Dialogic IP Media Library API Programming Guide and Library ...

Using the AMR-NB Audio Coder
1.80 kbps (assuming SID frames are continuously transmitted)
Note: The 1.80 kbit/s rate is not actually a voice signal, but the bit rate consumed when
Voice Activation Detection (VAD) is processing a silence.
This feature is only supported when using the Session Initiation Protocol (SIP). None of the
available SDP options are currently supported through Dialogic ® Global Call software (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.
8.2 API Library Support
The Dialogic ® IP Media Library API allows the application to provide a preferred receive bit rate,
a preferred transmit bit rate, and a rule to determine how changes in the received Codec Mode
Request (CMR) value control the transmitted bit rate. This API library support is described in the
following topics:
CMR Value (Preferred Receive Bit Rate)
Preferred Transmit Bit Rate
CMR Rules
RTP Payload Format
8.2.1 CMR Value (Preferred Receive Bit Rate)
The CMR value indicates a preferred receive bit rate on the local side. The CMR value is a
preference and is communicated to the remote side as a request.
To specify the CMR value, set eMediaType in the IPM_MEDIA structure to
MEDIATYPE_AUDIO_LOCAL_CODER_INFO and set eCoderType in the
IPM_AUDIO_CODER_INFO structure to a value that corresponds to the preferred receive bit rate
(CMR value). For example, to specify a CMR value of 5 which corresponds to a preferred receive
bit rate of 7.95 kbit/s, set eCoderType to CODER_TYPE_AMRNB_7_95K.
8.2.2 Preferred Transmit Bit Rate
The preferred transmit bit rate indicates the following:
The transmit bit rate to be used when a CMR value from the remote side has not been received
yet
The transmit bit rate to be used when the CMR value received from the remote side is 15 (don't
care)
The maximum transmit bit rate when the CMR rule is “CMR Limit” (see CMR Rules).
To specify the preferred transmit bit rate, set eMediaType in the IPM_MEDIA structure to
MEDIATYPE_AUDIO_REMOTE_CODER_INFO and set eCoderType in the
IPM_AUDIO_CODER_INFO structure to the desired transmit bit rate. For example, to specify a
40 Dialogic ® IP Media Library API Programming Guide and Library Reference
Dialogic Corporation