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RAW                                                      P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Informational                         G.Z. Papadopoulos
Expires: 7 January 2021                                   IMT Atlantique
                                                           R. Buddenberg
                                                             6 July 2020


         Reliable and Available Wireless Architecture/Framework
                   draft-pthubert-raw-architecture-04

Abstract

   Due to uncontrolled interferences, including the self-induced
   multipath fading, deterministic networking can only be approached on
   wireless links.  The radio conditions may change -way- faster than a
   centralized routing can adapt and reprogram, in particular when the
   controller is distant and connectivity is slow and limited.  RAW
   separates the routing time scale at which a complex path is
   recomputed from the forwarding time scale at which the forwarding
   decision is taken for an individual packet.  RAW operates at the
   forwarding time scale.  The RAW problem is to decide, within the
   redundant solutions that are proposed by the routing, which will be
   used for each individual packet to provide a DetNet service while
   minimizing the waste of resources.

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 7 January 2021.

Copyright Notice

   Copyright (c) 2020 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 Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Related Work at The IETF  . . . . . . . . . . . . . . . . . .   6
   4.  Use Cases and Requirements Served . . . . . . . . . . . . . .   6
     4.1.  Radio Access Protection . . . . . . . . . . . . . . . . .   7
     4.2.  End-to-End Protection in a Wireless Mesh  . . . . . . . .   8
   5.  RAW Considerations  . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Reliability and Availability  . . . . . . . . . . . . . .   8
       5.1.1.  High Availability Engineering Principles  . . . . . .   8
       5.1.2.  Applying Reliability Concepts to Networking . . . . .  11
       5.1.3.  Reliability in the Context of RAW . . . . . . . . . .  11
     5.2.  RAW Scope and Prerequisites . . . . . . . . . . . . . . .  13
     5.3.  Routing Time Scale vs. Forwarding Time Scale  . . . . . .  14
   6.  RAW Architecture Elements . . . . . . . . . . . . . . . . . .  15
     6.1.  Wireless Tracks . . . . . . . . . . . . . . . . . . . . .  15
     6.2.  PAREO Functions . . . . . . . . . . . . . . . . . . . . .  16
       6.2.1.  Packet Replication  . . . . . . . . . . . . . . . . .  17
       6.2.2.  Packet Elimination  . . . . . . . . . . . . . . . . .  18
       6.2.3.  Promiscuous Overhearing . . . . . . . . . . . . . . .  18
       6.2.4.  Constructive Interference . . . . . . . . . . . . . .  18
   7.  RAW Architecture  . . . . . . . . . . . . . . . . . . . . . .  19
     7.1.  PCE vs. PSE . . . . . . . . . . . . . . . . . . . . . . .  20
     7.2.  RAW OAM . . . . . . . . . . . . . . . . . . . . . . . . .  22
     7.3.  Flow Identification vs. Path Identification . . . . . . .  23
     7.4.  Source-Routed vs. Distributed Forwarding Decision . . . .  25
     7.5.  Encapsulation and Decapsulation . . . . . . . . . . . . .  26
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
     8.1.  Forced Access . . . . . . . . . . . . . . . . . . . . . .  26
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  26
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  27
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     12.2.  Informative References . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30





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1.  Introduction

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

   Wireless networks operate on a shared medium where uncontrolled
   interference, including the self-induced multipath fading, cause
   random transmission losses and add new dimensions to the statistical
   effects that affect the delivery.  Scheduling can alleviate those
   effects by enabling diverse transmissions in the spatial, time, code,
   and frequency domains.  Reliable and Available Wireless (RAW)
   leverages scheduling and all possible forms of diversity to defeat
   the possible causes of transmission loss while preserving energy and
   optimizing the use of the shared spectrum.

   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.  This innovation was introduced on wired networks
   with IEEE 802.1 TSN (for Ethernet LANs) and IETF DetNet.  It is
   getting traction in various industries including professional A/V,
   manufacturing, online gaming, and smartgrid automation, enabling cost
   and performance optimizations (e.g., vs. loads of P2P cables).

   The wireless and wired media are fundamentally different at the
   physical level, and 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.

   Uncontrolled interference and transmission obstacles may impede the
   wireless transmission, causing rapid variations of the throughput and
   packet delivery ratio (PDR) of the link.  This uncertainty limits the
   volume and/or duration of traffic that can be safely transmitted on
   the same link while conforming to a RAW Service Level Agreement
   (SLA).  Techniques such as beamforming with Multi-User MIMO can only
   alleviate some of those issues, and the term deterministic is usually
   not associated with a short range radio link, in particular one
   operated in the ISM band.




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   This increased complexity explains why the development of
   deterministic wireless technologies has been lagging behind the
   similar efforts for wired systems, both at the IEEE and the IETF.
   But recent progress on scheduled radios such as TSCH and OFDMA
   indicates that wireless is finally catching up at the lower layers.
   Sitting at the layer above, RAW takes up the challenge of providing
   highly available and reliable end-to-end performances in a network
   with scheduled wireless segments.

