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Reliable and Available Wireless Architecture
draft-ietf-raw-architecture-16

Document Type Active Internet-Draft (detnet WG)
Author Pascal Thubert
Last updated 2023-10-20
Replaces draft-pthubert-raw-architecture
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draft-ietf-raw-architecture-16
RAW                                                      P. Thubert, Ed.
Internet-Draft                                           20 October 2023
Intended status: Informational                                          
Expires: 22 April 2024

              Reliable and Available Wireless Architecture
                     draft-ietf-raw-architecture-16

Abstract

   Reliable and Available Wireless (RAW) provides for high reliability
   and availability for IP connectivity across any combination of wired
   and wireless network segments.  The RAW Architecture extends the
   DetNet Architecture and other standard IETF concepts and mechanisms
   to adapt to the specific challenges of the wireless medium, in
   particular intermittently lossy connectivity.  This document defines
   a network control loop that optimizes the use of constrained spectrum
   and energy while maintaining the expected connectivity properties,
   typically reliability and latency.  The loop involves DetNet
   Operational Plane functions, with a new recovery Function and a new
   Point of Local Repair operation, that dynamically selects the DetNet
   path(s) for the future packets to route around local degradations and
   failures.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 22 April 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   5
       2.1.1.  ARQ . . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.2.  FEC . . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.3.  HARQ  . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.4.  MCS . . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.5.  OAM . . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.6.  OODA  . . . . . . . . . . . . . . . . . . . . . . . .   6
       2.1.7.  PAREO . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.2.  Link and Direction  . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  Flapping  . . . . . . . . . . . . . . . . . . . . . .   7
       2.2.2.  Uplink  . . . . . . . . . . . . . . . . . . . . . . .   7
       2.2.3.  Downlink  . . . . . . . . . . . . . . . . . . . . . .   7
       2.2.4.  Downstream  . . . . . . . . . . . . . . . . . . . . .   7
       2.2.5.  Upstream  . . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  Path and Recovery Graphs  . . . . . . . . . . . . . . . .   7
       2.3.1.  Path  . . . . . . . . . . . . . . . . . . . . . . . .   7
       2.3.2.  Recovery Graph  . . . . . . . . . . . . . . . . . . .   8
       2.3.3.  Forward and Crossing  . . . . . . . . . . . . . . . .  10
       2.3.4.  Lane  . . . . . . . . . . . . . . . . . . . . . . . .  11
       2.3.5.  Segment . . . . . . . . . . . . . . . . . . . . . . .  11
     2.4.  Deterministic Networking  . . . . . . . . . . . . . . . .  11
       2.4.1.  Flow  . . . . . . . . . . . . . . . . . . . . . . . .  11
       2.4.2.  Deterministic Flow Identifier (L2)  . . . . . . . . .  11
       2.4.3.  Deterministic Flow Identifier (L3)  . . . . . . . . .  12
       2.4.4.  TSN . . . . . . . . . . . . . . . . . . . . . . . . .  12
     2.5.  Reliability and Availability  . . . . . . . . . . . . . .  12
       2.5.1.  Service Level Agreement . . . . . . . . . . . . . . .  12
       2.5.2.  Service Level Objective . . . . . . . . . . . . . . .  12
       2.5.3.  Service Level Indicator . . . . . . . . . . . . . . .  12
       2.5.4.  Reliability . . . . . . . . . . . . . . . . . . . . .  12
       2.5.5.  Available . . . . . . . . . . . . . . . . . . . . . .  13
       2.5.6.  Availability  . . . . . . . . . . . . . . . . . . . .  13
     2.6.  OAM variations  . . . . . . . . . . . . . . . . . . . . .  13
       2.6.1.  Active OAM  . . . . . . . . . . . . . . . . . . . . .  13
       2.6.2.  In-Band OAM . . . . . . . . . . . . . . . . . . . . .  13

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       2.6.3.  Out-of-Band OAM . . . . . . . . . . . . . . . . . . .  13
       2.6.4.  Limited OAM . . . . . . . . . . . . . . . . . . . . .  13
       2.6.5.  Upstream OAM  . . . . . . . . . . . . . . . . . . . .  14
       2.6.6.  Residence Time  . . . . . . . . . . . . . . . . . . .  14
       2.6.7.  Lower Layer information . . . . . . . . . . . . . . .  14
       2.6.8.  Additional References . . . . . . . . . . . . . . . .  14
   3.  Reliable and Available Wireless . . . . . . . . . . . . . . .  14
     3.1.  Reliability and Availability  . . . . . . . . . . . . . .  14
       3.1.1.  High Availability Engineering Principles  . . . . . .  14
       3.1.2.  Applying Reliability Concepts to Networking . . . . .  17
       3.1.3.  Wireless Effects Affecting Reliability  . . . . . . .  18
     3.2.  The RAW problem . . . . . . . . . . . . . . . . . . . . .  19
   4.  The RAW Conceptual Model  . . . . . . . . . . . . . . . . . .  23
     4.1.  The RAW Planes  . . . . . . . . . . . . . . . . . . . . .  23
     4.2.  RAW vs. Upper and Lower Layers  . . . . . . . . . . . . .  25
     4.3.  RAW and DetNet  . . . . . . . . . . . . . . . . . . . . .  26
   5.  The RAW Control Loop  . . . . . . . . . . . . . . . . . . . .  29
     5.1.  Routing Time Scale vs. Forwarding Time Scale  . . . . . .  29
     5.2.  A OODA Loop . . . . . . . . . . . . . . . . . . . . . . .  31
     5.3.  Observe: The RAW OAM  . . . . . . . . . . . . . . . . . .  32
     5.4.  Orient: The RAW-enhanced DetNet Operational Plane . . . .  33
     5.5.  Decide: The Path Selection Engine . . . . . . . . . . . .  34
     5.6.  Act: DetNet Path Selection and PAREO functions  . . . . .  36
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  37
     6.1.  Layer-2 encryption  . . . . . . . . . . . . . . . . . . .  37
     6.2.  Forced Access . . . . . . . . . . . . . . . . . . . . . .  37
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  37
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  37
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  38
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  38
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  38
     10.2.  Informative References . . . . . . . . . . . . . . . . .  40
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  41

1.  Introduction

   Deterministic Networking is an attempt to emulate the properties of a
   serial link over a switched fabric, by providing a bounded latency
   and eliminating congestion loss, even when co-existing with best-
   effort traffic.  It is getting traction in various industries
   including professional A/V, manufacturing, online gaming, and
   smartgrid automation, with both cost savings and complexity benefits
   (e.g., vs. loads of P2P cables).

   Bringing determinism in a packet network means eliminating the
   statistical effects of multiplexing that result in probabilistic
   jitter and loss.  This can be approached with a tight control of the
   physical resources to maintain the amount of traffic within a

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   budgeted volume of data per unit of time that fits the physical
   capabilities of the underlying network, and the use of time-shared
   resources (bandwidth and buffers) per circuit, and/or by shaping and/
   or scheduling the packets at every hop.

   This innovation was initially introduced on wired networks, with IEEE
   802.1 Time Sensitive networking (TSN) - for Ethernet LANs - and IETF
   DetNet.  But the wired and the wireless media are fundamentally
   different at the physical level and in the possible abstractions that
   can be built for IPv6 [IPv6], more in [IPoWIRELESS].  Nevertheless,
   deterministic capabilities are required in a number of wireless use
   cases as well [RAW-USE-CASES].  With new scheduled radios such as
   TSCH and OFDMA [RAW-TECHNOS] being developed to provide determinism
   over wireless links at the lower layers, providing DetNet
   capabilities is now becoming possible.

   Wireless networks operate on a shared medium where uncontrolled
   interference, including the self-induced multipath fading cause
   random transmission losses.  Fixed and mobile obstacles and
   reflectors may block or alter the signal, causing transient and
   unpredictable variations of the throughput and packet delivery ratio
   (PDR) of a wireless link.  This adds new dimensions to the
   statistical effects that affect the quality and reliability of the
   link.

   Reliable and Available Wireless (RAW) takes up the challenge of
   providing highly available and reliable end-to-end performances in a
   network with scheduled wireless segments.  To achieve this, RAW
   leverages multiple links and parallel transmissions, providing enough
   diversity and redundancy to ensure the timely packet delivery while
   preserving energy and optimizing the use of the shared spectrum.

   As opposed to routing trees, Distance-Vector protocols can enable
   more than one feasible successors along non-equal-cost multipath
   forwarding graphs.  This provide redundancy and allow to dynamically
   adapt the forwarding operation to the state of the links.  But this
   protection is limited since only a subset of the nodes along the path
   will have an alternate feasible successor.

   RAW solves that problem by defining Protection Paths that can be
   fully non-congruent and can be activated dynamically upon failures.
   This requires additional control to take the routing decision early
   enough along the possible paths to route around the failure.  RAW
   defines a end-to-end control loop that dynamically controls the
   activation and deactivation of the feasible Protection Paths.

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   This document presents the RAW problem and associated terminology in
   Section 3.2, presents a conceptual model for RAW in Section 4, and,
   based on that model, elaborates on an in-network optimization control
   loop in Section 5.2.

2.  Terminology

   RAW reuses terminology defined for DetNet in the "Deterministic
   Networking Architecture" [RFC8655], e.g., PREOF for Packet
   Replication, Elimination and Ordering Functions.  RAW inherits and
   augments the IETF art of Protection as seen in DetNet and Traffic
   Engineering.

