draft-ietf-roll-aodv-rpl-02.txt   draft-ietf-roll-aodv-rpl-03.txt 
ROLL S. Anamalamudi ROLL S. Anamalamudi
Internet-Draft Huaiyin Institute of Technology Internet-Draft Huaiyin Institute of Technology
Intended status: Standards Track M. Zhang Intended status: Standards Track M. Zhang
Expires: March 13, 2018 AR. Sangi Expires: September 6, 2018 Huawei Technologies
Huawei Technologies AR. Sangi
Huaiyin Institute of Technology
C. Perkins C. Perkins
Futurewei Futurewei
S.V.R.Anand S.V.R.Anand
Indian Institute of Science Indian Institute of Science
September 9, 2017 B. Liu
Huawei Technologies
March 5, 2018
Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs) Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs)
draft-ietf-roll-aodv-rpl-02 draft-ietf-roll-aodv-rpl-03
Abstract Abstract
Route discovery for symmetric and asymmetric Point-to-Point (P2P) Route discovery for symmetric and asymmetric Point-to-Point (P2P)
traffic flows is a desirable feature in Low power and Lossy Networks traffic flows is a desirable feature in Low power and Lossy Networks
(LLNs). For that purpose, this document specifies a reactive P2P (LLNs). For that purpose, this document specifies a reactive P2P
route discovery mechanism for hop-by-hop routing (storing mode) based route discovery mechanism for both hop-by-hop routing and source
on Ad Hoc On-demand Distance Vector Routing (AODV) based RPL routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL
protocol. Two separate Instances are used to construct directional protocol. Paired Instances are used to construct directional paths,
paths in case some of the links between source and target node are in case some of the links between source and target node are
asymmetric. asymmetric.
Status of This Memo Status of This Memo
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This Internet-Draft will expire on March 13, 2018. This Internet-Draft will expire on September 6, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 5 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6
4. AODV-RPL Mode of Operation (MoP) . . . . . . . . . . . . . . 5 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6
5. RREQ Message . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. AODV-RPL DIO RREQ Option . . . . . . . . . . . . . . . . 6
6. RREP Message . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. AODV-RPL DIO RREP Option . . . . . . . . . . . . . . . . 8
7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 12 4.3. AODV-RPL DIO Target Option . . . . . . . . . . . . . . . 10
8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 13 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13
9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 13 6.1. Generating Route Request at OrigNode . . . . . . . . . . 13
9.2. AODV-RPL Options: RREQ and RREP . . . . . . . . . . . . . 13 6.2. Receiving and Forwarding Route Request . . . . . . . . . 14
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 6.3. Generating Route Reply at TargNode . . . . . . . . . . . 15
11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 14 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 15 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17
Appendix A. ETX/RSSI Values to select S bit . . . . . . . . . . 15 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 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
1. Introduction 1. Introduction
RPL[RFC6550], the IPv6 distance vector routing protocol for Low-power RPL[RFC6550] is a IPv6 distance vector routing protocol for Low-power
and Lossy Networks (LLNs), is designed to support multiple traffic and Lossy Networks (LLNs), and is designed to support multiple
flows through a root-based Destination-Oriented Directed Acyclic traffic flows through a root-based Destination-Oriented Directed
Graph (DODAG). For traffic flows between routers within the DODAG Acyclic Graph (DODAG). Typically, a router does not have routing
(i.e., Point-to-Point (P2P) traffic), this means that data packets information for most other routers. Consequently, for traffic
either have to traverse the root in non-storing mode (source between routers within the DODAG (i.e., Point-to-Point (P2P) traffic)
routing), or traverse a common ancestor in storing mode (hop-by-hop data packets either have to traverse the root in non-storing mode, or
routing). Such P2P traffic is thereby likely to flow along sub- traverse a common ancestor in storing mode. Such P2P traffic is
optimal routes and may suffer severe traffic congestion near the DAG thereby likely to traverse sub-optimal routes and may suffer severe
root [RFC6997], [RFC6998]. congestion near the DAG root [RFC6997], [RFC6998].
