Thanks for reply.
Yes i aware maxcall value is in milliseconds. in that log which i mentioned don't have any maxcall value, it was set it as NULL. And it was only one call but ringing 7 times to SIP user due to null value of maxcall.
Here my question is maxcall is mandatory or not. If mandatory what would be perfect value for queue system.
Because if i set it as NULL then Calls disconnected immediately with one single ring. If i set it as longer then call disconnection taking very longer (It means SIP user got ringing after customer line got disconnected. My guess due to that high maxcall timer(20000 msec= 20 sec) it's keep ringing even if original call disconnected).