wdiff draft-ietf-roll-aodv-rpl-03.txt draft-ietf-roll-aodv-rpl-04.txt

ROLL S. Anamalamudi
Internet-Draft Huaiyin Institute of Technology SRM University-AP
Intended status: Standards Track M. Zhang
Expires: September 6, 2018 January 3, 2019 Huawei Technologies
AR. Sangi
Huaiyin Institute of Technology
C. Perkins
Futurewei
S.V.R.Anand
Indian Institute of Science
B. Liu
Huawei Technologies
March 5,
July 2, 2018

Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs)
draft-ietf-roll-aodv-rpl-03
draft-ietf-roll-aodv-rpl-04

Abstract

Route discovery for symmetric and asymmetric Point-to-Point (P2P)
traffic flows is a desirable feature in Low power and Lossy Networks
(LLNs). For that purpose, this document specifies a reactive P2P
route discovery mechanism for both hop-by-hop routing and source
routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL
protocol. Paired Instances are used to construct directional paths,
in case some of the links between source and target node are
asymmetric.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 6, 2018. January 3, 2019.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6
4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 7
4.1. AODV-RPL DIO RREQ Option . . . . . . . . . . . . . . . . 6 7
4.2. AODV-RPL DIO RREP Option . . . . . . . . . . . . . . . . 8 9
4.3. AODV-RPL DIO Target Option . . . . . . . . . . . . . . . 10
5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11
6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13
6.1. Generating Route Request at OrigNode Generation . . . . . . . . . . . . . . . . 13
6.2. Receiving and Forwarding Route Request RREQ messages . . . . . . . . . 14
6.2.1. General Processing . . . . . . . . . . . . . . . . . 14
6.2.2. Additional Processing for Multiple Targets . . . . . 15
6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . . . . 15 16
6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 15 16
6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16
6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 16
6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17
7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 18
8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 19
9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 20
11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 20
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
12.1. Normative References . . . . . . . . . . . . . . . . . . 20
12.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. Example: ETX/RSSI Values to select S bit . . . . . . 21
Appendix B. Changelog . . . . 21
Appendix B. . . . . . . . . . . . . . . . . . 22
B.1. Changes to version 02 . . . . . . . . . . . . . . . . . . 22
B.2. Changes to version 03 . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23

1. Introduction

RPL[RFC6550] is a IPv6 distance vector routing protocol for Low-power
and Lossy Networks (LLNs), and is designed to support multiple
traffic flows through a root-based Destination-Oriented Directed
Acyclic Graph (DODAG). Typically, a router does not have routing
information for most other routers. Consequently, for traffic
between routers within the DODAG (i.e., Point-to-Point (P2P) traffic)
data packets either have to traverse the root in non-storing mode, or
traverse a common ancestor in storing mode. Such P2P traffic is
thereby likely to traverse sub-optimal longer routes and may suffer severe
congestion near the DAG root [RFC6997], [RFC6998].

To discover optimal better paths for P2P traffic flows in RPL, P2P-RPL
[RFC6997] specifies a temporary DODAG where the source acts as a
temporary root. The source initiates DIOs encapsulating the P2P
Route Discovery option (P2P-RDO) with an address vector for both hop-
by-hop mode (H=1) and source routing mode (H=0). Subsequently, each
intermediate router adds its IP address and multicasts the P2P mode
DIOs, until the message reaches the target node (TargNode). TargNode (TargNode), which
then sends the "Discovery Reply" object. P2P-RPL is efficient for
source routing, but much less efficient for hop-by-hop routing due to
the extra address vector overhead. However, for symmetric links,
when the P2P mode DIO message is being multicast from the source hop-by-
hop, hop-
by-hop, receiving nodes can infer a next hop towards the source.
When TargNode subsequently replies to the source along the
established forward route, receiving nodes determine the next hop
towards TargNode. In other words, it is For hop-by-hop routes (H=1) over symmetric links,
this would allow efficient to use only of routing tables for P2P-RDO message messages
instead of the "Address vector" for hop-by-hop routes
(H=1) over symmetric links. Vector".

