An Optimization for the MANET Neighborhood Discovery Protocol (NHDP)
draft-dearlove-manet-nhdp-optimization-00

Mobile Ad hoc Networking (MANET)                             C. Dearlove
Internet-Draft                                           BAE Systems ATC
Updates: RFC 6130                                      February 14, 2014
(if approved)
Intended status: Standards Track
Expires: August 18, 2014

  An Optimization for the MANET Neighborhood Discovery Protocol (NHDP)
               draft-dearlove-manet-nhdp-optimization-00

Abstract

   This specification updates the MANET Neighborhood Discovery Protocol
   (NHDP) to ensure greater robustness of 2-hop neighbor information
   when using link quality information.  This specification also updates
   the Optimized Link State Routing Protocol (OLSRv2).

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 18, 2014.

Copyright Notice

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   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Applicability Statement . . . . . . . . . . . . . . . . . . . . 4
   4.  Changes to NHDP . . . . . . . . . . . . . . . . . . . . . . . . 4
     4.1.  Interface Information Bases . . . . . . . . . . . . . . . . 4
     4.2.  HELLO Message Processing  . . . . . . . . . . . . . . . . . 4
     4.3.  Information Base Changes  . . . . . . . . . . . . . . . . . 5
     4.4.  Constraints . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Changes to OLSRv2 . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  MIB Considerations  . . . . . . . . . . . . . . . . . . . . . . 7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8

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1.  Introduction

   The MANET Neighborhood Discovery Protocol (NHDP) [RFC6130] contains a
   mechanism known as "link quality" that allows a router using the
   protocol to disallow the consideration of some of its 1-hop
   neighbors.  This lasts as long as the quality of the link from that
   1-hop neighbor falls below an acceptable link quality threshold.

   A feature of this mechanism is that while the link quality remains
   too low, the link information, established by the exchange of HELLO
   messages, is retained.  Thus if the link quality goes back above the
   required threshold (note that a hysteresis mechanism means that two
   thresholds are used) then the link is immediately reestablished and
   will be immediately available for use.

   [RFC6130] collects not just 1-hop neighbor information, but also
   information about symmetric 2-hop neighbors.  However [RFC6130]
   specifies that if a 1-hop neighbor is considered no longer symmetric
   then the corresponding 2-Hop Tuples that record the 2-hop neighbor
   information are removed, without a retention mechanism for a
   (possibly temporary) loss due to link quality.

   This means that if there is a short period in which link quality is
   too low, then when the link quality is reestablished, all 1-hop
   neighbor information is immediately available for use again.  But for
   the corresponding symmetric 2-hop neighbor information, this must
   wait until the next corresponding HELLO message to restore this
   information.

   This is not necessary, and this specification describes how [RFC6130]
   can be updated to avoid this.  This update is strictly optional, and
   routers that do and do not implement it can interwork entirely
   successfully (as they also can with different link quality
   specifications).  In addition, by a suitable interpretation, this
   change can be invisible to any other protocols using [RFC6130], in
   particular [OLSRv2].  However the impact on [OLSRv2] when not so
   handled is also described, owing to the existence of implementations
   of that protocol that are not modularly separated from [RFC6130].

2.  Terminology

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

   Additionally, this document uses the terminology of [RFC6130] and

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   [OLSRv2].

3.  Applicability Statement

   This specification updates [RFC6130].  As such it is applicable to
   all implementations of this protocol.  The optimization presented in
   this specification is simply permissive, it allows an additional
   optimization, and there is no requirement for any implementation to
   include it.  However inclusion of this optimization is advised, it
   can, in some cases, enable formation of a more stable network.

   This specification also updates [OLSRv2].  This could be avoided by
   simply noting that this specification describes how the updates to
   [RFC6130] may be handled so as to be invisible to any other protocol
   using it.  However as it is known that some implementations of
   [OLSRv2] are not independent of the implementation of [RFC6130] that
   they use, it is useful to indicate the direct impact on [OLSRv2].

   A router that implements the optimization described in this
   specification will interoperate successfully with routers not
   implementing this optimization.

4.  Changes to NHDP

   The following changes are made to [RFC6130] if using this
   specification.  Note that while this specification is OPTIONAL, if
   any of these changes are made then all of these changes MUST be made.

4.1.  Interface Information Bases

   The 2-Hop Set is modified by adding this additional element to each
   2-Hop Tuple:

      N2_lost is a boolean flag, which indicates the state of the
      corresponding Link Tuple.  If L_status = SYMMETRIC (and thus
      L_lost = false), then N2_lost = false.  If L_SYM_time has not
      expired, and L_lost = false (and hence L_status = LOST), then
      N2_lost = true.

   In all other cases, including other cases with L_status = LOST, there
   will be no such 2-Hop Tuples.

4.2.  HELLO Message Processing

   In Section 12.6 of [RFC6130] make the following changes:

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   o  In point 2, change "L_status = SYMMETRIC" to "L_SYM_time not
      expired".

   o  When creating a 2-Hop Tuple, set N2_lost := L_lost.

