[Live-devel] Frame drop in TCP mode

[Ross Finlayson]

> I feel that in a 100Mbps isolated network, 3.5Mbps is a very nominal bitrate.

What you ‘feel’ is not relevant here.  The throughput of a TCP connection depends upon the round-trip-time (i.e. delay) between the two endpoints, and (especially) the packet loss rate over the connection.  See, for example, this page
	https://www.switch.ch/network/tools/tcp_throughput/
which lets you estimate the expected bitrate of a TCP connection.  Note that this has nothing to do with how fast your network interface happens to be.

For example, if you have a TCP connection between endpoints with a 200 ms round-trip time, and a 0.1% packet loss rate, then you would expect a bitrate of only 3.69 Mbps over the TCP connection.

Note that if your stream’s bitrate exceeds the capacity of your TCP connection, then eventually your sender OS’s TCP buffer will fill up, and (the server’s) writes to the TCP connection will start failing, causing RTP packets to be lost.  This is probably what is happening in your case.

This is why streaming over TCP is a bad idea, and should be avoided if at all possible.


> I tried enabling debug messages using DEBUG macro and increasing debugLevel using int Socket::DebugLevel = 4. Did not see message about drop.

The error message you want to look for is at line 344 of “liveMedia/RTPInterface.cpp”.  You can enable this by defining the
	DEBUG_SEND
macro when compiling this file.  This error message will get displayed when a write of a RTP (or RTCP) packet over the TCP connection fails (probably due to the stream’s bitrate exceeding the capacity of your TCP connection).


Ross Finlayson
Live Networks, Inc.
http://www.live555.com/