Internet Engineering Task Force M. Goyal, Ed.
Internet-Draft University of Wisconsin
Intended status: Experimental Milwaukee
Expires: July 22, 2012 E. Baccelli
M. Philipp
INRIA
A. Brandt
Sigma Designs
J. Martocci
Johnson Controls
January 19, 2012
Reactive Discovery of Point-to-Point Routes in Low Power and Lossy
Networks
draft-ietf-roll-p2p-rpl-06
Abstract
This document specifies a point-to-point route discovery mechanism,
complementary to the RPL core functionality. This mechanism allows
an IPv6 router to discover and establish, on demand, a route to
another IPv6 router in the LLN such that the discovered route meets
specified metrics constraints, without necessarily going along the
DAG links established by core RPL.
Status of this Memo
This Internet-Draft is submitted to IETF 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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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on July 22, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Functional Overview . . . . . . . . . . . . . . . . . . . . . 5
6. P2P Route Discovery Mode Of Operation . . . . . . . . . . . . 7
6.1. Setting a P2P Mode DIO . . . . . . . . . . . . . . . . . . 8
7. P2P Route Discovery Option (P2P-RDO) . . . . . . . . . . . . . 10
8. The Discovery Reply Object (DRO) . . . . . . . . . . . . . . . 13
8.1. Secure DRO . . . . . . . . . . . . . . . . . . . . . . . . 14
8.2. Setting a P2P-RDO Carried in a Discovery Reply Object . . 14
9. P2P-RPL Route Discovery By Creating a Temporary DAG . . . . . 15
9.1. Joining a Temporary DAG . . . . . . . . . . . . . . . . . 15
9.2. Trickle Operation For P2P Mode DIOs . . . . . . . . . . . 15
9.3. Processing a P2P Mode DIO . . . . . . . . . . . . . . . . 17
9.4. Additional Processing of a P2P Mode DIO At An
Intermediate Router . . . . . . . . . . . . . . . . . . . 18
9.5. Additional Processing of a P2P Mode DIO At The Target . . 18
9.6. Processing a DRO At An Intermediate Router . . . . . . . . 19
9.7. Processing a DRO At The Origin . . . . . . . . . . . . . . 20
10. The Discovery Reply Object Acknowledgement (DRO-ACK) . . . . . 21
11. Packet Forwarding Along a P2P-RPL Route . . . . . . . . . . . 22
12. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 23
13. Interoperability With Core RPL . . . . . . . . . . . . . . . . 23
14. Security Considerations . . . . . . . . . . . . . . . . . . . 23
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
15.1. Additions to DIO Mode of Operation . . . . . . . . . . . . 24
15.2. Additions to RPL Control Message Options . . . . . . . . . 24
15.3. Additions to RPL Control Codes . . . . . . . . . . . . . . 25
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 25
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
17.1. Normative References . . . . . . . . . . . . . . . . . . . 25
17.2. Informative References . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
Targeting Low power and Lossy Networks (LLNs), the RPL routing
protocol [I-D.ietf-roll-rpl] provides paths along a Directed Acyclic
Graph (DAG) rooted at a single router in the network. Establishment
and maintenance of the DAG is performed by each router in the LLN
using specific link-local multicast signaling (DIO messages).
When two arbitrary routers (neither of which is the DAG's root) need
to communicate, core RPL provides dog-legged paths along DAG links,
which may not be efficient enough for several Home and Building
Automation applications [RFC5826][RFC5867], for the following
reasons:
o The need to preprovision routes: each potential destination in the
network must declare itself as such, via specific additional
signaling (DAO messages).
o The need to route along DAG links: depending on the network
topology and metrics in use, the constraint to route along a DAG
may cause significantly suboptimal P2P routes and severe traffic
congestion near the DAG root.
This document thus describes a mechanism, complementary to the core
RPL functionality, that enables a router to discover on-demand a
route to another arbitrary router in the LLN, such that the
discovered route meets specified metrics constraints, without
necessarily going along an existing DAG. This reactive P2P route
discovery mechanism is henceforth referred to as P2P-RPL. P2P-RPL
allows for the discovery of source routes as well as hop-by-hop
routes. Discovered routes may not be the best available but are
guaranteed to satisfy the desired constraints in terms of the routing
metrics and are thus considered "good enough" from the application's
perspective.
A complementary functionality that helps decide whether or not to
initiate a P2P route discovery, is a mechanism to measure the end-to-
end cost of an existing route. Section 4 provides further details on
how such functionality, specified in [I-D.ietf-roll-p2p-measurement],
is used to determine the value of metric constraints for the route
discovery using P2P-RPL.
2. The Use Cases
P2P-RPL is intended to be employed as complementary to RPL in
specific scenarios that need P2P paths between arbitrary routers.
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One use case, common in a home environment, involves a remote control
(or a motion sensor) that suddenly needs to communicate with a lamp
module, whose network address is a-priori known. In this case, the
source of data (the remote control or the motion sensor) must be able
to discover a route to the destination (the lamp module) "on demand".
Another use case, common in a large commercial building environment,
involves a large LLN deployment where P2P communication along a
particular DAG among hundreds (or thousands) of routers creates
severe traffic congestion near that DAG's root, and thus routes
across this DAG are desirable.
The use cases also include scenarios where energy or latency
constraints are not satisfied by the routes provided by core RPL
along a DAG because they involve traversing many more intermediate
routers than necessary to reach the destination.
3. 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 terminology from
[I-D.ietf-roll-terminology] and [I-D.ietf-roll-rpl]. This document
introduces the following terms:
Origin : The RPL router initiating the P2P route discovery.
Target : The RPL router at the other end point of the P2P route(s) to
be discovered.
Intermediate Router: An RPL router that is neither the origin nor the
target.
Forward Route: A route in the forward direction, i.e., from the
origin to the target.
