CORE WG A. Rahman
Internet-Draft InterDigital Communications, LLC
Intended status: Standards Track October 08, 2013
Expires: April 11, 2014
Enhanced Sleepy Node Support for CoAP
draft-rahman-core-sleepy-04
Abstract
CoAP is a specialized web transfer protocol for constrained devices.
These devices typically have some combination of limited battery
power, small memory footprint and low throughput links. It is
expected that in CoAP networks there will be a certain portion of
devices that are "sleepy" and which may occasionally go into a sleep
mode (i.e. go into a low power state to conserve power) and
temporarily suspend CoAP protocol communication. This document
proposes a minimal and efficient mechanism building on the Resource
Directory (RD) functionality to enhance sleepy node support in CoAP
networks. The RD functionality may be incorporated as part of a CoAP
Proxy.
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 April 11, 2014.
Copyright Notice
Copyright (c) 2013 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Terminology and Conventions . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. RD Based Sleep Tracking . . . . . . . . . . . . . . . . . 4
3.2. Example of Synchronous RD Based Sleep Tracking . . . . . 4
3.3. Example of Asynchronous RD Based Sleep Tracking . . . . . 7
3.4. RD Caching Proxy . . . . . . . . . . . . . . . . . . . . 11
4. Performance Results . . . . . . . . . . . . . . . . . . . . . 11
4.1. Prototype Setup . . . . . . . . . . . . . . . . . . . . . 11
4.2. Initial Results . . . . . . . . . . . . . . . . . . . . . 13
4.3. Comparison with Observe . . . . . . . . . . . . . . . . . 13
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 14
8.2. Informative References . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
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] and [RFC6690]. In
addition, this document defines the following terminology:
Sleepy Node
A sleepy node is a CoAP client or server that may sometimes go
into a sleep mode (i.e. go into a low power state to conserve
power) and temporarily suspend CoAP protocol communication. A
sleepy node will otherwise remain in a fully powered on state
where it has the capability to perform full CoAP protocol
communication.
Non-Sleepy Node
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A non-sleepy node is a CoAP client or server that always remains
in a fully powered on state (i.e. always awake) where it has the
capability to perform full CoAP protocol communication. The
general operation of non-sleepy nodes is assumed to be well known
and so are not explicitly spelled out in this document except
where needed for clarity.
2. Introduction
The current CoAP approach provides a minimal support of sleepy nodes
as follows:
o [I-D.ietf-core-coap] defines CoAP proxies which can cache and
service requests for sleepy CoAP servers. A client explicitly
sends a CoAP request (GET) to a forward proxy (identified by its
IP address) while indicating the URI (of the resource of interest)
associated to a sleepy CoAP origin server. If the proxy has a
valid representation of the resource in its cache it can then
respond directly to the client regardless of the current sleep
state of the origin server. Otherwise the proxy has to attempt to
retrieve (GET) the resource from the sleepy origin server. The
attempt may or may not be successful depending on the sleep state
of the origin server.
o [RFC6690] and [I-D.ietf-core-resource-directory] defines a
Resource Directory (RD) mechanism where sleepy CoAP servers can
register/update (POST/PUT to "/.well-known/core") their list of
resources on a central (non-sleepy) RD server. This allows
clients to discover the list of resources from the RD (GET /rd-
lookup/...) for a sleepy server, regardless of its current sleep
state. Unlike a proxy, the RD stores only the URIs for other
nodes, and not the actual resource representation [RFC6690] . The
client then may attempt to operate on (GET/PUT/POST/DELETE) the
desired resource at the sleepy origin server. This attempt may or
may not be successful depending on the sleep state of the origin
server.
o Lower layer (i.e. below the IP layer) support for sleepy nodes
exist in most wireless technologies (e.g. IEEE 802.11 (WiFi), and
IEEE 802.15.4 (ZigBee)). For example, most wireless technologies
support limited functionality such as packet scheduling to account
for sleepy nodes in their physical and MAC layer protocols. This
lower layer functionality is not aware of any specific timing or
operational aspects of application layer protocols like CoAP.
