RTSP over UDP

About

• 10393 series
• /usr/bin/str

Notes

• In situations when streaming across middleboxes (switches and other devices) make sure the camera link is the slowest one.
• Example congestion situatation:

camera <-- 1000Mbps --> Gigabit switch <-- 100Mbps (PC NIC limited) --> PC
PC might not get all the packets depending on switch's buffers sizes (e.g. for netgear GS105 has 128kB which gets overflowed at image sizes 200+kB)

• Setting link speed examples:

ethtool -s eth0 speed 100 duplex half autoneg off
ethtool -s eth0 speed 1000 duplex full autoneg off

• dump UDP packets log on the camera (tcpdump if installed):

tcpdump -i eth0 -n udp port <someport> -w packets.pcap

• log network packets on PC:

wireshark works fine

• live555 is used by vlc and mplayer while gstreamer is standalone

As UDP has no congestion control there might be several workarounds:
1. patch live555 and gstreamer
2. slow down camera link

• Patching live555 options:

1. Stick close to RFC4585 and RFC6679, also checkout RFC8087 & RFC8311?
2. Make RTCP RR reports sent out by the receiver for every 50 (or any other number) packets received - implement handling this info in the sender (camera)
Implementing 2:
    RTCP.c:
        if (fSource != NULL && fSource->RTPgs() == RTCPgs) {
            // We're receiving RTCP reports that are multiplexed with RTP, so ask the RTP source
            // to give them to us:
            fSource->registerForMultiplexedRTCPPackets(this);
        } else {
            // need to register our RTCP instance here it will be passed to MultiFramedRTPSource.c which receive RTP packets
            // just reused the instance for multiplexed packets
            fSource->registerForMultiplexedRTCPPackets(this);
        }
    MultiFramedRTPSource.c:
        receptionStatsDB().noteIncomingPacket(...)
        // insert after this line something like:
        int pnum = receptionStatsDB().totNumPacketsReceived();
        if ((pnum%50)==0){
            if (fRTCPInstanceForMultiplexedRTCPPackets!=NULL){
                // here fRTCPInstanceForMultiplexedRTCPPackets is just reused
                fRTCPInstanceForMultiplexedRTCPPackets->sendReport();
            }
        }

• Patching gstreamer:

First, need to find how to make gstreamer send RR reports. Then proceed as with live555.

Other links

• Loss, Latency, and Speed - some general info
• RFC4585: Extended RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/AVPF)
• RFC6679: Explicit Congestion Notification (ECN) for RTP over UDP
• RFC8087: The Benefits of Using Explicit Congestion Notification (ECN)
• RFC8311: Relaxing Restrictions on Explicit Congestion Notification (ECN) Experimentation