CUCM Call Routing (part 1): Four components of dial plan

One of the most important aspects of any voice system is the call routing component. Cisco Unified Communications Manager (CUCM) call routing uses four important components:

• Route Pattern

• Route List

• Route Group

• Gateway/Trunk

A route pattern is a configured numeric pattern range. After the route pattern is matched, the call is routed to the final destination. Route patterns can have various wildcard patterns as follows:

• X Matches one single digit (0-9, *, or #)

• ! Matches one or more digits

• [x-y] Matches one single digit within a range of possible digits

• [^x-y] Exclusion range. Matches any one single digit other than the range of configured digits

• @ Matches any dialed pattern within the possibilities of the NANP (North American Numbering Plan)

• . Terminates the access code. Use for digit stripping

• # Terminated the inter-digit timeout. Very useful for International calls.

In the following NANP PSTN (Publish Switched Telephone Network) example, a 9 is used as an access code for all outgoing phone calls:

• 911 Emergency Call Routing

• 9.911 Emergency Call Routing prefixed with an access code of 9

• 9.[2-8]11 Three digit service codes

• 9.[2-9]XXXXXX Local 7-digit dialing

• 9.[2-9]XX[2-9]XXXXXX Local area code 10-digit dialing

• 9.1[2-9]XX[2-9]XXXXXX Long Distance 11-digit dialing

• 9.011! International dialing

• 9.011!# International dialing

The 911 and 9.911 route patterns should use CUCM’s “Urgent Priority” option. The urgent priority option will force a call routing decision even if there is an overlapping dial plan configured on CUCM. We will explore a situation where someone configured an extension of 9112, while the 911 route pattern has the Urgent Priority option provisioned. CUCM performs digit-by-digit analysis from a SCCP (Skinny Client Control Protocol) controlled phone. As soon as 911 is received, the call will be routed before the final 2 can be dialed. Normally, an overlapping dial plan entry will result in a 15 second wait before the call is routed. CUCM must wait to see if more digits will be dialed because there are multiple matches against the dialed pattern in the call routing database. The 15 second timer can be changed by modifying the T302 time in the CUCM service parameters. Cisco best practices recommend setting this timer to 5 seconds. The next blog entry will continue the coverage of the above dial plan and explain the Route List, Route Group, and Gateway/Trunk concepts.

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