Backward Route: A route in the backward direction, i.e., from the
target to the origin.
Bidirectional Route: A route that can be used in both forward and
backward directions.
Source Route: A complete and ordered list of routers that can be used
by a packet to travel from a source to a destination node.
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Hop-by-hop Route: The route characterized by each router on the route
using its routing table to determine the next hop on the route.
4. Applicability
A route discovery using P2P-RPL may be performed by an origin when no
route exists between itself and the target or when the existing
routes do not satisfy the application requirements. P2P-RPL is
designed to discover and establish one hop-by-hop route or discover
one or more source routes such that the discovered route(s) meet the
specified constraints. In some application contexts, the constraints
that the discovered route(s) must satisfy are intrinsically known or
can be specified by the application. For example, an origin that
expects a target to be less than 5 hops away may use "hop-count < 5"
as the constraint. In other application contexts, the origin may
need to measure the cost of an existing route to the target to
determine the constraints. For example, an origin that measures the
total ETX of its along-DAG route to the target to be 20 may use "ETX
< x*20", where x is a fraction that the origin decides, as the
constraint. A mechanism to measure the cost of an existing route
between the origin and the target is specified in
[I-D.ietf-roll-p2p-measurement]. If there is no existing route
between the origin and target or the cost measurement for the
existing route fails, the origin will have to guess the constraints
used in the initial route discovery. Once, the initial route
discovery succeeds or fails, the origin will have a better estimate
for the constraints to be used in the subsequent route discovery.
P2P-RPL may result in discovery of better P2P routes than the ones
available along a DAG designed to optimize routing cost to the DAG's
root. The improvement in route quality depends on a number of
factors including the network topology, the routing metrics in use
and the prevalent conditions in the network. A network designer may
take into consideration both the benefits (potentially better routes;
no need to maintain routes proactively) and costs (control messages
generated during the route discovery process) when using P2P-RPL.
5. Functional Overview
This section contains a high level description of P2P-RPL.
As is the case with core RPL, P2P-RPL uses IPv6 link-local multicast
DIO messages to establish a DAG (unlike core RPL, this DAG is
temporary). Each router joining the DAG determines a rank for itself
in the DAG and ignores the subsequent DIO messages received from
lower (higher in numerical value) ranked neighbors. Thus, the DIO
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messages propagate outward from the DAG root rather than return
inward towards the DAG root. As in core RPL, DIO message generation
at a router is further controlled by a Trickle timer that allows a
router to avoid generating unnecessary messages [RFC6206]. P2P-RPL
also uses the routing metrics [I-D.ietf-roll-routing-metrics],
objective functions and packet forwarding framework specified for
core RPL.
In P2P-RPL, a route discovery takes place by forming a temporary DAG
rooted at the origin. The DIOs, used to create the temporary DAG,
are identified by a new Mode of Operation (P2P Route Discovery mode
defined in Section 6) and carry the following information (in a P2P
Route Discovery Option defined in Section 7):
o An IPv6 address of the target.
o The nature of the route(s) to be discovered: hop-by-hop or source
routes. This specification allows for the discovery of one hop-
by-hop route or up to four source routes in the forward direction.
o The desired number of routes (if source routes are being
discovered).
o Whether the route(s) need to be bidirectional. If bidirectional
route(s) are being discovered, the target may store the route in
backward direction for use as a source route. This specification
does not provide for the establishment of backward hop-by-hop
routes.
The DIOs, listing the P2P Route Discovery mode as the Mode of
Operation, are henceforth referred to as the P2P mode DIOs. The P2P
mode DIOs MAY also carry the following information (in one or more
Metric Container Options):
o The relevant routing metrics
o The constraints that the discovered route must satisfy. These
constraints also limit how far the DIOs message may travel.
As the routers join the temporary DAG, they keep track of the best
(partial) route(s) they have seen and advertise these routes, along
with the corresponding routing metrics, in their P2P mode DIOs. The
routing metrics are measured in forward direction unless
bidirectional routes are being discovered, in which case the
measurement of routing metrics need to take into account both forward
and backward directions. A router, including the target, discards a
received P2P mode DIO if the aggregated routing metrics on the route
advertised by the DIO do not satisfy the listed constraints. These
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constraints can be used to limit the propagation of P2P mode DIO
messages. A router may also discard a received P2P mode DIO if it
does not wish to be a part of the discovered route due to limited
resources or due to policy reasons.
When the target receives a P2P mode DIO, it checks whether the route
advertised therein satisfies the routing constraints. If yes, the
target may select the route for further processing as described next.
This document does not specify a particular method for the target to
select a route among the ones that satisfy the route constraints.
Examples include selecting any route that meets the constraints or
selecting the best route(s) discovered over a certain time period.
If one or more source routes are being discovered, the target sends
the discovered source routes to the origin via Discovery Reply Object
(DRO) messages (defined in Section 8) with one DRO message carrying
one discovered route. On receiving a DRO message, the origin stores
the route contained therein in its memory.
If a hop-by-hop route is being discovered, the target sends a DRO
message to the origin after selecting a suitable route among the ones
that satisfy the route constraints. The DRO message travels towards
the origin along the discovered route, establishing state for this
route in the routers on the path.
The target may store a discovered route in its memory if it is
bidirectional and use it as a backward source-route to send packets
to the origin.
The target may request the origin to acknowledge the receipt of a DRO
message by sending back a DRO Acknowledgement (DRO-ACK) message
(defined in Section 10). The origin unicasts a DRO-ACK message to
the target. When the target does not receive the requested DRO-ACK
within a certain time interval of sending a DRO, it resends the DRO
message (up to a certain number of times) carrying the same route as
before.
The use of trickle timers to delay the propagation of DIO messages
may cause some nodes to generate these messages even when the desired
routes have already been discovered. In order to preempt the
generation of such unnecessary messages, the target may set a "stop"
bit in the DRO message to let the nodes in the LLN know about the
completion of the route discovery process.