3. Proposal
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3.1. RD Based Sleep Tracking
The current CoAP approach to support sleepy nodes can be
significantly improved by introducing RD based mechanisms for a CoAP
client to determine whether:
o A targeted resource is located on a sleepy server.
o A sleepy server is currently in sleep mode or not.
We define the following new parameters to characterize a sleepy node:
o SleepState - Indicates whether the node is currently in sleep mode
or not (i.e. Sleeping or Awake).
o SleepDuration - Indicates the maximum duration of time that the
node stays in sleep mode.
o TimeSleeping - Indicates the length of time the node has been
sleeping (i.e. if Sleep State = Sleeping).
o NextSleep - Indicates the next time the node will go to sleep
(i.e. if Sleep State = Awake).
These parameters are all server (node) level and are new parameters
added to the RD URI Template Variables defined in
[I-D.ietf-core-resource-directory].
We also define a new lookup-type ("ss") for the RD lookup interface
specified in [I-D.ietf-core-resource-directory]. This new lookup-
type supports looking up the SleepState of a specified end-point.
The three time based parameters (SleepDuration, TimeSleeping,
NextSleep) can be based on either an absolute network time (for a
time synchronized network) or a relative local time (measured at the
local node).
Following the approach of [RFC6690] and
[I-D.ietf-core-resource-directory], sleep parameters for sleepy
servers can be stored by the server in the RD and accessed by all
interested clients. Examples of using these parameters in a
synchronous or asynchronous manner are shown in the following
sections.
3.2. Example of Synchronous RD Based Sleep Tracking
Figure 1 shows an example of using RD based sleep tracking in a
synchronous fashion:
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(1) SleepyNode-1 is awake and having previously discovered the local
RD, stores its CORE link format in the RD (POST/rd) identified by its
entry point (?ep=SleepyNode-1). The sleep parameters are also
updated as part of this step.
(2)-(3) RD services the POST and stores the CORE link format and
starts the sleep timers for this node.
(4) SleepyNode-1 falls asleep.
(5) A client is interested in temperature sensors in this domain and
does a lookup on the RD.
(6) The RD does a lookup and finds that SleepyNode-1 is the only node
meeting the match and sends back the required info including the
Sleep parameters.
(7) From the sleep parameters, the client knows that the node is
currently asleep and so internally schedules to send the GET request
when the node wakes up (plus a small safety hysteresis).
(8)-(9) Client sends GET request for temperature sensors and
successfully receives the content as SleepyNode-1 is awake.
SleepyNode-1 Resource
Server Directory Client
| | |
+----------+ | |
| Time = 0 | | |
+----------+ | |
| | |
|(1) CoAP POST | |
| /rd, | |
| ?ep="SleepyNode-1"; | |
| ?SleepDuration="30-Minutes"; | |
| ?SleepState="Awake"; | |
| ?NextSleep="5-Minutes"; | |
| PAYLOAD: | |
| "</sensors...>" | |
|---------------------------------- >| |
| | |
| (2) RD services the | |
| Registration | |
| Request and | |
| starts Sleep | |
| timers | |
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| | |
|(3) 2.01 Created | |
| Location: /rd/4321 | |
|<-----------------------------------| |
| | |
+-------------------+ | |
| Time = 5 minutes | | |
+-------------------+ | |
| | |
|(4) SleepyNode-1 falls asleep | |
| | |
+-------------------+ | |
| Time = 15 minutes | | |
+-------------------+ | |
| | |
| |
| (5) CoAP GET |
| /rd-lookup/res?rt=Temperature |
| |<-------------------------|
| | |
| | |
| |
| (6) 2.05 Content |
| <coap://SleepyNode-1/temp>; |
| SleepDuration="30-Minutes"; |
| SleepState="Sleeping"; |
| TimeSleeping="10-Minutes"; |
| PAYLOAD: |
| rt="Temperature" |
| |------------------------->|
| | |
| | |
| | |
| | |
| |
| (7) Since node is asleep Client |
| waits 20 minutes until it awakes |
| | |
| | |
+-------------------+ | |
| Time = 31 minutes | | |
+-------------------+ | |
| | |
| |
| (8)CoAP GET |
| <coap://SleepyNode-1/temp> |
|<--------------------------------------------------------------|
| |
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|-------------------------------------------------------------->|
| (9) 2.05 Content |
| | |
| | |
Figure 1: Synchronous Resource Directory Based Sleep Tracking
3.3. Example of Asynchronous RD Based Sleep Tracking
Figure 2 shows an example of using RD based sleep tracking in an
asynchronous fashion:
(1) SleepyNode-1 is awake and having previously discovered the local
RD, stores its CORE link format in the RD (POST/rd) identified by its
entry point (?ep=SleepyNode-1).
