Internet DRAFT - draft-dean-manet-metrictlv

draft-dean-manet-metrictlv






Mobile Ad hoc Networking (MANET)                                 J. Dean
Internet-Draft                         Naval Research Lab, United States
Expires: January 25, 2008                                  July 24, 2007


                  Representing metric values in MANETs
                      draft-dean-manet-metriclv-00

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   Copyright (C) The IETF Trust (2007).















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Abstract

   This document defines two TLVs (type-length-value structures) for
   representing cost values using the generalized MANET packet/message
   format [1].  A message block TLV is defined for representing a cost
   value associated with the local node.  An address block TLV is
   defined for representing a cost value associated with links or a cost
   value associated with other nodes.  Both TLVs defined are for use
   within MANET protocols.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  5
   4.  Protocol Overview and Functioning  . . . . . . . . . . . . . .  6
   5.  Metric Representation of Cost Value  . . . . . . . . . . . . .  7
     5.1.  Linear Metric Representation . . . . . . . . . . . . . . .  7
     5.2.  Exponential Metric Representation  . . . . . . . . . . . .  7
   6.  Metric TLVs  . . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Message TLV  . . . . . . . . . . . . . . . . . . . . . . .  9
     6.2.  Address Block TLV  . . . . . . . . . . . . . . . . . . . .  9
       6.2.1.  Other Node Metric TLV  . . . . . . . . . . . . . . . .  9
       6.2.2.  Outbound Link Metric TLV . . . . . . . . . . . . . . .  9
       6.2.3.  Inbound Link Metric TLV  . . . . . . . . . . . . . . .  9
       6.2.4.  Symmetric Link Metric TLV  . . . . . . . . . . . . . .  9
   7.  Metric Subtype . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Metric Representation Semantics  . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 14
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
   Intellectual Property and Copyright Statements . . . . . . . . . . 16














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1.  Introduction

   The generalized packet/message format [1] specifies a signaling
   format which MANET protocols can employ for exchanging protocol
   information.  This format presents the ability to express and
   associate attributes to packets, messages or addresses, by way of a
   general TLV (type-length-value) mechanism.

   This document specifies a general Metric TLV structure, which can be
   used by any MANET protocol which needs to express/exchange values
   associated with a cost of using a node or a link.  This document does
   not specify how cost values are generated or used.  Differing
   physical and mac layers may have differing cost value generating
   capabilities and differing MANET protocols may have differing
   concepts and uses for sharing cost values.  This document specifies
   how to convey cost value information within a MANET using metric TLVs
   within the [1]b framework.


































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2.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [2].

   Additionally, this document uses terminology from [1], and introduces
   the following terminology:

   Node  - A MANET router.

   Link  - A pair of nodes, where at least one node is able to received
      traffic from the other.

   Symetric Link  - A link in which both nodes are able to received
      traffic from the other.

   Cost Value  - the value to be transmitted using metric
      representation.

   Metric  - an 8 bit number associated with the cost value.

   Node Metric  - a metric associated with the cost of using a node.

   Link Metric  - a metric associated with the cost of using a link.


























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3.  Applicability Statement

   The TLV described in this document is applicable whenever a metric
   associated with either a node or a link is required in a protocol
   using the generalized MANET packet/message format [1].  The metric
   value SHOULD represent a concept which is related to cost of routing.

   Examples of costs concepts to be represented by metrics that MAY be
   included in a protocol message are:

   o  The amount of power, normalized to some standard, a node has
      remaining represented as a node metric.

   o  The amount of bandwidth provided by a link represented by a
      symmetric link metric.

   o  The estimated quality of a link represented by a inbound or
      outbound link metric.

   The generation of values for transmission within a metric TLV is not
   defined in this document.  The usage of transmitted values by metric
   TLVs is also not defined in this document.  Protocols using this
   metric TLV must define the concept of the value to be transmitted,
   generation of the value, and protocol behavior when receiving metric
   TLVs.


























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4.  Protocol Overview and Functioning

   This document outlines mechanisms for encoding cost values using the
   TLV mechanism of [1].  Protocols using the mechanisms and TLVs
   specified in this document must ensure that they do so in a coherent
   way.  This document does not specify a protocol nor does it mandate
   specific node or protocol behavior.

   Node metrics SHOULD represent cost values associated with routing
   though that node.  Node metric TLVs can be either message TLVs, when
   representing a local node cost value, or address block TLVs, when
   representing a cost value associated with a node other than the
   originator.  Multiple node metric values MAY be associated with any
   one address.

   Link metrics SHOULD represent cost values associated with routing
   though links.  Link metric TLVs are contained only in address block
   TLVs.  More than one link metric TLV MAY be associated with each
   address.  Link metric TLVs can be either directional or
   directionless.































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5.  Metric Representation of Cost Value

   This document specifies a TLV structure in which a cost values can be
   represented as metrics.  One or more metrics, of a specific type may
   be included in a single TLV value field.  Each TLV only represents
   one type of cost.  However, multiple metric TLV's may be applied to
   an address or a group of addresses.  Allowing for multiple values and
   representation of those values to be associated with a single
   address.  Independent of cost type, two different metric
   representations are defined in this document: a linear representation
   and an exponential representation.

5.1.  Linear Metric Representation

   Each linear metric consists of 8 bits which directly map to the cost
   value being transmitted.  The linear metric consisting of all zeros
   MUST not be used.

   The minimum cost value that can be represented in this manner is 1.
   The maximum cost value that can be represented in this manner is 255.

