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
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at https://datatracker.ietf.org/drafts/current/.		Drafts is at https://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	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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	described in the Simplified BSD License.		described in the Simplified BSD License.
	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
End of changes. 118 change blocks.
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