| CORE WG | A. Rahman |
| Internet-Draft | InterDigital Communications, LLC |
| Intended status: Standards Track | February 24, 2013 |
| Expires: August 28, 2013 |
Enhanced Sleepy Node Support for CoAP
draft-rahman-core-sleepy-02
CoAP is a RESTful application 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 concept to enhance sleepy node support in CoAP networks.
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This Internet-Draft will expire on August 28, 2013.
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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:
The current CoAP approach assumes a minimal support of sleepy nodes as follows:
The current CoAP approach to support sleepy nodes can be significantly improved by introducing RD based mechanisms for a CoAP client to determine whether:
We define the following new parameters to characterize a sleepy node: [I-D.shelby-core-resource-directory].
These parameters are all server (node) level and are new parameters added to the RD URI Template Variables defined in
We also define a new lookup-type ("ss") for the RD lookup interface specified in [I-D.shelby-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.shelby-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.
Figure 1 shows an example of using RD based sleep tracking in a synchronous 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). 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 | |
| | |
|(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> |
|<--------------------------------------------------------------|
| |
|-------------------------------------------------------------->|
| (9) 2.05 Content |
| | |
| | |
Figure 1: Synchronous Resource Directory 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.
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 |
| |<-------------------------|
| | |
| | |
| (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 |
| 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> |
|<--------------------------------------------------------------|
| |
|-------------------------------------------------------------->|
| (23) 2.05 Content |
| |
Figure 2: Asynchronous Resource Directory Based Sleep Tracking
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): [I-D.shelby-core-resource-directory].
This parameter would be added to the RD URI Template Variables defined in
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:
Experimental results are being generated now and will be available for discussion during the IETF-86 meeting.
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: Experimental Setup
Thanks to Thomas Fossati, Salvatore Loreto, Dale Seed, and Zach Shelby for valuable discussions and feedback on this document.
This memo includes no request to IANA.
TBD. (All drafts are required to have a security considerations section. See RFC 3552 [RFC3552] for a guide.)
| [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. |
| [I-D.ietf-core-coap] | Shelby, Z., Hartke, K. and C. Bormann, "Constrained Application Protocol (CoAP)", Internet-Draft draft-ietf-core-coap-14, March 2013. |
| [I-D.ietf-core-observe] | Hartke, K., "Observing Resources in CoAP", Internet-Draft draft-ietf-core-observe-08, February 2013. |
| [RFC3552] | Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. |
| [I-D.shelby-core-resource-directory] | Shelby, Z., Krco, S. and C. Bormann, "CoRE Resource Directory", Internet-Draft draft-shelby-core-resource-directory-05, February 2013. |