To discover optimal paths for P2P traffic flows in RPL, P2P-RPL To discover optimal paths for P2P traffic flows in RPL, P2P-RPL
[RFC6997] specifies a temporary DODAG where the source acts as [RFC6997] specifies a temporary DODAG where the source acts as a
temporary root. The source initiates "P2P Route Discovery mode (P2P- temporary root. The source initiates DIOs encapsulating the P2P
RDO)" with an address vector for both non-storing mode (H=0) and Route Discovery option (P2P-RDO) with an address vector for both hop-
storing mode (H=1). Subsequently, each intermediate router adds its by-hop mode (H=1) and source routing mode (H=0). Subsequently, each
IP address and multicasts the P2P-RDO message, until the message intermediate router adds its IP address and multicasts the P2P mode
reaches the target node (TargNode). TargNode sends the "Discovery DIOs, until the message reaches the target node (TargNode). TargNode
Reply" option. P2P-RPL is efficient for source routing, but much sends the "Discovery Reply" object. P2P-RPL is efficient for source
less efficient for hop-by-hop routing due to the extra address vector routing, but much less efficient for hop-by-hop routing due to the
overhead. In fact, when the P2P-RDO message is being multicast from extra address vector overhead. However, for symmetric links, when
the source hop-by-hop, receiving nodes are able to determine a next the P2P mode DIO message is being multicast from the source hop-by-
hop towards the source in symmetric links. When TargNode hop, receiving nodes can infer a next hop towards the source. When
subsequently replies to the source along the established forward TargNode subsequently replies to the source along the established
route, receiving nodes can determine the next hop towards TargNode. forward route, receiving nodes determine the next hop towards
In other words, it is efficient to use only routing tables for P2P- TargNode. In other words, it is efficient to use only routing tables
RDO message instead of "Address vector" for hop-by-hop routes (H=1) for P2P-RDO message instead of "Address vector" for hop-by-hop routes
in symmetric links. (H=1) over symmetric links.
RPL and P2P-RPL both specify the use of a single DODAG in networks of RPL and P2P-RPL both specify the use of a single DODAG in networks of
symmetric links. But, application-specific routing requirements that symmetric links, where the two directions of a link MUST both satisfy
are defined in IETF ROLL Working Group [RFC5548], [RFC5673], the constraints of the objective function. This eliminates the
[RFC5826] and [RFC5867] may need routing metrics and constraints possibility to use asymmetric links which are qualified in one
enabling use of asymmetric bidirectional links. For this purpose, direction. But, application-specific routing requirements as defined
[I-D.thubert-roll-asymlink] describes bidirectional asymmetric links in IETF ROLL Working Group [RFC5548], [RFC5673], [RFC5826] and
for RPL [RFC6550] with Paired DODAGs, for which the DAG root [RFC5867] may be satisfied by routing paths using bidirectional
(DODAGID) is common for two Instances. This can satisfy application- asymmetric links. For this purpose, [I-D.thubert-roll-asymlink]
specific routing requirements for bidirectional asymmetric links in describes bidirectional asymmetric links for RPL [RFC6550] with
base RPL [RFC6550]. P2P-RPL for Paired DODAGs, on the other hand, Paired DODAGs, for which the DAG root (DODAGID) is common for two
requires two DAG roots: one for the source and another for the target Instances. This can satisfy application-specific routing
node due to temporary DODAG formation. For networks composed of requirements for bidirectional asymmetric links in core RPL
bidirectional asymmetric links (see Section 4), AODV-RPL specifies [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 P2P route discovery, utilizing RPL with a new MoP. AODV-RPL makes
use of two multicast messages to discover possibly asymmetric routes. use of two multicast messages to discover possibly asymmetric routes,
AODV-RPL eliminates the need for address vector control overhead, which can achieve higher route diversity. AODV-RPL eliminates the
significantly reducing the control packet size which is important for need for address vector control overhead in hop-by-hop mode. This
Constrained LLN networks. Both discovered routes meet the significantly reduces the control packet size, which is important for
application specific metrics and constraints that are defined in the Constrained LLN networks. Both discovered routes (upward and
Objective Function for each Instance [RFC6552]. 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 The route discovery process in AODV-RPL is modeled on the analogous
process that has been specified in AODV [RFC6550]. The on-demand procedure specified in AODV [RFC3561]. The on-demand nature of AODV
nature of AODV route discovery is natural for the needs of peer-to- route discovery is natural for the needs of peer-to-peer routing in
peer routing as envisioned for RPL-based LLNs. Similar terminology RPL-based LLNs. AODV terminology has been adapted for use with AODV-
has been adopted for use with the discovery messages, namely RREQ for RPL messages, namely RREQ for Route Request, and RREP for Route
Route Request, and RREP for Route Reply. AODV-RPL is, at heart, a Reply. AODV-RPL currently omits some features compared to AODV -- in
simpler protocol than AODV, since there are no analogous operations particular, flagging Route Errors, blacklisting unidirectional links,
for flagging Route Errors, blacklisting unidirectional links, multihoming, and handling unnumbered interfaces.
multihoming, or handling unnumbered interfaces. Some of the simpler
features of AODV, on the other hand, have been imported into AODV-RPL
-- for instance, prefix advertisement is allowed on RREP and RREQ
message where appropriate.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. Additionally, this document uses the following terms: [RFC2119]. Additionally, this document uses the following terms:
AODV AODV
Ad Hoc On-demand Distance Vector Routing[RFC3561]. Ad Hoc On-demand Distance Vector Routing[RFC3561].
AODV-Instance AODV-RPL Instance
Either the RREQ-Instance or RREP-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 Bi-directional Asymmetric Link
A link that can be used in both directions but with different link A link that can be used in both directions but with different link
characteristics (see [I-D.thubert-roll-asymlink]). characteristics.