   RAW also reuses terminology defined for MPLS in [RFC4427] such as the
   term recovery as covering both Protection and Restoration, a number
   of recovery types, That document defines a number of concepts like
   recovery domain that are used in thie RAW works, and creates the new
   term recovery graph.  A recovery graph associates a topological graph
   with usage metadata that represent how the paths within the recovery
   graph are built.

   RAW also reuses terminology defined for RSVP-TE in [RFC4090] such as
   the Point of Local Repair (PLR).  The concept of backup path is
   generalized with protection path, which is the term mostly found in
   recent standards and used in this document.

   RAW also reuses terminology defined for 6TiSCH in [6TiSCH-ARCHI] and
   equates the concept of recovery graph with that of a recovery graph.

   In an quantic analogy, a recovery graph is to a path what an atomic
   orbital is to a planetary orbit, in that the electron has a
   probability of presence within a known shape as opposed to a
   deterministic trajectory.

   The concept of recovery graph is agnostic to the underlaying
   technology and applies but is not limited to any fully or partially
   wireless mesh.  RAW specifies strict and loose recovery graphs
   depending on whether the path is fully controlled by RAW or traverses
   an opaque network where RAW cannot observe and control the individual
   hops.

   RAW uses the following terminology and acronyms:

2.1.  Acronyms

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2.1.1.  ARQ

   Automatic Repeat Request, enabling an acknowledged transmission and
   retries.  ARQ is a typical model at Layer-2 on a wireless medium.
   ARQ is typically implemented hop-by-hop and not end-to-end in
   wireless networks.  Else, it introduces excessive indetermination in
   latency, but a limited number of retries within a bounded time may be
   used within end-to-end constraints.

2.1.2.  FEC

   Forward Error Correction, adding redundant data to protect against a
   partial loss without retries.

2.1.3.  HARQ

   Hybrid Automatic Repeat Request, combining FEC and ARQ.

2.1.4.  MCS

   Modulation and Coding Scheme.  Controls the throughput of the Link to
   maintain reliable transmissions.

2.1.5.  OAM

   OAM stands for Operations, Administration, and Maintenance, and
   covers the processes, activities, tools, and standards involved with
   operating, administering, managing and maintaining any system.  This
   document uses the terms Operations, Administration, and Maintenance,
   in conformance with the 'Guidelines for the Use of the "OAM" Acronym
   in the IETF' [RFC6291] and the system observed by the RAW OAM is the
   recovery graph.

2.1.6.  OODA

   Observe, Orient, Decide, Act. The OODA Loop is a conceptual cyclic
   model developed by USAF Colonel John Boyd, and that is applicable in
   multiple domains where agility can provide benefits against brute
   force.

2.1.7.  PAREO

   Packet (hybrid) ARQ, Replication, Elimination and Ordering.  PAREO is
   a superset Of DetNet's PREOF that includes leveraging lower-layer
   (typically wireless) techniques such as short range broadcast,
   MUMIMO, PHY rate and other Modulation Coding Scheme (MCS) adaptation,
   constructive interference and overhearing, separately or in
   combination, to increase the end-to-end reliability.  PAREO functions

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   that are actuated at the lower layers may be controlled through
   abstract interfaces by the RAW extensions within the DetNet Service
   sub-layer.

2.2.  Link and Direction

2.2.1.  Flapping

   In the context of RAW, a link flaps when the reliability of the
   wireless connectivity drops abruptly for a short period of time,
   typically of a subsecond to seconds duration.

2.2.2.  Uplink

   Connection from end-devices to a data communication equipment.  In
   the context of wireless, uplink refers to the connection between a
   station (STA) and a controller (AP) or a User Equipment (UE) to a
   Base Station (BS) such as a 3GPP 5G gNodeB (gNb).

2.2.3.  Downlink

   The reverse direction from uplink.

2.2.4.  Downstream

   Following the direction of the flow data path along a recovery graph.

2.2.5.  Upstream

   Against the direction of the flow data path along a recovery graph.

2.3.  Path and Recovery Graphs

2.3.1.  Path

   Quoting section 1.1.3 of [INT-ARCHI]:

   |  At a given moment, all the IP datagrams from a particular source
   |  host to a particular destination host will typically traverse the
   |  same sequence of gateways.  We use the term "path" for this
   |  sequence.  Note that a path is unidirectional; it is not unusual
   |  to have different paths in the two directions between a given host
   |  pair.

   Section 2 of [I-D.irtf-panrg-path-properties] points to a longer,
   more modern definition of path, which begins as follows:

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   |  A sequence of adjacent path elements over which a packet can be
   |  transmitted, starting and ending with a node.  A path is
   |  unidirectional.  Paths are time-dependent, i.e., the sequence of
   |  path elements over which packets are sent from one node to another
   |  may change.  A path is defined between two nodes.

   It follows that the general acceptance of a path is a linear sequence
   of links and nodes, as opposed to a multi-dimensional graph, defined
   by the experience of the packet that went from a node A to a node B.
   In the context of this document, a path is observed by following one
   copy or one fragment of a packet that conserves its uniqueness and
   integrity.  For instance, if C replicates to E and F and D eliminates
   on the way from A to B, a packet from A to B experiences 2 paths,
   A->C->E->D->B and A->C->F->D->B.  The terms lane is used to clarify
   when dealing with such path.

   With DetNet and RAW, a packet may be duplicated, fragmented and
   network-coded, and the various byproducts may travel different paths
   that are not necessarily end-to-end between A and B; we refer to that
   complex experience as a DetNet path.  As such, the DetNet path
   extends the above description of a path, but it still matches the
   experience of a packet that traverses the network.

   With RAW, that experience is subject to change from a packet to the
   next, but all the possible experiences are all contained within a
   finite set.  Therefore, we introduce below the term of a recovery
   graph that coalesces that set and covers the overall topology where
   the possible DetNet paths are all contained.  As such, the recovery
   graph coalesces all the possible paths a flow may experience, each
   with its own statistical probability to be used.

2.3.2.  Recovery Graph

   A networking graph that can be followed to transport packets with
   equivalent treatment, associated with usage metadata; as opposed to
   the definition of a path above, a recovery graph represents not an
   actual but a potential, it is not necessarily a linear sequence like
   a simple path, and is not necessarily fully traversed (flooded) by
   all packets of a flow like a Detnet Path.  Still, and as a
   simplification, the casual reader may consider that a recovery graph
   is very much like a DetNet path, aggregating multiple paths that may
   overlap, fork and rejoin, for instance to enable a protection service
   by the PREOF operations.

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                     +---------+
                     | IoT G/W |
                     +---------+
                         EGR  <=== Elimination at Egress
                         | |
                 /------/   \-------\    Wired backbone
                 |                  |
              +--|--+            +--|--+
              |  |  | Backbone   |  |  | Backbone
              |  |  | Router     |  |  | Router
              +--|--+            +--|--+
                 |                  |
              o   \     o          /  lane
            o      o      o---o---o   o      o   o  o
                    \  o /    o          o         o
             o   o   \  /       o        low power lossy network
                      \/ o           o        o
                   o  IN <=== Replication at recovery graph Ingress
                       |
                       o <- source device

      Figure 1: Example IoT Recovery Graph to an IoT Gateway with 1+1
                                 Redundancy

   Refining further, a recovery graph is defined as the coalescence of
   the collection of all the feasible DetNet Paths that a packet which
   flow is assigned to the recovery graph may be forwarded along.  A
   packet that is assigned to the recovery graph will experience one of
   the feasible DetNet Paths based on the current selection by the PLR
   at the time the packet traverses the network.

   Refining even further, the feasible DetNet Paths within the recovery
   graph may or may not be computed in advance, but decided upon the
   detection of a change from a clean slate.  Furthermore, the PLR
   decision may be distributed, which yields a large combination of
   possible and dependant decisions, with no node in the network capable
   of reporting which is the current DetNet Path within the recovery
   graph.

   In DetNet [RFC8655] terms, a recovery graph has the following
   properties:

   *  A recovery graph is a Layer-3 abstraction built upon P2P IP links
      between routers.  A router may form multiple P2P IP links over a
      single radio interface.

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   *  A recovery graph has one Ingress and one Egress nodes, which
      operate as DetNet Edge nodes.

   *  The graph of a recovery graph is reversible, meaning that packets
      can be routed against the flow of data packets, e.g., to carry OAM
      measurements or control messages back to the Ingress.

   *  The vertices of that graph are DetNet Relay nodes that operate at
      the DetNet Service sub-layer and provide the PAREO functions.

   *  The topological edges of the graph are strict sequences of DetNet
      Transit nodes that operate at the DetNet Forwarding sub-layer.

   Figure 2 illustrates the generic concept of a recovery graph, between
   an Ingress Node and an Egress Node The recovery graph is composed of
   forward Lanes and forward or crossing Segments, see the definition
   for those terms in the next sections.  A Protection Path contains at
   least 2 Lanes as a main path and a backup path.

      ------------------- forward direction ---------------------->

            a ==> b ==> C -=- F ==> G ==> H     T1       I: Ingress
          /              \   /      |       \ /          E: Egress
        I                  o        n        E -=- T2    T1, T2, T3:
          \              /   \      |       / \            External
            p ==> q ==> R -=- T ==> U ==> v     T3         Targets

           Uppercase: DetNet Relay nodes
           Lowercase: DetNet Transit nodes

           I ==> a ==> b ==> C : an forward Segment to targets F and o
           C ==> o ==> T: an forward Segment to target T (and/or U)
           G | n | U : a crossing Segment to targets G or U
           I --> F --> E : an forward Lane to targets T1, T2, and T3

           I, a, b, C, F, G, H, E : a path to T1, T2, and/or T3
           I, p, q, R, o, F, G, H, E : lane-crossing alternate path

               Figure 2: A Recovery Graph and its Components

2.3.3.  Forward and Crossing

   Forward refers to progress towards the recovery graph Egress.
   Forward links are directional, and packets that are forwarded along
   the recovery graph can only be transmitted along the link direction.
   Crossing links are bidirectional, meaning that they can be used in
   both directions, though a given packet may use the link in one
   direction only.  A Segment can be forward, in which case it is

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   composed of forward links only, or crossing, in which case it is
   composed of crossing links only.  A lane is always forward, meaning
   that is is composed of forward links and Segments.

