Before you can use the PSTN enabled ser.cfg you we must take care of a few remaining items. The first thing to do is copy the following files which the permissions module will look for upon server startup.

cp [ser-source]/modules/permissions/config/permissions.allow /usr/local/etc/ser

cp [ser-source]/modules/permissions/config/permissions.deny /usr/local/etc/ser

The last thing to take care of before you can use the PSTN gateway example, namely add a record to the MySQL trusted table. To do so you can issue the following SQL command by opening up your MySQL terminal.

[#] mysql u ser p

-- enter your mysql password --

mysql> use ser;

mysql> insert into trusted values (192.0.2.245, any, ^sip:.*$);

NOTE: The above INSERT SQL statement tells SER to allow any protocol (udp or tcp) from IP 192.0.2.245 (the IP of the PSTN gateway) to send any message to SER without being challenged for credentials.

NOTE: You must restart SER when altering the trusted table because the entries in this table are read only during server start up. Alternatively, you can use the FIFO command: serctl fifo trusted_reload

Now that your SIP router is PSTN Enabled you can start dialing domestic and international destinations. A word of caution is that many PSTN gateways perform their own accounting. You must be certain that SER is properly record-routing all messages to guarantee that BYE messages are sent to the PSTN gateway.

If a BYE message is not delivered to a PSTN gateway then you run the risk of additional toll charges because the PSTN circuit could be left open.