One document matched: draft-thubert-6tsch-architecture-01.xml
<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc subcompact="no"?>
<?rfc authorship="yes"?>
<?rfc tocappendix="yes"?>
<rfc category="std" docName="draft-thubert-6tsch-architecture-01" ipr="trust200902">
<front>
<title abbrev="6tsch-architecture">An Architecture for IPv6 over Time Slotted Channel Hopping</title>
<author fullname="Pascal Thubert" initials="P" role="editor" surname="Thubert">
<organization abbrev="cisco">Cisco Systems, Inc</organization>
<address>
<postal>
<street>Building D</street>
<street>45 Allee des Ormes - BP1200 </street>
<city>MOUGINS - Sophia Antipolis</city>
<code>06254</code>
<country>FRANCE</country>
</postal>
<phone>+33 497 23 26 34</phone>
<email>pthubert@cisco.com</email>
</address>
</author>
<author fullname="Robert Assimiti" initials="RA" surname="Assimiti">
<organization abbrev="Nivis">Nivis</organization>
<address>
<postal>
<street>1000 Circle 75 Parkway SE, Ste 300</street>
<city>Atlanta</city>
<region>GA</region>
<code>30339</code>
<country>USA</country>
</postal>
<phone>+1 678 202 6859</phone>
<email>robert.assimiti@nivis.com</email>
</address>
</author>
<author initials="T" surname="Watteyne" fullname="Thomas Watteyne">
<organization>Linear Technology / Dust Networks</organization>
<address>
<postal>
<street>30695 Huntwood Avenue</street>
<city>Hayward</city>
<region>CA</region>
<code>94544</code>
<country>USA</country>
</postal>
<phone>+1 (510) 400-2978</phone>
<email>twatteyne@linear.com</email>
</address>
</author>
<date/>
<area>Internet Area</area>
<workgroup>6TSCH</workgroup>
<keyword>Draft</keyword>
<abstract>
<t>
This document presents an architecture for an IPv6 multilink subnet that
is composed of a high speed powered backbone and a number of
IEEE802.15.4e TSCH wireless networks attached and synchronized by
Backbone Routers. Route Computation may be achieved in a centralized
fashion by a Path Computation Element, in a distributed fashion using the
Routing Protocol for Low Power and Lossy Networks, or in a mixed mode.
The Backbone Routers perform proxy Neighbor discovery operations over the
backbone on behalf of the wireless device, so they can share a same subnet
and appear to be connected to the same backbone as classical devices.
</t>
</abstract>
<note title="Requirements Language">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY",
and "OPTIONAL" in this document are to be interpreted as described
in <xref target="RFC2119">RFC 2119</xref>.
</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>The emergence of radio technology enabled a large variety of new types of devices
to be interconnected, at a very low marginal cost compared to wire, at any range from
Near Field to interplanetary distances, and in circumstances where wiring could be less
than practical, for instance rotating devices.
</t>
<t>
At the same time, a new breed of Time Sensitive Networks is being developped to enable
traffic that is highly sensitive to jitter and quite sensitive to
latency. Such traffic is not limited to voice and video, but also
includes command and control operations such as found in industrial
automation or in-vehicule sensors and actuators.
</t>
<t>
At IEEE802.1, the "Audio/Video Task Group", was renamed TSN for
Time Sensitive Networking to address Deterministic Ethernet.
The IEEE802.15.4 Medium Access Control MAC) has evolved with
IEEE802.15.4e that provides in particular the Time Slotted
Channel Hopping (TSCH) mode for industrial-type applications.
</t>
<t>Though at a different time scale, both standards provide
Deterministic capabilities to the point that
a packet that pertains to a certain flow will cross the network from
node to node following a very precise schedule, like a train leaves
intermediate stations at precise times along its path. The time
slotted aspect reduces collisions, and saves energy, and enables to
more closely engineer the network for deterministic properties.
The channel hopping aspect is a simple and efficient technique
to get around statistical interference by WIFI emitters.
