mgcp: Attempt to count missing RTP packets with a basic calculation
This code compares the UDP sequence numbers of two RTP messages
and guesses if packets are missing. It is guessing in two ways:
1.) by default the sequence number is 0, so on the first
value we ignore the jump... we might ignore a real issue
in case of a wrap around which is easily possible as the
sequence should be a random number.
2.) the UDP stream might have been reordered on the network
and we would see the jump...
In any case these two shortcomings are acceptable for the feature
that is meant to provide some basic analysis..
diff --git a/openbsc/include/openbsc/mgcp_internal.h b/openbsc/include/openbsc/mgcp_internal.h
index d5aec30..918ba4b 100644
--- a/openbsc/include/openbsc/mgcp_internal.h
+++ b/openbsc/include/openbsc/mgcp_internal.h
@@ -61,6 +61,12 @@
/* statistics */
unsigned int in_bts;
unsigned int in_remote;
+
+ /* sequence bits */
+ uint16_t net_seq_no;
+ uint16_t bts_seq_no;
+ int net_lost_no;
+ int bts_lost_no;
};
#define ENDPOINT_NUMBER(endp) abs(endp - endp->cfg->endpoints)
diff --git a/openbsc/src/mgcp/mgcp_network.c b/openbsc/src/mgcp/mgcp_network.c
index 6e6b7a6..137aa93 100644
--- a/openbsc/src/mgcp/mgcp_network.c
+++ b/openbsc/src/mgcp/mgcp_network.c
@@ -94,17 +94,29 @@
endp->net_rtp, buf, 1);
}
-static void patch_payload(int payload, char *data, int len)
+static void patch_and_count(uint16_t *last_seq, int *lost, int payload, char *data, int len)
{
+ uint16_t seq;
struct rtp_hdr *rtp_hdr;
if (len < sizeof(*rtp_hdr))
return;
+ rtp_hdr = (struct rtp_hdr *) data;
+ seq = ntohs(rtp_hdr->sequence);
+
+ /* 0 is assumed to be not set */
+ if (*last_seq == 0)
+ *last_seq = seq;
+ else if (*last_seq + 1 != seq)
+ *lost += abs(*last_seq - seq);
+
+ *last_seq = seq;
+
+
if (payload < 0)
return;
- rtp_hdr = (struct rtp_hdr *) data;
rtp_hdr->payload_type = payload;
}
@@ -194,13 +206,15 @@
if (dest == DEST_NETWORK) {
if (proto == PROTO_RTP)
- patch_payload(endp->net_payload_type, buf, rc);
+ patch_and_count(&endp->bts_seq_no, &endp->bts_lost_no,
+ endp->net_payload_type, buf, rc);
return udp_send(fd->fd, &endp->remote,
proto == PROTO_RTP ? endp->net_rtp : endp->net_rtcp,
buf, rc);
} else {
if (proto == PROTO_RTP)
- patch_payload(endp->bts_payload_type, buf, rc);
+ patch_and_count(&endp->net_seq_no, &endp->net_lost_no,
+ endp->bts_payload_type, buf, rc);
return udp_send(fd->fd, &endp->bts,
proto == PROTO_RTP ? endp->bts_rtp : endp->bts_rtcp,
buf, rc);
diff --git a/openbsc/src/mgcp/mgcp_protocol.c b/openbsc/src/mgcp/mgcp_protocol.c
index d82bd68..8131277 100644
--- a/openbsc/src/mgcp/mgcp_protocol.c
+++ b/openbsc/src/mgcp/mgcp_protocol.c
@@ -764,4 +764,7 @@
endp->in_bts = endp->in_remote = 0;
memset(&endp->remote, 0, sizeof(endp->remote));
memset(&endp->bts, 0, sizeof(endp->bts));
+
+ endp->net_seq_no = endp->bts_seq_no = 0;
+ endp->net_lost_no = endp->bts_lost_no = 0;
}