Internet DRAFT - draft-rahman-core-sleepy-problem-statement
draft-rahman-core-sleepy-problem-statement
CORE WG A. Rahman
Internet-Draft InterDigital Communications, LLC
Intended status: Informational T. Fossati
Expires: April 24, 2013 KoanLogic
S. Loreto
Ericsson
M. Vial
Schneider-Electric
October 21, 2012
Sleepy Devices in CoAP - Problem Statement
draft-rahman-core-sleepy-problem-statement-01
Abstract
This document analyzes the COAP protocol issues related to sleeping
devices. The only goal of this document is to trigger discussions in
the CORE WG so that all relevant considerations for sleeping devices
are taken into account when designing CoAP.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 24, 2013.
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Table of Contents
1. Terminology and Conventions . . . . . . . . . . . . . . . . . . 3
2. What is a Sleeping Device? . . . . . . . . . . . . . . . . . . 4
2.1. Sleeping behaviors. . . . . . . . . . . . . . . . . . . . . 4
2.2. Different Sleep Modes . . . . . . . . . . . . . . . . . . . 5
2.2.1. Always-On . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.2. Intermittent Presence . . . . . . . . . . . . . . . . . 5
3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Terminology and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document assumes readers are familiar with the terms and
concepts that are used in [I-D.ietf-core-coap],
[I-D.ietf-core-link-format], [I-D.ietf-core-observe],
[I-D.shelby-core-resource-directory].
In addition, this document defines the following terminology:
Sleeping End Point (SEP): is a special kind of CoAP enabled device
that spends a large amount of its lifetime disconnected from the
network, mainly to save power, or just because it is downright
unable to store the energy required for its functioning. It
nonetheless owns and hosts a set of resources, and needs to make
them available to the other participants in the same constrained
RESTful environment. In this respect it has to devise and
implement the mechanisms that allows to work around its
limitation, and let its resources be accessible as if it were an
usual, always connected, CoAP server.
Resource Delegation: is the transfer of control over the handling of
a resource from an endpoint (the owner) to another (the deputy),
without the actual ownership being relinquished.
The retention of ownership implies two things: first, that a
genuine resource delegation cannot be recursive, and second, that
it must always be entirely reversible, at any time the owning
endpoint deems appropriate.
A Resource Delegation mechanism may comprise the transfer of the
following information from the owner to the deputy endpoint:
(a) complete or partial namespace,
(b) one or more representations of the resource,
(c) associated metadata,
(d) allowed methods,
(e) access control information,
(f) temporal bounds of the delegation.
Said mechanism may also provide authentication to the parties
involved in the delegation process.
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2. What is a Sleeping Device?
A Sleeping device is a device able to cut power to unneeded
subsystems and so significantly reduce battery consumption. Some
Sleeping devices only cut power to the radio system while continuing
to run normally the other ones. Other Sleeping devices are even more
energy efficient being able to save the machine state in the RAM
memory, putting the RAM into a minimum power state, and cutting power
to all the other subsystems. Finally other Sleeping device are able
to save the machine state on an hard disk and completely switching
off themselves.
2.1. Sleeping behaviors.
In this section we discuss different behaviors and scenarios of
sleeping nodes. Such behaviors can affect the design of applications
(such as CoAP) and network topologies (such as proxies and caching).
Sleeping nodes can have various sleeping patterns. Sleep patterns
can be predictable or totally unpredictable. For example, some nodes
sleep at a fixed interval or upon certain triggers. Some nodes may
sleep at irregular time intervals, or switch to sleep mode
spontaneously. Some nodes stay in sleep mode and only wake up upon
certain event triggers. A network may thus not be well aware of the
sleeping state of a node at a given time.
The duration of sleeping mode also varies largely, possibly from a
few seconds to days. From the perspective of applications, it may
not be affected by the sleeping period if it is very short. For
example, a HTTP/TCP connection may still work (even if sub-optimally)
if the sleep cycle is much shorter than the TCP retransmission timer.
In contrast, if the sleeping period of a node exceeds a certain
threshold it can impact an application. This threshold however, can
be difficult to predict and often can vary from device to device and
network to network. For example, this threshold can be very
dependent on the topology of a constrained network especially for the
case where a multi-hop path consists of multiple sleeping nodes. For
this case, the cumulative effect of multiple sleeping nodes must be
considered.
