Re: Hashing function for PSAMP

[Juergen Quittek <quittek@netlab.nec.de>]

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
--
Juergen Quittek        quittek@netlab.nec.de       Tel: +49 6221 90511-15
NEC Europe Ltd.,       Network Laboratories        Fax: +49 6221 90511-55
Kurfuersten-Anlage 36, 69115 Heidelberg, Germany   http://www.netlab.nec.de


--On 24.01.2005 16:56 Uhr +0100 Saverio Niccolini wrote:

> Dear all,
> I would like to ask a simple question to the list.
> As you have seen in the "Sampling and Filtering Techniques for IP Packet
> Selection" draft we have tried to give suggestions on which is the best
> hash function in order to do packet sampling.
>
> Hash Functions Suitable for Packet Selection
> 1. IPSX
> (2. BOB)
>
> Hash Functions Suitable for Packet Digesting
> 1. CRC-32
> (2. BOB)
>
> Thinking about it and doing some additional tests it turned out that:
> 1) IPSX can only accepts 16 bytes as input --> it is not useful for IPv6
> packets.
> Do we want to stay with IPSX that is 7 times faster than BOB but can not
> be used with IPv6 packets? What is the list feeling about this?
>
> 2) BOB is faster than CRC-32 (on software implementation) and achieves
> as good collision probability as CRC-32.
> Do we still want to recommend CRC-32 because we believe that hardware
> implementation of CRC-32 are already out or we just would like to
> promote BOB to recommended and CRC-32 as optional?
>
> I am asking this because we are going to submit a new version of the
> draft and we would definitely like to fix this issue.
>
> Thanks in advance for your comments,
> Saverio
>
> ============================================================
> Dr. Saverio Niccolini
> Research Staff Member
> Network Laboratories, NEC Europe Ltd.
> Kurfuerstenanlage 36, D-69115 Heidelberg
> Tel.     +49 (0)6221 90511-18
> Fax:     +49 (0)6221 90511-55
> e-mail:  saverio.niccolini@netlab.nec.de
> ============================================================
>
>
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