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+Internet Engineering Task Force (IETF)                        R. Presuhn
+Request for Comments: 6340                                   Independent
+Category: Standards Track                                    August 2011
+ISSN: 2070-1721
+
+
+  Textual Conventions for the Representation of Floating-Point Numbers
+
+Abstract
+
+   This memo defines a Management Information Base (MIB) module
+   containing textual conventions (TCs) to represent floating-point
+   numbers.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 5741.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/rfc6340.
+
+Copyright Notice
+
+   Copyright (c) 2011 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (http://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+
+
+
+
+
+
+
+
+Presuhn                      Standards Track                    [Page 1]
+
+RFC 6340           Floating-Point Textual Conventions        August 2011
+
+
+Table of Contents
+
+   1. Introduction ....................................................2
+   2. The Internet-Standard Management Framework ......................3
+   3. Applicability ...................................................3
+   4. Structure of the MIB Module .....................................4
+      4.1. MIB Modules Required for IMPORTS ...........................4
+      4.2. Documents Required for REFERENCE Clauses ...................4
+   5. Definitions .....................................................4
+   6. Security Considerations .........................................6
+   7. IANA Considerations .............................................6
+   8. Contributors ....................................................6
+   9. References ......................................................7
+      9.1. Normative References .......................................7
+      9.2. Informative References .....................................7
+
+1.  Introduction
+
+   This memo defines textual conventions for the representation of
+   floating-point numbers.  All of these definitions are in terms of the
+   IEEE "Standard for Floating-Point Arithmetic", IEEE 754-2008
+   [IEEE.754.2008].
+
+   The IEEE "Standard for Floating-Point Arithmetic", IEEE 754-2008
+   [IEEE.754.2008], provides for a variety of interchange formats for
+   floating-point numbers.  The need for three of these, namely
+
+   o  32-bit,
+
+   o  64-bit,
+
+   o  128-bit,
+
+   has been recognized in network management.  For example, Section
+   4.2.3 of the SMIng Objectives [RFC3216] elaborates the need for these
+   three floating-point data types in network management protocols.
+
+   The selection of a floating-point format involves many considerations
+   and trade-offs.  For an introduction to the fundamentals of floating-
+   point representations see Chapter 4 of [KNUTH]; for a discussion of
+   these issues specifically with respect to the IEEE formats, see
+   [GOLDBERG].
+
+   All of these textual conventions employ the binary interchange format
+   defined in [IEEE.754.2008].  Specifically, this means that for all of
+   them, the highest-order bit of the first byte is the sign bit, with
+   the remaining bits of the octet string corresponding to the exponent
+   and fraction parts, in network byte order.
+
+
+
+Presuhn                      Standards Track                    [Page 2]
+
+RFC 6340           Floating-Point Textual Conventions        August 2011
+
+
+2.  The Internet-Standard Management Framework
+
+   For a detailed overview of the documents that describe the current
+   Internet-Standard Management Framework, please refer to section 7 of
+   RFC 3410 [RFC3410].
+
+   Managed objects are accessed via a virtual information store, termed
+   the Management Information Base or MIB.  MIB objects are generally
+   accessed through the Simple Network Management Protocol (SNMP).
+   Objects in the MIB are defined using the mechanisms defined in the
+   Structure of Management Information (SMI).  This memo specifies a MIB
+   module that is compliant to the SMIv2, which is described in STD 58,
+   RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
+   [RFC2580].
+
+3.  Applicability
+
+   The following list highlights some of the issues MIB designers need
+   to consider when deciding whether to employ these textual
+   conventions:
+
+   o  Floating-point numbers are useful if the number space needs to
+      cover a large dynamic range.  For number spaces with a limited
+      range, fixed-point numbers can be more efficient and more precise.
+
+   o  Floating-point numbers are typically the wrong answer for data
+      that is truly decimal or can be handled adequately by re-thinking
+      the units and representing the scaled numbers as integers.
