Operations, Administration and Maintenance (OAM) features for RAW
draft-ietf-raw-oam-support-04

RAW                                                         F. Theoleyre
Internet-Draft                                                      CNRS
Intended status: Informational                         G.Z. Papadopoulos
Expires: 6 September 2022                                 IMT Atlantique
                                                               G. Mirsky
                                                                Ericsson
                                                           CJ. Bernardos
                                                                    UC3M
                                                            5 March 2022

   Operations, Administration and Maintenance (OAM) features for RAW
                     draft-ietf-raw-oam-support-04

Abstract

   Some critical applications may use a wireless infrastructure.
   However, wireless networks exhibit a bandwidth of several orders of
   magnitude lower than wired networks.  Besides, wireless transmissions
   are lossy by nature; the probability that a packet cannot be decoded
   correctly by the receiver may be quite high.  In these conditions,
   providing high reliability and a low delay is challenging.  This
   document lists the requirements of the Operation, Administration, and
   Maintenance (OAM) features are recommended to construct a predictable
   communication infrastructure on top of a collection of wireless
   segments.  This document describes the benefits, problems, and trade-
   offs for using OAM in wireless networks to achieve Service Level
   Objectives (SLO).

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 6 September 2022.

Theoleyre, et al.       Expires 6 September 2022                [Page 1]
Internet-Draft            OAM features for RAW                March 2022

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   6
   2.  Role of OAM in RAW  . . . . . . . . . . . . . . . . . . . . .   6
     2.1.  Link concept and quality  . . . . . . . . . . . . . . . .   7
     2.2.  Broadcast Transmissions . . . . . . . . . . . . . . . . .   8
     2.3.  Complex Layer 2 Forwarding  . . . . . . . . . . . . . . .   8
     2.4.  End-to-end delay  . . . . . . . . . . . . . . . . . . . .   8
   3.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.1.  Information Collection  . . . . . . . . . . . . . . . . .   9
     3.2.  Continuity Check  . . . . . . . . . . . . . . . . . . . .   9
     3.3.  Connectivity Verification . . . . . . . . . . . . . . . .   9
     3.4.  Route Tracing . . . . . . . . . . . . . . . . . . . . . .   9
     3.5.  Fault Verification/detection  . . . . . . . . . . . . . .  10
     3.6.  Fault Isolation/identification  . . . . . . . . . . . . .  10
   4.  Administration  . . . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  Worst-case metrics  . . . . . . . . . . . . . . . . . . .  11
     4.2.  Efficient measurement retrieval (Passive OAM) . . . . . .  11
     4.3.  Reporting OAM packets to the source (Active OAM)  . . . .  12
   5.  Maintenance . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Soft transition after reconfiguration . . . . . . . . . .  13
     5.2.  Predictive maintenance  . . . . . . . . . . . . . . . . .  13
   6.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  14
   10. Informative References  . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

Theoleyre, et al.       Expires 6 September 2022                [Page 2]
Internet-Draft            OAM features for RAW                March 2022

1.  Introduction

   Reliable and Available Wireless (RAW) is an effort that extends
   DetNet to approach end-to-end deterministic performances over a
   network that includes scheduled wireless segments.  In wired
   networks, many approaches try to enable Quality of Service (QoS) by
   implementing traffic differentiation so that routers handle each type
   of packets differently.  However, this differentiated treatment was
   expensive for most applications.

   Deterministic Networking (DetNet) [RFC8655] has proposed to provide a
   bounded end-to-end latency on top of the network infrastructure,
   comprising both Layer 2 bridged and Layer 3 routed segments.  Their
   work encompasses the data plane, OAM, time synchronization,
   management, control, and security aspects.

   However, wireless networks create specific challenges.  First of all,
   radio bandwidth is significantly lower than in wired networks.  In
   these conditions, the volume of signaling messages has to be very
   limited.  Even worse, wireless links are lossy: a Layer 2
   transmission may or may not be decoded correctly by the receiver,
   depending on a broad set of parameters.  Thus, providing high
   reliability through wireless segments is particularly challenging.