2.3.4.  Lane

   An end-to-end forward lane between the Ingress and Egress Nodes of a
   recovery graph.  A lane in a recovery graph is expressed as a strict
   sequence of DetNet Relay nodes or as a loose sequence of DetNet Relay
   nodes that are joined by recovery graph Segments.

2.3.5.  Segment

   A strict sequence of DetNet Transit nodes between 2 DetNet Relay
   nodes; a Segment of a recovery graph is composed topologically of two
   vertices of the recovery graph and one edge of the recovery graph
   between those vertices.

2.4.  Deterministic Networking

   This document reuses the terminology in section 2 of [RFC8557] and
   section 4.1.2 of [RFC8655] for deterministic networking and
   deterministic networks.

2.4.1.  Flow

   A collection of consecutive IP packets defined by the upper layers
   and signaled by the same 5 or 6-tuple, see section 5.1 of [RFC8939].
   Packets of the same flow must be placed on the same recovery graph to
   receive an equivalent treatment from Ingress to Egress within the
   recovery graph.  Multiple flows may be transported along the same
   recovery graph.  The DetNet Path that is selected for the flow may
   change over time under the control of the PLR.

2.4.2.  Deterministic Flow Identifier (L2)

   A tuple identified by a stream_handle, and provided by a bridge, in
   accordance with IEEE 802.1CB.  The tuple comprises at least source
   MAC, destination MAC, VLAN ID, and L2 priority.  Continuous streams
   are characterized by bandwidth and max packet size; scheduled streams
   are characterized by a repeating pattern of timed transmissions.

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2.4.3.  Deterministic Flow Identifier (L3)

   See section 3.3 of [DetNet-DP].  The classical IP 5-tuple that
   identifies a flow comprises the source IP, destination IP, source
   port, destination port, and the upper layer protocol (ULP).  DetNet
   uses a 6-tuple where the extra field is the DSCP field in the packet.
   The IPv6 flow label is not used for that purpose.

2.4.4.  TSN

   TSN stands for Time Sensitive Networking and denotes the efforts at
   IEEE 802 for deterministic networking, originally for use on
   Ethernet.  Wireless TSN (WTSN) denotes extensions of the TSN work on
   wireless media such as the selected RAW technologies [RAW-TECHNOS].

2.5.  Reliability and Availability

   In the context of the RAW work, Reliability and Availability are
   defined as follows:

2.5.1.  Service Level Agreement

   In the context of RAW, an SLA (service level agreement) is a contract
   between a provider, the network, and a client, the application flow,
   about measurable metrics such as latency boundaries, consecutive
   losses, and packet delivery ratio (PDR).

2.5.2.  Service Level Objective

   A service level objective (SLO) is one term in the SLA, for which
   specific network setting and operations are implemented.  For
   instance, a dynamic tuning of the packet redundancy will address an
   SLO of consecutive losses in a row by augmenting the chances of
   delivery of a packet that follows a loss.

2.5.3.  Service Level Indicator

   A service level indicator (SLI) measures the compliance of an SLO to
   the terms of the contract.  It can be for instance the statistics of
   individual losses and losses in a row as time series.).

2.5.4.  Reliability

   Reliability is a measure of the probability that an item will perform
   its intended function for a specified interval under stated
   conditions (SLA).  RAW expresses reliability in terms of Mean Time
   Between Failure (MTBF) and Maximum Consecutive Failures (MCF).  More
   in [NASA].).

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2.5.5.  Available

   That is exempt of unscheduled outage or derivation from the terms of
   the SLA.  A basic expectation for a RAW network is that the flow is
   maintained in the face of any single breakage or flapping.

2.5.6.  Availability

   Availability is a measure of the relative amount of time where a RAW
   Network operates in stated condition (SLA), expressed as
   (uptime)/(uptime+downtime).  Because a wireless lane may not be good
   enough to provide the required reliability, and even 2 parallel lanes
   may not be over a longer period of time, the RAW availability implies
   a journey that is a lot more complex than following a serial path.

2.6.  OAM variations

2.6.1.  Active OAM

   See [RFC7799].  In the context of RAW, Active OAM is used to observe
   a particular recovery graph, DetNet Path, or Segment of a recovery
   graph regardless of whether it is used for traffic at that time.

2.6.2.  In-Band OAM

   An active OAM packet is considered in-band for the monitored recovery
   graph when it traverses the same set of links and interfaces and if
   the OAM packet receives the same QoS and PAREO treatment as the
   packets of the data flows that are injected in the recovery graph.

2.6.3.  Out-of-Band OAM

   Out-of-band OAM is an active OAM whose path is not topologically
   congruent to the recovery graph, or its test packets receive a QoS
   and/or PAREO treatment that is different from that of the packets of
   the data flows that are injected in the recovery graph, or both.

2.6.4.  Limited OAM

   An active OAM packet is a Limited OAM packet when it observes the RAW
   operation over a node, a segment, or a DetNet Path of the recovery
   graph, though not from Ingress to Egress.  It is injected in the
   datapath and extracted from the datapath around the particular
   function or subnetwork (e.g., around a relay providing a Service sub-
   layer replication point) that is being tested.

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2.6.5.  Upstream OAM

   An upstream OAM packet is an Out-of-Band OAM packet that traverses
   the recovery graph from egress to ingress on the reverse direction,
   to capture and report OAM measurements upstream.  The collection may
   capture all information along the whole recovery graph, or it may
   only learn select data across all, or only a particular DetNet Path,
   or Segment of a recovery graph.

2.6.6.  Residence Time

   A residence time (RT) is defined as the time period between the
   reception of a packet starts and the transmission of the packet
   begins.  In the context of RAW, RT is useful for a transit node, not
   ingress or egress.

2.6.7.  Lower Layer information

   The RAW Operational Plane elements (PLR and OAM Supervisor) may
   gather aggregated information from lower layers about e.g., link
   quality.  This information may be obtained from inside the device
   using specialized API (e.g., L2 triggers) or via control protocols
   such as BFD [RFC5880] or DLEP [DLEP].  It may then be massaged and
   exported through oOAM messaging, and passed to the Controller Plane
   using the aCPF.h

2.6.8.  Additional References

   [DetNet-OAM] provides additional terminology related to OAM in the
   context of DetNet and by extension of RAW, whereas [RFC7799] defines
   the Active, Passive, and Hybrid OAM methods.

3.  Reliable and Available Wireless

3.1.  Reliability and Availability

3.1.1.  High Availability Engineering Principles

   The reliability criteria of a critical system pervades through its
   elements, and if the system comprises a data network then the data
   network is also subject to the inherited reliability and availability
   criteria.  It is only natural to consider the art of high
   availability engineering and apply it to wireless communications in
   the context of RAW.

   There are three principles [pillars] of high availability
   engineering:

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   1.  elimination of single points of failure
   2.  reliable crossover
   3.  prompt detection of failures as they occur.

   These principles are common to all high availability systems, not
   just ones with Internet technology at the center.  Examples of both
   non-Internet and Internet are included.

3.1.1.1.  Elimination of Single Points of Failure

   Physical and logical components in a system happen to fail, either as
   the effect of wear and tear, when used beyond acceptable limits, or
   due to a software bug.  It is necessary to decouple component failure
   from system failure to avoid the latter.  This allows failed
   components to be restored while the rest of the system continues to
   function.

   IP Routers leverage routing protocols to compute alternate routes in
   case of a failure.  There is a rather open-ended issue over alternate
   routes -- for example, when links are cabled through the same
   conduit, they form a shared risk link group (SRLG), and will share
   the same fate if the bundle is cut.  The same effect can happen with
   virtual links that end up in a same physical transport through the
   games of encapsulation.  In a same fashion, an interferer or an
   obstacle may affect multiple wireless transmissions at the same time,
   even between different sets of peers.

   Intermediate network Nodes such as routers, switches and APs, wire
   bundles and the air medium itself can become single points of
   failure.  For High Availability, it is thus required to use
   physically link- and Node-disjoint paths; in the wireless space, it
   is also required to use the highest possible degree of diversity
   (time, space, code, frequency, channel width) in the transmissions
   over the air to combat the additional causes of transmission loss.

   From an economics standpoint, executing this principle properly
   generally increases capitalization expense because of the redundant
   equipment.  In a constrained network where the waste of energy and
   bandwidth should be minimized, an excessive use of redundant links
   must be avoided; for RAW this means that the extra bandwidth must be
   used wisely and with parsimony.

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3.1.1.2.  Reliable Crossover

   Having a backup equipment has a limited value unless it can be
   reliably switched into use within the down-time parameters.  IP
   Routers execute reliable crossover continuously because the routers
   will use any alternate routes that are available [RFC0791].  This is
   due to the stateless nature of IP datagrams and the dissociation of
   the datagrams from the forwarding routes they take.  The "IP Fast
   Reroute Framework" [FRR] analyzes mechanisms for fast failure
   detection and path repair for IP Fast-Reroute, and discusses the case
   of multiple failures and SRLG.  Examples of FRR techniques include
   Remote Loop-Free Alternate [RLFA-FRR] and backup label-switched path
   (LSP) tunnels for the local repair of LSP tunnels using RSVP-TE
   [RFC4090].

