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White Paper

Cisco IOS Digit Manipulation

Date:
Dec. 20, 2013
Author:
Brian Mahler

Abstract

Need to control the digits contained in the telephone number that enter or leave a gateway? Digit manipulation involves adding, subtracting, and changing telephone numbers. You can manipulate calling numbers, called numbers, and redirecting numbers, as well as the numbering plan and ISDN number type. Learn about the techniques that are applied to incoming or outgoing calls, or globally to all calls. You can also manipulate telephone numbers before or after a dial peer is matched.

Sample

Introduction

You will probably encounter a situation where you will need to control the actual digits contained in the telephone number that enter or leave a gateway. You might need to add the area code to a call that is routed out to the public switched telephone network (PSTN), or remove a site code from an intercompany call, for instance. Digit manipulation encompasses adding, subtracting, and changing telephone numbers. You can manipulate calling numbers, called numbers, and redirecting numbers, in addition to the numbering plan and Integrated Services for Digital Network (ISDN) number type. You can use techniques that are applied to incoming or outgoing calls, or globally to all calls. You can manipulate telephone numbers before a dial peer is matched or afterwards.

In this paper, we will cover:

  • Basic digit manipulation techniques
  • Number expansion
  • Number translation
  • Ways to troubleshoot

Digit Striping

VoIP dial peers forward all digits by default; however, POTS dial peers strip any outbound digits that explicitly match their destination pattern. For instance, given the destination pattern of 55512, the called number transmitted to the PSTN would contain just the last two digits. The first five digits (, 55512) would be striped because they are explicitly matched digits. Given the destination pattern of 555[2-9]... and a digit string of 555422, only the 555 would be stripped.

Digit stripping is the default behavior of POTS dial peers, which can work to your advantage if you understand its effect. For instance, if a user dials nine to reach an outside number, you do not want the number nine sent to the PSTN-you can configure a POTS dial peer with a destination pattern of 9T-and so the nine is matched and stripped. Only the remaining digits are transmitted.

You can disable digit stripping with the command [no] digit strip under the post dial-peer configuration mode. The relevant command syntax is as follows:

Dial-peer voice 1 pots
[no] digit strip

Forward Digits

You can achieve more precise control over the number of digits that are transmitted to the PSTN with the following command:

Forward-digits [number|all|extra]

Where:

Number gives the number of digits to forward
 All means to forward all digits
 Extra tells the gateway to forward any digits that are longer than the length of the destination pattern

This command allows you to specify the exact number of digits to be forwarded. The following examples show which digits are sent when you dial the number 111-222-3333 and use various options of the forward-digits command.

The first case, the right most seven digits are sent:

# dial-peer voice 111 pots
# destination-pattern 111222..
# forward-digits 7

With this next configuration the entire number is sent:

# dial-peer voice 111 pots
# destination-pattern 111222..
# forward-digits all

Prefix Digits In some cases you, might need to transmit more numbers than what was dialed. For example, a call that would normally go across your IP network needs to be routed through the PSTN, requiring the addition of the appropriate area code and prefix. You can use the prefix command to replace some of those digits. This command is given under the dial-peer configuration mode. The prefix string can be any number from zero through nine and a comma that inserts a one-second pause. The gateway prefixes digits after the outgoing dial peer are matched, which is after digits are stripped and before it sends the call out.

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Total Pages:
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