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RAW                                                         F. Theoleyre
Internet-Draft                                                      CNRS
Intended status: Standards Track                         G. Papadopoulos
Expires: May 6, 2020                                      IMT Atlantique
                                                        November 3, 2019


   Operations, Administration and Maintenance (OAM) features for RAW
                   draft-theoleyre-raw-oam-support-01

Abstract

   The wireless medium presents significant specific challenges to
   achieve properties similar to those of wired deterministic networks.
   At the same time, a number of use cases cannot be solved with wires
   and justify the extra effort of going wireless.  This document
   presents some of these use-cases.

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 May 6, 2020.

Copyright Notice

   Copyright (c) 2019 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
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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Needs for OAM in RAW  . . . . . . . . . . . . . . . . . . . .   3
   3.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Connectivity Verification . . . . . . . . . . . . . . . .   4
     3.2.  Route Tracing . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Fault verification / detection  . . . . . . . . . . . . .   4
     3.4.  Fault isolation / identification  . . . . . . . . . . . .   5
   4.  Administration  . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Worst-case metrics  . . . . . . . . . . . . . . . . . . .   6
     4.2.  Energy efficiency constraint  . . . . . . . . . . . . . .   6
   5.  Maintenance . . . . . . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Multipath . . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Replication / Elimination . . . . . . . . . . . . . . . .   7
     5.3.  Resource Reservation  . . . . . . . . . . . . . . . . . .   7
     5.4.  Soft transition after reconfiguration . . . . . . . . . .   7
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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.  The wireless and
   wired media are fundamentally different at the physical level.
   Enabling thus reliable and available wireless communications is even
   more challenging than it is in wired IP networks, due to the numerous
   causes of loss in transmission that add up to the congestion losses
   and the delays caused by overbooked shared resources.  To provide
   quality of service along a multihop path that is composed of wired
   and wireless hops, additional methods needs to be considered to
   leverage the potential lossy wireless communication.

   Traceability belongs to Operations, Administration, and Maintenance
   (OAM) which is the toolset for fault detection and isolation, and for
   performance measurement.  More can be found on OAM Tools in
   [RFC7276].

   The main purpose of this document is to detail the 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.



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   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
   Agreements (SLA), such as delay and reliability, assigned to each
   data flow.

1.1.  Terminology

   o  OAM entity: a data flow to be controlled;

   o  OAM end-devices: the source or destination of a data flow;

   o  defect: a temporary change in the network characteristics (e.g.
      link quality degradation because of temporary external
      interference, a mobile obstacle)

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

2.  Needs for OAM in RAW

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

   To respect strict guarantees, RAW relies on a Path Computation
   Element (PCE) which will be responsible to schedule the transmissions
   in the deployed network.  Thus, resources have to be provisioned a
   priori to handle any defect.  OAM represents the core of the over
   provisioning process, and maintains the network operational by
   updating the schedule dynamically.

   Fault-tolerance also assumes that multiple path have to be
   provisioned so that an end-to-end circuit keeps on existing whatever
   the conditions.  OAM is in charge of controlling the replication/
   elimination processes.

   To be energy-efficient, reserving some dedicated out-of-band
   resources for OAM seems idealistic, and only in-band solutions are
   considered here.

   RAW supports both proactive and on-demand troubleshooting.





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3.  Operation

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

3.1.  Connectivity Verification

   We need to verify that two endpoints are connected with each other.
   Since we reserve resources along the path independently for each
   flow, we must be able to verify that the path exists for a given flow
   label.

   The control and data packets may not follow the same path, and the
   connectivity verification has to be triggered in-band without
   impacting the data traffic.  In particular, the control plane may
   work while the data plane may be broken.

   The ping packets must be labeled in the same way as the data packets
   of the flow to monitor.

3.2.  Route Tracing

   Ping and traceroute are two very common tools for diagnostic.  They
   help to identify the list of routers in the route.  However, to be
   predictable, resources are reserved per flow in RAW.  Thus, we need
   to define route tracing tools able to track the route for a specific
   flow.

   Because the network has to be fault-tolerant, multipath can be
   considered, with multiple Maintenance Intermediate Endpoints for each
   hop in the path.  Thus, all the possible paths between two
   maintenance endpoints should be retrieved.

