Private Line Automatic Ringdown

Private line automatic ringdown (PLAR) is used when a phone should dial a predefined number as soon as the phone goes off-hook. PLAR is typically used with button-free security phones in elevators and stairways.

Implement PLAR in CUCM by following these steps:

Step 1 Configure a translation pattern where the pattern is empty (null string pattern), and put it into a partition.

Step 2 Configure the number to be dialed by the PLAR-enabled phone in the called-party transformation mask of the translation pattern.

Step 3 Configure the first line of the phone that should use PLAR with a CSS that includes only the partition that was applied to the translation pattern.

Step 4 Make sure that the CSS of the translation pattern has access to the transformed number. The translation pattern CSS is used when making the call-routing decision for the translated number.

When the phone goes off-hook, the off-hook event triggers call processing (digit analysis) on CUCM, where the null dialed string matches the translation pattern and is translated to the PLAR number. The call is then extended toward the PLAR destination. CUCM performs digit analysis as each digit is received from the phone, starting with the off-hook event. Different call-processing protocols (SIP, Skinny Client Control Protocol [SCCP], H.323) and calling methods send their dialed digits in different manners (enbloc or digit by digit), and thus the way in which a call is routed with an overlapping dial plan. This information is covered in more detail in Chapter 7, "Endpoints."

In Figure 13-27, a null-string translation pattern is created and put into partition PLAR1234. The called-party transformation mask is 1234. The translation pattern has a CSS assigned that includes partition Phones (the partition of destination 1234).

Figure 13-27 PLAR Example

CSS:

PLAR1234

Phone 1

User Goes Off-Hook

Translation Pattern: "" (Null String)

Partition: PLAR1234

Called Party Transformation Mask: 1234-

CSS: Phones

DN: 1234 Partition: Hidden

Partition: Phones

DN: 1234 Partition: Hidden

Partition: Phones

Phone 1 is configured with a CSS that contains the PLAR1234 partition (the partition of the translation pattern).

Two phones exist with DN 1234: Phone 2 is in partition Phones, and Phone 3 is in partition Hidden.

When Phone 1 goes off-hook, the null-string pattern is matched, and the translation pattern transforms the dialed null-string to 1234 and sends a call-routing request to CUCM. This request uses the CSS of the translation pattern (Phones) and therefore finds only a single match (Phone 2). The call is extended to Phone 2.

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