Internet DRAFT - draft-ietf-roll-nsa-extension
draft-ietf-roll-nsa-extension
ROLL R.-A. Koutsiamanis, Ed.
Internet-Draft G.Z. Papadopoulos
Intended status: Standards Track N. Montavont
Expires: 11 May 2024 IMT Atlantique
P. Thubert
Cisco
8 November 2023
Common Ancestor Objective Function and Parent Set DAG Metric Container
Extension
draft-ietf-roll-nsa-extension-12
Abstract
High reliability and low jitter can be achieved by being able to send
data packets through multiple paths, via different parents, in a
network. This document details how to exchange the necessary
information within RPL control packets to let a node better select
the different parents that will be used to forward a packet over
different paths. This document also describes the Objective Function
which takes advantage of this information to implement multi-path
routing.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 11 May 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Common Ancestor AP Selection Policies . . . . . . . . . . . . 4
3.1. Common Ancestor Strict . . . . . . . . . . . . . . . . . 5
3.2. Common Ancestor Medium . . . . . . . . . . . . . . . . . 6
3.3. Common Ancestor Relaxed . . . . . . . . . . . . . . . . . 6
4. Common Ancestor Objective Function . . . . . . . . . . . . . 6
4.1. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Node State and Attribute (NSA) object type extension . . . . 9
5.1. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Controlling PRE . . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative references . . . . . . . . . . . . . . . . . . 13
10.2. Informative references . . . . . . . . . . . . . . . . . 13
Appendix A. Implementation Status . . . . . . . . . . . . . . . 14
Appendix B. Choosing an AP selection policy . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
Networks in the industrial context must provide stringent guarantees
in terms of reliability and predictability, with this domain being
one of the main ones addressed by Deterministic Networking [RFC8557].
One of the ways of achieving such guarantees is through Packet
Replication and Elimination (PRE) (Section 4.5.3 of [RFC9030]), a
technique which allows redundant paths in the network to be utilized
for traffic requiring higher reliability. Another is to have pre-
selected backup paths on standby for quick packet retransmission when
packet failures occur. Load-balancing can be also used to make sure
that not all traffic passes through the same nodes, to more evenly
spread the packet forwarding load. Allowing industrial applications
to function over wireless networks requires the application of the
principles and architecture of Deterministic Networking [RFC8655].
This results in designs that aim at optimizing packet delivery rate
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and bounding latency. Additionally, nodes operating on battery need
to minimize their energy consumption.
As an example, to meet this goal, IEEE Std. 802.15.4 [IEEE802154]
provides Time-Slotted Channel Hopping (TSCH), a mode of operation
that uses a common communication schedule based on timeslots to allow
deterministic medium access as well as channel hopping to work around
radio interference. However, since TSCH uses retransmissions in the
event of a failed transmission, end-to-end latency and jitter
performance can deteriorate.
Furthermore, the 6TiSCH working group, focusing on IPv6 over IEEE
Std. 802.15.4-TSCH, has worked on these issues and produced the
"6TiSCH Architecture" [RFC9030] to address that case.
Building a multi-path DODAG can be achieved based on the RPL
capability of having multiple parents for each node in a network, a
subset of which is used to forward packets. In order to select
parents to be part of this subset, the RPL Objective Function (OF)
needs additional information. This document describes an OF which
implements multi-path routing and specifies the transmission of this
specific path information.
This document describes a new Objective Function (OF) called the
Common Ancestor (CA) OF (see Section 4). A detailed description is
given of how the path information is used within the CA OF and how
the subset of parents for forwarding packets is selected. This
specification defines a new Objective Code Point (OCP) for the CA OF.
For the path information, this specification focuses on the
extensions to the DAG Metric Container [RFC6551] required for
supplying to the CA OF a part of the information it needs to operate.
This information is the RPL [RFC6550] parent address set of a node
and it must be sent to potential children of the node. The RPL DIO
Control Message is the canonical way of broadcasting this kind of
information and therefore its DAG Metric Container [RFC6551] field is
used to append a Node State and Attribute (NSA) object. The node's
parent address set is stored as an optional TLV within the NSA
object. This specification defines the type value and structure for
the parent address set TLV (see Section 5).
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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The draft uses the following Terminology from other RFCs:
Parent Set (PS): Defined in RPL [RFC6550].
Packet Replication and Elimination (PRE): A method that consists of
transmitting multiple copies of a packet using multi-path
forwarding over a multi-hop network and that consolidates multiple
received packet copies to control flooding. See "Complex Track
with Replication and Elimination" in Section 4.5.3 of [RFC9030]
for more details.
