Subject: Re: [Tsvwg] sctp performance

From: "Armando L. Caro Jr." <[email-masked]>
Date: Thu, 14 Oct 2004 12:36:47 -0400 (EDT)

On Wed, 13 Oct 2004, Brian F. G. Bidulock wrote:

> As I'm sure you know, the OpenSS7 SCTP implementation has been using a
> weighted version of the algorithms from the second paper since 2001.  It
> also uses a fast restoration technique for restoring suspect
> destinations since 2001.  The implementation also uses a (patentable) FR
> algorithm that is far simpler than the split-FR presented in the first
> paper.  These allow the implementation to exhibit multiplicative
> throughput and single RTO fail-over simultaneously.  Neither algorithm
> violates AIMD, FR or max burst rules.  They are in fact more
> conservative.
>
> I believe I sent you this weighted algorithm some years ago and said it
> was worthy of attention. ;)

To be honest, I didn't remember you sending me an algorithm. I dug through
my old mails and found a private discussion we had in Nov 2001. I found
the weighted algorithm that you're talking about, but the algorithm you
sent me was for selecting a destination to retransmit to and failover to.
Since the email was sent privately, I don't want to post the algorithm in
this public forum without your permission. But in any case, the
algorithm/selection process looks reasonable, but I don't see how it
applies to Concurrent Multipath Transfer (CMT).

Maybe I am misunerstanding you, and you are not doing CMT? Are you saying
that additional interfaces multiplies the throughput performance because
your failover algorithm is so agressive? You are advocating using PMR=0,
RTO.Min=0-10ms, etc. I have also done work that comes to the conclusion
that PMR=0 provides the best performance
(http://www.armandocaro.net/papers/2004.TR2005-04.acaro.pdf), but an
RTO.Min=0-10ms would only work on special case networks (eg, SS7)  and not
the Internet.

~armando

0--                                              --0
| Armando L. Caro Jr.  |  Protocol Engineering Lab |
| www.armandocaro.net  |    University of Delaware |
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From: Janardhan Iyengar <[email-masked]>
Date: Thu, 14 Oct 2004 12:49:30 -0400 (EDT)

Hi Brian/all,

(I trimmed the Cc list. And I apologize for posting on several lists. But
this discussion started on all these lists. Maybe it could move to
one/more lists as per interest?)

The papers that are referred to in this thread are:
http://www.cis.udel.edu/~iyengar/publications/2004.spects.iyengar.pdf
http://www.cis.udel.edu/~iyengar/publications/2004.icon.iyengar.pdf

I add another paper here, which is currently under submission and is a
continuation of CMT work:
http://www.cis.udel.edu/~iyengar/publications/2005.icdcs.iyengar.pdf

> weighted version of the algorithms from the second paper since 2001.

[...]

> The implementation also uses a (patentable) FR algorithm that is far
> simpler than the split-FR presented in the first paper.

I certainly did not know that you already implemented these algorithms. I
don't think any of the co-authors on the papers knew either. Could you
post the algos, or send a reference that we could look up?

If your FR algo is far simpler, I would certainly like to look at it,
because I could not get the SFR-CACC algo to be simpler than it is. Well,
it is simpler than it _was_, but I do not know how to make it any simpler.
Also, the first paper presents two other algos - the CUC and DAC algos. At
least the CUC algorithm is, IMHO, necessary to see expected throughput, at
least if the paths in question have different end-to-end delays. Did  you
implement something like CUC too?

You say the algo is "patentable" - I do not understand what that means.
Did you mean to say the algo is "patentED"? So, can you post the algo?

Note: The ID (draft-iyengar-sctp-cacc-xx.txt) which was first published in
Feb 2002 has expired now, but I'm planning to resubmit it in a new form
and with significant additions/modifications. I wanted to spend more time
looking at changeover/CMT concerns with SCTP before putting something out
as an ID.

regards,
jana

---------------------------------------------------------------
Janardhan R. Iyengar           http://www.cis.udel.edu/~iyengar
Protocol Engineering Lab  --   CIS   --  University Of Delaware
---------------------------------------------------------------