   RAW provides DetNet elements that are specialized for short range
   radios.  From this inheritance, RAW stays 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.

   The "Deterministic Networking Architecture" [RFC8655] is composed of
   three planes: the Application (User) Plane, the Controller Plane, and
   the Network Plane.  The RAW Architecture extends the DetNet Network
   Plane, to accomodate one or multiple hops of homogeneous or
   heterogeneous wireless technologies, e.g. a Wi-Fi6 Mesh or parallel
   CBRS access links federated by a 5G backhaul.

   The establishment of a path is not in-scope for RAW.  It may be the
   product of a centralized Controller Plane as described for DetNet.
   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 complex path 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 forwarding time scale where per-packet decisions
   are made.  RAW operates within the Network Plane at the forwarding
   time scale on one DetNet flow over a complex path called a Track.
   The Track 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 covers Network Plane protocol elements such as
   Operations, Administration and Maintenance (OAM) to observe some or
   all hops along a Track as well as the end-to-end packet delivery, and
   in-band control to optimize the use of redundancy to achieve the
   required SLA with minimal use of constrained resources.





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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 also reuses terminology defined for 6TiSCH in [6TiSCH-ARCHI] such
   as the term Track.  A Track as a complex path with associated PAREO
   operations.  The concept is abstract to the underlaying technology
   and applies to any fully or partially wireless mesh, including, e.g.,
   a Wi-Fi mesh.  RAW specifies strict and loose Tracks 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 term OAM as defined in [RFC6291].

   RAW defines the following terms:

   PAREO:  Packet (hybrid) ARQ, Replication, Elimination and Ordering.
      PAREO is a superset Of DetNet's PREOF that includes radio-specific
      techniques such as short range broadcast, MUMIMO, constructive
      interference and overhearing, which can be leveraged separately or
      combined to increase the reliability.

   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.

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

   Reliability:  Reliability is a measure of the probability that an
      item will perform its intended function for a specified interval
      under stated conditions.  For RAW, the service that is expected is
      delivery within a bounded latency and a failure is when the packet
      is either lost or delivered too late.  RAW expresses reliability
      in terms of Mean Time Between Failure (MTBF) and Maximum
      Consecutive Failures (MCF).  More in [NASA].

   Availability:  Availability is a measure of the relative amount of
      time where a path operates in stated condition, in other words
      (uptime)/(uptime+downtime).  Because a serial wireless path may
      not be good enough to provide the required availability, and even
      2 parallel paths may not be over a longer period of time, the RAW
      availability implies a path that is a lot more complex than what
      DetNet typically envisages (a Track).





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3.  Related Work at The IETF

   RAW intersects with protocols or practices in development at the IETF
   as follows:

   *  The Dynamic Link Exchange Protocol (DLEP) [RFC8175] from [MANET]
      can be leveraged at each hop to derive generic radio metrics
      (e.g., based on LQI, RSSI, queueing delays and ETX) on individual
      hops.

   *  OAM work at [detnet] such as [DetNet-IP-OAM] for the case of the
      IP Data Plane observes the state of DetNet paths, typically MPLS
      and IPv6 pseudowires [DetNet-DP-FW], in the direction of the
      traffic.  RAW needs feedback that flows on the reverse path and
      gathers instantaneous values from the radio receivers at each hop
      to inform back the source and replicating relays so they can make
      optimized forwarding decisions.  The work named ICAN may be
      related as well.

   *  [BFD] detect faults in the path between an Ingress and an Egress
      forwarding engines, but is unaware of the complexity of a path
      with replication, and expects bidirectionality.  BFD considers
      delivery as success whereas with RAW the bounded latency can be as
      important as the delivery itself.

   *  [SPRING] and [BIER] define in-band signaling that influences the
      routing when decided at the head-end on the path.  There's already
      one RAW-related draft at BIER [BIER-PREF] more may follow.  RAW
      will need new in-band signaling when the decision is distributed,
      e.g., required chances of reliable delivery to destination within
      latency.  This signaling enables relays to tune retries and
      replication to meet the required SLA.

   *  [CCAMP] defines protocol-independent metrics and parameters
      (measurement attributes) for describing links and paths that are
      required for routing and signaling in technology-specific
      networks.  RAW would be a source of requirements for CCAMP to
      define metrics that are significant to the focus radios.

4.  Use Cases and Requirements Served

   In order to focus on real-worlds issues and assert the feasibility of
   the proposed capabilities, RAW focuses on selected technologies that
   can be scheduled at the lower layers: IEEE Std. 802.15.4 timeslotted
   channel hopping (TSCH), 3GPP 5G ultra-reliable low latency
   communications (URLLC), IEEE 802.11ax/be where 802.11be is extreme
   high throughput (EHT), and L-band Digital Aeronautical Communications
   System (LDACS).  See [RAW-TECHNOS] for more.