(2)-(3) RD services the POST and stores the CORE link format.
(4) A client is interested in temperature sensors in this domain and
does a lookup on the RD for all sensors that are currently awake.
(5) The RD does a lookup and finds that SleepyNode-1 is the only node
meeting the match and sends back the required info.
(6)-(7) Using the sleep state lookup functionality (lookup-type :=
"ss"), the client adds itself to the list of observers to get
SleepState updates from RD for SleepyNode-1 [I-D.ietf-core-observe].
(8)-(9) Client performs RD 'resource' lookup to find URI of
temperature sensor of resource hosted on SleepyNode-1.
(10)-(13) SleepyNode-1 prepares to goes to sleep and updates the
SleepState in the RD.
(14) RD notifies the client through previously established observe
relationship.
(15) Client application wants to get the temperature now but does not
send the request as it knows SleepyNode-1 is currently sleeping.
(16)-(19) SleepyNode-1 wakes up and updates the SleepState in the RD.
(20)-(21) RD notifies the client through previously established
observe relationship.
(22)-(23) Client sends GET request for temperature sensors and
successfully receives the content as SleepyNode-1 is awake.
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SleepyNode-1 Resource
Server Directory Client
| | |
| | |
|(1) CoAP POST | |
| /rd, | |
| ?ep=SleepyNode-1; | |
| ?SleepState=Awake; | |
| PAYLOAD: | |
| "</sensors...>" | |
|---------------------------------- >| |
| | |
| (2) RD services the | |
| Registration | |
| Request | |
| | |
|(3) 2.01 Created | |
| Location: /rd/4321 | |
|<-----------------------------------| |
| | |
| | |
| (4) Client performs RD |
| end-point lookup to |
| find endpoint that |
| has temperature |
| sensor and is awake |
| |
| CoAP GET |
| /rd-lookup/ep?rt=Temperature&SleepState=Awake|
| |<-------------------------|
| | |
| | |
| (5) 2.05 Content |
| <coap://{ip:port}>;ep="SleepyNode-1" |
| |------------------------->|
| | |
| | |
| (6) Client adds itself |
| to list of observers|
| to get SleepState |
| updates from RD for |
| SleepyNode-1 |
| |
| |
| CoAP GET |
| /rd-lookup/ss?ep=SleepyNode-1 |
| Observe: 0 |
| Token: 0x4a |
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| |<-------------------------|
| | |
| | |
| (7) 2.05 Content |
| Observe: 1 |
| Token: 0x4a |
| SleepState="Awake" |
| |------------------------->|
| | |
| | |
| (8) Client performs RD |
| 'resource' lookup |
| to find URI of |
| temperature sensor |
| of resource hosted |
| on SleepyNode-1 |
| |
| CoAP GET |
| /rd-lookup/res?rt=Temperature&ep="SleepyNode-1"|
| |<-------------------------|
| | |
| | |
| (9) 2.05 Content |
| <coap://sleepyNode-1/temp>; |
| |------------------------->|
| | |
| | |
... ....