   Wired networks rely on the concept of _links_. All the devices
   attached to a link receive any transmission.  The concept of a link
   in wireless networks is somewhat different from what many are used to
   in wireline networks.  A receiver may or may not receive a
   transmission, depending on the presence of a colliding transmission,
   the radio channel's quality, and the external interference.  Besides,
   a wireless transmission is broadcast by nature: any _neighboring_
   device may be able to decode it.  This document includes detailed
   information on the implications for the OAM features.

   Last but not least, radio links present volatile characteristics.  If
   the wireless networks use an unlicensed band, packet losses are not
   anymore temporally and spatially independent.  Typically, links may
   exhibit a very bursty characteristic, where several consecutive
   packets may be dropped because of, e.g., temporary external
   interference.  Thus, providing availability and reliability on top of
   the wireless infrastructure requires specific Layer 3 mechanisms to
   counteract these bursty losses.

   Operations, Administration, and Maintenance (OAM) Tools are of
   primary importance for IP networks [RFC7276].  They define a toolset
   for fault detection, isolation, and performance measurement.

Theoleyre, et al.       Expires 6 September 2022                [Page 3]
Internet-Draft            OAM features for RAW                March 2022

   The primary purpose of this document is to detail the specific
   requirements of the OAM features recommended to construct a
   predictable communication infrastructure on top of a collection of
   wireless segments.  This document describes the benefits, problems,
   and trade-offs for using OAM in wireless networks to provide
   availability and predictability.

1.1.  Terminology

   In this document, the term OAM will be used according to its
   definition specified in [RFC6291].  We expect to implement an OAM
   framework in RAW networks to maintain a real-time view of the network
   infrastructure, and its ability to respect the Service Level
   Objectives (SLO), such as delay and reliability, assigned to each
   data flow.

   We re-use here the same terminology as
   [I-D.ietf-detnet-oam-framework]:

   *  OAM entity: a data flow to be monitored for defects and/or its
      performance metrics measured.;

   *  Test End Point (TEP): OAM devices crossed when entering/exiting
      the network.  In RAW, it corresponds mostly to the source or
      destination of a data flow.  OAM message can be exchanged between
      two TEPs;

   *  Monitoring endPoint (MonEP): an OAM system along the flow; a MonEP
      MAY respond to an OAM message generated by the TEP;

   *  control/management/data plane: the control and management planes
      are used to configure and control the network (long-term).  On a
      per-node basis, the data plane applies rules and policies for each
      packet.  For example, selecting the time-frequency block or the
      next hop on a packet-by-packet basis.  Relative to a data flow,
      the control and/or management plane can be out-of-band;

   *  Active measurement methods (as defined in [RFC7799]) modify a
      normal data flow by inserting novel fields, injecting specially
      constructed test packets [RFC2544]).  It is critical for the
      quality of information obtained using an active method that
      generated test packets are in-band with the monitored data flow.
      In other words, a test packet is required to cross the same
      network nodes and links and receive the same Quality of Service
      (QoS) treatment as a data packet.  Active methods may implement
      one of these two strategies:

Theoleyre, et al.       Expires 6 September 2022                [Page 4]
Internet-Draft            OAM features for RAW                March 2022

      -  In-band: control information follows the same path as the data
         packets.  In other words, a failure in the data plane may
         prevent the control information from reaching the destination
         (e.g., end-device or controller).

      -  out-of-band: control information is sent separately from the
         data packets.  Thus, the behavior of control vs. data packets
         may differ;

   *  Passive measurement methods [RFC7799] infer information by
      observing unmodified existing flows.

   We also adopt the following terminology, which is particularly
   relevant for RAW segments.

   *  piggybacking vs. dedicated control packets: control information
      may be encapsulated in specific (dedicated) control packets.
      Alternatively, it may be piggybacked in existing data packets,
      when the MTU is larger than the actual packet length.
      Piggybacking makes specifically sense in wireless networks, as the
      cost (bandwidth and energy) is not linear with the packet size.

   *  router-over vs. mesh under: a control packet is either forwarded
      directly to the layer-3 next hop (mesh under) or handled hop-by-
      hop by each router.  While the latter option consumes more
      resources, it allows collecting additional intermediary
      information, particularly relevant in wireless networks.