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   "Deterministic Networking Use Cases" [RFC8578] presents a number of
   wireless use cases including Wireless, such as application to
   Industrial Applications, Pro-Audio, and SmartGrid Automation.
   [RAW-USE-CASES] adds a number of use cases that demonstrate the need
   for RAW capabilities for new applications such as Pro-Gaming and
   drones.  The use cases can be abstracted in two families, Loose
   Protection, e.g., protecting the first hop in Radio Access Protection
   and Strict Protection, e.g., providing End-to-End Protection in a
   wireless mesh.

4.1.  Radio Access Protection

   To maintain the required SLA at all times, a wireless Host may use
   more than one Radio Access Network (RAN) in parallel.

                                      ...   ..
                    RAN 1  -----  ...     ..  ...
                 /              .      ..         ....
   +--------+  /              .                    ....    +-----------+
   |Wireless|-                .                     .....  |  Service  |
   | Device |-***-- RAN 2 -- .       Internet       ....---|     /     |
   |(STA/UE)|-                ..                   .....   |Application|
   +--------+  $$$             .               .......     +-----------+
                 \               ...   ...     .....
                    RAN n  --------  ...   .....

   *** = flapping at this time  $$$ expensive

                     Figure 1: Radio Access Protection

   The RANs may be heterogeneous, e.g., 3GPP 5G [RAW-5G] and Wi-Fi
   [RAW-TECHNOS] for high-speed communication, in which case a Layer-3
   abstraction becomes useful to select which of the RANs are used at a
   particular point of time, and the amount of traffic that is
   distributed over each RAN.

   The idea is that the rest of the path to the destination(s) is
   protected separately (e.g., uses non-congruent paths, leverages
   DetNet / TSN, etc...) and is a lot more reliable, e.g., wired.  In
   that case, RAW observes the reliability of the end-to-end operation
   through each of the RANs but only observes and controls the wireless
   operation the first hop.

   A variation of that use case has a pair of wireless Hosts connected
   over a wired core / backbone network.  In that case, RAW observes and
   controls the Ingress and Egress RANs, while neglecting the hops in
   the core.  The resulting loose Track may be instanciated, e.g., using
   tunneling or loose source routing between the RANs.



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4.2.  End-to-End Protection in a Wireless Mesh

   In radio technologies that support mesh networking (e.g., Wi-Fi and
   TSCH), a Track is a complex path with distributed PAREO capabilities.
   In that case, RAW operates through the multipath and makes decisions
   either at the Ingress or at every hop (more in Section 6.1).

                           A-------B-------C-----D
                          /  \   /       /        \
                   Ingress ----M-------N--zzzzz--- Egress
                          \      \   /            /
                           P--zzz--Q-------------R

                  zzz = flapping now

                      Figure 2: End-to-End Protection

   The Protection may be imposed by the source based on end-to-end OAM,
   or performed hop-by-hop, in which case the OAM must enables the
   intermediate Nodes to estimate the quality of the rest of the
   feasible paths in the remainder of the Track to the destination.

5.  RAW Considerations

5.1.  Reliability and Availability

5.1.1.  High Availability Engineering Principles

   The reliability criteria of a critical system pervade 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 communicaitons in
   the context of RAW.

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

   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.






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5.1.1.1.  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 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 parcimony.

5.1.1.2.  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].



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   Deterministic flows, on the contrary, are attached to specific paths
   where dedicated resources are reserved for each flow.  This is why
   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.

5.1.1.3.  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.

   "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
   complex path.  But RAW itself operates in the Network Plane at a
   faster time scale.  To act on the Data Plane, RAW needs live
   information from the Operational Plane , e.g., using Bidirectional
   Forwarding Detection [BFD] and its variants (bidirectional and remote
   BFD) to protect a link, and OAM techniques to protect a path.








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5.1.2.  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 measuremnents.

   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].

5.1.3.  Reliability in the Context of RAW

   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



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      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 the something moves that 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
      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 maximised to optimize the
   PDR.



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   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.

5.2.  RAW Scope and Prerequisites

   A prerequisite to the RAW work is that an end-to-end routing function
   computes a complex sub-topology along which forwarding can happen
   between a source and one or more destinations.  The concept of Track
   is specified in the 6TiSCH Architecture [6TiSCH-ARCHI] to represent
   that complex sub-topology.  Tracks provide a high degree of
   redundancy and diversity and enable the DetNet PREOF, network coding,
   and possibly RAW specific techniques such as PAREO, leveraging
   frequency diversity, time diversity, and possibly other forms of
   diversity as well.

   How the routing operation (e.g., PCE) in the Controlloer Plane
   computes the Track is out of scope for RAW.  The scope of the RAW
   operation is one Track, and the goal of the RAW operation is to
   optimize the use of the Track at the forwarding timescale to maintain
   the expected SLA while optimizing the usage of constrained resources
   such as energy and spectrum.