DODAG RREQ-Instance (or simply RREQ-Instance) DODAG RREQ-Instance (or simply RREQ-Instance)
AODV Instance built using the RREQ option; used for control RPL Instance built using the DIO with RREQ option; used for
transmission from OrigNode to TargNode, thus enabling data control message transmission from OrigNode to TargNode, thus
transmission from TargNode to OrigNode. enabling data transmission from TargNode to OrigNode.
DODAG RREP-Instance (or simply RREP-Instance) DODAG RREP-Instance (or simply RREP-Instance)
AODV Instance built using the RREP option; used for control RPL Instance built using the DIO with RREP option; used for
transmission from TargNode to OrigNode thus enabling data control message transmission from TargNode to OrigNode thus
transmission from OrigNode to TargNode. enabling data transmission from OrigNode to TargNode.
downstream Downward Direction
Routing along the direction from OrigNode to TargNode. The direction from the OrigNode to the TargNode.
Downward Route
A route in the downward direction.
hop-by-hop routing hop-by-hop routing
Routing when each node stores routing information about the next Routing when each node stores routing information about the next
hop. hop.
OrigNode OrigNode
The IPv6 router (Originating Node) initiating the AODV-RPL route The IPv6 router (Originating Node) initiating the AODV-RPL route
discovery to obtain a route to TargNode. discovery to obtain a route to TargNode.
Paired DODAGs Paired DODAGs
Two DODAGs for a single application. Two DODAGs for a single route discovery process of an application.
P2P P2P
Point-to-Point -- in other words, not constrained to traverse a Point-to-Point -- in other words, not constrained to traverse a
common ancestor. common ancestor.
RREQ message RREQ-DIO message
An AODV-RPL MoP DIO message containing the RREQ option. The An AODV-RPL MoP DIO message containing the RREQ option. The
InstanceID in the DIO object of the RREQ option MUST be always an RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode.
odd number.
RREP message RREP-DIO message
An AODV-RPL MoP DIO message containing the RREP option. The An AODV-RPL MoP DIO message containing the RREP option. The
InstanceID in the DIO object of the RREP option MUST be always an RPLInstanceID in RREP-DIO is typically paired to the one in the
even number (usually, InstanceID of RREQ-Instance+1). associated RREQ-DIO message.
source routing Source routing
The mechanism by which the source supplies the complete route The mechanism by which the source supplies the complete route
towards the target node along with each data packet. [RFC6997]. 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 TargNode
The IPv6 router (Target Node) for which OrigNode requires a route The IPv6 router (Target Node) for which OrigNode requires a route
and initiates Route Discovery within the LLN network. and initiates Route Discovery within the LLN network.
upstream Upward Direction
Routing along the direction from TargNode to OrigNode. The direction from the TargNode to the OrigNode.
Upward Route
A route in the upward direction.
3. Overview of AODV-RPL 3. Overview of AODV-RPL
With AODV-RPL, routes from OrigNode to TargNode within the LLN With AODV-RPL, routes from OrigNode to TargNode within the LLN
network established are "on-demand". In other words, the route network established are "on-demand". In other words, the route
discovery mechanism in AODV-RPL is invoked reactively when OrigNode discovery mechanism in AODV-RPL is invoked reactively when OrigNode
has data for delivery to the TargNode but existing routes do not has data for delivery to the TargNode but existing routes do not
satisfy the application's requirements. The routes discovered by satisfy the application's requirements. The routes discovered by
AODV-RPL are point-to-point; in other words the routes are not AODV-RPL are point-to-point; in other words the routes are not
constrained to traverse a common ancestor. Unlike base RPL [RFC6550] constrained to traverse a common ancestor. Unlike core RPL [RFC6550]
and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric communication and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric communication
paths in networks with bidirectional asymmetric links. For this paths in networks with bidirectional asymmetric links. For this
purpose, AODV-RPL enables discovery of two routes: namely, one from purpose, AODV-RPL enables discovery of two routes: namely, one from
OrigNode to TargNode, and another from TargNode to OrigNode. When OrigNode to TargNode, and another from TargNode to OrigNode. When
possible, AODV-RPL also enables symmetric routing along Paired DODAGs possible, AODV-RPL also enables symmetric route discovery along
(see Section 4). Paired DODAGs (see Section 5).
4. AODV-RPL Mode of Operation (MoP)
In AODV-RPL, route discovery is initiated by forming a temporary DAG In AODV-RPL, route discovery is initiated by forming a temporary DAG
rooted at the OrigNode. Paired DODAGs (Instances) are constructed rooted at the OrigNode. Paired DODAGs (Instances) are constructed
according to a new AODV-RPL Mode of Operation (MoP) during route according to a new AODV-RPL Mode of Operation (MoP) during route
formation between the OrigNode and TargNode. The RREQ-Instance is formation between the OrigNode and TargNode. The RREQ-Instance is
formed by route control messages from OrigNode to TargNode whereas formed by route control messages from OrigNode to TargNode whereas
the RREP-Instance is formed by route control messages from TargNode the RREP-Instance is formed by route control messages from TargNode
to OrigNode (as shown in Figure 2). Intermediate routers join the to OrigNode (as shown in Figure 4). Intermediate routers join the
Paired DODAGs based on the rank as calculated from the DIO message. Paired DODAGs based on the rank as calculated from the DIO message.
