WG Action: Formed IPv6 over the TSCH mode of IEEE 802.15.4e (6tisch)

[The IESG <[e-mail]>]

A new IETF working group has been formed in the Internet Area. For
additional information please contact the Area Directors or the WG
Chairs.

IPv6 over the TSCH mode of IEEE 802.15.4e (6tisch)
------------------------------------------------
Current Status: Proposed WG

Chairs:
  Pascal Thubert <[e-mail]>
  Thomas Watteyne <[e-mail]>

Assigned Area Director:
  Ted Lemon <[e-mail]>

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Charter:

6TiSCH: "IPv6 over the TSCH mode of IEEE 802.15.4e".

Background/Introduction:
------------------------

Low-power and Lossy Networks (LLNs) interconnect a possibly large number 
of resource-constrained nodes to form a wireless mesh network. The 
6LoWPAN, ROLL and CoRE IETF Working Groups have defined protocols at 
various layers of the protocol stack, including an IPv6 adaptation 
layer, a routing protocol and a web transfer protocol. This protocol 
stack has been used with IEEE802.15.4 low-power radios.

The IEEE802.15.4e Timeslotted Channel Hopping (TSCH) is a recent 
amendment to the Medium Access Control (MAC) portion of the IEEE802.15.4 
standard. TSCH is the emerging standard for industrial automation and 
process control LLNs, with a direct inheritance from WirelessHART and 
ISA100.11a. Defining IPv6 over TSCH, 6TiSCH is a key to enable the 
further adoption of IPv6 in industrial standards and the convergence of 
Operational Technology (OT) with Information Technology (IT).

The nodes in a IEEE802.15.4e TSCH network communicate by following a 
Time Division Multiple Access (TDMA) schedule. A timeslot in this 
schedule provides a unit of bandwidth that is allocated for 
communication between neighbor nodes. The allocation can be programmed 
such that the predictable transmission pattern matches the traffic. This 
avoids idle listening, and extends battery lifetime for constrained 
nodes. Channel-hopping improves reliability in the presence of narrow-
band interference and multi-path fading.

These techniques enable a new range of use cases for LLNs, including:
- Control loops in a wireless process control network, in which high
reliability and a fully deterministic behavior are required.
- Service Provider networks transporting data from different independent
clients, and for which an operator needs flow isolation and traffic 
shaping.
- Networks comprising energy harvesting nodes, which require an 
extremely low and predictable average power consumption.

IEEE802.15.4e only defines the link-layer mechanisms. It does not define 
how the network communication schedule is built and matched to the 
traffic requirements of the network.

Description of Working Group:
-----------------------------

The Working Group will focus on enabling IPv6 over the TSCH mode of the
IEEE802.15.4e standard. The extent of the problem space for the WG is 
one or more LLNs, eventually federated through a common backbone link 
via one or more LLN Border Routers (LBRs). The WG will rely on, and if 
necessary extend, existing mechanisms for authenticating LBRs.

Initially, the WG will limit its scope to distributed routing over a 
static schedule. In that case, a node's schedule can be either 
preconfigured, or learnt by a node when joining the network, but it 
remains unchanged after the node has joined a network. The Routing 
Protocol for LLNs (RPL) is used on the resulting network.

The WG will interface with other appropriate groups in the IETF 
Internet, Operations and Management, Routing and Security areas.

Work Items:
-----------

The group will:

1. Produce "6TiSCH architecture" to describe the design of 6TiSCH 
networks. This document will highlight the different architectural 
blocks and signalling flows, including the operation of the network in 
the presence of multiple LBRs. Initially, the document will focus on 
distributed routing operation over a static TSCH schedule.

2. Produce an Information Model containing the management requirements 
of a 6TiSCH node. This includes describing how an entity can manage the 
TSCH schedule on a 6TiSCH node, and query timeslot information from that 
node. A data model mapping for an existing protocol (such as Concise 
Binary Object Representation (CBOR) over the Constrained Application 
Protocol (CoAP)) will be provided.

3. Produce "Minimal 6TiSCH Configuration" defining how to build a 6TiSCH 
network using the Routing Protocol for LLNs (RPL) and a static TSCH 
schedule. It is expected that RPL and the Objective Function 0 (OF0) 
will be reused as-is.

The work will include a best practice configuration for RPL and OF0 
operation over the static schedule. Based on that experience the group 
may produce a requirements draft for OF0 extensions, to be studied in
ROLL.

Non-milestone work items:
-------------------------

The Working Group may maintain a number of running, often-respun 
documents, that evolve as the technology is refined for work items that 
do not affect the milestone work items:
- implementers guide: this document will collect clarifying information 
based on input from implementers, in particular as it becomes available 
from interoperability events. This guide will contain information about 
test harnesses used for interoperability testing.
- coexistence guide: this document will provide information on how 
6TiSCH can be operated in an environment shared with other protocols 
that use the same or a similar TSCH MAC, and/or operate on the same 
frequency band.

The WG will welcome requirements for dynamic timeslot operation, for 
example for centralized schedule computation.