In most voice configurations, fixed-length dialing plans, in which all the dial peer destination patterns have the same length, are sufficient because the telephone number strings are all the same length. However, in some voice network configurations, variable-length dial plans are required, especially if the network connects two or more countries where telephone number strings could be different lengths.
If you enter the "T" timer character in the destination pattern for your dial peer, the router can be configured to accept a fixed-length dial string, and then wait for additional dialed digits. For example, the following dial peer configuration shows how the T character can be set to allow variable-length dial strings:
dial peer voice 1 pots
In this example, the router accepts the digits 2222, and then waits for an unspecified number of dialed digits. If digits continue to be entered before the interdigit timeout expires, then the router will continue to gather up to 31 additional digits. Once the interdigit timeout expires, however, the router places the call. You can configure the interdigit timeout value by using the timeouts inter-digitcommand in voice-port configuration mode.
The interdigit timeout timer can be terminated by entering the "#" character. If the # character is entered while the router is waiting to accept additional digits, the # character is treated as an end-dial accelerator. The # character is not treated as an actual digit in the destination pattern and is not sent as part of the dialed string across the network.
However, if the # character is entered before the router is ready to accept additional digits (meaning before the "T" character is entered in the destination pattern), then the # character is treated as a dialed digit. For example, if a destination pattern is configured with the string 2222...T, then the digits 2222####1234567 can be gathered, but the digits 2222###1234#67 cannot be gathered because the final # character is treated as a terminator.
The default value for the interdigit timeout is 10 seconds. If the duration is not changed, using the "T" timer adds 10 seconds to each call setup time because the call is not attempted until the timer expires (unless the # character is used as a terminator). Because of this dependency, if a variable-length dial plan is used, the interdigit timeout should be reduced to reduce the call setup time. For more information, refer to the
"Variable-Length Matching" section on page 37