3.3.  Fault verification / detection

   RAW expects to operate fault-tolerant networks.  Thus, we need
   mechanisms able to detect faults, before they impact the network
   performance.

   The network has to detect when a fault occurred, i.e. the network has
   deviated from its expected behavior.  While the network must report
   an alarm, the cause may not be identified precisely.  For instance,
   the end-to-end reliability has decreased significantly, or a buffer
   overflow occurs.

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




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

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

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

   Thus, localized and centralized mechanisms have to be combined
   together, and additional control packets have to be triggered only
   after a fault detection.

3.4.  Fault isolation / identification

   The network has isolated and identified the cause of the fault.  For
   instance, the quality of a specific link has decreased, requiring
   more retransmissions, or the level of external interference has
   locally increased.

4.  Administration

   To take proper decisions, the network has to expose a collection of
   metrics, including:

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

   o  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;

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

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

   These metrics should be collected:

   o  per virtual circuit to measure the end-to-end performance for a
      given flow.  Each of the paths has to be isolated in multipath
      strategies;





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

   o  per device to detect misbehaving node, when it relays the packets
      of several flows.

4.1.  Worst-case metrics

   RAW aims to enable real-time communications on top of an
   heterogeneous architecture.  Since wireless networks are known to be
   lossy, RAW has to implement strategies to improve the reliability on
   top of unreliable links.  Hybrid Automatic Repeat reQuest (ARQ) has
   typically to enable retransmissions based on the end-to-end
   reliability and latency requirements.

   To take correct decisions, the controller needs to know the
   distribution of packet losses for each flow, and for each hop of the
   paths.  In other words, average end-to-end statistics are not enough.
   They must allow the controller to predict the worst-case.

4.2.  Energy efficiency constraint

   RAW targets also low-power wireless networks, where energy represents
   a key constraint.  Thus, we have to cake care of the energy and
   bandwidth consumption.  The following techniques aim to reduce the
   cost of such maintenance:

      piggybacking: some control information are 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;

      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.

5.  Maintenance

   RAW needs to implement a self-healing and self-optimization approach.
   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);



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      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.

5.1.  Multipath

   To be fault-tolerant, several paths can be reserved between two
   maintenance endpoints.  They must be node-disjoint, so that a path
   can be available at any time.

5.2.  Replication / Elimination

   When multiple paths are reserved between two maintenance endpoints,
   they may decide to replicate the packets to introduce redundancy, and
   thus to alleviate transmission errors and collisions.  For instance,
   in Figure 1, the source node S is transmitting the packet to both
   parents, nodes A and B.  Each maintenance endpoint will decide to
   trigger the replication / elimination process when a set of metrics
   passes through a threshold value.


                          ===> (A) => (C) => (E) ===
                        //        \\//   \\//       \\
              source (S)          //\\   //\\         (R) (root)
                        \\       //  \\ //  \\      //
                          ===> (B) => (D) => (F) ===


   Figure 1: Packet Replication: S transmits twice the same data packet,
                     to its DP (A) and to its AP (B).

5.3.  Resource Reservation

   Because the QoS criteria associated to a path may degrade, the
   network has to provision additional resources along the path.  We
   need to provide mechanisms to patch a schedule (changing the channel
   offset, allocating more timeslots, changing the path, etc.).

5.4.  Soft transition after reconfiguration

   Since RAW expects to support real-time flows, we have to support
   soft-reconfiguration, where the novel ressources are reserved before
   the ancient ones are released.  Some mechanisms have to be proposed
   so that packets are forwarded through the novel track only when the




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   resources are ready to be used, while maintaining the global state
   consistent (no packet re-ordering, duplication, etc.)

6.  Informative References

   [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>.

   [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>.

   [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>.

Authors' Addresses

   Fabrice Theoleyre
   CNRS
   Building B
   300 boulevard Sebastien Brant - CS 10413
   Illkirch - Strasbourg  67400
   FRANCE

   Phone: +33 368 85 45 33
   Email: theoleyre@unistra.fr
   URI:   http://www.theoleyre.eu


   Georgios Z. Papadopoulos
   IMT Atlantique
   Office B00 - 102A
   2 Rue de la Chataigneraie
   Cesson-Sevigne - Rennes  35510
   FRANCE

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







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