</t>
<t>
This document presents an architecture for an IPv6 multilink subnet
that is composed of a high speed powered backbone and a number of
IEEE802.15.4e TSCH wireless networks attached and synchronized by
backbone routers. Route Computation may be achieved in a centralized
fashion by a Path Computation Entity (PCE), in a distributed fashion
using the Routing Protocol for Low Power and Lossy Networks (RPL), or
in a mixed mode. The Backbone Routers perform proxy Ipv6 Neighbor
Discovery (ND) operations over the backbone on behalf of the wireless
device, so they can share a same IPv6 subnet and appear to be
connected to the same backbone as classical devices.
</t>
</section>
<section anchor="Terminology" title="Terminology">
<t>
The draft uses terminology defined in
<xref target="I-D.palattella-6tsch-terminology"/>,
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/>,
<xref target="RFC5191"/>
and <xref target="RFC4080"/>.
</t>
<t>
It conforms to the terms and models described for IPv6 in
<xref target="RFC5889"/> and uses the vocabulary and the concepts
defined in <xref target="RFC4291"/> for IPv6.
</t>
</section>
<section anchor="Goals" title="Applications and Goals">
<t>The architecture derives from existing industrial standards for Process
Control by its focus on Deterministic Networking, in particular with the use
of the IEEE802.15.4e TSCH MAC and the centralized path computation entity.
This approach leverages the TSCH MAC benefits for high reliability against interferences,
low-power consumption on deterministic traffic, and its Traffic Engineering capabilities.
Deterministic Networking applies in particular to open and close control loops,
as well as supervisory control flows, and management.
</t>
<t>Additional industrial use cases are addressed with the addition of a more
autonomic and distributed routing based on RPL. These use cases include
plant setup and decommissioning, as well as monitoring of lots of lesser
importance measurements such as corrosion and events.
RPL also enables mobile use cases such as mobile workers and cranes.
</t>
<t>A Backbone Router is included in order to scale the factory plant subnet to address
large deployments, with proxy ND and time synchronization over a high speed backbone.
</t>
<t>The architecture also applies to building automation that leverage RPL's storing
mode to address multipath over a large number of hops, in-vehicule command and control
that can be as demanding as industrial applications, commercial automation and asset
tracking with mobile scenarios, home automation and domotics which become more reliable
and thus provide a better user experience, and resource management (energy, water, etc...).
</t>
</section>
<section anchor="Scope" title="Overview and Scope">
<t>
The scope of the present work is a subnet that, in its basic
configuration, is made of a
<xref target="I-D.watteyne-6tsch-tsch-lln-context">
IEEE802.15.4e Time Slotted Channel Hopping (TSCH)</xref>
MAC Route-Over Low Power Lossy Network (LLN).
<figure anchor="fig1" title="Basic Configuration">
<artwork><![CDATA[
+-----+
| | LLN Border
| | router
+-----+
o o o
o o o o
o o LLN o o o
o o o o
o
]]></artwork>
</figure>
</t>
<t>
The LLN devices communicate over IPv6 <xref target="RFC2460"/>
using the
<xref target="RFC6282">6LoWPAN Header Compression (6LoWPAN HC)</xref>.
Neighbor Devices are discovered with <xref target="RFC6775"> 6LoWPAN
Neighbor Discovery (6LoWPAN ND)</xref> and <xref target="RFC6550">
the Routing Protocol for Low Power and Lossy Networks (RPL) </xref>
enables routing within the LLN. RPL forms Destination Oriented
Directed Acyclic Graphs (DODAGs) within instances of the protocol,
each instance being associated with an Objective Function (OF) to
form a routing topology. A particular LLN device, usually powered,
acts as RPL root, 6LoWPAN HC terminator, and LLN Border Router
(LBR) to the outside.
</t>
<t>
An extended configuration of the subnet comprises multiple LLNs.
The LLNs are interconnected and synchronized over a backbone, that
can be wired or wireless. The backbone can be a classical IPv6
network, with Neighbor Discovery operating as defined in
<xref target="RFC4861"/> and <xref target="RFC4862"/>.
