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Dialogic
®
Multimedia Software for ATCA Release 1.0 Release Update, Rev 06 — January 23, 2008 33
Dialogic Corporation
This feature is only supported when using the Session Initiation Protocol (SIP). None of the
available Session Description Protocol (SDP) options are currently supported through Global Call
(that is, direct first-party call control). The options are only available using third-party call control
(3PCC), where the application is responsible for interpreting received SDP text strings and for
constructing all outbound SDP text strings.
Dialogic
®
IP Media Library API Support
The bit rate can be controlled using a new media type in the IPM_MEDIA structure. The Dialogic
®
IP Media Library API allows the application to provide a preferred bit rate and a rule to determine
how changes in the received CMR value control the transmitted bit rate.
Preferred bit rate
The preferred bit rate is specified by setting the eMediaType in the IPM_MEDIA structure to
MEDIATYPE_AUDIO_REMOTE_CODER_INFO and setting the CoderInfo.eCoderType to
the desired transmit bit rate.
CMR value
The transmitted CMR value is specified by setting the eMediaType in the IPM_MEDIA
structure to MEDIATYPE_AUDIO_LOCAL_CODER_INFO and setting the
CoderInfo.eCoderType to the desired CMR value.
The CMR rules are specified by a new media type called
MEDIATYPE_AUDIO_REMOTE_CODER_OPTIONS_INFO. A new field
AudioCoderOptionsInfo (of type IPM_AUDIO_CODER_OPTIONS_INFO) has been added to the
IPM_MEDIA union. The CMR control is implemented by allowing the host application to specify
one of two rules.
• The first rule, “CMR Tracking,” indicates that the transmit bit rate should follow the CMR
value in the received packet.
• The second rule, “CMR Limit,” indicates that the transmit bit rate should follow the CMR
value in the received packet with a maximum value specified by the preferred bit rate.
With both CMR rules, it is necessary to specify a preferred rate to avoid the specific case of
determining what rate to transmit at before the first CMR value is received. The software will
transmit at the preferred rate before the first packet is received or when a CMR value of 15 (don't
care) is received from the opposite side.
The CMR rules are set in the AudioCoderOptionsInfo.unCoderOptions field by ORing in either
CODER_OPT_AMR_CMR_TRACK or CODER_OPT_AMR_CMR_LIMIT.
Specifying a CMR rule is mandatory and the rules are mutually exclusive.
Note: The CMR rules are not used by the MEDIATYPE_AUDIO_LOCAL_CODER_OPTIONS_INFO
eMediaTypes.
Supported RTP Payload Format
AMR supports two different formats for the RTP payload:
• “Bandwidth efficient,” to minimize the amount of network bandwidth.