RE: Pseudorandom Flow Labels

"Hemant Singh (shemant)" <shemant@cisco.com> Wed, 06 April 2011 01:13 UTC

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Subject: RE: Pseudorandom Flow Labels
Date: Tue, 5 Apr 2011 20:15:18 -0500
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Thread-Topic: Pseudorandom Flow Labels
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From: "Hemant Singh (shemant)" <shemant@cisco.com>
To: "james woodyatt" <jhw@apple.com>, <ipv6@ietf.org>
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Cc: Thomas Narten <narten@us.ibm.com>
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Snipped from RFC 4193 is this text.  "pseudo-randomly allocated global
ID".  If pseudo-random was accepted in this RFC, why are we discussing
pseudo-random again?  One reason is acceptable to me that over the years
we learn to be more precise or more audience read the documents and thus
more folks can ask for a better choice for a term.  I agree with Thomas
that we can pick a term but then the term has to be defined clearly.
Here is some text from RFC 4193 one could use.  This way we avoid the
IETF specifying what pseudo-random algorithm to use but still get a as
precise as possible definition that has been accepted in other RFCs such
as RFC 4193.

[Locally assigned Global IDs MUST be generated with a pseudo-random
algorithm consistent with [RANDOM].]  

Hemant

-----Original Message-----
From: ipv6-bounces@ietf.org [mailto:ipv6-bounces@ietf.org] On Behalf Of
james woodyatt
Sent: Tuesday, April 05, 2011 6:49 PM
To: Thomas Narten
Cc: 6MAN Working Group
Subject: Re: Pseudorandom Flow Labels

On Apr 5, 2011, at 14:48 , Thomas Narten wrote:
> [I wrote:]
>> 
>> I share your concern.  Would replacing "pseudo-random" with "low
discrepancy" address your concerns?
> 
> Replacing the term with another would be fine. That said, the real
issue is we need to define what we mean by whatever term we use.


Discrepancy is a measure of the deviation of a point set from a uniform
distribution.  Or, so Wolfram MathWorld tells me.
<http://mathworld.wolfram.com/Discrepancy.html>   A low discrepancy
sequence would be one that has *approximately* uniform distribution
[though, not necessarily *exactly* uniform], which is what seems to be
the object of the game here.

There are many excellent well-known low discrepancy sequences to choose
from, and I'm not sure IETF needs to specify a standard one, but it's
possible one could be found if we really tried hard.  If you want to get
hideously pedantic, you could specify a maximum discrepancy; I'm sure
Timothy Winters and his crew would just melt if you did that.

Note: another term for "low discrepancy" is "quasi-random" but I'm not
sure we want to go there.


--
james woodyatt <jhw@apple.com>;
member of technical staff, core os networking



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