[Live-devel] RTCP bug in multicast?

[Bruno Filipe Basilio]

Hi Mark,

> I just read the rtcp.cpp and find a problem in multicast mode.
> In RTCPInstance::incomingReportHandler1(), from line 342

There's a report of a similar problem which is affecting me also.
You can see the symptoms here:
http://lists.live555.com/pipermail/live-devel/2011-May/013313.html


>   To avoid this bug we must enable the code in
> Groupsock::multicastSendOnly(), so the server will not received any
> multicast packets that it just sent out.

I'm not shore how to implement your suggestion and I would very appreciated if could you help me on this?
Something like a patch would be great.


Best regards,
Bruno Basilio
Brisa Inovação e Tecnologia, S.A.

>
> ------------------------------
>
> Message: 5
> Date: Mon, 25 Apr 2011 14:10:32 +0800
> From: Mark <hustmark at gmail.com>
> To: live-devel <live-devel at ns.live555.com>
> Subject: [Live-devel] RTCP bug in multicast?
> Message-ID: <BANLkTinODCyKg=a-N892GmuQnqY7DXA5hg at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi Ross,
>    I just read the rtcp.cpp and find a problem in multicast mode.
>    In RTCPInstance::incomingReportHandler1(), from line 342 :
>
>    // Ignore the packet if it was looped-back from ourself:
>    if (RTCPgs()->wasLoopedBackFromUs(envir(), fromAddress)) {
>      // However, we still want to handle incoming RTCP packets from
>      // *other processes* on the same machine.  To distinguish this
>      // case from a true loop-back, check whether we've just sent a
>      // packet of the same size.  (This check isn't perfect, but it
> seems
>      // to be the best we can do.)
>      if (fHaveJustSentPacket && fLastPacketSentSize == packetSize) {
>        // This is a true loop-back:
>        fHaveJustSentPacket = False;
>        break; // ignore this packet
>      }
>    }
>
>  Here, the mechanism to prevent endless loop seems not perfect,
> checking the variables fHaveJustSentPacket  and fLastPacketSentSize is
> not enough.
>
>  Think about this situation:
>   1.  client1 sends out an RR(receive report)
>   2.  server receives the RR and run into
> RTCPInstance::incomingReportHandler1()
>   3.  before server runs to line 364 of rtcp.cpp (
> fRTCPInterface.sendPacket(pkt, packetSize); ) , client2 sends out an
> RR packet
>   4.  now server runs line 364-366;  resending the client1's RR
> packet to the multicast group, then modify fHaveJustSentPacket and
> fLastPacketSentSize;
>      fRTCPInterface.sendPacket(pkt, packetSize);
>      fHaveJustSentPacket = True;
>      fLastPacketSentSize = packetSize;
>   5. in the next SingleStep(),  the RTCP will receive the client2's
> RR packet and resending the packet( line 364-366 of  rtcp.cpp) to the
> multicast group
>   6. in the next SingleStep(), the RR packet in step 4 is arrived and
> server runs into RTCPInstance::incomingReportHandler1(), when it check
> looped-back packet in line 342,
>       the variables fHaveJustSentPacket  and fLastPacketSentSize are
> modified in step 5, so the checking is incorrect and may cause endless
> loop of multicast RTCP packet sending
>
>   To avoid this bug we must enable the code in
> Groupsock::multicastSendOnly(), so the server will not received any
> multicast packets that it just sent out.
>



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