CoRE P. van der Stok Internet-Draft Philips Research Intended status: Informational K. Lynn Expires: January 10, 2011 Consultant July 9, 2010 CoAP Utilization for Building Control draft-vanderstok-core-bc-01 Abstract This I-D describes an example use of the RESTful CoAP protocol for building control applications such as HVAC and lighting. A few basic design assumptions are stated first. The URI structure is exploited to define multicast as well as unicast scopes. RFC 3986 defines the URI components as (1) a scheme, (2) an authority, used here to locate the building, area, or node under control, (3) a path, used here to locate the resource under control, and (4) a query and fragment part, where fragments are not supported in CoAP. This proposal supports the view that (1) building control is likely to move in steps toward all-IP control networks based on the legacy efforts provided by DALI, LON, BACnet, ZigBee, and other standards, (2) service discovery is complimentary to resource discovery and facilitates control network scaling, and (3) the provision of a reliable group communication protocol is essential to support building control applications. 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 10, 2011. Copyright Notice van der Stok & Lynn Expires January 10, 2011 [Page 1] Internet-Draft CoAP Utilization for Building Control July 2010 Copyright (c) 2010 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 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. Conventions and Terminology Used in this Document . . . . . . 3 2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. URI structure . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Scheme part . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Authority part . . . . . . . . . . . . . . . . . . . . . . 6 3.3. Path part . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Group Addressing . . . . . . . . . . . . . . . . . . . . . . . 7 5. Reliable multicast . . . . . . . . . . . . . . . . . . . . . . 9 6. Application examples . . . . . . . . . . . . . . . . . . . . . 10 7. Discovery . . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 15 9. Security considerations . . . . . . . . . . . . . . . . . . . 15 10. IANA considerations . . . . . . . . . . . . . . . . . . . . . 16 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . . 16 12.2. Informative References . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 van der Stok & Lynn Expires January 10, 2011 [Page 2] Internet-Draft CoAP Utilization for Building Control July 2010 1. Conventions and Terminology Used in this Document 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 "Key words for use in RFCs to Indicate Requirement Levels" [RFC2119]. The term "service" may mean different things to different communities and sometimes different things to the same community. In building control protocol standards, service is often used to refer to a function in the RPC sense. In this context, we generally substitute the term "function". In the IETF community, service may often refer to an abstract capability such as "datagram delivery". In this submission we use the term service, in the sense defined by "DNS- based Service Discovery" [I-D.cheshire-dnsext-dns-sd], as equivalent to a CoAP end-point. A CoAP end-point is identified by the authority part of a URI. We refer to this end-point (which is resolved to an {IP address, port} tuple) as a "node". By "device" we generally mean the physical object handled by the installer. While a device may host more than one service, for simplicity we assume here that a given device may only host a single CoAP node. In examples below involving URIs, the authority is preceded by double slashes "//" and path is preceded by a single slash "/". The examples may make use of fully qualified or partial domain names and the difference should be clear from the context. 2. Motivation The CoAP protocol [I-D.ietf-core-coap] aims at providing a user application protocol architecture that is targeted to a network of nodes with a low resource provision such as memory, CPU capacity, and energy. In general, IT application manufacturers strive to provide the highest possible functionality and quality for a given price. In contrast, the building controls market is highly price sensitive and manufacturers tend to compete by delivering a given functionality and quality for the lowest price. The vast majority of nodes in a typical building control application are resource constrained, making the standardization of a lightweight application protocol like CoAP a necessary requirement for IP to penetrate the device market. This approach is further indicated by the low energy consumption requirement of battery-less nodes. Low resource budget implies low throughput and small packet size as for [IEEE.802.15.4]. Reduction of the packet size is obtained by using van der Stok & Lynn Expires January 10, 2011 [Page 3] Internet-Draft CoAP Utilization for Building Control July 2010 the header reduction of 6LoWPAN [RFC4944] and encouraging