RPL and P2P-RPL both specify the use of a single DODAG in networks of
symmetric links, where the two directions of a link MUST both satisfy
the constraints of the objective function. This eliminates disallows the
possibility to use of
asymmetric links which are qualified in one direction. But,
application-specific routing requirements as defined in IETF ROLL
Working Group [RFC5548], [RFC5673], [RFC5826] and [RFC5867] may be
satisfied by routing paths using bidirectional asymmetric links. For
this purpose, [I-D.thubert-roll-asymlink]
describes described bidirectional
asymmetric links for RPL [RFC6550] with Paired DODAGs, for which the
DAG root (DODAGID) is common for two Instances. This can satisfy
application-specific routing requirements for bidirectional
asymmetric links in core RPL [RFC6550]. Using P2P-RPL twice with
Paired DODAGs, on the other hand, requires two roots: one for the
source and another for the target node due to temporary DODAG
formation. For networks composed of bidirectional asymmetric links
(see Section 5), AODV-RPL specifies P2P route discovery, utilizing
RPL with a new MoP. AODV-RPL makes use of two multicast messages to
discover possibly asymmetric routes, which can achieve higher route
diversity. AODV-RPL eliminates the need for address vector control overhead
in hop-by-hop mode. This significantly reduces the control packet
size, which is important for Constrained LLN networks. Both
discovered routes (upward and downward) meet the application specific
metrics and constraints that are defined in the Objective Function
for each Instance [RFC6552].

The route discovery process in AODV-RPL is modeled on the analogous
procedure specified in AODV [RFC3561]. The on-demand nature of AODV
route discovery is natural for the needs of peer-to-peer routing in
RPL-based LLNs. AODV terminology has been adapted for use with AODV-
RPL messages, namely RREQ for Route Request, and RREP for Route
Reply. AODV-RPL currently omits some features compared to AODV -- in
particular, flagging Route Errors, blacklisting unidirectional links,
multihoming, and handling unnumbered interfaces.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. Additionally, this This document uses the following terms:

AODV
Ad Hoc On-demand Distance Vector Routing[RFC3561].

AODV-RPL Instance
Either the RREQ-Instance or RREP-Instance

Asymmetric Route
The route from the OrigNode to the TargNode can traverse different
nodes than the route from the TargNode to the OrigNode. An
asymmetric route may result from the asymmetry of links, such that
only one direction of the series of links fulfills the constraints
in route discovery. If the OrigNode doesn't require an upward
route towards itself, the route is also considered as asymmetric.

Bi-directional Asymmetric Link
A link that can be used in both directions but with different link
characteristics.

DIO
DODAG Information Object

DODAG RREQ-Instance (or simply RREQ-Instance)
RPL Instance built using the DIO with RREQ option; used for
control message transmission from OrigNode to TargNode, thus
enabling data transmission from TargNode to OrigNode.

DODAG RREP-Instance (or simply RREP-Instance)
RPL Instance built using the DIO with RREP option; used for
control message transmission from TargNode to OrigNode thus
enabling data transmission from OrigNode to TargNode.

Downward Direction
The direction from the OrigNode to the TargNode.

Downward Route
A route in the downward direction.

hop-by-hop routing
Routing when each node stores routing information about the next
hop.

on-demand routing
Routing in which a route is established only when needed.

OrigNode
The IPv6 router (Originating Node) initiating the AODV-RPL route
discovery to obtain a route to TargNode.

Paired DODAGs
Two DODAGs for a single route discovery process of an application. between OrigNode
and TargNode.

P2P
Point-to-Point -- in other words, not constrained a priori to
traverse a common ancestor.

reactive routing
Same as "on-demand" routing.

RREQ-DIO message
An AODV-RPL MoP DIO message containing the RREQ option. The
RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode.

RREP-DIO message
An AODV-RPL MoP DIO message containing the RREP option. The
RPLInstanceID in RREP-DIO is typically paired to the one in the
associated RREQ-DIO message.

Source routing
The
A mechanism by which the source supplies the complete route
towards the target node along with each data packet [RFC6550].

Symmetric route
The upstream and downstream routes traverse the same routers.
Both directions fulfill the constraints in route discovery.

TargNode
The IPv6 router (Target Node) for which OrigNode requires a route
and initiates Route Discovery within the LLN network.

Upward Direction
The direction from the TargNode to the OrigNode.

Upward Route
A route in the upward direction.

3. Overview of AODV-RPL

With AODV-RPL, routes from OrigNode to TargNode within the LLN
network established are "on-demand". In other words, the route
discovery mechanism in AODV-RPL is invoked reactively when OrigNode
has data for delivery to the TargNode but existing routes do not
satisfy the application's requirements. The routes discovered by
AODV-RPL are point-to-point; in other words the routes are not constrained to traverse a common ancestor. Unlike core
RPL [RFC6550] and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric
communication paths in networks with bidirectional asymmetric links.
For this purpose, AODV-RPL enables discovery of two routes: namely,
one from OrigNode to TargNode, and another from TargNode to OrigNode.
When possible, AODV-RPL also enables symmetric route discovery along
Paired DODAGs (see Section 5).

