Subject: Re: Hashing function for PSAMP

From: Benoit Claise <[email-masked]>
Date: Mon, 14 Feb 2005 18:07:53 +0100

Dear all,

Regarding PSAMP compliance, I was under the impression that the 
agreement was (even If I could not find a trace of it, after looking 
approx. 30 sec ;)):
If you want to be PSAMP compliant, you MUST implement at least one of 
the "method" described in the draft.
So I concluded that one filtering or one sampling mechanism would be 
sufficient.

Now, the discussion below is about a compulsory hash function.

Can we please clarify the situation regarding PSAMP compliance, so where 
is/are the MUST(s):
- MUST implement one of the filtering or sampling mechanism (note: 
hashing is a filtering function)?
- Or MUST implement one of the filtering and one of the sampling 
mechanism (note: hashing is a filtering function)?
- Or MUST implement one of the filtering, sampling, or hashing mechanism?
- Or MUST implement one of the filtering, sampling, and hashing mechanism?
- Or something else?

 From there, we will deduce if we even need a compulsory hash function...

Regards, Benoit.

> Dear all,
>
> Currently, the packet selection document has IPSX mandatory for packet
> selection and CRC32 mandatory for packet digest.
>
> The problem I see with this recommendation is that IPSX is not suitable
> for IPv6.  It does not sound like a good idea to have it mandatory for
> IPv6 systems.
>
> Here are two alternatives:
>
> 1. Make IPSX mandatory for IPv4 packet selection and BOB mandatory
>   for IPv6 packet selection.
>   Then, with BOB implemented anyway, we should then replace CRC32
>   with BOB for packet digest, because both perform similarly and
>   there is no good reason for forcing implementors to support also
>   a third hash function.
>
> 2. Just make BOB mandatory for packet selection and packet digest.
>   This would simplify implementation, because only a single function
>   is required.  For packet digest this should be OK, see 1.
>   A disadvantage is that BOB is slower than IPSX by factor 7.
>   An advantage is, that BOB is free of IPR, while IPSX is protected
>   by a patent.
>
> Does anybody have a preferences for 1., 2., or the current choice?
>
> Thanks,
>
>    Juergen

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From: Tanja Zseby <[email-masked]>
Date: Wed, 16 Feb 2005 09:39:51 +0100

Hi Benoit,

I remember that we decided that you MUST implement at least one of the 
selection method described in the draft in order to be PSAMP compliant.
So I agree, it is sufficient to implement either a sampling or a 
filtering method. We explicitely decided not to favor one scheme over 
another. The hash-section just gives recommendations for the case that 
someone decided to implement a hash-based scheme.  I see no reason to 
change this decision.

Regards
Tanja
P.S.: if you have time, can you call me and give me the list of typos 
that you have on your paper version ? Or we make a short editing session 
at the IETF ?
 
Benoit Claise wrote:

> Can we please clarify the situation regarding PSAMP compliance, so 
> where is/are the MUST(s):

-- 
Dipl.-Ing. Tanja Zseby			    	      	
Fraunhofer Institute FOKUS			Email: [email-masked]	
Kaiserin-Augusta-Allee 31			Phone: +49-30-3463-7153
D-10589 Berlin, Germany				Fax:   +49-30-3463-8153
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From: Benoit Claise <[email-masked]>
Date: Wed, 16 Feb 2005 10:34:09 +0100

Hi Tanja,

Thanks for the clarification/confirmation.
So I'm confused by the discussion in this thread, as it seems that we 
are discussing a mandatory hash function? Doesn't it contradict the 
statement "you MUST implement at least one of the selection method 
described in the draft in order to be PSAMP compliant."?

Regards, Benoit.

> that you have on your paper version ? Or we make a short editing 
> session at the IETF ?
>
> Benoit Claise wrote:
>
>> Dear all,
>>

---

From: Tanja Zseby <[email-masked]>
Date: Wed, 16 Feb 2005 10:41:15 +0100

Hi Benoit,

I fully agree. The discussion can be only about what we recommend IF 
someone decides to implement a hash-based packet selection.

Regards
Tanja

Benoit Claise wrote:

>> I remember that we decided that you MUST implement at least one of 
>> the selection method described in the draft in order to be PSAMP 
>> compliant.
>> another. The hash-section just gives recommendations for the case 
>> that someone decided to implement a hash-based scheme.  I see no 
>> reason to change this decision.
>>
>> Regards
>> Tanja
>>> If you want to be PSAMP compliant, you MUST implement at least one 
>>> of the "method" described in the draft.