rfc9033.original.xml   rfc9033.xml 
<?xml version='1.0' encoding='utf-8'?> <?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent"> <!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">
<?rfc toc="yes"?> <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft
<?rfc comments="yes"?> -ietf-6tisch-msf-18" number="9033" obsoletes="" updates="" submissionType="IETF"
<?rfc inline="yes"?> category="std" consensus="true" sortRefs="true" symRefs="true" xml:lang="en" to
<?rfc subcompact="yes"?> cInclude="true" version="3">
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" ipr="trust200902"
docName="draft-ietf-6tisch-msf-18" obsoletes="" updates="" consensus="true" sub
missionType="IETF" xml:lang="en" tocInclude="true" version="3">
<!-- xml2rfc v2v3 conversion 2.35.0 --> <!-- xml2rfc v2v3 conversion 2.35.0 -->
<front> <front>
<title> <title abbrev="6TiSCH MSF">
6TiSCH Minimal Scheduling Function (MSF) 6TiSCH Minimal Scheduling Function (MSF)
</title> </title>
<seriesInfo name="Internet-Draft" value="draft-ietf-6tisch-msf-18"/> <seriesInfo name="RFC" value="9033"/>
<author initials="T" surname="Chang" fullname="Tengfei Chang" role="edit or"> <author initials="T" surname="Chang" fullname="Tengfei Chang" role="edit or">
<organization>Inria</organization> <organization>Inria</organization>
<address> <address>
<postal> <postal>
<street>2 rue Simone Iff</street> <street>2 rue Simone Iff</street>
<city>Paris</city> <city>Paris</city>
<code>75012</code> <code>75012</code>
<country>France</country> <country>France</country>
</postal> </postal>
<email>tengfei.chang@inria.fr</email> <email>tengfei.chang@gmail.com</email>
</address> </address>
</author> </author>
<author initials="M." surname="Vucinic" fullname="Malisa Vucinic"> <author initials="M." surname="Vučinić" fullname="Mališa Vučinić">
<organization>Inria</organization> <organization>Inria</organization>
<address> <address>
<postal> <postal>
<street>2 rue Simone Iff</street> <street>2 rue Simone Iff</street>
<city>Paris</city> <city>Paris</city>
<code>75012</code> <code>75012</code>
<country>France</country> <country>France</country>
</postal> </postal>
<email>malisa.vucinic@inria.fr</email> <email>malisa.vucinic@inria.fr</email>
</address> </address>
skipping to change at line 56 skipping to change at line 53
<country>Spain</country> <country>Spain</country>
</postal> </postal>
<email>xvilajosana@uoc.edu</email> <email>xvilajosana@uoc.edu</email>
</address> </address>
</author> </author>
<author initials="S" surname="Duquennoy" fullname="Simon Duquennoy"> <author initials="S" surname="Duquennoy" fullname="Simon Duquennoy">
<organization>RISE SICS</organization> <organization>RISE SICS</organization>
<address> <address>
<postal> <postal>
<street>Isafjordsgatan 22</street> <street>Isafjordsgatan 22</street>
<city>164 29 Kista</city> <city>Kista</city>
<code>164 29</code>
<country>Sweden</country> <country>Sweden</country>
</postal> </postal>
<email>simon.duquennoy@gmail.com</email> <email>simon.duquennoy@gmail.com</email>
</address> </address>
</author> </author>
<author initials="D" surname="Dujovne" fullname="Diego Dujovne"> <author initials="D" surname="Dujovne" fullname="Diego Dujovne">
<organization>Universidad Diego Portales</organization> <organization>Universidad Diego Portales</organization>
<address> <address>
<postal> <postal>
<street>Escuela de Informatica y Telecomunicaciones</street> <street>Escuela de Informática y Telecomunicaciones</street>
<street>Av. Ejercito 441</street> <street>Av. Ejército 441</street>
<city>Santiago</city> <city>Santiago</city>
<region>Region Metropolitana</region> <region>Región Metropolitana</region>
<country>Chile</country> <country>Chile</country>
</postal> </postal>
<phone>+56 (2) 676-8121</phone> <phone>+56 (2) 676-8121</phone>
<email>diego.dujovne@mail.udp.cl</email> <email>diego.dujovne@mail.udp.cl</email>
</address> </address>
</author> </author>
<date/> <date year="2021" month="May"/>
<area>Internet Area</area> <area>Internet Area</area>
<workgroup>6TiSCH</workgroup> <workgroup>6TiSCH</workgroup>
<keyword>Draft</keyword>
<keyword>TSCH</keyword>
<keyword>communication schedule</keyword>
<keyword>6P</keyword>
<abstract> <abstract>
<t> <t>
This specification defines the 6TiSCH Minimal Scheduling Functio n (MSF). This specification defines the "IPv6 over the TSCH mode of IEEE 802.15.4" (6TiSCH) Minimal Scheduling Function (MSF).
This Scheduling Function describes both This Scheduling Function describes both
the behavior of a node when joining the network, and the behavior of a node when joining the network and
how the communication schedule is managed in a distributed fashi on. how the communication schedule is managed in a distributed fashi on.
MSF is built upon MSF is built upon
the 6TiSCH Operation Sublayer Protocol (6P) and the 6TiSCH Operation Sublayer Protocol (6P) and
the Minimal Security Framework for 6TiSCH. the minimal security framework for 6TiSCH.
</t> </t>
</abstract> </abstract>
<note>
<name>Requirements Language</name>
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NO
T", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTION
AL" in this document are to be interpreted as described in BCP 14 <xref target="
RFC2119" format="default"/> <xref target="RFC8174" format="default"/> when, and
only when, they appear in all capitals, as shown here.
</t>
</note>
</front> </front>
<middle> <middle>
<section anchor="sec_intro" numbered="true" toc="default"> <section anchor="sec_intro" numbered="true" toc="default">
<name>Introduction</name> <name>Introduction</name>
<t> <t>
The 6TiSCH Minimal Scheduling Function (MSF), defined in this sp ecification, is a 6TiSCH Scheduling Function (SF). The 6TiSCH Minimal Scheduling Function (MSF), defined in this sp ecification, is a 6TiSCH Scheduling Function (SF).
The role of an SF is entirely defined in <xref target="RFC8480" format="default"/>. The role of an SF is entirely defined in <xref target="RFC8480" format="default"/>.
This specification complements <xref target="RFC8480" format="de This specification complements <xref target="RFC8480" format="de
fault"/> by providing the rules of when to add/delete cells in the communication fault"/> by providing the rules of when to add and delete cells in the communica
schedule. tion schedule.
This specification satisfies all the requirements for an SF list This specification satisfies all the requirements for an SF list
ed in Section 4.2 of <xref target="RFC8480" format="default"/>. ed in <xref target="RFC8480" section="4.2" sectionFormat="of"/>.
</t> </t>
<t> <t>
MSF builds on top of the following specifications: MSF builds on top of the following specifications:
the Minimal IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) C "<xref target="RFC8180" format="title"/>" <xref target="RFC8180"
onfiguration <xref target="RFC8180" format="default"/>, format="default"/>,
the 6TiSCH Operation Sublayer Protocol (6P) <xref target="RFC848 "<xref target="RFC8480" format="title"/>" <xref target="RFC8480
0" format="default"/>, and " format="default"/>, and
the Minimal Security Framework for 6TiSCH <xref target="I-D.ietf "<xref target="RFC9031" format="title"/>" <xref target="RFC9031
-6tisch-minimal-security" format="default"/>. " format="default"/>.
</t> </t>
<t> <t>
MSF defines both MSF defines both
the behavior of a node when joining the network, and the behavior of a node when joining the network, and
how the communication schedule is managed in a distributed fashi on. how the communication schedule is managed in a distributed fashi on.
When a node running MSF boots up, it joins the network by follow ing the 6 steps described in <xref target="sec_boot" format="default"/>. When a node running MSF boots up, it joins the network by follow ing the six steps described in <xref target="sec_boot" format="default"/>.
The end state of the join process is that the node The end state of the join process is that the node
is synchronized to the network, is synchronized to the network,
has mutually authenticated with the network, has mutually authenticated with the network,
has identified a routing parent, has identified a routing parent,
and has scheduled one negotiated Tx cell (defined in <xref targe t="sec_traffic" format="default"/>) to/from its routing parent. and has scheduled one negotiated Tx cell (defined in <xref targe t="sec_traffic" format="default"/>) to/from its routing parent.
After the join process, the node can continuously add/delete/rel After the join process, the node can continuously add, delete, a
ocate cells, as described in <xref target="sec_add_delete" format="default"/>. nd relocate cells as described in <xref target="sec_add_delete" format="default"
It does so for 3 reasons: />.
It does so for three reasons:
to match the link-layer resources to the traffic, to match the link-layer resources to the traffic,
to handle changing parent and to handle changing parent, and
to handle a schedule collision. to handle a schedule collision.
</t> </t>
<t> <t>
MSF works closely with the IPv6 Routing Protocol for Low-Power a nd Lossy Networks (RPL), specifically the routing parent defined in <xref target ="RFC6550" format="default"/>. MSF works closely with the IPv6 Routing Protocol for Low-Power a nd Lossy Networks (RPL), specifically the routing parent defined in <xref target ="RFC6550" format="default"/>.
This specification only describes how MSF works with the routing parent; this parent is referred to as the "selected parent". This specification only describes how MSF works with the routing parent; this parent is referred to as the "selected parent".
The activity of MSF towards the single routing parent is called a "MSF session". The activity of MSF towards the single routing parent is called a "MSF session".
Though the performance of MSF is evaluated only when the "select ed parent" represents the node's preferred parent, there should be no restrictio ns to use multiple MSF sessions, one per parent. Though the performance of MSF is evaluated only when the "select ed parent" represents the node's preferred parent, there should be no restrictio ns to use multiple MSF sessions, one per parent.
The distribution of traffic over multiple parents is a routing d ecision that is out of scope for MSF. The distribution of traffic over multiple parents is a routing d ecision that is out of scope for MSF.
</t> </t>
<t> <t>
MSF is designed to operate in a wide range of application domain s. MSF is designed to operate in a wide range of application domain s.
It is optimized for applications with regular upstream traffic, from the nodes to the Destination-Oriented Directed Acyclic Graph (DODAG <xref t arget="RFC6550" format="default"/>) root. It is optimized for applications with regular upstream traffic, from the nodes to the Destination-Oriented Directed Acyclic Graph (DODAG) root < xref target="RFC6550" format="default"/>.
</t> </t>
<t> <t>
This specification follows the recommended structure of an SF sp ecification, given in Appendix A of <xref target="RFC8480" format="default"/>, w ith the following adaptations: This specification follows the recommended structure of an SF sp ecification, given in <xref target="RFC8480" section="A" sectionFormat="of" form at="default"/>, with the following adaptations:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li> <li>
We have reordered some sections, in particular to have the s ection on the node behavior at boot (<xref target="sec_boot" format="default"/>) appear early in this specification. We have reordered some sections, in particular to have the s ection on the node behavior at boot (<xref target="sec_boot" format="default"/>) appear early in this specification.
</li> </li>
<li> <li>
We added sections on We added sections on
the interface to the minimal 6TiSCH configuration (<xref tar get="sec_minimal" format="default"/>), the interface to the minimal 6TiSCH configuration (<xref tar get="sec_minimal" format="default"/>),
the use of the SIGNAL command (<xref target="sec_signal" for mat="default"/>), the use of the SIGNAL command (<xref target="sec_signal" for mat="default"/>),
the MSF constants (<xref target="sec_constants" format="defa ult"/>) and the MSF constants (<xref target="sec_constants" format="defa ult"/>), and
the MSF statistics (<xref target="sec_stats" format="default "/>). the MSF statistics (<xref target="sec_stats" format="default "/>).