Henceforth in this document, the RREQ-Instance message means the Henceforth in this document, the RREQ-DIO message means the AODV-RPL
AODV-RPL DIO message from OrigNode to TargNode, containing the RREQ mode DIO message from OrigNode to TargNode, containing the RREQ
option. Similarly, the RREP-Instance message means the AODV-RPL DIO option. Similarly, the RREP-DIO message means the AODV-RPL mode DIO
message from TargNode to OrigNode, containing the RREP option. message from TargNode to OrigNode, containing the RREP option.
Subsequently, the RREQ-Instance is used for data transmission from Subsequently, the route discovered in the RREQ-Instance is used for
TargNode to OrigNode and RREP-Instance is used for Data transmission data transmission from TargNode to OrigNode, and the route discovered
from OrigNode to TargNode. in RREP-Instance is used for Data transmission from OrigNode to
TargNode.
The AODV-RPL Mode of Operation defines a new bit, the Symmetric bit 4. AODV-RPL DIO Options
('S'), which is added to the base DIO message as illustrated in
Figure 1. OrigNode sets the the 'S' bit to 1 in the RREQ-Instance
message when initiating route discovery.
0 1 2 3 4.1. AODV-RPL DIO RREQ Option
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ A RREQ-DIO message MUST carry exactly one RREQ option.
| RPLInstanceID |Version Number | Rank |
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
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:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|0| MOP | Prf | DTSN |S| Flags | Reserved | | Type | Option Length |H|X| Compr | L | MaxRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|G| SHIFT | Reserved | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
+ +
| |
+ DODAGID +
| |
+ +
| | | |
| Address Vector (Optional, Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
Figure 1: DIO modification to support asymmetric route discovery Figure 2: DIO RREP option format for AODV-RPL MoP
A device originating a AODV-RPL message supplies the following Type
information in the DIO header of the message: The type of the RREP option (see Section 9.2)
'S' bit 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.
Symmetric bit in the DIO base object 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.
MOP X
MOP operation in the DIO object MUST be set to "5(TBD1)" for AODV- Reserved.
RPL DIO messages
RPLInstanceID Compr
4-bit unsigned integer. Same definition as in RREQ option.
RPLInstanceID in the DIO object MUST be the InstanceID of AODV- L
Instance(RREQ-Instance). The InstanceID for RREQ-Instance MUST be 2-bit unsigned integer with the same definition as in Section 4.1.
always an odd number.
DODAGID MaxRank
Same definition as in RREQ option.
For RREQ-Instance : 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.
DODAGID in the DIO object MUST be the IPv6 address of the device G
that initiates the RREQ-Instance. Gratuitous route (see Section 7).
For RREP-Instance 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.
DODAGID in the DIO object MUST be the IPv6 address of the device Reserved
that initiates the RREP-Instance. Reserved for future usage; MUST be initialized to zero and MUST be
ignored upon reception.
Rank 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.
Rank in the DIO object MUST be the the rank of the AODV-Instance 4.3. AODV-RPL DIO Target Option
(RREQ-Instance).
Metric Container Options 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.
AODV-Instance(RREQ-Instance) messages MAY carry one or more Metric A RREQ-DIO message MUST carry at least one AODV-RPL Target Options.
Container options to indicate the relevant routing metrics. 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.
The 'S' bit is set to mean that the route is symmetric. If the RREQ- If an OrigNode want to discover routes to multiple TargNodes, and
Instance arrives over an interface that is known to be symmetric, and these routes share the same constraints, then the OrigNode can
the 'S' bit is set to 1, then it remains set at 1, as illustrated in include all the addresses of the TargNodes into multiple AODV-RPL
Figure 2. In Figure 2 and Figure 3, BR is the BorderRouter, S is the Target Options in the RREQ-DIO, so that the cost can be reduced to
OrigNode, R is an intermediate node, and D is the TargNode. building only one DODAG. Different addresses of the TargNodes can
merge if they share the same prefix.
BR 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 |
R R R +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ \ | / \ | |
/ \ | / \ + |
/ \ | / \ | Target Prefix (Variable Length) |
R -------- R --- R ----- R -------- R . .
/ \ <--s=1--> / \ <--s=1--> / \ . .