The backbone can also support
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd">
Efficiency aware IPv6 Neighbor Discovery Optimizations </xref>
in mixed mode as described in
<xref target="I-D.thubert-6lowpan-backbone-router"/>.
</t>
<t>
Security is often handled at layer 2 and Layer 4. Authentication
during the join process is handled with the <xref target="RFC5191">
Protocol for Carrying Authentication for Network Access (PANA)</xref>.
</t>
<t>
The LLN devices are time-synchronized at MAC level. The MAC
coordinator that serves as time source through Enhanced Beacons (EB)
is loosely coupled with the RPL parent; this way, the time
synchronization starts at the RPL root and follows the RPL
DODAGs with no timing loop.
</t>
<t>
In the extended configuration, the functionality of the LBR is
enhanced to that of Backbone Router (BBR). A BBR is an LBR, but
also an Energy Aware Default Router (NEAR) as defined in
<xref target="I-D.chakrabarti-nordmark-6man-efficient-nd"/>.
The BBR performs ND proxy operations between the registered devices
and the classical ND devices that are located over the backbone.
6TSCH BBRs synchronize with one another over the backbone, so as
to ensure that the multiple LLNs that form the IPv6 subnet stay
tightly synchronized. If the Backbone is Deterministic (such as
defined by the Time Sensitive Networking WG at IEEE), then the
Backbone Router ensures that the end-to-end deterministic
behavior is maintained between the LLN and the backbone.
</t>
<t>
<figure anchor="fig2" title="Extended Configuration">
<artwork><![CDATA[
---+------------------------
| External Network
|
+-----+ +-----+
| | Router | | PCE
| | | |
+-----+ +-----+
| |
| Subnet Backbone |
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
o | | router | | router | | router
+-----+ +-----+ +-----+
o o o o o
o o o o o o o o o o o
o o o LLN o o o o
o o o o o o o o o o o o
]]></artwork>
</figure>
</t>
<t>
The main architectural blocks are arranged as follows:
<figure anchor="fig4" title="6TSCH stack">
<artwork><![CDATA[
+-----+-----+-----+-----+-------+-----+
|PCEP | CoAP |PANA |6LoWPAN| RPL |
| PCC |DTLS | | | ND | |
+-----+-----+-----+-----+-------+-----+-----+
| TCP | UDP | ICMP |RSVP |
+-----+-----+-----+-----+-------+-----+-----+
| IPv6 |
+-------------------------------------------+
| 6LoWPAN HC |
+-------------------------------------------+
| 6TUS |
+-------------------------------------------+
| 802.15.4e TSCH |
+-------------------------------------------+
]]></artwork>
</figure>
</t>
<t>RPL is the routing protocol of choice for LLNs. (TBD RPL) whether there is a need to define a 6TSCH OF.</t>
<t>(tbd NME) COMAN is working on network Management for LLN. They are considering
the Open Mobile Alliance (OMA) Lightweight M2M (LWM2M) Objet system. This standard includes
DTLS, CoAP (core plus the Block and Observe patterns), SenML and CoAP Resource Directory.</t>
<t>(tbd PCC) need to work with PCE WG to define flows to PCE, and define how to accomodate PCE routes and reservation. Will probably look a lot like GMPLS</t>
<t>(tbd Backbone Router) need to work woth 6MAN to define ND proxy. Also need BBR sync sync between deterministic ethernet and 6TSCH LLNs.</t>
<t>IEEE802.1TSN: external, maintain consistency.</t>
<t>IEEE802.15.4: external, (tbd need updates?).</t>
<t>ISA100.20 Common Network Management: external, maintain consistency.</t>
<t>IoT6 European Project: external, maintain consistency.</t>
</section>
<section anchor="PCEvsRPL" title="Centralized vs. Distributed Routing">
<t>
</t>
</section>
<section anchor="Flows" title="Functional Flows">
<t>
<list hangIndent="6" style="hanging">
<t hangText="Join:"></t>
<t hangText="Time Synchronization:"></t>
<t hangText="Setup for routing:"></t>
<t hangText="PCE reservation:"></t>
<t hangText="Distributed reservation:"></t>
<t hangText="Dynamic slot (de)allocation:"></t>
<t hangText="DSCP mapping:"></t>
</list>
</t>
</section>
<section anchor="Sync" title="Network Synchronization">
<t>
The mechanism(s) used for time synchronization is something that we might have to reconcile with RPL discovery and maintenance traffic.