   *  Defect: a temporary change in the network (e.g., a radio link
      which is broken due to a mobile obstacle);

   *  Fault: a definite change which may affect the network performance,
      e.g., a node runs out of energy.

   *  End-to-end delay: the time between the packet generation and its
      reception by the destination.

1.2.  Acronyms

   OAM Operations, Administration, and Maintenance

   DetNet Deterministic Networking

   PSE Path Selection Engine [I-D.pthubert-raw-architecture]

   QoS Quality of Service

   RAW Reliable and Available Wireless

Theoleyre, et al.       Expires 6 September 2022                [Page 5]
Internet-Draft            OAM features for RAW                March 2022

   SLO Service Level Objective

   SNMP Simple Network Management Protocol

   SDN Software-Defined Network

1.3.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Role of OAM in RAW

   RAW networks expect to make the communications reliable and
   predictable over a wireless network infrastructure.  Most critical
   applications will define an SLO required for the data flows it
   generates.  RAW considers network plane protocol elements such as OAM
   to improve the RAW operation at the service and the forwarding sub-
   layers.

   To respect strict guarantees, RAW relies on the Path Selection Engine
   (PSE) (as defined in [I-D.pthubert-raw-architecture] to monitor and
   maintain the L3 network.  An L2 scheduler may be used to allocate
   transmission opportunities, based on the radio link characteristics,
   SLO of the flows, the number of packets to forward.  The PSE exploits
   the L2 resources reserved by the scheduler and organizes the L3 paths
   to introduce redundancy, fault tolerance and create backup paths.
   OAM represents the core of the pre-provisioning process by
   supervising the network.  It maintains a global view of the network
   resources to detect defects, faults, over-provisioning, anomalies.

   Fault tolerance also assumes that multiple paths must be provisioned
   so that an end-to-end circuit remains operational regardless of the
   conditions.  The Packet Replication and Elimination Function
   ([I-D.thubert-bier-replication-elimination]) on a node is typically
   controlled by the PSE.  OAM mechanisms can be used to monitor that
   PREOF is working correctly on a node and within the domain.

   To be energy-efficient, out-of-band OAM SHOULD only be used to report
   aggregated statistics (e.g., counters, histograms) from the nodes
   using, e.g., SNMP or Netconf/Restconf using YANG-based data models.
   The out-of-band OAM flow MAY use a dedicated control and management
   channel, dedicated for this purpose.

Theoleyre, et al.       Expires 6 September 2022                [Page 6]
Internet-Draft            OAM features for RAW                March 2022

   RAW supports both proactive and on-demand troubleshooting.
   Proactively, it is necessary to detect anomalies, report defects, or
   reduce over-provisioning if it is not required.  However, on-demand
   may also be required to identify the cause of a specific defect.
   Indeed, some specific faults may only be detected with a global,
   detailed view of the network, which is too expensive to acquire in
   the normal operating mode.

   The specific characteristics of RAW are discussed below.

2.1.  Link concept and quality

   In wireless networks, a _link_ does not exist physically.  A device
   has a set of *neighbors* that correspond to all the devices that have
   a non-null probability of receiving its packets correctly.  We make a
   distinction between:

   *  point-to-point (p2p) link with one transmitter and one receiver.
      These links are used to transmit unicast packets.

   *  point-to-multipoint (p2mp) link associates one transmitter and a
      collection of receivers.  For instance, broadcast packets assume
      the existence of p2mp links to avoid duplicating a broadcast
      packet to reach each possible radio neighbor.

   In scheduled radio networks, p2mp and p2p links are commonly not
   scheduled simultaneously to save energy and/or to reduce the number
   of collisions.  More precisely, only one part of the neighbors may
   wake up at a given instant.

   Anycast is used in p2mp links to improve the reliability.  A
   collection of receivers are scheduled to wake up simultaneously, so
   that the transmission fails only if none of the receivers can decode
   the packet.