small payloads. Several legacy building control standards (e.g [BACnet], [LON], [DALI], [KNX], etc.) have been developed based on years of accumulated knowledge and industry cooperation. These standards generally specify a data model, functions, packet formats, and sometimes the physical medium for data objects and function invocation. Many of these industry standards also specify lower- level functionality such as proprietary transport protocols, necessitating expensive stateful gateways for these standards to interoperate. Many are in the process of transitioning to IP-based standards for transport and other functions such as naming and discovery. CoAP will be succesful in the building control market to the extent that it can represent a given standard's data objects and provide functions, e.g. resource discovery, that these standards depend on. From the above the basic syntax assumptions can be summarized as: - Generate small payloads. - Compatible with legacy standards (e.g LON, BACnet, DALI, ZigBee Device Objects). - Service/resource discovery in agreement with legacy standards and naming conventions. This submission aims at an approach in which the payload contains messages with a syntax defined by legacy control standards. Accordingly, the syntax of the service/resource discovery messages is related to the chosen legacy control standard. The intention is a progressive approach to all-IP in building control. In a first stage standard IETF based protocols (e.g CoAP, DNS-SD) are used for transport of control messages and discovery messages expressed in a legacy syntax. This approach enables the reuse of controllers based on the semantics of the chosen control standard. In a later stage a complete redesign of the controllers can be envisaged guided by the accumulated experience with all-IP control. Two concepts, hierarchy and group, are of prime importance in building control, particularly in lighting and HVAC. Many control messages or events are multicast from one device to a group of devices (e.g. from a light switch to all lights in a room). The scope of a multicast command or discovery message covers the group of nodes that is targeted. Defining multicast scopes on the basis of hop count or the existence of edge routers is not always sufficient in buildings where the network architecture may be independent of the van der Stok & Lynn Expires January 10, 2011 [Page 4] Internet-Draft CoAP Utilization for Building Control July 2010 controlled areas (e.g. rooms) in the building. As described in "Commercial Building Applications Requirements" [I-D.martocci-6lowapp-building-applications] it is typical practice to aggregate building control at the room, area, and supervisory levels. Furthermore, networks for different subsystems (lights, HVAC, etc.) or based on different legacy standards have historically been isolated from each other in so-called "silos". RESTful web services represent one possible way to expose functionality and normalize data representations between silos in order to facilitate higher order applications such as campus-wide energy management. Consequently, additional protocol oriented assumptions are: - A syntactic definition of the multicast scope applicable to all control application multicasts in the building. - Nodes may be addressed by more than one group. - Resources addressed by a group must be uniformly named across all targeted nodes. For clarity, this I-D limits itself to two types of applications: (1) M2M control applications running within a building area without any human intervention after commissioning of a given network segment and (2) maintenance oriented applications where data are collected from node in several building areas by nodes inside or outside the building, and humans may intervene to change control settings. 3. URI structure This I-D considers three elements of the URI: scheme, authority, and path, as defined in "Uniform Resource Identifier (URI): Generic Syntax" [RFC3986]. The authority is defined within the context of standard DNS host naming, while the path is valid in relation to a fully qualified domain name (FQDN) plus optional port (and protocol is implicit). An example based on RFC 3986 is: foo://host.example.com:8042/over/there?name=ferret#nose, where "foo" is the scheme, "host.example.com:8042" is the authority, "/over/ there" is the path, "name=ferret" is the query, and "nose" is the fragment. Fragments are not supported in CoAP. 3.1. Scheme part The default scheme in this submission is "coap" although the intention is that everything stated below about URIs SHOULD apply equally to "http" and might be exposed, say, through an http-to-coap van der Stok & Lynn Expires January 10, 2011 [Page 5] Internet-Draft CoAP Utilization for Building Control July 2010 gateway. That topic is beyond the scope of this document. 