Imported debug from /usr/lib/site-python/debug.pyc draft-ji-roll-traffic-aware-objective-function-03 - Traffic-aware Objective Function
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ROLL                                                          C. Ji, Ed.
Internet-Draft                             Alexander TEI of Thessaloniki
Intended status: Standards Track                         R. Koutsiamanis
Expires: April 22, 2019                                  G. Papadopoulos
                                                          IMT Atlantique
                                                              D. Dujovne
                                              Universidad Diego Portales
                                                            N. Montavont
                                                          IMT Atlantique
                                                        October 19, 2018


                    Traffic-aware Objective Function
           draft-ji-roll-traffic-aware-objective-function-03

Abstract

   This document proposes a remaining throughput metric for parent and
   DODAG selection.  This metric represents the amount of remaining
   traffic handling capacity that the node has.  This document also
   proposes an Objective Function (OF) which uses the proposed metric
   for parent and DODAG selection to balance the amount of traffic
   between nodes and DODAGs.

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 April 22, 2019.

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



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   (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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  DODAG construction in RPL . . . . . . . . . . . . . . . . . .   3
   4.  Load distribution problem in RPL  . . . . . . . . . . . . . .   3
     4.1.  Parent selection problem  . . . . . . . . . . . . . . . .   4
     4.2.  DODAG selection problem . . . . . . . . . . . . . . . . .   6
   5.  TAOF description  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  DIO Metric Container Type extension . . . . . . . . . . . . .   9
   7.  Enrollment  . . . . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   10. Informative references  . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   RPL [RFC6550] is an IPv6 Routing protocol for LLNs.  It uses
   Objective Functions (OF) to construct the Destination Oriented
   Directed Acyclic Graph (DODAG) containing the nodes of the network.
   The existing OFs defined are OF Zero (OF0) [RFC6552] and Minimum Rank
   with Hysteresis OF (MRHOF) [RFC6719].  These OFs specify how nodes in
   a DODAG select their preferred parent using different metrics.

   The metrics can be separated into two different types, link metrics
   (e.g.  ETX) and node metrics (e.g. energy).  Experimental results
   [I-D.qasem-roll-rpl-load-balancing] conclude that using the current
   OFs leads to an unbalanced network within which some nodes are
   overloaded.  Here, a node is overloaded in the sense that it forwards
   many more packets than it otherwise would if the network were
   balanced.  This problem has consequences for the lifetime of the
   network because overloaded nodes drain quicker than others, a problem
   which becomes even more significant when the overloaded nodes are
   near the DODAG root [I-D.qasem-roll-rpl-load-balancing].

   Similarly, one DODAG might be overloaded in the same sense compared
   to another DODAG, and this will lead to the same consequences for the
   whole DODAG as for a specific node.




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   This problem is still an open issue.  This draft proposes a new way
   of parent and DODAG selection as an attempt towards a solution.  This
   draft proposes a new OF that considers the remaining throughput as a
   representation of the remaining traffic handling capacity each node
   possesses and which uses this information to balance the amount of
   traffic between nodes and DODAGs.

   In brief, each node tracks its remaining throughput and appends this
   information as a DAG Metric Container option to DIO messages it
   sends.  When the DIO message is received by child nodes or potential
   child nodes, the remaining throughput information is stored and used
   to influence the result when RPL parent or DODAG selection is
   performed.

2.  Terminology

   The key words "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].

3.  DODAG construction in RPL

   RPL uses OFs to construct a DODAG.  OFs define the way the nodes
   select their preferred parent and DODAG and how they compute the new
   rank.  A node's rank is always larger than its parent's rank because
   the calculation of rank is based on an increment to the parent's
   rank.  This increment differs for each OF but all OFs include the
   MinHopRankIncrease, which is the minimum increase in rank between a
   node and a node's parent and a step.  Different OFs use different
   metrics or constraints to select the preferred parent and DODAG and
   to define the step, depending on application requirements.  Nodes
   obtain these values from DODAG Information Object (DIO) control
   messages sent by their neighbor nodes.

   The construction of a DODAG starts when the root node sends DIO
   messages to its neighbors.  After receiving the DIO, these neighbor
   nodes select the root as their preferred parent if they wish to join
   the DODAG.  To announce that they joined the DODAG as its child node,
   they send a Destination Advertisement Object (DAO) to their preferred
   parent - the DODAG root.  After joining the DODAG, these nodes send
   their own DIO messages with the new computed rank to their neighbors.
   This procedure repeats for every node which joins the DODAG.