</t>
<t>
Time synchronization in TSCH is based on three mechanisms:
<list>
<t>Enhanced Beacons</t>
<t>Enhanced ACKs </t>
<t>Frame based synchronization </t>
</list>
If a node communicates intermittently (sleepy, battery operated) it
can also proactively ping its time source and receive time stamps.
In order to maximize battery life and network throughput, it is
advisable that RPL ICMP discovery and maintenance traffic
(governed by the trickle timer) be somehow coordinated with
the transmission of time synch packets (especially with enhanced
beacons). This could be a function of the shim layer or it could
be deferred to the device management entity. Any suggestions,
ideas on this topic?
</t>
</section>
<section anchor="Sixtus" title="TSCH and 6TUS">
<section title="6tus">
<t>
6tus is an adaptation layer which is the next higher layer to TSCH and which offers a set of commands defining a data and management interface. 6tus is defined in <xref target="I-D.wang-6tsch-6tus"/>
</t>
<t>
The management interface of 6tus enables an upper layer to schedule cells and slotframes in the TSCH schedule.
</t>
<t>
If the scheduling entity explicitly specifies the slotOffset/channelOffset of the cells to be added/deleted, those cells are marked as "hard". 6tus can not move hard cells in the TSCH schedule. Hard cells are typically used by an central PCE.
</t>
<t>
6tus contains a monitoring process which monitors the performance of cells, and can move a cell in the TSCH schedule when it performs bad. This is only applicable to cells which are marked as "soft". To reserve a soft cell, the higher layer does not indicate the slotOffset/channelOffset of the cell to add, but rather the resulting bandwidth and QoS requirements. When the monitoring process triggers an cell reallocation, the two neighbor motes communication over this cells negociate the new position in the TSCH schedule of this cell.
</t>
</section>
<section anchor="slotframes" title="Slotframes and Priorities">
<t>
6tus uses priority queues to manage concurrent data flows of different prioroties. When a packet is received from an higher layer for transmission, the I-MUX module of 6tus inserts that packet in the outgoing queue which matches the packet best (DSCP can therefore be used). At each schedule transmit slot, the MUX module looks for the frame in all the outgoing queues that best matches the cells. If a frame is found, it is given to TSCH for transmission.
</t>
</section>
<section anchor="PCEFlow" title="Centralized Flow Reservation">
<t>
In a centralized setting, a PCE computes the TSCH schedule, and communicates with the different nodes in the network to configure their TSCH schedule. Since it has full knowledge of the network's topology, the PCE can compute a collision-free schedule, which result in a high degree of communication determinism.
</t>
<t>
The protocol for the PCE to communicate with the motes is not yet defined. This protocol typically reserves hard cells on the transmitter side of a dedicated cell, and the negociation protocol of 6tus takes care of reserving the same cell on the receiver node.
</t>
</section>
<section anchor="SettingUpAFlow" title="Distributed Flow Reservation">
<t>
In a distributed setting, no central PCE in present in the network. Nodes use 6tus to reserve soft cells with their neighbors. Since no node has full knowledge of the network's topology and the traffic requirements, scheduling collisions are possible, for example because of a hidden terminal problem.
</t>
<t>
A schedule collision can be detected if two motes have multiple dedicated cells schedule to one another. The statistics process of 6tus can be configure to continuously compute the packet delivery ratio of those cells, and the monitoring process of 6tus can declare a soft cell to perform bad when that statistics for that cell is significantly worse than for the other cell to the same neighbor.
</t>
<t>
When this happens, the monitoring process of 6tus moves the cell to another location in the 6TSCH schedule, through a re-negociation procedure with the neighbor.
</t>
<t>
The entity that builds and maintains the schedule in a distributed fashion is not yet defined.
