int sm_vmprx_config_codec_tetra(struct sm_vmprx_codec_tetra_parms *codecp)
typedef struct sm_vmprx_codec_tetra_parms {
tSMVMPrxId vmprx; /* in */
tSM_INT payload_type; /* in */
} SM_VMPRX_CODEC_TETRA_PARMS;
Configures a TETRA speech codec to the VMP[rx] setting the payload type mapping to payload_type.
It is possible to change the payload type mapping of a codec whilst a VMP[rx] remains valid by specifying a new payload type mapping for a given codec. This supersedes any previous mappings that were in effect for that codec.
If the call completes successfully, RTP packets arriving at the VMP[rx] with a payload type that matches a mapped type will be decoded using this codec.
If the codec is given the payload type -1 the codec is no
longer valid for this RTP session, unless it is subsequently
reconfigured.
There is not currently a standard packet encoding for wrapping TETRA-encoded speech into RTP. This implementation expects RTP frames that have standard RTP header followed by: ETSI two octet Payload header (with bits for framing rate, frame number, information element control, traffic type, contents control and payload) - the payload header follows the format described in ETSI TS 100 392-3-8 V0.0.8 section 5.2.1 TETRA ISI payload encoding. Two 18 octet tetra frames - each frame consisting of BFI bit followed by 137 bits of tetra encoded data (holding 30ms of encoded audio data according to traffic type 0 followed by 6 padding bits) - thus this pair of frames conveys 60ms of audio
The tetra encoded data in the 18 octet tetra frames is expected to be traffic type 0 - ACELP (ETS 300 395-2, 4.2.2.7) following MSB-LSB bit order.
The contents of the ETSI payload header are ignored apart from contents control bits which have following effect:
all other values: - we use packet loss concealment algorithm to fill in gap left by absent traffic 1 and traffic 2
Note for incoming data, the RTP timestamp is used to control jitter buffer frame numbers in Tetra payload header are ignored.
This requires the module tetra to have been downloaded.
-1 will remove any payload type configuration from the
codec preventing its use.
0 if call completed successfully, otherwise a standard error such as:
This function is part of the Prosody RTP processing API.