   Each wireless link is associated with a link quality, often measured
   as the Packet Delivery Ratio (PDR), i.e., the probability that the
   receiver can decode the packet correctly.  It is worth noting that
   this link quality depends on many criteria, such as the level of
   external interference, the presence of concurrent transmissions, or
   the radio channel state.  This link quality is even time-variant.
   For p2mp links, consequently, we have a collection of PDR (one value
   per receiver).  Other more sophisticated, aggregated metrics exist
   for these p2mp links, such as [anycast-property]

Theoleyre, et al.       Expires 6 September 2022                [Page 7]
Internet-Draft            OAM features for RAW                March 2022

2.2.  Broadcast Transmissions

   The unicast transmission is delivered exclusively to the destination
   in modern switching networks.  Wireless networks are much closer to
   the traditional *shared access* networks.  Practically, unicast and
   broadcast frames are handled similarly at the physical layer.  The
   link layer is just in charge of filtering the frames to discard
   irrelevant receptions (e.g., different unicast MAC addresses).

   However, contrary to wired networks, we cannot ensure that a packet
   is received by *all* the devices attached to the Layer 2 segment.  It
   depends on the radio channel state between the transmitter(s) and the
   receiver(s).  In particular, concurrent transmissions may be possible
   or not, depending on the radio conditions (e.g., do the different
   transmitters use a different radio channel or are they sufficiently
   spatially separated?)

2.3.  Complex Layer 2 Forwarding

   Multiple neighbors may receive a transmission.  Thus, anycast Layer 2
   forwarding helps to maximize reliability by assigning multiple
   receivers to a single transmission.  That way, the packet is lost
   only if *none* of the receivers decode it.  Practically, it has been
   proven that different neighbors may exhibit very different radio
   conditions, and that reception independence may hold for some of them
   [anycast-property].

2.4.  End-to-end delay

   In a wireless network, additional transmissions opportunities are
   provisioned to accommodate packet losses.  Thus, the end-to-end delay
   consists of:

   *  Transmission delay, which is fixed and depends mainly on the data
      rate, and the presence or absence of an acknowledgement.

   *  Residence time, corresponds to the buffering delay and depends on
      the schedule.  To account for retransmissions, the residence time
      is equal to the difference between the time of last reception from
      the previous hop (among all the retransmissions) and the time of
      emission of the last retransmission.

3.  Operation

   OAM features will enable RAW with robust operation both for
   forwarding and routing purposes.

Theoleyre, et al.       Expires 6 September 2022                [Page 8]
Internet-Draft            OAM features for RAW                March 2022

3.1.  Information Collection

   The model for exchanging information should be the same as for a
   DetNet network to ensure inter-operability.  YANG may typically
   fulfill this objective.

   However, RAW networks imply specific constraints (e.g., low
   bandwidth, packet losses, cost of medium access) that may require to
   minimize the volume of information to collect.  Thus, we discuss in
   Section 4.2 different ways to collect information, i.e., transfer the
   OAM information physically from the emitter to the receiver.  This
   corresponds to passive OAM as defined in [RFC7799]

3.2.  Continuity Check

   Similarly to DetNet, we need to verify that the source and the
   destination are connected (at least one valid path exists)

3.3.  Connectivity Verification

   As in DetNet, we have to verify the absence of misconnection.  We
   focus here on the RAW specificities.

   Because of radio transmissions' broadcast nature, several receivers
   may be active at the same time to enable anycast Layer 2 forwarding.
   Thus, the connectivity verification must test any combination.  We
   also consider priority-based mechanisms for anycast forwarding, i.e.,
   all the receivers have different probabilities of forwarding a
   packet.  To verify a delay SLO for a given flow, we must also
   consider all the possible combinations, leading to a probability
   distribution function for end-to-end transmissions.  If this
   verification is implemented naively, the number of combinations to
   test may be exponential and too costly for wireless networks with low
   bandwidth.

3.4.  Route Tracing

   Wireless networks are broadcast by nature: a radio transmission can
   be decoded by any radio neighbor.  In multihop wireless networks,
   several paths exist between two endpoints.  In hub networks, a device
   may be covered by several Access Points.  We should choose the most
   efficient path or AP, concerning specifically the reliability, and
   the delay.