   Another prerequisite is that an IP link can be established over the
   radio with some guarantees in terms of service reliability, e.g., it
   can be relied upon to transmit a packet within a bounded latency and
   provides a guaranteed BER/PDR outside rare but existing transient
   outage windows that can last from split seconds to minutes.  The
   radio layer can be programmed with abstract parameters, and can
   return an abstract view of the state of the Link to help the Network
   Layer forwarding decision (think DLEP from MANET).

   How the radio interface manages its lower layers is out of control
   and out of scope for RAW.  In the same fashion, the non-RAW portion
   along a loose Track is by definition out of control and out of scope
   for RAW.  Whether it is a single hop or a mesh is also unknown and
   out of scope.









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5.3.  Routing Time Scale vs. Forwarding Time Scale

   With DetNet, the Controller Plane Function that handles the routing
   computation and maintenance (the PCE) can be centralized and can
   reside outside the network.  In a wireless mesh, the path to the PCE
   can be expensive and slow, possibly going across the whole mesh and
   back.  Reaching to the PCE can also be slow in regards to the speed
   of events that affect the forwarding operation at the radio layer.

   Due to that cost and latency, the Controller Plane is not expected to
   be sensitive/reactive to 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.


                     +----------------+
                     |  Controller    |
                     |    [PCE]       |
                     +----------------+
                             ^
                             |
                            Slow
                             |
         _-._-._-._-._-._-.  |  ._-._-._-._-._-._-._-._-._-._-._-._-
       _-._-._-._-._-._-._-. | _-._-._-._-._-._-._-._-._-._-._-._-
                             |
                          Expensive
                             |
                      ....   |  .......
                  ....    .  | .       .......
               ....          v               ...
             ..    A-------B-------C---D        ..
          ...     /  \   /       /      \      ..
         .       I ----M-------N--***-- E        ..
         ..       \      \   /         /         ...
           ..      P--***--Q----------R        ....
             ..                              ....
              .   <----- Fast ------->    ....
               .......                ....
                      .................

      *** = flapping at this time


                           Figure 3: Time Scales



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   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
   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 complex Track that enables multiple Non-
   Equal Cost Multi-Path (N-ECMP) forwarding solutions, and leaves it to
   the Data 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).

6.  RAW Architecture Elements

   A RAW Network Plane may be strict or loose, 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 control 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.

6.1.  Wireless Tracks

   The "6TiSCH Architecture" [6TiSCH-ARCHI] introduces the concept of
   Track.  RAW extends the concept to any wireless mesh technology,
   including, e.g., Wi-Fi.  A simple Track is composed of a direct
   sequence of reserved hops to ensure the transmission of a single
   packet from a source Node to a destination Node across a multihop
   path.



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   A Complex Track provides multiple non-equal cost multipath (NECM)
   forwarding solutions.  The Complex Track enables to support multi-
   path redundant forwarding by employing PRE functions [RFC8655] and
   the ingress and within the Track.  For example, a Complex Track may
   branch off and rejoin over non-congruent segments.

   In the context of RAW, some links or segments in the Track may be
   reversible, meaning that they can be used in either direction.  In
   that case, an indication in the packet signals the direction of the
   reversible links or segments that the packet traverses and thus
   places a constraint that prevents loops from occuring.  An indidual
   packet follows a destination-oriented directed acyclic graph (DODAG)
   towards a destination Node inside the Complex Track.

6.2.  PAREO Functions

   RAW may control whether and how to use packet replication and
   elimination (PRE), Automatic Repeat reQuest (ARQ), Hybrid ARQ (HARQ)
   that includes Forward Error Correction (FEC) and coding, and other
   wireless-specific techniques such as overhearing and constructive
   interferences, in order to increase the reliabiility and availability
   of the end-to-end transmission.

   Collectively, those function are called PAREO for Packet (hybrid)
   ARQ, Replication, Elimination and Ordering.  By tuning dynamically
   the use of PAREO functions, RAW avoids the waste of critical
   resources such as spectrum and energy while providing that the
   guaranteed SLA, e.g., by adding redundancy only when a spike of loss
   is observed.

   In a nutshell, PAREO establishes several paths in a network to
   provide redundancy and parallel transmissions to bound the end-to-end
   delay to traverse the network.  Optionally, promiscuous listening
   between paths is possible, such that the Nodes on one path may
   overhear transmissions along the other path.  Considering the
   scenario shown in Figure 4, many different paths are possible for S
   to reach R.  A simple way to benefit from this topology could be to
   use the two independent paths via Nodes A, C, E and via B, D, F.  But
   more complex paths are possible by interleaving transmissions from
   the lower level of the path to the upper level.