</li> </li>
</ul> </ul>
<section>
<name>Requirements Language</name>
<t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14
>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>
", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bc
p14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and "<bcp14>OPTIO
NAL</bcp14>" in this document are to be interpreted as described in BCP&nbsp;14
<xref target="RFC2119" format="default"/> <xref target="RFC8174" format="default
"/> when, and only when, they appear in all capitals, as shown here.
</t>
</section>
<section>
<name>Related Documents</name>
<t>This specification uses messages and variables defined in
IEEE Std 802.15.4-2015 <xref target="IEEE802154" format="default"
/>. It is expected that
those resources will remain in the future versions of IEEE Std 80
2.15.4;
in which case, this specification also applies to those future ve
rsions.
In the remainder of the document, we use <xref target="IEEE802154
" format="default"/> to refer to
IEEE Std 802.15.4-2015 as well as future versions of IEEE Std 802
.15.4
that remain compatible.</t>
</section>
</section> </section>
<section anchor="sec_minimal" numbered="true" toc="default"> <section anchor="sec_minimal" numbered="true" toc="default">
<name>Interface to the Minimal 6TiSCH Configuration</name> <name>Interface to the Minimal 6TiSCH Configuration</name>
<t> <t>
In a TSCH network, time is sliced up into time slots. In a Time-Slotted Channel Hopping (TSCH) network, time is sliced
The time slots are grouped as one or multiple slotframes which r up into time slots.
epeat over time. The time slots are grouped as one or multiple slotframes that re
The TSCH schedule instructs a node what to do at each time slot, peat over time.
such as transmit, receive or sleep <xref target="RFC7554" format="default"/>. The TSCH schedule instructs a node what to do at each time slot,
In case of a slot to transmit or receive, a channel is assigned such as transmit, receive, or sleep <xref target="RFC7554" format="default"/>.
to the time slot. For time slots for transmitting or receiving, a channel is assi
The tuple (slot, channel) is indicated as a cell of TSCH schedul gned to the time slot.
e. The tuple (slot, channel) is indicated as a cell of the TSCH sch
edule.
MSF is one of the policies defining how to manage the TSCH sched ule. MSF is one of the policies defining how to manage the TSCH sched ule.
</t> </t>
<t> <t>
A node implementing MSF SHOULD implement the Minimal 6TiSCH Conf A node implementing MSF <bcp14>SHOULD</bcp14> implement the mini
iguration <xref target="RFC8180" format="default"/>, which defines the "minimal mal 6TiSCH configuration <xref target="RFC8180" format="default"/>, which define
cell", a single shared cell providing minimal connectivity between the nodes in s the "minimal cell", a single shared cell providing minimal connectivity betwee
the network. n the nodes in the network.
The MSF implementation provided in this specification is based o The MSF implementation provided in this specification is based o
n the implementation of the Minimal 6TiSCH Configuration. n the implementation of the minimal 6TiSCH configuration.
However, an implementor MAY implement MSF based on other specifi However, an implementor <bcp14>MAY</bcp14> implement MSF based o
cations as long as the specification defines a way to advertise the EB/DIO among n other specifications as long as the specification defines a way to advertise t
the network. he Enhanced Beacons (EBs) and DODAG Information Objects (DIOs) among the network
.
</t> </t>
<t> <t>
MSF uses the minimal cell for broadcast frames such as Enhanced Beacons (EBs) <xref target="IEEE802154" format="default"/> and broadcast DODAG I nformation Objects (DIOs) <xref target="RFC6550" format="default"/>. MSF uses the minimal cell for broadcast frames such as Enhanced Beacons (EBs) <xref target="IEEE802154" format="default"/> and broadcast DODAG I nformation Objects (DIOs) <xref target="RFC6550" format="default"/>.
Cells scheduled by MSF are meant to be used only for unicast fra mes. Cells scheduled by MSF are meant to be used only for unicast fra mes.
</t> </t>
<t> <t>
To ensure there is enough bandwidth available on the minimal cel To ensure there is enough bandwidth available on the minimal cel
l, a node implementing MSF SHOULD enforce some rules for limiting the traffic of l, a node implementing MSF <bcp14>SHOULD</bcp14> enforce some rules for limiting
broadcast frames. the traffic of broadcast frames.
For example, the overall broadcast traffic among the node and it For example, the overall broadcast traffic among the node and it
s neighbors SHOULD NOT exceed 1/3 of the bandwidth of minimal cell. s neighbors <bcp14>SHOULD NOT</bcp14> exceed one-third of the bandwidth of minim
One of the algorithms that fulfills this requirement is the Tric al cell.
kle timer defined in <xref target="RFC6206" format="default"/> which is applied One of the algorithms that fulfills this requirement is the Tric
on DIO messages <xref target="RFC6550" format="default"/>. kle timer defined in <xref target="RFC6206" format="default"/>, which is applie
d to DIO messages <xref target="RFC6550" format="default"/>.
However, any such algorithm of limiting the broadcast traffic to meet those rules is implementation-specific and is out of the scope of MSF. However, any such algorithm of limiting the broadcast traffic to meet those rules is implementation-specific and is out of the scope of MSF.
</t> </t>
<t> <t>
3 slotframes are used in MSF. Three slotframes are used in MSF.
MSF schedules autonomous cells at Slotframe 1 (<xref target="sec MSF schedules autonomous cells at Slotframe 1 (<xref target="sec
_autonomous_cells" format="default"/>) and 6P negotiated cells at Slotframe 2 (< _autonomous_cells" format="default"/>) and 6P negotiated cells at Slotframe 2 (<
xref target="sec_add_delete" format="default"/>) ,while Slotframe 0 is used for xref target="sec_add_delete" format="default"/>), while Slotframe 0 is used for
the bootstrap traffic as defined in the Minimal 6TiSCH Configuration. the bootstrap traffic as defined in the minimal 6TiSCH configuration.
The same slotframe length for Slotframe 0, 1 and 2 is RECOMMENDE The same slotframe length for Slotframe 0, 1, and 2 is <bcp14>RE
D. COMMENDED</bcp14>.
Thus it is possible to avoid the scheduling collision between th e autonomous cells and 6P negotiated cells (<xref target="sec_autonomous_cells" format="default"/>). Thus it is possible to avoid the scheduling collision between th e autonomous cells and 6P negotiated cells (<xref target="sec_autonomous_cells" format="default"/>).
The default slotframe length (SLOTFRAME_LENGTH) is RECOMMENDED f or Slotframe 0, 1 and 2, although any value can be advertised in the EBs. The default slotframe length (SLOTFRAME_LENGTH) is <bcp14>RECOMM ENDED</bcp14> for Slotframe 0, 1, and 2, although any value can be advertised in the EBs.
</t> </t>
</section> </section>
<section anchor="sec_autonomous_cells" numbered="true" toc="default"> <section anchor="sec_autonomous_cells" numbered="true" toc="default">
<name>Autonomous Cells</name> <name>Autonomous Cells</name>
<t> <t>
MSF nodes initialize Slotframe 1 with a set of default cells for unicast communication with their neighbors. MSF nodes initialize Slotframe 1 with a set of default cells for unicast communication with their neighbors.
These cells are called 'autonomous cells', because they are main These cells are called "autonomous cells", because they are main
tained autonomously by each node without negotiation through 6P. tained autonomously by each node without negotiation through 6P.
Cells scheduled by 6P transaction are called 'negotiated cells' Cells scheduled by 6P Transaction are called "negotiated cells",
which are reserved on Slotframe 2. which are reserved on Slotframe 2.
How to schedule negotiated cells is detailed in <xref target="se c_add_delete" format="default"/>. How to schedule negotiated cells is detailed in <xref target="se c_add_delete" format="default"/>.
There are two types of autonomous cells: There are two types of autonomous cells:
</t> </t>
<ul spacing="compact"> <dl spacing="normal">
<li> <dt>
Autonomous Rx Cell (AutoRxCell), one cell at a [slotOffset,c Autonomous Rx Cell (AutoRxCell):</dt><dd> One cell at a [slo
hannelOffset] computed as a hash of the EUI64 of the node itself (detailed next) tOffset,channelOffset] computed as a hash of the 64-bit Extended Unique Identifi
. er (EUI-64) of the node itself (detailed next).
Its cell options bits are assigned as TX=0, RX=1, SHARED=0. Its cell options bits are assigned as TX=0, RX=1, SHARED=0.
</li> </dd>
<li> <dt>
Autonomous Tx Cell (AutoTxCell), one cell at a [slotOffset,c Autonomous Tx Cell (AutoTxCell):</dt><dd> One cell at a [slo
hannelOffset] computed as a hash of the layer 2 EUI64 destination address in the tOffset,channelOffset] computed as a hash of the Layer 2 EUI-64 destination addr
unicast frame to be transmitted (detailed in <xref target="sec_join" format="de ess in the unicast frame to be transmitted (detailed in <xref target="sec_join"
fault"/>). format="default"/>).
Its cell options bits are assigned as TX=1, RX=0, SHARED=1. Its cell options bits are assigned as TX=1, RX=0, SHARED=1.
</li> </dd>
</ul> </dl>
<t> <t>
To compute a [slotOffset,channelOffset] from an EUI64 address, n odes MUST use the hash function SAX as defined in Section 2 of <xref target="SAX -DASFAA" format="default"/> with consistent input parameters, for example, those defined in <xref target="sec_hash_function" format="default"/>. To compute a [slotOffset,channelOffset] from an EUI-64 address, nodes <bcp14>MUST</bcp14> use the hash function SAX as defined in Section 2 of < xref target="SAX-DASFAA" format="default"/> with consistent input parameters, fo r example, those defined in <xref target="sec_hash_function" format="default"/>.
The coordinates are computed to distribute the cells across all channel offsets, and all but the first slot offset of Slotframe 1. The coordinates are computed to distribute the cells across all channel offsets, and all but the first slot offset of Slotframe 1.
The first time offset is skipped to avoid colliding with the min imal cell in Slotframe 0. The first time offset is skipped to avoid colliding with the min imal cell in Slotframe 0.
The slot coordinates derived from a given EUI64 address are comp uted as follows: The slot coordinates derived from a given EUI-64 address are com puted as follows:
</t> </t>
<ul spacing="compact"> <t indent="6">slotOffset(MAC) = 1 + hash(EUI64, length(Slotframe
<li>slotOffset(MAC) = 1 + hash(EUI64, length(Slotframe_1) - 1) < _1) - 1) </t>
/li> <t indent="6">channelOffset(MAC) = hash(EUI64, NUM_CH_OFFSET)</t
<li>channelOffset(MAC) = hash(EUI64, NUM_CH_OFFSET)</li> >
</ul>
<t> <t>
The second input parameter defines the maximum return value of t he hash function. The second input parameter defines the maximum return value of t he hash function.
Other optional parameters defined in SAX determine the performan ce of SAX hash function. Other optional parameters defined in SAX determine the performan ce of SAX hash function.
Those parameters could be broadcasted in EB frame or pre-configu Those parameters could be broadcast in an EB frame or preconfigu
red. red.
For interoperability purposes, the values of those parameters ca For interoperability purposes, <xref target="sec_hash_function"
n be referred from <xref target="sec_hash_function" format="default"/>. format="default"/> provides the reference values of those parameters.
</t> </t>
<t> <t>
AutoTxCell is not permanently installed in the schedule but adde d/deleted on demand when there is a frame to be sent. AutoTxCell is not permanently installed in the schedule but is a dded or deleted on demand when there is a frame to be sent.
Throughout the network lifetime, nodes maintain the autonomous c ells as follows: Throughout the network lifetime, nodes maintain the autonomous c ells as follows:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li> <li>
Add an AutoTxCell to the layer 2 destination address which i s indicated in a frame when there is no 6P negotiated Tx cell in schedule for th at frame to transmit. Add an AutoTxCell to the Layer 2 destination address, which is indicated in a frame when there is no 6P negotiated Tx cell in the schedule f or that frame to transmit.
