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You issue the following commands on a CME router:
Dial-peer voice 1 pots
Destination-pattern 9911
prefix 9
port 1/0/0
Which of the following digits will be forwarded to the PSTN when a caller dials 9911? (Select the best answer.)
- 9
- 911
- 9911
- No digits will be forwarded.
Explanation:
The following command set will forward the digit 9 to the public switched telephone network (PSTN) when a caller dials 9911:
Dial-peer voice 1 pots
Destination-pattern 9911
prefix 9
port 1/0/0
The dialpeer voice command is used to define how calls are routed to destination endpoints on either the PSTN or a Voice over IP (VoIP) network. To define call routing for the PSTN, you should issue the dialpeer voice command with the pots keyword.
The destinationpattern command is used to match both inbound and outbound dial peers. The sequence of dialed digits that will be matched for a dial peer can contain the digits 0 through 9, the asterisk (*), and the pound sign (#). In addition, you can use a period (.) as a wildcard symbol to refine the dialing pattern or to match multiple dial strings for a single dial peer. The command set in this scenario configures a dial peer on a Cisco Unified Communications Manager Express (CME) router to match the destination pattern 9911. By default, CME only forwards digits matched by wildcards in a destination pattern, not digits that are explicitly defined in the destination pattern. In the destinationpattern 9911 command, all the destination pattern digits are explicitly defined. Therefore, CME will not forward any of the digits in the destination pattern when a user dials 9911.
The prefix command is used to add one or more digits to the front of the dial string before the dial string is forwarded to the destination network. Issuing the prefix 9 command in this scenario ensures that the digit 9 will be forwarded to the PSTN, even though CME will automatically strip every digit in the destination pattern. Therefore, only the digit 9 will be forwarded to the PSTN when a caller dials 9911.
If the intent of the configuration in this scenario is to forward the emergency service code 911 to the PSTN, the configuration is incomplete. To configure the dial peer to forward the 911 emergency service code to the PSTN without forwarding the internal access code 9, you could do one of the following:
A. Issue the prefix 911 command instead of the prefix 9 command.
B. Issue the forwarddigits 3 command instead of the prefix 9 command.
The port command is used to configure a plain old telephone service (POTS) dial peer to send outgoing traffic destined for the PSTN through a specific port on a CME router. In addition, the port command is used to match incoming calls from the PSTN to POTS dial peers. In this scenario, the port 1/0/0 command configures CME to forward outgoing calls made to 9911 through port 1/0/0 to the PSTN.
The forwarddigits command configures a dial peer to forward the rightmost number of digits matched by the destination pattern, even if the digits are explicitly matched. The number of digits forwarded by CME depends on the value configured in the forwarddigits command. For example, if you were to issue the forwarddigits 4 command instead of the prefix 9 command in this scenario, CME would forward the digits 9911 to the PSTN when a caller dials 9911. If you were to issue the forwarddigits 4 command in addition to the prefix 9 command, CME would forward the digits 99911 to the PSTN when a caller dials 9911.
Issuing the forwarddigits implicit command or the no forwarddigits command configures a dial peer to its default behavior of stripping digits that are explicitly matched in the destination pattern. Issuing the forward-digits all command configures a dial peer to forward every digit that matches the destination pattern, even if the digits are explicitly matched.
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