Re: [ns] ECN ..

[Tan Koan-Sin <freedom@csie.nctu.edu.tw>]

On Tue, Jun 26, 2001 at 11:17:27PM +1200, hai22 wrote:
> I have some  simple questions ...
> 1-what does TCP Reno implementation in ns do if it receives an ack with
> ECN bit set  i.e ack with E flag ?

You mean CE bit, right? Check the source code

in RenoTcpAgent::recv() you could find,
	if (hdr_flags::access(pkt)->ecnecho() && ecn_)
                ecn(tcph->seqno());  
which means TcpAgent::ecn() will be called.

> 2-What does TCP vegas in ns do after receiveing the E  flag in ack ..
> I know that TCP Sack with rate halving reduces its rhcwnd for ECN .

Check the source code you will find the answer :-)

> 3-If we set ecn echo bit on in tcp reno with drop tail , then how ecn is
> indicated ?

ECN requires router support. If there is no AQM machenism to 
set CE bit, what can you expect?

> I would be very thankful for any reply in this matter because it puzzles
> me that what is use of E flag if Reno source do not reduce sending rate
> or congestion window cwnd_ ... 

Check TcpAgent::ecn()