</li> </li>
<li> <li>
<t> <t>
Remove an AutoTxCell when: Remove an AutoTxCell when:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>there is no frame to transmit on that cell, or</li> <li>there is no frame to transmit on that cell, or</li>
<li>there is at least one 6P negotiated Tx cell in the s chedule for the frames to transmit.</li> <li>there is at least one 6P negotiated Tx cell in the s chedule for the frames to transmit.</li>
</ul> </ul>
</li> </li>
</ul> </ul>
<t> <t>
The AutoRxCell MUST always remain scheduled after synchronizatio The AutoRxCell <bcp14>MUST</bcp14> always remain scheduled after
n. synchronization.
6P CLEAR MUST NOT erase any autonomous cells. 6P CLEAR <bcp14>MUST NOT</bcp14> erase any autonomous cells.
</t> </t>
<t> <t>
Because of hash collisions, there will be cases that the AutoTxC ell and AutoRxCell are scheduled at the same slot offset and/or channel offset. Because of hash collisions, there will be cases that the AutoTxC ell and AutoRxCell are scheduled at the same slot offset and/or channel offset.
In such cases, AutoTxCell always take precedence over AutoRxCell . In such cases, AutoTxCell always take precedence over AutoRxCell .
Notice AutoTxCell is a shared type cell which applies backs-off mechanism. Notice AutoTxCell is a shared type cell that applies a back-off mechanism.
When the AutoTxCell and AutoRxCell collide, AutoTxCell takes pr ecedence if there is a packet to transmit. When the AutoTxCell and AutoRxCell collide, AutoTxCell takes pr ecedence if there is a packet to transmit.
When in a back-off period, AutoRxCell is used. When in a back-off period, AutoRxCell is used.
In case of conflicting with a negotiated cell, autonomous cells In the case of conflict with a negotiated cell, autonomous cells
take precedence over negotiated cells, which is stated in <xref target="IEEE8021 take precedence over negotiated cells, which is stated in <xref target="IEEE802
54" format="default"/>. 154" format="default"/>.
However, when the Slotframe 0, 1 and 2 use the same length value However, when the Slotframe 0, 1, and 2 use the same length valu
, it is possible for a negotiated cell to avoid the collision with AutoRxCell. e, it is possible for a negotiated cell to avoid the collision with AutoRxCell.
Hence, the same slotframe length for Slotframe 0, 1 and 2 is REC Hence, the same slotframe length for Slotframe 0, 1, and 2 is <b
OMMENDED. cp14>RECOMMENDED</bcp14>.
</t> </t>
<t> <t>
</t> </t>
</section> </section>
<section anchor="sec_boot" numbered="true" toc="default"> <section anchor="sec_boot" numbered="true" toc="default">
<name>Node Behavior at Boot</name> <name>Node Behavior at Boot</name>
<t> <t>
This section details the behavior the node SHOULD follow from th e moment it is switched on, until it has successfully joined the network. This section details the behavior the node <bcp14>SHOULD</bcp14> follow from the moment it is switched on until it has successfully joined the n etwork.
Alternative behaviors may be involved, for example, when alterna tive security solutions are used for the network. Alternative behaviors may be involved, for example, when alterna tive security solutions are used for the network.
<xref target="sec_start_state" format="default"/> details the st art state; <xref target="sec_start_state" format="default"/> details the st art state;
<xref target="sec_end_state" format="default"/> details the en d state. <xref target="sec_end_state" format="default"/> details the en d state.
The other sections detail the 6 steps of the joining process. The other sections detail the six steps of the joining process.
We use the term "pledge" and "joined node", as defined in <xref We use the term "pledge" and "joined node", as defined in <xref
target="I-D.ietf-6tisch-minimal-security" format="default"/>. target="RFC9031" format="default"/>.
</t> </t>
<section anchor="sec_start_state" numbered="true" toc="default"> <section anchor="sec_start_state" numbered="true" toc="default">
<name>Start State</name> <name>Start State</name>
<t> <t>
A node implementing MSF SHOULD implement the Constrained Joi A node implementing MSF <bcp14>SHOULD</bcp14> implement the
n Protocol (CoJP) for 6TiSCH <xref target="I-D.ietf-6tisch-minimal-security" for Constrained Join Protocol (CoJP) for 6TiSCH <xref target="RFC9031" format="defau
mat="default"/>. lt"/>.
As a corollary, this means that a pledge, before being switc As a corollary, this means that a pledge, before being switc
hed on, may be pre-configured with the Pre-Shared Key (PSK) for joining, as well hed on, may be preconfigured with the Pre-Shared Key (PSK) for joining, as well
as any other configuration detailed in (<xref target="I-D.ietf-6tisch-minimal-s as any other configuration detailed in <xref target="RFC9031" format="default"/>
ecurity" format="default"/>). .
This is not necessary if the node implements a security solu This is not necessary if the node implements a security solu
tion not based on PSKs, such as (<xref target="I-D.ietf-6tisch-dtsecurity-zeroto tion that is not based on PSKs, such as <xref target="I-D.ietf-6tisch-dtsecurity
uch-join" format="default"/>). -zerotouch-join" format="default"/>.
</t> </t>
</section> </section>
<section anchor="sec_frequency" numbered="true" toc="default"> <section anchor="sec_frequency" numbered="true" toc="default">
<name>Step 1 - Choosing Frequency</name> <name>Step 1 - Choosing Frequency</name>
<t> <t>
When switched on, the pledge randomly chooses a frequency fr om the channels that the network cycles amongst, and starts listening for EBs on that frequency. When switched on, the pledge randomly chooses a frequency fr om the channels through which the network cycles and starts listening for EBs on that frequency.
</t> </t>
</section> </section>
<section anchor="sec_ebs" numbered="true" toc="default"> <section anchor="sec_ebs" numbered="true" toc="default">
<name>Step 2 - Receiving EBs</name> <name>Step 2 - Receiving EBs</name>
<t> <t>
Upon receiving the first EB, the pledge continues listening for additional EBs to learn: Upon receiving the first EB, the pledge continues listening for additional EBs to learn:
</t> </t>
<ol spacing="compact" type="1"> <ol spacing="normal" type="1">
<li>the number of neighbors N in its vicinity</li> <li>the number of neighbors N in its vicinity, and </li>
<li>which neighbor to choose as a Join Proxy (JP) for the jo <li>which neighbor to choose as a Join Proxy (JP) for the jo
ining process</li> ining process.</li>
</ol> </ol>
<t> <t>
After having received the first EB, a node MAY keep listenin g for at most MAX_EB_DELAY seconds or until it has received EBs from NUM_NEIGHBO URS_TO_WAIT distinct neighbors. After having received the first EB, a node <bcp14>MAY</bcp14 > keep listening for at most MAX_EB_DELAY seconds or until it has received EBs f rom NUM_NEIGHBOURS_TO_WAIT distinct neighbors.
This behavior is defined in <xref target="RFC8180" format="d efault"/>. This behavior is defined in <xref target="RFC8180" format="d efault"/>.
</t> </t>
<t> <t>
During this step, the pledge only gets synchronized when it During this step, the pledge only gets synchronized when it
received enough EB from the network it wishes to join. has received enough EB from the network it wishes to join.
How to decide whether an EB originates from a node from the How to decide whether an EB originates from a node from the
network it wishes to join is implementation-specific, but MAY involve filtering network it wishes to join is implementation-specific, but <bcp14>MAY</bcp14> inv
EBs by olve filtering EBs by
the PAN ID field it contains, the PANID field it contains,
the presence and contents of the IE defined in <xref target= the presence and contents of the Information Element (IE) de
"I-D.ietf-6tisch-enrollment-enhanced-beacon" format="default"/>, or fined in <xref target="RFC9032" format="default"/>, or
the key used to authenticate it. the key used to authenticate it.
</t> </t>
<t> <t>
The decision of which neighbor to use as a JP is implementat ion-specific, and discussed in <xref target="I-D.ietf-6tisch-minimal-security" f ormat="default"/>. The decision of which neighbor to use as a JP is implementat ion-specific and is discussed in <xref target="RFC9031" format="default"/>.
</t> </t>
</section> </section>
<section anchor="sec_join" numbered="true" toc="default"> <section anchor="sec_join" numbered="true" toc="default">
<name>Step 3 - Setting up Autonomous Cells for the Join Process< /name> <name>Step 3 - Setting up Autonomous Cells for the Join Process< /name>
<t> <t>
After having selected a JP, a node generates a Join Request and installs an AutoTxCell to the JP. After having selected a JP, a node generates a Join Request and installs an AutoTxCell to the JP.
The Join Request is then sent by the pledge to its selected JP over the AutoTxCell. The Join Request is then sent by the pledge to its selected JP over the AutoTxCell.
The AutoTxCell is removed by the pledge when the Join Reques t is sent out. The AutoTxCell is removed by the pledge when the Join Reques t is sent out.
The JP receives the Join Request through its AutoRxCell. The JP receives the Join Request through its AutoRxCell.
Then it forwards the Join Request to the join registrar/coor dinator (JRC), possibly over multiple hops, over the 6P negotiated Tx cells. Then it forwards the Join Request to the Join Registrar/Coor dinator (JRC), possibly over multiple hops, over the 6P negotiated Tx cells.
Similarly, the JRC sends the Join Response to the JP, possib ly over multiple hops, over AutoTxCells or the 6P negotiated Tx cells. Similarly, the JRC sends the Join Response to the JP, possib ly over multiple hops, over AutoTxCells or the 6P negotiated Tx cells.
When the JP received the Join Response from the JRC, it inst alls an AutoTxCell to the pledge and sends that Join Response to the pledge over AutoTxCell. When the JP receives the Join Response from the JRC, it inst alls an AutoTxCell to the pledge and sends that Join Response to the pledge over AutoTxCell.
The AutoTxCell is removed by the JP when the Join Response i s sent out. The AutoTxCell is removed by the JP when the Join Response i s sent out.
The pledge receives the Join Response from its AutoRxCell, t hereby learns the keying material used in the network, as well as other configur ation settings, and becomes a "joined node". The pledge receives the Join Response from its AutoRxCell, t hereby learns the keying material used in the network, as well as other configur ation settings, and becomes a "joined node".
</t> </t>
<t> <t>
When 6LoWPAN Neighbor Discovery (<xref target="RFC8505" form When 6LoWPAN Neighbor Discovery (ND) <xref target="RFC8505"
at="default"/>) (ND) is implemented, the unicast packets used by ND are sent on format="default"/> is implemented, the unicast packets used by ND are sent on th
the AutoTxCell. e AutoTxCell.
The specific process how the ND works during the Join proces The specific process how the ND works during the join proces
s is detailed in <xref target="I-D.ietf-6tisch-architecture" format="default"/>. s is detailed in <xref target="RFC9030" format="default"/>.
</t> </t>
</section> </section>
<section anchor="sec_rank" numbered="true" toc="default"> <section anchor="sec_rank" numbered="true" toc="default">
<name>Step 4 - Acquiring a RPL Rank</name> <name>Step 4 - Acquiring a RPL Rank</name>
<t> <t>
Per <xref target="RFC6550" format="default"/>, the joined no de Per <xref target="RFC6550" format="default"/>, the joined no de
receives DIOs, receives DIOs,
computes its own Rank, and computes its own Rank, and
selects a routing parent. selects a routing parent.
</t> </t>
</section> </section>
<section anchor="sec_negotiated_cells" numbered="true" toc="default" > <section anchor="sec_negotiated_cells" numbered="true" toc="default" >
<name>Step 5 - Setting up first Tx negotiated Cells</name> <name>Step 5 - Setting up First Tx Negotiated Cells</name>
<t> <t>
Once it has selected a routing parent, the joined node MUST generate a 6P ADD Request and install an AutoTxCell to that parent. Once it has selected a routing parent, the joined node <bcp1 4>MUST</bcp14> generate a 6P ADD Request and install an AutoTxCell to that paren t.
