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Versions: (draft-satish-roll-aodv-rpl) 00 01 02 03

ROLL                                                      S. Anamalamudi
Internet-Draft                           Huaiyin Institute of Technology
Intended status: Standards Track                                M. Zhang
Expires: September 6, 2018                           Huawei Technologies
                                                               AR. Sangi
                                         Huaiyin Institute of Technology
                                                              C. Perkins
                                                               Futurewei
                                                             S.V.R.Anand
                                             Indian Institute of Science
                                                                  B. Liu
                                                     Huawei Technologies
                                                           March 5, 2018


     Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs)
                      draft-ietf-roll-aodv-rpl-03

Abstract

   Route discovery for symmetric and asymmetric Point-to-Point (P2P)
   traffic flows is a desirable feature in Low power and Lossy Networks
   (LLNs).  For that purpose, this document specifies a reactive P2P
   route discovery mechanism for both hop-by-hop routing and source
   routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL
   protocol.  Paired Instances are used to construct directional paths,
   in case some of the links between source and target node are
   asymmetric.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 6, 2018.






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Copyright Notice

   Copyright (c) 2018 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
   (https://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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview of AODV-RPL  . . . . . . . . . . . . . . . . . . . .   6
   4.  AODV-RPL DIO Options  . . . . . . . . . . . . . . . . . . . .   6
     4.1.  AODV-RPL DIO RREQ Option  . . . . . . . . . . . . . . . .   6
     4.2.  AODV-RPL DIO RREP Option  . . . . . . . . . . . . . . . .   8
     4.3.  AODV-RPL DIO Target Option  . . . . . . . . . . . . . . .  10
   5.  Symmetric and Asymmetric Routes . . . . . . . . . . . . . . .  11
   6.  AODV-RPL Operation  . . . . . . . . . . . . . . . . . . . . .  13
     6.1.  Generating Route Request at OrigNode  . . . . . . . . . .  13
     6.2.  Receiving and Forwarding Route Request  . . . . . . . . .  14
     6.3.  Generating Route Reply at TargNode  . . . . . . . . . . .  15
       6.3.1.  RREP-DIO for Symmetric route  . . . . . . . . . . . .  15
       6.3.2.  RREP-DIO for Asymmetric Route . . . . . . . . . . . .  16
       6.3.3.  RPLInstanceID Pairing . . . . . . . . . . . . . . . .  16
     6.4.  Receiving and Forwarding Route Reply  . . . . . . . . . .  17
   7.  Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . .  18
   8.  Operation of Trickle Timer  . . . . . . . . . . . . . . . . .  19
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  New Mode of Operation: AODV-RPL . . . . . . . . . . . . .  19
     9.2.  AODV-RPL Options: RREQ, RREP, and Target  . . . . . . . .  19
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  20
   11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  20
     12.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Appendix A.  ETX/RSSI Values to select S bit  . . . . . . . . . .  21
   Appendix B.  Changes to version 02  . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  23





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1.  Introduction

   RPL[RFC6550] is a IPv6 distance vector routing protocol for Low-power
   and Lossy Networks (LLNs), and is designed to support multiple
   traffic flows through a root-based Destination-Oriented Directed
   Acyclic Graph (DODAG).  Typically, a router does not have routing
   information for most other routers.  Consequently, for traffic
   between routers within the DODAG (i.e., Point-to-Point (P2P) traffic)
   data packets either have to traverse the root in non-storing mode, or
   traverse a common ancestor in storing mode.  Such P2P traffic is
   thereby likely to traverse sub-optimal routes and may suffer severe
   congestion near the DAG root [RFC6997], [RFC6998].

   To discover optimal paths for P2P traffic flows in RPL, P2P-RPL
   [RFC6997] specifies a temporary DODAG where the source acts as a
   temporary root.  The source initiates DIOs encapsulating the P2P
   Route Discovery option (P2P-RDO) with an address vector for both hop-
   by-hop mode (H=1) and source routing mode (H=0).  Subsequently, each
   intermediate router adds its IP address and multicasts the P2P mode
   DIOs, until the message reaches the target node (TargNode).  TargNode
   sends the "Discovery Reply" object.  P2P-RPL is efficient for source
   routing, but much less efficient for hop-by-hop routing due to the
   extra address vector overhead.  However, for symmetric links, when
   the P2P mode DIO message is being multicast from the source hop-by-
   hop, receiving nodes can infer a next hop towards the source.  When
   TargNode subsequently replies to the source along the established
   forward route, receiving nodes determine the next hop towards
   TargNode.  In other words, it is efficient to use only routing tables
   for P2P-RDO message instead of "Address vector" for hop-by-hop routes
   (H=1) over symmetric links.