4.  Load distribution problem in RPL

   According to the experiments conducted using existing OFs RPL faces a
   load distribution problem in large LLNs.  With RPL using existing
   OFs, such as MRHOF, an unbalanced network is formed with some nodes



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   overloaded and other nodes at rest.  This problem is severe for
   network performance because overloaded nodes will use up their
   available energy faster than other nodes.  This is exacerbated for
   nodes near the root (within 1 hop distance) or nodes which are the
   only parent candidate for other nodes.  Additionally, when the
   overloaded node shuts down, a big part of the network will become
   disconnected and will have to be transferred to another parent or
   DODAG.  There is a high probability that the children nodes will also
   select the same new node as their parent or the same DODAG, leading
   to another overloaded node/DODAG.  Also, when a node has selected its
   parent, it will change only when the parent node is not reachable
   (due to battery depletion or packet losses).

   The existing OFs usually use a single metric to compare parent
   candidates, for example, as described in [RFC6719] the default metric
   used in MRHOF is ETX [RFC6551], which represents the number of
   transmissions a node expects to make to a destination to successfully
   deliver one packet.  The result from using a single metric is that
   nodes prefer to select the same node as their parent, which according
   to [I-D.qasem-roll-rpl-load-balancing] leads to an unbalanced network
   with overloaded nodes (node load is indicated by a node's child
   count).  But the child count does not accurately indicate the load
   because among the child nodes some may have higher traffic load and
   others may have lower.

   The network traffic can be quantified by tracking the packets a node
   generates/sends/receives and the amount of energy it consumes.
   Energy consumption is strongly correlated to the amount of network
   traffic handled by a node since the energy consumption for the
   operation of the radio is the primary energy consumer in typical
   nodes.  However, directly measuring the remaining throughput is both
   more accurate and also works when nodes have atypical energy
   consumption profiles (e.g. increased node processing or high energy
   consumption sensors).

   Calculating the remaining throughput then requires knowledge of the
   total throughput supported by a node and subtraction of the used
   throughput.

4.1.  Parent selection problem











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           T:4p/s               |         T:4p/s
           U:4p/s (R)           |         U:4p/s (R)
                   ^            |                 ^
                   |            |                 |
            +--------------+    |          +------+-------+
            |              |    |          |              |
    T:2p/s  +      T:2p/s  +    |  T:2p/s  +      T:2p/s  +
    U:3p/s (A)     U:1p/s (B)   |  U:2p/s (A)     U:2p/s (B)
            ^              ^    |          ^              ^
            |              |    |          |              |
      +-----+------+       |    |    +-----+       +------+
      |     |      |       |    |    |     |       |      |
      +     +      +       +    |    +     +       +      +
     (C1)  (C2)   (C3)    (D1)  |   (C1)  (C2)    (C3)   (D1)
   U:1p/s U:1p/s U:1p/s  U:1p/s | U:1p/s U:1p/s  U:1p/s U:1p/s
                                |
             Unbalanced         |            Balanced

      Figure 1: Use of Remaining Throughput with nodes with the same
                               requirements

   As a first simple example, an unbalanced network with nodes which all
   use the same throughput ("U:") is shown in Figure 1.  Nodes A and B
   have the same total throughput ("T:"), but node A is overloaded due
   to trying to handle more than its ability while node B has a spare
   throughput of 2-1=1p/s.  Its transformation into a balanced network
   is shown on the right and it involves a node (C3) switching parents
   from A to B so that the capacity of its parent is no longer exceeded.























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            T:6p/s               |          T:6p/s
            U:6p/s (R)           |          U:6p/s (R)
                    ^            |                  ^
                    |            |                  |
             +------+-------+    |           +--------------+
             |              |    |           |              |
     T:3p/s  +      T:3p/s  +    |   T:3p/s  +      T:3p/s  +
     U:2p/s (A)     U:4p/s (B)   |   U:3p/s (A)     U:3p/s (B)
             ^              ^    |           ^              ^
             |              |    |           |              |
       +-----+       +------+    |     +-----+------+       |
       |     |       |      |    |     |     |      |       |
       +     +       +      +    |     +     +      +       +
      (C1)  (C2)    (D1)   (D2)  |    (C1)  (C2)   (D1)    (D2)
    U:1p/s U:1p/s  U:1p/s U:3p/s |  U:1p/s U:1p/s U:1p/s  U:3p/s
                                 |
                Unbalanced       |            Balanced

      Figure 2: Use of Remaining Throughput with nodes with different
                               requirements

   As a second simple example, an unbalanced network with nodes which
   have different throughput ("U:") is shown in Figure 2.  In this case,
   node B is overloaded and node D1 should move to parent A, which as a
   space throughput of 1p/s.  Its transformation into a balanced
   equivalent network is shown on the right.