   Deterministic flows, on the contrary, are attached to specific paths
   where dedicated resources are reserved for each flow.  Therefore each
   DetNet path must inherently provide sufficient redundancy to provide
   the guaranteed SLA at all times.  The DetNet PREOF typically
   leverages 1+1 redundancy whereby a packet is sent twice, over non-
   congruent paths.  This avoids the gap during the fast reroute
   operation, but doubles the traffic in the network.

   In the case of RAW, the expectation is that multiple transient faults
   may happen in overlapping time windows, in which case the 1+1
   redundancy with delayed reestablishment of the second path will not
   provide the required guarantees.  The Data Plane must be configured
   with a sufficient degree of redundancy to select an alternate
   redundant path immediately upon a fault, without the need for a slow
   intervention from the Controller Plane.

3.1.1.3.  Prompt Notification of Failures

   The execution of the two above principles is likely to render a
   system where the user will rarely see a failure.  But someone needs
   to in order to direct maintenance.

   There are many reasons for system monitoring (FCAPS for fault,
   configuration, accounting, performance, security is a handy mental
   checklist) but fault monitoring is sufficient reason.

   "An Architecture for Describing Simple Network Management Protocol
   (SNMP) Management Frameworks" [STD 62] describes how to use SNMP to
   observe and correct long-term faults.

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   "Overview and Principles of Internet Traffic Engineering" [TE]
   discusses the importance of measurement for network protection, and
   provides abstract an method for network survivability with the
   analysis of a traffic matrix as observed by SNMP, probing techniques,
   FTP, IGP link state advertisements, and more.

   Those measurements are needed in the context of RAW to inform the
   controller and make the long term reactive decision to rebuild a
   recovery graph based on statistical and aggregated information.  RAW
   itself operates in the DetNet Network Plane at a faster time scale
   with live information on speed, state, etc...  This live information
   can be obtained directly from the lower layer, e.g., using L2
   triggers, read from a protocol such as the Dynamic Link Exchange
   Protocol (DLEP) [DLEP], or transported over multiple hops using OAM
   and reverse OAM, as illustrated in Figure 10.

3.1.2.  Applying Reliability Concepts to Networking

   The terms Reliability and Availability are defined for use in RAW in
   Section 2 and the reader is invited to read [NASA] for more details
   on the general definition of Reliability.  Practically speaking a
   number of nines is often used to indicate the reliability of a data
   link, e.g., 5 nines indicate a Packet Delivery Ratio (PDR) of
   99.999%.

   This number is typical in a wired environment where the loss is due
   to a random event such as a solar particle that affects the
   transmission of a particular frame, but does not affect the previous
   or next frame, nor frames transmitted on other links.  Note that the
   QoS requirements in RAW may include a bounded latency, and a packet
   that arrives too late is a fault and not considered as delivered.

   For a periodic networking pattern such as an automation control loop,
   this number is proportional to the Mean Time Between Failures (MTBF).
   When a single fault can have dramatic consequences, the MTBF
   expresses the chances that the unwanted fault event occurs.  In data
   networks, this is rarely the case.  Packet loss cannot never be fully
   avoided and the systems are built to resist to one loss, e.g., using
   redundancy with Retries (HARQ) or Packet Replication and Elimination
   (PRE), or, in a typical control loop, by linear interpolation from
   the previous measurements.

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   But the linear interpolation method cannot resist multiple
   consecutive losses, and a high MTBF is desired as a guarantee that
   this will not happen, IOW that the number of losses-in-a-row can be
   bounded.  In that case, what is really desired is a Maximum
   Consecutive Failures (MCF).  If the number of losses in a row passes
   the MCF, the control loop has to abort and the system, e.g., the
   production line, may need to enter an emergency stop condition.

   Engineers that build automated processes may use the network
   reliability expressed in nines or as an MTBF as a proxy to indicate
   an MCF, e.g., as described in section 7.4 of the "Deterministic
   Networking Use Cases" [RFC8578].

3.1.3.  Wireless Effects Affecting Reliability

   In contrast with wired networks, errors in transmission are the
   predominant source of packet loss in wireless networks.

   The root cause for the loss may be of multiple origins, calling for
   the use of different forms of diversity:

   Multipath Fading:  A destructive interference by a reflection of the
      original signal.

      A radio signal may be received directly (line-of-sight) and/or as
      a reflection on a physical structure (echo).  The reflections take
      a longer path and are delayed by the extra distance divided by the
      speed of light in the medium.  Depending on the frequency, the
      echo lands with a different phase which may add up to
      (constructive interference) or cancel the direct signal
      (destructive interference).

      The affected frequencies depend on the relative position of the
      sender, the receiver, and all the reflecting objects in the
      environment.  A given hop will suffer from multipath fading for
      multiple packets in a row till a physical movement changes the
      reflection patterns.

   Co-channel Interference:  Energy in the spectrum used for the
      transmission confuses the receiver.

      The wireless medium itself is a Shared Risk Link Group (SRLG) for
      nearby users of the same spectrum, as an interference may affect
      multiple co-channel transmissions between different peers within
      the interference domain of the interferer, possibly even when they
      use different technologies.

   Obstacle in Fresnel Zone:  The optimal transmission happens when the

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      Fresnel Zone between the sender and the receiver is free of
      obstacles.

      As long as a physical object (e.g., a metallic trolley between
      peers) that affects the transmission is not removed, the quality
      of the link is affected.

   In an environment that is rich of metallic structures and mobile
   objects, a single radio link will provide a fuzzy service, meaning
   that it cannot be trusted to transport the traffic reliably over a
   long period of time.

   Transmission losses are typically not independent, and their nature
   and duration are unpredictable; as long as a physical object (e.g., a
   metallic trolley between peers) that affects the transmission is not
   removed, or as long as the interferer (e.g., a radar) keeps
   transmitting, a continuous stream of packets will be affected.

   The key technique to combat those unpredictable losses is diversity.
   Different forms of diversity are necessary to combat different causes
   of loss and the use of diversity must be maximized to optimize the
   PDR.

   A single packet may be sent at different times (time diversity) over
   diverse paths (spatial diversity) that rely on diverse radio channels
   (frequency diversity) and diverse PHY technologies, e.g., narrowband
   vs. spread spectrum, or diverse codes.  Using time diversity will
   defeat short-term interferences; spatial diversity combats very local
   causes such as multipath fading; narrowband and spread spectrum are
   relatively innocuous to one another and can be used for diversity in
   the presence of the other.

3.2.  The RAW problem

   While the generic "Deterministic Networking Problem Statement"
   [RFC8557] applies to both the wired and the wireless media, the
   methods to achieve RAW must extend those used to support time-
   sensitive networking over wires, as a RAW solution has to address
   less consistent transmissions, energy conservation and shared
   spectrum efficiency.

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   Operating at the Layer-3, RAW does not change the wireless technology
   at the lower layers.  OTOH, it can further increase diversity in the
   spatial, time, code, and frequency domains by enabling multiple link-
   layer wired and wireless technologies in parallel or sequentially,
   for a higher resilience and a wider applicability.  RAW can also
   provide homogeneous services to critical applications beyond the
   boundaries of a single subnetwork, e.g., controlling the use of
   diverse radio access technologies to optimize the end-to-end
   application experience.

   RAW improves the DetNet services by providing elements that are
   specialized for transporting IP flows over deterministic radios
   technologies such as listed in [RAW-TECHNOS].  Conceptually, RAW is
   agnostic to the radio layer underneath though the capability to
   schedule transmissions is assumed.  How the PHY is programmed to do
   so, and whether the radio is single-hop or meshed, are unknown at the
   IP layer and not part of the RAW abstraction.  Nevertheless, cross-
   layer optimizations may take place to ensure proper link awareness
   (think, link quality) and packet handling (think, scheduling).

   The "Deterministic Networking Architecture" [RFC8655] is composed of
   three planes: the Application (User) Plane, the Controller Plane, and
   the Network Plane.  The DetNet Network Plane is composed a Dataplane
   (packet forwarding) and an Operational Plane where OAM operations
   take place.  In the Network Plane, the DetNet service sub-layer
   focuses on flow protection (e.g., using redundancy) and can be fully
   operated at Layer-3, while the DetNet forwarding sub-layer that
   associates the flows to the paths, ensures the availability of the
   necessary resources, must leverage Layer-2 functionalities for timely
   delivery to the next DetNet system.

   The RAW Architecture extends the DetNet Network Plane, to accommodate
   one or multiple hops of homogeneous or heterogeneous wired and
   wireless technologies.  RAW adds reactivity to the DetNet service
   sub-layer to compensate the dynamics for the radio links in terms of
   lossiness and bandwidth.  This may apply for instance to mesh
   networks as illustrated in Figure 3, or diverse radio access networks
   as illustrated in Figure 9.

   As opposed to wired links, the availability and performance of an
   individual wireless link cannot be trusted over the long term; it
   will vary with transient service discontinuity, and any lane that
   includes wireless hops is bound to face short periods of high loss.
   On the other hand, being broadcast in nature, the wireless medium
   provides capabilities that are atypical on modern wired links and
   that the RAW Architecture leverages opportunistically to improve the
   end-to-end reliability over a collection of paths.

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   Those capabilities include:

   Promiscuous Overhearing:  Because the medium is broadcast as opposed
      to physically point to point like a wire, more than one node in
      the forward direction of the packet may hear or overhear a
      transmission, and the reception by one may compensate the loss by
      another.  The concept of path can be revisited in favor multipoint
      to multipoint progress in the orward direction and statistical
      chances of successful reception of any of the transmissions by any
      of the receivers.