   RPL and P2P-RPL both specify the use of a single DODAG in networks of
   symmetric links, where the two directions of a link MUST both satisfy
   the constraints of the objective function.  This eliminates the
   possibility to use asymmetric links which are qualified in one
   direction.  But, application-specific routing requirements as defined
   in IETF ROLL Working Group [RFC5548], [RFC5673], [RFC5826] and
   [RFC5867] may be satisfied by routing paths using bidirectional
   asymmetric links.  For this purpose, [I-D.thubert-roll-asymlink]
   describes bidirectional asymmetric links for RPL [RFC6550] with
   Paired DODAGs, for which the DAG root (DODAGID) is common for two
   Instances.  This can satisfy application-specific routing
   requirements for bidirectional asymmetric links in core RPL
   [RFC6550].  Using P2P-RPL twice with Paired DODAGs, on the other
   hand, requires two roots: one for the source and another for the
   target node due to temporary DODAG formation.  For networks composed
   of bidirectional asymmetric links (see Section 5), AODV-RPL specifies
   P2P route discovery, utilizing RPL with a new MoP.  AODV-RPL makes



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   use of two multicast messages to discover possibly asymmetric routes,
   which can achieve higher route diversity.  AODV-RPL eliminates the
   need for address vector control overhead in hop-by-hop mode.  This
   significantly reduces the control packet size, which is important for
   Constrained LLN networks.  Both discovered routes (upward and
   downward) meet the application specific metrics and constraints that
   are defined in the Objective Function for each Instance [RFC6552].

   The route discovery process in AODV-RPL is modeled on the analogous
   procedure specified in AODV [RFC3561].  The on-demand nature of AODV
   route discovery is natural for the needs of peer-to-peer routing in
   RPL-based LLNs.  AODV terminology has been adapted for use with AODV-
   RPL messages, namely RREQ for Route Request, and RREP for Route
   Reply.  AODV-RPL currently omits some features compared to AODV -- in
   particular, flagging Route Errors, blacklisting unidirectional links,
   multihoming, and handling unnumbered interfaces.

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 following terms:

   AODV
      Ad Hoc On-demand Distance Vector Routing[RFC3561].

   AODV-RPL Instance
      Either the RREQ-Instance or RREP-Instance

   Asymmetric Route
      The route from the OrigNode to the TargNode can traverse different
      nodes than the route from the TargNode to the OrigNode.  An
      asymmetric route may result from the asymmetry of links, such that
      only one direction of the series of links fulfills the constraints
      in route discovery.  If the OrigNode doesn't require an upward
      route towards itself, the route is also considered as asymmetric.

   Bi-directional Asymmetric Link
      A link that can be used in both directions but with different link
      characteristics.

   DODAG RREQ-Instance (or simply RREQ-Instance)
      RPL Instance built using the DIO with RREQ option; used for
      control message transmission from OrigNode to TargNode, thus
      enabling data transmission from TargNode to OrigNode.

   DODAG RREP-Instance (or simply RREP-Instance)



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      RPL Instance built using the DIO with RREP option; used for
      control message transmission from TargNode to OrigNode thus
      enabling data transmission from OrigNode to TargNode.

   Downward Direction
      The direction from the OrigNode to the TargNode.

   Downward Route
      A route in the downward direction.

   hop-by-hop routing
      Routing when each node stores routing information about the next
      hop.

   OrigNode
      The IPv6 router (Originating Node) initiating the AODV-RPL route
      discovery to obtain a route to TargNode.

   Paired DODAGs
      Two DODAGs for a single route discovery process of an application.

   P2P
      Point-to-Point -- in other words, not constrained to traverse a
      common ancestor.

   RREQ-DIO message
      An AODV-RPL MoP DIO message containing the RREQ option.  The
      RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode.

   RREP-DIO message
      An AODV-RPL MoP DIO message containing the RREP option.  The
      RPLInstanceID in RREP-DIO is typically paired to the one in the
      associated RREQ-DIO message.

   Source routing
      The mechanism by which the source supplies the complete route
      towards the target node along with each data packet [RFC6550].

   Symmetric route
      The upstream and downstream routes traverse the same routers.
      Both directions fulfill the constraints in route discovery.

   TargNode
      The IPv6 router (Target Node) for which OrigNode requires a route
      and initiates Route Discovery within the LLN network.

   Upward Direction
      The direction from the TargNode to the OrigNode.



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   Upward Route
      A route in the upward direction.

3.  Overview of AODV-RPL

   With AODV-RPL, routes from OrigNode to TargNode within the LLN
   network established are "on-demand".  In other words, the route
   discovery mechanism in AODV-RPL is invoked reactively when OrigNode
   has data for delivery to the TargNode but existing routes do not
   satisfy the application's requirements.  The routes discovered by
   AODV-RPL are point-to-point; in other words the routes are not
   constrained to traverse a common ancestor.  Unlike core RPL [RFC6550]
   and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric communication
   paths in networks with bidirectional asymmetric links.  For this
   purpose, AODV-RPL enables discovery of two routes: namely, one from
   OrigNode to TargNode, and another from TargNode to OrigNode.  When
   possible, AODV-RPL also enables symmetric route discovery along
   Paired DODAGs (see Section 5).