                             (A) -- (C) -- (E)
                           /                   \
                   Ingress    |      |      |    Egress
                           \                   /
                             (B) -- (D) -- (F)

              Figure 4: A Ladder Shape with Two Parallel Paths



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   PAREO may also take advantage of the shared properties of the
   wireless medium to compensate for the potential loss that is incurred
   with radio transmissions.

   For instance, when the source sends to Node A, Node B may listen
   promiscuously and get a second chance to receive the frame without an
   additional transmission.  Note that B would not have to listen if it
   already received that particular frame at an earlier timeslot in a
   dedicated transmission towards B.

   The PAREO model can be implemented in both centralized and
   distributed scheduling approaches.  In the centralized approach, a
   Path Computation Element (PCE) scheduler calculates a Track and
   schedules the communication.  In the distributed approach, the Track
   is computed within the network, and signaled in the packets, e.g.,
   using BIER-TE, Segment Routing, or a Source Routing Header.

6.2.1.  Packet Replication

   By employing a Packet Replication procedure, a Node forwards a copy
   of each data packet to more than one successor.  To do so, each Node
   (i.e., Ingress and intermediate Node) sends the data packet multiple
   times as separate unicast transmissions.  For instance, in Figure 5,
   the Ingress Node is transmitting the packet to both successors, nodes
   A and B, at two different times.

                          ===> (A) => (C) => (E) ===
                        //        \\//   \\//       \\
                Ingress           //\\   //\\          Egress
                        \\       //  \\ //  \\      //
                          ===> (B) => (D) => (F) ===


                        Figure 5: Packet Replication

   An example schedule is shown in Table 1.  This way, the transmission
   leverages with the time and spatial forms of diversity.

       +=========+======+======+======+======+======+======+======+
       | Channel |  0   |  1   |  2   |  3   |  4   |  5   |  6   |
       +=========+======+======+======+======+======+======+======+
       | 0       | S->A | S->B | B->C | B->D | C->F | E->R | F->R |
       +---------+------+------+------+------+------+------+------+
       | 1       |      | A->C | A->D | C->E | D->E | D->F |      |
       +---------+------+------+------+------+------+------+------+

               Table 1: Packet Replication: Sample schedule




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6.2.2.  Packet Elimination

   The replication operation increases the traffic load in the network,
   due to packet duplications.  This may occur at several stages inside
   the Track, and to avoid an explosion of the number of copies, a
   Packet Elimination procedure must be applied as well.  To this aim,
   once a Node receives the first copy of a data packet, it discards the
   subsequent copies.

   The logical functions of Replication and Elimination may be
   collocated in an intermediate Node, the Node first eliminating the
   redundant copies and then sending the packet exactly once to each of
   the selected successors.

6.2.3.  Promiscuous Overhearing

   Considering that the wireless medium is broadcast by nature, any
   neighbor of a transmitter may overhear a transmission.  By employing
   the Promiscuous Overhearing operation, the next hops have additional
   opportunities to capture the data packets.  In Figure 6, when Node A
   is transmitting to its DP (Node C), the AP (Node D) and its sibling
   (Node B) may decode this data packet as well.  As a result, by
   employing corellated paths, a Node may have multiple opportunities to
   receive a given data packet.

                      ===> (A) ====> (C) ====> (E) ====
                    //     ^ | \\                      \\
             Ingress       | |   \\                      Egress
                    \\     | v     \\                  //
                      ===> (B) ====> (D) ====> (F) ====

                     Figure 6: Unicast with Overhearing

6.2.4.  Constructive Interference

   Constructive Interference can be seen as the reverse of Promiscuous
   Overhearing, and refers to the case where two senders transmit the
   exact same signal in a fashion that the emitted symbols add up at the
   receiver and permit a reception that would not be possible with a
   single sender at the same PHY mode and the same power level.

   Constructive Interference was proposed on 5G, Wi-Fi7 and even tested
   on IEEE Std 802.14.5.  The hard piece is to synchronize the senders
   to the point that the signals are emitted at slightly different time
   to offset the difference of propagation delay that corresponds to the
   difference of distance of the transmitters to the receiver at the
   speed of light to the point that the symbols are superposed long
   enough to be recognizable.



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7.  RAW Architecture

   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.

   A Controller Plane Function (CPF) called the Path Computation Element
   (PCE) [RFC4655] interacts with RAW Nodes over a Southbound API.  The
   RAW Nodes are DetNet relays that are capable of additional diversity
   mechanisms and measurement functions related to the radio interface,
   in particular the PAREO diversity mechanisms.

   The PCE defines a complex Track between an Ingress End System and an
   Egress End System, and indicates to the RAW Nodes where the PAREO
   operations may be actionned in the Network Plane.  The Track may be
   expressed loosely to enable traversing a non-RAW subnetwork.  In that
   case, the expectation is that the non-RAW subnetwork can be neglected
   in the RAW computation, that is, considered infinitely fast, reliable
   and/or available in comparison with the links between RAW nodes.

