Call Routing Part 9: Tail End Hop Off (TEHO)

In the last blog, we explored an inter-site call routing scenario where 5-digit dialing was used over the IP WAN between Cisco Unified Communications Manager clusters (trunks) and 11-digit dialing was used to route inter-site calls over the PSTN. Since inter-site call routing over the IP WAN circuit between New York and San Jose was so successful, the company has decided to route long distance PSTN calls from New York to the local San Jose area code 408 through the IP WAN circuit. Call routing in New York is currently setup so that all 11-digit long distance numbers match the 9.1[2-9]XX[2-9]XXXXXX Route Pattern. We will add a new Route Pattern for all calls destined to 9.1408[2-9]XXXXXX. The new Route Pattern will be pointed to a Route List called SJC_TEHO_RL (San Jose Tail End Hop Off Route List). The SJC_TEHO_RL will have two Route Groups. The first priority Route Group will be the WAN_RG used in the last blog. After the Route Group is added to the Route List, the Route List Details for the WAN Route Group will be modified. The Calling Party’s External Phone Number Mask should be set to On so the Caller ID (ANI) sent on the PSTN is the 10-digit phone number of the calling party. The Called Party Transformations section will have a Digit Discard rule of PreDot to strip out the 9. If 9 1-408-555-1212 is dialed, the DNIS string of 1-408-555-1212 will be routed over the trunk to the San Jose cluster. Prefix Digits of 9 will be prefixed on this route Group so the call that is routed to San Jose is 9 1 408 555 1212. This will ensure that the 9.1[2-9]XX[2-9]XXXXXX Route Pattern in San Jose is matched. The last paragraph assumes that San Jose must route 11-digit phone calls for local 408 area code dialing. If the San Jose PSTN provider required local 10-digit dialing to route calls to the PSTN, a Called Party Transformation Mask of XXXXXXXXXX (10 X’s) would be required to convert the 11-digit pattern to a 10-digit pattern. The final result would be 9 408 5551212 forwarded from the NYC cluster to the San Jose cluster. Let’s examine a scenario where San Jose, California’s PSTN provider required 7-digit local calling. The Called Party Transformation Mask in this scenario would be configured as XXXXXXX (7 X’s). This would ensure that we drop the long distance code (1) and the area code (408) from the dialed digits. Alternatively, the San Jose cluster could have translation patterns configured to match on patterns and convert those patterns. The next blog will continue the call routing conversation and discuss translation patterns.


Copyright © 2008 IDG Communications, Inc.

The 10 most powerful companies in enterprise networking 2022