[Iccrg] RE: On the deployment of Explicit Rate Notificationprotocols

[SCHARF, Michael]

Hi Dino,

the core idea of this framework is to allow only sending rates slower
than the one of the end-to-end congestion control, right?

This IMHO raises a couple of questions:

* Is there a significant benefit? If a router wants to slow down a given
flow, it can use ECN markings right now (or just packet drops).
Additional feedback from the network may enable a more fine-grained
control, which may improve fairness and convergence speed. But I am not
sure whether this improvement e. g. to ECN is really significant, if no
speedup compared to end-to-end is allowed.

* I think that the equation "cwnd_ = min (cwnd_, cwnd_ern_)" can be
understood and implemented in two different ways: 

  (1): Use one cwnd only. Then, the minumum is taken probably always
whenever cwnd is updated. But then some corner cases could be tricky, e.
g., when cwnd is inflated during fast rtx.

  (2): Use a shadow cwnd, i. e., "cwnd_ = min (cwnd_shadow_,
cwnd_ern_)", wherein cwnd_shadow is updated by the end-to-end algorithm
independent of ERN. Then one key question is how to deal with
connections that are limited by cwnd_ern. One might need a kind of
congestion window validation to ensure TCP compatibility.

* Apparently, the reseach community failed so far to agree on the header
information that explicit rate notification would actually need. The
draft seems to leave that question open. For a framework document, this
may be OK. But I could imagine that proposals would - at least in theory
- require also signaling of information in the SYNs. This is not
foreseen in your architecture, right?

BTW, I guess that you are aware of the challenges listed in section 3.1
of RFC 6077.

Michael


> -----Original Message-----
> From: iccrg-bounces at cs.ucl.ac.uk 
> [mailto:iccrg-bounces at cs.ucl.ac.uk] On Behalf Of Murari Sridharan
> Sent: Monday, September 26, 2011 10:12 AM
> To: Dino LOPEZ; michawe at ifi.uio.no; iccrg at cs.ucl.ac.uk
> Subject: [Iccrg] RE: On the deployment of Explicit Rate 
> Notificationprotocols
> 
> +iccrg
> 
> -----Original Message-----
> From: Dino LOPEZ [mailto:dino.lopez at unice.fr]
> Sent: Monday, September 26, 2011 1:07 AM
> To: michawe at ifi.uio.no; Murari Sridharan
> Subject: On the deployment of Explicit Rate Notification protocols
> 
> Dear ICCRG chairs,
> 
> We have submitted a new Internet draft which provides an 
> architecture to allow the deployment of congestion control 
> protocols with explicit rate notification from forwarding 
> devices (Explicit Rate Notification protocols).
> 
> This draft is currently available at
> http://www.ietf.org/internet-drafts/draft-lopez-ietf-tsvwg-ipe
> rn-00.txt
> 
> We will be grateful if you can relay this information to the 
> ICCRG community and we can receive any feedback from the you 
> all (at http://trac.tools.ietf.org/group/irtf/trac/wiki/ICCRG 
> it is remarked that one should send an email to the chairs 
> requesting that the ICCRG perform a review of the document)
> 
> Best Regards,
> 
> The authors
> Lochin, Emmanuel (emmanuel.lochin at isae.fr) Lopez Pacheco, 
> Dino (dino.lopez at unice.fr) Sathiaseelan, Arjuna 
> (arjuna.sathiaseelan at gmail.com)
> 
> 
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