In AODV-RPL, route discovery is initiated routes are discovered by first forming a temporary DAG
rooted at the OrigNode. Paired DODAGs (Instances) are constructed
according to a new the AODV-RPL Mode of Operation (MoP) during route
formation between the OrigNode and TargNode. The RREQ-Instance is
formed by route control messages from OrigNode to TargNode whereas
the RREP-Instance is formed by route control messages from TargNode
to OrigNode (as shown in Figure 4). OrigNode. Intermediate routers join the Paired DODAGs based on
the rank as calculated from the DIO message. Henceforth in this
document, the RREQ-DIO message means the AODV-RPL mode DIO message
from OrigNode to TargNode, containing the RREQ
option. option (see
Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL
mode DIO message from TargNode to OrigNode, containing the RREP option.
Subsequently, the
option (see Section 4.2). The route discovered in the RREQ-Instance
is used for transmitting data transmission from TargNode to OrigNode, and the
route discovered in RREP-Instance is used for Data transmission transmitting data from
OrigNode to TargNode.

4. AODV-RPL DIO Options

4.1. AODV-RPL DIO RREQ Option

OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO
message. A RREQ-DIO message MUST carry exactly one RREQ 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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: option:

Type
The type of assigned to the RREQ option(see option (see Section 9.2).

Option Length

Length
The length of the option in octets 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 transmitting this RREQ-DIO. The bit SHOULD be set to 1 in
the RREQ-DIO when the OrigNode initiates the route discovery.

Reserved.

The OrigNode sets this flag
Set to one if it desires for a hop-by-hop route. It sets this flag Set to zero if it desires for a source
route. This flag is valid to controls both the downstream route and upstream
route.

X
Reserved.

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. This field is only used in source
routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be
set to zero and ignored upon reception.

2-bit unsigned integer. This field indicates integer determining the duration that a node joining is
able to belong to 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 for the "L" bit is similar to
that found in
[RFC6997]. [RFC6997], except that the values are adjusted to
enable arbitrarily long route lifetime.

* 0x00: No duration time limit imposed.
* 0x01: 2 seconds
* 0x02: 16 seconds
* 0x03: 64 seconds

It should be indicated here that

L is not independent from 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 (calculated using the limit. DAGRank() macro defined in [RFC6550]).
A value of 0 in this field indicates the limit is infinity. For more details please
refer to [RFC6997].

OrigNode Sequence Number

Orig SeqNo
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.

A node MUST NOT join a RREQ instance if its own rank would equal to
or higher than MaxRank. Targnode can join the RREQ instance at a
rank whose integer portion is equal to the MaxRank. A router MUST
discard a received RREQ if the integer part of the advertised rank
equals or exceeds the MaxRank limit. This definition of MaxRank is
the same as that found in [RFC6997].

4.2. AODV-RPL DIO RREP Option

TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO
message. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Option Length |H|X| |G|H|X| Compr | L | MaxRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|G| SHIFT | Reserved
| Shift |Rsv| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+ |
| |
| |
| Address Vector (Optional, Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: DIO RREP option format for AODV-RPL MoP

Type
The type of assigned to the RREP option (see Section 9.2)

Option Length
Length
The length of the option in octets octets, excluding the Type and Length
fields. Variable due to the presence of the address vector and
the number of octets elided according to the Compr value.

H
This bit indicates the downstream

G
Gratuitous route is (see Section 7).

H
Requests either source routing (H=0) or hop-by-hop (H=1). (H=1) for the
downstream route. It SHOULD MUST be set to be the same as the 'H' bit in
RREQ option.

X
Reserved.

Compr
4-bit unsigned integer. Same definition as in RREQ option.

L
2-bit unsigned integer with the same definition as in Section 4.1.

MaxRank
Same definition defined as in RREQ option.

T
'T' is set to 1

MaxRank
Similarly to indicate that MaxRank in the RREP-DIO MUST include exactly
one AODV-RPL Target Option. Otherwise, RREQ message, this field indicates the Target Option is not
necessary
upper limit on the integer portion of the rank. A value of 0 in
this field indicates the RREP-DIO.

G
Gratuitous route (see Section 7).

SHIFT limit is infinity.

Shift
6-bit unsigned integer. This field indicates the how many is used to recover the
original InstanceID (see Section 6.3.3) is shifted (added an
integer from 0 to 63). 6.3.3); 0 indicates that the
original InstanceID is used.

Reserved
Reserved for future usage;

Rsv
MUST be initialized to zero and MUST be ignored upon reception.

Address Vector (Optional)
It is only
Only present when the 'H' bit is set to 0. For an asymmetric
route, it is a vector of the Address Vector represents the IPv6 addresses representing of the
route that the RREP-DIO has passed. For a symmetric route, it is
the accumulated vector Address Vector when the RREQ-DIO arrives at the
TargNode. TargNode,
unchanged during the transmission to the OrigNode.

4.3. AODV-RPL DIO Target Option

The AODV-RPL Target Option is defined based on the Target Option in
core RPL [RFC6550]: the Destination Sequence Number of the TargNode
is added.