3.2. Authority part The authority part is either a literal IP address or a DNS name comprised of a global part specifying the domain and a local part specifying the logical hierarchical structure of the building control network, down to the group or node level. An optional port number may be included in the authority following a single colon ":" if the service port is other than the default CoAP value. A building can be unambiguously addressed by it GPS coordinates or more functionally by its zip or postal code. For example the Dutch Internet provider, KPN, assigns to each subscriber a host name based on its postcode. Analogously, an example authority for a building may be given by: //bldg.zipcode-localnr.Country/ or more concretely an imaginary address in the Netherlands as: //bldg.5533BA-125a.nl/. The "bldg" prefix can specify the target node within the building. Arriving at the node identified by //bldg.5533BA-125a.nl, the receiving service can parse the path portion of the URI and perform the requested method on the specified resource. Buildings have a logical internal structure dependent on their size and function. This ranges from a single hall without any structure to a complex building with wings, floors, offices and possibly a structure within individual rooms. The naming of the building control equipment and the actual control strategy are intimately linked to the building structure. It is therefore natural to name the equipment based on their location within the building. Consequently, the local part of the URI identifying a piece of equipment is expressed in the building structure. An example is: //light-27.floor-1.west-wing... This proposal assumes a basic level of cooperation between the IT and building management infrastructure, namely the ability of the former to delegate DNS subdomains to the latter. This allows the building controls installer to implement an appropriate naming scheme with the required granularity. For institutional real estate such as a college or corporate campus, the authority might be based on the organization's domain, e.g. //node-or- group.floor.wing.bldg.campus.example.com/. In cases where subdomain delegation is not an option, structure can still be represented in a "flat" namespace, subject to the 63 octet limit for a DNS sub- string: //group1-floor2-west-bldg3-campus.example.com. Most communication is device to device (M2M) within the building. Often a device needs to communicate to all devices of a given type within a given area of the building. For example a thermostat may van der Stok & Lynn Expires January 10, 2011 [Page 6] Internet-Draft CoAP Utilization for Building Control July 2010 access all radiator actuators in a zone. A light switch located at room 25b006 of floor one, expressed as: //switch0.25b006.floor1.5533BA-125a.nl/, might specify a command to light1 within the same room with //light1.25b006.floor1.5533BA- 125a.nl/. This approach seems to lead to rather verbose URI strings in the packet, contrary to the small packet assumption. However, the design of CoAP is such that the authority portion of the URI need not be transmitted in requests sent to origin servers. The question arises as to whether the syntax of the authority part needs to be standardized for building control. Given the examples later in the text, this appears more to be the concern of the building owner or the installer. 3.3. Path part Every network addressable resource is completely identified by a URI scheme://authority/path. The path part of the URI specifies the resource within a given node. The representation of object types and their associated attributes are typically subjects for standardization. There is no widely accepted standard for uniformly naming building control device structure in a URI. A vigorous effort is undertaken by the oBIX working group of OASIS [oBIX]. When a GET method with an URI like: //t-sensor1.25b006.floor1/ temperature is sent, it represents an a priori understanding that the node with name t-sensor1 exists, is of a given standard type (e.g BACnet temperature sensor), and that this standard type has the readable attribute: temperature. However, in the case of multicast commands to a group of nodes it is necessary that the targeted resource have the same path on all targeted nodes. Therefore, it is necessary to establish at least a local uniform path naming convention to achieve this. One approach is to include the name of the standard, e.g BACnet, as the first element in the path and then employ the standard's natural data scheme (in the case of BACnet, device/object/property). 