   L2-aware routing:  As the quality and speed of a link variates over
      time, the concept of metric must also be revisited.  Shortest path
      loses its absolute value, and hop count turns into a bad idea as
      the link budget drops with the distance.  Routing over radio
      requires both 1) a new and more dynamic sense of the link, with
      new protocols such as DLEP and L2-trigger to maintain L3 up to
      date with the link quality and availability, and 2) a new approach
      to multipath routing, where non-equal cost multipath becomes the
      norm as shortest path loses its meaning with the instability of
      the metrics.

   ARQ, FEC and codes:  Though feasible on any technology, proactive
      (forward) and reactive (ARQ) error correction are typical to the
      wireless media.  Bounded latency can still be obtained on a
      wireless link while operating those technologies, provided that
      the extra transmission happens within the budget allocated to that
      hop, or that the introduced delay is compensated along the path.
      In the case of coded fragments and retries, it makes sense to
      variate all the possible physical properties of the transmission
      to reduce the chances that the same effect causes the loss of both
      original and redundant transimissions.

   Relay Coordination and constructive interference:  Though it can be
      difficult to achieve at high speed, a fine time synchronization
      and a precise sense of phase allows the energy from multiple
      coordinated senders to add up at the receiver and actually improve
      the signal quality, compensating for either distance or physical
      objects in the Fresnel zone that would reduce the link budget.

   RAW and DetNet route application flows that require a special
   treatment along the paths that will provide that treatment.  This may
   be seen as a form of Path Aware Networking and may be subject to
   impediments documented in [RFC9049].

   The establishment of a path is not in-scope for RAW.  It may be,
   e.g., the product of a centralized Controller Plane Function (CPF)
   like a Path computation Element (PCE) [RFC4655], or may be computed

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   in a distributed fashion ala Resource ReSerVation Protocol (RSVP)
   [RFC2205].  On the other hand, RAW leverages DetNet Network Plane
   enhancements to optimize the use of the paths and match the quality
   of the transmissions over time.

   As opposed to wired networks, the action of installing a path over a
   set of wireless links may be very slow relative to the speed at which
   the radio conditions vary, and it makes sense in the wireless case to
   provide redundant forwarding solutions along a (see Section 2.3) and
   to leave it to the Network Plane to select which of those forwarding
   solutions are to be used for a given packet based on the current
   conditions.

   RAW distinguishes the longer time scale at which routes are computed
   from the the shorter time scale where forwarding decisions are made
   for a limited time RAW Network Plane operations happen at a time
   scale that sits between the routing and the forwarding time scales,
   on one DetNet flow, to select a DetNet path within the resources
   delineated by a recovery graph (see Section 2.3.2).  The recovery
   graph is preestablished and installed by means outside of the scope
   of RAW; it may be strict or loose depending on whether each or just a
   subset of the hops are observed and controlled by RAW.

   The RAW Architecture is based on an abstract OODA Loop (Observe,
   Orient, Decide, Act).  The generic concept involves:

   1.  Operational Plane measurement protocols for Operations,
       Administration and Maintenance (OAM) to Observe some or all hops
       along a recovery graph as well as the end-to-end packet delivery

   2.  The DetNet Controller Plane Function (CPF) is split with an
       optional asynchronous CPF (aCPF) that reports data and
       information such as link statistics to be used asynchronously by
       the routing CPF (rCPF) to compute, install, and maintain the
       recovery graphs, e.g., by generating knowledge and wisdom such as
       a trained model for link quality prediction, which in turn can be
       used by the aCPF to Orient the Path selection by the PLR within
       the RAW OODA loop.

   3.  An Operational Plane PLR that hosts the Decision function of
       which DetNet Paths to use for the future packets that will be
       routed within the recovery graph

   4.  Packet (hybrid) ARQ, Replication, Elimination and Ordering
       Dataplane actions that operate at the DetNet Service sub-layer to
       increase the reliability of the end-to-end transmissions.  The
       RAW architecture also covers in-situ signaling when the decision
       is Acted by a node that down the recovery graph from the PLR.

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   The overall OODA Loop optimizes the use of redundancy to achieve the
   required reliability and availability Service Level Agreement (SLA)
   while minimizing the use of constrained resources such as spectrum
   and battery.

4.  The RAW Conceptual Model

   RAW inherits the conceptual model described in section 4 of the
   DetNet Architecture [RFC8655].  RAW extends the DetNet service layer
   to provide additional agility against transmission loss.

4.1.  The RAW Planes

   A RAW Network Plane may be strict (as illustrated in Figure 5 or
   loose (as illustrated in Figure 6, depending on whether RAW observes
   and takes actions on all hops or not.  For instance, the packets
   between two wireless entities may be relayed over a wired
   infrastructure such as a Wi-Fi extended service set (ESS) or a 5G
   Core; in that case, RAW observes and controls the transmission over
   the wireless first and last hops, as well as end-to-end metrics such
   as latency, jitter, and delivery ratio.  This operation is loose
   since the structure and properties of the wired infrastructure are
   ignored, and may be either controlled by other means such as DetNet/
   TSN, or neglected in the face of the wireless hops.

   The RAW Nodes are DetNet relays that operate in the RAW Network Plane
   and are capable of additional diversity mechanisms and measurement
   functions related to the radio interface, in particular the PAREO
   diversity mechanisms.  RAW leverages a CPF that operates inside the
   RAW Nodes (typically the Ingress Edge Nodes) to dynamically adapt the
   path of the packets and optimizes the resource usage.

   An RAW-enhanced rCPF interacts with RAW Nodes over a Southbound API.
   It consumes data and information from the network and generates
   knowledge and wisdom to help steer the traffic optimally inside a
   recovery graph.

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                            DetNet Routing

           rCPF               rCPF          rCPF                 rCPF

                          Southbound API
      _-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-
    _-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-._-

                    RAW  --/   RAW  --/   RAW  --/   RAW
                /-- Node  /--  Node  /--  Node  /--  Node --/
     Ingress --/    /          /                           /-- Egress
     End           /          /         .. .                   End
     Node   ---/   /          /       .. ..  .             /-- Node
              /-- RAW  --/   RAW     ( non-RAW ) -- RAW --/
                  Node  /--  Node --- ( Nodes  )   Node
                                         ... .
     --/   wireless           wired
      /--  link           --- link

                            Figure 3: RAW Nodes

   When a new flow is defined, the rCPF uses it current knowledge of the
   network to build a new recovery graph between an Ingress End System
   and an Egress End System for that flow; it indicates to the RAW Nodes
   where the PAREO operations may be actioned in the Network Plane.

   *  The recovery graph may be strict, meaning that the DetNet
      forwarding sub-layer operations are enforced end-to-end

   *  The recovery graph may be expressed loosely to enable traversing a
      non-RAW subnetwork as in Figure 6.  In that case, RAW can not
      leverage end-to-end DetNet and cannot provide latency guarantees.
      The non-RAW subnetwork is neglected in the RAW computation, that
      is, considered jitterless, and infinitely reliable and/or
      available in comparison with the links between RAW nodes, so loss
      and jitter that is measured end-to-end is attributed to the RAW
      hops (typically an access link).

   A local asynchronous CPF in the RAW node reports the Link-Layer
   metrics to the rCPF in a time-aggregated, e.g., statistical fashion.
   Example Link-Layer metrics include typical Link bandwidth (the medium
   speed depends dynamically on the PHY mode), number of flows
   (bandwidth that can be reserved for a flow depends on the number and
   size of flows sharing the spectrum) and average and mean squared
   deviation of availability and reliability figures such as Packet
   Delivery Ratio (PDR) over long periods of time.

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   Based on those metrics, the DetNet r CPF installs the recovery graph
   with enough redundant forwarding solutions to ensure that the Network
   Plane can reliably deliver the packets within a System Level
   Agreement (SLA) associated to the flows that it transports.  The SLA
   defines end-to-end reliability and availability requirements, where
   reliability may be expressed as a successful delivery in order and
   within a bounded delay of at least one copy of a packet.

   Depending on the use case and the SLA, the recovery graph may
   comprise non-RAW segments, either interleaved inside the recovery
   graph, or all the way to the Egress End Node (e.g., a server in the
   Internet).  RAW observes the Lower-Layer Links between RAW nodes
   (typically, radio links) and the end-to-end Network Layer operation
   to decide at all times which of the PAREO diversity schemes is
   actioned by which RAW Nodes.

   Once a recovery graph is established, per-segment and end-to-end
   reliability and availability statistics are periodically reported to
   the rCPF to assure that the SLA can be met or have it recompute the
   recovery graph if not.

4.2.  RAW vs. Upper and Lower Layers

   RAW improves the reliability of transmissions and the availability of
   the communication resources, but does not provide scheduling and
   shaping, so RAW itself does not provide guarantees such as latency
   for the application payload.  Rather, it should be seen as a dynamic
   optimization of the use of redundancy to maintain it within certain
   boundaries.  For instance, ARQ, which is part of the PAREO
   capabilities (see Section 5.6) is operated by the lower layers and
   RAW will only abstract the concept and hint the lower layers on the
   desired outcome, as opposed to performing the retries at Layer-3.

   Guarantees such as bounded latency depend on the upper layers
   (Transport or Application) to provide the payload in volumes and at
   times that match the contract with the DetNet sub-layers and the
   layers below.  Excess of incoming traffic at the DetNet Ingress will
   cause either dropping, queueing, or reclassification of the packets,
   and entail loss, latency, or jitter, and moot the guarantees that are
   provided inside the DetNet Network.