+
+   o  The SNMP "lexicographical" ordering for INDEX objects using these
+      floating-point textual conventions will simply be that of the
+      octet strings corresponding to the floating-point representations,
+      which will not always reflect the numerical ordering of the
+      corresponding floating-point values.  Even if MIB designers take
+      this into account, users might still find the results of a MIB
+      "walk" surprising.  Consequently, it is suggested that whenever
+      one of these textual conventions is used for an INDEX object, that
+      the DESCRIPTION clause should provide some warning.
+
+   o  Embedded systems sometimes lack floating-point support, which can
+      complicate the implementation of MIB objects using floating-point
+      numbers.
+
+   o  In choosing from among the types defined in this memo, MIB
+      designers need to consider both the range and the precision
+      needed, as well as recognize that it could be inefficient to use,
+      for example, Float128TC when Float64TC would do.
+
+
+
+
+Presuhn                      Standards Track                    [Page 3]
+
+RFC 6340           Floating-Point Textual Conventions        August 2011
+
+
+   o  Since these textual conventions are defined in terms of the OCTET
+      STRING type, the SMI's mechanisms for formally setting range
+      constraints are not available.  MIB designers using these textual
+      conventions will need to use DESCRIPTION clauses to spell out any
+      applicable range constraints beyond those implied by the
+      underlying IEEE types.
+
+   o  Whenever these textual conventions are used in a MIB module, the
+      associated DESCRIPTION clause will need to clearly specify whether
+      denormalized numbers, NaNs ("not a number") or infinities are
+      permitted, along with any special semantics associated with these
+      cases.  This is especially important for writeable objects.
+
+4.  Structure of the MIB Module
+
+   This MIB module defines three textual conventions.  It defines no MIB
+   objects.
+
+4.1.  MIB Modules Required for IMPORTS
+
+   This MIB module employs definitions from [RFC2578] and [RFC2579].
+
+4.2.  Documents Required for REFERENCE Clauses
+
+   This MIB module contains REFERENCE clauses making reference to IEEE
+   754-2008 [IEEE.754.2008].
+
+5.  Definitions
+
+  FLOAT-TC-MIB DEFINITIONS ::= BEGIN
+
+  IMPORTS
+      MODULE-IDENTITY,
+      mib-2                                 FROM SNMPv2-SMI  -- RFC 2578
+      TEXTUAL-CONVENTION                    FROM SNMPv2-TC;  -- RFC 2579
+
+  floatTcMIB    MODULE-IDENTITY
+      LAST-UPDATED "201107270000Z"          -- July 27, 2011
+      ORGANIZATION "IETF OPSAWG Working Group"
+      CONTACT-INFO "WG Email: opsawg@ietf.org
+
+                    Editor: Randy Presuhn
+                    randy_presuhn@mindspring.com"
+
+      DESCRIPTION  "Textual conventions for the representation
+                    of floating-point numbers.
+
+
+
+
+
+Presuhn                      Standards Track                    [Page 4]
+
+RFC 6340           Floating-Point Textual Conventions        August 2011
+
+
+                    Copyright (c) 2011 IETF Trust and the persons
+                    identified as authors of the code.  All rights
+                    reserved.
+
+                    Redistribution and use in source and binary forms,
+                    with or without modification, is permitted pursuant
+                    to, and subject to the license terms contained in,
+                    the Simplified BSD License set forth in Section
+                    4.c of the IETF Trust's Legal Provisions Relating
+                    to IETF Documents
+                    (http://trustee.ietf.org/license-info).
+
+                    This version of this MIB module is part of RFC 6340;
+                    see the RFC itself for full legal notices."
+
+      REVISION     "201107270000Z"          -- July 27, 2011
+      DESCRIPTION  "Initial version, published as RFC 6340."
+       ::= { mib-2 201 }
+
+  Float32TC ::= TEXTUAL-CONVENTION
+      STATUS       current
+      DESCRIPTION  "This type represents a 32-bit (4-octet) IEEE
+                    floating-point number in binary interchange format."
+      REFERENCE    "IEEE Standard for Floating-Point Arithmetic,
+                    Standard 754-2008"
+      SYNTAX       OCTET STRING (SIZE(4))
+
+
+  Float64TC ::= TEXTUAL-CONVENTION
+      STATUS       current
+      DESCRIPTION  "This type represents a 64-bit (8-octet) IEEE
+                    floating-point number in binary interchange format."
