CORE WG A. Rahman Internet-Draft InterDigital Communications, LLC Intended status: Standards Track July 6, 2012 Expires: January 7, 2013 Enhanced Sleepy Node Support for CoAP draft-rahman-core-sleepy-00 Abstract 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. 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 Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on January 7, 2013. Copyright Notice Copyright (c) 2012 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 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Rahman Expires January 7, 2013 [Page 1] Internet-Draft Enhanced Sleepy Node Support July 2012 to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Terminology and Conventions . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. RD Based Sleep Tracking . . . . . . . . . . . . . . . . . 4 3.2. Example of Synchronous RD Based Sleep Tracking . . . . . . 5 3.3. Example of Asynchronous RD Based Sleep Tracking . . . . . 7 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 7.1. Normative References . . . . . . . . . . . . . . . . . . . 12 7.2. Informative References . . . . . . . . . . . . . . . . . . 12 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12 Rahman Expires January 7, 2013 [Page 2] Internet-Draft Enhanced Sleepy Node Support July 2012 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 [I-D.ietf-core-link-format]. 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 may also sometimes remain in a fully powered on state where it has the capability to perform full CoAP protocol communication. Non-Sleepy Node 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 are 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 assumes 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 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 [I-D.ietf-core-link-format] and [I-D.shelby-core-resource-directory] defines a Resource Directory (RD) mechanism where sleepy CoAP servers can register/update Rahman Expires January 7, 2013 [Page 3] Internet-Draft Enhanced Sleepy Node Support July 2012 (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 (i.e. CORE Link Format) for other nodes, and not the actual resource representation. The client then may attempt to retrieve (GET) the actual representation of the desired resource from the sleepy origin server. The 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. These lower layer functionalities are not aware of any specific timing or operational aspects of application layer protocols like CoAP. 3. Proposal 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 Rahman Expires January 7, 2013 [Page 4] Internet-Draft Enhanced Sleepy Node Support July 2012 [I-D.shelby-core-resource-directory]. 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 [I-D.ietf-core-link-format] 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. 3.2. Example of Synchronous RD Based Sleep Tracking 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. Rahman Expires January 7, 2013 [Page 5] Internet-Draft Enhanced Sleepy Node Support July 2012 SleepyNode-1 Resource Server Directory Client | | | +----------+ | | | Time = 0 | | | +----------+ | | | | | |(1) CoAP POST | | | /rd, | | | ?ep="SleepyNode-1"; | | | ?SleepDuration="30-Minutes"; | | | ?SleepState="Awake"; | | | ?NextSleep="5-Minutes"; | | | PAYLOAD: | | | "" | | |---------------------------------- >| | | | | | (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 | | ; | | SleepDuration="30-Minutes"; | | SleepState="Sleeping"; | Rahman Expires January 7, 2013 [Page 6] Internet-Draft Enhanced Sleepy Node Support July 2012 | TimeSleeping="10-Minutes"; | | PAYLOAD: | | rt="Temperature" | | |------------------------->| | | | | | | | | | | | | | | | (7) Since node is asleep Client | | waits 20 minutes until it awakes | | | | | | | +-------------------+ | | | Time = 31 minutes | | | +-------------------+ | | | | | | | | (8)CoAP GET | | | |<--------------------------------------------------------------| | | |-------------------------------------------------------------->| | (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 := Rahman Expires January 7, 2013 [Page 7] Internet-Draft Enhanced Sleepy Node Support July 2012 "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: | | | "" | | |---------------------------------- >| | | | | | (2) RD services the | | | Registration | | | Request | | | | | |(3) 2.01 Created | | | Location: /rd/4321 | | |<-----------------------------------| | | | | | | | | (4) Client performs RD | | end-point lookup to | Rahman Expires January 7, 2013 [Page 8] Internet-Draft Enhanced Sleepy Node Support July 2012 | find endpoint that | | has temperature | | sensor and is awake | | | | CoAP GET | | /rd-lookup/ep?rt=Temperature&SleepState=Awake| | |<-------------------------| | | | | | | | (5) 2.05 Content | | ;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 | Rahman Expires January 7, 2013 [Page 9] Internet-Draft Enhanced Sleepy Node Support July 2012 | ; | | |------------------------->| | | | | | | ... .... |(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; | | |---------------------------------- >| | Rahman Expires January 7, 2013 [Page 10] Internet-Draft Enhanced Sleepy Node Support July 2012 | | | | | | | (18) RD updates | | | sleep state | | | | | |(19) 2.04 Changed | | |<-----------------------------------| | | | | | (20) 2.05 Content | | Observe: 3 | | Token: 0x4a | | ; | | SleepState="Awake" | | |------------------------->| | | | | | | | | (21) Client detects | | | SleepyNode-1 is | | | awake | | | | | (22) CoAP GET | | | |<--------------------------------------------------------------| | | |-------------------------------------------------------------->| | (23) 2.05 Content | | | Figure 2: Asynchronous Resource Directory Based Sleep Tracking 4. Acknowledgements Thanks to Zach Shelby for valuable discussions and feedback on this document. 5. IANA Considerations This memo includes no request to IANA. 6. Security Considerations TBD. (All drafts are required to have a security considerations section. See RFC 3552 [RFC3552] for a guide.) Rahman Expires January 7, 2013 [Page 11] Internet-Draft Enhanced Sleepy Node Support July 2012 7. References 7.1. Normative References [I-D.ietf-core-coap] Shelby, Z., Hartke, K., Bormann, C., and B. Frank, "Constrained Application Protocol (CoAP)", draft-ietf-core-coap-10 (work in progress), June 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-05 (work in progress), March 2012. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References [I-D.shelby-core-resource-directory] Shelby, Z. and S. Krco, "CoRE Resource Directory", draft-shelby-core-resource-directory-03 (work in progress), May 2012. [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. Author's Address Akbar Rahman InterDigital Communications, LLC Montreal, Quebec H3A 3G4 Canada Phone: +1-514-585-0761 Email: akbar.rahman@interdigital.com Rahman Expires January 7, 2013 [Page 12]