   When the traffic from upper layers matches the expectation of the
   lower layers, RAW still depends on the lower layers to provide the
   timing and physical resources guarantees that are needed to match the
   traffic SLA.  When the availability of the physical resource varies,
   RAW will act on the distribution of the traffic to leverage
   alternates within a finite set of potential resources.

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4.3.  RAW and DetNet

   RAW leverages the DetNet Forwarding sub-layer and requires the
   support of in-situ OAM in DetNet Transit Nodes (see fig 3 of
   [RFC8655] for the dynamic acquisition of link capacity and state to
   maintain a strict RAW service, end-to-end, over a DetNet Network.
   RAW enhances DetNet to improve the protection against link errors
   such as transient flapping that are far more common in wireless
   links.  Nevertheless, the RAW methods are for the most part
   applicable to wired links as well, e.g., when energy savings are
   desirable and the available path diversity exceeds 1+1 linear
   redundancy.

   RAW adds a Management sub-layer that operates in the DetNet
   Operational Plane.  The RAW Management sub-layer typically runs only
   in the DetNet Ingress Edge Node or End System, though it may also run
   in DetNet Relay Nodes when the RAW Control sub-layer is distributed
   along the recovery graph.  The RAW Management sub-layer functionality
   includes the PLR that decides the DetNet Path for the future packets
   of a flows and controls the PAREO Actuators along the DetNet Path
   through specific signaling, and the OAM Supervisor that triggers, and
   learns from, OAM observations, and feeds the PLR for its next
   decision.

   RAW extends the DetNet Stack (see fig 4 of [RFC8655]) with additional
   functionality at the DetNet Service sub-layer for the actuation of
   the PLR decision by the PAREO Actuator.  Layer-3 in general and
   DetNet in particular operates on abstractions of the lower layers and
   through APIs to control those abstractions.  For instance, DetNet
   already leverages lower layers for time-sensitive operations such as
   time synchronization and traffic shapers.  Because the performances
   of the radio layers are subject to rapid changes, so RAW needs more
   dynamic gauges and knobs.  To that effect, the DetNet PREOF is
   extended with the PAREO capabilities (see Section 5.6) and the RAW
   PAREO Actuator manages dynamically the PAREO operations, which may be
   performed either within the DetNet sub-layers or at a lower layer,
   using a common radio abstraction and APIs in the latter case.  In
   particular, PAREO needs the capability to push reliability and timing
   hints like suggest X retries (min, max) within a time window, or send
   unicast (one next hop) or multicast (for overhearing).  The other way
   around RAW needs hints about the radio conditions like L2 triggers
   (RSSI, LQI, ETX…) over all the wireless hops.  This information is
   useful to both the aCPF and the PLR.

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   The RAW Service sub-layer also adds the OAM Propagator that
   (re)generates the OAM information as it is formed and propagated In-
   Band or Out-of-Band.  The RAW Service sub-layer may be present in
   DetNet Edge and Relay Nodes, though the PAREO Actuator has no
   operation in the Egress Edge Node.

    +------------------------------+ +--------------------------------+
    |                              | |                                |
   .....................................................................
    |                              | |                                |
    | +--------------------------+ | | +----------------------------+ |
    | |     aCPF                 | | | |         aCPF               | |
    | +--------------------------+ | | +----------------------------+ |
    | +----------+  +------------+ | | .-.-.-.-.-.--.  .-.-.-.-.-.--. |
    | | PLR      |  | OAM        | | | | Distr. PLR |  | Distr. OAM | |
    | |          |  | Supervisor | | | |            |  | Supervisor | |
    | +----------+  +------------+ | | .-.-.-.-.-.--.  .-.-.-.-.-.--. |
    |                              | |    optional         optional   |
       RAW Management sub-layer
   .....................................................................
       DetNet Service sub-layer
    |                              | |                                |
    | +----------+  +------------+ | | +------------+  +------------+ |
    | | PAREO    |  |  OAM       | | | |  PAREO     |  |  OAM       | |
    | | Actuator |  |  Observer  | | | |  Actuator  |  |  Observer  | |
    | +----------+  +------------+ | | +------------+  +------------+ |
    |                              | |                                |
       DetNet Service sub-layer
   .....................................................................
       DetNet Forwarding sub-layer
    |                              | |                                |
    |               +------------+ | |                 +------------+ |
    |               |In-Situ OAM | | |                 |In-Situ OAM | |
    |               +------------+ | |                 +------------+ |
    |                              | |                                |
    +------------------------------+ +--------------------------------+

            End System or                       Relay
          Ingress Edge Node                     Node

         Figure 4: RAW functional posture within DetNet sub-layers

   There are 2 main proposed models to deploy RAW and DetNet.  In the
   first model (strict) illustrated in Figure 5, RAW operates over a
   continuous DetNet Service end-to-end between the Ingress and the
   Egress Edge Nodes or End Systems.

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   A minimal Forwarding sub-layer service is provided at all DetNet
   Nodes to ensure that the OAM information flows.  Relay Nodes may or
   may not support RAW services, and the Edge nodes do support RAW.
   DetNet guarantees such as latency are provided end-to-end, and RAW
   supports the DetNet Service to optimize the use of resources.

   --------------------Flow Direction---------------------------------->

   +---------+
   | RAW     |
   | Control |
   +---------+                           +---------+        +---------+
   | RAW +   |                           | RAW +   |        | RAW +   |
   | DetNet  |                           | DetNet  |        | DetNet  |
   | Service |                           | Service |        | Service |
   +---------+---------------------------+---------+--------+---------+
   |                       DetNet                                     |
   |                     Forwarding                                   |
   +------------------------------------------------------------------+

     Ingress             Transit            Relay              Egress
     Edge      ...       Nodes     ...      Nodes     ...        Edge
     Node                                                        Node

   <--------------------Full Guarantees------------------------------->

                     Figure 5: (Strict) RAW over DetNet

   In the second model (loose), illustrated in Figure 6, RAW operates
   over a partial DetNet Service where typically only the Ingress and
   the Egress End Systems support RAW.  The DetNet Domain may extend
   beyond the Ingress node, or there may be a DetNet domain starting at
   an Ingress Edge Node at the first hop after the End System.

   In the loose model, RAW cannot observe the hops in network, and the
   path beyond the first hop is opaque; RAW can still observe the end-
   to-end behavior and use Layer-3 measurements to decide whether to
   replicate a packet and select the first hop interface(s).

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   --------------------Flow Direction---------------------------------->

   +---------+
   | RAW     |
   | Control |
   +---------+            +---------+                       +---------+
   | RAW +   |            | DetNet  |                       | RAW +   |
   | DetNet  |            |  Only   |                       | DetNet  |
   | Service |            | Service |                       | Service |
   +---------+----------------------+---+               +---+---------+
   |          DetNet                    |               |   DetNet    |
   |         Forwarding                 |               | Forwarding  |
   +------------------------------------+               +-------------+

    Ingress    Transit       Relay           Internet           Egress
    End  ...   Nodes   ...   Nodes    ...                ...       End
    System                                                      System

   <----------------------No Guarantee-------------------------------->

                            Figure 6: Loose RAW

5.  The RAW Control Loop

5.1.  Routing Time Scale vs. Forwarding Time Scale

   With DetNet, the Controller Plane Function handles the routing
   computation and maintenance.  With RAW, the routing part of the CPF
   (rCPF) is segregated from the RAW Control Loop, so it may reside
   outside of the RAW network.  To achieve RAW capabilities, the rCPF is
   enhanced to generate the information required by the local aCPF,
   which acts as the orientation component in the loop.  The rCPF may,
   e.g., propose DetNet Paths to be used as a reflex action in response
   to network events, or by provide aggregated history that the aCPF can
   use to make an oriented decision.

   In a wireless mesh, the path to the DetNet CPF can be expensive and
   slow, possibly going across the whole mesh and back.  Reaching to the
   CPF can also be slow in regards to the speed of events that affect
   the forwarding operation at the radio layer.  Note that a distributed
   routing protocol may also take time and consume excessive wireless
   resources to reconverge to a new optimized state.

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   As a result, the DetNet CPF is not expected to be aware of and to
   react to very transient changes.  The abstraction of a link at the
   routing level is expected to use statistical metrics that aggregate
   the behavior of a link over long periods of time, and represent its
   properties as shades of gray as opposed to numerical values such as a
   link quality indicator, or a boolean value for either up or down.

   The interaction with the (remote) RAW rCPF is handled by a (local)
   aCPF that builds reports to the rCPF and digests the control
   information back, to be used inside a forwarding control loop for
   traffic steering.

                     +----------------+
                     |     DetNet     |
                     |    Routing     |
                     |      CPF       |
                     +----------------+
                             ^
                             |
                            Slow
                             |
         _-._-._-._-._-._-.  |  ._-._-._-._-._-._-._-._-._-._-._-._-
       _-._-._-._-._-._-._-. | _-._-._-._-._-._-._-._-._-._-._-._-
                             |
                          Expensive
                             |
                      ....   |  .......
                  ....    .  | .       .......
               ....          v               ...
             ..    A-------B-------C---D        ..
          ...     /  \           /      \      ..
         .       I ----M-------N--***-- E        ..
         ..       \         /         /         ...
           ..      P--***--Q-----M---R        ....
             ..                              ....
              .   <----- Fast ------->    ....
               .......                ....
                      .................

      *** = flapping at this time

                           Figure 7: Time Scales

   In the case of wireless, the changes that affect the forwarding
   decision can happen frequently and often for short durations, e.g., a
   mobile object moves between a transmitter and a receiver, and will

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   cancel the line of sight transmission for a few seconds, or a radar
   measures the depth of a pool and interferes on a particular channel
   for a split second.