+      REFERENCE    "IEEE Standard for Floating-Point Arithmetic,
+                    Standard 754-2008"
+      SYNTAX       OCTET STRING (SIZE(8))
+
+
+  Float128TC ::= TEXTUAL-CONVENTION
+      STATUS       current
+      DESCRIPTION  "This type represents a 128-bit (16-octet) IEEE
+                    floating-point number in binary interchange format."
+      REFERENCE    "IEEE Standard for Floating-Point Arithmetic,
+                    Standard 754-2008"
+      SYNTAX       OCTET STRING (SIZE(16))
+
+  END
+
+
+
+
+
+Presuhn                      Standards Track                    [Page 5]
+
+RFC 6340           Floating-Point Textual Conventions        August 2011
+
+
+6.  Security Considerations
+
+   This module does not define any management objects.  Instead, it
+   defines a set of textual conventions that can be used by other MIB
+   modules to define management objects.
+
+   Meaningful security considerations can only be written in the MIB
+   modules that define management objects.  Therefore, this memo has no
+   impact on the security of the Internet.
+
+7.  IANA Considerations
+
+   The MIB module in this document uses the following IANA-assigned
+   OBJECT IDENTIFIER value recorded in the SMI Numbers registry:
+
+      Descriptor        OBJECT IDENTIFIER value
+      ----------        -----------------------
+      floatTcMIB        { mib-2 201 }
+
+8.  Contributors
+
+   The following people provided helpful comments during the development
+   of this document:
+
+   o  Andy Bierman
+
+   o  Martin Duerst
+
+   o  Alfred Hoenes
+
+   o  Juergen Quittek
+
+   o  Juergen Schoenwaeder
+
+   o  Dave Shield
+
+   o  Robert Story
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Presuhn                      Standards Track                    [Page 6]
+
+RFC 6340           Floating-Point Textual Conventions        August 2011
+
+
+9.  References
+
+9.1.  Normative References
+
+   [IEEE.754.2008]  Institute of Electrical and Electronics Engineers,
+                    "Standard for Floating-Point Arithmetic",
+                    IEEE Standard 754, August 2008.
+
+   [RFC2578]        McCloghrie, K., Ed., Perkins, D., Ed., and J.
+                    Schoenwaelder, Ed., "Structure of Management
+                    Information Version 2 (SMIv2)", STD 58, RFC 2578,
+                    April 1999.
+
+   [RFC2579]        McCloghrie, K., Ed., Perkins, D., Ed., and J.
+                    Schoenwaelder, Ed., "Textual Conventions for SMIv2",
+                    STD 58, RFC 2579, April 1999.
+
+   [RFC2580]        McCloghrie, K., Perkins, D., and J. Schoenwaelder,
+                    "Conformance Statements for SMIv2", STD 58,
+                    RFC 2580, April 1999.
+
+9.2.  Informative References
+
+   [GOLDBERG]       Goldberg, D., "What Every Computer Scientist Should
+                    Know About Floating-Point Arithmetic", ACM Computing
+                    Surveys Volume 23, Issue 1, March 1991.
+
+   [KNUTH]          Knuth, D., "Seminumerical Algorithms", The Art of
+                    Computer Programming (Second Edition) Vol. 2, 1981.
+
+   [RFC3216]        Elliott, C., Harrington, D., Jason, J.,
+                    Schoenwaelder, J., Strauss, F., and W. Weiss, "SMIng
+                    Objectives", RFC 3216, December 2001.
+
+   [RFC3410]        Case, J., Mundy, R., Partain, D., and B. Stewart,
+                    "Introduction and Applicability Statements for
+                    Internet-Standard Management Framework", RFC 3410,
+                    December 2002.
+
+Author's Address
+
+   Randy Presuhn
+   San Jose, CA  95120
+   USA
+
+   EMail: randy_presuhn@mindspring.com
+
+
+
+
+
+Presuhn                      Standards Track                    [Page 7]
+