Mobile Ad hoc Networking (MANET)                              T. Clausen
Internet-Draft                          LIX, Ecole Polytechnique, France
Intended status: Standards Track                             C. Dearlove
Expires: May 19, 2008                    BAE Systems Advanced Technology
                                                                  Centre
                                                       November 16, 2007


                Representing multi-value time in MANETs
                      draft-ietf-manet-timetlv-04

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   Copyright (C) The IETF Trust (2007).












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Abstract

   This document describes a general and flexible TLV (type-length-value
   structure) for representing time using the generalized MANET packet/
   message format.  It defines two message and two address block TLVs
   for representing validity and interval times for MANET routing
   protocols.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Applicability Statement  . . . . . . . . . . . . . . . . . . .  5
   4.  Protocol Overview and Functioning  . . . . . . . . . . . . . .  6
   5.  Representing Time  . . . . . . . . . . . . . . . . . . . . . .  7
   6.  General Time TLV Structure . . . . . . . . . . . . . . . . . .  8
   7.  Message TLVs . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  VALIDITY_TIME TLV  . . . . . . . . . . . . . . . . . . . . 10
     7.2.  INTERVAL_TIME TLV  . . . . . . . . . . . . . . . . . . . . 10
   8.  Address Block TLVs . . . . . . . . . . . . . . . . . . . . . . 11
     8.1.  VALIDITY_TIME TLV  . . . . . . . . . . . . . . . . . . . . 11
     8.2.  INTERVAL_TIME TLV  . . . . . . . . . . . . . . . . . . . . 11
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     9.1.  Message TLV Types  . . . . . . . . . . . . . . . . . . . . 12
     9.2.  Address Block TLV Types  . . . . . . . . . . . . . . . . . 13
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     11.2. Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
   Intellectual Property and Copyright Statements . . . . . . . . . . 18


















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1.  Introduction

   The generalized packet/message format [1] specifies a signaling
   format which MANET routing 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 Time TLV structure, which can be
   used by any MANET routing protocol that needs to express either
   single time-values or a set of time-values with each time-value
   associated with a range of distances.  Distances may be equated to
   hop count, as provided by [1].  This allows a receiving node to
   determine a single time-value if either it knows its distance from
   the originator node, or the Time TLV specifies a single time-value.

   This document also specifies two message TLV types, which use the TLV
   structure proposed.  These TLV types are INTERVAL_TIME and
   VALIDITY_TIME, specifying respectively the maximum time before
   another message of the same type as this message from the same
   originator should be received, and the duration for which the
   information in this message is valid after receipt.  Note that, if
   both are present, then the latter will usually be greater than the
   former in order to allow for possible message loss.

   This document also specifies two address block TLV types, which use
   the TLV structure proposed.  These TLV types are INTERVAL_TIME and
   VALIDITY_TIME, defined equivalently to the two message TLVs with the
   same names.






















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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:

   Distance  - the distance from the message originator to the message
      recipient.  If the distance is equated to the messages hop count,
      then this may be indicated using the <hop-count> field in the full
      message header defined in [1], after being incremented on
      reception.

   Time-value  - a time, measured in seconds.

   Time-code  - an 8 bit field, representing a time-value.

































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3.  Applicability Statement

   The TLV described in this document is applicable whenever a single
   time-value, or a time-value that varies with distance from the
   originator of a message, is required in a protocol using the
   generalized MANET packet/message format [1].

   Examples of time-values that may be included in a protocol message
   are:

   o  The maximum time interval until the next message of the same type
      is to be generated by the message's originator node.

   o  The validity time of the information with which the time-value is
      associated.

   Either of these may vary with the distance between the originating
   and receiving nodes, e.g. if messages of the same type are sent with
   different hop limits as defined in [1].

   Parts of this document have been generalized from material in the
   proactive MANET routing protocol OLSR (The Optimized Link State
   Routing Protocol) [4].




























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4.  Protocol Overview and Functioning

   This document does not specify a protocol nor does it mandate
   specific node or protocol behavior.  Rather, it outlines mechanisms
   for encoding time-values using the TLV mechanism of [1].














































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5.  Representing Time

   This document specifies a TLV structure in which time-values are each
   represented in an 8 bit time-code, one or more of which may be used
   in a TLV's <value> field.  Of these 8 bits, the least significant 3
   bits represent the mantissa (a), and the most significant 5 bits
   represent the exponent (b), so that:

   o  time-value = (1 + a/8) * 2^b * C

   o  time-code = 8 * b + a

   All nodes in the network MUST use the same value of the constant C,
   which will be specified in seconds, hence so will be all time-values.
   C MUST be greater than 0 seconds.  Note that ascending values of the
   time-code represent ascending time-values, time-values may thus be
   compared by comparison of time-codes.

