I have just added Fernando Cela Diaz's RFC 793 TCP implementation to the NS distribution, with his add-ons for educational purposes. This is explained at "http://www.ce.chalmers.se/~fcela/rfc793edu.html", and, after the nightly snapshot appears tonight, can be demonstrated with the command "./test-all-rfc793edu" in "tcl/test". It is pretty nice... - Sally