4.2.  DODAG selection problem

   The purpose of the following example is to show the problem of DODAG
   selection, and not to focus on selecting the best parent.




















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   .... DODAG 1 ... ... DODAG 2 .... | .... DODAG 1 ... ... DODAG 2 ....
   .               .               . | .               .               .
   .  T:4p/s       .  T:4p/s       . | .  T:4p/s       .  T:4p/s       .
   .  U:4p/s (R1)  .  U:3p/s (R2)  . | .  U:5p/s (R1)  .  U:3p/s (R2)  .
   .          ^    .          ^    . | .          ^    .          ^    .
   .          |    .          |    . | .          |    .          |    .
   .    +-----+    .    +-----+    . | .    +-----+    .    +-----+    .
   .    |     |    .    |     |    . | .    |     |    .    |     |    .
   .    +     +    .    +     +    . | .    +     +    .    +     +    .
   .   (A1)  (B1)  .   (A2)  (B2)  . | .   (A1)  (B1)  .   (A2)  (B2)  .
   . U:3p/s U:1p/s . U:2p/s U:1p/s . | . U:3p/s U:1p/s . U:2p/s U:1p/s .
   ................ ................ | ................ ................
                                     |            ^
                                     |            |
                   ^                 |            +----+
                   |                 |                 |
                   +                 |                 +
                  (C)                |                (C)
                U:1p/s               |              U:1p/s
                                     |
               Joining               |        Joined - Unbalanced

   Figure 3: DODAG selection example leading to unbalanced traffic with
                                 RT metric

   In the example in Figure 3, there are two DODAGs (DODAG 1 and DODAG
   2) that belong to the same RPL Instance and a node (C) that must
   select a DODAG.  Node C has to pick from the information provided by
   its two reachable neighbors: B1 and A2.  On the left, node C is shown
   before selecting the preferred DODAG, while on the right it is shown
   after the DODAG selection.

   Node C might choose B1 in DODAG 1 to be its preferred parent since
   the traffic information of the two DODAGs is not available.  However,
   at the root node (R1), it can be observed that the total network
   traffic is higher in DODAG 1 and that after node C joins it, the
   traffic handling capacity of the root R1 has been exceeded.














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   .... DODAG 1 ... ... DODAG 2 .... | .... DODAG 1 ... ... DODAG 2 ....
   .               .               . | .               .               .
   .  T:4p/s       .  T:4p/s       . | .  T:4p/s       .  T:4p/s       .
   .  U:4p/s (R1)  .  U:3p/s (R2)  . | .  U:4p/s (R1)  .  U:4p/s (R2)  .
   .          ^    .          ^    . | .          ^    .          ^    .
   .          |    .          |    . | .          |    .          |    .
   .    +-----+    .    +-----+    . | .    +-----+    .    +-----+    .
   .    |     |    .    |     |    . | .    |     |    .    |     |    .
   .    +     +    .    +     +    . | .    +     +    .    +     +    .
   .   (A1)  (B1)  .   (A2)  (B2)  . | .   (A1)  (B1)  .   (A2)  (B2)  .
   . U:3p/s U:1p/s . U:2p/s U:1p/s . | . U:3p/s U:1p/s . U:2p/s U:1p/s .
   ................ ................ | ................ ................
                                     |                      ^
                                     |                      |
                   ^                 |                 +----+
                   |                 |                 |
                   +                 |                 +
                  (C)                |                (C)
                U:1p/s               |              U:1p/s
                                     |
               Joining               |          Joined - Balanced

   Figure 4: DODAG selection example leading to balanced traffic with RT
                                  metric

   If the traffic handling capacity information is available, then node
   C could make a more efficient decision by using DODAG 2 and selecting
   node A2 as the preferred parent, as shown in Figure 4.  Such a
   selection is based on the traffic of the entire DODAG and would not
   lead to exceeding the traffic handling capacity of the root R2 since
   this root had spare capacity.

