gsm620.c File Reference

GSM 06.20 - GSM HR codec. More...

#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <osmocom/core/bitvec.h>
#include <osmocom/core/utils.h>
#include <osmocom/codec/codec.h>

Functions
bool	osmo_hr_check_sid (const uint8_t *rtp_payload, size_t payload_len)
	Check whether RTP frame contains HR SID code word according to TS 101 318 §5.2.2. More...
void	osmo_hr_sid_reset (uint8_t *rtp_payload)
	Reset the SID field of a potentially corrupted, but still valid GSM-HR SID frame in TS 101 318 format to its pristine state (full SID codeword). More...

Variables
const uint16_t	gsm620_unvoiced_bitorder [112]
const uint16_t	gsm620_voiced_bitorder [112]

Detailed Description

GSM 06.20 - GSM HR codec.

Function Documentation

osmo_hr_check_sid()

bool osmo_hr_check_sid	(	const uint8_t *	rtp_payload,
		size_t	payload_len
	)

Check whether RTP frame contains HR SID code word according to TS 101 318 §5.2.2.

Parameters

[in]	rtp_payload	Buffer with RTP payload
[in]	payload_len	Length of payload

Returns

true if code word is found, false otherwise

References bitvec_get_bit_pos(), bitvec::cur_bit, bitvec::data, bitvec::data_len, and ONE.

osmo_hr_sid_reset()

void osmo_hr_sid_reset

(

uint8_t *

rtp_payload

)

Reset the SID field of a potentially corrupted, but still valid GSM-HR SID frame in TS 101 318 format to its pristine state (full SID codeword).

Parameters

[in]

rtp_payload

Buffer with RTP payload - must be writable!

Per GSM 06.22 section 5.3, a freshly minted SID frame consists of 33 bits of comfort noise parameters and 79 bits of SID codeword (all 1s). Network elements that receive SID frames from call leg A uplink and need to retransmit them on leg B downlink should "rejuvenate" received SID frames prior to retransmission by resetting the SID field to its pristine state of all 1s; this function does the job.

Important note: because of HR-specific quirks (lack of exact bit counting rules in GSM 06.41 spec compared to 06.31 & 06.81, plus the fact that such bit counting can only be done efficiently in the GSM 05.03 channel decoder prior to bit reordering based on voiced or unvoiced mode), a generic (usable from any network element) SID classification function similar to osmo_{fr,efr}_sid_classify() unfortunately cannot exist for HR. Therefore, the triggering condition for invoking this SID rejuvenation/reset function can only be an out-of-band SID indication, as in GSM 08.61 TRAU frames or RFC 5993 ToC octet.

Variable Documentation

gsm620_unvoiced_bitorder

const uint16_t gsm620_unvoiced_bitorder[112]

gsm620_voiced_bitorder

const uint16_t gsm620_voiced_bitorder[112]