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codec: new function osmo_hr_sid_reset() 

If a network element that receives call leg A UL and is responsible
for preparing leg B DL receives a GSM-HR SID frame whose SID field
is not all 1s but which is marked as valid SID by out-of-band means
(TRAU-UL frame control bits or the FT field in RFC 5993 ToC octet),
this SID frame should be rejuvenated (SID field reset to all 1s)
prior to retransmission on call leg B DL.  Provide a function
that performs this operation.

Related: OS#6036
Change-Id: Iebc0863ffcc3f8f25aeb54d4b14fac0487bc2bbb
This commit is contained in:
Mychaela N. Falconia 2023-05-26 21:15:06 +00:00 committed by falconia
parent 2974a23c75
commit 18e5af55be
2 changed files with 30 additions and 0 deletions
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1
include/osmocom/codec/codec.h
View File

@ -131,6 +131,7 @@ bool osmo_fr_sid_preen(uint8_t *rtp_payload);
bool osmo_efr_sid_preen(uint8_t *rtp_payload);
void osmo_fr_sid_reset(uint8_t *rtp_payload);
void osmo_hr_sid_reset(uint8_t *rtp_payload);
void osmo_efr_sid_reset(uint8_t *rtp_payload);
int osmo_amr_rtp_enc(uint8_t *payload, uint8_t cmr, enum osmo_amr_type ft,

29
src/codec/gsm620.c
View File

@ -21,6 +21,7 @@
#include <stdint.h>
#include <stdbool.h>
#include <string.h>
#include <osmocom/core/bitvec.h>
#include <osmocom/core/utils.h>
@ -285,3 +286,31 @@ bool osmo_hr_check_sid(const uint8_t *rtp_payload, size_t payload_len)
return true;
}
/*! 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).
* \param[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.
*/
void osmo_hr_sid_reset(uint8_t *rtp_payload)
{
/* set all 79 SID codeword bits to 1 */
rtp_payload[4] |= 0x7F;
memset(rtp_payload + 5, 0xFF, 9);
}