No SS7 signaling in call trace on remote IMG

Symptom:

In troubleshooting a call processing issue on a Dialogic IMG Integrated Media Gateway or Dialogic BorderNet™ 2020 Integrated Media Gateway where the SS7 messages are needed, IMG call tracing is enabled; however, although one or both legs of the call uses SS7 signaling, no SS7 messages appear in the trace. 

All other signaling - SIP, H323 or ISDN -  is displayed in the trace, along with all of the routing and translation information, but the SS7 signaling is missing.

Reason for the issue:

The above behavior is normal for an IMG whose CICs are controlled remotely by another IMG.  

On an IMG that terminates an SS7 link, call tracing will display all components of the call, inlcuding all signaling, routing and translation information.   

On an IMG whose CICs are controlled remotely by another SS7 signaling IMG, there is no SS7 signaling, therefore it cannot be printed in the call trace of this IMG.

Summary:

• The SS7 signaling will be printed in the call trace of the IMG that terminates the SS7 link

• All other components will be printed in the call trace of the remote IMG. 

Solution:

In order to view SS7 signaling for calls on remotely controlled CICs, it is necessary to enable call tracing on both the remote IMG, as well as the SS7 signaling IMG.  Then, once the call is identified in the call trace of the remote IMG, the SS7 signaling for that call can be located in the trace of the SS7 signaling IMG.

In the following example, an SS7 IAM comes in to IMG node 1.  The CIC number in the IAM refers to a CIC that is physically on IMG node 3.  So via Ethernet, using a proprietary protocol, the pertinent parameters of the IAM, such as Called Party and Calling Party Address, are passed from node 1 to node 3.  Then Node 3 routes the call to a SIP endpoint.  To match the call in both traces:
 

1. In the remote node call trace, find the RFS for the call.  In this case we could search for the specific DN, for example:

2. In the same call trace, immediately preceediing the RFS, will be a setup indication that was forwarded from the SS7 signaling on the SS7 node.  Make a note of the timestamp of this event:

3. In the SS7 node  call trace, using the timestamp in step 2, find the corresponding IAM that triggered the Setup Indication.  In this case, the IAM was logged on node 1, a fraction of a second before the setup was forwarded to node 3.  We can also see that the call came in on CIC 496, which will correlate to the CIC on bearer 0 channel 1 on node 3:
    
   NOTE: the call reference number, in this case 00001, will usually vary between nodes, and therefore cannot be used to match the call between the traces of both IMG's.  That is why the timestamp and CIC number are used.

In another example, for a call that originates on node 3 using SIP and then is routed to an SS7 CIC on node 3:

1. Again, in the remote node call trace, find the RFS for the call.  Note that the node id in the call trace is node 3, which is where the INVITE was received.  In the previous example, the node id was 1, where the IAM was received:

2. Further along in the same call on node 3, 03:00001, find the line that correlates to where the call was sent, an "Outseize Control," from the remote node to SS7 on node 1:

3. In the SS7 node call trace, using the timestamp in step 2, find the corresponding "Outseize Control" and resulting IAM:

All SS7 messages for this call can now be located using a combination of the timestamp, point codes and CIC number.

Product List

Dialogic IMG 1010 Integrated Media Gateway
Dialogic IMG 1004 Integrated Media Gateway
Dialogic IMG 2020 Integrated Media Gateway (IMG 2020), formerly referred to as Dialogic BorderNet™ 2020 Session Border Controller

Glossary of Acronyms / Terms

RFS = Request for Service
DN = Dialed Number