   In AODV-RPL, route discovery is initiated by forming a temporary DAG
   rooted at the OrigNode.  Paired DODAGs (Instances) are constructed
   according to a new AODV-RPL Mode of Operation (MoP) during route
   formation between the OrigNode and TargNode.  The RREQ-Instance is
   formed by route control messages from OrigNode to TargNode whereas
   the RREP-Instance is formed by route control messages from TargNode
   to OrigNode (as shown in Figure 4).  Intermediate routers join the
   Paired DODAGs based on the rank as calculated from the DIO message.
   Henceforth in this document, the RREQ-DIO message means the AODV-RPL
   mode DIO message from OrigNode to TargNode, containing the RREQ
   option.  Similarly, the RREP-DIO message means the AODV-RPL mode DIO
   message from TargNode to OrigNode, containing the RREP option.
   Subsequently, the route discovered in the RREQ-Instance is used for
   data transmission from TargNode to OrigNode, and the route discovered
   in RREP-Instance is used for Data transmission from OrigNode to
   TargNode.

4.  AODV-RPL DIO Options

4.1.  AODV-RPL DIO RREQ Option

   A RREQ-DIO message MUST carry exactly one RREQ option.










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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Type      | Option Length |S|H|X| Compr | L |  MaxRank    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |  Orig SeqNo   |                                               |
     +-+-+-+-+-+-+-+-+                                               |
     |                                                               |
     |                                                               |
     |         Address Vector (Optional, Variable Length)            |
     |                                                               |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 1: DIO RREQ option format for AODV-RPL MoP

   OrigNode supplies the following information in the RREQ option of the
   RREQ-Instance message:

   Type

      The type of the RREQ option(see Section 9.2).

   Option Length

      Length of the option in octets excluding the Type and Length
      fields.  Variable due to the presence of the address vector and
      the number of octets elided according to the Compr value.

   S

      Symmetric bit indicating a symmetric route from the OrigNode to
      the router issuing this RREQ-DIO.  The bit SHOULD be set to 1 in
      the RREQ-DIO when the OrigNode initiates the route discovery.

   X

      Reserved.

   H

      The OrigNode sets this flag to one if it desires a hop-by-hop
      route.  It sets this flag to zero if it desires a source route.
      This flag is valid to both downstream route and upstream route.

   Compr





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      4-bit unsigned integer.  Number of prefix octets that are elided
      from the Address Vector.  The octets elided are shared with the
      IPv6 address in the DODAGID.

   L
      2-bit unsigned integer.  This field indicates the duration that a
      node joining the temporary DAG in RREQ-Instance, including the
      OrigNode and the TargNode.  Once the time is reached, a node MUST
      leave the DAG and stop sending or receiving any more DIOs for the
      temporary DODAG.  The detailed definition can be found in
      [RFC6997].

      *  0x00: No duration time imposed.
      *  0x01: 2 seconds
      *  0x02: 16 seconds
      *  0x03: 64 seconds

      It should be indicated here that L is not the route lifetime,
      which is defined in the DODAG configuration option.  The route
      entries in hop-by-hop routing and states of source routing can
      still be maintained even after the DAG expires.

   MaxRank

      This field indicates the upper limit on the integer portion of the
      rank.  A node MUST NOT join a temporary DODAG if its own rank
      would equal to or higher than the limit.  A value of 0 in this
      field indicates the limit is infinity.  For more details please
      refer to [RFC6997].

   OrigNode Sequence Number

      Sequence Number of OrigNode, defined similarly as in AODV
      [RFC3561].

   Address Vector (Optional)

      A vector of IPv6 addresses representing the route that the RREQ-
      DIO has passed.  It is only present when the 'H' bit is set to 0.
      The prefix of each address is elided according to the Compr field.

4.2.  AODV-RPL DIO RREP Option

   A RREP-DIO message MUST carry exactly one RREP option.

   The TargNode supplies the following information in the RREP option:





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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      | Option Length |H|X| Compr | L |   MaxRank     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |T|G|  SHIFT    |    Reserved   |                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
       |                                                               |
       |                                                               |
       |         Address Vector (Optional, Variable Length)            |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 2: DIO RREP option format for AODV-RPL MoP

   Type
      The type of the RREP option (see Section 9.2)

   Option Length
      Length of the option in octets excluding the Type and Length
      fields.  Variable due to the presence of the address vector and
      the number of octets elided according to the Compr value.

   H
      This bit indicates the downstream route is source routing (H=0) or
      hop-by-hop (H=1).  It SHOULD be set to be the same as the 'H' bit
      in RREQ option.

   X

      Reserved.

   Compr
      4-bit unsigned integer.  Same definition as in RREQ option.

   L
      2-bit unsigned integer with the same definition as in Section 4.1.

   MaxRank
      Same definition as in RREQ option.

   T
      'T' is set to 1 to indicate that the RREP-DIO MUST include exactly
      one AODV-RPL Target Option.  Otherwise, the Target Option is not
      necessary in the RREP-DIO.

   G



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      Gratuitous route (see Section 7).

   SHIFT
      6-bit unsigned integer.  This field indicates the how many the
      original InstanceID (see Section 6.3.3) is shifted (added an
      integer from 0 to 63).  0 indicates that the original InstanceID
      is used.

   Reserved
      Reserved for future usage; MUST be initialized to zero and MUST be
      ignored upon reception.

   Address Vector (Optional)
      It is only present when the 'H' bit is set to 0.  For an
      asymmetric route, it is a vector of IPv6 addresses representing
      the route that the RREP-DIO has passed.  For symmetric route, it
      is the accumulated vector when the RREQ-DIO arrives at the
      TargNode.