A RREQ-DIO message MUST carry at least one AODV-RPL Target Options.
A RREP-DIO message MUST carry exactly one AODV-RPL Target Option
encapsulating the address of the OrigNode if the 'T' bit is set to 1.

If an OrigNode want to discover routes to multiple TargNodes, and
these routes share the same constraints, then the Option.

OrigNode can include all the multiple TargNode addresses of the TargNodes into via multiple AODV-RPL AODV-
RPL Target Options in the RREQ-DIO, so for routes that share the same
constraints. This reduces the cost can be reduced to building only one DODAG. Different addresses of the TargNodes
Furthermore, a single Target Option can
merge be used for different
TargNode addresses if they share the same prefix. prefix; in that case the
use of the destination sequence number is not defined in this
document.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Option Length | Dest SeqNo | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ |
| Target Prefix (Variable Length) |
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Target option format for AODV-RPL MoP

Type
The type of assigned to the AODV-RPL Target Option (see Section 9.2)

Destination Sequence Number

Dest SeqNo

In RREQ-DIO, if nonzero, it is the last known Sequence Number for
TargNode for which a route is desired. In RREP-DIO, it is the
destination sequence number associated to the route.

5. Symmetric and Asymmetric Routes

In Figure 4 and Figure 5, BR is the BorderRouter, Border Router, O is the OrigNode,
R is an intermediate router, and T is the TargNode. If the RREQ-DIO
arrives over an interface that is known to be symmetric, and the 'S'
bit is set to 1, then it remains as 1, as illustrated in Figure 4.
An
If an intermediate router sends out RREQ-DIO with the 'S' bit set to
1,
meaning that then all the one-hop links on the route from the OrigNode O to
this router meet the requirements of route discovery; thus discovery, and 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; O-->T; Data: D-->S) T-->O) ------->
<---- RREP-Instance (Control: D-->S; T-->O; Data: S-->D) O-->T) -------<

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
determines whether 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 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
T determines whether or not the route is symmetric before
transmitting the RREP-DIO message upstream towards the OrigNode. OrigNode O.

The criterion and the corresponding metric criteria used to determine if a
one-hop whether or not each link is symmetric or not
is implementation specific and beyond the scope of the document. Also, the difference in the metric
values for upward document, and downward directions of a link that can may be
establish its symmetric and asymmetric nature is implementation 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 use averaging techniques or
any other means that is as appropriate to the application context.
application.

Appendix A describes an example method using the ETX and RSSI to
estimate whether the link is symmetric in terms of link quality is
given in using an averaging technique.

BR
/ | \
/----+----\
/ | \
/ | \
R R R
/ \ | / \
/ \ | / \
/ \ | / \
R --------- R --- R ---- R --------- R
/ \ --S=1--> / \ --S=0--> / \
--S=1--> \ / \ / --S=0-->
/ \ / \ / \
O ---------- R ------ R------ R ----- R ----------- T
/ \ / \ / \ / \
/ <--S=0-- / \ / \ / <--S=0--
/ \ / \ / \ / \
R ----- R ----------- R ----- R ----- R ----- R ---- R----- R
<--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0--

>---- RREQ-Instance (Control: S-->D; O-->T; Data: D-->S) T-->O) ------->
<---- RREP-Instance (Control: D-->S; T-->O; Data: S-->D) O-->T) -------<

Figure 5: AODV-RPL with Asymmetric Paired Instances

6. AODV-RPL Operation

6.1. Generating Route Request at OrigNode Generation

The route discovery process is initiated on-demand when an application at the
OrigNode has data to be transmitted to the TargNode, but no does not
have a route for the target exists or the current routes
don't fulfill that fulfills the requirements of the
data transmission. In this case, the OrigNode MUST build builds a local
RPLInstance and a DODAG rooted at itself. Then it begins to send out transmits a DIO
message in AODV-RPL MoP containing exactly one RREQ option (see Section 4.1) 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. (see Section 4.3). The 'S' bit in RREQ-DIO sent out by
the OrigNode is set as to 1.

The maintenance of Originator and Destination OrigNode maintains its Sequence Number in the
RREQ option is as defined in AODV
[RFC3561]. Namely, the OrigNode increments its Sequence number each
time it initiate a new route discovery operation by transmitting a
new RREQ message. Similarly, TargNode increments its Sequence number
each time it transmits a RREP message in response to a new RREQ
message (one with an incremented Sequence Number for OrigNode).

The address in the AODV-RPL Target Option can be a unicast IPv6
address, a prefix or a multicast address. prefix. 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

OrigNode can maintain different RPLInstances to discover routes with
different requirements to the same targets. Due to Using the InstanceID
pairing mechanism (see Section 6.3.3, 6.3.3), route replies (RREP-DIOs)
from for
different paired RPLInstances can be distinguished.

