Table of Contents

Destination Pattern Wildcards
Number Expansion

Create a Number Expansion Table

Variable-Length Dial Plans
Excess Digits Playout
Forward Digits and Voice Default Routes
Hunt Groups and Preference Configuration

Voice Dial Plan Considerations

Depending on your configuration, you may need to consider different strategies for how you organize the dial plan when configuring voice dial peers. This chapter is divided into the following topics regarding dial-peer configuration that you may need to consider:

• Destination Pattern Wildcards

• Number Expansion

• Variable-Length Dial Plans

• Excess Digits Playout

• Forward Digits and Voice Default Routes

• Hunt Groups and Preference Configuration

Destination Pattern Wildcards

The dial-peer destination pattern can incorporate wildcards using the period (.) character. Using wildcards can reduce dial plan administration, especially when numbering plans allocate contiguous blocks of numbers to different locations.

For example, the following dial-peer configuration shows how the wildcard character can be used in the destination pattern.

dial peer voice 1 pots
destination-pattern 22..
port 1/1

In this configuration, the Cisco MC3810 will match any four-digit dial string starting with 22 (for example, 2201, 2235, or 2299). Because two wildcard characters are entered in the destination pattern, the dial peer will only match a dial string of four digits or more. If a three-digit number such as 222 is entered, the dial peer would not match the destination pattern. If the Cisco MC3810 could not match any other dial peer for this call request, the call would be aborted after the interdigit timeout duration following the last two digits entered.

Wild cards can only be used in the trailing part of the destination pattern, and cannot be used in between digits. For example, the string 22.. is a valid use of wildcards, but the string 2..2 is not valid.

Number Expansion

In most corporate environments, the telephone network is configured so that you can reach a destination by dialing only a portion (an extension number) of the full E.164 telephone number. Voice over Frame Relay (VoFR) and Voice over ATM (VoATM) can be configured to recognize extension numbers and expand them into their full E.164 dialed number by using two commands in tandem: destination-pattern and num-exp. Before you configure these two commands, it is helpful to map individual telephone extensions with their full E.164 dialed numbers. This can be done easily by creating a number expansion table.

Create a Number Expansion Table

In Figure 9-1, a small company wants to use VoFR to integrate its telephony network with its existing Frame Relay network. The destination pattern (or expanded telephone number) associated with Cisco MC3810 No. 1 (located to the left of the Frame Relay cloud) is (408)  555-6xxx, (408) 555-7xxx or (408) 555-8xxx, where xxx identifies the individual dial peers by extension. The destination pattern (or expanded telephone number) associated with Cisco MC3810 No. 2 (located to the right of the Frame Relay cloud) is (729)  555-1xxx.

Table 9-1 shows the number expansion table for this scenario.

Variable-Length Dial Plans

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 crosses country boundaries and the telephone number strings are of different lengths.

By entering the "T" timer character in the destination pattern, the Cisco MC3810 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
destination-pattern 2222T
port 1/1

In this example, the Cisco MC3810 accepts the digits 2222, and then waits for an unspecified number of dialed digits. If digits continue to be entered before the inter-digit timeout expires, then the Cisco  MC3810 will gather up to 31 additional digits. Once the interdigit timeout expires, the Cisco  MC3810 places the call. The interdigit timeout is set by the timeouts inter-digit voice-port command.

The interdigit timeout timer can be immediately terminated by entering the "#" character. If the # character is entered while the Cisco MC3810 is waiting for the 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 Cisco MC3810 is waiting for the 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 using variable-length dial plans, the interdigit timeout should be reduced to reduce the call setup time. For more information on configuring the timeouts inter-digit command, see the "General Voice-Port Tuning Options" section.

Excess Digits Playout

Excess digits are defined as received digits that are beyond the length of the destination pattern on a terminating router. A terminating Cisco MC3810 will forward excess digits to the telephony interface. For example, if the digits "123456789" are matched on a terminating Cisco MC3810 with a destination pattern of "1.....," the "6789" are excess digits and will be forwarded.

A Cisco MC3810 that is originating a call will only collect digits up to the length of a defined destination pattern. When a number is dialed that is longer than the destination pattern, after the last digit in the destination pattern is dialed, the call is immediately placed, and the additional digits are not collected by the Cisco MC3810.

For example, if the digits "123456789" are dialed on an originating Cisco MC3810 with a destination pattern of 1...., then "6789" are not collected. The call is placed immediately after the digit "5" is dialed. The additional digits "6789" are not collected, but are passed through the audio path.

In configurations where a phone on a Foreign Exchange Station (FXS) port on the Cisco MC3810 is connected to the Public Switched Telephone Network (PSTN) through a Foreign Exchange Office (FXO) port on the same Cisco MC3810, additional steps are necessary to enable a call to go through. Because the uncollected excess digits are passed through the audio path, the excess digits might not go through if the audio path isn't ready when the excess digit is dialed. When dialing a destination pattern in this situation, pause and wait for a second dial tone before dialing the excess digits. This will give the audio path time to accept the excess digits.

Forward Digits and Voice Default Routes

Voice default routing for fixed-length dial plans can be used with larger PBX configurations to forward digits to Cisco MC3810 telephony interfaces.

Figure 9-2 shows an example of routing voice calls through a PBX using forward digits. In the configuration, the Cisco MC3810-t and Cisco MC3810-T are tandem nodes, and are required to support forwarding digits so that calls to extension "8208" can be made from Cisco MC3810 concentrators 0, 5, or 9.

The concept of voice default routes is also shown in Figure 9-2. In the example, the configurations for the destination dial plans "8..." in both the tandem nodes are voice default routes because all voice calls dialed that start with 8 followed by three digits will either match on 8208 or end up with 8...., which is the last resort voice route used by Cisco MC3810-t if no other route is discovered.

Hunt Groups and Preference Configuration

When configuring the destination pattern for voice-telephony dial peers (such as to a PBX), if you configure each dial peer with a different destination pattern, then you may have limitations on the availability of calls getting through. This is because when you configure each dial peer with a different destination pattern, the destination is a single DS0 timeslot on the voice connection to the PBX. If that timeslot gets busy, then a call attempt to the dial peer mapped to that DS0 timeslot will fail.

dial-peer voice 1 pots

  destination-pattern 3001

  port 1/1
dial-peer voice 2 pots

  destination-pattern 3002

  port 1/2
dial-peer voice 3 pots

  destination-pattern 3003

  port 1/3
dial-peer voice 4 pots

  destination-pattern 3004

  port 1/4

dial-peer voice 1 pots

  destination pattern 3000

  port 1/1

  preference 0
dial-peer voice 2 pots

  destination pattern 3000

  port 1/2

  preference 1
dial-peer voice 3 pots

  destination pattern 3000

  port 1/3

  preference 2
dial-peer voice 4 pots

  destination pattern 3000

  port 1/4

  preference 3

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