   An algorithm for computing the time-code representing the smallest
   representable time-value not less than the time-value t is:

   1.  find the largest integer b such that t/C >= 2^b;

   2.  set a = 8 * (t / (C * 2^b) - 1), rounded up to the nearest
       integer;

   3.  if a == 8 then set b = b + 1 and set a = 0;

   4.  if 0 <= a <= 7, and 0 <= b <= 31, then the required time-value
       can be represented by the time-code 8 * b + a, otherwise it can
       not.

   The minimum time-value that can be represented in this manner is C.
   The maximum time-value that can be represented in this manner is 15 *
   2^28 * C, or about 4.0 * 10^9 * C. If, for example, C = 1/1024
   second, then this is about 45 days.

   A protocol using this time representation MUST define the value of C.
   A protocol using this specification MAY specify that the all bits
   zero time-value (0) represents a time-value of zero and/or that the
   all bits one time-value (255) represents an indefinitely large time-
   value.









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6.  General Time TLV Structure

   A Time TLV may be a packet, message or address block TLV.  If it is a
   packet or message TLV then it must be a single value TLV as defined
   in [1].  If it is an address block TLV then it may be single value or
   multivalue TLV.  Note that even a single value Time TLV may contain a
   multiple octet <value> field.

   The purpose of a single value Time TLV is to allow a single time-
   value to be determined by a node receiving an entity containing the
   Time TLV, based on its distance from the entity's originator.  The
   Time TLV may contain information that allows that time-value to be a
   function of distance, and thus different receiving nodes may
   determine different time-values.  If a receiving node will not be
   able to determine its distance from the originating node, then the
   form of this Time TLV with a single time-code in a <value> field (or
   single value subfield) SHOULD be used.

   The <value> field of a single value Time TLV is specified, using the
   regular expression syntax of [1], by:

       <value> = {<time><distance>}*<time>

   where:

   <time>  is an 8 bit field containing a time-code as defined in
      Section 5.

   <distance>  is an 8 bit field specifying a distance from the message
      originator.

   A single value <value> field thus consists of an odd number of
   octets; with a repetition factor of n for the (time, distance) pairs
   in the regular expression syntax it contains 2n+1 octets, thus the
   <length> field of a single value Time TLV, which MUST always be
   present, is given by:

   o  <length> = 2n+1

   A single value <value> field may be thus represented by:

       <t_1><d_1><t_2><d_2> ... <t_i><d_i> ...  <t_n><d_n><t_default>

   <d_1>, ... <d_n>, if present, MUST be a strictly increasing sequence.
   Then, at the receiving node's distance from the originator node, the
   time-value indicated is that represented by the time-code:





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   o  <t_1>, if n > 0 and distance <= <d_1>;

   o  <t_i+1>, if n > 1 and <d_i> < distance <= <d_i+1> for some i such
      that 1 <= i < n;

   o  <t_default> otherwise, i.e. if n == 0 or distance > <d_n>.

   In a multivalue Time TLV, each single value subfield of the
   multivalue Time TLV is defined as above.  Note that [1] requires that
   each single value subfield has the same length (i.e. the same value
   of n) but they need not use the same values of <d_1> to <d_n>.








































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7.  Message TLVs

   Two message TLVs are defined, for signaling message validity time
   (VALIDITY_TIME) and message interval (INTERVAL_TIME).

7.1.  VALIDITY_TIME TLV

   A VALIDITY_TIME TLV is a message TLV that defines the validity time
   of the information carried in the message in which the TLV is
   contained.  After this time the receiving node MUST consider the
   message content to no longer be valid (unless repeated in a later
   message).  The validity time of a message MAY be specified to depend
   on the distance from its originator.  (This is appropriate if
   messages are sent with different hop limits, so that receiving nodes
   at greater distances receive information less frequently and must
   treat is as valid for longer.)

   A message MUST NOT include more than one VALIDITY_TIME TLV.

   A VALIDITY_TIME TLV is an example of a Time TLV specified as in
   Section 5.

7.2.  INTERVAL_TIME TLV

   An INTERVAL_TIME TLV is a message TLV that defines the maximum time
   before another message of the same type as this message from the same
   originator should be received.  This interval time MAY be specified
   to depend on the distance from the originator.  (This is appropriate
   if messages are sent with different hop limits, so that receiving
   nodes at greater distances have an increased interval time.)

   A message MUST NOT include more than one INTERVAL_TIME TLV.

   An INTERVAL_TIME TLV is an example of a Time TLV specified as in
   Section 5.
















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8.  Address Block TLVs

   Two address block TLVs are defined, for signaling address validity
   time (VALIDITY_TIME) and address advertisement interval
   (INTERVAL_TIME).

8.1.  VALIDITY_TIME TLV

   A VALIDITY_TIME TLV is an address block TLV that defines the validity
   time of the addresses to which the TLV is associated.  After this
   time the receiving node MUST consider the addresses to no longer be
   valid (unless these are repeated in a later message).  The validity
   time of an address MAY be specified to depend on the distance from
   its originator.  (This is appropriate if addresses are contained in
   messages sent with different hop limits, so that receiving nodes at
   greater distances receive information less frequently and must treat
   is as valid for longer.)