The transmission of RREQ-DIO follows obeys the Trickle timer. When If the L
duration specified by the "L" bit has transpired, elapsed, the OrigNode MUST
leave the DODAG and stop sending any RREQ-DIOs in the related
RPLInstance.

6.2. Receiving and Forwarding Route Request RREQ messages

6.2.1. General Processing

Upon receiving a RREQ-DIO, a router out of which does not belong to the
RREQ-instance goes through the following steps:

Step 1:

If the 'S' bit in the received RREQ-DIO is set to 1, the router
MUST look into check the two directions of the link by which the RREQ-
DIO 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 sent out MUST be set as 0. If the 'S' bit in the received
RREQ-DIO is set to 0, the router MUST look only checks into the upward
direction (i.e. towards (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
not exceed the MaxRank limit, the router chooses to join in joins the DODAG of the
RREQ-Instance. The router issuing that transmitted the received RREQ-
DIO RREQ-DIO
is selected as the preferred parent. Afterwards, Later, other RREQ-
DIO message can RREQ-DIO
messages might be received. How to maintain the parent set,
select the preferred parent, and update the router's rank follows obeys
the core RPL and the OFs defined in ROLL WG. In case that the
constraint or the MaxRank limit is not fulfilled, the router MUST NOT join in the DODAG. Otherwise, go to the
following steps 2, 3, 4 and 5.

A router MUST
discard a the received RREQ-DIO if the advertised rank
equals or exceeds and MUST NOT join the MaxRank limit. DODAG.

Step 2:

Then the router checks if one of its addresses is included in one
of the AODV-RPL Target Options or belongs to the indicated
multicast group. Options. If so, this router is one of the
TargNodes. Otherwise, it is an intermediate router.

Step 3:

If the 'H' bit is set to 1, then the router (TargNode or
intermediate) MUST build the upward route entry towards its preferred parent. accordingly. The
route entry SHOULD be stored along with MUST include at least the associated
RPLInstanceID and DODAGID. following items: Source
Address, InstanceID, Destination Address, Next Hop and Lifetime.
The Destination Address and the InstanceID can be respectively
learned from the DODAGID and the RPLInstanceID of the RREQ-DIO,
and the Source Address is copied from the AODV-RPL Target Option.
The next hop is the preferred parent. And the lifetime is set
according to DODAG configuration and can be extended when the
route is actually used.

If the 'H' bit is set to 0, an intermediate router MUST include
the address of the interface receiving the RREQ-DIO into the
address vector.

Step 4:

An intermediate router transmits a RREQ-DIO via link-local
multicast. TargNode prepares a RREP-DIO.

6.2.2. Additional Processing for Multiple Targets

If there are the OrigNode tries to reach multiple AODV-RPL Target Options TargNodes in the received
RREQ-DIO, a TargNode single RREQ-
instance, one of the TargNodes can be an intermediate router to the
others, therefore it SHOULD continue sending RREQ-DIO to reach other
targets. When preparing its own RREQ-DIO, In this case, before rebroadcasting the RREQ-DIO, a
TargNode MUST delete the AODV-RPL Target Option related to encapsulating its own address,
so that the downstream routers which with higher ranks would know the do not try to create a
route to this
target has already been found. When an TargetNode.

An intermediate router
receives could receive several RREQ-DIOs which include from routers
with lower ranks in the same RREQ-instance but have different lists
of AODV-
RPL Target Options, Options. When rebroadcasting the RREQ-DIO, the
intersection of these lists will SHOULD be included. For example, suppose
two RREQ-DIOs are received with the same RPLInstance and OrigNode.
Suppose further that the first RREQ has (T1, T2) as the targets, and
the second one has (T2, T4) as targets. Then only T2 needs to be
included in its own the generated RREQ-DIO. If the intersection is empty, it
means that all the targets have been reached, and the router SHOULD
NOT send out any RREQ-DIO. Any RREQ-DIO message with different AODV-RPL AODV-
RPL Target Options coming from a router with higher rank is ignored.

Step 5:

For an intermediate router, it sends out its own RREQ-DIO via
link-local multicast. For a TargNode, it can begin to prepare the
RREP-DIO.

6.3. Generating Route Reply (RREP) at TargNode

6.3.1. RREP-DIO for Symmetric route

When

If a RREQ-DIO arrives at a TargNode with the 'S' bit set to 1, it
means there exists is
a symmetric route in along which the two both directions can fulfill the
requirements. Other RREQ-DIOs can bring the upward
direction of might later provide asymmetric upward
routes (i.e. S=0). How to choose Selection between a qualified symmetric route
and an asymmetric route hopefully having that might have better performance is
implementation-specific and out of scope. If the implementation choose to use uses
the symmetric route, the TargNode MAY send out delay transmitting the RREP-DIO after a
for duration RREP_WAIT_TIME to wait for
the convergence of RD to an optimal await a better symmetric route.