The draft introduces the following Terminology:
Alternative Parent (AP): An RPL parent in the parent set of a node
is used to forward a packet copy when replicating packets.
Alternative Parent (AP) Selection: The mechanism for choosing the
next hop node to forward a packet copy when replicating packets.
Preferred Grand Parent (PGP): The preferred parent of the preferred
parent of a node.
3. Common Ancestor AP Selection Policies
In the RPL protocol, each node maintains a list of potential parents.
When more than one parent is required, as when performing PRE, the
RPL DODAG Preferred Parent node is used, as per RPL [RFC6550] parent
selection, effectively depending on the OF used. If the CA OF is
used, the way this choice is made is described in Section 4.
Furthermore, to construct an alternative path toward the root, in
addition to the PP node, each node in the network selects one or more
parents, called Alternative Parents (APs), from its Parent Set (PS).
There are multiple possible policies for selecting the AP node. This
section details three such possible policies.
All three policies defined perform AP selection based on common
ancestors, named Common Ancestor Strict, Common Ancestor Medium, and
Common Ancestor Relaxed, depending on how restrictive the selection
process is. A more restrictive policy will limit flooding but might
fail to select an appropriate AP, while a less restrictive one will
more often find an appropriate AP but might increase flooding.
All three policies apply their corresponding common ancestor
criterion to filter the list of candidate neighbors in the
Alternative Parent set.
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If after the filtering there are multiple condition-meeting candidate
nodes, the node MUST select at least one of them as its AP node. The
way this choice is made depends on which OF is used. If the CA OF is
used, the way this choice is made is described in Section 4.
3.1. Common Ancestor Strict
In the CA Strict OF the node will check if its Preferred Grand Parent
(PGP), the PP of its PP, is the same as the PP of the potential AP.
( R ) root
. PS(S) = {A, B, C, D}
. PP(S) = C
. PP(PP(S)) = Y
.
PS(A) = {W, X}
( W ) ( X ) ( Y ) ( Z ) PP(A) = X
^ ^ ^^ ^ ^ ^^^^ ^ ^ ^^
| \ // | \ // || \ / || PS(B) = {W, X, Y}
| // | // || / || PP(B) = Y
| // \ | // \ || / \ ||
| // \ | // \ || / \ || PS(C) = {X, Y, Z}
( A ) ( B ) ( C ) ( D ) PP(C) = Y
^ ^ ^^ ^
\ \ || / PS(D) = {Y, Z}
\ \ || / PP(D) = Z
\ \ || /
\----\\ || / || Preferred Parent
( S ) source | Potential Alt. Parent
Figure 1: Example Common Ancestor Strict Alternative Parent
Selection policy
For example, in Figure 1, the source node S must know its grandparent
sets through nodes A, B, C, and D. The Parent Sets (PS) and the
Preferred Parents (PS) of nodes A, B, C, and D are shown on the side
of the figure. The CA Strict parent selection policy will select an
AP for node S for which PP(PP(S)) = PP(AP). Given that PP(PP(S)) =
Y:
* Node A: PP(A) = X and therefore it is different than PP(PP(S))
* Node B: PS(B) = Y and therefore it is equal to PP(PP(S))
* Node D: PS(D) = Z and therefore it is different than PP(PP(S))
Therefore, node S MUST select node B as its AP node, since PP(PP(S))
= Y = PP(B).
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3.2. Common Ancestor Medium
In the CA Medium OF the node will check if its Preferred Grand Parent
(PGP), the PP of its PP, is contained in the PS of the potential AP.
Using the same example, in Figure 1, the CA Medium parent selection
policy will select an AP for node S for which PP(PP(S)) is in PS(AP).
Given that PP(PP(S)) = Y:
* Node A: PS(A) = {W, X} and therefore PP(PP(S)) is not in the set
* Node B: PS(B) = {W, X, Y} and therefore PP(PP(S)) is in the set
* Node D: PS(D) = {Y, Z} and therefore PP(PP(S)) is in the set
Therefore, S MUST select at least one node among B and D as its AP
node.
3.3. Common Ancestor Relaxed
In the CA Relaxed OF the node will check if the Parent Set (PS) of
its Preferred Parent (PP) has a node in common with the PS of the
potential AP.