The 6P ADD Request is sent out through the AutoTxCell, conta ining the following fields: The 6P ADD Request is sent out through the AutoTxCell, conta ining the following fields:
</t> </t>
<ul spacing="compact"> <dl newline="false">
<li>CellOptions: set to TX=1,RX=0,SHARED=0</li> <dt>CellOptions:</dt><dd>Set to TX=1, RX=0, SHARED=0.</dd>
<li>NumCells: set to 1</li> <dt>NumCells:</dt><dd>Set to 1.</dd>
<li>CellList: at least 5 cells, chosen according to <xref ta <dt>CellList:</dt><dd>At least 5 cells, chosen according to
rget="sec_celllist" format="default"/></li> <xref target="sec_celllist" format="default"/>.</dd>
</ul> </dl>
<t> <t>
The joined node removes the AutoTxCell to the selected paren t when the 6P Request is sent out. The joined node removes the AutoTxCell to the selected paren t when the 6P Request is sent out.
That parent receives the 6P ADD Request from its AutoRxCell. That parent receives the 6P ADD Request from its AutoRxCell.
Then it generates a 6P ADD Response and installs an AutoTxCe ll to the joined node. Then it generates a 6P ADD Response and installs an AutoTxCe ll to the joined node.
When the parent sends out the 6P ADD Response, it MUST remov When the parent sends out the 6P ADD Response, it <bcp14>MUS
e that AutoTxCell. T</bcp14> remove that AutoTxCell.
The joined node receives the 6P ADD Response from its AutoRx The joined node receives the 6P ADD Response from its AutoRx
Cell and completes the 6P transaction. Cell and completes the 6P Transaction.
In case the 6P ADD transaction failed, the node MUST issue a In the case that the 6P ADD transaction failed, the node <bc
nother 6P ADD Request and repeat until the Tx cell is installed to the parent. p14>MUST</bcp14> issue another 6P ADD Request and repeat until the Tx cell is in
stalled to the parent.
</t> </t>
</section> </section>
<section anchor="sec_eb_dio" numbered="true" toc="default"> <section anchor="sec_eb_dio" numbered="true" toc="default">
<name>Step 6 - Send EBs and DIOs</name> <name>Step 6 - Sending EBs and DIOs</name>
<t> <t>
The node starts sending EBs and DIOs on the minimal cell, wh ile following the transmit rules for broadcast frames from <xref target="sec_min imal" format="default"/>. The node starts sending EBs and DIOs on the minimal cell, wh ile following the transmit rules for broadcast frames from <xref target="sec_min imal" format="default"/>.
</t> </t>
</section> </section>
<section anchor="sec_end_state" numbered="true" toc="default"> <section anchor="sec_end_state" numbered="true" toc="default">
<name>End State</name> <name>End State</name>
<t> <t>
For a new node, the end state of the joining process is: At the end state of the joining process, a new node:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>it is synchronized to the network</li> <li>is synchronized to the network,</li>
<li>it is using the link-layer keying material it learned th <li>is using the link-layer keying material it learned throu
rough the secure joining process</li> gh the secure joining process,</li>
<li>it has selected one neighbor as its routing parent</li> <li>has selected one neighbor as its routing parent,</li>
<li>it has one AutoRxCell</li> <li>has one AutoRxCell,</li>
<li>it has one negotiated Tx cell to the selected parent</li <li>has one negotiated Tx cell to the selected parent,</li>
> <li>starts to send DIOs, potentially serving as a router for
<li>it starts to send DIOs, potentially serving as a router other nodes' traffic, and</li>
for other nodes' traffic</li> <li>starts to send EBs, potentially serving as a JP for new
<li>it starts to send EBs, potentially serving as a JP for pledges.</li>
new pledges</li>
</ul> </ul>
</section> </section>
</section> </section>
<section anchor="sec_add_delete" numbered="true" toc="default"> <section anchor="sec_add_delete" numbered="true" toc="default">
<name>Rules for Adding/Deleting Cells</name> <name>Rules for Adding and Deleting Cells</name>
<t> <t>
Once a node has joined the 6TiSCH network, it adds/deletes/reloc ates cells with the selected parent for three reasons: Once a node has joined the 6TiSCH network, it adds/deletes/reloc ates cells with the selected parent for three reasons:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>to match the link-layer resources to the traffic between the <li>to match the link-layer resources to the traffic between the
node and the selected parent (<xref target="sec_traffic" format="default"/>)</l node and the selected parent (<xref target="sec_traffic" format="default"/>),</
i> li>
<li>to handle switching parent or(<xref target="sec_switching_pa <li>to handle switching the parent (<xref target="sec_switching_
rent" format="default"/>)</li> parent" format="default"/>), or</li>
<li>to handle a schedule collision (<xref target="sec_collision" <li>to handle a schedule collision (<xref target="sec_collision"
format="default"/>)</li> format="default"/>).</li>
</ul> </ul>
<t> <t>
Those cells are called 'negotiated cells' as they are scheduled These cells are called "negotiated cells" as they are scheduled
through 6P, negotiated with the node's parent. through 6P and negotiated with the node's parent.
Without specific declaration, all cells mentioned in this sectio Without specific declaration, all cells mentioned in this sectio
n are negotiated cells and they are installed at Slotframe 2. n are negotiated cells, and they are installed at Slotframe 2.
</t> </t>
<section anchor="sec_traffic" numbered="true" toc="default"> <section anchor="sec_traffic" numbered="true" toc="default">
<name>Adapting to Traffic</name> <name>Adapting to Traffic</name>
<t> <t>
A node implementing MSF MUST implement the behavior describe d in this section. A node implementing MSF <bcp14>MUST</bcp14> implement the be havior described in this section.
</t> </t>
<t> <t>
The goal of MSF is to manage the communication schedule in t he 6TiSCH schedule in a distributed manner. The goal of MSF is to manage the communication schedule in t he 6TiSCH schedule in a distributed manner.
For a node, this translates into monitoring the current usag e of the cells it has to one of its neighbors, in most cases to the selected par ent. For a node, this translates into monitoring the current usag e of the cells it has to one of its neighbors, in most cases to the selected par ent.
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li> <li>
If the node determines that the number of link-layer fra mes it is attempting to exchange with the selected parent per unit of time is la rger than the capacity offered by the TSCH negotiated cells it has scheduled wit h it, the node issues a 6P ADD command to that parent to add cells to the TSCH s chedule. If the node determines that the number of link-layer fra mes it is attempting to exchange with the selected parent per unit of time is la rger than the capacity offered by the TSCH negotiated cells it has scheduled wit h it, the node issues a 6P ADD command to that parent to add cells to the TSCH s chedule.
</li> </li>
<li> <li>
If the traffic is lower than the capacity, the node issu es a 6P DELETE command to that parent to delete cells from the TSCH schedule. If the traffic is lower than the capacity, the node issu es a 6P DELETE command to that parent to delete cells from the TSCH schedule.
</li> </li>
</ul> </ul>
<t> <t>
The node MUST maintain two separate pairs of the following c ounters for the selected parent, The node <bcp14>MUST</bcp14> maintain two separate pairs of the following counters for the selected parent:
one for the negotiated Tx cells to that parent and one for the negotiated Tx cells to that parent and
one for the negotiated Rx cells to that parent. one for the negotiated Rx cells to that parent.
</t> </t>
<dl newline="false" spacing="compact" indent="4"> <dl newline="false">
<dt>NumCellsElapsed :</dt> <dt>NumCellsElapsed:</dt>
<dd> <dd>
Counts the number of negotiated cells that have elapsed since the counter was initialized. Counts the number of negotiated cells that have elapsed since the counter was initialized.
This counter is initialized at 0. This counter is initialized at 0.
When the current cell is declared as a negotiated cell t o the selected parent, NumCellsElapsed is incremented by exactly 1, regardless o f whether the cell is used to transmit/receive a frame. When the current cell is declared as a negotiated cell t o the selected parent, NumCellsElapsed is incremented by exactly 1, regardless o f whether the cell is used to transmit or receive a frame.
</dd> </dd>
<dt>NumCellsUsed:</dt> <dt>NumCellsUsed:</dt>
<dd> <dd>
<t> <t>
Counts the number of negotiated cells that have been used. Counts the number of negotiated cells that have been used.
This counter is initialized at 0. This counter is initialized at 0.
NumCellsUsed is incremented by exactly 1 when, durin g a negotiated cell to the selected parent, either of the following happens: NumCellsUsed is incremented by exactly 1 when, durin g a negotiated cell to the selected parent, either of the following happens:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li> <li>
The node sends a frame to the parent. The node sends a frame to the parent.
The counter increments regardless of whether a l ink-layer acknowledgment was received or not. The counter increments regardless of whether a l ink-layer acknowledgment was received or not.
</li> </li>
<li> <li>
The node receives a valid frame from the parent. The node receives a valid frame from the parent.
The counter increments only when the frame is a valid IEEE802.15.4 frame. The counter increments only when a valid frame p er <xref target="IEEE802154" format="default"/> is received by the node from its parent.
</li> </li>
</ul> </ul>
</dd> </dd>
</dl> </dl>
<t> <t>
The cell option of cells listed in CellList in 6P Request fr The cell option of cells listed in CellList in a 6P Request
ame SHOULD be either (Tx=1, Rx=0) only or (Tx=0, Rx=1) only. frame <bcp14>SHOULD</bcp14> be either (Tx=1, Rx=0) only or (Tx=0, Rx=1) only.
Both NumCellsElapsed and NumCellsUsed counters can be used f Both NumCellsElapsed and NumCellsUsed counters can be used f
or both type of negotiated cells. or both types of negotiated cells.
</t> </t>
<t> <t>
As there is no negotiated Rx Cell installed at initial time, the AutoRxCell is taken into account as well for downstream traffic adaptation. As there is no negotiated Rx cell installed at initial time, the AutoRxCell is taken into account as well for downstream traffic adaptation.
In this case: In this case:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li> <li>
NumCellsElapsed is incremented by exactly 1 when the cur rent cell is AutoRxCell. NumCellsElapsed is incremented by exactly 1 when the cur rent cell is AutoRxCell.
</li> </li>
<li> <li>
NumCellsUsed is incremented by exactly 1 when the node r eceives a frame from the selected parent on AutoRxCell. NumCellsUsed is incremented by exactly 1 when the node r eceives a frame from the selected parent on AutoRxCell.
</li> </li>
</ul> </ul>
<t> <t>
Implementors MAY choose to create the same counters for each neighbor, and add them as additional statistics in the neighbor table. Implementors <bcp14>MAY</bcp14> choose to create the same co unters for each neighbor and add them as additional statistics in the neighbor t able.
</t> </t>
<t> <t>
The counters are used as follows: The counters are used as follows:
</t> </t>
<ol spacing="compact" type="1"> <ol spacing="normal" type="1">
<li> <li>
Both NumCellsElapsed and NumCellsUsed are initialized to 0 when the node boots. Both NumCellsElapsed and NumCellsUsed are initialized to 0 when the node boots.
</li> </li>
<li> <li anchor="counter_step2">
<t> <t>
When the value of NumCellsElapsed reaches MAX_NUM_CE LLS: When the value of NumCellsElapsed reaches MAX_NUM_CE LLS:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>If NumCellsUsed &gt; LIM_NUMCELLSUSED_HIGH, trig <li>If NumCellsUsed is greater than LIM_NUMCELLSUSED
ger 6P to add a single cell to the selected parent</li> _HIGH, trigger 6P to add a single cell to the selected parent.</li>
<li>If NumCellsUsed &lt; LIM_NUMCELLSUSED_LOW, trig <li>If NumCellsUsed is less than LIM_NUMCELLSUSED_LO
ger 6P to remove a single cell to the selected parent</li> W, trigger 6P to remove a single cell to the selected parent.</li>
<li>Reset both NumCellsElapsed and NumCellsUsed to <li>Reset both NumCellsElapsed and NumCellsUsed to 0
0 and go to step 2.</li> and restart <xref target="counter_step2" format="none">#2</xref>.</li>
</ul> </ul>
</li> </li>
</ol> </ol>
<t> <t>
The value of MAX_NUM_CELLS is chosen according to the traffi c type of the network. The value of MAX_NUM_CELLS is chosen according to the traffi c type of the network.