           CPF               CPF          CPF                 CPF


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


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

                            Figure 7: RAW Nodes

   The Link-Layer metrics are reported to the PCE 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 and the number of users 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 PCE installs the Track 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 Track may comprise non-RAW
   segments, either interleaved inside the Track, 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 Track is established, per-segment and end-to-end reliability
   and availability statistics are periodically reported to the PCE to
   assure that the SLA can be met or have it recompute the Track if not.

7.1.  PCE vs. PSE

   RAW separates the path computation time scale at which a complex path
   is recomputed from the path selection time scale at which the
   forwarding decision is taken for one or a few packets (more in
   Section 5.3).  RAW operates at the path selection time scale.  The
   RAW problem is to decide, within the redundant solutions that are
   proposed by the PCE, 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 (PSE) that is
   the counter-part of the PCE to perform rapid local adjustments of the
   forwarding tables within the diversity that the PCE has selected for
   the Track.  The PSE enables to exploit the richer forwarding
   capabilities with PAREO and scheduled transmissions at a faster time
   scale over the smaller domain that is the Track, in either a loose or
   a strict fashion.

   Compared to the PCE, the PSE operates on metrics that evolve faster,
   but that needs to be advertised at a fast rate but only locally,
   within the Track.  The forwarding decision may also change rapidly,
   but wiht a scope that is also contained within the Track, with no
   visibility to the other Tracks and flows in the network.  This is as
   opposed to the PCE that needs to observe the whole network, and
   optimize all the Tracks globally, which can only be done at a slow
   pace and using long-term statistical metrics, as presented in
   Table 2.




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      +===============+========================+===================+
      |               |   PCE (Not in Scope)   |   PSE (In Scope)  |
      +===============+========================+===================+
      | Operation     |      Centralized       |  Source-Routed or |
      |               |                        |    Distributed    |
      +---------------+------------------------+-------------------+
      | Communication |    Slow, expensive     |    Fast, local    |
      +---------------+------------------------+-------------------+
      | Time Scale    |    hours and above     | seconds and below |
      +---------------+------------------------+-------------------+
      | Network Size  | Large, many Tracks to  | Small, within one |
      |               |   optimize globally    |       Track       |
      +---------------+------------------------+-------------------+
      | Considered    | Averaged, Statistical, |  Instant values / |
      | Metrics       |     Shade of grey      | boolean condition |
      +---------------+------------------------+-------------------+

                           Table 2: PCE vs. PSE

   The PSE sits in the DetNet Service sub-Layer of Edge and Relay Nodes.
   On the one hand, it operates on the packet flow, learning the Track
   and path selection information from the packet, possibly making local
   decision and retagging the packet to indicate so.  On the other hand,
   the PSE interacts with the lower layers and with its peers to obtain
   up-to-date information about its radio links and the quality of the
   overall Track, respectively, as illustrated in Figure 8.

               |
        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 8: PSE



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7.2.  RAW OAM

   The RAW OAM operation in the Network Plane observes either a full
   Track or subTracks that are being used at this time.  This
   observeation feeds the RAW PSE that makes the decision on which PAREO
   function in actioned at which RAW Node, for one a small continuous
   series of packets.

                                         ...   ..
                      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 Track
   is strict and congruent with the path so all links are observed.
   Conversely, in the case of Radio Access Protection, the Track is
   Loose and in that case only the first hop is observed; the rest of
   the path is abstracted and considered infinitely reliable.

   In the case of the Radio Access Protection, only the first hop is
   protected; the loss of a packet that was sent over one of the
   possible first hops is attributed to that first hop, even if a
   particular loss effectively happens farther down the path.

   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.








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7.3.  Flow Identification vs. Path Identification

   Section 4.7 of the DetNet Architecture [RFC8655] ties the app-flow
   identification which is an appliation layer concept with the network
   path identification that depends on the networking technology by
   "exporting of flow identification", e.g., to a MPLS label.

   With RAW, this exporting operation is injective but not bijective.
   e.g., a flow is fully placed within one RAW Track, but not all
   packets along that Track are necessarily part of the same flow.  For
   instance, out-of-band OAM packets must circulate in the exact same
   fashion as the flows that they observe.  It results that the flow
   identification that maps to to app-flow at the network layer must be
   separate from the path identification that is used to forward a
   packet.

   Section 3.4 of the DetNet data-plane framework [DetNet-DP-FW]
   indicates that for a DetNet IP Data Plane, a flow is identified by an
   IPv6 6-tuple.  With RAW, that 6-tuple is not what indicates the
   Track, in other words, the flow ID is not the Track ID.

   For instance, the 6TiSCH Architecture [6TiSCH-ARCHI] uses a
   combination of the address of the Egress End System and an instance
   identifier in a Hop-by-hop option to indicate a Track.  This way, if
   a packet "escapes" the Track, it will reach the Track Egress point
   through normal routing and be treated at the service layer through,
   say, elimination and reordering.

