Reliable and Available Wireless Technologies
draft-thubert-raw-technologies-00
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| Author | Pascal Thubert | ||
| Last updated | 2019-05-21 | ||
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draft-thubert-raw-technologies-00
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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