<--s=1--> \ / \ / <--s=1--> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ \ / \ / \
S ---------- R ------ R------ R ----- R ----------- D
/ \ / \ / \ / \
/ \ / \ / \ / \
/ \ / \ / \ / \
R ----- R ----------- R ----- R ----- R ----- R ---- R----- R
>---- RREQ-Instance (Control: S-->D; Data: D-->S) -------> Figure 3: Target option format for AODV-RPL MoP
<---- RREP-Instance (Control: D-->S; Data: S-->D) -------<
Figure 2: AODV-RPL with Symmetric Paired Instances Type
The type of the AODV-RPL Target Option (see Section 9.2)
If the RREQ-Instance arrives over an interface that is not known to Destination Sequence Number
be symmetric, or is known to be asymmetric, the 'S' bit is set to be
0. Moreover, if the 'S' bit arrives already set to be '0', it is set In RREQ-DIO, if nonzero, it is the last known Sequence Number for
to be '0' on retransmission (Figure 3). Based on the 'S' bit TargNode for which a route is desired. In RREP-DIO, it is the
received in RREQ-Instance, the TargNode decides whether or not the destination sequence number associated to the route.
route is symmetric before transmitting the RREP-Instance message
upstream towards the OrigNode. The metric used to determine symmetry 5. Symmetric and Asymmetric Routes
(i.e., set the "S" bit to be "1" (Symmetric) or "0" (asymmetric)) is
implementation specific. We used ETX/RSSI to verify the feasibility In Figure 4 and Figure 5, BR is the BorderRouter, O is the OrigNode,
of the protocol operations in this draft, as discussed in Appendix A. 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.
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.
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 BR
/ | \ / | \
/ | \ / | \
/ | \ / | \
R R R R R R
/ \ | / \ / \ | / \
/ \ | / \ / \ | / \
/ \ | / \ / \ | / \
R --------- R --- R ---- R --------- R R --------- R --- R ---- R --------- R
/ \ --s=1--> / \ --s=0--> / \ / \ --S=1--> / \ --S=0--> / \
--s=1--> \ / \ / --s=0--> --S=1--> \ / \ / --S=0-->
/ \ / \ / \ / \ / \ / \
S ---------- R ------ R------ R ----- R ----------- D O ---------- R ------ R------ R ----- R ----------- T
/ \ / \ / \ / \ / \ / \ / \ / \
/ <--s=0-- / \ / \ / <--s=0-- / <--S=0-- / \ / \ / <--S=0--
/ \ / \ / \ / \ / \ / \ / \ / \
R ----- R ----------- R ----- R ----- R ----- R ---- R----- R R ----- R ----------- R ----- R ----- R ----- R ---- R----- R
<--s=0-- <--s=0-- <--s=0-- <--s=0-- <--s=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0--
>---- RREQ-Instance (Control: S-->D; Data: D-->S) -------> >---- RREQ-Instance (Control: S-->D; Data: D-->S) ------->
<---- RREP-Instance (Control: D-->S; Data: S-->D) -------< <---- RREP-Instance (Control: D-->S; Data: S-->D) -------<
Figure 3: AODV-RPL with Asymmetric Paired Instances Figure 5: AODV-RPL with Asymmetric Paired Instances
5. RREQ Message 6. AODV-RPL Operation
0 1 2 3 6.1. Generating Route Request at OrigNode
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 | Orig SeqNo | Dest SeqNo |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| TargNode IPv6 Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: DIO RREQ option format for AODV-RPL MoP 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.
OrigNode supplies the following information in the RREQ option of the The maintenance of Originator and Destination Sequence Number in the
RREQ-Instance message: RREQ option is as defined in AODV [RFC3561].
Type The address in the AODV-RPL Target Option can be a unicast IPv6
address, a prefix or a multicast address. The OrigNode can initiate
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 type of the RREQ option(see Section 9.2). 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.
Orig SeqNo The transmission of RREQ-DIO follows the Trickle timer. When the L
Sequence Number of OrigNode. duration has transpired, the OrigNode MUST leave the DODAG and stop
sending any RREQ-DIOs in the related RPLInstance.
Dest SeqNo 6.2. Receiving and Forwarding Route Request
If nonzero, the last known Sequence Number for TargNode for which Upon receiving a RREQ-DIO, a router out of the RREQ-instance goes
a route is desired. through the following steps:
TargNode IPv6 Address Step 1:
IPv6 address of the TargNode that receives RREQ-Instance message. 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 order to establish the upstream route from TargNode to OrigNode, In case that the constraint or the MaxRank limit is not fulfilled,
OrigNode multicasts the RREQ-Instance message (see Figure 4) to its the router MUST NOT join in the DODAG. Otherwise, go to the
one-hop neighbours. In order to enable intermediate nodes R_i to following steps 2, 3, 4 and 5.
associate a future RREP message to an incoming RREQ message, the
InstanceID of RREQ-Instance MUST assign an odd number.
Each intermediate node R_i computes the rank for RREQ-Instance and A router MUST discard a received RREQ-DIO if the advertised rank
creates a routing table entry for the upstream route towards the equals or exceeds the MaxRank limit.
source if the routing metrics/constraints are satisfied. For this
purpose R_i must use the asymmetric link metric measured in the
upstream direction, from R_i to its upstream neighbor that
multicasted the RREQ-Instance message.
When an intermediate node R_i receives a RREQ message in storing Step 2:
mode, it MUST store the OrigNode's InstanceID (RREQ-Instance) along
with the other routing information needed to establish the route back
to the OrigNode. This will enable R_i to determine that a future
RREP message (containing a paired InstanceID for the TargNode) must
be transmitted back to the OrigNode's IP address.