|(10) SleepyNode-1 prepares to go | |
| to sleep so it updates | |
| SleepState | |
| | |
| CoAP PUT | |
| /rd/4321, | |
| ?SleepState=Sleeping | |
|---------------------------------- >| |
| | |
| (11) RD updates | |
| SleepState of | |
| SleepyNode-1 | |
| | |
|(12) 2.04 Changed | |
|<-----------------------------------| |
| | |
|(13) SleepyNode-1 goes to sleep | |
| | |
| | |
| (14) RD sends notification to client |
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| 2.05 Content |
| Observe: 2 |
| Token: 0x4a |
| SleepState="Sleeping" |
| |------------------------->|
... ....
| | |
| | (15) Client has GET |
| | request for |
| | SleepyNode-1 but |
| | cannot send it since|
| | SleepyNode-1 is not |
| | awake |
|(16) SleepyNode-1 wakes up | |
| | |
| | |
|(17) SleepyNode-1 updates | |
| SleepState | |
| | |
| CoAP PUT | |
| /rd/4321, | |
| ?SleepState=Awake; | |
|---------------------------------- >| |
| | |
| | |
| (18) RD updates | |
| sleep state | |
| | |
|(19) 2.04 Changed | |
|<-----------------------------------| |
| | |
| (20) 2.05 Content |
| Observe: 3 |
| Token: 0x4a |
| <coap://sleepyNode-1/temp>; |
| SleepState="Awake" |
| |------------------------->|
| | |
| | |
| | (21) Client detects |
| | SleepyNode-1 is |
| | awake |
| | |
| (22) CoAP GET |
| <coap://SleepyNode-1/temp> |
|<--------------------------------------------------------------|
| |
|-------------------------------------------------------------->|
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| (23) 2.05 Content |
| |
Figure 2: Asynchronous Resource Directory Based Sleep Tracking
3.4. RD Caching Proxy
It would be useful for an RD to be able to indicate which proxy
performs caching for Sleepy CoAP nodes (see Section 2). This would
be done through a new RD "CachingProxy" attribute for each device
(similiar to the attributes defined in Section 3.1):
o An RD may be co-located with a proxy that performs caching for
CoAP nodes. In this case, the RD automatically adds itself to
each CachingProxy entry.
o The sleepy node itself could suggest the CachingProxy if it is
peered to a specific proxy.
This parameter would be added to the RD URI Template Variables
defined in [I-D.ietf-core-resource-directory].
4. Performance Results
4.1. Prototype Setup
A simple prototype was implemented to validate certain aspects of the
performance of the proposed CoAP sleepy node support protocol
enhancement. The network for the prototype is shown in Figure 3.
Key aspects of the prototype are as follows:
o There are two modes of operation: "Caching Only" and "Caching and
Sleep Aware"
o In "Caching Only" mode the Reverse Proxy will cache responses and
service new requests according to the "Max-Age" parameter as
defined in [I-D.ietf-core-coap].
o In "Caching and Sleep Aware" mode the Reverse Proxy will also
cache responses and service new requests according to "Max-Age".
However, if the cache is empty (e.g. exceeded Max-Age) then there
will be extra sleep aware functionality. Specifically, the proxy
will also be aware of the "SleepDuration", "NextSleep" and
"SleepState" sleepy node parameters as defined in Section 3.1.
Based on these sleep parameters:
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* For servers that are asleep but expected to wake up soon: The
proxy will immediately send a non-piggy backed ACK to the
client. Then store-and-forward the request to the server when
it wakes up, and then return the non-piggybacked response to
the client thereafter.
