 to capture packet on interface connect to SIP provider, then i see that for failed calls, UCM6510 doesn’t send SIP 200 OK after sending “trying” message.
I m using the newest firmware


Need the pcap file, not an image. On the surface, it looks like the provider sent a cancel to the INVITE, but not enough info to know that for certain.


Hi Ipneblett, here is the pcap file. Let see the message time. UCM send trying and then after 24s, it doesn’t send 200 OK. Customer don’t hear anything so they hang up, at that time SIP provider send CANCEL.
I spend 3 whole days to see this issue, i am sure the problem come from UCM



And it happen similar for outgoing call also. When concurrent calls reach more than 20, it is very easy to get failed call ( in and out). I took a test call from extension 5555 and i see UCM didn’t send 200 OK to 5555 in 30s after sent trying message.

And for outgoing call failed, there is no records on UCM CDR

capture file: https://drive.google.com/open?id=1BgGurilVnDlhgztTwyQNY9kJxtt2TiZG


I see that phone do not respond not UCM, not sure but maybe have bug ?


I think we are only seeing one interface. Please advise network mode.


Trace : https://drive.google.com/open?id=1Jj-ErfrAXH5ldflCLZ6osxBlwL4pmNnG

The above trace only shows 2 error codes above 400
packet 58616 error 487 request terminated * ( I have only looked at this packet )
Packet 71135 error 487 request terminated

  • The ucm is not sending a 200 ok because the cancel came in even before a 180 ringing after the cancel the ucm sends a 200 ok its has received the cancel and then 487 that is has began to tear down the session. So there is no 200 as the call was never established.

On this call it is clear the calling party cancelled the call before the ext on ucm could answer and there is no problem on the UCM side

  • also what is the number of similtaneous calls your provider allows you on your sip trunk.
    ** In addition Marcin can be correct the phone is not ringing due to a bug what is the end point ( make model firmware) this with explain why the delay of no 180 ringing
  • when the call comes in is that end point physically ringing under active calls on the ucm what does it show the call.


Hi guy
Did you see the message time, normally right after UCM send trying, it should send 200 OK to provider. Because i set up when caller call to UCM, it will play IVR (no busy, no unavailable in this case).
Let me show you a normal call:
06:54:18 send trying
06:54:18 send 200 OK

But for 3 failed calls i showed above, you can see UCM send trying and doesn’t send 200 OK after 24s. That is so long time then SIP provider send CANCEL. Of course, in this case caller can not hear anything in 30s, they hang up.


Hi man, you never focus on the problem. My network mode is dual. LAN1 for company LAN, LAN2 connect to SIP provider.
How come network mode can cause this issue. Remember that i capture right on UCM. It doesn’t send message we need, so no other network device can stop it.


Hi man
For outgoing call failed, i am talking about this call. I tested it, and after 30s, i don’t hear anything, i hang up, that why the phone send CANCEL


No, I clearly focused on the problem; hence why I asked what network mode you were operating in as you never stated it and it makes a difference. It might be helpful to see a capture using both interfaces.

I see the firmware version is, which is the most recent. Was the problem evident on an earlier version?

Please show screen shot of SIP Settings, NAT page.



So the incoming call goes to the IVR and not and endpoint.

if so when the call reachs the IVR the ucm does not send any options to the end point.

in any event you will not get the 180 ringing and then the 200ok for that transaction as there is no ringing

is you dtmf set to rfc2833 on the UCM

The above sucessful call you posted is made from another incoming number 091 734534 and the failed call was made from 091 2426080

it is possibel the caller from the fist call (091 2426080) get to the IVR the DTMF is mismatched the caller hear or even when hearing presss soem keys gets no response andthen puts down hence the cancel.

what happens if you sned the call directly to the an endpoint do you have access the number 0912426080 to test with that exact endpoint /line to your ucm.



The IVR does not send any options. There would be an announcement in most cases which prompts the caller to enter the option for the destination desired.

There will be no DTMF either as the 200OK/SDP was absent which means that the call has yet to be established and an audio channel has yet to be defined. Regardless of the DTMF type used, the IVR is not connected and therefor unable to do anything about it. The 200OK is conditioned upon a device/endpoint, be it a phone, Q or IVR, etc. seeing the INVITE and reacting to same so that the response is generated back to the originator.

24 sec is a long time waiting for the response, hence; why I would like to see both sides of the interface as well as the NAT and perhaps inbound route for the DID.


perharps this will explain a little betetr to you on the options the ucm will send after the IVR is played.



Another possible reason for delayed response is DNS you may want to check the DNS the ucm is using.


Sorry, but this doesn’t really tell me anything. The options are being sent to something on the same subnet as the LAN. I see nothing other than an OK going back to the SIP server and the audio stream starts some 11 seconds later.


thats a sceenshot of a successful call to an IVR from another ucm pabx showing what I meant by I did not see the options being sent from the ucm after the IVR.

Non the less we being side tracked from the original issue …

My 2 cents is that the call has reached the ivr where the caller does not hear anything or if he does hear the prompts but gets no response. the other possibility is the DNS being used by the UCM. The call does reach the IVR it is why the 100 trying follows in that time the caller hangs up generating the cancel before anything else can happen.

Should this not be the case it may be more productive letting us know what is happening rather than what is not happening …what is not happening is quite obvious.


in his capture and looking at the call he referenced, there is no audio as there was no 183 or a 200. The call was never established and as such, the SIP server can only send a cancel on a timeout as a BYE is not applicable.


I used firmware when i got this issue. After upgrade to, nothing changes. I also change the UCM6510 appliance, but it still happen


The incoming failed call can not reach IVR, and they don’t hear anything (i also call back them to check)