</t>
</section>
<section anchor="Packet" title="Packet Marking and Handling">
<t>
</t>
<figure anchor="fig5" title="NSIS flow">
<artwork><![CDATA[
---+----------------
Sender Receiver
+-----------+ +----+ +----+ +----+ +-----------+
|Application|---->| R1 |---->| R2 |----->|BBR |----->|Application|
| +--+ | |+--+| |+--+| |+--+| | +--+ |
| |NE|====|=====||NE||=====||NE||======||NE||======|===|NE| |
| +--+ | |+--+| |+--+| |+--+| | +--+ |
| |^ | | |^ | | |^ | | |^ | | |^ |
| v| | | v| | | v| | | v| | | v| |
| +--+ | |+--+| |+--+| |+--+| | +--+ |
| |6T| | ||6T|| ||6T|| ||6T|| | |6T| |
| |us| | ||us|| ||us|| ||us|| | |us| |
| +--+ | |+--+| |+--+| |+--+| | +--+ |
+-----------+ +----+ +----+ +----+ +-----------+
+--+
|NE| = NSIS ==== = Signaling ---> = Data flow messages
+--+ Entity Messages (unidirectional)
+--+
|6T| 6TUS layer
|us| (and IEEE802.15.4e TSCH MAC below)
+--+
]]></artwork>
</figure>
<t>
reservation
Deterministic flow allocation (hard reservation of time slots) eg centralized RSVP? metrics?
Hop-by-hop interaction with 6TUS.
Lazy reservation (use shared slots to transport extra burst and then dynamically (de)allocate)
Classical QoS (dynamic based on observation)
</t>
</section>
</section>
<section anchor="MGT" title="Management">
<t>
</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>
This specification does not require IANA action.
</t>
</section>
<section anchor="Sec" title="Security Considerations">
<t>
This specification is not found to introduce new security threat.
</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>
</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.2460"?>
<?rfc include="reference.RFC.4080"?>
<?rfc include="reference.RFC.4291"?>
<?rfc include="reference.RFC.4861"?>
<?rfc include="reference.RFC.4862"?>
<?rfc include="reference.RFC.5191"?>
<?rfc include="reference.RFC.5889"?>
<?rfc include="reference.RFC.5974"?>
<?rfc include="reference.RFC.6282"?>
<?rfc include="reference.RFC.6550"?>
<?rfc include="reference.RFC.6775"?>
</references>
<references title="Informative References">
<?rfc include='reference.I-D.wang-6tsch-6tus.xml'?>
<?rfc include='reference.I-D.palattella-6tsch-terminology.xml'?>
<?rfc include='reference.I-D.watteyne-6tsch-tsch-lln-context.xml'?>
<?rfc include='reference.I-D.watteyne-6tsch-tsch-lln-context.xml'?>
<?rfc include='reference.I-D.watteyne-6tsch-tsch-lln-context.xml'?>
<?rfc include='reference.I-D.chakrabarti-nordmark-6man-efficient-nd.xml'?>
<?rfc include='reference.I-D.thubert-6lowpan-backbone-router.xml'?>
<?rfc include='reference.I-D.svshah-tsvwg-lln-diffserv-recommendations.xml'?>
</references>
<references title="External Informative References">
<reference anchor="IEEE802.1TSNTG" target="http://www.ieee802.org/1/pages/avbridges.html">
<front>
<title>IEEE 802.1 Time-Sensitive Networks Task Group</title>
<author>
<organization>IEEE Standards Association</organization>
</author>
<date day="08" month="March" year="2013" />
</front>
</reference>
<reference anchor="HART">
<front>
<title>Highway Addressable Remote Transducer, a group of specifications for industrial process and control devices administered by the HART Foundation</title>
<author>
<organization>www.hartcomm.org</organization>
</author>
<date></date>
</front>
</reference>
<reference anchor="ISA100.11a" target="http://www.isa.org/Community/SP100WirelessSystemsforAutomation">
<front>
<title>ISA100, Wireless Systems for Automation</title>
<author>
<organization>ISA</organization>
</author>
<date day="05" month="May" year="2008" />
</front>
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-22 03:11:53 |