6. P2P Route Discovery Mode Of Operation
This section specifies a new RPL Mode of Operation (MOP), P2P Route
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Discovery mode (or P2P mode, for short), with value 4 (to be
confirmed by IANA). A DIO message, listing P2P mode as the MOP, is
identified as performing reactive P2P route discovery by creating a
temporary DAG. A P2P mode DIO MUST carry one P2P Route Discovery
Option (specified in Section 7).
6.1. Setting a P2P Mode DIO
The Base Object in a P2P mode DIO message MUST be set in the
following manner:
o RPLInstanceID: RPLInstanceID MUST be a local value as described in
Section 5.1 of [I-D.ietf-roll-rpl]. The origin MUST NOT use the
same RPLInstanceID in two or more concurrent route discoveries.
The origin MAY use the same RPLInstanceID value to establish hop-
by-hop P2P-RPL routes to different target routers as long as these
route discoveries are not concurrent.
o Version Number: MUST be set to zero. The temporary DAG used for
P2P-RPL route discovery does not exist long enough to have new
versions.
o Grounded (G) Flag: MUST be cleared since this DAG is temporary in
nature, is created solely for the purpose of P2P-RPL route
discovery and MUST NOT be used for packet routing.
o Mode of Operation (MOP): MUST be set to 4, corresponding to P2P
Route Discovery mode.
o DTSN: MUST be set to value zero on transmission and ignored on
reception.
o DODAGPreference (Prf): This field MUST be set to value 0 (least
preferred).
o DODAGID: This field MUST be set to an IPv6 address of the origin.
o The other fields in the DIO Base Object can be set in the desired
fashion as per the rules described in [I-D.ietf-roll-rpl].
The DODAG Configuration Option, inside a P2P mode DIO MUST be set in
the following manner:
o MaxRankIncrease: This field MUST be set to 0 to disable local
repair of the temporary DAG.
o Trickle parameters (DIOIntervalDoublings, DIOIntervalMin,
DIORedundancyConstant) SHOULD be set as described in Section 9.2.
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o The Default Lifetime and Lifetime Unit parameters in DODAG
Configuration option indicate the life time of the state the
routers maintain for a hop-by-hop route established using P2P-RPL
and may be set as desired.
o The other fields in the DODAG Configuration Option, including the
OCP identifying the Objective function, can be set in the desired
fashion as per the rules described in [I-D.ietf-roll-rpl].
A default DODAG Configuration Option comes in effect if a P2P mode
DIO does not carry an explicit one. The default DODAG Configuration
Option has the following parameter values:
o Authentication Enabled: 0
o DIORedundancyConstant: 1
o MaxRankIncrease: 0
o Default Lifetime: 0xFF
o Lifetime Unit: 0xFFFF
o Objective Code Point: 0, i.e., OF0 [I-D.ietf-roll-of0] is the
default objective function.
o The remaining parameters have default values as specified in
[I-D.ietf-roll-rpl].
The routing metrics and constraints [I-D.ietf-roll-routing-metrics]
used in P2P-RPL route discovery are included in one or more Metric
Container options [I-D.ietf-roll-rpl] inside the P2P mode DIO. Note
that a DIO need not include a Metric Container if OF0 is the
objective function in effect. In that case, a P2P mode DIO may still
specify an upper limit on the maximum rank, that a router may have in
the temporary DAG, inside the P2P Route Discovery Option (described
in Section 7).
A P2P mode DIO:
o MUST NOT carry any Route Information or Prefix Information Options
(described in [I-D.ietf-roll-rpl]).
o MUST carry one (and only one) P2P Route Discovery Option
(described in Section 7).
A router MUST discard a received P2P mode DIO if it violates any of
the rules listed above.
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7. P2P Route Discovery Option (P2P-RDO)
This section specifies a new RPL option, P2P Route Discovery Option
(P2P-RDO), one instance of which MUST be carried inside a P2P mode
DIO message.
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 = 10 | Option Length |D|H| N | Compr | L |MaxRank/NH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Target |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address[1..n] |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of P2P Route Discovery Option (P2P-RDO)
The format of a P2P-RDO is illustrated in Figure 1. A P2P mode DIO
and a DRO (defined in Section 8 message MUST carry one P2P-RDO. A
P2P-RDO consists of the following fields:
o Option Type: 0x0A (to be confirmed by IANA).
o Option Length: 8-bit unsigned integer, representing the length in
octets of the option, not including the Option Type and Option
Length fields.
o Direction (D): This flag indicates the direction in which the
desired routes should be optimized. The flag is set to 1 if the
routes are to be optimized for use in both forward and backward
directions. If the discovered routes need to be optimized in the
forward direction only, the flag is reset to 0. Note that the
discovered routes should have bidirectional reachability
irrespective of the value of the D flag. This is because DRO
messages travel from the target back to the origin along one of
the discovered routes. The link-level metric objects contained in
the P2P mode DIO SHOULD be measured in the direction indicated by
the D flag.
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o Hop-by-hop (H): This flag is set to 1 if a hop-by-hop route is
desired. The flag is reset to zero if source routes are desired.