   Thus, multipath routing / multi-attachment can be viewed as making
   the network more fault-tolerant.  Even better, we can exploit the
   broadcast nature of wireless networks: we may have multiple
   Monitoring Endpoints (MonEP) for each of these kinds of hop.  While

Theoleyre, et al.       Expires 6 September 2022                [Page 9]
Internet-Draft            OAM features for RAW                March 2022

   it may be reasonable in the multi-attachment case, the complexity
   quickly increases with the path length.  Indeed, each Maintenance
   Intermediate Endpoint has several possible next hops in the
   forwarding plane.  Thus, all the possible paths between two
   maintenance endpoints should be retrieved, which may quickly become
   intractable if we apply a naive approach.

3.5.  Fault Verification/detection

   Wired networks tend to present stable performances.  On the contrary,
   wireless networks are time-variant.  We must consequently make a
   distinction between normal evolutions and malfunction.

3.6.  Fault Isolation/identification

   The network has isolated and identified the cause of the fault.
   While DetNet already expects to identify malfunctions, some problems
   are specific to wireless networks.  We must consequently collect
   metrics and implement algorithms tailored for wireless networking.

   For instance, the decrease in the link quality may be caused by
   several factors: external interference, obstacles, multipath fading,
   mobility.  It is fundamental to be able to discriminate the different
   causes to make the right decision.

4.  Administration

   The RAW network has to expose a collection of metrics to support an
   operator making proper decisions, including:

   *  Packet losses: the time-window average and maximum values of the
      number of packet losses have to be measured.  Many critical
      applications stop working if a few consecutive packets are
      dropped;

   *  Received Signal Strength Indicator (RSSI) is a very common metric
      in wireless to denote the link quality.  The radio chipset is in
      charge of translating a received signal strength into a normalized
      quality indicator;

   *  Delay: the time elapsed between a packet generation / enqueuing
      and its reception by the next hop;

   *  Buffer occupancy: the number of packets present in the buffer, for
      each of the existing flows.

Theoleyre, et al.       Expires 6 September 2022               [Page 10]
Internet-Draft            OAM features for RAW                March 2022

   *  Battery lifetime: the expected remaining battery lifetime of the
      device.  Since many RAW devices might be battery-powered, this is
      an important metric for an operator to make proper decisions.

   *  Mobility: if a device is known to be mobile, this might be
      considered by an operator to take proper decisions.

   These metrics should be collected per device, virtual circuit, and
   path, as DetNet already does.  However, in RAW, we have to deal with
   them at a finer granularity:

   *  per radio channel to measure, e.g., the level of external
      interference, and to be able to apply counter-measures (e.g.,
      blacklisting).

   *  per physical radio technology / interface, if a device has
      multiple NICs.

   *  per link to detect misbehaving link (asymmetrical link,
      fluctuating quality).

   *  per resource block: a collision in the schedule is particularly
      challenging to identify in radio networks with spectrum reuse.  In
      particular, a collision may not be systematic (depending on the
      radio characteristics and the traffic profile).

4.1.  Worst-case metrics

   RAW inherits the same requirements as DetNet: we need to know the
   distribution of a collection of metrics.  However, wireless networks
   are known to be highly variable.  Changes may be frequent, and may
   exhibit a periodical pattern.  Collecting and analyzing this amount
   of measurements is challenging.

   Wireless networks are known to be lossy, and RAW has to implement
   strategies to improve reliability on top of unreliable links.
   Reliability is typically achieved through Automatic Repeat Request
   (ARQ), and Forward Error Correction (FEC).  Since the different flows
   don't have the same SLO, RAW must adjust the ARQ and FEC based on the
   link and path characteristics.

4.2.  Efficient measurement retrieval (Passive OAM)

   We have to minimize the number of statistics / measurements to
   exchange:

   *  energy efficiency: low-power devices have to limit the volume of
      monitoring information since every bit consumes energy.

Theoleyre, et al.       Expires 6 September 2022               [Page 11]
Internet-Draft            OAM features for RAW                March 2022

   *  bandwidth: wireless networks exhibit a bandwidth significantly
      lower than wired, best-effort networks.

   *  per-packet cost: it is often more expensive to send several
      packets instead of combining them in a single link-layer frame.

