Re: [ns] ECN!!!

[Kaleelazhicathu R R Kumar <kaleelaz@comp.nus.edu.sg>]

hi,
 thanks for the reply.Can you please let me know if the two way tcp
supports ECN??according to the ns manual,no validations have been done for
this.I am using a tcp-full.
   thanks.
   Renjish.

On Mon, 23 Oct 2000, Sally Floyd wrote:

> >as far as i understand,the sender
> >sets the ecn capable flag(N)  and the receiver sets the ecn echo
> >flag(C) depending on the presence of congestion experienced flag.
> 
> Oops.  I have corrected the manual, and it should appear
> tomorrow, as follows:
> 
>  Four of the flags are used for ECN:  ``E'' for Congestion Experienced
>  (CE) and ``N'' for ECN-Capable-Transport (ECT) indications in the
>  IP header, and ``C'' for ECN-Echo and ``A'' for Congestion Window
>  Reduced (CWR) in the TCP header.  This is also in the flags.h file,
>  and is illustrated in the validation tests in "./test-all-ecn".
> 
> However, the first packets of the TCP connection in the one-way TCP
> implementation in NS are special, and play the role of the SYN and
> SYN-ACK packets in TCP.  From RFC 2481, the SYN packet sets the
> ECN-Echo and CWR bits in the TCP header, and the SYN-ACK packet sets
> the ECN-Echo bit.  This is the negotiation of ECN-capability.
> However, I just checked, and for some reason the line about setting
> the CWR bit in the first (SYN) packet is commented-out in tcp.cc, so the
> first TCP packet in NS (for one-way TCP) only contains the ECN-Echo bit 
> and not the CWR bit.  I will correct it shortly, so that it
> corresponds to the RFC.
> 
> - Sally
> --------------------------------
> http://www.aciri.org/floyd/
> --------------------------------
>