This specification allows for the establishment of one hop-by-hop
route or up to four source routes in the forward direction. This
specification does not allow for the establishment of hop-by-hop
routes in the backward direction. If a bidirectional route is
discovered, the target MAY use the route in backward direction as
a source route to reach the origin, irrespective of the value of
the H flag.
o Number of Routes (N): When source routes are being discovered, the
value in this field plus one indicates the desired number of
routes. When a hop-by-hop route is being discovered this field
MUST be set to zero on transmission and ignored on reception.
o Compr: 4-bit unsigned integer indicating the number of prefix
octets that are elided from the Target field and the Address
vector. For example, Compr value will be 0 if full IPv6 addresses
are carried in the Target field and the Address vector.
o Life Time (L): A 2-bit field that indicates the suggested life
time of the temporary DAG, i.e., the suggested duration a router
joining the temporary DAG SHOULD maintain its membership in the
DAG. The mapping between the values in this field and the life
time of the temporary DAG is as follows:
* 0x00: 1 second;
* 0x01: 4 seconds;
* 0x02: 16 seconds;
* 0x03: 64 seconds;
The origin sets this field based on its expectation regarding the
time required for the DIOs to reach the target. Note that a
router MAY detach from the temporary DAG sooner if it receives a
DRO message concerning this DAG with "stop" bit set.
o MaxRank/NH:
* When a P2P Route Disovery Option is included in a P2P mode DIO,
this field indicates the upper limit on the integer portion of
the rank (calculated using the DAGRank() macro defined in
[I-D.ietf-roll-rpl]) that a router may have in the temporary
DAG being created. An intermediate router MUST NOT join a
temporary DAG being created by a P2P mode DIO if the integer
portion of its rank would be equal to or higher (in numerical
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value) than the MaxRank limit. The target can join the
temporary DAG at a rank whose integer portion is equal to the
MaxRank. A router MUST discard a received P2P mode DIO if the
integer part of the advertized rank equals or exceeds the
MaxRank limit. A value 0 in this field indicates that the
MaxRank is infinity.
* When a P2P-RDO is included in a DRO message, this field
indicates the index of the next hop address inside the Address
vector.
o Target: The IPv6 address of the target after eliding Compr number
of prefix octets.
o Address[1..n]: A vector of IPv6 addresses representing a (partial)
route in the forward direction:
* Each element in the Address vector has size (16 - Compr) octets
and MUST contain a valid IPv6 address with first Compr octets
elided.
* The total number of elements inside the Address vector is given
by n = (Option Length - 2 - (16 - Compr))/(16 - Compr).
* The Address vector is used to accumulate a route optimized in
the direction specified by the D flag.
* The IPv6 addresses in the Address vector MUST be accessible in
both forward and backward directions. Accessibility in the
backward direction is required because the DRO message uses the
route accumulated in the Address vector to travel from the
target to the origin.
* The Address vector MUST carry the accumulated route in the
forward direction, i.e., the first element in the Address
vector must contain the IPv6 address of the router next to the
origin and so on.
* The origin and target addresses MUST NOT be included in the
Address vector.
* A router adding its address to the vector MUST ensure that its
address does not already exist in the vector. A router
specifying a complete route in the Address vector MUST ensure
that the vector does not contain any address more than once.
* The Address vector MUST NOT contain any multicast addresses.
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8. The Discovery Reply Object (DRO)
This section defines two new RPL Control Message types, the Discovery
Reply Object (DRO), with code 0x04 (to be confirmed by IANA), and the
Secure DRO, with code 0x84 (to be confirmed by IANA). A DRO serves
one of the following functions:
o Carry a discovered source route from the target to the origin;
o Establish a hop-by-hop route as it travels from the target to the
origin.
A DRO message MAY also serve the function of letting the routers in
the LLN know that a P2P-RPL route discovery is complete and no more
DIO messages need to be generated for the corresponding temporary
DAG. A DRO message MUST carry one P2P-RDO and travel from the target
to the origin via link-local multicast along the route specified
inside the Address vector in the P2P-RDO.
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 |Seq|S|A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DODAGID |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
Figure 2: Format of the base Discovery Reply Object (DRO)
The format of the base Discovery Reply Object (DRO) is shown in
Figure 2. A base DRO consists of the following fields:
o RPLInstanceID: The RPLInstanceID of the temporary DAG used for
route discovery.
o Version: The Version of the temporary DAG used for route
discovery. Since a temporary DAG always has value zero for the
Version, this field MUST always be set to zero.
o Sequence Number (Seq): This 2-bit field indicates the sequence
number for the DRO. This field is relevant when the A flag
(specified below) is set, i.e., the target requests an
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acknowledgement from the origin for a received DRO. The origin
includes the RPLInstanceID, the DODAGID and the Sequence Number of
the received DRO inside the DRO-ACK message it sends back to the
target.
o Stop (S): This flag, when set by the target, indicates that the
P2P-RPL route discovery is over. All the routers receiving such a
DRO, including the ones not listed in the route carried inside
P2P-RDO, SHOULD cancel any pending DIO transmissions for the
temporary DAG created for the route discovery and MAY detach from
this DAG immediately. Note that the stop flag serves to stop
further DIO transmissions for a P2P-RPL route discovery but it
does not affect the processing of DRO messages at either the
origin or the intermediate routers. In other words, a router (the
origin or an intermediate router) MUST continue to process the DRO
messages even if an earlier DRO message (with same RPLInstanceID,
DODAGID and Version Number fields) had the stop flag set.
o Ack Required (A): This flag, when set by the target, indicates
that the origin SHOULD unicast a DRO-ACK message (defined in
Section 10) to the target when it receives the DRO.
o Reserved: These bits are reserved for future use. These bits MUST
be set to zero on transmission and MUST be ignored on reception.
o DODAGID: The DODAGID of the temporary DAG used for route
discovery. The DODAGID also identifies the origin. The
RPLInstanceID, the Version and the DODAGID together uniquely
identify the temporary DAG used for route discovery and can be
copied from the DIO message advertizing the temporary DAG.
o Options: The DRO message MUST carry one P2P-RDO that MUST specify
a complete route between the target and the origin. The DRO
message MAY carry a Metric Container Option that contains the
aggregated routing metrics values for the route specified in P2P-
RDO.
8.1. Secure DRO
A Secure DRO message follows the format in Figure 7 of
[I-D.ietf-roll-rpl], where the base format is the base DRO shown in
Figure 2.
