Dial Peers

General

  • The automatic digit stripping function is specific to POTS dial peers. VoIP dial peers do not automatically strip digits.
  • The primary difference between the POTS and VoIP dial peer configuration is the use of the session target command rather than the port command
  • Default codec value for VoIP dial peers is G.729

Dial peer type

  1. Plain old telephone service (POTS) – Maps a dial string to a specific voice port on the local gateway. The voice port connects the gateway to the PSTN, PBX, or analog telephone.
  2. VOIP Dial peer: Use session target command to forward an IP call to other gateway or call routing server.
  3. Multimedia Mail overlap (MMolP) The dial peer is mapped to tie email address of the SMTP server. This type of dial peer is used for store-and-forward fax (on-ramp and off-ramp faxing).

Default Dial peer

 

All inbound call legs must have an inbound dial-peer, therefore a system default dial-peer exists which is the last resort match. This is also known as dial-peer zero and cannot be modified or disabled. Default dial peers apply only to the inbound call leg. For the default VoIP dial peer the following applies

  • Any voice codec:G.729 or G.711 codec
  • No DTMF relay
  • IP Precedence 0
  • Voice Activity Detection (VAD) enabled
  • No Resource Reservation Protocol (RSVP) support:
  • No application support.
  • No Direct Inward Dial (DID) support

Dial peer – VOIP

  • Signaling protocol: H.323 is the default setting. The protocol can be changed to SIPv2. MGCP control can only be configured for POTS dial peers; it is not available for VoIP.
  • Digit strip or manipulation: VoIP dial peers doesn’t strip Digits
  • Session target
  • Direct inward dialing (DID- Not require
  • Dial peer matching is described further section
dial-peer 100 voice voip
 description Outbound voip to callmanager
 destination-pattern 4...
 session-target ipv4:10.0.0.20
 no vad
 dtmf-relay h245-alphanumeric
 voice-class codec 100
 voice-class h323 200
 ip qos dscp cs3 signaling

Dial peer – POTS

Inbound dial peer POTS

  • Direct-inward-dialing only support on all digital interfaces and FXS-DID
  • Over analog interfaces (FXS-DID): The digits are automatically signaled to the destination gateway by the switch, without the requirement of the secondary dial tone.
  • Over digital interfaces: The CO switch sends a call setup message that contains the entire DNIS. The DNIS is mapped to the outbound dial peer. The gateway forwards the call directly to the configured destination.

Inbound Dial-peer matching

Precedence of matching criteria for inbound dial peers:

  1. incoming called-number-Matches called number – Most explicit match
  2. answer-address- Matches calling number-Most explicit match
  3. Destination-pattern- Matches calling number – Most explicit match port.
  4. If multiple dial peers have the same port, selects the dial peer added to the configuration earlier
  5. default dial peer-Predefined parameters
  6. Only one condition must be met.
  7. The gateway stops searching when a dial-peer match is found.

Outbound Dial peer matching

Criteria required for outbound dial peers:

  • destination-pattern
  • Uses the called number to match the outbound dial peer
  • Most explicit match rule applies

By default pots dial-peers will strip all initial explicitly matched digits, leaving only the wildcard and unmatched portion of the number.

This behavior can be modified with one of the following commands

command

use

prefix <digits> Prefixes the specified digits after any explicitly matched digits are stripped
forward-digits <number> Strips all but the <number> right most digits
forward-digits all Forwards all digits
forward-digits extra {inband} Forwards numbers that appear after the matched portion, if inband is specified these are sent as DTMF tones
no digit strip Disables default digit stripping on pots dial-peers

Digit manipulation order

  1.  Num-exp
  2. Automatic digit strip only for pots
  3. Voice translation profile
  4. Prefix digit.
  5. Forward-digit

Wild card .T

  • If you plan to create a dial peer using only the T wildcard as the destination pattern, Cisco recommends that you create the destination as .T. This requires a user to dial at least one digit to match the destination pattern. Otherwise, a phone left off-hook for too long without a dialed digit will match the destination pattern.
  • The prefix <number> command will add any specified digits to the front of the dialed number before routing the call
  • An asterisk (•) and pound sign {#) are not considered special characters They appear on standard touch-tone dial pads and may be used when passing a call to an automated application that requires these characters to signal the use of a special feature.
 dial-peer 200 voice pots
 description Outbound pots
 destination-pattern 9.T
 port 1/0:15

Dial Peer Destination-Pattern Matching

The following characters have special meaning in patterns in IOS.

Character

Meaning

0-9 The literal digit 0-9
. Matches any single character
[] Matches any one of the numbers within the brackets, e.g. [2,3,4] matches 2, 3 or 4
- Matches a range of numbers (used within brackets). e.g. [2-4] matches 2,3 or 4
+ At start of string indicates an E.164 number
+ Within a string indicates the previous digit matched one or more times
? Indicates the previous digit matched zero or exactly one time, Press control and v and then enter
% Indicates the previous digit marched zero or more times
* Literal * dialed on keypad
# Literal # dialed on keypad
, Inserts a one second pause (not used for matching)
$ At the end of a pattern indicates additional digits are not allowed (used in two stage daling)
T At the end of a matched string indicates to wait for the interdigit timeout
() indicates a pattern

Dial  Peer hunting

Usually the longest match on destination pattern selects a dial peer; however it may be that two or more dial peers have the same destination pattern. In this case the preference command can be added to each dial-peer to set a priority (with preference 0 being the default and highest preference).

If multiple dial peers have the same preference then a random selection is made. You can change this behavior with the following global command

dial-peer hunt //<0-7>//

 By default, dial peers in a hunt group are selected according to the following criteria, in the order listed:

  • Longest match in phone number—Destination pattern that matches the greatest number of dialed digits. For example, if one dial peer is configured with a dial string of 345…. and a second dial peer is configured with 3456789, the router would first select 3456789 because it has the longest explicit match of the two dial peers.
  • Explicit preference—Priority configured by using the preference dial peer command.
  • Random selection—all destination patterns weighted equally.

You can change this default selection order or choose different methods for hunting dial peers by using the dial-peer hunt global configuration command. An additional selection criterion is “least recent use,” which selects the destination pattern that has waited the longest since being selected.

Troubleshooting Command

·         debug voip dialpeer inout
·         show dialplan number 012312321
·         debug voice ccapi inout
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One response

  1. IT,
    In regards to your Default Dial peer explanation i.e. ””’Default dial peers apply only to the inbound call leg.””’, i would like to share my recent findings.
    Following are the debugs for one of the failed call to a number wherein Default dial peer is used as the outbound dial peer is apparently not configured…

    Called Number=(TON=Unknown, NPI=Unknown), Calling Translated=FALSE,
    Subscriber Type Str=, FinalDestinationFlag=FALSE, Outgoing Dial-peer=0, Call Count On=FALSE,
    Source Trkgrp Route Label=, Target Trkgrp Route Label=, tg_label_flag=0, Application Call Id=)

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