   The RAW service includes forwarding over a subset of the Links that
   form the Track (a subTrack).  Packets from the same or a different
   flow that are routed through the same Track will not necessarily
   traverse the same Links.  The PSE selects a subTrack for a packet
   based on the links that are preferred and those that should be
   avoided at this time.

   Each packet is forwarded within the subTrack that provides the best
   adequation with the SLA of the flow and the energy and bandwidth
   constraints of the network.













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                        Flow 1 (6-tuple) ----+
                                             |
                   Flow 2 (6-tuple)  ---+    |
                                        |    |
                OAM     -----------+    |    |
                                   |    |    |
                                   |    |    |
                              |    |    |    |    |
                              |    v    v    v    |
                              |                   |
                              +---------+---------+
                                        |
                                        |
                        Track i (Egress IP Address, instanceId)
                                        |
                                        |
                                        |
                        +---------+-----+--....-------+
                        |         |                   |
                        |         |                   |
                 subTrack 1    subTrack 2          subTrack n
                        |         |                   |
                        |         |                   |
                        V         V                   V
                     +-----------------------------------+
                     |                                   |
                     |         Destination               |
                     |                                   |
                     +-----------------------------------+




                         Figure 10: Flow Injection

   With 6TiSCH, packets are tagged with the same (destination address,
   instance ID) will experience the same RAW service regardless of the
   IPv6 6-tuple that indicates the flow.  The forwarding does not depend
   on whether the packets transport application flows or OAM.  In the
   generic case, the Track or the subTrack can be signaled in the packet
   through other means, e.g., encoded in the suffix of the destination
   address as a Segment Routing Service Instruction [SR-ARCHI], or
   leveraging Bit Index Explicit Replication [BIER] Traffic Engineering
   [BIER-TE].







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7.4.  Source-Routed vs. Distributed Forwarding Decision

   Within a large routed topology, the route-over mesh operation builds
   a particular complex Track with one source and one or more
   destinations; within the Track, packets may follow different paths
   and may be subject to RAW forwarding operations that include
   replication, elimination, retries, overhearing and reordering.

   The RAW forwarding decisions include the selection of points of
   replication and elimination, how many retries can take place, and a
   limit of validity for the packet beyond which the packet should be
   destroyed rather than forwarded uselessly further down the Track.

   The decision to apply the RAW techniques must be done quickly, and
   depends on a very recent and precise knowledge of the forwarding
   conditions within the complex Track.  There is a need for an
   observation method to provide the RAW Data Plane with the specific
   knowledge of the state of the Track for the type of flow of interest
   (e.g., for a QoS level of interest).  To observe the whole Track in
   quasi real time, RAW considers existing tools such as L2-triggers,
   DLEP, BFD and leverages in-band and out-of-band OAM to capture and
   report that information to the PSE.

   One possible way of making the RAW forwarding decisions within a
   Track is to position a unique PSE at the Ingress and express its
   decision in-band in the packet, which requires the explicit signaling
   of the subTrack within the Track.  In that case, the RAW forwarding
   operation along the Track is encoded by the source, e.g., by
   indicating the subTrack in the Segment Routing (SRv6) Service
   Instruction, or by leveraging BIER-TE such as done with [BIER-PREF].

   The alternate way is to operate the PSE in each forwarding Node,
   which makes the RAW forwarding decisions for a packet on its own,
   based on its knowledge of the expectation (timeliness and
   reliability) for that packet and a recent observation of the rest of
   the way across the possible paths based on OAM.  Information about
   the desired service should be placed in the packet and matched with
   the forwarding Node's capabilities and policies.

   In either case, a per-track/subTrack state is installed in all the
   intermediate Nodes to recognize the packets that are following a
   Track and determine the forwarding operation to be applied.









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7.5.  Encapsulation and Decapsulation

   In the generic case where the Track Ingress Node is not the source of
   the Packet, the Ingress Node needs to encapsulate IP-in-IP to ensure
   that the Destination IP Address is that of the Egress Node and that
   the necessary Headers (Router Header, Segment Routing Header and/or
   Hop-By-Hop Header) can be added to the packet to signal the Track or
   the subTrack, conforming [IPv6] that discourages the insertion of a
   Header on the fly.

   In the specific case where the Ingress Node is the source of the
   packet, the encapsulation can be avoided, provided that the source
   adds the necessary headers and that the destination is set to the
   Egress Node.  Forwarding to a final destination beyond the Egress
   Node is possible, e.g., with a Segment Routing Header that signals
   the rest of the way.  In that case a Hop-by-Hop Header is not
   recommmended since its validity is within the Track only.


8.  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.

8.1.  Forced Access

   RAW will typically select the cheapest collection of links that
   matches the requested SLA, for instance, leverage 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.