4.3.  AODV-RPL DIO Target Option

   The AODV-RPL Target Option is defined based on the Target Option in
   core RPL [RFC6550]: the Destination Sequence Number of the TargNode
   is added.

   A RREQ-DIO message MUST carry at least one AODV-RPL Target Options.
   A RREP-DIO message MUST carry exactly one AODV-RPL Target Option
   encapsulating the address of the OrigNode if the 'T' bit is set to 1.

   If an OrigNode want to discover routes to multiple TargNodes, and
   these routes share the same constraints, then the OrigNode can
   include all the addresses of the TargNodes into multiple AODV-RPL
   Target Options in the RREQ-DIO, so that the cost can be reduced to
   building only one DODAG.  Different addresses of the TargNodes can
   merge if they share the same prefix.
















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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      | Option Length |   Dest SeqNo  | Prefix Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               |
       |                Target Prefix (Variable Length)                |
       .                                                               .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 3: Target option format for AODV-RPL MoP

   Type
      The type of the AODV-RPL Target Option (see Section 9.2)

   Destination Sequence Number

      In RREQ-DIO, if nonzero, it is the last known Sequence Number for
      TargNode for which a route is desired.  In RREP-DIO, it is the
      destination sequence number associated to the route.

5.  Symmetric and Asymmetric Routes

   In Figure 4 and Figure 5, BR is the BorderRouter, O is the OrigNode,
   R is an intermediate router, and T is the TargNode.  If the RREQ-DIO
   arrives over an interface that is known to be symmetric, and the 'S'
   bit is set to 1, then it remains as 1, as illustrated in Figure 4.
   An intermediate router sends out RREQ-DIO with the 'S' bit set to 1,
   meaning that all the one-hop links on the route from the OrigNode to
   this router meet the requirements of route discovery; thus the route
   can be used symmetrically.


















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                                      BR
                                  /    |    \
                                /      |      \
                              /        |         \
                             R         R           R
                          /   \        |          /  \
                         /     \       |         /     \
                        /       \      |        /        \
                      R -------- R --- R ----- R -------- R
                   /   \   <--S=1-->  / \    <--S=1-->   /  \
             <--S=1-->  \            /   \             /   <--S=1-->
               /         \          /     \          /         \
             O ---------- R ------ R------ R ----- R ----------- T
            / \                   / \             / \           / \
           /   \                 /   \           /   \         /   \
          /     \               /     \         /     \       /     \
         R ----- R ----------- R ----- R ----- R ----- R ---- R----- R

         >---- RREQ-Instance (Control: S-->D;  Data: D-->S) ------->
         <---- RREP-Instance (Control: D-->S;  Data: S-->D) -------<

            Figure 4: AODV-RPL with Symmetric Paired Instances

   Upon receiving a RREQ-DIO with the 'S' bit set to 1, a node MUST
   decide if this one-hop link can be used symmetrically, i.e., both the
   two directions meet the requirements of data transmission.  If the
   RREQ-DIO arrives over an interface that is not known to be symmetric,
   or is known to be asymmetric, the 'S' bit is set to 0.  Moreover, if
   the 'S' bit arrives already set to be '0', it is set to be '0' on
   retransmission (Figure 5).  Therefore, for asymmetric route, there is
   at least one hop which doesn't fulfill the constraints in the two
   directions.  Based on the 'S' bit received in RREQ-DIO, the TargNode
   decides whether or not the route is symmetric before transmitting the
   RREP-DIO message upstream towards the OrigNode.

   The criterion and the corresponding metric used to determine if a
   one-hop link is symmetric or not is implementation specific and
   beyond the scope of the document.  Also, the difference in the metric
   values for upward and downward directions of a link that can be
   establish its symmetric and asymmetric nature is implementation
   specific.  For instance, the intermediate routers MAY choose to use
   local information (e.g., bit rate, bandwidth, number of cells used in
   6tisch), a priori knowledge (e.g. link quality according to previous
   communication) or estimate the metric using averaging techniques or
   any other means that is appropriate to the application context.






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   Appendix A describes an example method using the ETX and RSSI to
   estimate whether the link is symmetric in terms of link quality is
   given in using an averaging technique.

                                     BR
                                 /    |    \
                               /      |      \
                             /        |        \
                           R          R          R
                         / \          |        /   \
                       /     \        |       /      \
                     /         \      |      /         \
                    R --------- R --- R ---- R --------- R
                  /  \   --S=1-->   / \    --S=0-->   /   \
            --S=1-->   \           /    \            /   --S=0-->
             /          \        /       \         /         \
           O ---------- R ------ R------ R ----- R ----------- T
          / \                   / \             / \           / \
         /  <--S=0--           /   \           /   \         / <--S=0--
        /     \               /     \         /     \       /     \
       R ----- R ----------- R ----- R ----- R ----- R ---- R----- R
                   <--S=0--   <--S=0-- <--S=0-- <--S=0--    <--S=0--

       >---- RREQ-Instance (Control: S-->D;  Data: D-->S) ------->
       <---- RREP-Instance (Control: D-->S;  Data: S-->D) -------<

