RAW                                                         F. Theoleyre
Internet-Draft                                                      CNRS
Intended status: Standards Track                         G. Papadopoulos
Expires: January 6, 2020                                  IMT Atlantique
                                                            July 5, 2019

   Operations, Administration and Maintenance (OAM) features for RAW


   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.

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   This Internet-Draft will expire on January 6, 2020.

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   the Trust Legal Provisions and are provided without warranty as
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  OAM to provision appropriately the resources  . . . . . . . .   3
   3.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Administration  . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Worst-case constraint . . . . . . . . . . . . . . . . . .   5
     4.2.  Energy efficiency constraint  . . . . . . . . . . . . . .   5
   5.  Maintenance . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Informative References  . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   RAW (Reliable and Available Wireless) is an effort to provide
   deterministic behavior over a network that includes a wireless
   physical layer.  Enabling the wireless communication reliable and
   available is even more challenging than it is with wires, 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 .

   The main purpose of this document is to details the requirements of
   the OAM features recommended to construct a predictable communication
   infrastructure on top of a collection of wireless networks.  In
   particular, we expect to provide packet loss evaluation, self-testing
   and automated adaptation to enable trade-offs between resilience and
   energy consumption.

   This document describes the benefits, problems, and trade-offs for
   using OAM in wireless networks to provide availability and

   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 (delay, reliability) assigned to each data flow.

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1.1.  Terminology

   o  OAM entity: a data flow to be controled;

   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.  OAM to provision appropriately the resources

   RAW networks expect to make the communications predictable on top of
   a wireless network infrastructure.  Most critical applications will
   define a Service Level Agreeemnt to respect for the data flows it
   generates.  Thus, the wireless networks have to be dimensionned to
   respect these SLAs.

   To respect strict guarantees, RAW relies on a PCE which has to
   schedule the transmissions in the different wireless networks.  Thus,
   resources have to be provisionned to handle any defect.  OAM
   represents the core of the overprovisonning process, and maintains
   the network operational by updating the schedule dynmically.

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

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

3.  Operation

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

   We make a distinction between the two following complementary

   o  Detection: the network detects that a fault occured, i.e. the
      network has deviated from its expected behavior.  While the
      network must report an alarm, the cause may not be identified

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      precisely.  For instance, the end-to-end reliability has decreased
      significantly, or a buffer overflow occurs;

   o  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.

   These two-steps identification is required since RAW expects to rely
   on wireless networks.  Thus, we have to minimize the amount of
   statistics / measurements to exchange:

   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.

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

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

   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 strngth 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 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

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

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

4.1.  Worst-case constraint

   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 has inserted in the data
      packets if they don't 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 them accurately.  A sequence number field may
      help to detect packet losses.  Similarly, path inference tools
      such as [ipath] insert additionnal 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, control packets have to be transmitted.

   Thus, reconfiguration may only be triggered if the gain is

   Since RAW expects to support real-time flows, we have to 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
   resources are ready to be used, while maintaining the global state
   consistent (no packet re-ordering, duplication, etc.)

   In particular, RAW has to support the following modifications:

      patching a schedule, relocating some radion resources (radio
      channel, timeslots);

      a device can be reset (e.g. firmware upgrade) safely, all the
      flows being forwarded temporarly through alternative paths;

      a better path (delay, reliability, energy consumption) has been

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,

Authors' Addresses

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

   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

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

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