Using the same example, in Figure 1, the CA Relaxed parent selection
policy will select an AP for node S for which PS(PP(S)) has at least
one node in common with PS(AP). Given that PS(PP(S)) = {X, Y, Z}:
* Node A: PS(A) = {W, X} and the common nodes are {X}
* Node B: PS(B) = {W, X, Y} and the common nodes are {X, Y}
* Node D: PS(D) = {Y, Z} and the common nodes are {Y, Z}
Therefore, S MUST select at least one node among A, B, and D as its
AP node.
4. Common Ancestor Objective Function
An OF which allows the multiple paths to remain correlated is
detailed here. More specifically, when using this OF a node will
select an AP node "close" to its PP node to allow the operation of
overhearing between parents. Closeness here is not strictly defined,
however, the premise is that those candidate parent nodes that have
common parents themselves have a higher probability of being within
each other's radio range, though it's of course not guaranteed. For
more details about overhearing and its use in this context see the
"Complex Track with Replication and Elimination" in Section 4.5.3 of
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[RFC9030]. If multiple potential APs match this condition, one of
the APs with the lowest rank will be registered, with the choice
between multiple nodes with the same lowest rank being
implementation-specific.
The OF described here is an extension of The Minimum Rank with
Hysteresis Objective Function (MRHOF) [RFC6719]. The CA OF does not
update [RFC6719]. Rather, it uses the existing definition of MRHOF
in [RFC6719] to build a new OF (with a new Objective Code Point
(OCP)) which provides additional functionality, while maintaining
compatibility by retaining the existing functionality of MRHOF for
the preferred parent. To be precise, this OF extends MRHOF by
specifying how an AP is selected while the selection and switching of
the PP remain unaltered. Importantly, the calculation of the rank of
the node through each candidate neighbor and the selection of the PP
is kept the same as in MRHOF.
How the CA OF differs from MRHOF in a section-by-section manner
follows in detail:
[RFC6719], Section 2: "Terminology". Term "Selected Metric":
The CA OF uses only one metric, like MRHOF, for rank calculation,
with the same MRHOF semantics. For selecting the AP, the PS TLV
(stored in the DIO Metric Container Node State and Attribute (NSA)
object body, see Section 5) is used. This additional NSA metric
is disregarded for rank calculation.
[RFC6719], Section 3 "The Minimum Rank with Hysteresis Objective
Function":
Same as MRHOF extended to AP selection. Minimum Rank path
selection and switching apply correspondingly to the AP with the
extra CA requirement of having some match between ancestors,
according to one of the Common Ancestor AP selection policies
defined in Section 3.
[RFC6719], Section 3.1 "Computing the Path Cost":
Same as MRHOF extended to AP selection. If a candidate neighbor
does not fulfill the CA requirement then the path cost through
that neighbor MUST be set to MAX_PATH_COST, the same value used by
MRHOF. As a result, the node MUST NOT select the candidate
neighbor as its AP.
[RFC6719], Section 3.2 "Parent Selection":
Same as MRHOF extended to AP selection. To allow hysteresis, AP
selection maintains a variable, cur_ap_min_path_cost, which is the
path cost of the current AP.
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[RFC6719], Section 3.2.1 "When Parent Selection Runs":
Same as MRHOF.
[RFC6719], Section 3.2.2 "Parent Selection Algorithm":
Same as MRHOF extended to AP selection. If the smallest path cost
for paths through the candidate neighbors is smaller than
cur_ap_min_path_cost by less than PARENT_SWITCH_THRESHOLD (the
same variable as MRHOF uses), the node MAY continue to use the
current AP. Additionally, if there is no PP selected, there MUST
NOT be any AP selected either. Finally, as with MRHOF, a node MAY
include up to PARENT_SET_SIZE-1 additional candidate neighbors in
its Alternative Parent set. The value of PARENT_SET_SIZE is the
same as in MRHOF.
[RFC6719], Section 3.3 "Computing Rank":
Same as MRHOF.
[RFC6719], Section 3.4 "Advertising the Path Cost":
Same as MRHOF.
[RFC6719], Section 3.5 "Working without Metric Containers":
The CA OF can work without metric containers identically to MRHOF.
Nodes that transmit DIO messages without the Metric Container will
never be selected as an AP by the CA OF of another node but can be
selected as the PP as per the operation of MRHOF. Effectively,
the lack of Metric Containers is equivalent to operating with a
Parent Set TLV where there are no PS IPv6 addresses and the PS
Length is 0.
[RFC6719], Section 4 "Using MRHOF for Metric Maximization":
Same as MRHOF.