   A protocol using this TLV and the similarly named message TLV MUST
   specify how to interpret the case when both are present (typically
   that the former over-rides the latter for those addresses which are
   covered by the former).

   A VALIDITY_TIME TLV is an example of a Time TLV specified as in
   Section 5.

8.2.  INTERVAL_TIME TLV

   An INTERVAL_TIME TLV is an address block TLV that defines the maximum
   time before this address from the same originator should be received.
   This interval time MAY be specified to depend on the distance from
   the originator.  (This is appropriate if addresses are contained in
   messages sent with different hop limits, so that receiving nodes at
   greater distances have an increased interval time.)

   A protocol using this TLV and the similarly named message TLV MUST
   specify how to interpret the case when both are present (typically
   that the former over-rides the latter for those addresses which are
   covered by the former).

   An INTERVAL_TIME TLV is an example of a Time TLV specified as in
   Section 5.









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9.  IANA Considerations

   This specification defines two message TLV types, which must be
   allocated from the "Assigned Message TLV Types" repository of [1] as
   specified in Table 1 and two address block TLV types, which must be
   allocated from the "Assigned Address Block TLV Types" repository of
   [1] as specified in Table 2.

   IANA is requested to assign the same numerical value to the message
   TLV and address block TLV types with the same mnemonic.

9.1.  Message TLV Types

   +---------------+------+-----------+--------------------------------+
   |      Name     | Type |    Type   | Description                    |
   |               |      | Extension |                                |
   +---------------+------+-----------+--------------------------------+
   | VALIDITY_TIME | TBD1 |     0     | The time from receipt of the   |
   |               |      |           | message during which the       |
   |               |      |           | information contained in the   |
   |               |      |           | message is to be considered    |
   |               |      |           | valid                          |
   |               |      |           |                                |
   |               |      |   1-255   | RESERVED                       |
   |               |      |           |                                |
   | INTERVAL_TIME | TBD2 |     0     | The maximum time before        |
   |               |      |           | another message of the same    |
   |               |      |           | type as this message from the  |
   |               |      |           | same originator should be      |
   |               |      |           | received                       |
   |               |      |           |                                |
   |               |      |   1-255   | RESERVED                       |
   +---------------+------+-----------+--------------------------------+

                                  Table 1

   Type extensions indicated as RESERVED may be allocated by standards
   action, as specified in [3].













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9.2.  Address Block TLV Types

   +---------------+------+-----------+--------------------------------+
   |      Name     | Type |    Type   | Description                    |
   |               |      | extension |                                |
   +---------------+------+-----------+--------------------------------+
   | VALIDITY_TIME | TBD1 |     0     | The time from receipt of the   |
   |               |      |           | address during which the       |
   |               |      |           | information regarding this     |
   |               |      |           | address is to be considered    |
   |               |      |           | valid                          |
   |               |      |           |                                |
   |               |      |   1-255   | RESERVED                       |
   |               |      |           |                                |
   | INTERVAL_TIME | TBD2 |     0     | The maximum time before        |
   |               |      |           | another message of the same    |
   |               |      |           | type as this message from the  |
   |               |      |           | same originator and containing |
   |               |      |           | this address should be         |
   |               |      |           | received                       |
   |               |      |           |                                |
   |               |      |   1-255   | RESERVED                       |
   +---------------+------+-----------+--------------------------------+

                                  Table 2

   Type extensions indicated as RESERVED may be allocated by standards
   action, as specified in [3].























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10.  Security Considerations

   This document does not specify any security considerations.
















































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11.  References

11.1.  Normative References

   [1]  Clausen, T., Dearlove, C., Dean, J., and C. Adjih, "Generalized
        MANET Packet/Message Format", Work In
        Progress draft-ietf-manet-packetbb-11.txt, November 2007.

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

   [3]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
        Considerations Section in RFCs", RFC 2434, BCP 26, October 1998.

11.2.  Informative References

   [4]  Clausen, T. and P. Jacquet, "The Optimized Link State Routing
        Protocol", RFC 3626, October 2003.

































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Appendix A.  Acknowledgements

   The authors would like to thank Brian Adamson and Justin Dean (both
   NRL) for their contributions, and Alan Cullen (BAE Systems) for his
   careful review of this specification.














































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Authors' Addresses

   Thomas Heide Clausen
   LIX, Ecole Polytechnique, France

   Phone: +33 6 6058 9349
   Email: T.Clausen@computer.org
   URI:   http://www.ThomasClausen.org/


   Christopher Dearlove
   BAE Systems Advanced Technology Centre

   Phone: +44 1245 242194
   Email: chris.dearlove@baesystems.com
   URI:   http://www.baesystems.com/



































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