[Users] port setting

[unplug]

Hi,
Can I add some more ports for openser other than 5060?  Is there any
port range using in openser?

I have set one more port 6060 in my configuration file as below.
listen=IP:5060
listen=IP:6060
port=5060
children=4

Users using port 5060 is working fine.  However, those users using
6060 will experience call drop around 1 minute after connection.
In the log from ngrep, I find message 408.
SIP/2.0 408 Request Timeout
It may the cause to drop the call.  However, I have no idea why 6060
will get a call drop problem.  Does it any other reason for it?
Thanks for help.