LabN Consulting, L.L.C.

ekinzie@labn.net

LabN Consulting, L.L.C.

dfedyk@labn.net

This document defines a YANG data model that describes the times at which network links are available for use. The model is intended for use in networks where links can be predictably lost and re-established, and neighbors may change as a function of time. The intent is for this information to be used by a Time-Variant Routing (TVR) system which may route network traffic based on mobility, energy costs or expected user data volumes, and handle such predictable changes in a non-disruptive manner.

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 when, and only when, they appear in all capitals, as shown here.

For some networks, the times at which one router will be able to establish a link with another router can be predicted. Links can be predictably lost and re-established, and neighbors may change as a function of time. For examples of such networks see, TVR (Time-Variant Routing) Use Cases . This document defines a YANG data model that describes the times at which network links are available for use. The contents of this module are intended to be flexible enough to describe an entire network when required, but can also be used to focus on a single node's view. The defined YANG model can be used to support Network topology data that is augmented to include links that are expected, but not yet present. Time-based link availability has utility in areas such as resource planning for energy conservation, resource allocation for scheduled bulk data transfers, and avoiding service disruption through make-before-break strategies. Data presented with this module could be used as a source of information for time-variant IGP extensions currently being developed in . One example of where such information is applicable is a constellation of satellites. Since orbits are known, satellites' positions relative to one another, positions relative to ground stations, and many sources of interference can be calculated days in advance. For the purpose of describing link properties, the defined YANG module reuses attributes defined in , , , , and .

The link-availability container describes the times at which one or more links are available. Links are modeled as unidirectional. Any one link supports unidirectional traffic flow, from the source node to the destination node. The bidirectional traffic between a pair of network nodes requires at least two links. A Link is considered to be available at the time it is first able to support delivery of packets until the time at which it becomes unable to do so. Valid until times may be set to a time when the link will last support the advertised characteristics. Routers and/or controllers can choose to move traffic prior to the valid-until time when trying to minimize disruption. Available times do not take into account, for example, the time required for carrier to be detected after the interfaces at either end have been powered on; the interfaces in this example would be powered on some time before availability starts.

Link availabilities obtained from data represented by this module are considered "current" until the time specified in the next-update time. Any availability received by a network management client after the specified next-update time has passed SHOULD be discarded.

Link availability is described from the viewpoint of a particular source node (the transmitting node) and beginning at a particular time.

Each link in the list contains the range of times during which it is available. In the event that a link formed by a given combination of source node, source-link identifier, and destination node is available at multiple times, each occurrence is a separate entry in the list and can be distinguished by the avail-from value. Availability time ranges for the same source node, source-link identifier, and destination node MUST NOT overlap. However, note that the time ranges are specified such that avail-from is inclusive and avail-until is exclusive. That is, the avail-until time in one link availability MAY be the same as the avail-from in a subsequent availability for the same combination of endpoints. This can happen if one or more link attributes change over the life of a link. A list element MUST NOT have an avail-from that occurs after its avail-until. The avail-until value is optional. If avail-until is absent from a list element, the link is considered to be available until the time of the next expected update (next-update). Should the next update not arrive at or before the expected time, an entry without an avail-until time is considered to be no longer available. An entry with an unexpired avail-until time remains available until the specified time, even if the next update does not arrive when expected. An avail-from value indicating a time prior to when the link availability data was received implies that the link is immediately available. A list entry with an avail-until time that has already passed can be ignored. A list entry MAY have an avail-from time after the time of the next expected update. List elements can be added and removed by the source of information at any time. This may result in a link availability being removed before its previously specified avail-until time. Such a list element that is removed implies that the link is no longer available. The availability times in a list element do not "change"; a list element may be deleted and another list element with the same endpoints may be inserted with different available times.

Any string may be used to identify a node in the source-node and destination-node elements. It is expected, but not required, that a node string will refer to data described by another YANG module.

Any string may be used to identify a link as viewed from the source-node. It is expected, but not required, that the value of a source-link-id leaf will refer to data described by another YANG module.

These are predicted link attributes. Bandwidth specifies the total link bandwidth and does not take into account resource reservations that may utilize a link. If the observed bandwidth negotiated for a link is greater than the predicted value, the predicted value SHOULD be used for the purposes of routing decisions. Otherwise, if the observed bandwidth is less, the observed value SHOULD be used. Delay is the link propagation time and does not include queuing delays. If no measured delay is available or if the measured value is less than the predicted delay, the predicted value SHOULD be used for routing decisions. Otherwise, the observed value SHOULD be used. A number of time variant metrics and attributes may be included. The Interior Gateway Protocol (IGMP) link metric is an optional value for the predicted OSPF or IS-IS link metric. The default TE metric specifies the link metric for route and/or path computation purposes. Generic link affinities and Shared links resource groups may be specified as list of strings. This can be used for predicting traffic engineering usage.

The following is the YANG tree diagram for the link-availability container.