If the paths to and from TargNode are not known, the intermediate Then the router checks if one of its addresses is included in one
node multicasts the RREQ-Instance message with updated rank to its of the AODV-RPL Target Options or belongs to the indicated
next-hop neighbors until the message reaches TargNode (Figure 2). multicast group. If so, this router is one of the TargNodes.
Based on the 'S' bit in the received RREQ message, the TargNode will Otherwise, it is an intermediate router.
decide whether to unicast or multicast the RREP message back to
OrigNode.
As described in Section 7, in certain circumstances R_i MAY unicast a Step 3:
Gratuitous RREP towards OrigNode, thereby helping to minimize
multicast overhead during the Route Discovery process.
6. RREP Message 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.
The TargNode supplies the following information in the RREP message: Step 4:
0 1 2 3 If there are multiple AODV-RPL Target Options in the received
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 RREQ-DIO, a TargNode SHOULD continue sending RREQ-DIO to reach
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ other targets. When preparing its own RREQ-DIO, the TargNode MUST
| Type | Dest SeqNo | Prefix Sz |T|G| Rsvd | 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
| TargNode IPv6 Address (when present) | 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.
Figure 5: DIO RREP option format for AODV-RPL MoP Step 5:
Type 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.
The type of the RREP option (see Section 9.2) 6.3. Generating Route Reply at TargNode
Dest SeqNo 6.3.1. RREP-DIO for Symmetric route
The Sequence Number for the TargNode for which a route is When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 1, it
established. 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.
Prefix Sz 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].
The size of the prefix which the route to the TargNode is 6.3.2. RREP-DIO for Asymmetric Route
available. This allows routing to other nodes on the same subnet
as the TargNode.
'T' bit 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.
'T' is set to true to indicate that the TargNode IPv6 Address The settings of the RREP-DIO are the same as in symmetric route.
field is present
'G' bit 6.3.3. RPLInstanceID Pairing
(see Section 7) 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.
TargNode IPv6 Address (when present) Typically, the two InstanceIDs are set as the local InstanceID in
core RPL:
IPv6 address of the TargNode that receives RREP-Instance message. 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|D| ID | Local RPLInstanceID in 0..63
+-+-+-+-+-+-+-+-+
In order to reduce the need for the TargNode IPv6 Address to be Figure 6: Local Instance ID
included with the RREP message, the InstanceID of the RREP-Instance
is paired, whenever possible, with the InstanceID from the RREQ
message, which is always an odd number. The pairing is accomplished
by adding one to the InstanceID from the RREQ message and using that,
whenever possible, as the InstanceID for the RREP message. If this
is not possible (for instance because the incremented InstanceID is
still a valid InstanceID for another route to the TargNode from an
earlier Route Discovery operation), then the 'T' bit is set and an
alternative even number is chosen for the InstanceID of RREP from
TargNode.
The OrigNode IP address for RREQ-Instance is available as the DODAGID The first bit is set to 1 indicating the RPLInstanceID is local. The
in the DIO base message (see Figure 1). When TargNode receives a 'D' bit here is used to distinguish the two AODV-RPL instances: D=0
RREQ message with the 'S' bit set to 1 (as illustrated in Figure 2), for RREQ-Instance, D=1 for RREP-Instance. The ID of 6 bits SHOULD be
it unicasts the RREP message with the 'S' bit set to 1. In this the same for RREQ-Instance and RREP-Instance. Here, the 'D' bit is
case, route control messages and application data between OrigNode used slightly differently than in RPL.
and TargNode for both RREQ-Instance and RREP-Instance are transmitted
along symmetric links. When the 'T' bit is set to "1" in the RREP-
Instance, then the TargNode IPv6 Address is transmitted in the RREP
option. Otherwise, the TargNode IPv6 Address is elided in the RREP
option.
When (as illustrated in Figure 3) the TargNode receives RREQ message When preparing the RREP-DIO, a TargNode could find the RPLInstanceID
with the 'S' bit set to 0, it also multicasts the RREP message with to be used for the RREP-Instance is already occupied by another
the 'S' bit set to 0. Intermediate nodes create a routing table instance from an earlier route discovery operation which is still
entry for the path towards the TargNode while processing the RREP active. In other words, two OrigNodes need routes to the same
message to OrigNode. Once OrigNode receives the RREP message, it TargNode and they happen to use the same RPLInstanceID for RREQ-
starts transmitting the application data to TargNode along the path Instance. In this case, the occupied RPLInstanceID MUST NOT be used
as discovered through RREP messages. On the other hand, application again. Then this RPLInstanceID SHOULD be shifted into another
data from TargNode to OrigNode is transmitted through the path that integer and shifted back to the original one at the OrigNode. In
is discovered from RREQ message. 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:
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 7. Gratuitous RREP
Under some circumstances, an Intermediate Node that receives a RREQ In some cases, an Intermediate router that receives a RREQ-DIO
message MAY transmit a "Gratuitous" RREP message back to OrigNode message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode
instead of continuing to multicast the RREQ message towards TargNode. instead of continuing to multicast the RREQ-DIO towards TargNode.
