Parameter: Filter by Local Port
From TBwiki
The Filter by local port parameter is used to determine if the NAP will accept only incoming calls arriving on one of it's assigned SIP Transport Server. (This option has no effect on outgoing calls on this NAP)
When this parameter is enabled
When this parameter is enabled (which we highly recommend), only incoming calls received on a SIP Transport Server assigned to a NAP will be considered as coming from that NAP.
When this parameter is disabled
When this parameter is disabled (not recommended), an incoming call received from this NAP's proxy will be considered as coming from this NAP no matter which local SIP Transport Server the call was received on (including from a SIP Transport Server that is not assigned to the NAP).
