falconia submitted this change.
rtp2trau HR: bring TRAU-16k support into alignment with TRAU-8k
GSM 08.61 defines two TRAU frame formats for HRv1 codec, using
either 16 kbit/s or 8 kbit/s submultiplexing. The 8k format is
the one actually implemented in legacy E1 BTS hardware, and is
also needed for global interoperability in TFO - whereas HR-16k
TRAU frame format appears to be a paper-only spec that was never
implemented in any hardware.
Despite the lack of hardware implementations, support for TRAU-16k
format for GSM-HR is already present in libosmotrau, originally
implemented along with FR and EFR. Removing this support from
Osmocom would look bad (there is always that off-chance that
perhaps some BSS vendor did implement this format after all),
hence let us do the next best thing: bring TRAU-16k support into
alignment with the actually working TRAU-8k support for the same
codec.
Thanks to previous clean-up patches in this area, rtp2trau support
for GSM-HR TRAU-DL output was already fully consistent between 16k
and 8k formats, but TRAU-UL output code was wildly inconsistent.
TRAU-8k-UL output code is new, takes TW-TS-002 input and can be
used to implement TFO (primary intended use) or emulate an E1 BTS.
However, previous TRAU-16k-UL output code dates back to the initial
creation of TRAU<->RTP code in 2020, has never been updated until
now, and is woefully inadequate for the task of emulating an E1 BTS.
(Because TFO always uses 8k format for HRv1, software emulation of
an E1 BTS is the only remaining plausible application for GSM-HR
TRAU-16k-UL output.)
With the present patch, the behavior of osmo_rtp2trau() for
OSMO_TRAU16_FT_HR UL changes drastically: TS 101 318 input is no
longer accepted, RFC 5993 input is still accepted but is not
functionally complete, and the proper/expected input format becomes
TW-TS-002, of which RFC 5993 is a subset. However, the detailed
behavior of osmo_rtp2trau() for HRv1 codec is now exactly the same
between 8k and 16k formats, in both DL and UL directions.
Change-Id: I1c19592967e7c6becc710990f512da5dee5043d2
---
M src/trau/trau_rtp_conv.c
1 file changed, 128 insertions(+), 47 deletions(-)
diff --git a/src/trau/trau_rtp_conv.c b/src/trau/trau_rtp_conv.c
index d5ac1fa..867a4e4 100644
--- a/src/trau/trau_rtp_conv.c
+++ b/src/trau/trau_rtp_conv.c
@@ -676,7 +676,7 @@
return 0;
}
-static int rtp2trau_hr16(struct osmo_trau_frame *tf, const uint8_t *data, size_t data_len)
+static int rtp2trau_hr16_dl(struct osmo_trau_frame *tf, const uint8_t *data, size_t data_len)
{
/* accept both TS 101 318 and RFC 5993 payloads */
switch (data_len) {
@@ -695,57 +695,26 @@
tf->type = OSMO_TRAU16_FT_HR;
- if (tf->dir == OSMO_TRAU_DIR_UL) {
- /* C1 .. C5 */
- tf->c_bits[0] = 0;
- tf->c_bits[1] = 0;
- tf->c_bits[2] = 0;
- tf->c_bits[3] = 1;
- tf->c_bits[4] = 1;
- } else {
- /* C1 .. C5 */
- tf->c_bits[0] = 1;
- tf->c_bits[1] = 1;
- tf->c_bits[2] = 1;
- tf->c_bits[3] = 0;
- tf->c_bits[4] = 1;
- }
+ /* C1 .. C5 */
+ tf->c_bits[0] = 1;
+ tf->c_bits[1] = 1;
+ tf->c_bits[2] = 1;
+ tf->c_bits[3] = 0;
+ tf->c_bits[4] = 1;
/* C6.. C11: Time Alignment */
memset(tf->c_bits + 5, 0, 6);
- if (tf->dir == OSMO_TRAU_DIR_UL) {
- /* BFI */
- if (data_len == 0)
- tf->c_bits[11] = 1;
- else
- tf->c_bits[11] = 0;
- if (osmo_hr_check_sid(data, data_len)) {
- /* SID=2 is a valid SID frame */
- tf->c_bits[12] = 1;
- tf->c_bits[13] = 0;
- } else {
- tf->c_bits[12] = 0;
- tf->c_bits[13] = 0;
- }
- /* FIXME: C15: TAF */
+ tf->c_bits[11] = 1; /* C12: UFE */
+ tf->c_bits[12] = 1; /* C13: spare */
+ tf->c_bits[13] = 1; /* C14: spare */
+ tf->c_bits[14] = 1; /* C15: spare */
+ if (osmo_hr_check_sid(data, data_len))
tf->c_bits[15] = 0; /* C16: SP */
- tf->c_bits[16] = 0; /* C17: DTXd shall not be applied */
- } else {
- tf->c_bits[11] = 1; /* C12: UFE */
- tf->c_bits[12] = 1; /* C13: spare */
- tf->c_bits[13] = 1; /* C14: spare */
- tf->c_bits[14] = 1; /* C15: spare */
- if (osmo_hr_check_sid(data, data_len))
- tf->c_bits[15] = 0; /* C16: SP */
- else
- tf->c_bits[15] = 1; /* C16: SP */
- tf->c_bits[16] = 1; /* C17: spare */
- }
+ else
+ tf->c_bits[15] = 1; /* C16: SP */
+ tf->c_bits[16] = 1; /* C17: spare */
memset(tf->c_bits+17, 1, 4); /* C18..C21: spare */
memset(&tf->t_bits[0], 1, 4);
- if (tf->dir == OSMO_TRAU_DIR_UL)
- tf->ufi = 0;
- else
- tf->ufi = 1;
+ tf->ufi = 1; /* spare bit in TRAU-DL */
if (data_len)
osmo_pbit2ubit(tf->d_bits, data, GSM_HR_BYTES * 8);
else
@@ -756,6 +725,118 @@
return 0;
}
+static int rtp2trau_hr16_ul(struct osmo_trau_frame *tf, const uint8_t *data, size_t data_len)
+{
+ uint8_t ft;
+ enum osmo_gsm631_sid_class sidc;
+ bool data_bits_req, bfi;
+
+ /* In TRAU-UL direction we require/expect TW-TS-002 RTP payload format;
+ * RFC 5993 is also accepted because it is a subset of TW-TS-002.