8.2. Setting a P2P-RDO Carried in a Discovery Reply Object
A Discovery Reply Object MUST carry one P2P-RDO, which MUST be set as
defined in Section 7 with the following exceptions:
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o Direction (D): This flag MUST be set to zero on transmission and
ignored on reception.
o Number of Routes (N): This field MUST be set to zero on
transmission and ignored on reception.
o Life Time (L): This field MUST be set to zero on transmission and
ignored on reception.
o MaxRank/NH: This field indicates the index of the next hop address
in the Address vector. When a target generates a DRO message, the
NH field is set to n = (Option Length - 2 - (16 - Compr))/(16 -
Compr).
o Address[1..n]: The Address vector MUST contain a complete route
between the origin and the target such that the first element in
the vector contains the IPv6 address of the router next to the
origin and the last element contains the IPv6 address of the
router next to the target.
9. P2P-RPL Route Discovery By Creating a Temporary DAG
This section details the functioning of P2P-RPL route discovery by
creating a temporary DAG, using the P2P mode DIO, DRO and DRO-ACK
messages.
9.1. Joining a Temporary DAG
All the routers participating in a P2P-RPL route discovery, including
the origin and the target, MUST join the temporary DAG being created
for the purpose. When a router joins a temporary DAG advertized by a
P2P mode DIO, it SHOULD maintain its membership in the temporary DAG
for the suggested Life Time duration listed in the P2P-RDO. The only
purpose of a temporary DAG's existence is to facilitate the P2P-RPL
route discovery process. The temporary DAG MUST NOT be used to route
packets. A router SHOULD detach from the temporary DAG once the
duration of its membership in the DAG has exceeded the DAG's
suggested life time. A router MAY detach from a temporary DAG sooner
when it receives a DRO about the temporary DAG with the stop flag
set.
9.2. Trickle Operation For P2P Mode DIOs
An RPL router uses a Trickle timer [RFC6206] to control DIO
transmissions. The Trickle control of DIO transmissions provides
quick resolution of any "inconsistency" while avoiding redundant DIO
transmissions. The Trickle algorithm also imparts protection against
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loss of DIOs due to inherent lack of reliability in wireless
communication. When controlling the transmissions of a P2P mode DIO,
a Trickle timer SHOULD follow the following rules:
o The receipt of a P2P mode DIO, that allows the router to advertise
a better route (in terms of the routing metrics and the OF in use)
than before, is considered "inconsistent" and hence resets the
Trickle timer. Note that the first receipt of a P2P mode DIO
advertising a particular temporary DAG is always considered an
"inconsistent" event.
o The receipt of a P2P mode DIO from a parent in the temporary DAG
is considered neither "consistent" nor "inconsistent" if it does
not allow the router to advertise a better route than before.
Thus, the receipt of such DIOs has no impact on the Trickle
operation. Note that this document does not impose any
requirements on how a router might choose its parents in the
temporary DAG.
o The receipt of a P2P mode DIO is considered "consistent" if the
source of the DIO is not a parent in the temporary DAG and either
of the following conditions is true:
* The DIO advertises a better route than the router but does not
allow the router to advertise a better route itself; or
* The DIO advertises a route as good as the route (to be)
advertised by the router.
Note that Trickle algorithm's DIO suppression rules are in effect
at all times. Hence, a P2P-RPL router may suppress a DIO
transmission even if it has not made any DIO transmission yet.
o The receipt of a P2P mode DIO, that advertises a worse route than
what the router advertises (or would advertise when it gets a
chance to generate its DIO), is considered neither "consistent"
nor "inconsistent", i.e., the receipt of such a DIO has no impact
on the Trickle operation.
o The Imin parameter SHOULD be set taking in account the
connectivity within the network. For highly connected networks, a
small Imin value (of the order of the typical transmission delay
for a DIO) may lead to congestion in the network as a large number
of routers reset their Trickle timers in response to the first
receipt of a DIO from the origin. These routers would generate
their DIOs within Imin interval and cause additional routers to
reset their trickle timers and generate more DIOs. Thus, for
highly connected networks, the Imin parameter SHOULD be set to a
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value at least one order of magnitude larger than the typical
transmission delay for a DIO. For sparsely connected networks,
the Imin parameter can be set to a value that is a small multiple
of the typical transmission delay for a DIO. Note that the Imin
value has a direct impact on the time required for a P2P-RPL route
discovery to complete. In general, the time required for a P2P-
RPL route discovery would increase approximately linearly with the
value of the Imin parameter.
o The Imax parameter SHOULD be set to a large value (several orders
of magnitude higher than the Imin value) and is unlikely to be
critical for P2P-RPL operation. This is because the first receipt
of a P2P mode DIO for a particular temporary DAG is considered an
inconsistent event and would lead to resetting of Trickle timer
duration to the Imin value. Given the temporary nature of the
DAGs used in P2P-RPL, Trickle timer may not get a chance to
increase much.
o The recommended value of redundancy constant "k" is 1. With this
value of "k", a DIO transmission will be suppressed if the router
receives even a single "consistent" DIO during a timer interval.
This setting for the redundancy constant is designed to reduce the
number of messages generated during a route discovery process and
is suitable for environments with low or moderate packet loss
rates. In environments with high packet loss rates, a higher
value for the redundancy constant may be more suitable.
9.3. Processing a P2P Mode DIO
The rules for DIO processing and transmission, described in Section 8
of RPL [I-D.ietf-roll-rpl], apply to P2P mode DIOs as well except as
modified in this document.
The following rules for processing a P2P mode DIO apply to both
intermediate routers and the target.