Generally speaking, the larger the value MAX_NUM_CELLS is, t Generally speaking, the larger the value MAX_NUM_CELLS is, t
he more accurate the cell usage is calculated. he more accurately the cell usage is calculated.
The 6P traffic overhead using a larger value of MAX_NUM_CELL By using a larger value of MAX_NUM_CELLS, the 6P traffic ove
S could be reduced as well. rhead could be reduced as well.
Meanwhile, the latency won't increase much by using a larger value of MAX_NUM_CELLS for periodic traffic type. Meanwhile, the latency won't increase much by using a larger value of MAX_NUM_CELLS for periodic traffic type.
For bursty traffic, larger value of MAX_NUM_CELLS indeed int For bursty traffic, a larger value of MAX_NUM_CELLS indeed i
roduces higher latency. ntroduces higher latency.
The latency caused by slight changes of traffic load can be The latency caused by slight changes of traffic load can be
absolved by the additional scheduled cells. alleviated by the additional scheduled cells.
In this sense, MSF is a scheduling function trading latency In this sense, MSF is a Scheduling Function that trades late
with energy by scheduling more cells than needed. ncy with energy by scheduling more cells than needed.
Setting MAX_NUM_CELLS to a value at least 4x of the recent m Setting MAX_NUM_CELLS to a value at least four times the rec
aximum number of cells used in a slot frame is RECOMMENDED. ent maximum number of cells used in a slotframe is <bcp14>RECOMMENDED</bcp14>.
For example, a 2 packets/slotframe traffic load results an a For example, a two packets/slotframe traffic load results in
verage 4 cells scheduled (2 cells are used), using at least the value of double an average of four cells scheduled (two cells are used), using at least the val
number of scheduled cells (which is 8) as MAX_NUM_CELLS gives a good resolution ue of double the number of scheduled cells (which is eight) as MAX_NUM_CELLS giv
on cell usage calculation. es a good resolution on the cell usage calculation.
</t> </t>
<t> <t>
In case that a node booted or disappeared from the network, In the case that a node has booted or has disappeared from t
the cell reserved at the selected parent may be kept in the schedule forever. he network, the cell reserved at the selected parent may be kept in the schedule
A clean-up mechanism MUST be provided to resolve this issue. forever.
The clean-up mechanism is implementation-specific. A cleanup mechanism <bcp14>MUST</bcp14> be provided to resol
The goal is to confirm those negotiated cells are not used a ve this issue.
nymore by the associated neighbors and remove them from the schedule. The cleanup mechanism is implementation-specific.
The goal is to confirm that those negotiated cells are not u
sed anymore by the associated neighbors and remove them from the schedule.
</t> </t>
</section> </section>
<section anchor="sec_switching_parent" numbered="true" toc="default" > <section anchor="sec_switching_parent" numbered="true" toc="default" >
<name>Switching Parent</name> <name>Switching Parent</name>
<t> <t>
A node implementing MSF SHOULD implement the behavior descri bed in this section. A node implementing MSF <bcp14>SHOULD</bcp14> implement the behavior described in this section.
</t> </t>
<t> <t>
Part of its normal operation, the RPL routing protocol can h As part of its normal operation, RPL can have a node switch
ave a node switch parent. parent.
The procedure for switching from the old parent to the new p The procedure for switching from the old parent to the new p
arent is: arent is the following:
</t> </t>
<ol spacing="compact" type="1"> <ol spacing="normal" type="1">
<li>the node counts the number of negotiated cells it has pe <li>The node counts the number of negotiated cells it has pe
r slotframe to the old parent</li> r slotframe to the old parent.</li>
<li>the node triggers one or more 6P ADD commands to schedul <li>The node triggers one or more 6P ADD commands to schedul
e the same number of negotiated cells with same cell options to the new parent</ e the same number of negotiated cells with same cell options to the new parent.<
li> /li>
<li>when that successfully completes, the node issues a 6P C <li>When that successfully completes, the node issues a 6P C
LEAR command to its old parent</li> LEAR command to its old parent.</li>
</ol> </ol>
<t> <t>
For what type of negotiated cell should be installed first, it depends on which traffic has the higher priority, upstream or downstream, whi ch is application-specific and out-of-scope of MSF. The type of negotiated cell that should be installed first de pends on which traffic has the higher priority, upstream or downstream, which is application-specific and out of scope of MSF.
</t> </t>
</section> </section>
<section anchor="sec_collision" numbered="true" toc="default"> <section anchor="sec_collision" numbered="true" toc="default">
<name>Handling Schedule Collisions</name> <name>Handling Schedule Collisions</name>
<t> <t>
A node implementing MSF SHOULD implement the behavior descri A node implementing MSF <bcp14>SHOULD</bcp14> implement the
bed in this section. behavior described in this section.
Other schedule collisions handling algorithm can be an alter Other algorithms for handling schedule collisions can be an
native of the algorithm proposed in this section. alternative to the algorithm proposed in this section.
</t> </t>
<t> <t>
Since scheduling is entirely distributed, there is a non-zer o probability that two pairs of nearby neighbor nodes schedule a negotiated cell at the same [slotOffset,channelOffset] location in the TSCH schedule. Since scheduling is entirely distributed, there is a nonzero probability that two pairs of nearby neighbor nodes schedule a negotiated cell at the same [slotOffset,channelOffset] location in the TSCH schedule.
In that case, data exchanged by the two pairs may collide on that cell. In that case, data exchanged by the two pairs may collide on that cell.
We call this case a "schedule collision". We call this case a "schedule collision".
</t> </t>
<t> <t>
The node MUST maintain the following counters for each negot iated Tx cell to the selected parent: The node <bcp14>MUST</bcp14> maintain the following counters for each negotiated Tx cell to the selected parent:
</t> </t>
<dl newline="false" spacing="compact" indent="4"> <dl newline="false">
<dt>NumTx:</dt> <dt>NumTx:</dt>
<dd> <dd>
Counts the number of transmission attempts on that cell. Counts the number of transmission attempts on that cell.
Each time the node attempts to transmit a frame on that cell, NumTx is incremented by exactly 1. Each time the node attempts to transmit a frame on that cell, NumTx is incremented by exactly 1.
</dd> </dd>
<dt>NumTxAck:</dt> <dt>NumTxAck:</dt>
<dd> <dd>
Counts the number of successful transmission attempts on that cell. Counts the number of successful transmission attempts on that cell.
Each time the node receives an acknowledgment for a tran smission attempt, NumTxAck is incremented by exactly 1. Each time the node receives an acknowledgment for a tran smission attempt, NumTxAck is incremented by exactly 1.
</dd> </dd>
</dl> </dl>
<t> <t>
Since both NumTx and NumTxAck are initialized to 0, we neces Since both NumTx and NumTxAck are initialized to 0, we neces
sarily have NumTxAck &lt;= NumTx. sarily have NumTxAck less than or equal to NumTx.
We call Packet Delivery Ratio (PDR) the ratio NumTxAck/NumTx We call Packet Delivery Ratio (PDR) the ratio NumTxAck/NumTx
; and represent it as a percentage. and represent it as a percentage.
A cell with PDR=50% means that half of the frames transmitte A cell with a PDR equal to 50% means that half of the frames
d are not acknowledged. transmitted are not acknowledged.
</t> </t>
<t> <t>
Each time the node switches parent (or during the join proce Each time the node switches parent (or during the join proce
ss when the node selects a parent for the first time), both NumTx and NumTxAck M ss when the node selects a parent for the first time), both NumTx and NumTxAck <
UST be reset to 0. bcp14>MUST</bcp14> be reset to 0.
They increment over time, as the schedule is executed and th They increment over time, as the schedule is executed, and t
e node sends frames to that parent. he node sends frames to that parent.
When NumTx reaches MAX_NUMTX, both NumTx and NumTxAck MUST b When NumTx reaches MAX_NUMTX, both NumTx and NumTxAck <bcp14
e divided by 2. >MUST</bcp14> be divided by 2.
MAX_NUMTX needs to be a power of two to avoid division error . MAX_NUMTX needs to be a power of two to avoid division error .
For example, when MAX_NUMTX is set to 256, from NumTx=255 an For example, when MAX_NUMTX is set to 256, and NumTx=255 and
d NumTxAck=127, the counters become NumTx=128 and NumTxAck=64 if one frame is se NumTxAck=127, the counters become NumTx=128 and NumTxAck=64 if one frame is sen
nt to the parent with an Acknowledgment received. t to the parent with an acknowledgment received.
This operation does not change the value of the PDR, but all This operation does not change the value of the PDR but allo
ows the counters to keep incrementing. ws the counters to keep incrementing.
The value of MAX_NUMTX is implementation-specific. The value of MAX_NUMTX is implementation-specific.
</t> </t>
<t> <t>
The key for detecting a schedule collision is that, if a nod e has several cells to the selected parent, all cells should exhibit the same PD R. The key for detecting a schedule collision is that, if a nod e has several cells to the selected parent, all cells should exhibit the same PD R.
A cell which exhibits a PDR significantly lower than the oth ers indicates than there are collisions on that cell. A cell that exhibits a PDR significantly lower than the othe rs indicates that there are collisions on that cell.
</t> </t>
<t> <t>
Every HOUSEKEEPINGCOLLISION_PERIOD, the node executes the fo llowing steps: Every HOUSEKEEPINGCOLLISION_PERIOD, the node executes the fo llowing steps:
</t> </t>
<ol spacing="compact" type="1"> <ol spacing="normal">
<li> <li>
It computes, for each negotiated Tx cell with the parent (not for the autonomous cell), that cell's PDR. It computes, for each negotiated Tx cell with the parent (not for the autonomous cell), that cell's PDR.
</li> </li>
<li> <li>
Any cell that hasn't yet had NumTx divided by 2 since it was last reset is skipped in steps 3 and 4. Any cell that hasn't yet had NumTx divided by 2 since it was last reset is skipped in steps 3 and 4.
This avoids triggering cell relocation when the values o f NumTx and NumTxAck are not statistically significant yet. This avoids triggering cell relocation when the values o f NumTx and NumTxAck are not statistically significant yet.
</li> </li>
<li> <li>
It identifies the cell with the highest PDR. It identifies the cell with the highest PDR.
</li> </li>
skipping to change at line 581 skipping to change at line 594
For any other cell, it compares its PDR against that of the cell with the highest PDR. For any other cell, it compares its PDR against that of the cell with the highest PDR.
If the subtraction difference between the PDR of the cel l and the highest PDR is larger than RELOCATE_PDRTHRES, it triggers the relocati on of that cell using a 6P RELOCATE command. If the subtraction difference between the PDR of the cel l and the highest PDR is larger than RELOCATE_PDRTHRES, it triggers the relocati on of that cell using a 6P RELOCATE command.
</li> </li>
</ol> </ol>
<t> <t>
The RELOCATION for negotiated Rx cells is not supported by M SF. The RELOCATION for negotiated Rx cells is not supported by M SF.
</t> </t>
</section> </section>
</section> </section>
<section anchor="sec_signal" numbered="true" toc="default"> <section anchor="sec_signal" numbered="true" toc="default">
<name>6P SIGNAL command</name> <name>6P SIGNAL Command</name>
<t> <t>
The 6P SIGNAL command is not used by MSF. The 6P SIGNAL command is not used by MSF.
</t> </t>
</section> </section>
<section anchor="sec_sfid" numbered="true" toc="default"> <section anchor="sec_sfid" numbered="true" toc="default">
<name>Scheduling Function Identifier</name> <name>Scheduling Function Identifier</name>
<t> <t>
The Scheduling Function Identifier (SFID) of MSF is IANA_6TISCH_ The Scheduling Function Identifier (SFID) of MSF is 0.