The network topology also affects how to handle sleeping nodes. For
example, in a star shaped network, a proxy node (assuming to be not a
sleeping node) can cache for the sleeping nodes within the network in
a centralized manner. However, in a P2P or mesh network, especially
when multi-hops are involved, caching can be difficult and delivering
of messages can be largely delayed due to nodes' sleeping cycles. In
this case distributed proxying and caching at intermediate nodes
within the network (rather than just a single node such as the border
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node or sink) may make sense, if intermediate nodes are not sleeping
nodes and have adequate resources to support caching.
2.2. Different Sleep Modes
2.2.1. Always-On
Any sleep is so short that it is invisible to L3 and upper which
gives the illusion of the sleepy node of being always on => usual
Server Model can be efficiently used.
2.2.2. Intermittent Presence
Long and possibly non pre-determined sleep periods (more than 1 sec,
but typically in the order of minutes or hours) => Server Model not
working anymore. SEP state must be handled by other mechanisms.
3. Assumptions
The characteristics of SEPs varies widely. Some may be cheap,
rudimentary widgets with very limited computational and storage
capabilities; other can be more functional devices yet in need to
save energy since they have to be in operation for a long period
while battery powered.
This great variance implies that a fair number of often contradictory
assumptions must be taken into consideration, and carefully weighted,
when designing a comprehensive solution for the problem. For
example:
o Is SEP able to maintain soft state ?
o Is SEP sleep/awake scheduling predictable ?
o Is SEP able to handle bidirectional communication ?
Luckily, and by definition, it can be assumed that all the SEPs
participating in a CoRE domain share a (realistically limited) subset
of the REST principles. At the very least we will assume a SEP
understands and implements:
o the concept of information resource and its representational
state;
o the semantics and syntax of CoAP URIs;
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o the semantics associated with the methods PUT or POST, and DELETE;
in a way that is conformant with the CoAP protocol. This will
provide the common ground on which to build their integration into
the hosting CoRE domain.
4. Objectives
The CORE WG aim is to design a solution that, leveraging on the
existing CoAP features and its REST architecture, allows SEP devices
to be easily and smoothly integrated within any CoRE domain together
with the all the other CoAP enabled devices.
The ideal solution should:
o Make the set of resource owned and hosted by any SEP available to
all the other participants, in the same constrained RESTful
environment, without making any assumption on the presence of
specific or special entities neither on the network topology.
o Provide the possibility to use Client or Observer Model to access
resources owned and hosted by a SEP.
o Allow the (Secure) delegation of resource handling while retaining
ownership.
o Minimize the configuration needs to bootstrap a SEP within an
existing CoRE domain.
o Maximize the integration with base CoRE Features (i.e. Resource
Discovery, Multicast, Observer, Block).
o Reuse already available CoAP mechanisms as much as possible.
5. Acknowledgements
TBD.
6. IANA Considerations
This memo includes no request to IANA.
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7. Security Considerations
TBD. (All drafts are required to have a security considerations
section. See RFC 3552 [RFC3552] for a guide.)
8. References
8.1. Normative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
"Constrained Application Protocol (CoAP)",
draft-ietf-core-coap-12 (work in progress), October 2012.
[I-D.ietf-core-link-format]
Shelby, Z., "CoRE Link Format",
draft-ietf-core-link-format-14 (work in progress),
June 2012.
[I-D.ietf-core-observe]
Hartke, K., "Observing Resources in CoAP",
draft-ietf-core-observe-06 (work in progress),
September 2012.
[I-D.shelby-core-resource-directory]
Shelby, Z., Krco, S., and C. Bormann, "CoRE Resource
Directory", draft-shelby-core-resource-directory-04 (work
in progress), July 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
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Authors' Addresses
Akbar Rahman
InterDigital Communications, LLC
Montreal, Quebec H3A 3G4
Canada
Phone: +1-514-585-0761
Email: akbar.rahman@interdigital.com
Thomas Fossati
KoanLogic
Email: tho@koanlogic.com
Salvatore Loreto
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Salvatore.Loreto@ericsson.com
Matthieu Vial
Schneider-Electric
Email: matthieu.vial@schneider-electric.com
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