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RAW                                                      P. Thubert, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Informational                              May 21, 2019
Expires: November 22, 2019


              Reliable and Available Wireless Technologies
                   draft-thubert-raw-technologies-00

Abstract

   This document presents a series of recent technologies that are
   capable of time synchronization and scheduling of transmission,
   making them suitable to carry time-sensitive flows with requirements
   of both reliable delivery in bounded time, and availability at all
   times, regardless of packet transmission or individual equipement
   failures.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on November 22, 2019.

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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   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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  On Scheduling . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Benefits of Scheduling on Wires . . . . . . . . . . . . .   4
     3.2.  Benefits of Scheduling on Wireless  . . . . . . . . . . .   4
   4.  tech X  . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Provenance and Documents  . . . . . . . . . . . . . . . .   5
     4.2.  General Characteristics . . . . . . . . . . . . . . . . .   5
     4.3.  Applicability to deterministic flows  . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When used in math or philosophy, the term "deterministic" generally
   refers to a perfection where all aspect are understood and
   predictable.  A perfectly Deterministic Network would ensure that
   every packet reach its destination following a predetermined path
   along a predefined schedule to be delivered at the exact due time.
   In a real and imperfect world, a Deterministic Network must highly
   predictable, which is a combination of reliability and availability.
   On the one hand the network must be reliable, meaning that it will
   perform as expected for all packets and in particular that it will
   always deliver the packet at the destination in due time.  On the
   other hand, the network must be available, meaning that it is
   resilient to any single outage, whether the cause is a software, a
   hardware or a transmission issue.

   RAW (Reliable and Available Wireless) is an effort to provide
   Deterministic Networking on across a path that include a a wireless
   physical layer.  Making Wireless 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.  In order to maintain a
   similar quality of service along a multihop path that is composed of
   wired and wireless hops, additional methods that are specific to
   wireless must be leveraged to combat the sources of loss that are
   also specific to wireless.



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   Such wireless-specific methods include per-hop retransmissions (HARQ)
   and P2MP overhearing whereby multiple receivers are scheduled to
   receive the same transmission, which balances the adverse effects of
   the transmission losses that are eperienced when a radio is used as
   pure P2P.

2.  Terminology

   This specification uses a number of terms that are uncommon on
   protocols that ensure bets effort transmissions for stochastics
   flows, such as found in the traditional Internet and other
   statistically multiplexed packet networks.

   Reliable:  That consistently performs as expected, the expectation
         for a network being to always deliver a packet in due time.

   Available:  That is exempt of unscheduled outage, the expectation for
         a network being that the flow is maintained in the face of any
         single breakage.

   PAREO (functions):  the wireless extension of DetNet PREOF.  PAREO
         functions include scheduled ARQ at selected hops, and expect
         the use of new operations like overhearing where available.

   Track:  A DODAG oriented to a destination,and that enables Packet
         ARQ, Replication, Elimination, and Ordering Functions.

   ARQ:  Automatic Repeat Request, enabling an acknowledged
         transmission, which is the typical model at Layer-2 on a
         wireless medium.

   HARQ: Forward error correction, sending redundant coded data to help
         the receiver recover transmission errors.

   HARQ: Hybrid ARQ, a combination of FEC and ARQ .

3.  On Scheduling

   The operations of a Deterministic Network often rely on precisely
   applying a tight schedule, in order to avoid collision loss and
   guarantee the worst case time of delivery . To achieve this, there
   must be a shared sense of time throughout the network.  The sense of
   time is usually provided by the lower layer and is not in scope for
   RAW.







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3.1.  Benefits of Scheduling on Wires

   A network is reliable when the statistical effects that affect the
   packet transmission are eliminated.  This involves maintaining at all
   time the amount of critical packets within the physical capabilities
   of the hardware and that of the radio medium.  This is achieved by
   controlling the use of time-shared resources such as CPUs and
   buffers, by shaping the flows and by scheduling the time of
   transmission of the packets that compose the flow at every hop.

   Equipment failure, such as an access point rebooting, a broken radio
   adapter, or a permanent obstacle to the transmission, is a secondary
   source of packet loss.  When a breakage occurs, multiple packets are
   lost in a row before the flows are rerouted or the system may
   recover.  This is not acceptable for critical applications such as
   related to safety.  A typical process control loop will tolerate an
   occasional packet loss, but a loss of several packets in a row will
   cause an emergency stop (e.g., after 4 packets lost, within a period
   of 1 second).

   Network Availability is obtained by making the transmission resilient
   against hardware failures and radio transmission losses due to
   uncontrolled events such as co-channel interferers, multipath fading
   or moving obstacles.  The best results are typically achieved by
   pseudo randomly cumulating all forms of diversity, in the spatial
   domain with replication and elimination, in the time domain with ARQ
   and diverse scheduled transmissions, and in the frequency domain with
   frequency hopping or channel hopping between frames.

3.2.  Benefits of Scheduling on Wireless

   In addition to the benefits listed in Section 3.1, scheduling
   transmissions provides specific value to the wireless medium.

   On the one hand, scheduling avoids collisions between scheduled
   transmissions and can ensure both time and frequency diversity
   between retries in order to defeat co-channel interference from
   uncontroller transmitters as well as multipath fading.  Transmissions
   can be scheduled on multiple channels in parallel, which enables to
   use the full available spectrum while avoiding the hidden terminal
   problem, e.g., when the next packet in a same flow interferes on a
   same channel with the previous one that progressed a few hops
   farther.

   On the other hand, scheduling optimizes the bandwidth usage: compared
   to classical Collision Avoidance techniques, there is no blank time
   related to inter-frame space (IFS) and exponential back-off in
   scheduled operations.  A minimal Clear Channel Assessment may be



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   needed to comply with the local regulations such as ETSI 300-328, but
   that will not detect a collision when the senders are synchronized.
   And because scheduling allows a time sharing operation, there is no
   limit to the ratio of isolated critical traffic.

   Finally, scheduling plays a critical role to save energy.  In IOT,
   energy is the foremost concern, and synchronizing sender and listener
   enables to maintain them in deep sleep at all times when there is no
   scheduled transmission.  This avoids idle listening and long
   preambles and enables long sleep periods between traffic and
   resynchronization, allowing battery-operated nodes to operate in a
   mesh topology for multiple years.

4.  tech X

4.1.  Provenance and Documents

4.2.  General Characteristics

4.3.  Applicability to Deterministic Flows

5.  IANA Considerations

   This specification does not require IANA action.

6.  Security Considerations

   Most RAW technologies integrate some authentication or encryption
   mechanisms that were defined outside the IETF.

7.  Acknowledgments

   Many thanks to the participants of the RAW WG where a lot of the work
   discussed here happened.

8.  References

8.1.  Normative References

   [I-D.ietf-6tisch-architecture]
              Thubert, P., "An Architecture for IPv6 over the TSCH mode
              of IEEE 802.15.4", draft-ietf-6tisch-architecture-20 (work
              in progress), March 2019.

   [RFC8200]  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>.



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8.2.  Informative References

   [IEEE80211]
              "IEEE Standard 802.11 - IEEE Standard for Information
              Technology - Telecommunications and information exchange
              between systems Local and metropolitan area networks -
              Specific requirements - Part 11: Wireless LAN Medium
              Access Control (MAC) and Physical Layer (PHY)
              Specifications.".

   [IEEE802154]
              IEEE standard for Information Technology, "IEEE Std.
              802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
              and Physical Layer (PHY) Specifications for Low-Rate
              Wireless Personal Area Networks".

Author's Address

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

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
























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