            Figure 5: AODV-RPL with Asymmetric Paired Instances

6.  AODV-RPL Operation

6.1.  Generating Route Request at OrigNode

   The route discovery process is initiated on-demand when an
   application at the OrigNode has data to be transmitted to the
   TargNode, but no route for the target exists or the current routes
   don't fulfill the requirements of the data transmission.  In this
   case, the OrigNode MUST build a local RPLInstance and a DODAG rooted
   at itself.  Then it begins to send out DIO message in AODV-RPL MoP
   via link-local multicast.  The DIO MUST contain exactly one RREQ
   option as defined in Section 4.1, and at least one AODV-RPL Target
   Option as defined in Figure 3.  This DIO message is noted as RREQ-
   DIO.  The 'S' bit in RREQ-DIO sent out by the OrigNode is set as 1.

   The maintenance of Originator and Destination Sequence Number in the
   RREQ option is as defined in AODV [RFC3561].

   The address in the AODV-RPL Target Option can be a unicast IPv6
   address, a prefix or a multicast address.  The OrigNode can initiate



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   the route discovery process for multiple targets simultaneously by
   including multiple AODV-RPL Target Options, and within a RREQ-DIO the
   requirements for the routes to different TargNodes MUST be the same.

   The OrigNode can maintain different RPLInstances to discover routes
   with different requirements to the same targets.  Due to the
   InstanceID pairing mechanism Section 6.3.3, route replies (RREP-DIOs)
   from different paired RPLInstances can be distinguished.

   The transmission of RREQ-DIO follows the Trickle timer.  When the L
   duration has transpired, the OrigNode MUST leave the DODAG and stop
   sending any RREQ-DIOs in the related RPLInstance.

6.2.  Receiving and Forwarding Route Request

   Upon receiving a RREQ-DIO, a router out of the RREQ-instance goes
   through the following steps:

   Step 1:

      If the 'S' bit in the received RREQ-DIO is set to 1, the router
      MUST look into the two directions of the link by which the RREQ-
      DIO is received.  In case that the downward (i.e. towards the
      TargNode) direction of the link can't fulfill the requirements,
      then the link can't be used symmetrically, thus the 'S' bit of the
      RREQ-DIO to be send out MUST be set as 0.  If the 'S' bit in the
      received RREQ-DIO is set to 0, the router MUST look only into the
      upward direction (i.e. towards the OrigNode) of the link.  If the
      upward direction of the link can fulfill the requirements
      indicated in the constraint option, and the router's rank would be
      inferior to the MaxRank limit, the router chooses to join in the
      DODAG of the RREQ-Instance.  The router issuing the received RREQ-
      DIO is selected as the preferred parent.  Afterwards, other RREQ-
      DIO message can be received.  How to maintain the parent set,
      select the preferred parent, and update the router's rank follows
      the core RPL and the OFs defined in ROLL WG.

      In case that the constraint or the MaxRank limit is not fulfilled,
      the router MUST NOT join in the DODAG.  Otherwise, go to the
      following steps 2, 3, 4 and 5.

      A router MUST discard a received RREQ-DIO if the advertised rank
      equals or exceeds the MaxRank limit.

   Step 2:

      Then the router checks if one of its addresses is included in one
      of the AODV-RPL Target Options or belongs to the indicated



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      multicast group.  If so, this router is one of the TargNodes.
      Otherwise, it is an intermediate router.

   Step 3:

      If the 'H' bit is set to 1, then the router (TargNode or
      intermediate) MUST build route entry towards its preferred parent.
      The route entry SHOULD be stored along with the associated
      RPLInstanceID and DODAGID.  If the 'H' bit is set to 0, an
      intermediate router MUST include the address of the interface
      receiving the RREQ-DIO into the address vector.

   Step 4:

      If there are multiple AODV-RPL Target Options in the received
      RREQ-DIO, a TargNode SHOULD continue sending RREQ-DIO to reach
      other targets.  When preparing its own RREQ-DIO, the TargNode MUST
      delete the AODV-RPL Target Option related to its own address, so
      that the routers which higher ranks would know the route to this
      target has already been found.  When an intermediate router
      receives several RREQ-DIOs which include different lists of AODV-
      RPL Target Options, the intersection of these lists will be
      included in its own RREQ-DIO.  If the intersection is empty, the
      router SHOULD NOT send out any RREQ-DIO.  Any RREQ-DIO message
      with different AODV-RPL Target Options coming from a router with
      higher rank is ignored.

   Step 5:

      For an intermediate router, it sends out its own RREQ-DIO via
      link-local multicast.  For a TargNode, it can begin to prepare the
      RREP-DIO.

6.3.  Generating Route Reply at TargNode

6.3.1.  RREP-DIO for Symmetric route

   When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 1, it
   means there exists a symmetric route in which the two directions can
   fulfill the requirements.  Other RREQ-DIOs can bring the upward
   direction of asymmetric routes (i.e.  S=0).  How to choose between a
   qualified symmetric route and an asymmetric route hopefully having
   better performance is implementation-specific and out of scope.  If
   the implementation choose to use the symmetric route, the TargNode
   MAY send out the RREP-DIO after a duration RREP_WAIT_TIME to wait for
   the convergence of RD to an optimal symmetric route.





