Configuring Codecs and Tone Detection 63
Smart Media Software Configuration Guide 3 • Configuring an ISDN-SIP Gateway
Table 11 shows the list of codec payload type values per RFC3551:
When you use dynamic payload types, you need to spe
cify the additional encoding information using the
attribute for media announcement.
Attribute for Media Announcement
A media description may have any number of attributes ("a=" fields) which are media specific. The format of
attri
bute is as follows.
a=<attribute>
or
a=<attribute>:<value>
Here are some examples of attributes:
Dynamic payload type. You specify the additional encoding information for dynamic payload type in the fol-
lowing format:
a=rtpmap:<payload type> <encoding name>/<clock rate>[/<encoding parameters>]
For audio streams, <encoding parameters> may specify the number of audio channels. This parameter may be
omitted if the number of channels is one provided no additional parameters are needed.
Other media specific attribute. The use of other media specific attributes depends on the specification of the
RTP
payload format for the specific media type. Here are some example of attributes.
a=fmtp:<format> <format specific parameters>
This attribute allows parameters that are specific to a particular format to be conveyed in a way that SDP
doesn't have to understand them. The format must be one of the formats specified for the media. Format-spe-
Table 11. Codec Payload Type Values
Codec Payload Type Value
G.711 uLaw 0
G.723.1 4
G.711 aLaw 8
Comfort Noise 13
G.728 15
G.729AB 18
G.726-40 dynamic
G.726-32 2 or dynamic (depends on network)
G.726-24 dynamic
G.726-16 dynamic
G.729EG dynamic
AMR dynamic
EVRC dynamic
QCELP dynamic