A router SHOULD discard a received P2P mode DIO with no further
processing if it does not have bidirectional reachability with the
neighbor that originated the received DIO. This is to ensure that a
discovered route can be used to send a DRO message from the target to
the origin. Note that bidirectional reachability does not mean that
the link must have the same values for a routing metric in both
directions. A router SHOULD update the values of the link-level
routing metrics included inside the DIO in the direction indicated by
the D flag in the P2P-RDO. If the D flag is 0, i.e., the discovered
routes need not be bidirectional, the link-level routing metrics
SHOULD be measured in the forward direction, i.e., towards the node
receiving the DIO. If the D flag is 1, i.e., bidirectional routes
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are desired, the link-level routing metrics SHOULD be calculated so
as to take into account the metric's value in both forward and
backward directions.
A router MUST discard the received P2P mode DIO with no further
processing:
o If the DIO advertises INFINITE_RANK as defined in
[I-D.ietf-roll-rpl].
o If the integer part of the rank advertised in the DIO equals or
exceeds the MaxRank limit listed in the P2P Route Discovery
Option.
o If the router cannot evaluate the mandatory route constraints
listed in the DIO or if the routing metric values do not satisfy
one or more of the mandatory constraints.
9.4. Additional Processing of a P2P Mode DIO At An Intermediate Router
An intermediate router MUST discard a received P2P mode DIO with no
further processing if the router cannot elide Compr (as specified in
the P2P-RDO) prefix octets from its IPv6 address.
On receiving a P2P mode DIO, an intermediate router MUST determine
whether this DIO advertises a better route than the router itself and
whether the receipt of the DIO would allow the router to advertise a
better route than before. Accordingly, the router SHOULD consider
this DIO as consistent/inconsistent from Trickle perspective as
described in Section 9.2. Note that the route comparison in a P2P-
RPL route discovery is performed using the parent selection rules of
the OF in use as specified in Section 14 of RPL [I-D.ietf-roll-rpl].
If the received DIO would allow the router to improve the route it
advertises, the router MUST store the route advertised in the DIO in
memory (after adding its own IPv6 address to the route) for inclusion
in its future DIOs. When an intermediate router adds itself to a
route, it MUST ensure that the IPv6 address added to the route is
accessible in both forward and backward directions. To improve the
diversity of the routes being discovered, an intermediate router
SHOULD keep track of multiple partial routes to be advertised in the
P2P-RDO inside its DIO. When the router generates its DIO, it SHOULD
randomly select the partial route to be included in the P2P-RDO.
9.5. Additional Processing of a P2P Mode DIO At The Target
The target discards a received P2P mode DIO with no further
processing if the routing metrics inside the DIO do not satisfy the
mandatory constraints. Otherwise, the target MAY select the route
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contained in the P2P-RDO for further processing. This document does
not prescribe a particular method for the target to select such
routes. Examples include selecting the desired number of routes as
they are identified or selecting the best routes discovered over a
certain time period. If multiple routes are desired, the target
SHOULD avoid selecting routes that have large segments in common. If
a discovered route is bidirectional (D=1), the target MAY store the
route in backward direction, obtained by reversing the discovered
forward route, for use as a source route to reach the origin. After
selecting a route, the target sends a Discovery Reply Object (DRO)
message back to the origin (identified by the DODAGID field in the
DIO). In this DRO, the target includes a P2P-RDO that contains the
selected route inside the Address vector. The P2P-RDO included in
the DRO message MUST copy the H flag from the P2P-RDO inside the
received DIO message. The other fields inside the P2P-RDO MUST be
set as specified in Section 7. The mechanism for the propagation of
DRO messages is described in Section 8.
The target MAY set the A flag inside the DRO message if it desires
the origin to send back a DRO-ACK message on receiving the DRO. In
this case, the target waits for DRO_ACK_WAIT_TIME duration for the
DRO-ACK message to arrive. Failure to receive the DRO-ACK message
within this time duration causes the target to retransmit the DRO
message. The target MAY retransmit the DRO message in this fashion
up to MAX_DRO_RETRANSMISSIONS times. The values of DRO_ACK_WAIT_TIME
and MAX_DRO_RETRANSMISSIONS are defined in Section 12.
The target MAY include a Metric Container Option in the DRO message.
This Metric Container contains the end-to-end routing metric values
for the route specified in the P2P-RDO. The target MAY set the stop
flag inside the DRO message (and detach from the temporary DAG) if it
has already selected the desired number of routes. A target MUST NOT
forward a P2P mode DIO any further.
9.6. Processing a DRO At An Intermediate Router
When a router receives a DRO message that does not list its IPv6
address in the DODAGID field, the router MUST process the received
message in the following manner:
o If the stop flag inside the received DRO is set and the router
currently belongs to the temporary DAG identified by the
(RPLInstanceID, DODAGID and Version fields of the) DRO, the router
SHOULD cancel any pending DIO transmissions for this temporary
DAG. Additionally, the router MAY detach from the temporary DAG
immediately.
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o An intermediate router MUST ignore any Metric Container Option
contained in the DRO message.
o If Address[NH] element inside the Route Discovery Option lists the
router's own IPv6 address, the router is a part of the route
carried in the P2P-RDO. In this case, the router MUST do the
following:
* If the H flag inside the P2P-RDO inside the DRO message is set,
the router SHOULD store the state for the forward hop-by-hop
route carried inside the P2P-RDO. This state consists of:
+ The RPLInstanceID and the DODAGID fields of the DRO.
+ The route's destination, the target (identified by Target
field in P2P-RDO).
+ The IPv6 address of the next hop, Address[NH+1] (unless NH
value equals the number of elements in the Address vector,
in which case the target itself is the next hop).
The router MUST drop the DRO message with no further processing
if the H flag inside the P2P-RDO is set but the router chooses
not to store the state for the hop-by-hop route.