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   For symmetric route, the RREP-DIO message is sent via unicast to the
   OrigNode; therefore the DODAG in RREP-Instance doesn't need to be
   actually built.  The RPLInstanceID in the RREP-Instance is paired as
   defined in Section 6.3.3.  The 'S' bit in the base DIO remains as 1.
   In the RREP option, The 'SHIFT' field and the 'T' bit are set as
   defined in Section 6.3.3.  The address vector received in the RREQ-
   DIO MUST be included in this RREP option in case the 'H' bit is set
   to 0 (both in RREQ-DIO and RREP-DIO).  If the 'T' bit is set to 1,
   the address of the OrigNode MUST be encapsulated in an AODV-RPL
   Target Option and included in this RREP-DIO message, and the
   Destination Sequence Number is set according to AODV [RFC3561].

6.3.2.  RREP-DIO for Asymmetric Route

   When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 0, the
   TargNode MUST build a DODAG in the RREP-Instance rooted at itself in
   order to discover the downstream route from the OrigNode to the
   TargNode.  The RREP-DIO message MUST be send out via link-local
   multicast until the OrigNode is reached or the MaxRank limit is
   exceeded.

   The settings of the RREP-DIO are the same as in symmetric route.

6.3.3.  RPLInstanceID Pairing

   Since the RPLInstanceID is assigned locally (i.e., there is no
   coordination between routers in the assignment of RPLInstanceID) the
   tuple (RPLInstanceID, DODAGID, Address in the AODV-RPL Target Option)
   is needed to uniquely identify a DODAG in an AODV-RPL instance.
   Between the OrigNode and the TargNode, there can be multiple AODV-RPL
   instances when applications upper layer have different requirements.
   Therefore the RREQ-Instance and the RREP-Instance in the same route
   discovery MUST be paired.  The way to realize this is to pair their
   RPLInstance IDs.

   Typically, the two InstanceIDs are set as the local InstanceID in
   core RPL:

                   0 1 2 3 4 5 6 7
                  +-+-+-+-+-+-+-+-+
                  |1|D|    ID     |  Local RPLInstanceID in 0..63
                  +-+-+-+-+-+-+-+-+

                        Figure 6: Local Instance ID

   The first bit is set to 1 indicating the RPLInstanceID is local.  The
   'D' bit here is used to distinguish the two AODV-RPL instances: D=0
   for RREQ-Instance, D=1 for RREP-Instance.  The ID of 6 bits SHOULD be



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   the same for RREQ-Instance and RREP-Instance.  Here, the 'D' bit is
   used slightly differently than in RPL.

   When preparing the RREP-DIO, a TargNode could find the RPLInstanceID
   to be used for the RREP-Instance is already occupied by another
   instance from an earlier route discovery operation which is still
   active.  In other words, two OrigNodes need routes to the same
   TargNode and they happen to use the same RPLInstanceID for RREQ-
   Instance.  In this case, the occupied RPLInstanceID MUST NOT be used
   again.  Then this RPLInstanceID SHOULD be shifted into another
   integer and shifted back to the original one at the OrigNode.  In
   RREP option, the SHIFT field indicates the how many the original
   RPLInstanceID is shifted.  When the new InstanceID after shifting
   exceeds 63, it will come back counting from 0.  For example, the
   original InstanceID is 60, and shifted by 6, the new InstanceID will
   be 2.  The 'T' MUST be set to 1 to make sure the two RREP-DIOs can be
   distinguished by the address of the OrigNode in the AODV-RPL Target
   Option.

6.4.  Receiving and Forwarding Route Reply

   Upon receiving a RREP-DIO, a router out of the RREP-Instance goes
   through the following steps:

   Step 1:

      If the 'S' bit of the RREP-DIO is set to 0, the router MUST look
      into the downward direction of the link (towards the TargNode) by
      which the RREP-DIO is received.  If the downward direction of the
      link can fulfill the requirements indicated in the constraint
      option, and the router's rank would be inferior to the MaxRank
      limit, the router chooses to join in the DODAG of the RREP-
      Instance.  The router issuing the received RREP-DIO is selected as
      the preferred parent.  Afterwards, other RREQ-DIO messages can be
      received.  How to maintain the parent set, select the preferred
      parent, and update the router's rank follows the core RPL and the
      OFs defined in ROLL WG.

      If the constraints are not fulfilled, the router MUST NOT join in
      the DODAG, and will not go through steps 2, 3, and 4.

      A router MUST discard a received RREQ-DIO if the advertised rank
      equals or exceeds the MaxRank limit.

      If the 'S' bit is set to 1, the router does nothing in this step.

   Step 2:




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      Then the router checks if one of its addresses is included in the
      AODV-RPL Target Option.  If so, this router is the OrigNode of the
      route discovery.  Otherwise, it is an intermediate router.

   Step 3:

      If the 'H' bit is set to 1, then the router (OrigNode or
      intermediate) MUST build route entry including the RPLInstanceID
      of RREP-Instance and the DODAGID.  For symmetric route, the route
      entry is to the router from which the RREP-DIO is received.  For
      asymmetric route, the route entry is to the preferred parent in
      the DODAG of RREQ-Instance.

