When high call volume is active on the application server, the server will eventually hang and requires a restart. No errors are logged in the application logs and the application logs stops whenever the tomcat hangs and the log is resumed after Tomcat is restarted.

When we analyzed the trace log, we found the IVR disconnected the call but it did not disconnect immediately, it was removed from tomcat post idle timeout of 30 minutes (SCESession removal). IVR is sending END signal (/SG_APP/END and /MY_APP/END) but the call did not get disconnected immediately.

Line 292727: 13/07/2018 11:26:15:624 DEBUG - 8265571867C54715375D023049152FF6:/MY_APP : *** Reply for [/MY_APP/END] ***
Line 292728: 13/07/2018 11:26:15:624 DEBUG - 8265571867C54715375D023049152FF6:/MY_APP : 0:<?xml version="1.0" encoding="UTF-8"?>
Line 600081: 13/07/2018 11:57:00:936 INFO - 8265571867C54715375D023049152FF6:/MY_APP : HTTP Session lost removing SCESession 8265571867C54715375D023049152FF6
Line 600081: 13/07/2018 11:57:00:936 INFO - 8265571867C54715375D023049152FF6:/MY_APP : HTTP Session lost removing SCESession 8265571867C54715375D023049152FF6
Line 600082: 13/07/2018 11:57:00:936 INFO - 8265571867C54715375D023049152FF6:/MY_APP : SCESession Removed
Line 600083: 13/07/2018 11:57:00:936 DEBUG - 8265571867C54715375D023049152FF6:/MY_APP : Removing 1 session stack frames.
Line 600084: 13/07/2018 11:57:00:936 INFO - 8265571867C54715375D023049152FF6:/MY_APP : ** Popped Stack Frame [/MY_APP]

We found that the AvayaSessionTermination Servlet signal does appear on the IVR application from AEP/MPP level to release the call.
Hence the call remained active until it is eventually removed due to tomcat post idle timeout (30 minutes for MY and 10 minutes for Singapore).

Below is an example of AvayaSessionTermination Servlet being called:

Line 1665: 13/07/2018 10:16:09:072 DEBUG - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : *** Reply for [/SG_APP/END] ***
Line 1666: 13/07/2018 10:16:09:072 DEBUG - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : 0:<?xml version="1.0" encoding="UTF-8"?>
Line 1686: 13/07/2018 10:16:09:075 INFO - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : Removing session from AvayaSessionTermination Servlet
Line 1687: 13/07/2018 10:16:09:076 INFO - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : Termination URL reply : <?xml version="1.0" encoding="UTF-8"?>
Line 1691: 13/07/2018 10:16:09:076 INFO - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : HTTP Session lost removing SCESession 0D4ABFD7A3D3B4B954EDAE936C793E7A
Line 1691: 13/07/2018 10:16:09:076 INFO - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : HTTP Session lost removing SCESession 0D4ABFD7A3D3B4B954EDAE936C793E7A
Line 1692: 13/07/2018 10:16:09:076 INFO - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : SCESession Removed
Line 1694: 13/07/2018 10:16:09:076 INFO - 0D4ABFD7A3D3B4B954EDAE936C793E7A:/SG_APP : ** Popped Stack Frame [/SG_APP].

Is there something that I am missing here?

There are 2 possible reasons why the termination servlet was not called. One is the AVB/platform did call it. The other is the app server is too busy to process the request. For reason one, you would have to look into the AVB/platform log to see if the call was indeed disconnected and AVB issue a http request to the termination servlet. For reason two, you can take a look at the Tomcat localhost_access log which logs the incoming requests.

Thank you for the response Wilson. Can I ask you to help clarify so that my understanding is correct,

For reason (1) AVB/platform, this AVB/platform is referring to the Voice Portal?

Yes, that EP/VP. The logs name sessionlog*.log would be of interest to look at.