   In conclusion, we have to take care of power and bandwidth
   consumption.  The following techniques aim to reduce the cost of such
   maintenance:

   *  on-path collection: some control information is inserted in the
      data packets if they do not fragment the packet (i.e., the MTU is
      not exceeded).  Information Elements represent a standardized way
      to handle such information.  IP hop by hop extension headers may
      help to collect metrics all along the path;

   *  flags/fields: we have to set-up flags in the packets to monitor to
      be able to monitor the forwarding process accurately.  A sequence
      number field may help to detect packet losses.  Similarly, path
      inference tools such as [ipath] insert additional information in
      the headers to identify the path followed by a packet a
      posteriori.

   *  hierarchical monitoring: localized and centralized mechanisms have
      to be combined together.  Typically, a local mechanism should
      continuously monitor a set of metrics and trigger remote OAM
      exchanges only when a fault is detected (but possibly not
      identified).  For instance, local temporary defects must not
      trigger expensive OAM transmissions.  Besides, the wireless
      segments often represent the weakest parts of a path: the volume
      of control information they produce has to be fixed accordingly.

   Several passive techniques can be combined.  For instance, the DetNet
   forwarding sublayer MAY combine In-band Network Telemetry (INT) with
   P4, iOAM and iPath to compute and report different statistics in the
   track (e.g., number of link-layer retransmissions, link reliability).

4.3.  Reporting OAM packets to the source (Active OAM)

   The Test EndPoint will collect measurements from the OAM probes
   received in the monitored track.  However, the aggregated statistics
   must then be reported to the other Test Endpoint that injected the
   probes.  Unfortunately, the monitored track MAY be unidirectional.
   In this case, the statistics have to be reported out-of-band
   (through, e.g., a dedicated control or management channel).

Theoleyre, et al.       Expires 6 September 2022               [Page 12]
Internet-Draft            OAM features for RAW                March 2022

   It is worth noting that Active OAM and Passive OAM techniques are not
   mutually exclusive.  In particular, Active OAM is useful when a
   statistic cannot be acquired accurately passively.

   Besides, Active OAM may also use piggybacking techniques: the OAM
   packet may be piggybacked in a frame if the MTU is sufficient.
   Indeed, increasing the number of transmissions in radio netwrks may
   impact very negatively the performance of radio networks,
   particularly for scheduled access, with fixed timeslot durations.
   Thus, OAM packets may be buffered until another frame has sufficient
   space, and has to be transmitted to the same neighbor.  In
   conclusion, active OAM packets may be out-of-band or in-band.

5.  Maintenance

   Maintenance needs to facilitate the maintenance (repairs and
   upgrades).  In wireless networks, repairs are expected to occur much
   more frequently, since the link quality may be highly time-variant.
   Thus, maintenance represents a key feature for RAW.

5.1.  Soft transition after reconfiguration

   Because of the wireless medium, the link quality may fluctuate, and
   the network needs to reconfigure itself continuously.  During this
   transient state, flows may begin to be gradually re-forwarded,
   consuming resources in different parts of the network.  OAM has to
   make a distinction between a metric that changed because of a legal
   network change (e.g., flow redirection) and an unexpected event
   (e.g., a fault).

5.2.  Predictive maintenance

   RAW needs to implement self-optimization features.  While the network
   is configured to be fault-tolerant, a reconfiguration may be required
   to keep on respecting long-term objectives.  Obviously, the network
   keeps on respecting the SLO after a node's crash, but a
   reconfiguration is required to handle future faults.  In other words,
   the reconfiguration delay MUST be strictly smaller than the inter-
   fault time.

   The network must continuously retrieve the state of the network, to
   judge about the relevance of a reconfiguration, quantifying:

   *  the cost of the sub-optimality: resources may not be used
      optimally (e.g., a better path exists);

Theoleyre, et al.       Expires 6 September 2022               [Page 13]
Internet-Draft            OAM features for RAW                March 2022

   *  the reconfiguration cost: the controller needs to trigger some
      reconfigurations.  For this transient period, resources may be
      twice reserved, and control packets have to be transmitted.

   Thus, reconfiguration may only be triggered if the gain is
   significant.