5.  TAOF description

   In this specification, a metric is proposed to be used in the parent
   and DODAG selection mechanism, the Remaining Throughput (RT) which
   represents the number of packets each node can transmit (send or
   forward) during a certain time period.  The period used, named
   THROUGHPUT_PERIOD, is a parameter common to the whole RPL instance.
   This parameter CAN be pre-configured on all the nodes.  The period
   used SHOULD coincide with a sliding window of the same size used to
   calculate the packets transferred during this period to facilitate
   the calculation of the remaining possible packet transmissions.
   Therefore, whenever the RT value is reported it will refer to the
   previous THROUGHPUT_PERIOD period of time.  This information is added
   in DIO messages and is broadcast to every neighbor.





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   At first, each node MUST identify from their neighbor set which nodes
   are acceptable to be selected as a parent.  For this purpose, the
   metric ETX is used as a filter to filter out parent candidates with
   low link quality with a preference for nodes with link quality below
   a given threshold.  The ETX threshold SHOULD be different depending
   on application requirements.  The suggested value for the relevant
   threshold MAX_PATH_COST from MRHOF [RFC6719] is 32768, which means
   the specific path has expected transmission counts greater than 256.

   When the ETX value is used as a filter, nodes with bad link quality
   will not be included in the parent set.  This ensures that undue
   retransmissions caused by bad links will be avoided.  After all the
   filtering is done, if any, the node chooses the parent candidate or
   DODAG with the highest remaining throughput.

   For the purpose of DODAG specifically, the A field in the Routing
   Metric/Constraint Flag field object [RFC6551] SHOULD be set to 1,
   indicating that the value reported is a maximum.  Furthermore, when a
   node is calculating the value of RT to broadcast in a DIO, the value
   reported SHOULD be the minimum of two values: its parent RT and the
   node's own calculated remaining throughput.  Thus, the value
   broadcasted will be the available remaining throughput in the whole
   path from the node to the DODAG root.

   This proposal is expected to increase the frequency of parent changes
   because the remaining throughput is more likely to be different
   between DIO messages, even for DIO messages from the same node.
   There are multiple ways to minimize the frequency of unnecessary
   parent changes:

   a.  Use the remaining throughput in combination with another metric
       (e.g. child count, hop counts).

   b.  Use a threshold when comparing the remaining throughput, similar
       to the approach in MRHOF [RFC6719].  Switch parents when the
       difference of remaining throughput between the original parent
       and the alternative parent is above a threshold.  This threshold
       depends on different factors (e.g. network size, average traffic
       load) and SHOULD be defined differently for each use case.

6.  DIO Metric Container Type extension










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        0                   1
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              RT               |    RT: Remaining Throughput
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 5: DAG metric container type format.

   A DIO message carries fields as described in RFC6550 [RFC6550] and
   the available options for the DAG metric container are described in
   RFC6551 [RFC6551].  In this specification, a metric container option
   is proposed and the detailed format is shown in Figure 5.  The
   information carried is the RT, represented as a 2 byte unsigned
   integer and the unit is packets per THROUGHPUT_PERIOD time.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | RPLInstanceID |Version Number |             Rank              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |G|0| MOP | Prf |     DTSN      |     Flags     |   Reserved    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                            DODAGID                            +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | DAGMC Type (2)| DAGMC Length  |                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   //                   DAG Metric Container data                 //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


     Figure 6: Example DIO Message with a DAG Metric Container option

   The structure of the DIO Control Message when a DAG Metric Container
   option is included is shown in Figure 6.  The DAG Metric Container
   option type (DAGMC Type in Figure 6) has the value 0x02 as per the
   IANA registry for the RPL Control Message Options and is defined in
   [RFC6550].  The DAG Metric Container option length (DAGMC Length in
   Figure 6) expresses the DAG Metric Container length in bytes.  DAG
   Metric Container data holds the actual data and is shown further
   expanded in Figure 7.



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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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Routing-MC-Type|Res Flags|P|C|O|R| A   |  Prec | Length (bytes)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             RT                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


    Figure 7: DAG Metric Container (MC) data with Remaining Throughput
                             (RT) object body

   An example DAG Metric Container containing the proposed Metric
   Container object is shown in Figure 7.  The explicit definition of
   the fields is:

   Routing-MC-Type:  TBD1.  The type of the proposed DAGMC extension.
         To be assigned by IANA.

   Remaining Throughput (RT):  The remaining throughput, represented as
         a 2-byte unsigned integer in units of packets per
         THROUGHPUT_PERIOD time.