SFID_MSF. How the value of 0 was chosen is described in <xref target="sec_
How the value of IANA_6TISCH_SFID_MSF is chosen is described in iana" format="default"/>.
<xref target="sec_iana" format="default"/>.
</t> </t>
</section> </section>
<section anchor="sec_celllist" numbered="true" toc="default"> <section anchor="sec_celllist" numbered="true" toc="default">
<name>Rules for CellList</name> <name>Rules for CellList</name>
<t> <t>
MSF uses 2-step 6P Transactions exclusively. MSF uses two-step 6P Transactions exclusively.
6P transactions are only initiated by a node towards its parent. 6P Transactions are only initiated by a node towards its parent.
As a result, the cells to put in the CellList of a 6P ADD comman As a result, the cells to put in the CellList of a 6P ADD comman
d, and in the candidate CellList of a RELOCATE command, are chosen by the node i d, and in the candidate CellList of a RELOCATE command, are chosen by the node i
nitiating the 6P transaction. nitiating the 6P Transaction.
In both cases, the same rules apply: In both cases, the same rules apply:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>The CellList is RECOMMENDED to have 5 or more cells.</li> <li>The CellList is <bcp14>RECOMMENDED</bcp14> to have five or m
<li>Each cell in the CellList MUST have a different slotOffset v ore cells.</li>
alue.</li> <li>Each cell in the CellList <bcp14>MUST</bcp14> have a differe
<li>For each cell in the CellList, the node MUST NOT have any sc nt slotOffset value.</li>
heduled cell on the same slotOffset.</li> <li>For each cell in the CellList, the node <bcp14>MUST NOT</bcp
<li>The slotOffset value of any cell in the CellList MUST NOT be 14> have any scheduled cell on the same slotOffset.</li>
the same as the slotOffset of the minimal cell (slotOffset=0).</li> <li>The slotOffset value of any cell in the CellList <bcp14>MUST
<li>The slotOffset of a cell in the CellList SHOULD be random NOT</bcp14> be the same as the slotOffset of the minimal cell (slotOffset=0).</
ly and uniformly chosen among all the slotOffset values that satisfy the restric li>
tions above.</li> <li>The slotOffset of a cell in the CellList <bcp14>SHOULD</b
<li>The channelOffset of a cell in the CellList SHOULD be random cp14> be randomly and uniformly chosen among all the slotOffset values that sati
ly and uniformly chosen in [0..numFrequencies], where numFrequencies represents sfy the restrictions above.</li>
the number of frequencies a node can communicate on.</li> <li>The channelOffset of a cell in the CellList <bcp14>SHOULD</b
cp14> be randomly and uniformly chosen from [0..numFrequencies], where numFreque
ncies represents the number of frequencies a node can communicate on.</li>
</ul> </ul>
<t> <t>
As a consequence of random cell selection, there is a non-zero c As a consequence of random cell selection, there is a nonzero ch
hance that nodes in the vicinity installed cells with same slotOffset and channe ance that nodes in the vicinity have installed cells with same slotOffset and ch
lOffset. annelOffset.
An implementer MAY implement a strategy to monitor the candidate An implementer <bcp14>MAY</bcp14> implement a strategy to monito
cells before adding them in CellList to avoid collision. r the candidate cells before adding them in CellList to avoid collision.
For example, a node MAY maintain a candidate cell pool for the C For example, a node <bcp14>MAY</bcp14> maintain a candidate cell
ellList. pool for the CellList.
The candidate cells in the pool are pre-configured as Rx cells t The candidate cells in the pool are preconfigured as Rx cells to
o promiscuously listen to detect transmissions on those cells. promiscuously listen to detect transmissions on those cells.
If IEEE802.15.4 transmissions are observed on one cell over mult If transmissions that rely on <xref target="IEEE802154" format="
iple iterations of the schedule, that cell is probably used by a TSCH neighbor. default"/> are observed on one cell over multiple iterations of the schedule, th
It is moved out from the pool and a new cell is selected as a ca at cell is probably used by a TSCH neighbor.
ndidate cell. It is moved out from the pool, and a new cell is selected as a c
andidate cell.
The cells in CellList are picked from the candidate pool directl y when required. The cells in CellList are picked from the candidate pool directl y when required.
</t> </t>
</section> </section>
<section anchor="sec_timeout" numbered="true" toc="default"> <section anchor="sec_timeout" numbered="true" toc="default">
<name>6P Timeout Value</name> <name>6P Timeout Value</name>
<t> <t>
The timeout value is calculated for the worst case that a 6P res ponse is received, which means the 6P response is sent out successfully at the v ery latest retransmission. The timeout value is calculated for the worst case that a 6P res ponse is received, which means the 6P response is sent out successfully at the v ery latest retransmission.
And for each retransmission, it backs-off with largest value. And for each retransmission, it backs off with largest value.
Hence the 6P timeout value is calculated as ((2^MAXBE)-1)*MAXRET Hence the 6P timeout value is calculated as ((2<sup>MAXBE</sup>)
RIES*SLOTFRAME_LENGTH, where: - 1) * MAXRETRIES * SLOTFRAME_LENGTH, where:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>MAXBE, defined in IEEE802.15.4, is the maximum backoff expo <li>MAXBE, defined in <xref target="IEEE802154" format="default"
nent used</li> />, is the maximum backoff exponent used.</li>
<li>MAXRETRIES, defined in IEEE802.15.4, is the maximum retransm <li>MAXRETRIES, defined in <xref target="IEEE802154" format="def
ission times</li> ault"/>, is the maximum retransmission times.</li>
<li>SLOTFRAME_LENGTH represents the length of slotframe</li> <li>SLOTFRAME_LENGTH represents the length of slotframe.</li>
</ul> </ul>
</section> </section>
<section anchor="sec_ordering" numbered="true" toc="default"> <section anchor="sec_ordering" numbered="true" toc="default">
<name>Rule for Ordering Cells</name> <name>Rule for Ordering Cells</name>
<t> <t>
Cells are ordered slotOffset first, channelOffset second. Cells are ordered by slotOffset first, channelOffset second.
</t> </t>
<t> <t>
The following sequence is correctly ordered (each element repres ents the [slottOffset,channelOffset] of a cell in the schedule): The following sequence is correctly ordered (each element repres ents the [slotOffset,channelOffset] of a cell in the schedule):
</t> </t>
<t> <t>
[1,3],[1,4],[2,0],[5,3],[6,0],[6,3],[7,9] [1,3],[1,4],[2,0],[5,3],[6,0],[6,3],[7,9]
</t> </t>
</section> </section>
<section anchor="sec_metadata" numbered="true" toc="default"> <section anchor="sec_metadata" numbered="true" toc="default">
<name>Meaning of the Metadata Field</name> <name>Meaning of the Metadata Field</name>
<t> <t>
The Metadata field is not used by MSF. The Metadata field is not used by MSF.
</t> </t>
</section> </section>
<section anchor="sec_error" numbered="true" toc="default"> <section anchor="sec_error" numbered="true" toc="default">
<name>6P Error Handling</name> <name>6P Error Handling</name>
<t> <t>
Section 6.2.4 of <xref target="RFC8480" format="default"/> lists <xref target="RFC8480" section="6.2.4" sectionFormat="of"/> list
the 6P Return Codes. s the 6P return codes.
<xref target="tab_error" format="default"/> lists the same error <xref target="tab_error" format="default"/> lists the same error
codes, and the behavior a node implementing MSF SHOULD follow. codes and the behavior a node implementing MSF <bcp14>SHOULD</bcp14> follow.
</t> </t>
<figure anchor="tab_error"> <table anchor="tab_error">
<name>Recommended behavior for each 6P Error Code.</name> <name>Recommended Behavior for Each 6P Error Code</name>
<artwork name="" type="" align="left" alt=""><![CDATA[
+-----------------+----------------------+ <thead>
| Code | RECOMMENDED behavior | <tr>
+-----------------+----------------------+
| RC_SUCCESS | nothing | <th>Code</th>
| RC_EOL | nothing | <th><bcp14>RECOMMENDED</bcp14> Behavior</th>
| RC_ERR | quarantine | </tr>
| RC_RESET | quarantine | </thead>
| RC_ERR_VERSION | quarantine | <tbody>
| RC_ERR_SFID | quarantine | <tr>
| RC_ERR_SEQNUM | clear | <td> RC_SUCCESS
| RC_ERR_CELLLIST | clear | </td><td> nothing</td>
| RC_ERR_BUSY | waitretry | </tr>
| RC_ERR_LOCKED | waitretry | <tr>
+-----------------+----------------------+
]]></artwork> <td> RC_EOL
</figure> </td><td> nothing</td>
</tr>
<tr>
<td> RC_ERR
</td><td> quarantine</td>
</tr>
<tr>
<td> RC_RESET
</td><td> quarantine </td>
</tr>
<tr>
<td> RC_ERR_VERSION</td>
<td> quarantine</td>
</tr>
<tr>
<td> RC_ERR_SFID</td>
<td> quarantine</td>
</tr>
<tr>
<td> RC_ERR_SEQNUM</td>
<td> clear</td>
</tr>
<tr>
<td> RC_ERR_CELLLIST </td>
<td> clear</td>
</tr>
<tr>
<td> RC_ERR_BUSY</td>
<td> waitretry</td>
</tr>
<tr>
<td> RC_ERR_LOCKED</td>
<td> waitretry</td>
</tr>
</tbody>
</table>
<t> <t>
The meaning of each behavior from <xref target="tab_error" forma t="default"/> is: The meaning of each behavior from <xref target="tab_error" forma t="default"/> is:
</t> </t>
<dl newline="false" spacing="compact" indent="4"> <dl newline="false">
<dt>nothing:</dt> <dt>nothing:</dt>
<dd> <dd>
Indicates that this Return Code is not an error. Indicates that this return code is not an error.
No error handling behavior is triggered. No error handling behavior is triggered.
</dd> </dd>
<dt>clear:</dt> <dt>clear:</dt>
<dd> <dd>
Abort the 6P Transaction. Abort the 6P Transaction.
Issue a 6P CLEAR command to that neighbor (this command may fail at the link layer). Issue a 6P CLEAR command to that neighbor (this command may fail at the link layer).
Remove all cells scheduled with that neighbor from the local schedule. Remove all cells scheduled with that neighbor from the local schedule.
</dd> </dd>
<dt>quarantine:</dt> <dt>quarantine:</dt>
<dd> <dd>
Same behavior as for "clear". Same behavior as for "clear".
In addition, remove the node from the neighbor and routing t ables. In addition, remove the node from the neighbor and routing t ables.
Place the node's identifier in a quarantine list for QUARANT INE_DURATION. Place the node's identifier in a quarantine list for QUARANT INE_DURATION.
When in quarantine, drop all frames received from that node. When in quarantine, drop all frames received from that node.
</dd> </dd>
<dt>waitretry:</dt> <dt>waitretry:</dt>
<dd> <dd>
Abort the 6P Transaction. Abort the 6P Transaction.
Wait for a duration randomly and uniformly chosen in [WAIT_D URATION_MIN,WAIT_DURATION_MAX]. Wait for a duration randomly and uniformly chosen from [WAIT _DURATION_MIN,WAIT_DURATION_MAX].
Retry the same transaction. Retry the same transaction.
</dd> </dd>
</dl> </dl>
</section> </section>
<section anchor="sec_inconsistency" numbered="true" toc="default"> <section anchor="sec_inconsistency" numbered="true" toc="default">
<name>Schedule Inconsistency Handling</name> <name>Schedule Inconsistency Handling</name>
<t> <t>
The behavior when schedule inconsistency is detected is explaine d in <xref target="tab_error" format="default"/>, for 6P Return Code RC_ERR_SEQN UM. The behavior when schedule inconsistency is detected is explaine d in <xref target="tab_error" format="default"/>, for 6P return code RC_ERR_SEQN UM.
