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mgcp-client: always send 'm=audio' line 

Re-add the m=audio line to SDP emitted from libosmo-mgcp-client, even if
the audio port is not set yet

Patch a5acaa68db introduced a presence
flag for the RTP audio port number. This flag, when unset, also omitted
the 'm=audio...' line completely, dropping the PT number definitions.

Correct:

  m=audio 1234 RTP/AVP 96             <--- anounce 96
  a=rtpmap:96 VND.3GPP.IUFP/16000     <--- further specify 96
  a=fmtp:96 ...                       <--- further specify 96

When m=audio is missing, we only have orphaned rtpmap and fmtp entries.
They are supposed to further specify the 96 listed in 'RTP/AVP 96',
instead they are without context:

  a=rtpmap:96 VND.3GPP.IUFP/16000
  a=fmtp:96 ...

When the presence map indicates no port known, we still need to emit the
list of PT numbers; so we're forced to send a port of 0:

  m=audio 0 RTP/AVP 96
  a=rtpmap:96 VND.3GPP.IUFP/16000
  a=fmtp:96 ...

This is an important fix for osmo-hnbgw, which sends the first CRCX with
an IUFP codec, at a time when the remote port is not yet known. osmo-mgw
requires an m=audio line to accept incoming IuUP Initializaition
requests. When m=audio is missing, osmo-mgw does not parse the IUFP
codec, and 3G voice fails completely. This mgcp-client patch will emit
valid codec config also when port == 0, fixing osmo-hnbgw voice, because
osmo-mgw will know about IUFP from the start.

Related: SYS#6907 SYS#6974
Related: osmo-mgw a5acaa68db
Change-Id: Id95b629453aec999100b5af821c6a0b9562bb597
This commit is contained in:
Neels Hofmeyr 2024-04-25 00:55:02 +02:00
parent fa393fa1e9
commit 36c823eef1
1 changed files with 9 additions and 6 deletions
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15
src/libosmo-mgcp-client/mgcp_client.c
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@ -1315,6 +1315,7 @@ static int add_sdp(struct msgb *msg, struct mgcp_msg *mgcp_msg, struct mgcp_clie
int local_ip_family, audio_ip_family;
const char *codec;
unsigned int pt;
uint16_t audio_port;
#define MSGB_PRINTF_OR_RET(FMT, ARGS...) do { \
if (msgb_printf(msg, FMT, ##ARGS) != 0) { \
@ -1366,17 +1367,19 @@ static int add_sdp(struct msgb *msg, struct mgcp_msg *mgcp_msg, struct mgcp_clie
MSGB_PRINTF_OR_RET("t=0 0\r\n");
/* Add RTP address port and codecs */
if (mgcp_msg->presence & MGCP_MSG_PRESENCE_AUDIO_PORT) {
if (mgcp_msg->audio_port == 0) {
audio_port = 0;
if ((mgcp_msg->presence & MGCP_MSG_PRESENCE_AUDIO_PORT)) {
audio_port = mgcp_msg->audio_port;
if (!audio_port) {
LOGPMGW(mgcp, LOGL_ERROR,
"Invalid port number, can not generate MGCP message\n");
return -EINVAL;
}
MSGB_PRINTF_OR_RET("m=audio %u RTP/AVP", mgcp_msg->audio_port);
for (i = 0; i < mgcp_msg->ptmap_len; i++)
MSGB_PRINTF_OR_RET(" %u", mgcp_msg->ptmap[i].pt);
MSGB_PRINTF_OR_RET("\r\n");
}
MSGB_PRINTF_OR_RET("m=audio %u RTP/AVP", audio_port);
for (i = 0; i < mgcp_msg->ptmap_len; i++)
MSGB_PRINTF_OR_RET(" %u", mgcp_msg->ptmap[i].pt);
MSGB_PRINTF_OR_RET("\r\n");
/* Add optional codec parameters (fmtp) */
if (mgcp_msg->param_present) {