[RFC6719], Section 5 "MRHOF Variables and Parameters":
Same as MRHOF extended to AP selection. The CA OF operates like
MRHOF for AP selection by maintaining separate:
AP: Corresponding to the MRHOF PP. Hysteresis is configured for
AP with the same PARENT_SWITCH_THRESHOLD parameter as in MRHOF.
The AP MUST NOT be the same as the PP.
Alternative parent set: Corresponding to the MRHOF parent set.
The size is defined by the same PARENT_SET_SIZE parameter as in
MRHOF. The Alternative parent set MUST be a strict subset of
the parent set.
cur_ap_min_path_cost: Corresponding to the MRHOF
cur_min_path_cost variable. To support the operation of the
hysteresis function for AP selection.
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[RFC6719], Section 6 "Manageability":
Same as MRHOF.
[RFC6719], Section 6.1 "Device Configuration":
Same as MRHOF.
[RFC6719], Section 6.2 "Device Monitoring":
Same as MRHOF.
4.1. Usage
All the Common Ancestor AP Selection Policies (Section 3) apply their
corresponding criterion to filter the list of candidate neighbors in
the Alternative Parent set. The AP is then selected from the
Alternative Parent set based on Rank and using hysteresis as is done
for the PP in MRHOF. It is noteworthy that the OF uses the same
Objective Code Point (OCP): (TBD1) for all policies used.
The PS information can be used by any of the described AP selection
policies or other ones not described here, depending on requirements.
It is optional for all nodes to use the same AP selection policies.
Different nodes may use different AP selection policies since the
selection policy is local to each node. For example, using different
policies can be used to vary the transmission reliability in each
hop. Some suggestions are provided in Appendix B.
5. Node State and Attribute (NSA) object type extension
In order to select their AP node, nodes need to be aware of their
grandparent node sets. Within RPL [RFC6550], the nodes use the DODAG
Information Object (DIO) Control Message to broadcast information
about themselves to potential children. However, RPL [RFC6550], does
not define how to propagate information related to the parent set,
which is what this document addresses.
DIO messages can carry multiple options, out of which the DAG Metric
Container option [RFC6551] is the most suitable structurally and
semantically to carry the parent set. The DAG Metric Container
option itself can carry different nested objects, out of which the
Node State and Attribute (NSA) [RFC6551] is appropriate for
transferring generic node state data. Within the Node State and
Attribute, it is possible to store optional TLVs representing various
node characteristics. As per the Node State and Attribute (NSA)
[RFC6551] description, no TLV has been defined for use. This
document defines one TLV for transmitting a node's parent set.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID |Version Number | Rank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|G|0| MOP | Prf | DTSN | Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ DODAGID +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DAGMC Type (2)| DAGMC Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
// DAG Metric Container data //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Example DIO Message with a DAG Metric Container option
Figure 2 shows the structure of the DIO Control Message when a DAG
Metric Container option is included. The DAG Metric Container option
type (DAGMC Type in Figure 2) has the value 0x02 as per the IANA
registry for the RPL Control Message Options, and is defined in
[RFC6550]. The DAG Metric Container option length (DAGMC Length in
Figure 2) expresses the DAG Metric Container length in bytes. DAG
Metric Container data holds the actual data and is shown expanded in
Figure 3.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Routing-MC-Type|Res Flags|P|C|O|R| A | Prec | Length (bytes)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Flags |A|O| PS type | PS Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PS IPv6 address(es) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: DAG Metric Container (MC) data with Node State and
Attribute (NSA) object body and a TLV
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The structure of the DAG Metric Container data in the form of a Node
State and Attribute (NSA) object with a TLV in the NSA Optional TLVs
field is shown in Figure 3. The first 32 bits comprise the DAG
Metric Container header and all the following bits are part of the
Node State and Attribute object body, as defined in [RFC6551]. This
document defines a new TLV, which MUST be carried in the Node State
and Attribute (NSA) object Optional TLVs field within the context of
the use of the CA OF. The TLV is named Parent Set and is abbreviated
as PS in Figure 3.
PS type: The type of the Parent Set TLV. The value is (TBD2).
PS Length: The total length of the TLV value field (PS IPv6
address(es)) in bytes (0 included). The length is an integral
multiple of 16, the number of bytes in an IPv6 address.
PS IPv6 address(es) One or more 128-bit IPv6 addresses, without any
separator between them. The field consists of one IPv6 address
per parent in the parent set. The parent addresses are listed
in decreasing order of preference and not all parents in the
parent set need to be included. The selection of how many
parents from the parent set will be included is left to the
implementation. The number of parent addresses in the PS IPv6
address(es) field can be deduced by dividing the length of the
PS IPv6 address(es) field in bytes by 16, the number of bytes
in an IPv6 address.