5.2.  Exponential Metric Representation

   Each exponential metric consists of 8 bits, the least significant
   four bits represent the mantissa (a), and the most significant four
   bits represent the exponent (b), so that:

   o  cost value = (1 + a/16) * 2^b

   o  exponential metric = 16 * b + a

   Note that ascending values of the exponential metric represent
   ascending cost values, cost values may thus be compared by comparison
   of exponential metrics.

   An algorithm for computing the exponential metric representing the
   smallest representable cost value not less than the cost value v is:

   1.  find the largest integer b such that v >= 2^b;

   2.  set a = 16 * (t / (2^b) - 1), rounded up to the nearest integer;

   3.  if a == 16 then set b = b + 1 and set a = 0;

   4.  if a and b are in the range 0 and 15 then the required time value
       can be represented by the exponential metric 16 * b + a,
       otherwise it can not.




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   The minimum cost value that can be represented in this manner is 1.
   The maximum cost value that can be represented in this manner is
   63488.  Not all integers between 1-63488 can be expressed using this
   representation.















































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6.  Metric TLVs

   This document defines one message block TLV and one address block
   metric TLV.  Address block TLVs are broken down further into four
   different generalized types; node, outbound, inbound, and symmetric.

6.1.  Message TLV

   The message block TLV is used for signaling values associated with
   the local node.  If a metric message TLV is to be included in a
   message, the 0 bit of the msg-semantics field MUST be cleared and the
   originator-address MUST be included in the msg-header-info as defined
   in [1] .

6.2.  Address Block TLV

   The address block TVL is used for signaling values associated with
   addresses contained within the address block.

6.2.1.  Other Node Metric TLV

   The cost value carried by the metric is associated with the
   appropriate address contained in the address block.

6.2.2.  Outbound Link Metric TLV

   The cost value carried by the metric is associated with the
   directional link originating from the originator address and ending
   at the associated address contained in the address block.

6.2.3.  Inbound Link Metric TLV

   The cost value carried by the metric is associated with the
   directional link originating from the originator address and ending
   at the associated address contained in the address block.

6.2.4.  Symmetric Link Metric TLV

   The cost value carried by the metric is associated with the bi-
   directional link formed from the originator address and the
   associated address contained in the address block.










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7.  Metric Subtype

   TLVs defined in this document MUST have the hassubtype bit set to 1
   in the tlv-semantics field as defined in [1] .  The subtype field of
   a metric TLV as defined in this document is comprised of two parts,
   the metric representation and the value type.  The three upper bits
   define which metric representation the values represent.  Usage of
   these bits is defined below.  The five lower bits allow for differing
   value types (delay and power being examples of differing value types)
   Usage and definitions for values included in this field is not
   defined in this document.

7.1.  Metric Representation Semantics

   bit 0 (exprep)  : If bit is set the cost value is stored using an
      exponential metric representation as defined in Section 5.2 .  If
      bit is unset the cost value is stored using a linear metric
      representation as defined in Section 5.1 .

   bit 1 (outbound) and bit 2 (inbound)  : Bits 1 and 2 are defined in
      Table 1 .

     +--------------+---------+--------------------------------------+
     |   Outbound   | Inbound | Value representation                 |
     +--------------+---------+--------------------------------------+
     |       0      |    0    | Node Metric                          |
     |              |         |                                      |
     |       0      |    1    | Inbound Link Metric                  |
     |              |         |                                      |
     |       1      |    0    | Outbound Link Metric                 |
     |              |         |                                      |
     |       1      |    1    | Symmetric Link Metric                |
     +--------------+---------+--------------------------------------+

                                  Table 1

   An outbound link metric is associated with a link which originates
   from the originator address and ends at the appropriate address.  An
   inbound link originates for the appropriate address and ends at the
   originator address.











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8.  IANA Considerations

   This specification defines one message TLV type, and one address TLV
   type which must be allocated from the "Assigned Message TLV Types"
   repository of [1].

   +-------------+------+---------+------------------------------------+
   |   Mnemonic  | Type | Subtype | Description                        |
   +-------------+------+---------+------------------------------------+
   |    METRIC   |  TBD |    0    | RESERVED                           |
   |             |      |         |                                    |
   |             |  TBD |  1-255  | Bits 0-2 as defined in this        |
   |             |      |         | document.  Bits 3-7 as defined in  |
   |             |      |         | documents using this               |
   |             |      |         | specification.                     |
   +-------------+------+---------+------------------------------------+

                                  Table 2

   Lower bit subtype definitions may be based per protocol as differing
   information MAY be useful to differing protocols.  Protocol goals and
   usages as well as radio technology suggests protocol dependant type
   assignment.




























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9.  Security Considerations

   This document does not specify any security considerations.
















































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10.  References

10.1.  Normative References

   [1]  Clausen, T., Dean, J., Dearlove, C., and C. Adjih, "Generalized
        MANET Packet/Message Format", Work In
        Progress draft-ietf-manet-packetbb-03.txt, June 2006.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, BCP 14, March 1997.

10.2.  Informative References







































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Appendix A.  Acknowledgements

   The author would like to thank Brian Adamson, Ian Chakares, Thomas
   Clausen, Chris Dearlove, and Joe Macker for their input which helped
   shape this document.














































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Author's Address

   Justin Wendell Dean
   Naval Research Lab, United States

   Phone: +1 202 767 3397
   Email: jdean@itd.nrl.navy.mil
   URI:   http://pf.itd.nrl.navy.mil/











































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