Called Party Transformation Patterns: Example and Validation

Scenario: We have a CUCM cluster servicing disparate geographic locations and want to use the Local Route Group (LRG) feature for PSTN call routing.  We also want to ensure that PSTN calls are routed to an alternate gateway if the local gateway is not available.  To do this, we will globalize PSTN calls, apply call routing, and then use Called Party Transformation Patterns to localize calls at each gateway based on PSTN requirements.

Call Flow:

1. We have a Translation Pattern of 9.555XXXX configured in the PSTN partition for Site 1.  This translation globalizes the call by discarding pre-dot digits and applying a prefix of +1202.  The end result is that a user at Site 1 dials a 7-digit PSTN pattern (9.555XXXX) and the call is globalized to an E.164 pattern (+1202555XXXX).
2. The Calling Search Space (CSS) applied to the translation contains a partition for cluster-wide, globalized Route Patterns.  In this example, we have configured a default Route Pattern of +! that routes all globalized PSTN calls to a standard, cluster-wide PSTN Route List.
3. Our standard, cluster-wide Route List is configured to prefer the “Standard Local Route Group” followed by a Route Group associated with the PSTN gateway in Site 2.

At this point, we have the following:

User dials a PSTN pattern -> Call is globalized to an E.164 pattern -> Call is routed to a PSTN gateway

Without further configuration, a local call to 5551000 at Site 1 will first be sent to the local gateway as +12025551000; however, the local PSTN requirement is 7-digit dialing.  If the local gateway were unavailable, this call would be routed to Site 2; however, the PSTN requirement for routing the call out of the Site 2 gateway might be 1+10 digit (long distance) dialing.  In either case, we need to localize the call and verify the digit manipulation.

To route local calls out of the local gateway at Site 1 as 7-digit local calls, we add the following CUCM configurations:

1. We have a Called Party Transformation Pattern of +1202.555XXXX configured in the Xform-DNIS partition for Site 1.  This transformation localizes PSTN calls by discarding pre-dot digits. We have a CSS used for outbound transformations at Site 1, which contains the Xform-DNIS partition for Site 1.
2. The PSTN gateway for Site 1 is assigned to a Device Pool.  The Called Party Transformation CSS applied in the Device Pool associated with the PSTN gateway for Site 1 specifies the CSS used for outbound transformation at Site 1.  The end result is that E.164 patterns (+1202555XXXX) for local PSTN calls at Site 1 are localized to 7-digit patterns (555XXXX) before they are handed off to the PSTN.

Now we have an example of why and how you might use Called Party Transformation Patterns but we want to know that it works.  As I said earlier, DNA is a great tool but it doesn’t work for everything and it’s nice to verify that a configuration is working end-to-end as expected sooner rather than later in the build process, if possible.  You can still use DNA to verify the basic call routing; however, you won’t see the transformed number applied at the gateway in the DNA output.

Verify Digit Manipulation: To verify that proper digit manipulation is being applied when using Called Party Transformation Patterns as outlined above, you can use the “debug voice ccapi inout” IOS debug command.  Using the example above, let’s login to the local PSTN gateway for Site 1 and verify that localization works for local 7-digit calls routed to the local gateway:

In the debug output, you can see that the Destination and Called Number have been localized to 7-digit patterns.  Using the logic/approach defined above, we would just need to add configurations to complete the CUCM build/deployment.