   There is thus a desire to separate the long term computation of the
   route and the short term forwarding decision.  In that model, the
   routing operation computes a recovery graph that enables multiple
   Non-Equal Cost Multi-Path (N-ECMP) forwarding solutions along so-
   called protection paths, and leaves it to the Network Plane to make
   the per-packet decision of which of these possibilities should be
   used.

   In the wired world, and more specifically in the context of Traffic
   Engineering (TE), an alternate path can be used upon the detection of
   a failure in the main path, e.g., using OAM in MPLS-TP or BFD over a
   collection of SD-WAN tunnels.  RAW formalizes a forwarding time scale
   that is an order(s) of magnitude shorter than the controller plane
   routing time scale, and separates the protocols and metrics that are
   used at both scales.  Routing can operate on long term statistics
   such as delivery ratio over minutes to hours, but as a first
   approximation can ignore flapping.  On the other hand, the RAW
   forwarding decision is made at the scale of the packet rate, and uses
   information that must be pertinent at the present time for the
   current transmission(s).

5.2.  A OODA Loop

   OODA (Observe, Orient, Decide, Act) is a generic formalism to
   represent the operational steps in a Control Loop.  The RAW
   Architecture applies that generic model to continuously optimize the
   spectrum and energy used to forward packets within a recovery graph,
   instantiating the OODA steps as follows:

   Observe:  Network Plane measurements, including protocols for
      Operations, Administration and Maintenance (OAM), to Observe the
      local state of the links and some or all hops along a recovery
      graph as well as the end-to-end packet delivery, more in
      Section 5.3;

   Orient:  An asynchronous CPF that reports data and information such
      as the link statistics, and leverages offline-computed wisdom and
      knowledge to Orient the PLR for its forwarding decision, more in
      Section 5.4;

   Decide:  A local PLR that decides which DetNet Path to use for the
      future packet(s) that are routed along the recovery graph, more in
      Section 5.5;

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   Act:  PAREO Dataplane actions are controlled from the DetNet Service
      sub-layer to increase the reliability of the end-to-end
      transmission.  The RAW architecture also covers in-situ signaling
      when the decision is Acted by a node that down the recovery graph
      from the PLR, more in Section 5.6.

                     +-------> Orient (aCPF) -------+
                     |        reflex actions        |
                     |       pre-trained model      |
                     |             ...              |
                     |                              v
                 Observe (OAM)                Decide (PLR)
                     ^                              |
                     |                              |
                     |                              |
                     +-------- Act (PAREO) <--------+
                                At DetNet
                             Service sub-layer

                        Figure 8: The RAW OODA Loop

   The overall OODA Loop optimizes the use of redundancy to achieve the
   required reliability and availability Service Level Agreement (SLA)
   while minimizing the use of constrained resources such as spectrum
   and battery.

5.3.  Observe: The RAW OAM

   RAW In-situ OAM operation in the Network Plane may observe either a
   full recovery graph or the DetNet Path that is being used at this
   time.  As packets may be load balanced, replicated, eliminated, and /
   or fragmented for Network Coding (NC) forward error correction (FEC),
   the RAW In-situ operation needs to be able to signal which operation
   occured to an individual packet.

   Active RAW OAM may be needed to observe the unused segments and
   evaluate the desirability of a rerouting decision.

   Finally, the RAW Service sub-layer Assurance may observe the
   individual PAREO operation of a relay node to ensure that it is
   conforming; this might require injecting an OAM packet at an upstream
   point inside the recovery graph and extracting that packet at another
   point downstream before it reaches the egress.

   This observation feeds the RAW PLR that makes the decision on which
   PAREO function is actioned at which RAW Node, for one a small
   continuous series of packets.

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                                         ...   ..
                      RAN 1  -----  ...      ..  ...
                   /              .    ..          ....
      +-------+  /              .            ..      ....    +------+
      |Ingress|-                .                     .....  |Egress|
      |  End  |------ RAN 2 -- .       Internet       ....---| End  |
      |System |-                ..                   .....   |System|
      +-------+  \               .               ......      +------+
                   \               ...   ...     .....
                      RAN n  --------  ...   .....

             <------------------> <-------------------->
                Observed by OAM       Opaque to OAM

            Figure 9: Observed Links in Radio Access Protection

   In the case of a End-to-End Protection in a Wireless Mesh, the
   recovery graph is strict and congruent with the path so all links are
   observed.

   Conversely, in the case of Radio Access Protection illustrated in
   Figure 9, the recovery graph is Loose and only the first hop is
   observed; the rest of the path is abstracted and considered
   infinitely reliable.  The loss if a packet is attributed to the first
   hop Radio Access Network (RAN), even if a particular loss effectively
   happens farther down the path.  In that case, RAW enables technology
   diversity (e.g.  Wi-Fi and 5G) which in turn improves the diversity
   in spectrum usage.

   The Links that are not observed by OAM are opaque to it, meaning that
   the OAM information is carried across and possibly echoed as data,
   but there is no information capture in intermediate nodes.  In the
   example above, the Internet is opaque and not controlled by RAW;
   still the RAW OAM measures the end-to-end latency and delivery ratio
   for packets sent via each if RAN 1, RAN 2 and RAN 3, and determines
   whether a packet should be sent over either or a collection of those
   access links.

5.4.  Orient: The RAW-enhanced DetNet Operational Plane

   RAW separates the long time scale at which a recovery graph is
   elaborated and installed, from the short time scale at which the
   forwarding decision is taken for one or a few packets (see in
   Section 5.1) that will experience the same path until the network
   conditions evolve and another path is selected within the same
   recovery graph.

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   The recovery graph computation is out of scope, but RAW expects that
   the CPF that installs the recovery graph also provides related
   knowledge in the form of meta data about the links, segments and
   possible DetNet Paths.  That meta data can be a pre-digested
   statistical model, and may include prediction of future flaps and
   packet loss, as well as recommended actions when that happens.

   The meta data may include:

   *  A set of Pre-Determined DetNet Paths that are prepared to match
      expected link degradation profiles, so the DDCPEs can take reflex
      rerouting actions when facing a degradation that matches one such
      profile.

   *  Link Quality Statistics history and pre-trained models, e.g., to
      predict the short-term variation of quality of the links in a
      recovery graph

   The recovery graph is installed with measurable objectives that are
   computed by the rCPF to achieve the RAW SLA.  The objectives can be
   expressed as any of maximum number of packet lost in a row, bounded
   latency, maximal jitter, maximum number of interleaved out of order
   packets, average number of copies received at the elimination point,
   and maximal delay between the first and the last received copy of the
   same packet.

5.5.  Decide: The Path Selection Engine

   The RAW OODA Loop operates at the path selection time scale to
   provide agility vs. the brute force approach of flooding the whole
   recovery graph.  The OODA Loop controls, within the redundant
   solutions that are proposed by the acynchronous CPF, which will be
   used for each packet to provide a Reliable and Available service
   while minimizing the waste of constrained resources.

   To that effect, RAW defines the Path Selection Engine (PLR) as a
   synchronous CPF that performs rapid local adjustments of the
   forwarding tables within the diversity that the asynchronous CPF has
   in store for the recovery graph.  The PLR enables to exploit the
   richer forwarding capabilities with PAREO and scheduled transmissions
   at a faster time scale over the smaller domain that is the recovery
   graph, in either a loose or a strict fashion.

   The PLR operates on metrics that evolve faster, but that need to be
   advertised at a fast rate but only locally, within the recovery
   graph, and reacts on the metrics updates by changing the DetNet path
   in use for the affected flows.

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   The rapid changes in the forwarding decisions are made and contained
   within the scope of a recovery graph and the actions of the PLR are
   not signaled outside the recovery graph.  This is as opposed to the
   rCPF that must observe the whole network and optimize all the
   recovery graphs globally, which can only be done at a slow pace and
   using long-term statistical metrics, as presented in Table 1.

    +===============+=============================+===================+
    |               |             rCPF            |   PLR (In Scope)  |
    +===============+=============================+===================+
    | Operation     |    Typically Centralized    |  Source-Routed or |
    |               |                             |    Distributed    |
    +---------------+-----------------------------+-------------------+
    | Communication |       Slow, expensive       |    Fast, local    |
    +---------------+-----------------------------+-------------------+
    | Time Scale    |       hours and above       | seconds and below |
    +---------------+-----------------------------+-------------------+
    | Network Size  | Large, many recovery graphs | Small, within one |
    |               |     to optimize globally    |   recovery graph  |
    +---------------+-----------------------------+-------------------+
    | Considered    |    Averaged, Statistical,   |  Instant values / |
    | Metrics       |        Shade of grey        | boolean condition |
    +---------------+-----------------------------+-------------------+

                            Table 1: CPF vs. PLR

   The PLR sits in the DetNet Service sub-Layer of Edge and Relay Nodes.
   On the one hand, it operates on the packet flow, learning the
   recovery graph and path selection information from the packet,
   possibly making local decision and retagging the packet to indicate
   so.  On the other hand, the PLR interacts with the lower layers
   (through triggers and DLEP) and with its peers (through iOAM and
   oOAM) to obtain up-to-date information about its links and the
   quality of the overall recovery graph, respectively, as illustrated
   in Figure 10.