* If the router already maintains a hop-by-hop state listing the
target as the destination and carrying same RPLInstanceID and
DODAGID fields as the received DRO and the next hop information
in the state does not match the next hop indicated in the
received DRO, the router MUST drop the DRO message with no
further processing.
* The router MUST decrement the NH field inside the P2P-RDO and
send the DRO further via link-local multicast.
9.7. Processing a DRO At The Origin
When a router receives a DRO message that lists its IPv6 address in
the DODAGID field, the router recognizes itself as the origin for the
corresponding P2P-RPL route discovery and processes the P2P-RDO
contained in the DRO in the following manner.
If the stop flag inside the received DRO is set and the origin still
belongs to the temporary DAG it initiated, it SHOULD cancel any
pending DIO transmissions for this temporary DAG. Additionally, the
origin MAY detach from the temporary DAG immediately.
If the P2P-RDO inside the DRO identifies the discovered route as a
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source route (H=0), the origin SHOULD store in its memory the
discovered route contained in the Address vector.
If the P2P-RDO inside the DRO identifies the discovered route as a
hop-by-hop route (H=1), the origin SHOULD store in its memory the
state for the discovered route in the manner described in
Section 9.6.
If the received DRO message contains a Metric Container Option as
well, the origin MAY store the values of the routing metrics
associated with the discovered route in its memory. This information
may be useful in formulating the constraints for any future P2P-RPL
route discovery to the target.
If the A flag is set to one in the received DRO message, the origin
SHOULD generate a DRO-ACK message as described in Section 10 and
unicast the message to the target. The origin MAY source route the
DRO-ACK message to the target using the route contained in the
received DRO. If the received DRO established a hop-by-hop route to
the target, the origin MAY send the DRO-ACK message along this route.
Section 11 describes how a packet may be forwarded along a route
discovered using P2P-RPL.
10. The Discovery Reply Object Acknowledgement (DRO-ACK)
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 |Seq| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| DODAGID |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Format of the base Discovery Reply Object Acknowledgement
(DRO-ACK)
A DRO message may fail to reach the origin due to a number of
reasons. Unlike the DIO messages that benefit from Trickle-
controlled retransmissions, the DRO messages are prone to loss due to
reasons associated with wireless communication. Since a DRO message
travels via link-local multicast, it cannot use link-level
acknowledgements to improve the reliability of its transmission.
Also, an intermediate router may drop the DRO message (e.g., because
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of its inability to store the state for the hop-by-hop route the DRO
is establishing). To protect against the potential failure of a DRO
message to reach the origin, the target MAY request the origin to
send back a DRO Acknowledgement (DRO-ACK) message on receiving a DRO
message. Failure to receive such an acknowledgement within the
DRO_ACK_WAIT_TIME interval of sending the DRO message forces the
target to resend the message.
This section defines two new RPL Control Message types: DRO
Acknowledgement (DRO-ACK; with code 0x05; to be confirmed by IANA)
and Secure DRO-ACK (with code 0x85; to be confirmed by IANA). A DRO-
ACK message MUST travel as a unicast message from the origin to the
target. The format of a base DRO-ACK message is shown in Figure 3.
Various fields in a DRO-ACK message MUST have the same values as the
corresponding fields in the DRO message. The field marked as
"Reserved" MUST be set to zero on transmission and MUST be ignored on
reception. A Secure DRO-ACK message follows the format in Figure 7
of [I-D.ietf-roll-rpl], where the base format is same as the base
DRO-ACK shown in Figure 3.
11. Packet Forwarding Along a P2P-RPL Route
This document specifies a mechanism to discover P2P routes, which can
be either source routes or hop-by-hop ones. A packet MAY use an SRH
header [I-D.ietf-6man-rpl-routing-header] to travel along a source
route discovered using P2P-RPL. Travel along a hop-by-hop route,
established using P2P-RPL, requires specifying the RPLInstanceID and
the DODAGID to identify the route. This is because P2P-RPL route
discovery does not use globally unique RPLInstanceID values and hence
both the RPLInstanceID, which is a local value assigned by the
origin, and the DODAGID, which is an IPv6 address belonging to the
origin, are required to uniquely identify a P2P-RPL hop-by-hop route
to a particular destination. A packet MAY include an RPL option
[I-D.ietf-6man-rpl-option] inside the IPv6 hop-by-hop options header
to travel along a hop-by-hop route established using P2P-RPL. In
this case, the origin MUST set the DODAGID of the P2P-RPL route as
the source IPv6 address of the packet. Further, the origin MUST
specify the RPLInstanceID, associated with the P2P-RPL route, inside
the RPL option and set the O flag inside the RPL option to 1. A
router receiving this packet will check the O flag inside the RPL
option and correctly infer the source IPv6 address of the packet as
the DODAGID of the hop-by-hop route to be used for forwarding the
packet further.
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12. Constants
This document defines the following constants:
o DRO_ACK_WAIT_TIME: The time duration a target waits for the DRO-
ACK before retransmitting a DRO message. DRO_ACK_WAIT_TIME has a
value of 1 second.
o MAX_DRO_RETRANSMISSIONS: The maximum number of times a DRO message
may be retransmitted if the target does not receive a DRO-ACK in
response. MAX_DRO_RETRANSMISSIONS has a value 2.
13. Interoperability With Core RPL
This section describes how RPL routers that implement P2P-RPL
interact with RPL routers that do not. In general, P2P-RPL operation
does not affect core RPL operation and vice versa. However, core RPL
does allow a router to join a DAG as a leaf node even if it does not
understand the Mode of Operation (MOP) used in the DAG. Thus, an RPL
router that does not implement P2P-RPL may conceivably join a
temporary DAG being created for a P2P-RPL route discovery as a leaf
node and maintain its membership even though the DAG no longer
exists. This may impose a drain on the router's memory. However,
such RPL-only leaf nodes do not interfere with P2P-RPL route
discovery since a leaf node may only generate a DIO advertising an
INFINITE_RANK and all routers implementing P2P-RPL are required to
discard such DIOs.
