I'm trying to build an RTP packet metric analyzer in C, but i ended up in a strange issue, I'm cutting down implementation details for ease of exposure:
Since the RTP packets are contained in UDP my socket is initalized with the following parameters:
sock_domain = AF_INET;
sock_type = SOCK_DGRAM;
sock_proto = IPPROTO_UDP;
and binded with those parameters:
socket_addr.sin_family = AF_INET;
socket_addr.sin_port = 10000; // My server is streaming on 10000
socket_addr.sin_addr.s_addr = INADDR_ANY;
and joined the multicast group:
mgroup_req.imr_multiaddr.s_addr = inet_addr("224.1.0.1"); // Multicast group of the stream
mgroup_req.imr_interface.s_addr = INADDR_ANY;
set the multicast group from which i receive to:
mgroup_addr.sin_family = socket_addr.sin_family;
mgroup_addr.sin_port = socket_addr.sin_port;
mgroup_addr.sin_addr.s_addr = mgroup_req.imr_multiaddr.s_addr;
receiving packets with recvfrom function:
errcode = recvfrom(sockfd, &recvbuff, IPMAXSIZE, 0, (struct sockaddr *)&mgroup_addr, &mgroup_addr_len)
Something goes wrong, while i can receive standard UDP packets addressed to the multicast group 224.1.0.1, the RTP packets are not received the first time, but sending them again makes the trick.
Scenario 1:
I send n UDP packets: They are correctly received
Scenario 2:
I send n RTP packets: Nothing happens
I send again the same n RTP packets: They are correctly received
whatever the n number of packets is... so weird but true.
edit: At the analyzer side I'm running a sniffer and it shows both the packet bursts, so messages arrives at the analyzer side, it's not a sender related problem.
Question:
the code is exactly the same (read: Same executable) for the RTP scenario AND the UDP scenario. What am I doing wrong?
Side notes:
RTP manage libraries or high-level RTP libraries suggestions are a no-no, I MUST work at this level of abstraction because of the metrics i need to analyze.
Also Network metrics analyzer are a no-no, I MUST do this with my own code.
Thanks in advance.