9.  IANA Considerations

   This document has no IANA actions.

10.  Contributors

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

   Remous-Aris Koutsiamanis:  IMT Atlantique

   Nicolas Montavont:  IMT Atlantique




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11.  Acknowledgments

   TBD

12.  References

12.1.  Normative References

   [6TiSCH-ARCHI]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", Work in Progress, Internet-Draft,
              draft-ietf-6tisch-architecture-28, 29 October 2019,
              <https://tools.ietf.org/html/draft-ietf-6tisch-
              architecture-28>.

   [RAW-TECHNOS]
              Thubert, P., Cavalcanti, D., Vilajosana, X., Schmitt, C.,
              and J. Farkas, "Reliable and Available Wireless
              Technologies", Work in Progress, Internet-Draft, draft-
              thubert-raw-technologies-05, 18 May 2020,
              <https://tools.ietf.org/html/draft-thubert-raw-
              technologies-05>.

   [RAW-USE-CASES]
              Papadopoulos, G., Thubert, P., Theoleyre, F., and C.
              Bernardos, "RAW use cases", Work in Progress, Internet-
              Draft, draft-bernardos-raw-use-cases-03, 8 March 2020,
              <https://tools.ietf.org/html/draft-bernardos-raw-use-
              cases-03>.

   [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>.

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

   [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>.

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



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   [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>.

   [SR-ARCHI] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [BIER]     Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8175]  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>.

   [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>.

12.2.  Informative References

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

   [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>.





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   [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>.

   [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>.

   [BIER-PREF]
              Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER-
              TE extensions for Packet Replication and Elimination
              Function (PREF) and OAM", Work in Progress, Internet-
              Draft, draft-thubert-bier-replication-elimination-03, 3
              March 2018, <https://tools.ietf.org/html/draft-thubert-
              bier-replication-elimination-03>.

   [DetNet-IP-OAM]
              Mirsky, G., Chen, M., and D. Black, "Operations,
              Administration and Maintenance (OAM) for Deterministic
              Networks (DetNet) with IP Data Plane", Work in Progress,
              Internet-Draft, draft-mirsky-detnet-ip-oam-02, 23 March
              2020, <https://tools.ietf.org/html/draft-mirsky-detnet-ip-
              oam-02>.

   [DetNet-DP-FW]
              Varga, B., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "DetNet Data Plane Framework", Work in Progress,
              Internet-Draft, draft-ietf-detnet-data-plane-framework-06,
              6 May 2020, <https://tools.ietf.org/html/draft-ietf-
              detnet-data-plane-framework-06>.

   [RAW-5G]   Farkas, J., Dudda, T., Shapin, A., and S. Sandberg, "5G -
              Ultra-Reliable Wireless Technology with Low Latency", Work
              in Progress, Internet-Draft, draft-farkas-raw-5g-00, 1
              April 2020,
              <https://tools.ietf.org/html/draft-farkas-raw-5g-00>.

   [BIER-TE]  Eckert, T., Cauchie, G., and M. Menth, "Tree Engineering
              for Bit Index Explicit Replication (BIER-TE)", Work in
              Progress, Internet-Draft, draft-ietf-bier-te-arch-07, 9
              March 2020,
              <https://tools.ietf.org/html/draft-ietf-bier-te-arch-07>.



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

   [MANET]    IETF, "Mobile Ad hoc Networking",
              <https://dataTracker.ietf.org/doc/charter-ietf-manet/>.

   [detnet]   IETF, "Deterministic Networking",
              <https://dataTracker.ietf.org/doc/charter-ietf-detnet/>.

   [SPRING]   IETF, "Source Packet Routing in Networking",
              <https://dataTracker.ietf.org/doc/charter-ietf-spring/>.

   [BIER]     IETF, "Bit Indexed Explicit Replication",
              <https://dataTracker.ietf.org/doc/charter-ietf-bier/>.

   [BFD]      IETF, "Bidirectional Forwarding Detection",
              <https://dataTracker.ietf.org/doc/charter-ietf-bfd/>.

   [CCAMP]    IETF, "Common Control and Measurement Plane",
              <https://dataTracker.ietf.org/doc/charter-ietf-ccamp/>.

Authors' Addresses

   Pascal Thubert (editor)
   Cisco Systems, Inc
   Building D
   45 Allee des Ormes - BP1200
   06254 MOUGINS - Sophia Antipolis
   France

   Phone: +33 497 23 26 34
   Email: pthubert@cisco.com


   Georgios Z. Papadopoulos
   IMT Atlantique
   Office B00 - 114A
   2 Rue de la Chataigneraie
   35510 Cesson-Sevigne - Rennes
   France

   Phone: +33 299 12 70 04
   Email: georgios.papadopoulos@imt-atlantique.fr







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   Rex Buddenberg
   CA
   United States of America

   Email: buddenbergr@gmail.com














































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