Note that core RPL does not require a router to join a DAG whose MOP
it does not understand. Moreover, RPL routers would, in practice,
have strict restrictions on the DAGs that may join. Thus, the
problem described in the preceding paragraph may not occur in
practice.
The P2P-RPL mechanism described in this document works best when all
the RPL routers in the LLN implement P2P-RPL. In general, the
ability to discover routes as well as the quality of discovered
routes would deteriorate with the fraction of RPL routers that
implement P2P-RPL.
14. Security Considerations
The security considerations for the operation of the reactive P2P
route discovery mechanism described in this document are similar to
the ones for the operation of RPL (as described in Section 19 of
[I-D.ietf-roll-rpl]). Section 10 of RPL specification
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[I-D.ietf-roll-rpl] describes a variety of security mechanisms to
provide data confidentiality, authentication, replay protection and
delay protection services. Each RPL control message has a secure
version that allows the specification of the level of security and
the algorithms used to secure the message. The mechanism defined in
this document is based on the use of DIOs to form temporary DAGs and
discover P2P routes. These DIOs can be used in their secure versions
if desired. New RPL control messages defined in this document (DRO
and DRO-ACK) have secure versions as well. Thus, a particular
deployment of the reactive P2P route discovery mechanism described in
this document can analyze its security requirements and use the
appropriate set of RPL security mechanisms that meet those
requirements.
15. IANA Considerations
15.1. Additions to DIO Mode of Operation
IANA is requested to allocate a new value in the "DIO Mode of
Operation" registry for the "P2P Route Discovery Mode" described in
this document.
+----------+-----------------------------------------+--------------+
| MOP | Description | Reference |
| Value | | |
+----------+-----------------------------------------+--------------+
| 4 | Reactive P2P route discovery mode of | This |
| | operation | document |
+----------+-----------------------------------------+--------------+
DIO Mode of Operation
15.2. Additions to RPL Control Message Options
IANA is requested to allocate a new value in the "RPL Control Message
Options" registry for the "Route Discovery Option" described in this
document.
+-------+---------------------+---------------+
| Value | Meaning | Reference |
+-------+---------------------+---------------+
| 10 | P2P Route Discovery | This document |
+-------+---------------------+---------------+
RPL Control Message Options
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15.3. Additions to RPL Control Codes
IANA is requested to allocate new code points in the "RPL Control
Codes" registry for the "Discovery Reply Object" and "Discovery Reply
Object Acknowledgement" (and their secure versions) described in this
document.
+------+--------------------------------------------+---------------+
| Code | Description | Reference |
+------+--------------------------------------------+---------------+
| 0x04 | Discovery Reply Object | This document |
| 0x05 | Discovery Reply Object Acknowledgement | This document |
| 0x84 | Secure Discovery Reply Object | This document |
| 0x85 | Secure Discovery Reply Object | This document |
| | Acknowledgement | |
+------+--------------------------------------------+---------------+
RPL Control Codes
16. Acknowledgements
Authors gratefully acknowledge the contributions of the following
individuals (in alphabetical order) in the development of this
document: Dominique Barthel, Jakob Buron, Thomas Clausen, Richard
Kelsey, Phil Levis, Zach Shelby, Pascal Thubert, Hristo Valev and JP
Vasseur.
17. References
17.1. Normative References
[I-D.ietf-roll-routing-metrics]
Vasseur, J., Kim, M., Pister, K., Dejean, N., and D.
Barthel, "Routing Metrics used for Path Calculation in Low
Power and Lossy Networks",
draft-ietf-roll-routing-metrics-19 (work in progress),
March 2011.
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-19 (work in
progress), March 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
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Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", RFC 6206, March 2011.
17.2. Informative References
[I-D.ietf-6man-rpl-option]
Hui, J. and J. Vasseur, "RPL Option for Carrying RPL
Information in Data-Plane Datagrams",
draft-ietf-6man-rpl-option-06 (work in progress),
December 2011.
[]
Hui, J., Vasseur, J., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with RPL",
draft-ietf-6man-rpl-routing-header-07 (work in progress),
December 2011.
[I-D.ietf-roll-of0]
Thubert, P., "RPL Objective Function Zero",
draft-ietf-roll-of0-20 (work in progress), September 2011.
[I-D.ietf-roll-p2p-measurement]
Goyal, M., Baccelli, E., Brandt, A., and J. Martocci, "A
Mechanism to Measure the Quality of a Point-to-point Route
in a Low Power and Lossy Network",
draft-ietf-roll-p2p-measurement-02 (work in progress),
October 2011.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-06 (work in
progress), September 2011.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
[RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
Goyal, et al. Expires July 22, 2012 [Page 26]
Internet-Draft draft-ietf-roll-p2p-rpl-06 January 2012
Authors' Addresses
Mukul Goyal (editor)
University of Wisconsin Milwaukee
3200 N Cramer St
Milwaukee, WI 53201
USA
Phone: +1 414 2295001
Email: mukul@uwm.edu
Emmanuel Baccelli
INRIA
Phone: +33-169-335-511
Email: Emmanuel.Baccelli@inria.fr
URI: http://www.emmanuelbaccelli.org/
Matthias Philipp
INRIA
Phone: +33-169-335-511
Email: Matthias.Philipp@inria.fr
Anders Brandt
Sigma Designs
Emdrupvej 26A, 1.
Copenhagen, Dk-2100
Denmark
Phone: +45-29609501
Email: abr@sdesigns.dk
Jerald Martocci
Johnson Controls
507 E Michigan St
Milwaukee, WI 53202
USA
Phone: +1 414-524-4010
Email: jerald.p.martocci@jci.com
Goyal, et al. Expires July 22, 2012 [Page 27]