[e2e] Can feedback be generated more fast in ECN?

[Rogerio de Carvalho Andrade]

Hi, Zhang.

We have discussed it some time ago. I worked with this kind of "reverse
notification" in my master dissertation (finished last month) using 
ICMP-SQM. We create an algorithm, named SQM-Response, that improve
TCP congestion control mechanism.

If you (all) are interested, you can download a postscript version of
my dissertation from http://www.cin.ufpe.br/~rca3/tese/ (in portuguese)

   Andrade, Rogerio. "Algoritmo SQM-Response para Controle de
     Congestionamento do TCP em Redes com QoS" - UFPE - 2001 
     (in portuguese) - http://www.cin.ufpe.br/~rca3/tese/

We are working on a paper (in english) about it and we intend to submit it
soon!

Best regards,
Rogerio.

Zhang Miao wrote:
> 
> Hi,
>    In ECN-RED, router only marks the packet and let the receiving end to "echo" the
> congestion notification to the sender.
>    I have a naive question. Can the feedback be sent directly from the congested router
> to the TCP sender?
>    Some schemes of action at router are listed here:
> 1. Only mark the packet. (ECN)
> 2. Mark the packet and send a feedback to TCP sender immediately.
> 3. Send a feedback to TCP sender and drop the packet.
>    This scheme can be used for droptail.
> 
> The advantages of sending a feedback directly:
> 1. reduce the response time.
> 2. reduce the loss probability of feedback.
>    consider the path of marked packet and the ACK with CN bit set.
> 
> Disadvantages:
> 1. add more burden the reverse direction of the link.
> 2. add more burden to the router.
> 
>    Some mechanisms also need to be added to TCP to cope with the duplicate feedback
> in scheme 2.
> 
>    The designer of ECN must have thought of the scheme above. Can anyone tell me why
> this scheme was not used when ECN was designed?
> 
> Thanks!
> 
> *****************************************************************
> *    Zhang Miao                                                 *
> *    Ph.D candidate,Department of Computer Science & Technology *
> *    Tsinghua University,Beijing,China(100084)                  *
> *    Tel: (8610)-62785822                                       *
> *    Email: zm at csnet1.cs.tsinghua.edu.cn                        *
> *****************************************************************