For these circumstances, the 'G' bit of the RREP option is provided The intermediate router effectively builds the RREP-Instance on
to distinguish the Gratuitous RREP sent by the Intermediate node from behalf of the actual TargNode. The 'G' bit of the RREP option is
the RREP sent by TargNode. provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the
Intermediate node from the RREP-DIO sent by TargNode (G=0).
When an Intermediate node R receives a RREQ message and has recent The gratuitous RREP-DIO can be sent out when an intermediate router R
information about the cost of an upstream route from TargNode to R, receives a RREQ-DIO for a TargNode T, and R happens to have both
then R MAY unicast the Gratuitous RREP (GRREP) message to OrigNode. forward and reverse routes to T which also fulfill the requirements.
R determines whether its information is sufficiently recent by
comparing the value it has stored for the Sequence Number of TargNode In case of source routing, the intermediate router R MUST unicast the
against the DestSeqno in the incoming RREQ message. R also must have received RREQ-DIO to TargNode T including the address vector between
information about the metric information of the upstream route from the OrigNode O and the router R. Thus T can have a complete address
TargNode. The GRREP message MUST have PrefixSz == 0 and the 'G' bit vector between O and itself. Then T MUST unicast a RREP-DIO
set to 1. R SHOULD also unicast the RREQ message to TargNode, to including the address vector between T and R.
make sure that TargNode will have a route to OrigNode.
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 8. Operation of Trickle Timer
The trickle timer operation to control RREQ-Instance/RREP-Instance The trickle timer operation to control RREQ-Instance/RREP-Instance
multicast is similar to that in P2P-RPL [RFC6997]. multicast is similar to that in P2P-RPL [RFC6997].
9. IANA Considerations 9. IANA Considerations
9.1. New Mode of Operation: AODV-RPL 9.1. New Mode of Operation: AODV-RPL
IANA is required to assign a new Mode of Operation, named "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. 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 The value of TBD1 is assigned from the "Mode of Operation" space
[RFC6550]. [RFC6550].
+-------------+---------------+---------------+ +-------------+---------------+---------------+
| Value | Description | Reference | | Value | Description | Reference |
+-------------+---------------+---------------+ +-------------+---------------+---------------+
| TBD1 (5) | AODV-RPL | This document | | TBD1 (5) | AODV-RPL | This document |
+-------------+---------------+---------------+ +-------------+---------------+---------------+
Figure 6: Mode of Operation Figure 7: Mode of Operation
9.2. AODV-RPL Options: RREQ and RREP 9.2. AODV-RPL Options: RREQ, RREP, and Target
Two entries are required for new AODV-RPL options "RREQ-Instance" and Three entries are required for new AODV-RPL options "RREQ", "RREP"
"RREQ-Instance", with values of TBD2 (0x0A) and TBD3 (0x0B) from the and "AODV-RPL Target" with values of TBD2 (0x0A), TBD3 (0x0B) and
"RPL Control Message Options" space [RFC6550]. TBD4 (0x0C) from the "RPL Control Message Options" space [RFC6550].
+-------------+---------------------+---------------+ +-------------+------------------------+---------------+
| Value | Meaning | Reference | | Value | Meaning | Reference |
+-------------+---------------------+---------------+ +-------------+------------------------+---------------+
| TBD2 (0x0A) | RREQ Option | This document | | TBD2 (0x0A) | RREQ Option | This document |
+-------------+---------------------+---------------+ +-------------+------------------------+---------------+
| TBD3 (0x0B) | RREP Option | This document | | TBD3 (0x0B) | RREP Option | This document |
+-------------+---------------------+---------------+ +-------------+------------------------+---------------+
| TBD3 (0x0C) | AODV-RPL Target Option | This document |
+-------------+------------------------+---------------+
Figure 7: AODV-RPL Options Figure 8: AODV-RPL Options
10. Security Considerations 10. Security Considerations
This document does not introduce additional security issues compared This document does not introduce additional security issues compared
to base RPL. For general RPL security considerations, see [RFC6550]. to base RPL. For general RPL security considerations, see [RFC6550].
11. Future Work 11. Future Work
It may become feasible in the future to design a non-storing version
of AODV-RPL's route discovery protocol. Under the current assumption
of route asymmetry across bidirectional links, the specification is
expected to be straightforward. It should be possible to re-use the
same methods of incremental construction for source routes within
analogous fields within AODV-RPL's RREQ and RREP messages as is
currently done for DAO messages -- in other words the RPL messages
for DODAG construction.
There has been some discussion about how to determine the initial There has been some discussion about how to determine the initial
state of a link after an AODV-RPL-based network has begun operation. state of a link after an AODV-RPL-based network has begun operation.