      If the 'H' bit is set to 0, for asymmetric route, an intermediate
      router MUST include the address of the interface receiving the
      RREP-DIO into the address vector, and for symmetric route, there
      is nothing to do in this step.

   Step 4:

      For an intermediate router, in case of asymmetric route, the RREP-
      DIO is sent out via link-local multicast; in case of symmetric
      route, the RREP-DIO is unicasted to the OrigNode via the next hop
      in source routing (H=0), or via the next hop in the route entry
      built in the RREQ-Instance (H=1).  For the OrigNode, it can start
      transmitting the application data to TargNode along the path as
      discovered through RREP-Instance.

7.  Gratuitous RREP

   In some cases, an Intermediate router that receives a RREQ-DIO
   message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode
   instead of continuing to multicast the RREQ-DIO towards TargNode.
   The intermediate router effectively builds the RREP-Instance on
   behalf of the actual TargNode.  The 'G' bit of the RREP option is
   provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the
   Intermediate node from the RREP-DIO sent by TargNode (G=0).

   The gratuitous RREP-DIO can be sent out when an intermediate router R
   receives a RREQ-DIO for a TargNode T, and R happens to have both
   forward and reverse routes to T which also fulfill the requirements.

   In case of source routing, the intermediate router R MUST unicast the
   received RREQ-DIO to TargNode T including the address vector between
   the OrigNode O and the router R.  Thus T can have a complete address
   vector between O and itself.  Then T MUST unicast a RREP-DIO
   including the address vector between T and R.




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   In case of hop-by-hop routing, R MUST unicast the received RREQ-DIO
   to T.  The routers along the route SHOULD build new route entries
   with the related RPLInstanceID and DODAGID in the downward direction.
   Then T MUST unicast the RREP-DIO to R, and the routers along the
   route SHOULD build new route entries in the upward direction.  Upon
   received the unicast RREP-DIO, R sends the gratuitous RREP-DIO to the
   OrigNode as the same way defined in Section 6.3.

8.  Operation of Trickle Timer

   The trickle timer operation to control RREQ-Instance/RREP-Instance
   multicast is similar to that in P2P-RPL [RFC6997].

9.  IANA Considerations

9.1.  New Mode of Operation: AODV-RPL

   IANA is required to assign a new Mode of Operation, named "AODV-RPL"
   for Point-to-Point(P2P) hop-by-hop routing under the RPL registry.
   The value of TBD1 is assigned from the "Mode of Operation" space
   [RFC6550].

                  +-------------+---------------+---------------+
                  |    Value    |  Description  |   Reference   |
                  +-------------+---------------+---------------+
                  |   TBD1 (5)  |   AODV-RPL    | This document |
                  +-------------+---------------+---------------+

                        Figure 7: Mode of Operation

9.2.  AODV-RPL Options: RREQ, RREP, and Target

   Three entries are required for new AODV-RPL options "RREQ", "RREP"
   and "AODV-RPL Target" with values of TBD2 (0x0A), TBD3 (0x0B) and
   TBD4 (0x0C) from the "RPL Control Message Options" space [RFC6550].

            +-------------+------------------------+---------------+
            |    Value    |        Meaning         |   Reference   |
            +-------------+------------------------+---------------+
            | TBD2 (0x0A) |      RREQ Option       | This document |
            +-------------+------------------------+---------------+
            | TBD3 (0x0B) |      RREP Option       | This document |
            +-------------+------------------------+---------------+
            | TBD3 (0x0C) | AODV-RPL Target Option | This document |
            +-------------+------------------------+---------------+

                        Figure 8: AODV-RPL Options




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10.  Security Considerations

   This document does not introduce additional security issues compared
   to base RPL.  For general RPL security considerations, see [RFC6550].

11.  Future Work

   There has been some discussion about how to determine the initial
   state of a link after an AODV-RPL-based network has begun operation.
   The current draft operates as if the links are symmetric until
   additional metric information is collected.  The means for making
   link metric information is considered out of scope for AODV-RPL.  In
   the future, RREQ and RREP messages could be equipped with new fields
   for use in verifying link metrics.  In particular, it is possible to
   identify unidirectional links; an RREQ received across a
   unidirectional link has to be dropped, since the destination node
   cannot make use of the received DODAG to route packets back to the
   source node that originated the route discovery operation.  This is
   roughly the same as considering a unidirectional link to present an
   infinite cost metric that automatically disqualifies it for use in
   the reverse direction.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3561]  Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
              Demand Distance Vector (AODV) Routing", RFC 3561,
              DOI 10.17487/RFC3561, July 2003,
              <https://www.rfc-editor.org/info/rfc3561>.

   [RFC5548]  Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and
              D. Barthel, Ed., "Routing Requirements for Urban Low-Power
              and Lossy Networks", RFC 5548, DOI 10.17487/RFC5548, May
              2009, <https://www.rfc-editor.org/info/rfc5548>.

   [RFC5673]  Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
              Phinney, "Industrial Routing Requirements in Low-Power and
              Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October
              2009, <https://www.rfc-editor.org/info/rfc5673>.






