Number Expansion

Number expansion is another way to add digits to an outgoing called number; however, number expansion is applied to the gateway as a whole, and acts on all calls, not just those matching a designated dial peer. As with the previous three techniques, this manipulates only the called number. Number expansion manipulation occurs before any outbound dial peer is matched. Thus, you must configure outbound dial peers to match the expanded numbers, not the original ones.

The command for number expansion is num-exp original-number expanded-number, configured at global configuration mode. Although it is called number expansion, the manipulated number can contain fewer digits than the original, or it can contain more.

Example 10-2 shows two instances of number expansion configured. The first expands any four-number extension beginning with 1 to a seven-digit number beginning with 5551. The second changes any seven-digit number beginning with 5551 to a four-digit extension.

In the results of the show dialplan number command, notice that although the number entered in the command is the original number, the router looked for a match to the expanded number. The show dialplan number command is also useful for verifying that you have a dial peer to match the expanded number.