+ * TS 101 318 input is not supported for TRAU-UL output! */
+ if (data_len < 1)
+ return -EINVAL;
+ ft = data[0] >> 4;
+ switch (ft) {
+ case FT_GOOD_SPEECH:
+ bfi = false;
+ sidc = OSMO_GSM631_SID_CLASS_SPEECH;
+ data_bits_req = true;
+ break;
+ case FT_INVALID_SID:
+ /* There are 3 possible BFI/SID combinations in TRAU-16k-UL
+ * format for GSM-HR that all collapse to the same
+ * "invalid SID" code in TRAU-8k-UL and TW-TS-002 formats.
+ * Here we arbitrarily choose BFI=1 SID=1: compared to the
+ * other two options, this one has the greatest Hamming
+ * distance (in C-bits) to good speech or valid SID codes.
+ */
+ bfi = true;
+ sidc = OSMO_GSM631_SID_CLASS_INVALID;
+ data_bits_req = false;
+ break;
+ case FT_GOOD_SID:
+ bfi = false;
+ sidc = OSMO_GSM631_SID_CLASS_VALID;
+ data_bits_req = true;
+ break;
+ case FT_BFI_WITH_DATA:
+ bfi = true;
+ sidc = OSMO_GSM631_SID_CLASS_SPEECH;
+ data_bits_req = true;
+ break;
+ case FT_NO_DATA:
+ bfi = true;
+ sidc = OSMO_GSM631_SID_CLASS_SPEECH;
+ data_bits_req = false;
+ break;
+ default:
+ return -EINVAL;
+ }
+ /* If the frame type is one that includes data bits, the payload length
+ * per RFC 5993 and TW-TS-002 is 15 bytes. If the frame type is one
+ * that does not include data bits, then the payload length per the
+ * same specs is only 1 byte - but we also accept 15-byte payloads
+ * in this case to make life easier for applications that pass the
+ * content of a buffer.
+ *
+ * When we make a TRAU-UL frame from FT=1 or FT=7, we fill all Dn bits
+ * with zeros if we got a short (1 byte) payload. However, if the
+ * application passed us a long (15 byte) payload despite FT being
+ * 1 or 7, we fill Dn bits with application-provided payload.
+ */
+ switch (data_len) {
+ case GSM_HR_BYTES_RTP_RFC5993:
+ break;
+ case 1:
+ if (data_bits_req)
+ return -EINVAL;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ tf->type = OSMO_TRAU16_FT_HR;
+
+ /* C1 .. C5 */
+ tf->c_bits[0] = 0;
+ tf->c_bits[1] = 0;
+ tf->c_bits[2] = 0;
+ tf->c_bits[3] = 1;
+ tf->c_bits[4] = 1;
+ /* C6.. C11: Time Alignment */
+ memset(tf->c_bits + 5, 0, 6);
+ tf->c_bits[11] = bfi; /* C12: BFI */
+ tf->c_bits[12] = (sidc >> 1) & 1; /* C13: SID msb */
+ tf->c_bits[13] = (sidc >> 0) & 1; /* C14: SID lsb */
+ tf->c_bits[14] = data[0] & 0x01; /* C15: TAF */
+ tf->c_bits[15] = 1; /* C16: spare */
+ tf->c_bits[16] = (data[0] & 0x08) >> 3; /* C17: DTXd */
+ memset(tf->c_bits+17, 1, 4); /* C18..C21: spare */
+ memset(&tf->t_bits[0], 1, 4);
+ tf->ufi = (data[0] & 0x02) >> 1;
+ if (data_len > 1)
+ osmo_pbit2ubit(tf->d_bits, data + 1, GSM_HR_BYTES * 8);
+ else
+ memset(tf->d_bits, 0, GSM_HR_BYTES * 8);
+ /* CRC is *not* computed by TRAU frame encoder - we have to do it */
+ osmo_crc8gen_set_bits(&gsm0860_efr_crc3, tf->d_bits, 44, tf->crc_bits);
+
+ return 0;
+}
+
+static int rtp2trau_hr16(struct osmo_trau_frame *tf, const uint8_t *data, size_t data_len)
+{
+ switch (tf->dir) {
+ case OSMO_TRAU_DIR_DL:
+ return rtp2trau_hr16_dl(tf, data, data_len);
+ case OSMO_TRAU_DIR_UL:
+ return rtp2trau_hr16_ul(tf, data, data_len);
+ default:
+ return -EINVAL;
+ }
+}
+
static int rtp2trau_hr8_dl(struct osmo_trau_frame *tf, const uint8_t *data, size_t data_len)
{
/* accept both TS 101 318 and RFC 5993 payloads */
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