Transformation Masks
Dialing transformations allow the call-routing component to modify either the calling (initiator) or called (destination) digits of a call. Transformations that modify the calling number (automatic number identification [ANI]) are calling party transformations; transformations that modify the called party (dialed digits) are called party transformations. Dialed Number Identification System (DNIS) is a public standard implemented in the PSTN for modifying called party numbers.
Digit translation is possible in CUCM mainly through the Transformation Mask feature that can be found in various configuration options in CUCM (for example, route list details and translation pattern). CUCM overlays the calling or called party number with the transformation mask so that the last character of the mask aligns with the last digit of the calling or called party number. CUCM uses the original calling or called party digit of the source number anytime the mask contains an X. The X acts as a binary OR function. If the number is longer than the mask, the mask will add extra digits to the original calling or called party pattern.
Figure 11-9 illustrates an approach typically used to change the calling party (ANI) of internal directory numbers when he or she makes calls that are routed to the PSTN. The five-digit extension of 45000 in Figure 11-9 is transformed into a ten-digit pattern for the purposes of caller ID (ANI) on the PSTN. There is a distinction between ANI and caller ID that I would like to point out. Caller ID (CLID) refers to the presentation of the calling party name and number, whereas automatic number identification (ANI) refers only to the calling number. The mask of 8086236XXX has been applied to 45000 in Figure 11-9, resulting in 45 being replaced with 36, while the first five digits of 80862 are prefixed before the number so that users connected to the PSTN can return phone calls to the presented calling party number.
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Figure 11-9 Transformation Mask Operation
Figure 11-10 illustrates the process in which a ten-digit number from the PSTN could be converted to a five-digit number using transformation masks. This process would be useful if the incoming called party from the PSTN gateway to CUCM was ten digits long, but incoming calls had to be converted to an abbreviated five-digit internal dial plan. Masks are always processed from right to left in CUCM. Transformation masks can be used to manipulate either the calling or called party number. A ten-digit pattern with a five-digit mask applied to it will result in a five-digit number. Figure 11-10 illustrates a ten-digit pattern with a five-digit pattern of 45XXX, which indicates that the last three digits will not change but the leading two digits will be set to 45, regardless of the incoming pattern.
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Figure 11-10 Transformation Mask Operation
Transformation masks are configurable at various CUCM configuration levels including route patterns, translation patterns, and route lists (per route group).
The calling and called party transformation settings are assigned to route groups in the route list details of the route list that the route pattern is pointed to. Route pattern transformations apply only when a route pattern is pointed directly to a gateway. Route patterns are normally pointed to a route list. Multiple route patterns can point to the same route list, but multiple route patterns cannot point directly to the same gateway. Inserting gateways into route groups allows the gateways to be used for many different route patterns.
Most intersite calls in private companies are routed over WAN links as Voice over IP (VoIP) calls, but routed over PSTN links if the WAN is down or congested. Distributed Multi-Cluster Call Processing architectures require call routing to be configured for all intersite calls that cross cluster boundaries. Intercluster calls are routed over trunks in CUCM. H.225 trunks, SIP trunks, nongatekeeper-controlled intercluster trunks, and gatekeeper-controlled intercluster trunks are covered in more detail in Implementing Cisco Unified Communications Manager, Part 2 (CIPT2) Foundation Learning Guide.
The call routing between sites that belong to different CUCM clusters is normally configured to have a PSTN route group and an IP WAN route group. The IP WAN route group includes one or more intercluster trunks (ICT) or SIP trunks, while the PSTN route group contains one or more gateway endpoints (MGCP) or gateway devices (H.323/SIP) that connect the cluster to the PSTN. CUCM will forward the internal abbreviated dialing extension number if proper digit manipulation has not been configured. CUCM routes calls to a gateway in the PSTN route group. Proper digit manipulation requires that the calling pattern reflect a phone number that can be called back on the PSTN and that the dialed digits are properly routed.