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 The Digit Prefix feature prepends digits to a number. Any phone keypad digits from 0 to 9,
and the * and # digits, can be prepended to the calling or called numbers.
The Digit Prefix feature can be applied to a calling-party or a called-party number and
configured under the corresponding transformation setting in the route-pattern, route-list,
or translation-pattern configuration.
Figure 12-6 displays the calling- and called-party prefix configuration available at the
route-pattern, route-list, and translation-pattern configuration areas.
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 (for
example, when an access code is needed to route the call to the PSTN, but the PSTN switch
does not expect that access code).
Digit stripping is configured under the called-party transformations by selecting a DDI. It
can be configured at route patterns and at route groups of a route list.
For North American Numbering Plan (NANP) patterns (@), the entire range of DDIs is
supported; with non-@ patterns, only DDIs <None>, NoDigits, and PreDot can be used.
CUCM Digit Prefix and Stripping 289
Figure 12-6 Digit Manipulation: Prefix Digits
For the PreDot DDI to work, the route pattern has to include a period (.) delimiter. DDIs
are available at the route-pattern and route-list (route-group link) levels, as shown in
Figure 12-6 (discard digits).
Table 12-2 displays different DDIs and how they would apply to a route pattern of 9.5@
with some dialed digit examples. An access code with two digits before the @ symbol is
not used in most systems, but has been used in the example to illustrate the flexibility of
DDIs. The digits that would be discarded appear in bold and are highlighted.
Table 12-2 Digit Discard Instructions
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 longdistance
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 #
Removal of # sign for PSTN compatibility
9
290 Chapter 12: Digit Manipulation
PreDot and NoDigits DDIs are the only DDIs that can be used if the pattern does not
contain the @ sign.
Figure 12-7 illustrates a call in which CUCM applies the PreDot DDI to the 9.8XXX route
pattern. The access code of 9 is stripped from the dialed digits, and four digits of 8123 are
routed to a traditional PBX. The traditional PBX may have a Session Initiation Protocol
(SIP) trunk to CUCM, or there may be a gateway between the devices so that a traditional
telephony interface can be used to connect the two systems.
Figure 12-7 PreDot Digit Discard Instructions
Figure 12-8 illustrates the PreDot 10-10-Dialing DDI applied to the 9.@ route pattern. This
compound DDI strips the access code (9) from the dialed number (91010288 1 214 555-
1212), removes the carrier selection (1010) and carrier identification code (288), and then
sends the 11-digit long-distance phone number 1 214 555-1212 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 minimum guarantees with the longdistance
provider of their choice. Although end users might believe that they are saving the
company money by routing the call across an advertised carrier, they may 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 the same functionality without
introducing a route pattern with the @ symbol into the dial plan.