[Ns-bugs] [Bug 166] Loss of Tag and change in size of Packet using TCP.

[bugzilla-daemon@nsnam-www.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=166





------- Comment #6 from raj.b at gatech.edu  2008-04-15 10:19 -------
The tag being lost is a "feature" (but kind of a bug :-).  The implementation
of TCP simply copies the data in a packet into an internal TX buffer.  Then TCP
copies segments out of this buffer, packetizes them, and sends them according
to its congestion control algorithm.  Unfortunately, this is where the tag is
lost.  The way I conceived of the TCP API was that it dealt with real world
buffers, not with ns3::Packets.  This is because even if you send a single
tagged Packet with TCP, there is no guarantee that that information will go on
the wire as one packet (in fact if the data is larger than an MSS, it WILL NOT
hit the wire as one packet).

I think a solution that preserves tags might be possible if some kind of tag
structure is kept in paralell to the TX buffer...but what about a case where
the MSS boundaries overlap two differently tagged packets?  I'm not sure what
to do in this case...


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