For a symmetric route, the RREP-DIO message is sent via unicast to the
OrigNode; therefore next
hop according to the accumulated address vector (H=0) or the route
entry (H=1). Thus the DODAG in RREP-Instance doesn't does not 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 case the RREP option, The 'SHIFT' field and the 'T' 'H' bit are is set as
defined in Section 6.3.3. The to 0, the address
vector received in the RREQ-
DIO 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 RREP-DIO.
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 Dest
SeqNo is set according to incremented, as is done in AODV [RFC3561].

6.3.2. RREP-DIO for Asymmetric Route

When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 0, the
TargNode MUST build a DODAG in the RREP-Instance rooted at itself in
order to discover the downstream route from the OrigNode to the
TargNode. The RREP-DIO message MUST be send out re-transmitted via link-local
multicast until the OrigNode is reached or the MaxRank limit is exceeded.

The settings of the RREP-DIO fields in RREP option are the same as in
symmetric route. route except for the 'S' bit.

6.3.3. RPLInstanceID Pairing

Since the RPLInstanceID is assigned locally (i.e., there is no
coordination between routers in the assignment of RPLInstanceID) RPLInstanceID), the
tuple (RPLInstanceID, DODAGID, Address in the AODV-RPL Target Option) (OrigNode, TargNode, RPLInstanceID) 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 discovered route. The upper layer applications may have
different requirements.
Therefore the RREQ-Instance requirements and the RREP-Instance in the same route
discovery MUST be paired. The way to realize this is to pair their
RPLInstance IDs.

Typically, the two InstanceIDs are set as the local InstanceID in
core RPL:

0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|D| ID | Local RPLInstanceID in 0..63
+-+-+-+-+-+-+-+-+

Figure 6: Local Instance ID

The first bit is set to 1 indicating the RPLInstanceID is local. The
'D' bit here is used to distinguish the two AODV-RPL instances: D=0
for RREQ-Instance, D=1 for RREP-Instance. The ID they can initiate the route discoveries
simultaneously. Thus between the same pair of 6 bits SHOULD OrigNode and TargNode,
there can be multiple AODV-RPL instances. To avoid any mismatch, the same for
RREQ-Instance and RREP-Instance. Here, the 'D' bit is
used slightly differently than RREP-Instance in RPL. the same route discovery MUST
be paired somehow, e.g. using the RPLInstanceID.

When preparing the RREP-DIO, a TargNode could find the RPLInstanceID
to be used for the RREP-Instance is already occupied by another
instance RPL
Instance from an earlier route discovery operation which is still
active. In other words, it might happen that two distinct OrigNodes
need routes to the same
TargNode TargNode, and they happen to use the same
RPLInstanceID for RREQ-
Instance. RREQ-Instance. In this case, the occupied
RPLInstanceID MUST NOT be used again. Then this the second RPLInstanceID SHOULD
MUST be shifted into another integer and shifted back to the original one at so that the OrigNode. two RREP-instances
can be distinguished. In RREP option, the SHIFT Shift field indicates the how many the
shift to be applied to original
RPLInstanceID is shifted. RPLInstanceID. When the new
InstanceID after shifting exceeds 63, it will come back counting from rolls over starting at 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 Related operations can be
distinguished by the address of the OrigNode found in the AODV-RPL Target
Option.
Section 6.4.

6.4. Receiving and Forwarding Route Reply

Upon receiving a RREP-DIO, a router out of which does not belong to the RREP-Instance
RREQ-instance goes through the following steps:

Step 1:

If the 'S' bit is set to 1, the router proceeds to step 2.

If the 'S' bit of the RREP-DIO is set to 0, the router MUST look
into check
the downward direction of the link (towards the TargNode) by over
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 not exceed the MaxRank limit,
the router chooses to join in joins the DODAG of the RREP-
Instance. RREP-Instance. The router issuing that
transmitted the received RREP-DIO is selected as the preferred
parent. Afterwards, other RREQ-DIO RREP-DIO messages can be received. How
to maintain the parent set, select the preferred parent, and
update the router's rank follows obeys 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
DODAG; the 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 RREQ-DIO, and does nothing not execute
the remaining steps in this step. section.

Step 2:

Then the

The router next 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 a downward route entry. The route entry including
SHOULD include at least the RPLInstanceID
of RREP-Instance following items: OrigNode Address,
InstanceID, TargNode Address as destination, Next Hop and the DODAGID.
Lifetime. For a symmetric route, the next hop in the route entry
is to the router from which the RREP-DIO is received. For an
asymmetric route, the next hop is the preferred parent in the
DODAG of RREQ-Instance. The InstanceID in the route entry MUST be
the original RPLInstanceID (after subtracting the Shift field
value). The source address is learned from the AODV-RPL Target
Option, and the destination address is learned from the DODAGID.
The lifetime is set according to DODAG configuration and can be
extended when the route entry is to the preferred parent in
the DODAG of RREQ-Instance. actually used.