</t> </t>
</section> </section>
<section anchor="sec_constants" numbered="true" toc="default"> <section anchor="sec_constants" numbered="true" toc="default">
<name>MSF Constants</name> <name>MSF Constants</name>
<t> <t>
<xref target="tab_constants" format="default"/> lists MSF Consta nts and their RECOMMENDED values. <xref target="tab_constants" format="default"/> lists MSF consta nts and their <bcp14>RECOMMENDED</bcp14> values.
</t> </t>
<figure anchor="tab_constants"> <table anchor="tab_constants">
<name>MSF Constants and their RECOMMENDED values.</name> <name>MSF Constants and Their <bcp14>RECOMMENDED</bcp14> Values</n
<artwork name="" type="" align="left" alt=""><![CDATA[ ame>
+------------------------------+-------------------+ <thead>
| Name | RECOMMENDED value | <tr>
+------------------------------+-------------------+ <th>Name</th>
| SLOTFRAME_LENGTH | 101 slots | <th><bcp14>RECOMMENDED</bcp14> value</th>
| NUM_CH_OFFSET | 16 | </tr>
| MAX_NUM_CELLS | 100 | </thead>
| LIM_NUMCELLSUSED_HIGH | 75 | <tbody>
| LIM_NUMCELLSUSED_LOW | 25 | <tr>
| MAX_NUMTX | 256 |
| HOUSEKEEPINGCOLLISION_PERIOD | 1 min | <td> SLOTFRAME_LENGTH</td>
| RELOCATE_PDRTHRES | 50 % | <td>101 slots</td>
| QUARANTINE_DURATION | 5 min | </tr>
| WAIT_DURATION_MIN | 30 s | <tr>
| WAIT_DURATION_MAX | 60 s |
+------------------------------+-------------------+ <td> NUM_CH_OFFSET </td>
]]></artwork> <td>16</td>
</figure> </tr>
<tr>
<td> MAX_NUM_CELLS</td>
<td>100</td>
</tr>
<tr>
<td> LIM_NUMCELLSUSED_HIGH</td>
<td>75</td>
</tr>
<tr>
<td> LIM_NUMCELLSUSED_LOW </td>
<td>25</td>
</tr>
<tr>
<td> MAX_NUMTX</td>
<td>256</td>
</tr>
<tr>
<td> HOUSEKEEPINGCOLLISION_PERIOD</td>
<td>1 min</td>
</tr>
<tr>
<td> RELOCATE_PDRTHRES</td>
<td>50 %</td>
</tr>
<tr>
<td> QUARANTINE_DURATION</td>
<td>5 min</td>
</tr>
<tr>
<td> WAIT_DURATION_MIN</td>
<td>30 s</td>
</tr>
<tr>
<td> WAIT_DURATION_MAX </td>
<td>60 s</td>
</tr>
</tbody>
</table>
</section> </section>
<section anchor="sec_stats" numbered="true" toc="default"> <section anchor="sec_stats" numbered="true" toc="default">
<name>MSF Statistics</name> <name>MSF Statistics</name>
<t> <t>
<xref target="tab_stats" format="default"/> lists MSF Statistics and their RECOMMENDED width. <xref target="tab_stats" format="default"/> lists MSF statistics and their <bcp14>RECOMMENDED</bcp14> widths.
</t> </t>
<figure anchor="tab_stats"> <table anchor="tab_stats">
<name>MSF Statistics and their RECOMMENDED width.</name> <name>MSF Statistics and Their <bcp14>RECOMMENDED</bcp14> Widths
<artwork name="" type="" align="left" alt=""><![CDATA[ </name>
+-----------------+-------------------+
| Name | RECOMMENDED width | <thead>
+-----------------+-------------------+ <tr>
| NumCellsElapsed | 1 byte | <th>Name</th>
| NumCellsUsed | 1 byte | <th><bcp14>RECOMMENDED</bcp14> width</th>
| NumTx | 1 byte | </tr>
| NumTxAck | 1 byte | </thead>
+-----------------+-------------------+ <tbody>
]]></artwork> <tr>
</figure> <td> NumCellsElapsed</td>
<td>1 byte</td>
</tr>
<tr>
<td> NumCellsUsed</td>
<td>1 byte</td>
</tr>
<tr>
<td> NumTx</td>
<td>1 byte</td>
</tr>
<tr>
<td> NumTxAck</td>
<td>1 byte</td>
</tr>
</tbody>
</table>
</section> </section>
<section anchor="sec_security" numbered="true" toc="default"> <section anchor="sec_security" numbered="true" toc="default">
<name>Security Considerations</name> <name>Security Considerations</name>
<t> <t>
MSF defines a series of "rules" for the node to follow. MSF defines a series of "rules" for the node to follow.
It triggers several actions, that are carried out by the protoco It triggers several actions that are carried out by the protocol
ls defined in the following specifications: s defined in the following specifications:
the Minimal IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) C "<xref target="RFC8180" format="title"/>" <xref target="RFC8180"
onfiguration <xref target="RFC8180" format="default"/>, format="default"/>,
the 6TiSCH Operation Sublayer Protocol (6P) <xref target="RFC848 "<xref target="RFC8480" format="title"/>" <xref target="RFC8480"
0" format="default"/>, and format="default"/>, and
the Constrained Join Protocol (CoJP) for 6TiSCH <xref target="I- "<xref target="RFC9031" format="title"/>" <xref target="RFC9031"
D.ietf-6tisch-minimal-security" format="default"/>. format="default"/>.
Confidentiality and authentication of MSF control and data traff ic are provided by these specifications whose security considerations continue t o apply to MSF. Confidentiality and authentication of MSF control and data traff ic are provided by these specifications whose security considerations continue t o apply to MSF.
In particular, MSF does not define a new protocol or packet form at. In particular, MSF does not define a new protocol or packet form at.
</t> </t>
<t> <t>
MSF uses autonomous cells for initial bootstrap and the transpor t of join traffic. MSF uses autonomous cells for initial bootstrap and the transpor t of join traffic.
Autonomous cells are computed as a hash of nodes’ EUI64 addresse Autonomous cells are computed as a hash of nodes' EUI-64 address
s. es.
This makes the coordinates of autonomous cell an easy target for This makes the coordinates of autonomous cell an easy target for
an attacker, as EUI64 addresses are visible on the wire and are not encrypted b an attacker, as EUI-64 addresses are visible on the wire and are not encrypted
y the link-layer security mechanism. by the link-layer security mechanism.
With the coordinates of autonomous cells available, the attacker With the coordinates of autonomous cells available, the attacker
can launch a selective jamming attack against any nodes’ AutoRxCell. can launch a selective jamming attack against any node's AutoRxCell.
If the attacker targets a node acting as a JP, it can prevent pl edges from using that JP to join the network. If the attacker targets a node acting as a JP, it can prevent pl edges from using that JP to join the network.
The pledge detects such a situation through the absence of a lin k-layer acknowledgment for its Join Request. The pledge detects such a situation through the absence of a lin k-layer acknowledgment for its Join Request.
As it is expected that each pledge will have more than one JP av As it is expected that each pledge will have more than one JP av
ailable to join the network, one available countermeasure for the pledge is to p ailable to join the network, one available countermeasure for the pledge is to p
seudo-randomly select a new JP when the link to the previous JP appears bad. seudorandomly select a new JP when the link to the previous JP appears bad.
Such strategy alleviates the issue of the attacker randomly jamm Such a strategy alleviates the issue of the attacker randomly ja
ing to disturb the network but does not help in case the attacker is targeting a mming to disturb the network but does not help in the case the attacker is targe
particular pledge. ting a particular pledge.
In that case, the attacker can jam the AutoRxCell of the pledge, In that case, the attacker can jam the AutoRxCell of the pledge
in order to prevent it from receiving the join response. in order to prevent it from receiving the join response.
This situation should be detected through the absence of a parti cular node from the network and handled by the network administrator through out -of-band means. This situation should be detected through the absence of a parti cular node from the network and handled by the network administrator through out -of-band means.
</t> </t>
<t> <t>
MSF adapts to traffic containing packets from the IP layer. MSF adapts to traffic containing packets from the IP layer.
It is possible that the IP packet has a non-zero DSCP (Diffserv Code Point <xref target="RFC2474" format="default"/>) value in its IPv6 header. It is possible that the IP packet has a nonzero DSCP (Differenti ated Services Code Point) <xref target="RFC2474" format="default"/> value in its IPv6 header.
The decision how to handle that packet belongs to the upper laye r and is out of scope of MSF. The decision how to handle that packet belongs to the upper laye r and is out of scope of MSF.
As long as the decision is made to hand over to MAC layer to tra nsmit, MSF will take that packet into account when adapting to traffic. As long as the decision is made to hand over to MAC layer to tra nsmit, MSF will take that packet into account when adapting to traffic.
</t> </t>
<t> <t>
Note that non-zero DSCP value may imply that the traffic is orig Note that nonzero DSCP values may imply that the traffic origina
inated at unauthenticated pledges, referring to <xref target="I-D.ietf-6tisch-mi ted at unauthenticated pledges (see <xref target="RFC9031" format="default"/>).
nimal-security" format="default"/>. The implementation at the IPv6 layer <bcp14>SHOULD</bcp14> rate
The implementation at IPv6 layer SHOULD rate-limit this join tra limit this join traffic before it is passed to the 6top sublayer where MSF can o
ffic before it is passed to 6top sublayer where MSF can observe it. bserve it.
In case there is no rate limit for join traffic, intermediate no If there is no rate limit for join traffic, intermediate nodes i
des in the 6TiSCH network may be prone to a resource exhaustion attack, with the n the 6TiSCH network may be prone to a resource exhaustion attack, with the atta
attacker injecting unauthenticated traffic from the network edge. cker injecting unauthenticated traffic from the network edge.
The assumption is that the rate limiting function is aware of th The assumption is that the rate-limiting function is aware of th
e available bandwidth in the 6top L3 bundle(s) towards a next hop, not directly e available bandwidth in the 6top Layer 3 bundle(s) towards a next hop, not dire
from MSF, but from an interaction with the 6top sublayer that manages ultimately ctly from MSF, but from an interaction with the 6top sublayer that ultimately ma
the bundles under MSF's guidance. nages the bundles under MSF's guidance.
How this rate-limit is implemented is out of scope of MSF. How this rate limit is implemented is out of scope of MSF.
</t> </t>
</section> </section>
<section anchor="sec_iana" numbered="true" toc="default"> <section anchor="sec_iana" numbered="true" toc="default">
<name>IANA Considerations</name> <name>IANA Considerations</name>
<section anchor="sec_iana_sfid" numbered="true" toc="default"> <section anchor="sec_iana_sfid" numbered="true" toc="default">
<name>MSF Scheduling Function Identifiers</name> <name>MSF Scheduling Function Identifiers</name>
<t> <t>
This document adds the following number to the This document adds the following number to the
"6P Scheduling Function Identifiers" sub-registry, "6P Scheduling Function Identifiers" subregistry,
part of the "IPv6 over the TSCH mode of IEEE 802.15.4e (6TiS part of the "IPv6 Over the TSCH Mode of IEEE 802.15.4 (6TiSC
CH) parameters" registry, H)" registry,
as defined by <xref target="RFC8480" format="default"/>: as defined by <xref target="RFC8480" format="default"/>:
</t> </t>
<figure anchor="fig_iana_sfid">
<name>New SFID in 6P Scheduling Function Identifiers subregi <table anchor="fig_iana_sfid">
stry.</name> <name>New SFID in the "6P Scheduling Function Identifiers" Sub
<artwork name="" type="" align="left" alt=""><![CDATA[ registry</name>
+----------------------+-----------------------------+-------------+ <thead>
| SFID | Name | Reference | <tr>
+----------------------+-----------------------------+-------------+ <th>SFID</th>
| IANA_6TISCH_SFID_MSF | Minimal Scheduling Function | RFC_THIS | <th>Name</th>
| | (MSF) | | <th>Reference</th>
+----------------------+-----------------------------+-------------+ </tr>
]]></artwork> </thead>
</figure> <tbody>
<tr>
<td>0</td>
<td>Minimal Scheduling Function (MSF)</td>
<td>RFC 9033</td>
</tr>
</tbody>
</table>
<t> <t>
IANA_6TISCH_SFID_MSF is chosen from range 0-127, which is us ed for IETF Review or IESG Approval. The SFID was chosen from the range 0-127, which has the regi stration procedure of IETF Review or IESG Approval <xref target="RFC8126"/>.