The following is the YANG module for reporting link availabilities. file "ietf-link-availability@2023-06-15.yang" module ietf-link-availability { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-link-availability"; prefix ln-avail; import ietf-yang-types { prefix yang; } import ietf-te-types { prefix te-types; } organization "IETF Time-Variant Routing Working Group"; contact "WG Web: WG List: Editors: Eric Kinzie Don Fedyk "; description "This YANG module contains YANG definitions for describing network links with an time-variant availability schedule. Copyright (c) 2023 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. 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 BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2023-06-15 { description "Initial revision"; reference "RFC XXXX A YANG Data Model for Time Variant Link Availability"; } container link-availability { config false; leaf next-update { type yang:date-and-time; description "This data is current until the specified time."; } list link { key "avail-from source-node source-link-id"; leaf avail-from { type yang:date-and-time; description "The time at which this link becomes available."; } leaf source-node { type string; description "A name that refers to the source (transmitting) node of the link."; } leaf source-link-id { type string; description "A name, as known to the source node, that refers to this link."; } leaf destination-node { type string; description "A name that refers to the destination (receiving) node of the link."; } leaf avail-until { type yang:date-and-time; description "The time at which this link is no longer available."; } leaf bandwidth { type te-types:te-bandwidth; description "The predicted link capacity specified in a generic format. If the value measured by the system is less than this value, the system value is used. If the value measured by the system is greater than this value the predicted value SHOULD be used."; reference "RFC 8776: Common YANG Data Types for Traffic Engineering"; } leaf delay { type uint32 { range "0..16777215"; } description "The one-way delay or latency in microseconds. If the value measured by the system is less than this value the predicted value SHOULD be used."; reference "RFC 8776: Common YANG Data Types for Traffic Engineering"; } leaf igp-link-metric { type uint32; description "OSPF or IS-IS link metric. If this metric is supplied it is the predicted metric that is used by the system. The system may adjust operational metric as needed."; reference "RFC 9129: YANG Data Model for the OSPF Protocol RFC 9130: YANG Data Model for the IS-IS Protocol"; } leaf te-default-metric { type uint32; description "The Traffic Engineering metric. The system may adjust this value on the operational link."; reference "RFC 3630: Traffic Engineering (TE) Extensions to OSPF Version 2 RFC 5305: IS-IS Extensions for Traffic Engineering"; } container link-affinity-names { description "Link affinities represented as names."; list link-affinity-name { key "usage"; description "An optional list of named affinity constraints."; leaf usage { type identityref { base te-types:resource-affinities-type; } description "Identifies an entry in the list of named affinity constraints."; } list affinity-name { key "name"; leaf name { type string; description "Identifies a named affinity entry."; } description "List of named affinities."; reference "RFC 8776: Common YANG Data Types for Traffic Engineering"; } } } container link-srlgs-names { description "Container for the list of named SRLGs."; list link-srlgs-name { key "usage"; description "List of named SRLGs to be included or excluded."; leaf usage { type identityref { base te-types:route-usage-type; } description "Identifies an entry in a list of named SRLGs to either include or exclude."; } leaf-list names { type string; description "List of named SRLGs."; reference "RFC 8776: Common YANG Data Types for Traffic Engineering"; } } } description "This list represents a set of links each which has time variant link attributes."; } description "A container with a list links with time variant link availabilities."; } } ]]>

The contents of source-node and destination node are not well defined.

It is requested that the following URI be added to the "ns" subregistry within the "IETF XML Registry" . It is requested that the following YANG module be added to the "YANG Module Names" subregistry within the "YANG Parameters" registry.

The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF or RESTCONF . The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) . The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS . The Network Configuration Access Control Model (NACM) provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content.

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support Traffic Engineering (TE). This document extends the IS-IS protocol by specifying new information that an Intermediate System (router) can place in Link State Protocol Data Units (LSP). This information describes additional details regarding the state of the network that are useful for traffic engineering computations. [STANDARDS-TRACK] This document describes extensions to the OSPF protocol version 2 to support intra-area Traffic Engineering (TE), using Opaque Link State Advertisements. This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas. YANG is a data modeling language used to model configuration and state data manipulated by the Network Configuration Protocol (NETCONF), NETCONF remote procedure calls, and NETCONF notifications. [STANDARDS-TRACK] The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] This document describes a method for invoking and running the Network Configuration Protocol (NETCONF) within a Secure Shell (SSH) session as an SSH subsystem. This document obsoletes RFC 4742. [STANDARDS-TRACK] This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF). RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document captures the current syntax used in YANG module tree diagrams. The purpose of this document is to provide a single location for this definition. This syntax may be updated from time to time based on the evolution of the YANG language. The standardization of network configuration interfaces for use with the Network Configuration Protocol (NETCONF) or the RESTCONF protocol requires a structured and secure operating environment that promotes human usability and multi-vendor interoperability. There is a need for standard mechanisms to restrict NETCONF or RESTCONF protocol access for particular users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. This document defines such an access control model. This document obsoletes RFC 6536. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document defines a collection of common data types and groupings in YANG data modeling language. These derived common types and groupings are intended to be imported by modules that model Traffic Engineering (TE) configuration and state capabilities. This document defines a YANG data model that can be used to configure and manage OSPF. The model is based on YANG 1.1 as defined in RFC 7950 and conforms to the Network Management Datastore Architecture (NMDA) as described in RFC 8342. This document defines a YANG data model that can be used to configure and manage the IS-IS protocol on network elements. JHU/APL Thales Alenia Space Futurewei Technologies This document introduces use cases where Time-Variant Routing (TVR) computations (i.e. routing computations taking into considerations time-based or scheduled changes to a network) could improve routing protocol convergence and/or network performance. ZTE Corporation ZTE Corporation TVR needs IGP to calculate different results depending on the time, without convergence after the detection of link or nodes. IGP nodes need to learn the predictable and scheduled changes in advance. This document defines the IGP extensions for predictable and scheduled changes of TVR.

The authors would like to thank Acee Lindem and Lou Berger for their reviews and suggested improvements.