5.1. Usage
The PS is used in the process of parent selection, and especially in
AP selection since it can help the alternative path to not
significantly deviate from the preferred path. The Parent Set is
information local to the node that broadcasts it.
The PS is used only within NSA objects configured as a metric,
therefore the DAG Metric Container field "C" MUST be 0.
Additionally, since the information in the PS needs to be propagated
downstream but cannot be aggregated, the DAG Metric Container field
"R" MUST be 1. Finally, since the information contained is by
definition partial, specifically just the parent set of the DIO-
sending node, the DAG Metric Container field "P" MUST be 1.
The presence of incorrectly configured flags MUST render the Parent
Set TLV invalid. This case MUST be handled equivalently to operating
with a Parent Set TLV where there are no PS IPv6 addresses and the PS
Length is 0.
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The presence of a PS Length value that is not a multiple of 16 or
larger than 240 MUST render the Parent Set TLV invalid. This case
MUST be handled equivalently to operating with a Parent Set TLV where
there are no PS IPv6 addresses and the PS Length is 0.
6. Controlling PRE
PRE is very helpful when the aim is to increase reliability for a
certain path, however, its use creates additional traffic as part of
the replication process. It is conceivable that not all paths have
stringent reliability requirements. Therefore, a way to control
whether PRE is applied to a path's packets SHOULD be implemented.
For example, a traffic class label can be used to determine this
behavior per flow type as described in Deterministic Networking
Architecture [RFC8655].
7. Security Considerations
All the security considerations from [RFC6550], [RFC6551], and
[RFC6719] apply.
In this document, the structure of the DIO control message is
extended, within the pre-defined DIO options. The additional
information is the list of IPv6 addresses of the parent set of the
node transmitting the DIO. This use of this additional information
can have the following additional potential consequences:
* A malicious node that can send DIOs can use the parent set
extension to convince neighbors to route through itself, instead
of the normal preferred parent they would use. However, this is
already possible with other OFs (like OF0 [RFC6552] and MRHOF
[RFC6719]) by reporting a fake rank value in the DIO, thus
masquerading as the DODAG root.
8. IANA Considerations
This document requests the allocation of a new value (TBD1) from the
"Objective Code Point (OCP)" registry in the "Routing Protocol for
Low Power and Lossy Networks (RPL)" registry group. The Description
field should have the value "Common Ancestor Objective Function
(CAOF)".
This document also requests the allocation of a new value (TBD2) for
the "Parent Set" TLV from the "Routing Metric/Constraint TLVs"
registry in the "Routing Protocol for Low Power and Lossy Networks
(RPL) Routing Metric/Constraint" registry group. The Description
field should have the value "Parent Set".
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9. Acknowledgments
We are very grateful to Dominique Barthel, Rahul Jadhav, Fabrice
Theoleyre, Diego Dujovne, Derek Jianqiang Hou, Michael Richardson,
and Alvaro Retana for their comments, feedback, and support which
lead to many improvements to this document. We would also like to
thank Tomas Lagos Jenschke very much for helping in the
implementation and evaluation of this document.
10. References
10.1. 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>.
[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>.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<https://www.rfc-editor.org/info/rfc6551>.
[RFC6719] Gnawali, O. and P. Levis, "The Minimum Rank with
Hysteresis Objective Function", RFC 6719,
DOI 10.17487/RFC6719, September 2012,
<https://www.rfc-editor.org/info/rfc6719>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative references
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[IEEE802154]
IEEE standard for Information Technology, "IEEE Std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks", December 2015,
<http://standards.ieee.org/findstds/
standard/802.15.4-2015.html>.
[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>.
[RFC8557] Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019,
<https://www.rfc-editor.org/info/rfc8557>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time-
Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
RFC 9030, DOI 10.17487/RFC9030, May 2021,
<https://www.rfc-editor.org/info/rfc9030>.
Appendix A. Implementation Status
A research-stage implementation of the PRE mechanism using the
proposed extension as part of a 6TiSCH IOT use case was developed at
IMT Atlantique, France by Tomas Lagos Jenschke and Remous-Aris
Koutsiamanis. It was implemented on the open-source Contiki OS and
tested with the Cooja simulator. The DIO DAGMC NSA extension is
implemented with a configurable number of parents from the parent set
of a node to be reported.
