mgcp: Allow switching the audio streams, patch the header
Patch the sequence number, the SSRC and the timestamp to
allow to mix various voice streams, e.g. toggling the loop
during the call.
diff --git a/openbsc/include/openbsc/mgcp_internal.h b/openbsc/include/openbsc/mgcp_internal.h
index adb01f4..f6f8d6e 100644
--- a/openbsc/include/openbsc/mgcp_internal.h
+++ b/openbsc/include/openbsc/mgcp_internal.h
@@ -39,8 +39,13 @@
struct mgcp_rtp_state {
int initialized;
+ uint32_t orig_ssrc;
+ uint32_t ssrc;
uint16_t seq_no;
int lost_no;
+ int seq_offset;
+ uint32_t last_timestamp;
+ int32_t timestamp_offset;
};
struct mgcp_endpoint {
diff --git a/openbsc/src/mgcp/mgcp_network.c b/openbsc/src/mgcp/mgcp_network.c
index d2dbeeb..b5e2cdd 100644
--- a/openbsc/src/mgcp/mgcp_network.c
+++ b/openbsc/src/mgcp/mgcp_network.c
@@ -97,6 +97,7 @@
static void patch_and_count(struct mgcp_rtp_state *state, int payload, char *data, int len)
{
uint16_t seq;
+ uint32_t timestamp;
struct rtp_hdr *rtp_hdr;
if (len < sizeof(*rtp_hdr))
@@ -104,15 +105,36 @@
rtp_hdr = (struct rtp_hdr *) data;
seq = ntohs(rtp_hdr->sequence);
+ timestamp = ntohl(rtp_hdr->timestamp);
if (!state->initialized) {
- state->seq_no = seq;
+ state->seq_no = seq - 1;
+ state->ssrc = state->orig_ssrc = rtp_hdr->ssrc;
state->initialized = 1;
- } else if (state->seq_no + 1u != seq)
- state->lost_no = abs(seq - (state->seq_no + 1));
+ state->last_timestamp = timestamp;
+ } else if (state->ssrc != rtp_hdr->ssrc) {
+ state->ssrc = rtp_hdr->ssrc;
+ state->seq_offset = (state->seq_no + 1) - seq;
+ state->timestamp_offset = state->last_timestamp - timestamp;
+ LOGP(DMGCP, LOGL_NOTICE, "The SSRC changed... SSRC: %u offset: %d\n",
+ state->ssrc, state->seq_offset);
+ }
+ /* apply the offset and store it back to the packet */
+ seq += state->seq_offset;
+ rtp_hdr->sequence = htons(seq);
+ rtp_hdr->ssrc = state->orig_ssrc;
+
+ timestamp += state->timestamp_offset;
+ rtp_hdr->timestamp = htonl(timestamp);
+
+ /* seq changed, now compare if we have lost something */
+ if (state->seq_no + 1u != seq)
+ state->lost_no = abs(seq - (state->seq_no + 1));
state->seq_no = seq;
+ state->last_timestamp = timestamp;
+
if (payload < 0)
return;