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CUCM Digit Prefix and Stripping

The Digit Prefix feature prepends digits to the beginning of a dialed number. Any digits that can be entered from a standard phone (0 through 9, *, and #) can be prepended to the calling or called party numbers. Digit prefixing is available for either the calling or called party number and can be configured at the route pattern, route list, or translation pattern configuration levels.

Figure 11-11 displays the calling and called party prefix configuration available at the route pattern, route list, and translation pattern configuration levels.

Figure 11-11

Figure 11-11 Digit Manipulation: Prefix Digits

Digit discard instructions (DDI) remove parts of the dialed digit string before passing the number on to the adjacent system. A DDI removes a certain portion of the dialed string (called party). Access codes are typically used to make a phone call that will be routed to the PSTN. The PSTN switch does not expect the access code, so the access code must be stripped out of the called party number before sending the call to the carrier.

Digit stripping is configured in the Called Party Transformations section by selecting a Discard Digits setting from the drop-down menu. Discard digits can be configured at the route pattern and at the route group details level of the route list.

The entire range of discard digits are supported if the @ wildcard pattern is used in the route pattern. If the @ wildcard is not used in the route pattern, only the <None>, NoDigits, PreDot, PreDot Trailing #, and Trailing # discard digits can be used.

Table 11-2 displays different digit discard instructions and their effects on dialed digits leveraging a route pattern of 9.5@. 9.5@ would not be used in most deployments, but it is a good example that can use various DDIs that are not available without the @ wildcard character. The digits that would be discarded appear in bold in Table 11-2.

Table 11-2. Digit Discard Instructions 9.5@

Instructions

Discarded Digits

Used For

PreDot

95 1 214 555 1212

Removes access code

PreAt

95 1 214 555 1212

Removes all digits that are in front of a valid numbering plan pattern

11D/10D@7D

95 1 214 555 1212

Removes PreDot/PreAt digits and local or long-distance area code

11D@10D

95 1 214 555 1212

Removes long-distance identifier

IntlTollBypass

95 011 33 1234 #

Removes international access (011) and country code

10-10-Dialing

95 1010321 1 214 555 1212

Removes carrier access (1010) and following carrier ID code

Trailing #

95 1010321 011 33 1234 #

Removes the # sign for PSTN compatibility

The PreAt, 11D/10D@7D, 11D@10D, IntlTollBypass, and 10-10-Dialing complex DDIs are not available without the @ symbol in the route pattern.

Figure 11-12 illustrates a call in which CUCM applies the PreDot DDI to the 9.8XXX route pattern, resulting in the access code (9) being stripped out of the dialed digits. The resulting four digits of 8123 are routed to the traditional PBX across a gateway or trunk device. The PBX analyzes the called party number and forwards the call to the necessary device. If the 8123 pattern did not match on a device in the PBX, it is very probable that the PBX would route the call back to CUCM, causing a call-routing loop. The PBX can have a route pattern–like configuration that routes all calls four digits in length beginning with an 8 (8XXX) to CUCM to accommodate phones that have been migrated to CUCM. CUCM probably has a route pattern of 8XXX to accommodate phones that have not been migrated from the PBX yet. If neither system has line 8123 configured on a device, a call-routing loop will normally occur. CUCM has service provider call-loop protection mechanisms that will only process each call reference value a certain number of times within a time interval. Supplementary service actions (call forward, conference, park, and so on) result in a new call reference value.

Figure 11-12

Figure 11-12 PreDot Digit Discard Instructions

Figure 11-13 illustrates the PreDot 10-10-Dialing DDI applied to the 9.@ route pattern. The PreDot 10-10-Dialing compound DDI strips the access code (9), the carrier selection code (1010), and the carrier identification code (288) from the called party number. The resulting 11-digit long-distance called party number of 1 214 555-1212 is then routed to the gateway device. Removing the 10-10 dialing parameters guarantees that long-distance calls will be billed by the preferred carrier. Most organizations contract a minimum number of long-distance minutes per month with the long-distance carrier. Although end users might believe that they are saving the company money by routing the call across an advertised carrier, they might be incurring additional costs to the organization. This compound DDI works only if the @ symbol is part of the route pattern. Translation patterns could perform similar functionality without introducing a route pattern with the @ symbol into the dial plan.

Figure 11-13

Figure 11-13 Compound Digit Discard Instructions

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