Discard Digit Instructions

Discard Digit Instructions (DDIs) allow conversions of a dialed number specific to a national numbering plan. Typically, companies use a route pattern such as 9.@ to access the PSTN. However, only the internal IP telephony network uses the 9 access code to reach the PSTN. If the Cisco CallManager were to keep the access code prefixed to the number to forward to the PSTN, the call would not complete. To avoid this, you can use DDIs to strip extra digits before the call reaches the PSTN.

In general, administrators apply DDIs to route patterns that contain the @ wildcard; however, you can use the DDI PreDot with route patterns that use the "." wildcard even if the route patterns do not contain the @ wildcard. Cisco CallManager applies DDIs to the called-party transformation masks at the route pattern, the route details of a route list, or a translation pattern. DDI identifiers, shown in Figure 11-6, are additive. The DDI PreDot 10-10-Dialing combines the effects of each individual identifier. Table 11-3 depicts the most commonly used DDIs in the Cisco CallManager route plan.

Figure 11-6. Digit Discard Instructions

Table 11-3. Cisco CallManager Digit Discard Instructions

You can configure DDIs at multiple places in the CallManager route plan. One of the more common places is at the route pattern configuration. As shown in Figure 11-6, you can find the DDIs under the Called Party Transformations near the end of the Route Pattern Configuration window.

Tip

Digit Discard Instructions applied at the route pattern level are visible to the end user. For example, if the caller dials 914085551212 and the DDI removes the 9, the user will see the number change to 14085551212 on the LCD display of their IP Phone. DDIs applied at the route group level (from within the route list) are not visible to the end user. Applying DDIs at the route group level is covered later in this chapter.

As you can see, CallManager offers a variety of combinations of all the DDIs listed in Table 11-3.

Transformation Masks