CUCM Digit Manipulation

Digit manipulation is often used to change calling-party numbers for caller ID purposes on outgoing PSTN calls. Digit manipulation is also used to strip public switched telephone network (PSTN) access codes before extending calls to the PSTN. Other uses of digit manipulation involve expanding or modifying abbreviated dialing options. Inbound calls from the PSTN may be ten digits in length, whereas the internal dial plan is only four or five digits. These inbound calls would need to have the E.164 PSTN numbers converted to the internal dial plan, which could be significantly smaller. It is normally required to manipulate the calling-party (initiator) and called-party (destination) numbers when routing a call to the PSTN. The PSTN access code needs to be stripped from the called number before sending it out to PSTN. Most organizations use the number 8 or 9 as the access code to the PSTN. The calling-party number also needs to be changed from the abbreviated internal extension number to a full E.164 PSTN number to allow for easier redial.

CUCM Digit Manipulation Overview

In Figure 12-1, an IP phone with extension 1002 calls a phone on the PSTN with a phone number of 408 555-111. The user at extension 1002 must first dial a PSTN access code of 9 to direct a call to the PSTN. It is important to strip the 9 from the called number before sending the call to PSTN; otherwise, the PSTN switch will not be able to route the call, and the user will receive a reorder tone because no numbers on the PSTN in North America begin with a 9 (except for 911 for emergency call routing). The calling-party number needs to be expanded to a full PSTN number so that the PSTN user can see the proper, routable caller ID of 706 555-1002, and not the extension of 1002, which is not routable on the PSTN. This functionality will provide proper caller ID, which can be used by a variety of features.

NOTE In some countries, the calling-party number must be set to the correct PSTN number of the used PSTN subscriber line or trunk.

Table 12-1 displays some often used digit manipulation requirements and the method in which they are handled in CUCM.

Figure 12-1 Digit Manipulation Overview

1 408 555-1111





1 706 555-1002



1 408 555-1111

Table 12-1 Digit Manipulation Methods


Call Type


Expand calling-party directory number to full E.164 PSTN number

Internal to PSTN

Use calling-party's external phone number mask. The calling-party transformation in route pattern or route list provides additional manipulation.

Strip PSTN access code

Internal to PSTN

Use digit stripping in the route pattern or route list.

Expand abbreviated number

Internal to internal

Use called-party transformation in the translation pattern.

Convert E.164 PSTN called-party directory number to internal number

PSTN to internal

Use called-party transformation in the translation pattern, or use significant digits.

Expand endpoint directory numbers to accomodate overlapping dial plan

Internal to internal PSTN to internal

Use called-party transformation in the translation pattern.

Figure 12-2 illustrates an internal caller dialing a PSTN number using a PSTN access code 9 followed by the 11-digit PSTN number, where the following digit manipulations occurs:

1. CUCM discards the digit 9 before routing the call to the PSTN.

2. The internal extension calling-party number is expanded to the full 11-digit PSTN number.

Simple called and calling-party transformations are used in the PSTN route list at the route group level to achieve these two objectives. The calling-party transformation is often dependent on the external phone number mask configuration on the directory number (DN).

Figure 12-2 Outgoing Call to PSTN

Dials: 9 1 303 555-6007

Dials: 9 1 303 555-6007

Figure 12-3 illustrates an incoming PSTN call to an internal phone, which is routed as follows:

Figure 12-3 illustrates an incoming PSTN call to an internal phone, which is routed as follows:

1. The PSTN phone calls the full E.164 number of the destination; the call is received by the PSTN gateway with ten digits. Digit manipulation occurs on the gateway or on CUCM to convert the full E.164 number to the internal dial plan. The gateway configuration in CUCM is the easiest place to manipulate the incoming digits.

2. The destination DN can also be converted using a translation pattern that matches the digits received from the provider. Translation patterns are not necessary to change the incoming E.164 number to an internal directory number unless the incoming number does not map directly or additional digit manipulation is required. To make it easier for the IP phone user to call back the number, the calling-party transformation mask of the translation pattern can be used to insert 91 to the caller's number. This step is optional because the IP phone user can always edit the number and manually add access code 9 and possibly the long-distance code 1 before calling back the PSTN number.

3. The IP phone receives the call, and the call is listed in the Received Calls menu.

Figure 12-3 Incoming Call from PSTN

Figure 12-3 Incoming Call from PSTN

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