6.  Requirements

   This section lists requirements for OAM in a RAW domain:

   1.  Each Test and Monitoring Endpoint device MUST expose a list of
       available metrics per track.  It MUST at least provide the end-
       to-end Packet Delivery Ratio, end-to-end latency, and Maximum
       Consecutive Failures (MCF).

   2.  PREOF functions MUST guarantee order preservation in the
       (sub)track.

   3.  OAM nodes MUST provide aggregated statistics to reduce the volume
       of traffic for measurements.  They MAY send a compressed
       distribution of measurements, or MIN / MAX values over a time
       interval.

   4.  Monitoring Endpoints SHOULD support route tracing with passive
       OAM techniques.

7.  IANA Considerations

   This document has no actionable requirements for IANA.  This section
   can be removed before the publication.

8.  Security Considerations

   This section will be expanded in future versions of the draft.

9.  Acknowledgments

   TBD

10.  Informative References

   [anycast-property]
              Teles Hermeto, R., Gallais, A., and F. Theoleyre, "Is
              Link-Layer Anycast Scheduling Relevant for IEEE
              802.15.4-TSCH Networks?", 2019,
              <https://doi.org/10.1109/LCNSymposium47956.2019.9000679>.

Theoleyre, et al.       Expires 6 September 2022               [Page 14]
Internet-Draft            OAM features for RAW                March 2022

   [I-D.ietf-detnet-oam-framework]
              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-05, 14 October 2021,
              <https://datatracker.ietf.org/doc/html/draft-ietf-detnet-
              oam-framework-05>.

   [I-D.pthubert-raw-architecture]
              Thubert, P., Papadopoulos, G. Z., and L. Berger, "Reliable
              and Available Wireless Architecture/Framework", Work in
              Progress, Internet-Draft, draft-pthubert-raw-architecture-
              09, 7 July 2021, <https://datatracker.ietf.org/doc/html/
              draft-pthubert-raw-architecture-09>.

   [I-D.thubert-bier-replication-elimination]
              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://datatracker.ietf.org/doc/html/draft-
              thubert-bier-replication-elimination-03>.

   [ipath]    Gao, Y., Dong, W., Chen, C., Bu, J., Wu, W., and X. Liu,
              "iPath: path inference in wireless sensor networks.",
              2016, <https://doi.org/10.1109/TNET.2014.2371459>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544,
              DOI 10.17487/RFC2544, March 1999,
              <https://www.rfc-editor.org/info/rfc2544>.

   [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>.

Theoleyre, et al.       Expires 6 September 2022               [Page 15]
Internet-Draft            OAM features for RAW                March 2022

   [RFC7276]  Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
              Weingarten, "An Overview of Operations, Administration,
              and Maintenance (OAM) Tools", RFC 7276,
              DOI 10.17487/RFC7276, June 2014,
              <https://www.rfc-editor.org/info/rfc7276>.

   [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>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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>.

Authors' Addresses

   Fabrice Theoleyre
   CNRS
   Building B
   300 boulevard Sebastien Brant - CS 10413
   67400 Illkirch - Strasbourg
   France
   Phone: +33 368 85 45 33
   Email: fabrice.theoleyre@cnrs.fr
   URI:   http://www.theoleyre.eu

   Georgios Z. Papadopoulos
   IMT Atlantique
   Office B00 - 102A
   2 Rue de la Chataigneraie
   35510 Cesson-Sevigne - Rennes
   France
   Phone: +33 299 12 70 04
   Email: georgios.papadopoulos@imt-atlantique.fr

   Greg Mirsky
   Ericsson
   Email: gregimirsky@gmail.com

Theoleyre, et al.       Expires 6 September 2022               [Page 16]
Internet-Draft            OAM features for RAW                March 2022

   Carlos J. Bernardos
   Universidad Carlos III de Madrid
   Av. Universidad, 30
   28911 Leganes, Madrid
   Spain
   Phone: +34 91624 6236
   Email: cjbc@it.uc3m.es
   URI:   http://www.it.uc3m.es/cjbc/

Theoleyre, et al.       Expires 6 September 2022               [Page 17]