CUCM Digit Manipulation

Before plunging into the world of CUCM digit manipulation, let us learn what an E.164 number is.

What is E.164?

E.164 is an ITU-T recommendation for international PSTN numbering. It is meant to be a way to globalize phone numbers, which means to define and standardize the format of phone numbers around the world. Historically, E.164 evolved from the ITU-T E.163 created in 1997.

E.164 format

E.164 introduces a powerful symbol: the plus sign “+”. If you take a look at the résumé of an international consultant or a Sales Manager who travels frequently, did you notice something special in the phone number section? The plus sign for example, in front of the phone number? That’s what I’m talking about. The phone number of our Sales Manager is written in the E.164 format.

For example, in the US, if you want to dial long distance number 512.555.1234, its E.164 format will be +1.512.555.1234. You won’t dial the dots of course they’re just seperators for easy reading :)

An international number in the E.164 format has the following parts:

  • Exit code: the code to exit the current country
  • Country code: the code related to the country of the called party
  • Subscriber code: identifies the called party in his country

Cisco Call Manager E.164 support

Cisco CUCM supports E.164 in its constructs. Indeed, you can create Translation Patterns, Hunt Pilots, Translation Patterns and Transformation Patterns with the plus sign in them.

Digit Manipulation: Attendant DN

The Attendant DN feature is a digit manipulation technique for inbound calls. To understand it, let’s assume we have an analog trunk port such as FXO port on a voice gateway. When the gateway receives a call on the FXO port, the FXO port becomes in the off-hook state which closes a circuit between the central office and the gateway, like in home phone dialing. CUCM plays a dial tone (instead of the central office) and the FXO port is waiting for the user to dial more digits.
At this point comes the Attendant DN feature. The Attendant DN allows to send a set of digits to the call routing component as soon as the analog port goes off-hook. So instead of waiting for additional digits to be dialed, CUCM dials a new batch of digits (the Attendant DN value) and transmits them to the call routing component.

The Attendant feature is similar to the Prefix Digits where CUCM adds a set of digits before transmitting the call to the call routing component.

Attendant DN configuration

The Attendant DN is configurable on analog ports such as FXO and FXS ports. It is not configurable on digital trunk ports, simply because digital gateway protocols such as MGCP PRI, H323 and SIP trunks use enbloc dialing. So they get the whole dialed number in the inbound call.

Example 1: Attendant DN setting on an analog voice gateway, equipped with a Ground Start FXS port


Example2: Attendant DN setting on an analog voice gateway, equipped with a Loop Start FXO port


Digit Manipulation: Significant Digits

  • Useful for inbound calls into the CUCM cluster.
  • configured in the CUCM gateway page or the CUCM Trunk page.
  • in most implementations, we configure it to 4 or 5. Here is the Significant Digits configuration on a H.323 gateway.
digit-manipulation-2016-05-29 18_17_19

The number of digits to consider “significant” depends on:

  • the DID block we purchased from Telco,
  • the number of digits the Telco is sending
  • the internal numbering plan of the company.

Digit Manipulation: Strip # Sign from Called Party number

digit-manipulation-2016-05-29 18_22_47
digit-manipulation-2016-05-29 18_23_04

In the home lab, I found no difference in dialing behaviour, by enabling or disabling this service parameter.

Digit Manipulation: Discard Digit Instructions

See the Cisco CallManager Discard Digits Instructions DDI article.

We usually have use of DDI in route patterns.

Digit Manipulation: Prefix Digits

“Prefix Digits” is a dialing transformation for both inbound and outbound calls. It allows to prepend the called number or the calling number with a set of digits before sending the call to the next stage of call routing. This next stage can be the call routing component (if the call is inbound) or a gateway/trunk (if the call is outbound).

On one hand, Prefix Digits is a feature that we can apply to the digits received on inbound calls, for the following ports and gateways:
– ports: FXS, FXO, E&M, digital access PRI and BRI
– gateways: H323, H225 trunks
On the other hand, in Calling Party Transformations and Called Party Transformations, Prefix Digits is applied for outbound calls only. That’s why we see the field named  Prefix Digits (Outbound Calls) in CUCM. Since Calling and Called Party Transformations are applied in route patterns, translation patterns and Hunt Pilots, we can say that Prefix Digits in these constructs is applied for outbound calls only.

In Prefix Digits -or Prefix DN- The choice of the digits to prepend is any combination of the following alphanumeric characters: *,#,0-9,+.

Prefix Digits Configuration in CUCM

In CUCM, we can configure the Prefix DN feature on digital gateways and on trunks.


In our lab, I’m going to set the calling party number transformation in the route list detail level with Prefix Digits:

digit-manipulation-2016-06-04 09_09_10

We test:

digit-manipulation-2016-06-04 11_03_58
the PSTN receives the call from HQ in a 10-digit format

Please click on the next page to read the rest of the article.

Pages: 1 2 3 4 5

Be First to Comment

Leave a Reply

Your email address will not be published. Required fields are marked *