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   [RFC5826]  Brandt, A., Buron, J., and G. Porcu, "Home Automation
              Routing Requirements in Low-Power and Lossy Networks",
              RFC 5826, DOI 10.17487/RFC5826, April 2010,
              <https://www.rfc-editor.org/info/rfc5826>.

   [RFC5867]  Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen,
              "Building Automation Routing Requirements in Low-Power and
              Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June
              2010, <https://www.rfc-editor.org/info/rfc5867>.

   [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
              Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
              JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
              Low-Power and Lossy Networks", RFC 6550,
              DOI 10.17487/RFC6550, March 2012,
              <https://www.rfc-editor.org/info/rfc6550>.

   [RFC6552]  Thubert, P., Ed., "Objective Function Zero for the Routing
              Protocol for Low-Power and Lossy Networks (RPL)",
              RFC 6552, DOI 10.17487/RFC6552, March 2012,
              <https://www.rfc-editor.org/info/rfc6552>.

   [RFC6997]  Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
              J. Martocci, "Reactive Discovery of Point-to-Point Routes
              in Low-Power and Lossy Networks", RFC 6997,
              DOI 10.17487/RFC6997, August 2013,
              <https://www.rfc-editor.org/info/rfc6997>.

   [RFC6998]  Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci,
              "A Mechanism to Measure the Routing Metrics along a Point-
              to-Point Route in a Low-Power and Lossy Network",
              RFC 6998, DOI 10.17487/RFC6998, August 2013,
              <https://www.rfc-editor.org/info/rfc6998>.

12.2.  Informative References

   [I-D.thubert-roll-asymlink]
              Thubert, P., "RPL adaptation for asymmetrical links",
              draft-thubert-roll-asymlink-02 (work in progress),
              December 2011.

Appendix A.  ETX/RSSI Values to select S bit

   We have tested the combination of "RSSI(downstream)" and "ETX
   (upstream)" to decide whether the link is symmetric or asymmetric at
   the intermediate nodes.  The example of how the ETX and RSSI values
   are used in conjuction is explained below:




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       Source---------->NodeA---------->NodeB------->Destination

          Figure 9: Communication link from Source to Destination

   +-------------------------+----------------------------------------+
   | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA |
   +-------------------------+----------------------------------------+
   |          > -15          |                  150                   |
   |        -25 to -15       |                  192                   |
   |        -35 to -25       |                  226                   |
   |        -45 to -35       |                  662                   |
   |        -55 to -45       |                  993                   |
   +-------------------------+----------------------------------------+

         Table 1: Selection of 'S' bit based on Expected ETX value

   We tested the operations in this specification by making the
   following experiment, using the above parameters.  In our experiment,
   a communication link is considered as symmetric if the ETX value of
   NodeA->NodeB and NodeB->NodeA (See Figure.8) are, say, within 1:3
   ratio.  This ratio should be taken as a notional metric for deciding
   link symmetric/asymmetric nature, and precise definition of the ratio
   is beyond the scope of the draft.  In general, NodeA can only know
   the ETX value in the direction of NodeA -> NodeB but it has no direct
   way of knowing the value of ETX from NodeB->NodeA.  Using physical
   testbed experiments and realistic wireless channel propagation
   models, one can determine a relationship between RSSI and ETX
   representable as an expression or a mapping table.  Such a
   relationship in turn can be used to estimate ETX value at nodeA for
   link NodeB--->NodeA from the received RSSI from NodeB.  Whenever
   nodeA determines that the link towards the nodeB is bi-directional
   asymmetric then the "S" bit is set to "S=0".  Later on, the link from
   NodeA to Destination is asymmetric with "S" bit remains to "0".

Appendix B.  Changes to version 02

   o  Include the support for source routing.

   o  Bring some features from [RFC6997], e.g., choice between hop-by-
      hop and source routing, duration of residence in the DAG, MaxRank,
      etc.

   o  Define new target option for AODV-RPL, including the Destination
      Sequence Number in it.  Move the TargNode address in RREQ option
      and the OrigNode address in RREP option into ADOV-RPL Target
      Option.

   o  Support route discovery for multiple targets in one RREQ-DIO.



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   o  New InstanceID pairing mechanism.

Authors' Addresses

   Satish Anamalamudi
   Huaiyin Institute of Technology
   No.89 North Beijing Road, Qinghe District
   Huaian  223001
   China

   Email: satishnaidu80@gmail.com


   Mingui Zhang
   Huawei Technologies
   No. 156 Beiqing Rd. Haidian District
   Beijing  100095
   China

   Email: zhangmingui@huawei.com


   Abdur Rashid Sangi
   Huaiyin Institute of Technology
   No.89 North Beijing Road, Qinghe District
   Huaian  223001
   P.R. China

   Email: sangi_bahrian@yahoo.com


   Charles E. Perkins
   Futurewei
   2330 Central Expressway
   Santa Clara  95050
   Unites States

   Email: charliep@computer.org


   S.V.R Anand
   Indian Institute of Science
   Bangalore  560012
   India

   Email: anand@ece.iisc.ernet.in





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   Bing Liu
   Huawei Technologies
   No. 156 Beiqing Rd. Haidian District
   Beijing  100095
   China

   Email: remy.liubing@huawei.com












































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