Ghost Calls Reported When User Does Not Answer Call

Asset ID:	1-72-2118015.1
Update Date:	2017-05-15
Keywords:

Solution Type Problem Resolution Sure

Solution 2118015.1 : Ghost Calls Reported When User Does Not Answer Call

Applies to:

Acme Packet 4500 - Version S-Cx6.4.x and later
Information in this document applies to any platform.

Symptoms

Service Provider SBC customers were making international calls and when calling party abandons the call while its ringing, the called user is later called several times after a few minutes without an effort from the A side (Ghost call).

When the called party answers these ghost calls there is no audio.

If the calling party carrier does a search they see only the failed call and not subsequent attempts. When we look for traces in Service Provider network (where we have SBC) we see that several calls are initiated from the SBC to three of the soft switches with the same call-id.

So, in summary, one call comes to SBC, goes to one soft switch. During ringing calling party abandons (send a cancel, which is responded by 487 Request Terminated). After some time SBC sends another invite to second soft switch with same call-id and then the third.

When calling party disconnects the call (while its ringing), the Called party receives the same call, and when answered there is no audio at all.

Cause

We checked wireshark traces and found the subsequent invites being generated by SBC after the original call was terminated by CANCEL

sag

As per local-policy, call are getting routed through a Session Agent Group as below:

session-group
                       group-name SAG_1
                       description
                       state enabled
                       app-protocol SIP
                       strategy RoundRobin
                        dest
                               xx.xx.xx.xx
                               yy.yy.yy.yy
                       trunk-group
                      sag-recursion enabled
                      stop-sag-recurse 401,404,407-408,480,484,486

The first call is routed to destination xx.xx.xx.xx, and when the call is unsuccessful (Cancel or 487 request terminated is received), as per recursion configuration, call is again routed by SBC to another destination in SAG : yy.yy.yy.yy.

If in the SAG configuration, we add code '487 in "stop-sag-recurse", this call will not be routed or subsequent attempts will not be made to the next destination in the list.

Solution

Add code '487 in "stop-sag-recurse" so that SBC does not make subsequent attempts in case of CANCEL.

References

<NOTE:1598273.1> - What Log Files are Required when Opening a Service Request with Acme Packet Regarding Call Flow Issues

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