Time-Variant Routing
charter-ietf-tvr-01

Existing IETF routing protocols expect to maintain contemporaneous, end-to-end
connected paths across a network. Changes to that connectivity, such as the
loss of an adjacent peer, need the routing protocols to react to reduce the
impact on the network traffic.

However, a growing number of use cases exist where predicted variations
(restoration, activation, or loss) to the topology are an expected part of
normal network operations. For example, in networks with mobile nodes, such as
aerial vehicles and some orbiting spacecraft constellations, links can be lost
and re-established, or neighbors may change as a function of their mobility.
Similarly, network traffic might be routed based on energy costs or expected
user data volumes, which may vary predictably over time in networks
prioritizing green computing and energy efficiency. In these cases, the
predicted loss and restoration of an adjacency, or formation of an alternate
adjacency, should be seen as non-disruptive events. Support for such use cases
and expected changes in a routing system is called Time-Variant Routing (TVR).

The Time-Variant Routing Working Group (TVR WG) is chartered to define
information and data models that address time-based, scheduled changes to a
network. Time-based changes may include changes to links, adjacencies, cost,
and - in some cases - traffic volumes. The models are expected to satisfy the
non-terrestrial networks' requirements as their main driver. Still, they
should be general enough to encompass other types of networks and use cases.
They should also be agnostic with respect to other control plane elements.

The WG may also define terminology and concepts where needed, as well as
address the impacts of a continually changing topology on the hierarchical
structure of the network.

The TVR WG will collaborate with groups working on non-terrestrial networks,
including DTN, CCAMP, DETNET, RAW, and DRIP. In addition, the outputs from the
WG will be provided to other working groups for consideration, which may use
the material to incorporate time-variant attributes and behaviors into
individual protocols.

Specifically, the TVR WG will work on these items:

(1) Problem Statement and Use cases

This document (or set of documents) should include a description of the problem
statement and related use cases to guide the remaining work. It exists to
support the efforts of the Working Group and help newcomers, and it might not
be published as an IETF Stream RFC.

(2) Requirements

This document should include definitions, requirements, notes, rationales, and
examples.

(3) Information Model

This document (or set of documents) should describe the attributes needed, and
the relationship between them, to enable routing and forwarding decisions in
the presence of time-variant network parameters.

(4) Data Model

This document (or set of documents) should specify a YANG Data Model (or
multiple modules), based on the Information Model, for configuration and
monitoring.

(5) Applicability Statement

This document should provide an applicability statement on how the information
and data models may be used, along with required ancillary IETF technology, to
solve the use cases and requirements.

(6) Implementation and Operational Considerations

This document should provide advice and guidance to implementors and operators.