Determining Route Patterns in Cisco Unified Communications Managers

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When multiple route patterns match a dialed number in Cisco Unified Communications Manager (CUCM), the system determines which pattern to use by following a specific algorithm that takes into account several factors.

The algorithm used by CUCM is called digit analysis, and it involves the following steps:

1. Digit Collection: The CUCM collects all the digits that the user dials and identifies the type of dialing. For example, if the user dials a local call, the system identifies it as a 7-digit dialing pattern.

2. Digit Manipulation: The CUCM can manipulate the digits before analyzing them. Digit manipulation can include adding, removing, or changing digits to meet the requirements of the dial plan.

3. Digit Analysis: The CUCM compares the collected and manipulated digits against the route patterns that are defined in the dial plan. It starts with the most specific route pattern and works its way to the least specific. It compares the dialed digits to each route pattern's mask, which is a string of characters that identifies the pattern.

4. Best Match Selection: When multiple route patterns match the dialed digits, the CUCM uses a set of criteria to determine the best match, as follows:

• Longest Match: The CUCM selects the route pattern with the longest match, meaning the pattern that matches the most significant number of digits. For example, if the user dials 5551234 and two route patterns match it, one with the pattern 5551XXX and another with the pattern 555123X, the CUCM selects the second route pattern because it matches more digits.

• Closest Match: If two or more patterns match the same number of digits, the CUCM selects the one with the closest match. The closest match is determined by comparing the dialed digits to each route pattern's mask and selecting the pattern that has the smallest number of wildcard characters (X).

• Precedence: If two or more patterns match the same number of digits and have the same number of wildcard characters, the CUCM selects the pattern that appears first in the dial plan. The dial plan is ordered by priority, with higher priority patterns at the top of the list.

• Discard Digits: If a route pattern has the Discard Digits instruction, the CUCM removes the specified number of digits from the beginning of the dialed number and matches the remaining digits against the route pattern. If multiple route patterns match the remaining digits, the CUCM applies the previous selection criteria to determine the best match.

In conclusion, when multiple route patterns match a dialed number in CUCM, the system selects the best match based on the longest match, closest match, precedence, and discard digits criteria. This algorithm ensures that the CUCM routes calls efficiently and accurately, according to the dial plan's configuration.