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               |
        packet | going
      down the | stack
    +==========v==========+=====================+=====================+
    |   (iOAM + iCTRL)    | (L2 Triggers, DLEP) |       (oOAM)        |
    +==========v==========+=====================+=====================+
    |     Learn from      |                     |    Learn from       |
    |    packet tagging   >       Maintain      <    end-to-end       |
    +----------v----------+      Forwarding     |    OAM packets      |
    | Forwarding decision <        State        +---------^-----------|
    +----------v----------+                     |      Enrich or      |
    +    Retag Packet     |  Learn abstracted   >     Regenerate      |
    |    and Forward      | metrics about Links |     OAM packets     |
    +..........v..........+..........^..........+.........^.v.........+
    |                          Lower layers                           |
    +..........v.....................^....................^.v.........+
         frame | sent          Frame | L2 Ack        oOAM | | packet
          over | wireless        In  |                 In | | and out
               v                     |                    | v

                         Figure 10: PLR Interfaces

5.6.  Act: DetNet Path Selection and PAREO functions

   The main action by the PLR is the swapping of the DetNet Path within
   the recovery graph for the future packets.  The candidate DetNet
   Paths represent different energy and spectrum profiles, and provide
   protection against different failures.

   RAW also extends the DetNet protection services (typically, PREOF) to
   possibly control lower layer one-hop reliability functions that are
   more typical to wireless than wires, including Automatic Repeat
   reQuest (ARQ), Forward Error Correction (FEC), Hybrid ARQ (HARQ) that
   includes both, and other techniques such as overhearing and
   constructive interferences.  Because RAW may be leveraged on wired
   links, e.g., to save power, it is not expected that all lower layers
   support all those capabilities.

   RAW manipulates abstractions of the lower layer services to hint on
   the desired outcome, and the lower layer acts on those hints to
   provide the best approximation of that outcome, e.g., a level of
   reliability for one-hop transmission within a bounded budget of time
   and/or energy.  The term PAREO is coined to represent both that the
   set of PREOF reliability functions is extended and the fact that some
   extensions are only controlled from Layer-3 using an abstract
   interface, while they are really operated at the lower layers.

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   The RAW Path Selection can be implemented in both centralized and
   distributed scheduling approaches.  In the centralized approach, the
   PLR may obtain a set of pre-computed DetNet paths matching a set of
   expected failures, and apply the appropriate DetNet paths for the
   current state of the wireless links.  In the distributed approach,
   the signaling in the packet may be more abstract than an explicit
   Path, and the PLR decision might be revised along the select DetNet
   Path based on a better knowledge of the rest of the way.

   The dynamic DetNet Path selection in RAW avoids the waste of critical
   resources such as spectrum and energy while providing for the
   guaranteed SLA, e.g., by rerouting and/or adding redundancy only when
   a spike of loss is observed.

6.  Security Considerations

   RAW uses all forms of diversity including radio technology and
   physical path to increase the reliability and availability in the
   face of unpredictable conditions.  While this is not done
   specifically to defeat an attacker, the amount of diversity used in
   RAW makes an attack harder to achieve.

6.1.  Layer-2 encryption

   Radio networks typically encrypt at the MAC layer to protect the
   transmission.  If the encryption is per pair of peers, then certain
   RAW operations like promiscuous overhearing become impossible.

6.2.  Forced Access

   A RAW policy may typically select the cheapest collection of links
   that matches the requested SLA, e.g., use free Wi-Fi vs. paid 3GPP
   access.  By defeating the cheap connectivity (e.g., PHY-layer
   interference) the attacker can force an End System to use the paid
   access and increase the cost of the transmission for the user.

7.  IANA Considerations

   This document has no IANA actions.

8.  Contributors

   The editor wishes to thank the document co-authors:

   Lou Berger:  Lab N

   Xavi Vilajosana:  Wireless Networks Research Lab, Universitat Oberta
      de Catalunya

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   Geogios Papadopolous:  IMT Atlantique

   Remous-Aris Koutsiamanis:  IMT Atlantique

   Rex Buddenberg:  Individual contributor

   Greg Mirsky:  Ericsson

   for their contributions to the text and ideas exposed in this
   document.

9.  Acknowledgments

   This architecture could never have been completed without the support
   and recommendations from the DetNet Chairs Janos Farkas and Lou
   Berger, and Dave Black, the DetNet Tech Advisor.  Many thanks to all
   of you.

   The authors wish to thank Balazs Varga, Dave Cavalcanti, Don Fedyk,
   Nicolas Montavont, and Fabrice Theoleyre for their in-depth reviews
   during the development of this document.

10.  References

10.1.  Normative References

   [6TiSCH-ARCHI]
              Thubert, P., Ed., "An Architecture for IPv6 over the Time-
              Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)",
              RFC 9030, DOI 10.17487/RFC9030, May 2021,
              <https://www.rfc-editor.org/info/rfc9030>.

   [INT-ARCHI]
              Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <https://www.rfc-editor.org/info/rfc1122>.

   [RFC4427]  Mannie, E., Ed. and D. Papadimitriou, Ed., "Recovery
              (Protection and Restoration) Terminology for Generalized
              Multi-Protocol Label Switching (GMPLS)", RFC 4427,
              DOI 10.17487/RFC4427, March 2006,
              <https://www.rfc-editor.org/info/rfc4427>.

   [RAW-TECHNOS]
              Thubert, P., Cavalcanti, D., Vilajosana, X., Schmitt, C.,
              and J. Farkas, "Reliable and Available Wireless
              Technologies", Work in Progress, Internet-Draft, draft-

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              ietf-raw-technologies-08, 10 July 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-raw-
              technologies-08>.

   [RAW-USE-CASES]
              Bernardos, C. J., Papadopoulos, G. Z., Thubert, P., and F.
              Theoleyre, "RAW Use-Cases", Work in Progress, Internet-
              Draft, draft-ietf-raw-use-cases-11, 17 April 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-raw-use-
              cases-11>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC6291]  Andersson, L., van Helvoort, H., Bonica, R., Romascanu,
              D., and S. Mansfield, "Guidelines for the Use of the "OAM"
              Acronym in the IETF", BCP 161, RFC 6291,
              DOI 10.17487/RFC6291, June 2011,
              <https://www.rfc-editor.org/info/rfc6291>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC8578]  Grossman, E., Ed., "Deterministic Networking Use Cases",
              RFC 8578, DOI 10.17487/RFC8578, May 2019,
              <https://www.rfc-editor.org/info/rfc8578>.

   [IPv6]     Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8557]  Finn, N. and P. Thubert, "Deterministic Networking Problem
              Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019,
              <https://www.rfc-editor.org/info/rfc8557>.

   [RFC8655]  Finn, N., Thubert, P., Varga, B., and J. Farkas,
              "Deterministic Networking Architecture", RFC 8655,
              DOI 10.17487/RFC8655, October 2019,
              <https://www.rfc-editor.org/info/rfc8655>.

   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
              <https://www.rfc-editor.org/info/rfc8939>.

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   [RFC9049]  Dawkins, S., Ed., "Path Aware Networking: Obstacles to
              Deployment (A Bestiary of Roads Not Taken)", RFC 9049,
              DOI 10.17487/RFC9049, June 2021,
              <https://www.rfc-editor.org/info/rfc9049>.

10.2.  Informative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, DOI 10.17487/RFC2205,
              September 1997, <https://www.rfc-editor.org/info/rfc2205>.

   [TE]       Awduche, D., Chiu, A., Elwalid, A., Widjaja, I., and X.
              Xiao, "Overview and Principles of Internet Traffic
              Engineering", RFC 3272, DOI 10.17487/RFC3272, May 2002,
              <https://www.rfc-editor.org/info/rfc3272>.

   [STD 62]   Harrington, D., Presuhn, R., and B. Wijnen, "An
              Architecture for Describing Simple Network Management
              Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
              DOI 10.17487/RFC3411, December 2002,
              <https://www.rfc-editor.org/info/rfc3411>.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <https://www.rfc-editor.org/info/rfc4090>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [FRR]      Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <https://www.rfc-editor.org/info/rfc5714>.

   [RLFA-FRR] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,
              <https://www.rfc-editor.org/info/rfc7490>.

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   [DetNet-DP]
              Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane
              Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,
              <https://www.rfc-editor.org/info/rfc8938>.

   [DLEP]     Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B.
              Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175,
              DOI 10.17487/RFC8175, June 2017,
              <https://www.rfc-editor.org/info/rfc8175>.

   [I-D.irtf-panrg-path-properties]
              Enghardt, R. and C. Krähenbühl, "A Vocabulary of Path
              Properties", Work in Progress, Internet-Draft, draft-irtf-
              panrg-path-properties-08, 6 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-irtf-panrg-
              path-properties-08>.

   [IPoWIRELESS]
              Thubert, P. and M. Richardson, "Architecture and Framework
              for IPv6 over Non-Broadcast Access", Work in Progress,
              Internet-Draft, draft-thubert-6man-ipv6-over-wireless-15,
              8 March 2023, <https://datatracker.ietf.org/doc/html/
              draft-thubert-6man-ipv6-over-wireless-15>.

   [DetNet-OAM]
              Mirsky, G., Theoleyre, F., Papadopoulos, G. Z., Bernardos,
              C. J., Varga, B., and J. Farkas, "Framework of Operations,
              Administration and Maintenance (OAM) for Deterministic
              Networking (DetNet)", Work in Progress, Internet-Draft,
              draft-ietf-detnet-oam-framework-09, 5 October 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-detnet-
              oam-framework-09>.

   [NASA]     Adams, T., "RELIABILITY: Definition & Quantitative
              Illustration", <https://kscddms.ksc.nasa.gov/Reliability/
              Documents/150814-3bWhatIsReliability.pdf>.

Author's Address

   Pascal Thubert (editor)
   06330 Roquefort-les-Pins
   France
   Email: pascal.thubert@gmail.com

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