7.  Enrollment

   The RT metric SHOULD be used not only for ongoing parent selection
   but also especially within enrollment, i.e. the process a node
   follows to join a 6TiSCH network.  In accordance to
   [I-D.ietf-6tisch-enrollment-enhanced-beacon], the value in RT SHOULD
   be used to affect the enrollment process so that a new node will be
   able to directly select a DODAG which will be able to cover its
   traffic needs and to spread the traffic load between different
   DODAGs.  More specifically, the pan priority field described in
   [I-D.ietf-6tisch-enrollment-enhanced-beacon] can be derived from the
   RT value.  For this purpose, the RT value SHOULD be used with the
   maximum value aggregation mode (A field in the Routing Metric/
   Constraint Flag field object [RFC6551] set to 1), to report the
   maximum remaining throughput in the whole path to the DODAG root.
   The pan priority field is an unsigned 8-bit integer with lower values
   signifying higher priority while the RT value is a 16-bit unsigned
   integer with higher values signifying more remaining throughput.  To
   convert the RT value to a pan priority the following formula should
   be used:

   pan priority = 16 - FLOOR(LOG2(RT + 1))

   where LOG2 is the logarithm function with a base of 2.  The use of
   the LOG function allows having higher accuracy in the low values of



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   the remaining throughput, where small value differences are
   significant, and lower accuracy in the high values of the remaining
   throughput, where small differences are less significant.  The
   addition of 1 to the RT allows converting RT=0.

8.  Security Considerations

   The structure of the DIO control message is extended, within the pre-
   defined DIO options.  Therefore, the security mechanisms defined in
   RPL [RFC6550] apply to this proposed extension.

9.  IANA Considerations

   This proposal requests the allocation of a new value TBD1 for the
   metric type "RT" in the Routing-MC-Type field in the DAG MC from
   IANA.

   Additionally, an Objective Code Point (OCP) with value TBD2 for TAOF
   needs to be assigned in the Objective Code Point Registry as
   described in Section 20.5 of [RFC6550].

10.  Informative references

   [I-D.ietf-6tisch-enrollment-enhanced-beacon]
              Dujovne, D. and M. Richardson, "IEEE802.15.4 Informational
              Element encapsulation of 6tisch Join and Enrollment
              Information", draft-ietf-6tisch-enrollment-enhanced-
              beacon-00 (work in progress), July 2018.

   [I-D.qasem-roll-rpl-load-balancing]
              Qasem, M., Al-Dubai, A., Romdhani, I., Ghaleb, B., Hou,
              J., and R. Jadhav, "Load Balancing Objective Function in
              RPL", draft-qasem-roll-rpl-load-balancing-02 (work in
              progress), October 2017.

   [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>.

   [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>.





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Internet-Draft              Traffic-aware OF                October 2018


   [RFC6551]  Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
              and D. Barthel, "Routing Metrics Used for Path Calculation
              in Low-Power and Lossy Networks", RFC 6551,
              DOI 10.17487/RFC6551, March 2012,
              <https://www.rfc-editor.org/info/rfc6551>.

   [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>.

   [RFC6719]  Gnawali, O. and P. Levis, "The Minimum Rank with
              Hysteresis Objective Function", RFC 6719,
              DOI 10.17487/RFC6719, September 2012,
              <https://www.rfc-editor.org/info/rfc6719>.

Authors' Addresses

   Chenyang Ji (editor)
   Alexander TEI of Thessaloniki
   Department of Informatics
   Thessaloniki  57400
   GREECE

   Email: jichenyang920@gmail.com


   Remous-Aris Koutsiamanis
   IMT Atlantique
   Office B00 - 126A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

   Phone: +33 299 12 70 49
   Email: aris@ariskou.com


   Georgios Papadopoulos
   IMT Atlantique
   Office B00 - 114A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

   Phone: +33 299 12 70 04
   Email: georgios.papadopoulos@imt-atlantique.fr




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   Diego Dujovne
   Universidad Diego Portales
   Escuela de Informatica y Telecomunicaciones, Av. Ejercito 441
   Santiago, Region Metropolitana
   Chile

   Phone: +56 (2) 676-8121
   Email: diego.dujovne@mail.udp.cl


   Nicolas Montavont
   IMT Atlantique
   Office B00 - 106A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

   Phone: +33 299 12 70 23
   Email: nicolas.montavont@imt-atlantique.fr
































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