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
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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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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