If the 'H' bit is set to 0, for an asymmetric route, an
intermediate router MUST include the address of the interface
receiving the RREP-DIO into the address vector, and vector; for a symmetric
route, there is nothing to do in this step.

Step 4:

For an intermediate router,

If the receiver is the OrigNode, it can start transmitting the
application data to TargNode along the path as provided in RREP-
Instance, and processing for the RREP-DIO is complete. Otherwise,
in case of an asymmetric route, the RREP-
DIO is sent out intermediate router transmits
the RREP-DIO via link-local multicast; in multicast. In case of a symmetric
route, the RREP-DIO message is unicasted unicast to the OrigNode via the next hop
in source routing (H=0), or via according
to the next hop address vector in the RREP-DIO (H=0) or the local route
entry
built (H=1). The RPLInstanceID in the RREQ-Instance (H=1). For transmitted RREP-DIO is the OrigNode, it can start
transmitting
same as the application data to TargNode along value in the path as
discovered through RREP-Instance. received RREP-DIO.

7. Gratuitous RREP

In some cases, an Intermediate router that receives a RREQ-DIO
message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode
instead of continuing to multicast the RREQ-DIO towards TargNode.
The intermediate router effectively builds the RREP-Instance on
behalf of the actual TargNode. The 'G' bit of the RREP option is
provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the
Intermediate node from the RREP-DIO sent by TargNode (G=0).

The gratuitous RREP-DIO can be sent out when an intermediate router R
receives a RREQ-DIO for a TargNode T, and R happens to have both
forward
downward and reverse upward routes to T which also fulfill the requirements.

In case of source routing, the intermediate router R MUST unicast the
received RREQ-DIO to TargNode T including the address vector between
the OrigNode O and the router R. Thus T can have a complete upward
route address vector between O and itself. from itself to O. Then T R MUST unicast a send out the
gratuitous RREP-DIO including the address vector between T and R. from R to T.

In case of hop-by-hop routing, R MUST unicast the received RREQ-DIO
to T. The routers along the route SHOULD build new route entries
with the related RPLInstanceID and DODAGID in the downward direction.
Then T MUST unicast the RREP-DIO to R, and the routers along the
route SHOULD build new route entries in the upward direction. Upon
received the unicast RREP-DIO, R sends the gratuitous RREP-DIO to the
OrigNode as the same way defined in Section 6.3.

8. Operation of Trickle Timer

The trickle timer operation to control RREQ-Instance/RREP-Instance
multicast is similar to that in P2P-RPL [RFC6997].

9. IANA Considerations

9.1. New Mode of Operation: AODV-RPL

IANA is required to assign a new Mode of Operation, named "AODV-RPL"
for Point-to-Point(P2P) hop-by-hop routing under the RPL registry.
The value of TBD1 is assigned from the "Mode of Operation" space
[RFC6550].

+-------------+---------------+---------------+
| Value | Description | Reference |
+-------------+---------------+---------------+
| TBD1 (5) | AODV-RPL | This document |
+-------------+---------------+---------------+

Figure 7: 6: Mode of Operation

9.2. AODV-RPL Options: RREQ, RREP, and Target

Three entries are required for new AODV-RPL options "RREQ", "RREP"
and "AODV-RPL Target" with values of TBD2 (0x0A), TBD3 (0x0B) and
TBD4 (0x0C) from the "RPL Control Message Options" space [RFC6550].

Figure 8: 7: AODV-RPL Options

10. Security Considerations

This document does not introduce additional security issues compared
to base RPL. For general RPL security considerations, see [RFC6550].

11. Future Work

There has been some discussion about how to determine the initial
state of a link after an AODV-RPL-based network has begun operation.
The current draft operates as if the links are symmetric until
additional metric information is collected. The means for making
link metric information is considered out of scope for AODV-RPL. In
the future, RREQ and RREP messages could be equipped with new fields
for use in verifying link metrics. In particular, it is possible to
identify unidirectional links; an RREQ received across a
unidirectional link has to be dropped, since the destination node
cannot make use of the received DODAG to route packets back to the
source node that originated the route discovery operation. This is
roughly the same as considering a unidirectional link to present an
infinite cost metric that automatically disqualifies it for use in
the reverse direction.

12. References

12.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On-
Demand Distance Vector (AODV) Routing", RFC 3561,
DOI 10.17487/RFC3561, July 2003,
<https://www.rfc-editor.org/info/rfc3561>.

[RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and
D. Barthel, Ed., "Routing Requirements for Urban Low-Power
and Lossy Networks", RFC 5548, DOI 10.17487/RFC5548, May
2009, <https://www.rfc-editor.org/info/rfc5548>.

[RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
Phinney, "Industrial Routing Requirements in Low-Power and
Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October
2009, <https://www.rfc-editor.org/info/rfc5673>.

[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, DOI 10.17487/RFC5826, April 2010,
<https://www.rfc-editor.org/info/rfc5826>.

[RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June
2010, <https://www.rfc-editor.org/info/rfc5867>.

[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.

[RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing
Protocol for Low-Power and Lossy Networks (RPL)",
RFC 6552, DOI 10.17487/RFC6552, March 2012,
<https://www.rfc-editor.org/info/rfc6552>.

[RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
J. Martocci, "Reactive Discovery of Point-to-Point Routes
in Low-Power and Lossy Networks", RFC 6997,
DOI 10.17487/RFC6997, August 2013,
<https://www.rfc-editor.org/info/rfc6997>.

[RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci,
"A Mechanism to Measure the Routing Metrics along a Point-
to-Point Route in a Low-Power and Lossy Network",
RFC 6998, DOI 10.17487/RFC6998, August 2013,
<https://www.rfc-editor.org/info/rfc6998>.

12.2. Informative References

[I-D.thubert-roll-asymlink]
Thubert, P., "RPL adaptation for asymmetrical links",
draft-thubert-roll-asymlink-02 (work in progress),
December 2011.

Appendix A. Example: ETX/RSSI Values to select S bit

We have tested the combination of "RSSI(downstream)" and "ETX
(upstream)" to decide determine whether the link is symmetric or asymmetric
at the intermediate nodes. The example of how the ETX and RSSI
values are used in conjuction is explained below:

Source---------->NodeA---------->NodeB------->Destination

Figure 9: 8: Communication link from Source to Destination

+-------------------------+----------------------------------------+
| RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA |
+-------------------------+----------------------------------------+
| > -15 | 150 |
| -25 to -15 | 192 |
| -35 to -25 | 226 |
| -45 to -35 | 662 |
| -55 to -45 | 993 |
+-------------------------+----------------------------------------+

Table 1: Selection of 'S' bit based on Expected ETX value

We tested the operations in this specification by making the
following experiment, using the above parameters. In our experiment,
a communication link is considered as symmetric if the ETX value of
NodeA->NodeB and NodeB->NodeA (See Figure.8) are, say, within 1:3
ratio. This ratio should be taken as a notional metric for deciding
link symmetric/asymmetric nature, and precise definition of the ratio
is beyond the scope of the draft. In general, NodeA can only know
the ETX value in the direction of NodeA -> NodeB but it has no direct
way of knowing the value of ETX from NodeB->NodeA. Using physical
testbed experiments and realistic wireless channel propagation
models, one can determine a relationship between RSSI and ETX
representable as an expression or a mapping table. Such a
relationship in turn can be used to estimate ETX value at nodeA for
link NodeB--->NodeA from the received RSSI from NodeB. Whenever
nodeA determines that the link towards the nodeB is bi-directional
asymmetric then the "S" bit is set to "S=0". Later on, the link from
NodeA to Destination is asymmetric with "S" bit remains to "0".

Appendix B. Changelog

B.1. Changes to version 02

o Include the support for source routing.

o Bring Import some features from [RFC6997], e.g., choice between hop-by-
hop and source routing, the "L" bit which determines the 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.

B.2. Changes to version 03

o Updated RREP option format. Remove the 'T' bit in RREP option.

o Using the same RPLInstanceID for RREQ and RREP, no need to update
[RFC6550].

o Explanation of Shift field in RREP.

o Multiple target options handling during transmission.

Authors' Addresses

Satish Anamalamudi
Huaiyin Institute of Technology
No.89 North Beijing Road, Qinghe District
Huaian 223001
China
SRM University-AP
Amaravati Campus
Amaravati, Andhra Pradesh 522 502
India

Email: satishnaidu80@gmail.com

Mingui Zhang
Huawei Technologies
No. 156 Beiqing Rd. Haidian District
Beijing 100095
China

Email: zhangmingui@huawei.com

Abdur Rashid Sangi
Huaiyin Institute of Technology
No.89 North Beijing Road, Qinghe District
Huaian 223001
P.R. China

Email: sangi_bahrian@yahoo.com
Charles E. Perkins
Futurewei
2330 Central Expressway
Santa Clara 95050
Unites States

Email: charliep@computer.org

S.V.R Anand
Indian Institute of Science
Bangalore 560012
India

Email: anand@ece.iisc.ernet.in

Bing Liu
Huawei Technologies
No. 156 Beiqing Rd. Haidian District
Beijing 100095
China

Email: remy.liubing@huawei.com