IPv6 over the TSCH mode of IEEE 802.15.4e
charter-ietf-6tisch-02

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 Timeslotted Channel Hopping (TSCH) mode was introduced in 2012 as an
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 IEEE802.15.4 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.

IEEE802.15.4 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
IEEE802.15.4 standard. The extent of the problem space for the WG is
one or more LLNs, possibly 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 has limited its scope to distributed routing over a
static schedule using the Routing Protocol for LLNs (RPL) on the
resulting network. This new charter allows for the dynamic allocation of
cells and their exchange between adjacent peers to accommodate the
available bandwidth to the variations of throughput in IP traffic.

The WG will continue working on securing the join process and making
that fit within the constraints of high latency, low throughput and
small frame sizes that characterize IEEE802.15.4 TSCH.

Additionally, IEEE802.15.4 TSCH being a deterministic MAC, it is
envisioned that 6TiSCH will benefit from the work of DetNet WG to
establish the so-called deterministic tracks. The group will define the
objects and methods that need to be configured, and provide the
associated requirements to DetNet.

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

Work Items:

The group will:

• Produce a specification of the 6top sublayer that describes the
  protocol for neighbor nodes to negotiate adding/removing cells. This
  work will leverage cross participation from IEEE members including the
  IEEE 6TiSCH Interest Group (IG 6T) to define protocol elements and
  associated frame formats.

• Produce a specification for a default 6top Scheduling Function
  including the policy to enable distributed dynamic scheduling of
  timeslots for IP traffic. This may include the capability for nodes to
  appropriate chunks of the matrix without starving, or interfering with
  other 6TiSCH nodes. This particular work will focus on IP traffic since
  the work on tracks is not yet advanced enough to specify their
  requirements.

• Produce requirements to the DetNet WG, detailing 6TiSCH chunks and
  tracks, and the data models to manipulate them from an external
  controller such as a PCE.

• Produce a specification for a secure 6TiSCH network bootstrap, adapted
  to the constraints of 6TiSCH nodes and leveraging existing art when
  possible.

• Keep updating the "6TiSCH architecture" that describes the design of
  6TiSCH networks. This document highlights the different architectural
  blocks, signaling and data flows, including the operation of the network
  in the presence of multiple LBRs. The existing document will be
  augmented to cover dynamic scheduling and application of the DetNet work
  but will not be delivered within this round of chartering.

• Producing YANG Data Models to manage 6tisch is foreseen, but left to a
  later phase.

Non-milestone work items:

The Working Group regularly organizes interoperability events with
support from ETSI (i.e., ETSI 6TiSCH Plugtests) to get feedback from
implementers early on in the standardization process, and produce better
standards.