Subject: [ipfix] Floating point numbers in IPFIX

From: Andrew Johnson <[email-masked]>
Date: Thu, 15 Dec 2005 17:46:56 +0000

Hi all

In the IPFIX protocol draft, section 3.1.5, we have a definition
of a floating point number.  This definition allows export of
floating point numbers using the 32-bit format as specified in
IEEE.754.  This same standard also allows floating point numbers
to be defined in a 64-bit format.

I would like to see a float64 type added and the abiltity to
send float64 fields using float32 using a variation of the
Reduced Size Encoding as used with the integers.

I would like to propose that at the next editing phase we add
the following type to the information model:

3.1.6.  float64

 The type "float64" corresponds to an IEEE double-precision 64-bit
 floating point type as defined in [IEEE.754.1985].

In the protocol, section 6.2 could also be expanded to encompase
the Reduced Size encoding for the floating point types. i.e.

6.2      Reduced Size Encoding of Integer Types 

  Information Elements containing integer, float, string, and ...
                                           ^^^^^^^
  octetarray types in the information model MAY be encoded using fewer
  octets than those implied by their type in the information model
  definition [IPFIX-INFO], ...

  ...
   
  If reduced sizing is used, it MUST only be applied to the following 
  integer types: unsigned64, signed64, unsigned32, signed32, 
  unsigned16, signed16.  ...

@@[NOTE: the signed types above are not in the data model]@@

  Reduced sizing can also be used on the float64 and float32.  The
  float32 not only has a reduced number range, but due to the
  smaller mantissa is also less precise.

  The reduced size encoding MUST NOT be applied to ...

Andrew

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From: Stewart Bryant <[email-masked]>
Date: Fri, 16 Dec 2005 08:29:00 +0000

These are good suggestions.

We need to add signed types to the data model, and I think that
we should add float64 with the export compresion to float32.

- Stewart