[e2e] question about ECN implementation ?

[K. K. Ramakrishnan]

Guy,

With respect to your question:

"Does someone know how a TCP receiver responds to a CE IP code that
comes in a packet that has the CWR flag set in the TCP header?
Means, should the receiver continue sending the ECN-echo bit set,
and ignore the CWR flag, or the opposite,
ignore the CE flag in the IP and reset the ECN-echo flag?"

My understanding of what we have in RFC 3168 is as follows:

As a receiver, it would interpret the receipt of the CWR flag as
an indication that the sender reduced the window in response to earlier
ECN-Echo flags it received. So, the sender sent the CWR packet (a
data packet with the CWR flag set) with data in it. If the CWR packet
encountered congestion (CE flag set), the receiver would interpret it as 
the
beginning of another epoch, and "the receiver should once again
send ACK packets with the ECN-Echo flag set."

The receiver in this case is not "ignoring" the flags. It treats the
two flags in the right way: The CWR flag is used to tell the receiver
do not send the ECN-Echo flag for non-CE data packets until you
receive another CE packet. Since we have received the "next" CE packet,
the receiver "would once again send ACK packets with the ECN-Echo flag set".


Hope this helps.
 Thanks,
        K. K. Ramakrishnan

Guy Kaminitz wrote:

>Hi,
>
>The question is about the TCP ECN algorithm.
>
>Does someone know how a TCP receiver responds to a CE IP code that comes in a packet that has the CWR flag set in the TCP header?
>Means, should the receiver continue sending the ECN-echo bit set, and ignore the CWR flag, or the opposite, ignore the CE flag in the IP and reset the ECN-echo flag?
>Should the receiver send a CWR TCP header with the ECT(0) or ECT(1) bit set ? If not, it solves the small detail I encountered.
>
>Thank,
>Guy Kaminitz
>
>
>  
>

-- 
K. K. Ramakrishnan                     Email: kkrama at research.att.com
AT&T Labs-Research, Rm. A117           Tel: (973)360-8764
180 Park Ave, Florham Park, NJ 07932   Fax: (973) 360-8050
      URL: http://www.research.att.com/info/kkrama