* For servers that are asleep but not expected to wake up soon:
The proxy will immediately send a "5.03 Service Unavailable
(and retry after)" to the client.
o The key variables in the experiment are: (1) Number of clients;
(2) Number of sleepy servers; (3) Delay between client requests;
(4) MaxAge; (5) SleepDuration; (6) NextSleep; and (7) SleepState.
o The target of the experiment will be to measure the amount of
traffic over the network in the two modes of operation (for the
same input client requests profile). It is hypothesized that the
"Caching and Sleep Aware" mode will have the minimal amount of
network traffic indicating that the Sleep Aware network will be
the most efficient.
Constrained Network
--------------------
/ \
--- +----------+ /-----\ \
/ \ | CoAP | CoAP \
| | | Reverse | server \
CoAP | | | Proxy | \-----/ ||
+------+ Request | | | | ||
|CoAP |-------------| |---->| +-----+ | Req /-----\ ||
|Client| | | | |Cache| |------->| CoAP ||
| |<------------| |-----| +-----+ |<-------|server ||
+------+ CoAP | | | | Resp \-----/ ||
Response | Corp| |------ | ||
| LAN | |RD | | ||
| | |Sleep| | ||
\ / |Param| | /
--- | | | /
+----------+ /-----\ /
\ CoAP /
\ server /
\ \-----/ /
----------------
Figure 3: Prototype Configuration
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4.2. Initial Results
Baseline performance results of A CoAP system with Sleep Aware Proxy
support described in Section 4.1 is given in [IETF86Results] (see pg.
65-95). Key conclusions were:
o If only GETs are considered, a cache based system is efficient as
long as the cache is valid (i.e before Max-Age).
o However, since the cache often expires, a Sleep Aware Proxy
further minimizes the number of GET transactions. Also, the Sleep
Aware Proxy reduces number of transactions for other methods (e.g.
PUTs) where a cache does not help.
4.3. Comparison with Observe
A comparison of the performance of a CoAP system with Sleep Aware
Proxy versus a CoAP system supporting Observe is given in
[IETF87Results] (see pg. 150-182). Key conclusions were:
o If only GETs are considered, an Observe based system is quite
efficient.
o However, Observe in combination with Sleep Aware Proxy further
minimizes the number of GET transactions. Also, the Sleep Aware
Proxy reduces number of transactions for other methods (e.g. PUTs)
where Observe does not help.
5. Acknowledgements
Thanks to Carsten Bormann, Esko Dijk, Thomas Fossati, Salvatore
Loreto, Dale Seed, and Zach Shelby for valuable discussions and
feedback on this document.
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
TBD. (All drafts are required to have a security considerations
section. See RFC 3552 [RFC3552] for a guide.)
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8. References
8.1. Normative References
[I-D.ietf-core-coap]
Shelby, Z., Hartke, K., and C. Bormann, "Constrained
Application Protocol (CoAP)", draft-ietf-core-coap-18
(work in progress), June 2013.
[I-D.ietf-core-observe]
Hartke, K., "Observing Resources in CoAP", draft-ietf-
core-observe-10 (work in progress), September 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, August 2012.
8.2. Informative References
[I-D.ietf-core-resource-directory]
Shelby, Z., Krco, S., and C. Bormann, "CoRE Resource
Directory", draft-ietf-core-resource-directory-00 (work in
progress), June 2013.
[IETF86Results]
Rahman, A., "IETF-86 Sleepy Node Performance Results",
March 2013, <http://www.ietf.org/proceedings/86/slides/
slides-86-core-1.pdf>.
[IETF87Results]
Rahman, A., "IETF-87 Sleepy Node Performance Results",
July 2013, <http://www.ietf.org/proceedings/87/slides/
slides-87-core-0.pdf>.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, July
2003.
Author's Address
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Akbar Rahman
InterDigital Communications, LLC
Montreal, Quebec H3A 3G4
Canada
Phone: +1-514-585-0761
Email: akbar.rahman@interdigital.com
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