Transformation Masks

Dialing transformations allow the call-routing component to modify either the calling number or the dialed digits of a call. Transformations that modify the calling number are calling-party transformations; transformations that modify the dialed digits are called-party transformations.

Calling-party transformation settings allow you to manipulate the appearance of the calling-party number for outgoing calls. A common application of a calling-party transformation is to use the company external phone number of a calling station in place of the directory number (DN) for outgoing calls. The calling-party number is used for Calling Line Identification (CLID). During an outgoing call, the CLID is passed to each PBX, CO, and interexchange carrier (IXC) as the call progresses. The CLID is also delivered to the calling party when the call is completed.

Note

Caller ID is also referred to as Automatic Number Identification (ANI).

Called-party transformation settings allow you to manipulate the dialed digits, or called-party number, for outgoing calls. Examples of manipulating called numbers include appending or removing prefix digits (outgoing calls), appending area codes to calls that are dialed as seven-digit numbers, appending area codes and office codes to interoffice calls that are dialed as four- or five-digit extensions, and suppressing carrier access codes for outgoing calls.

When configuring calling- or called-party transformations, a transformation mask operation allows the suppression of leading digits, the change of some digits while leaving others unmodified, and the insertion of leading digits. A transformation mask requires two pieces of information: the number that you want to mask and the mask itself.

In the transformation mask operation, Cisco CallManager aligns the number with the mask so that the last character of the mask aligns with the last digit of the number. Cisco CallManager uses the corresponding digit of the number wherever the mask contains an X. If the number is longer than the mask, the mask removes the leading digits. Figure 11-7 demonstrates the transformation mask logic.

Figure 11-7. Transformation Mask Logic

As you can see from Figure 11-7, the initial number (which could be dialed or caller ID information, depending on the type of transformation mask you choose) passes through the first transformation mask. By right-justifying the digits, CallManager passes the number 35453 through the first transformation mask. The digits match to the right-justified X wildcards, causing it to pass through. CallManager prepends the additional digits to the left of the wildcards. As it passes through the second transformation mask, the numbers are again right-justified. This time, only the "35" digits pass through the X wildcards; CallManager replaces the rest of the string with the hard-coded digits to the left and right of the X wildcards.

Calling-Party Transformations

The example in Figure 11-8 shows the applicable settings for calling-party transformations and the order in which Cisco CallManager processes those instructions.

Figure 11-8. Calling-Party Transformations

You can configure three types of calling-party transformations in the call-routing component and on route lists:

• Use the external phone number mask, which instructs the call-routing component to use the external phone number of a calling station rather than its DN or the caller ID information. Without the external phone number mask, the calling number might appear as an extension number to the PSTN rather than a fully routable PSTN phone number. You can apply the external phone number mask on a line-by-line basis through the DN configuration screen on the device.
• The calling-party transformation mask allows the suppression of leading digits, leaves other digits unmodified, and inserts leading digits. As shown in Figure 11-8, the post-external phone number mask caller ID information is 2147135062. This passes through the calling-party transformation mask of 40885XX0000, which allows only the numbers "35" to pass through the XX wildcards. The resulting caller ID information is 4088535000.
• Prefix digits allow the prepending of specified digits to the calling number.

Cisco CallManager applies the transformations in the order that is presented in the example.

Tip

Remember, the calling-party transformations transform caller ID information (the number of the person who is calling).

Called-Party Transformations

The example in Figure 11-9 shows the applicable settings for called-party transformations and the order in which Cisco CallManager processes those instructions.

Figure 11-9. Called-Party Transformations

You can configure the following three types of called-party transformations in the call-routing component and on route lists:

• DDIs allow the discarding of digits in the dialed number. Such instructions are critical for implementing toll-bypass solutions. This need arises when Cisco CallManager must convert the long-distance number that the calling party has dialed into a local number. This number allows Cisco CallManager to pass the digits to the PSTN. You can also use DDIs to discard PSTN access codes, such as 9. Figure 11-9 demonstrates the removal of the 10-10-Dialing portions of the call to eliminate other long-distance carriers a user might choose to use.
• The called-party transformation allows the suppression of leading digits, changes the existing digits while leaving others unmodified, and inserts leading digits. Figure 11-9 illustrates the use of a called-party transformation mask consisting of ten "X" wildcards. This has the effect of stripping any preceding digit beyond the ten wildcards (in this case, CallManager strips the 9 and the 1). This might be necessary when configuring toll-bypass on the CallManager. For example, you might have a location that can access the 808 area code without incurring toll charges. You can configure the Cisco CallManager to route the call across the IP WAN then out a LEC.
• Prefix digits allow the prepending of one or more digits to the called number. Figure 11-9 illustrates prefixing an 8 to the front of the original dialed number. This might be required by a PBX at a remote site. For example, the call is transformed using the called-party transformation mask, then prefixed with an 8 and routed across the IP WAN. When the PBX at the remote site received the string, it recognizes the 8 as an outside access code and routes the call to the PSTN LEC.

Cisco CallManager applies the transformation in the order that is presented in the example.

Note

You could accomplish the same result shown in Figure 11-9 by simply applying a called-party transformation mask of 8XXXXXXXXXX. This is a more efficient method; the called-party transformations shown are used to illustrate the various transformations and the order in which the CallManager applies them.

Tip

Remember, the called-party transformations transform dialed-number information (the number that a user called).

Configuring Calling- and Called-Party Transformation Masks

You can apply calling- and called-party transformations at the route pattern, route list, or translation pattern configuration windows. The calling-party transformation setting that is used in route lists applies to the individual route groups that make up the list rather than to the entire route list. The calling-party transformation settings that are assigned to the route groups in a route list override any calling-party transformation settings that are assigned to a route pattern that is associated with that route list.

Because you can be more specific, network administrators usually apply transformation masks at the route list level. In this way, you can assign a different transformation mask for each route group in the route list. Transformation masks configured at the route list level have priority over those configured at the route pattern level because they are processed last. If you have configured a transformation at the route pattern level, it becomes more of a "global" translation, that is, as soon as the pattern is matched, the transformation takes effect. As the route pattern sends the call to the route list and the prioritized route group is chosen, the transformations relating to that specific route group apply second, transforming the already transformed number from the route pattern into whatever you have defined.

For example, in the network illustrated in Figure 11-10, a network administrator has two route groups created: the PSTN route group and the IP WAN route group. Both of these route groups contain multiple gateways that connect to their respective networks. When Cisco CallManager forwards a call to a gateway in the PSTN route group, the network administrator applies a mask that transforms the number into an E.164-compliant phone number. However, when Cisco CallManager uses a gateway from the IP WAN route group, Cisco CallManager leaves the number as a four-digit extension.

Figure 11-10. Transformation Network Design

Transformation Example

Figure 11-11 summarizes how transformations to the called-party (dialed digits) and to the calling-party numbers are made within Cisco CallManager. In Figure 11-11, a user dials a number to which Cisco CallManager first applies a calling-party transformation ("calling party" refers to the person who originated the call). This action changes the caller ID number that is displayed on the destination phone. Cisco CallManager then applies a called-party transformation to change the number that is dialed.

Figure 11-11. Called-Party Transformations

The two transformations are explained in the figure and, for user A specifically, in the following steps: