Re: [ns] Minor Bug in TCP code

[Sugat Jain <sugat@cs.utexas.edu>]

On Sun, 2 Dec 2001, Lloyd Wood wrote:
>
>I'm confused.
>
>In ns, only FullTcp attempts to simulate SYN/ACK exchanges (well,
>that's what the documentation says - can't see a mention of the syn_
>boolean there), although the tcp.cc code is shared by both.
>
>What TCP agent are you trying to fix the problem for?


I haven't looked at the FullTCP code yet. However I saw this problem while
using the basic TCP (i.e. Agent/TCP which I guess in Tahoe implemented in
tcp.cc) and TCPReno.  For TCPReno, it has the problem as it derives from
TCP.

Also there is a syn_ flag that is set in ns-defaults and has been set to
true. So for, I guess any TCP variant, which derives from the basic TCP
class and does not override it, will have the problem of the first packet
being overridden by a SYN packet, at least in terms of size.

As I have not studied all the code in great detail, my understanding may
be wrong, but I think this minor error may have been introduced while
adding support for another variant of TCP.

>
>(last I looked, FullTcp receivers still relied on packet size as a way
>of detecting SYN etc. - breaking FullTcp is a useful way to
>demonstrate that you're not adding/removing tunnelling overhead
>correctly or symmetrically.)
>
>L.
>

Sugat