[Live-devel] About RTSP over UDP behind firewall.

[Fang Laifa]

Dear all,

    I am now studying RTSP playback the content from m.youtube.com using
Mplayer/Live555. This is my testing environment: Ubuntu 7.0.4,
Mplayer-1.0rc2, live.2008.07.06. rtsp-stream-over-tcp is enabled at
first when trying to play
rtsp://bfug.rtsp-youtube.l.google.com/Ci4LENy73wIaJQlajfjZ7w0SCxMYDSANFE
IJbXYtZ29vZ2xlSARSB2RldGFpbHMM/0/0/0/video.3gp. However Mplayer reported
"Unsupported Transport". It seems that the server from m.youtube.com
could not support RTP over TCP. So rtsp-stream-over-tcp is disabled
instead. Then Mplayer also failed to play the rtsp using RTP over UDP
since my testing PC is behind my company's firewall.

   But the problem is that the real player can play the same rtsp
without any problem, which is also on another pc behind the firewall.
Both Mplayer and realplayer packets are captured using wireshark while
playing the rtsp. The captured files realplayer_rtsp_m_youtube.cap and
mplayer_rtsp_m_youtube.cap are attached FYR. From the captured packets,
the real player also uses RTP over UDP. But it can actually go through
the firewall. Also from realplayer_rtsp_m_youtube.cap, there are two RTP
packets which are sent from my local PC (10.6.64.218) to m.youtube.com
(72.14.209.177) before actual RTP/UDP packets receiving from youtube
server. It seems that these two RTP packets with empty content triggered
the firewall bypass. From mplayer_rtsp_m_youtube.cap, there are no such
kind of triggered packets. So by my estimation, this is probably the
reason that realplayer can bypass the firewall but mplayer cannot.

   So my question is that whether live55 have any plan to support
similar mechanism with RTP over UDP to bypass the firewall?
   Another question regarding the packets from wireshark. I can find
such warnings "Checksum: 0x65bf [incorrect, should be 0x60a6 (maybe
caused by "TCP checksum offload"?)]" for some rtsp/tcp packets. Does
anybody know what's the problem? 
   Thanks.

Rgds,
Laifa


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