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( R )
(11) (12) (13) (14) (15) (16)
(21) (22) (23) (24) (25) (26)
(31) (32) (33) (34) (35) (36)
(41) (42) (43) (44) (45) (46)
(51) (52) (53) (54) (55) (56)
( S )
Figure 4: Simulation Topology
The simulation setup is:
Topology: 32 nodes structured in a regular grid as shown in
Figure 4. Node S (source) is the only data packet sender and
sends data to node R (root). The parent set of each node (except
R) is all the nodes in the immediately higher row, the immediately
above 6 nodes. For example, each node in {51, 52, 53, 54, 55, 56}
is connected to all of {41, 42, 43, 44, 45, 46}. Nodes 11, 12,
13, 14, 15, and 16 have a single upwards link to R.
MAC: TSCH with 1 retransmission
Platform: Cooja
Schedule: Static, 2 timeslots per link from each node to each parent
in its parent set, 1 broadcast EB slot, 1 sender-based shared
timeslot (for DIO and DIS) per node (total of 32).
Simulation lifecycle: Allow link formation for 100 seconds before
starting to send data packets. Afterward, S sends data packets to
R. The simulation terminates when 1000 packets have been sent by
S.
Radio Links: Every 60 s, a new Packet Delivery Rate is randomly
drawn for each link, with a uniform distribution spanning the 70%
to 100% interval.
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Traffic Pattern: CBR, S sends one non-fragmented UDP packet every 5
seconds to R.
PS extension size: 3 parents.
Routing Methods:
* RPL: The default RPL non-PRE implementation in Contiki OS.
* 2nd ETX: PRE with a parent selection method which picks as AP
the 2nd best parent in the parent set based on ETX.
* CA Strict: As described in Section 3.1.
* CA Medium: As described in Section 3.2.
Simulation results:
+=========+===================+===================+===============+
| Routing | Average Packet | Average Traversed | Average |
| Method | Delivery Rate (%) | Nodes/packet (#) | Duplications/ |
| | | | packet (#) |
+=========+===================+===================+===============+
| RPL | 82.70 | 5.56 | 7.02 |
+---------+-------------------+-------------------+---------------+
| 2nd ETX | 99.38 | 14.43 | 31.29 |
+---------+-------------------+-------------------+---------------+
| CA | 97.32 | 9.86 | 18.23 |
| Strict | | | |
+---------+-------------------+-------------------+---------------+
| CA | 99.66 | 13.75 | 28.86 |
| Medium | | | |
+---------+-------------------+-------------------+---------------+
Table 1
Links:
* Contiki OS DIO DAGMC NSA extension (draft-koutsiamanis-roll-nsa-
extension branch) (https://github.com/ariskou/contiki/tree/draft-
koutsiamanis-roll-nsa-extension)
* Wireshark dissectors (for the optional PS TLV) - currently merged
/ in master (https://code.wireshark.org/review/gitweb?p=wireshark.
git;a=commit;h=e2f6ba229f45d8ccae2a6405e0ef41f1e61da138)
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Appendix B. Choosing an AP selection policy
The manner of choosing an AP selection policy is left to the
implementation, for maximum flexibility.
For example, a different policy can be used per traffic type. The
network configurator can choose the CA Relaxed policy to increase
reliability (thus producing some flooding) for specific, extremely
important, alert packets. On the other hand, all normal data traffic
uses the CA Strict policy. Therefore, an exception is made just for
the alert packets.
Another option would be to devise a new disjoint policy, where the
paths are on purpose non-correlated, to increase path diversity and
resilience against whole groups of nodes failing. The disadvantage
may be increased jitter.
Finally, a network configurator may provide the CA policies with a
preference order of Strict > Medium > Relaxed as a means of falling
back to more flood-prone policies to maintain reliability.
Authors' Addresses
Remous-Aris Koutsiamanis (editor)
IMT Atlantique
Office B220
4 rue Alfred Kastler, BP 20722
44307 Nantes Cedex 3
France
Email: aris@ariskou.com
Georgios Papadopoulos
IMT Atlantique
Office B00 - 114A
2 Rue de la Chataigneraie
35510 Cesson-Sevigne - Rennes
France
Phone: +33 299 12 70 04
Email: georgios.papadopoulos@imt-atlantique.fr
Nicolas Montavont
IMT Atlantique
Office B00 - 106A
2 Rue de la Chataigneraie
35510 Cesson-Sevigne - Rennes
France
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Phone: +33 299 12 70 23
Email: nicolas.montavont@imt-atlantique.fr
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
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