Digit Manipulation

You might encounter situations where you need to control the actual digits contained in the telephone numbers that enter or leave the gateway. You might need to add the area code to a call that is routed out of the public switched telephone network (PSTN), or remove a site code from an intracompany 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 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 afterward.

In this chapter, you will learn

• Ways that a router applies digit manipulation
• Basic digit manipulation techniques, such as digit stripping, prefixing, and forwarding
• Number expansion
• Number translation
• Control of the calling line identification (CLID) number
• Ways to troubleshoot and verify the telephone number changes that are applied