Ringback Issue with Blind Call Transfer

[Suresh Subramanian]

Hello,

we are facing ringback issue when inbound external call to the cisco phone is transferred back to another extenal number.

Call Flow: Cisco phone----CUCM-----SIP-----CUBE----SIP----ITSP.

Investigation done:

- if both PRACK & EO are disabled, we hear the ringback on blind call transfer. In fact it is continuous ringback tone. Though the other end rejects the call, we hear this continuous ringback. Also, we don't hear any announcement played from provider side.

- If PRACK enabled & EO Disabled, same as above

- if PRACK disabled & EO enabled, same as above

- if both either PRACK and Early Offer are enabled, we don't hear the ringback during blind call transfer but we hear announcement from provider

To address both the continuous ringback & provider announcement issues, we enabled the MTP on the SIP Trunk in CUCM to CUBE.

Is there anything we can do to address these issues instead of enabling MTP on the sip trunk for all calls?

I also tried resetting the ANN and assigning dedicated ANNs in the SIP Trunk MRGL.

any help would be much appreciated. Thanks.

[Suresh Subramanian]

When looking at the logs which was collected with MTP checked, I don't see the Reinvites coming to CUBE from CUCM for Call Hold & MoH and we heard the ringback when the call was transferred. but the calling party still heard the MoH. I couldn't understand this behaviour.

calling: 918066914754

called: 5816280216 (mask: 6048959000)

Transferred to 919886001322

[Ayodeji Okanlawon]

This is perfectly normal..

When MTP is involved, CUCM keeps the media leg between MTP and CUBE from beginning to end; when necessary, it just updates another leg of MTP between MTP and CUBE. However it looks like you have disabled UPDATES on your sip profile, so you wont even see that in the logs.

The called party should generate ring back. So that means itsp in this case.Yes packet captures will tell us if Cube is receiving ring back or not. I looked at a similar issue a few weeks back.

Does ring back work, if the transferred destination is an internal extension?

[Suresh Subramanian]

yes, when transferring the external call from one ip phone to another ip phone, we hear the ringback at the original calling party phone.

We've blocked the update for an external voicemail issue.

[Ayodeji Okanlawon]

Okay please send the captures once you have done them

[Ayodeji Okanlawon]

Okay..You didn't mention what you get when you transfer the call though (silence)? or announcement from ITSP?

We will need to enable packet capture on CUBEs..

Packet capture from cube.

1. Configure capture profile

               !
               ip traffic-export profile TAC mode capture
               bidirectional
               !

               interface fa0/0  ----> Interface which routes the traffic to ITSP
               ip traffic-export apply TAC 99999999

2. Capture traffic with these exec (enable) level commands

Note: The exec cmds don’t appear until a profile has been configured

router#traffic-export interface fa0/0 clear
router#traffic-export interface fa0/0 start

Do your test and after test is complete

router#traffic-export interface fa0/0 stop

3. Export the pcap file to a server

router#traffic-export interface fa0/0 copy ftp://x.x.x.x/capture.pcap

[Suresh Subramanian]

ah ok, it was complete silence on the original calling party when the final destination was actually alerting.

when the transfer is completed and the destination is being alerted, is it ITSP responsibility to provide the ringback to original calling party?

if so, will we able to hear it with the CUBE packet captures?

Also I'm wondering who is generating the ringback when MTP is checked. the same ITSP or the ANN in the trunk?

[Suresh Subramanian]

Here are the pcap & debug collected for the nonworking call.

calling: 918066914754

CIPC_called: 5816280216 (mask: 6048959000)

Transferred to 919886001322

when the CIPC put the first call on hold, the calling party heard the MoH. when the CIPC calls the 2nd number, it hears the ringback song but when the transfer is completed, the calling party didn't hear the same song. Please check.

Renamed the pcap file extension to steu2.pps. please change the extension back.

[Ayodeji Okanlawon]

Suresh,

Its been a long day..so sorry for the late reply. Been busy.

I have looked at the captures. Can you confirm the (I love you my sweet heart song) is the ring back that should be played during the final transfer?

[Suresh Subramanian]

Hey Deji, same here. Exhausted. 

Yes, you are right, that is the song should be heard by original calling party.