The current draft operates as if the links are symmetric until The current draft operates as if the links are symmetric until
additional metric information is collected. The means for making additional metric information is collected. The means for making
link metric information is considered out of scope for AODV-RPL. In link metric information is considered out of scope for AODV-RPL. In
the future, RREQ and RREP messages could be equipped with new fields the future, RREQ and RREP messages could be equipped with new fields
for use in verifying link metrics. In particular, it is possible to for use in verifying link metrics. In particular, it is possible to
identify unidirectional links; an RREQ received across a identify unidirectional links; an RREQ received across a
unidirectional link has to be dropped, since the destination node unidirectional link has to be dropped, since the destination node
cannot make use of the received DODAG to route packets back to the cannot make use of the received DODAG to route packets back to the
skipping to change at page 16, line 5 skipping to change at page 22, line 5
draft-thubert-roll-asymlink-02 (work in progress), draft-thubert-roll-asymlink-02 (work in progress),
December 2011. December 2011.
Appendix A. ETX/RSSI Values to select S bit Appendix A. ETX/RSSI Values to select S bit
We have tested the combination of "RSSI(downstream)" and "ETX We have tested the combination of "RSSI(downstream)" and "ETX
(upstream)" to decide whether the link is symmetric or asymmetric at (upstream)" to decide whether the link is symmetric or asymmetric at
the intermediate nodes. The example of how the ETX and RSSI values the intermediate nodes. The example of how the ETX and RSSI values
are used in conjuction is explained below: are used in conjuction is explained below:
Source---------->NodeA---------->NodeB------->Destination Source---------->NodeA---------->NodeB------->Destination
Figure 8: Communication link from Source to Destination Figure 9: Communication link from Source to Destination
+-------------------------+----------------------------------------+ +-------------------------+----------------------------------------+
| RSSI at NodeA for NodeB | Expected ETX at NodeA for nodeB->nodeA | | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA |
+-------------------------+----------------------------------------+ +-------------------------+----------------------------------------+
| > -15 | 150 | | > -15 | 150 |
| -25 to -15 | 192 | | -25 to -15 | 192 |
| -35 to -25 | 226 | | -35 to -25 | 226 |
| -45 to -35 | 662 | | -45 to -35 | 662 |
| -55 to -45 | 993 | | -55 to -45 | 993 |
+-------------------------+----------------------------------------+ +-------------------------+----------------------------------------+
Table 1: Selection of 'S' bit based on Expected ETX value Table 1: Selection of 'S' bit based on Expected ETX value
skipping to change at page 16, line 39 skipping to change at page 22, line 39
way of knowing the value of ETX from NodeB->NodeA. Using physical way of knowing the value of ETX from NodeB->NodeA. Using physical
testbed experiments and realistic wireless channel propagation testbed experiments and realistic wireless channel propagation
models, one can determine a relationship between RSSI and ETX models, one can determine a relationship between RSSI and ETX
representable as an expression or a mapping table. Such a representable as an expression or a mapping table. Such a
relationship in turn can be used to estimate ETX value at nodeA for relationship in turn can be used to estimate ETX value at nodeA for
link NodeB--->NodeA from the received RSSI from NodeB. Whenever link NodeB--->NodeA from the received RSSI from NodeB. Whenever
nodeA determines that the link towards the nodeB is bi-directional 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 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". 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.
o New InstanceID pairing mechanism.
Authors' Addresses Authors' Addresses
Satish Anamalamudi Satish Anamalamudi
Huaiyin Institute of Technology Huaiyin Institute of Technology
No.89 North Beijing Road, Qinghe District No.89 North Beijing Road, Qinghe District
Huaian 223001 Huaian 223001
China China
Email: satishnaidu80@gmail.com Email: satishnaidu80@gmail.com
Mingui Zhang Mingui Zhang
Huawei Technologies Huawei Technologies
No. 156 Beiqing Rd. Haidian District No. 156 Beiqing Rd. Haidian District
Beijing 100095 Beijing 100095
China China
Email: zhangmingui@huawei.com Email: zhangmingui@huawei.com
Abdur Rashid Sangi Abdur Rashid Sangi
Huawei Technologies Huaiyin Institute of Technology
No.156 Beiqing Rd. Haidian District No.89 North Beijing Road, Qinghe District
Beijing 100095 Huaian 223001
P.R. China P.R. China
Email: sangi_bahrian@yahoo.com Email: sangi_bahrian@yahoo.com
Charles E. Perkins Charles E. Perkins
Futurewei Futurewei
2330 Central Expressway 2330 Central Expressway
Santa Clara 95050 Santa Clara 95050
Unites States Unites States
Email: charliep@computer.org Email: charliep@computer.org
S.V.R Anand S.V.R Anand
Indian Institute of Science Indian Institute of Science
Bangalore 560012 Bangalore 560012
India India
Email: anand@ece.iisc.ernet.in Email: anand@ece.iisc.ernet.in
Bing Liu
Huawei Technologies
No. 156 Beiqing Rd. Haidian District
Beijing 100095
China
Email: remy.liubing@huawei.com
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