Sometimes it is necessary to have a phone dial a preset destination any time it goes off hook. This is common in lobby phones, or the push button intercoms used on doors and gates. This configuration is called Private Line Automatic Ringdown, or PLAR. The way Cisco has handled this is to have you create a calling search space (CSS) that contains a single partition that contains an empty translation pattern with the called party mask set to the destination you want the phone to ring to. While this works fine, it can require a huge number of partitions and calling search spaces if you need to configure a lot of PLAR phones.
Starting with CUCM 8, there is is a feature that allows you to achieve this with only 2 partitions and Calling Search Spaces, plus translations, no matter how many source/destination sets you have. This significantly reduces complexity and the likelihood of error. A configuration example follows.
Create 2 partitions, “PLAR Pilot” and “PLAR Patterns.” We will use PLAR Pilot to hold the single empty translation pattern, like in the classic configuration.
Now create two calling search spaces, PLAR Device, which contains only the PLAR Pilot partition, and PLAR Patterns, which contains only the PLAR Patterns partition.
The “Route Next Hop By Calling Party” option looks for a match in the CSS Partitions using the calling number rather than the called number.
Next, we determine the calling number, and the number is should call to. In this case, DN 3300 should call 3000 when it is taken off hook.
Assign the PLAR Device CSS to the phone/line 3000.
When 3000 goes off hook, it matches the blank pattern in PLAR Pilot. The call then looks for a match for the calling number 3000 in the PLAR Patterns partition, and matches the 3000 translation pattern. The translation pattern then sets the called number to 3300, and proceeds to ring the phone.
This configuration can greatly simplify the configuration of PLAR on a CUCM cluster, requiring only 2 partitions and calling search spaces, and one translation pattern per source/destination and one for the initial match.