4. Group Addressing As suggested by the examples above, the scope of the messages can be logically associated with the URI authority. This provides a better handle to define the multicast scope than the traditional TTL counter preventing the multicast message to pass one or more routers. This more sophisticated scoping mechanism is needed to decouple multicast scopes from the network layout. This is reflected by the capability provided in [BACnet] to define the scope of its service/resource discovery messages. van der Stok & Lynn Expires January 10, 2011 [Page 7] Internet-Draft CoAP Utilization for Building Control July 2010 Given a network configuration and associated prefixes, the network operator needs to define an appropriate set of multicast groups which can be mapped to the building areas. Knowledge about the hierarchical structure of the building areas may assist in defining a network architecture which encourages an efficient multicast implementation. Example multicast groups become: URI authority Targeted group //all.bldg6 "all nodes in building 6" //all.west.bldg6 "all nodes in west wing, building 6" //all.floor1.west.bldg6 "all nodes on floor 1, west wing, ..." //all.bu036.floor1.west.bldg6 "all nodes in office bu036, ..." The granularity of this example is for illustration rather than a recommendation. Experience will dictate the appropriate hierarchy for a given structure as well as the appropriate number of groups per subdomain. Note that in this example, the group name "all" is used to identify the group of all nodes in each subdomain. In practice, "all" would name an address record in each of the DNS zones shown above and would bind to a different multicast address [RFC3596] in each zone. Highly granular multicast scopes are only possible using IPv6. The multicast address allocation strategy is beyond the scope of this I-D, but various alternatives have been proposed [RFC3306][RFC3307][RFC3956]. Some techniques in this proposal, e.g. service discovery as described below, can be accomplished with a single coap-specific multicast address as long as the desired scope is building-wide. To illustrate the concept of multiple group names within a given multicast scope, consider the definition, as done with [DALI], of scenes within the context of a floor or a single office. For example, the setting of all blue lights in office bu036 of floor 1 can be realized by multicasting a message to the group "//blue- lights.bu036.floor1". Each group is associated with an IP address. Consequently, when the application specifies the sending of an "on" message to all blue lights in the office, the message is multicast to the associated IP address. The uri-authority option [I-D.ietf-core-coap] need not be sent as part of the message. A group defines a set of nodes. All resources on a given node are referenced by the multicast address(es) to which the node belongs. A given node might belong to a number of groups. For example the node belonging to the "blue-lights" group in a given corridor might also belong to the groups: "whole building", "given wing", "given floor", "given corridor", and "lights in given corridor". In summary, the authority portion of the URI is used to identify a node (group) and the resulting DNS name is bound to a unicast van der Stok & Lynn Expires January 10, 2011 [Page 8] Internet-Draft CoAP Utilization for Building Control July 2010 (multicast) address, resulting in an associated unicast (multicast) scope. Naming is building or organization dependent, must be flexible, and does not require standardization efforts but SHOULD conform to some uniform convention. In the context of an administrated professional building, groups can be defined off-line and stored in DNS server configuration. Automated enumeration, based on service discovery methods described below, may be used to locate nodes and add them to groups during the building commissioning phase. 5. Reliable multicast A reliable group communication (multicast) is essential for an efficient building control application. Reliable multicast supports guaranteed delivery of messages to a group of nodes. The representative example is a group of lights that need to be switched on simultaneously. Although the delay between sending the command message (e.g. from a switch) to the effective switching on of the lights may be up to one second, all lights in the group should appear to switch on simultaneously (within an interval of 100-200 msec). Examples of reliable multicast specifications are cited in [Mullender]. In the case of real-time control of devices, the following specification applies: Validity - If sender sends message, m, to a group, g, of destinations, a path exists between sender and destinations, and sender and destinations are correct, all destinations in g eventually receive m. Integrity - destination receives m at most once from sender and only if sender sent m to a group including destination. Agreement - If a correct destination of g receives m, then all correct destinations of g receive m. Timeliness - There is a known constant D such that if m is sent at time t, no correct destination receives m after t+D. Assuming that every new multicast message contains a unique transaction identifier, the integrity requirement can be met by checking this identifier. The agreement and timeliness requirements can be met by multicast algorithms developed for real time computing. It is assumed that the clocks of the nodes are synchronized and multiple redundant paths can be used to reach all destinations either directly or via other nodes. Especially for battery-less nodes it is interesting to note that when