4.3.  Information Base Changes

   In Section 13, replace the second bullet point by:

   o  A Link Tuple's L_status changes from SYMMETRIC, L_SYM_time
      expires, or the Link Tuple is removed.  In this case, the actions
      specified in Section 13.2 are performed.

   and replace the paragraph after the bullet points by:

   If a Link Tuple is removed, or if L_HEARD_time expires and either
   L_status changes from SYMMETRIC or L_SYM_time expires, then the
   actions specified in Section 13.2 MUST be performed before the
   actions specified in Section 13.3 are performed for that Link Tuple.

   In Section 13.2 of [RFC6130], add the following, before all other
   text:

   For each Link Tuple that has L_SYM_time not expired:

   1.  If L_SYM_time then expires, or if the Link Tuple is removed:

       1.  Remove each 2-Hop Tuple for the same MANET interface with:

           +  N2_neighbor_iface_addr_list contains one or more network
              addresses in L_neighbor_iface_addr_list.

   2.  If L_status then changes from SYMMETRIC to LOST because L_lost is
       set to true:

       1.  For each 2-Hop Tuple for the same MANET interface with:

           +  N2_neighbor_iface_addr_list contains one or more network
              addresses in L_neighbor_iface_addr_list;

           set N2_lost := true.

   Also in Section 13.2 of [RFC6130], remove point 2, renumbering point
   2 as point 1.

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4.4.  Constraints

   In Appendix B, under "In each 2-Hop Tuple:" change the first bullet
   point to:

   o  There MUST be a Link Tuple associated with the same MANET
      interface with:

      *  L_neighbor_iface_addr_list = N2_neighbor_iface_addr_list; AND

      *  L_SYM_time not expired; AND

      *  L_lost = N2_lost.

5.  Changes to OLSRv2

   If the implementation of [RFC6130] conceals from any protocol using
   it the existence of all 2-Hop Tuples with N2_lost = true, then no
   changes are required to any protocol using [RFC6130], in particular
   no changes are required to [OLSRv2].

   However if instead the implementation of [RFC6130] makes all 2-Hop
   Tuples visible, including those with N2_lost = true, then protocols
   using [RFC6130] MUST ignore such 2-Hop Tuples.  For OLSRv2 this means
   behaving as if all of the following changes were to be made to
   [OLSRv2]:

   o  In Section 17.6 of [OLSRv2], point 1, replace the final two bullet
      points with:

      *  A 2-Hop Tuple with N2_out_metric != UNKNOWN_METRIC and N2_lost
         = false is added or removed, OR;

      *  A 2-Hop Tuple with N2_out_metric != UNKNOWN_METRIC has N2_lost
         changed, OR;

      *  The N2_out_metric of any 2-Hop Tuple with N2_lost = false
         changes, and either the flooding MPR selection process uses
         metric values (see Section 18.4) or the change is to or from
         UNKNOWN_METRIC.

   o  In Section 17.6 of [OLSRv2], point 3, replace the final two bullet
      points with:

      *  A 2-Hop Tuple with N2_in_metric != UNKNOWN_METRIC and N2_lost =
         false is added or removed, OR;

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      *  A 2-Hop Tuple with N2_in_metric != UNKNOWN_METRIC has N2_lost
         changed, OR;

      *  The N2_in_metric of any 2-Hop Tuple with N2_lost = false
         changes.

   o  In Section 17.7 of [OLSRv2], in the fifth bullet point, add "and
      N2_lost = false" after "N2_out_metric != UNKNOWN_METRIC".

   o  In Section 18.4 of [OLSRv2], in the third bullet point, add ",
      N2_lost = false" after "N2_out_metric != UNKNOWN_METRIC".

   o  In Section 18.5 of [OLSRv2], in the third bullet point, add ",
      N2_lost = false" after "N2_in_metric != UNKNOWN_METRIC".

   o  In Section 19.1 of [OLSRv2], in the final main bullet point
      (marked as "(OPTIONAL)"), add "and N2_lost = false" after
      "N2_out_metric != UNKNOWN_METRIC".

   o  In Appendix C.7 of [OLSRv2], in point 1, add "and N2_lost = false"
      after "N2_out_metric != UNKNOWN_METRIC".

6.  MIB Considerations

   TBD.

7.  IANA Considerations

   This document has no actions for IANA.

   [This section may be removed by the RFC Editor.]

8.  Security Considerations

   The update to [RFC6130] enables the retention and reuse of some
   information collected by that protocol, for only the duration that it
   could have been used in any case.  As such, this protocol introduces
   no new security considerations to an implementation of [RFC6130] or
   of any other protocol that uses it, such as [OLSRv2].

9.  Acknowledgments

   The author would like to thank Liz Cullen (BAE Systems) for first
   illustrating the issue addressed in this specification.

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10.  References

   [OLSRv2]   Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
              "The Optimized Link State Routing Protocol version 2",
              work in progress draft-ietf-manet-olsrv2-19, March 2013.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC6130]  Clausen, T., Dean, J., and C. Dearlove, "Mobile Ad Hoc
              Network (MANET) Neighborhood Discovery Protocol (NHDP)",
              RFC 6130, April 2011.

Author's Address

   Christopher Dearlove
   BAE Systems Advanced Technology Centre
   West Hanningfield Road
   Great Baddow, Chelmsford
   United Kingdom

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

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