</t> </t>
</section> </section>
</section> </section>
<section anchor="sec_contributors" numbered="true" toc="default">
<name>Contributors</name>
<ul spacing="compact">
<li>Beshr Al Nahas (Chalmers University, beshr@chalmers.se)</li>
<li>Olaf Landsiedel (Chalmers University, olafl@chalmers.se)</li
>
<li>Yasuyuki Tanaka (Inria-Paris, yasuyuki.tanaka@inria.fr)</li>
</ul>
</section>
</middle> </middle>
<back> <back>
<displayreference target="I-D.ietf-6tisch-dtsecurity-zerotouch-join" to="ZEROTOU
CH-JOIN"/>
<references> <references>
<name>References</name> <name>References</name>
<references> <references>
<name>Normative References</name> <name>Normative References</name>
<!-- RFC 6TiSCH-->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8180.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8180.xml"/>
<!-- Minimal IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) Configuration -->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8480.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8480.xml"/>
<!-- 6TiSCH Operation Sublayer (6top) Protocol (6P) -->
<!-- RFC others -->
<!-- RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
-->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.6550.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.6550.xml"/>
<!-- Key words for use in RFCs to Indicate Requirement Levels -- >
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.2119.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.2119.xml"/>
<!--Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words -- > <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8126.xml"/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8174.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8174.xml"/>
<!-- Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers -->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.2474.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.2474.xml"/>
<!-- Registration Extensions for IPv6 over Low-Power Wireless Pe
rsonal Area Network (6LoWPAN) Neighbor Discovery --> <reference anchor="RFC9031" target="https://www.rfc-editor.org/info/rfc9031">
<!-- I-D 6TiSCH --> <front>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx <title>Constrained Join Protocol (CoJP) for 6TiSCH</title>
ml3/reference.I-D.draft-ietf-6tisch-minimal-security-15.xml"/> <author initials="M" surname="Vučinić" fullname=" Mališa Vučinić" role="edit
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx or">
ml3/reference.I-D.draft-ietf-6tisch-enrollment-enhanced-beacon-14.xml"/> <organization/>
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx </author>
ml3/reference.I-D.draft-ietf-6tisch-architecture-28.xml"/> <author initials="J" surname="Simon" fullname="Jonathan Simon">
<!-- I-D others --> <organization/>
<!-- external --> </author>
<reference anchor="IEEE802154" target='http://ieeexplore.ieee.or <author initials="K" surname="Pister" fullname="Kris Pister">
g/document/7460875/'> <organization/>
<front> </author>
<title> <author initials="M" surname="Richardson" fullname="Michael Richardson">
IEEE Std 802.15.4 Standard for Low-Rate Wireless Per <organization/>
sonal Area Networks (WPANs) </author>
</title> <date month="May" year="2021"/>
<author> </front>
<organization>IEEE standard for Information Technolo <seriesInfo name="RFC" value="9031"/>
gy</organization> <seriesInfo name="DOI" value="10.17487/RFC9031"/>
</author> </reference>
<date/>
</front> <reference anchor="RFC9032" target="https://www.rfc-editor.org/info/rfc9032">
<seriesInfo name='DOI' value='10.1109/IEEE P802.15.4-REVd/D0 <front>
1'/> <title>Encapsulation of 6TiSCH Join and Enrollment Information Elements</tit
</reference> le>
<author initials="D" surname="Dujovne" fullname="Diego Dujovne" role="editor
">
<organization/>
</author>
<author initials="M" surname="Richardson" fullname="Michael Richardson">
<organization/>
</author>
<date month="May" year="2021"/>
</front>
<seriesInfo name="RFC" value="9032"/>
<seriesInfo name="DOI" value="10.17487/RFC9032"/>
</reference>
<reference anchor="RFC9030" target="https://www.rfc-editor.org/info/rfc9030">
<front>
<title>An Architecture for IPv6 over the Time-Slotted Channel Hopping Mode
of IEEE 802.15.4 (6TiSCH)</title>
<author initials="P" surname="Thubert" fullname="Pascal Thubert" role="edi
tor">
<organization/>
</author>
<date month="May" year="2021"/>
</front>
<seriesInfo name="RFC" value="9030"/>
<seriesInfo name="DOI" value="10.17487/RFC9030"/>
</reference>
<reference anchor="IEEE802154" target="https://ieeexplore.ieee.org/documen
t/7460875">
<front>
<title>IEEE Standard for Low-Rate Wireless Networks</title>
<author>
<organization>IEEE</organization>
</author>
<date month="April" year="2016"/>
</front>
<seriesInfo name="IEEE Standard" value="802.15.4-2015"/>
<seriesInfo name="DOI" value=" 10.1109/IEEESTD.2016.7460875"/>
</reference>
<reference anchor="SAX-DASFAA"> <reference anchor="SAX-DASFAA">
<front> <front>
<title> Performance in Practice of String Hashing Functi ons</title> <title> Performance in Practice of String Hashing Functi ons</title>
<seriesInfo name="DASFAA" value=""/> <author initials="M.V." surname="Ramakrishna"/>
<author initials="M.V" surname="Ramakrishna"/>
<author initials="J" surname="Zobel"/> <author initials="J" surname="Zobel"/>
<date year="1997"/> <date year="1997"/>
</front> </front>
<seriesInfo name='DOI' value='10.1142/9789812819536_0023'/> <refcontent>DASFAA</refcontent>
<seriesInfo name="DOI" value="10.1142/9789812819536_0023"/>
</reference> </reference>
</references> </references>
<references> <references>
<name>Informative References</name> <name>Informative References</name>
<!-- RFC 6TiSCH-->
<!-- Using IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in
the Internet of Things (IoT): Problem Statement -->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.7554.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.7554.xml"/>
<!-- 6tisch Zero-Touch Secure Join protocol --> <xi:include href="https://datatracker.ietf.org/doc/bibxml3/refer
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ence.I-D.ietf-6tisch-dtsecurity-zerotouch-join.xml"/>
ml3/reference.I-D.draft-ietf-6tisch-dtsecurity-zerotouch-join-04.xml"/>
<!-- RFC others -->
<!-- The Trickle Algorithm -->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.6206.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.6206.xml"/>
<!-- 6LoWPAN Neighbor Discovery -->
<xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8505.xml"/> <xi:include href="https://xml2rfc.tools.ietf.org/public/rfc/bibx ml/reference.RFC.8505.xml"/>
<!-- I-D 6TiSCH -->
<!-- I-D others -->
<!-- external -->
</references> </references>
</references> </references>
<section anchor="sec_hash_function" numbered="true" toc="default"> <section anchor="sec_hash_function" numbered="true" toc="default">
<name>Example of Implementation of SAX hash function</name> <name>Example Implementation of the SAX Hash Function</name>
<t> <t>
Considering the interoperability, this section provides an examp le of implemention SAX hash function <xref target="SAX-DASFAA" format="default"/ >. To support interoperability, this section provides an example i mplementation of the SAX hash function <xref target="SAX-DASFAA" format="default "/>.
The input parameters of the function are: The input parameters of the function are:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>T, which is the hashing table length</li> <li>T, which is the hashing table length.</li>
<li>c, which is the characters of string s, to be hashed</li> <li>c, which is the characters of string s, to be hashed.</li>
</ul> </ul>
<t> <t>
In MSF, the T is replaced by the length of slotframe 1. In MSF, the T is replaced by the length of slotframe 1.
String s is replaced by the mote EUI64 address. The characters o f the string c0, c1, ..., c7 are the 8 bytes of EUI64 address. String s is replaced by the node EUI-64 address. The characters of the string, c0 through c7, are the eight bytes of the EUI-64 address.
</t> </t>
<t> <t>
The SAX hash function requires shift operation which is defined as follow: The SAX hash function requires shift operation, which is defined as follow:
</t> </t>
<ul spacing="compact"> <ul spacing="normal">
<li>L_shift(v,b), which refers to left shift variable v by b bi <li>L_shift(v,b), which refers to the left shift of variable v b
ts</li> y b bits</li>
<li>R_shift(v,b), which refers to right shift variable v by b bi <li>R_shift(v,b), which refers to the right shift of variable v
ts</li> by b bits</li>
</ul> </ul>
<t> <t>
The steps to calculate the hash value of SAX hash function are: The steps to calculate the hash value of SAX hash function are:
</t> </t>
<ol spacing="compact" type="1"> <ol spacing="normal">
<li>initialize variable h to h0 and variable i to 0, where h is <li anchor="sax_step1">Initialize variable h, which is the inter
the intermediate hash value and i is the index of the bytes of EUI64 address</li mediate hash value, to h0 and variable i, which is the index of the bytes of the
> EUI-64 address, to 0.</li>
<li>sum the value of L_shift(h,l_bit), R_shift(h,r_bit) and ci</ <li anchor="sax_step2">Sum the value of L_shift(h,l_bit), R_shif
li> t(h,r_bit), and ci.</li>
<li>calculate the result of exclusive or between the sum value i <li anchor="sax_step3">Calculate the result of the exclusive OR
n Step 2 and h</li> between the sum value in <xref target="sax_step2" format="none">Step 2</xref> an
<li>modulo the result of Step 3 by T</li> d h.</li>
<li>assign the result of Step 4 to h</li> <li anchor="sax_step4">Modulo the result of <xref target="sax_st
<li>increase i by 1</li> ep3" format="none">Step 3</xref> by T.</li>
<li>repeat Step2 to Step 6 until i reaches to 8 </li> <li anchor="sax_step5">Assign the result of <xref target="sax_st
ep4" format="none">Step 4</xref> to h.</li>
<li anchor="sax_step6">Increase i by 1.</li>
<li anchor="sax_step7">Repeat <xref target="sax_step2" format="n
one">Step 2</xref> to <xref target="sax_step6" format="none">Step 6</xref> until
i reaches to 8. </li>
</ol> </ol>
<t> <t>
The value of variable h is the hash value of SAX hash function. The value of variable h is the hash value of the SAX hash functi on.
</t> </t>
<t> <t>
The values of h0, l_bit and r_bit in Step 1 and 2 are configured as: The values of h0, l_bit, and r_bit in <xref target="sax_step1" f ormat="none">Step 1</xref> and <xref target="sax_step2" format="none">Step 2</xr ef> are configured as:
</t> </t>
<ul spacing="compact"> <t indent="6">h0 = 0</t>
<li>h0 = 0</li> <t indent="6">l_bit = 0</t>
<li>l_bit = 0</li> <t indent="6">r_bit = 1</t>
<li>r_bit = 1</li>
</ul>
<t> <t>
The appropriate values of l_bit and r_bit could vary depending o n the the set of motes' EUI64 address. The appropriate values of l_bit and r_bit could vary depending o n the set of nodes' EUI-64 address.
How to find those values is out of the scope of this specificati on. How to find those values is out of the scope of this specificati on.
</t> </t>
</section>
<section anchor="sec_contributors" numbered="false">
<name>Contributors</name>
<contact fullname="Beshr Al Nahas">
<organization>Chalmers University</organization>
<address>
<email>beshr@chalmers.se</email>
</address>
</contact>
<contact fullname="Olaf Landsiedel">
<organization>Chalmers University</organization>
<address>
<email>olafl@chalmers.se</email>
</address>
</contact>
<contact fullname="Yasuyuki Tanaka">
<organization>Toshiba</organization>
<address>
<email>yatch1.tanaka@toshiba.co.jp</email>
</address>
</contact>
</section> </section>
</back> </back>
</rfc> </rfc>
 End of changes. 149 change blocks. 
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