Subject: [re-ECN] VIability issue #2

From: Leslie Daigle <[email-masked]>
Date: Thu, 05 Nov 2009 01:06:46 -0500

[This attempts to outline an issue that could be perceived as 
challenging the viability of congestion exposure work.  The goal is to 
capture the issue, as well as itemize reasonable supporting arguments 
(for viability) and remaining questions to be addressed.  Please respond 
with suggestions as needed for each section.  ]

Viability Issue #2

The expectation is that congestion exposure information will be carried 
in IP packet headers.  Is there really enough room to do that 
effectively (in IPv4)?

For discussion:
This assumes tight timing -- that feedback is received and acted upon 
such that subsequent flows will experience the same or similar network 
state.  What are the implications (or likelihood) of different paths? 
Or, are there other network state changes that will (could) change in 
that timeframe (now or in future developments).

Leslie.

-- 

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"Reality:
      Yours to discover."
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Leslie Daigle
[email-masked]
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From: <[email-masked]>
Date: Thu, 5 Nov 2009 12:47:47 -0000

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On
> Behalf Of Leslie Daigle
> Sent: 05 November 2009 06:07
> To: [email-masked]
> Subject: [re-ECN] VIability issue #2
> 
> 

Hopefully, but it is certainly tight... The key thing here is that the
IETF may have to actually decide the time has come to "unreserve" the
reserved flag! 

> that timeframe (now or in future developments).

There are issues to be resolved here about how quickly congestion may be
assumed to vary, how much impact a given flow may have on that
congestion level and as Leslie points out, the impact of path changes.
We also will later have to address how to aggregate and use the CONEX
info (eg using moving averages or counters...)

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From: João Taveira Araújo <[email-masked]>
Date: Fri, 06 Nov 2009 11:25:07 +0000

Hi,

Leslie Daigle wrote:
> Viability Issue #2
>
> The expectation is that congestion exposure information will be 
> carried in IP packet headers.  Is there really enough room to do that 
> effectively (in IPv4)?

There is also the question of whether the hop-by-hop IPv6 extension 
header is good enough. It has the space, but there are limits to what 
you can do in practice (encapsulation etc). Might be worth discussing.

Joao.