Information Technology Reference
In-Depth Information
Any voice codec:
Dial peer 0 handles any incoming voice codec; it is not hard-
coded to any specific codec.
■
Key
To p i c
No DTMF relay:
DTMF relay sends dialed digits outside of the audio stream. This is
useful because compressed codecs often distort dialed tones on the call.
■
IP Precedence 0:
This is probably the most painful default of dial peer 0. Setting
the traffic to IP Precedence (IPP) to 0 strips all QoS markings. The router now treats
the voice traffic the same as the data traffic.
■
Voice Activity Detection (VAD) enabled:
VAD allows you to save bandwidth by
eliminating voice traffic during periods of silence on the call.
■
No Resource Reservation Protocol (RSVP) support:
The lack of RSVP goes
right along with the lack of any QoS for the voice calls. The router does not reserve
any bandwidth specifically for dial peer 0 calls.
■
Fax-rate voice:
The router limits the bandwidth available to fax signals to the maxi-
mum allowed by the VoIP codec. This could devastate fax calls if you are using a low-
bandwidth compressed codec.
■
No application support:
Dial peer 0 cannot refer calls to outside applications, such
as an Interactive Voice Response (IVR) system.
■
No DID support:
Dial peer 0 cannot use the DID feature to automatically forward
calls from an outside PSTN carrier to internal devices.
■
In light of this list of dial peer 0 features, it is best to always match an inbound dial peer
where you can control the configuration.
Using Digit Manipulation
Digit manipulation is the process of adding or removing digits from a dialed number to
help a call reach an intended destination. You have already seen a few of the digit manipu-
lation commands during the discussion of the automatic digit-stripping feature of POTS
dial peers (such as the no digit-strip and forward-digit commands). Before we look at some
practical examples, Table 6-6 shows a list of common digit-manipulation commands you
can use on a Cisco router.
Key
To p i c
Table 6-6
Common Digit-Manipulation Methods on Cisco Routers
Command
Mode
Description
prefix digits
POTS dial peer
Allows you to specify digits for the router to add before
the dialed digits. Example:
prefix
011 adds the numbers
011 to the front of the originally dialed number.
forward-digits
number
POTS dial peer
Allows you to specify the number of right-justified dig-
its to forward. Example:
forward-digits 4
forwards only
the rightmost four digits from the dialed number.