the message arrives reliably at one correct destination, it will be passed on to all other correct destinations and in the contrary case is received by none van der Stok & Lynn Expires January 10, 2011 [Page 9] Internet-Draft CoAP Utilization for Building Control July 2010 [Mullender]. The consequence of such a specification is also that when a light in a group does not switch on, the lamp is faulty (either the lamp or the associated node). Satisfaction of the validity requirement does not rely on returning acknowledgement messages, but on sufficient redundancy in nodes and network links. The scope of the multicast helps to send the message only to a subset of interested nodes. However, a minimum set of nodes is needed to deliver the message reliably. Dividing the building network in multicast areas helps to confine the multicast while at the same time assuring the minimum number of participants. The choice of areas is a design parameter not discussed here. Such areas can be supported with route-over or mesh-under routing. Another approach, favored by some implementations, is to send a packet n times over a wireless link with given intervals dependent on deployed physical medium. It can be expected that several techniques will be advocated in the future. Interoperability between wireless nodes from different manufacturers participating in a muticast requires that reliable multicast is standardized. The challenges posed by the wireless, real-time, and battery-less aspects of these control networks motivate the specification of an appropriate (possibly new) multicast protocol. 6. Application examples It is assumed that devices may exchange messages with a content defined by one of the existing building control standards e.g BACnet, LON, DALI, ZigBee Device Objects (ZDO), KNX, and others. All of these standards have defined concepts like type (class) and type (class) instances. Within a given type a number of attributes exists that can be modified or read with a more or less complex invocation syntax. This draft proposes that the path portion of the URI first identify the standard and then continue with a standard dependent syntax, to be defined by the standardization body interested in utilizing CoAP. For example, a command to a heating unit with a BACnet interface can be expressed as //authority/BACnet/BACnet-defined-command or a command to a DALI light can be expressed as //authority/DALI/ DALI-defined-command. The example request: PUT //light1.bu036.floor1/DALI/Intensity = 30 would translate to CoAP header [I-D.ietf-core-coap]: van der Stok & Lynn Expires January 10, 2011 [Page 10] Internet-Draft CoAP Utilization for Building Control July 2010 - dest IP address determined by resolving: //light1.bu036.floor1 - T bits to 0: Confirmable message - Code = 2: PUT method - OC bits set to 1 (for one Mime option) - Transaction ID set - Option type= 1, content type: /application/DALI - DALI command: set Intensity attribute to 30 The new option content type shows that new application mime types need to be defined to cover the building control standards: e.g. /application/DALI, /application/BACnet, etc. Examples of wireless, battery-less nodes are sensors used for measuring presence, temperature, light intensity, or humidity. Battery-less means that the nodes are switched off most of the time and sporadically power up and send out their current measured value. This value is either sent to a controller node or to a group of actuator nodes. Examples are presence detection sent to lamps, or humidity level to a fan. The destination nodes of the measurements are probably powered by the mains or a derivative of the mains. It seems unrealistic to have the controller or the actuator nodes send request messages to the battery-less nodes, after which the sender has to wait an interval determined by the duty cycle of the actuator or controller. More natural is that the battery-less node wakes up and sends its message to its controller or actuator nodes which are always ready to receive a message. For example, without a controller node, the presence detector can send presence regularly to a group of lights. The group can be defined on-line, by having the lights subscribe to the presence service, or the group can be defined off-line by the manager of the control network. On-line definition is more natural in a dynamic home environment, while off-line is more natural in the office environment. Off-line has the added advantage of checking on missing nodes. For subscription the subscribing nodes have to learn the IP address(es) of the service(s) to which they want to subscribe. In case of off-line the servers have to learn the IP address of the multicast group. The latter can be learned from DHCP options, by inserting the destination IP address inside the configuration file of the battery-less node. van der Stok & Lynn Expires January 10, 2011 [Page 11] Internet-Draft CoAP Utilization for Building Control July 2010 The CoAP protocol foresees the use of a non confirmable message packet to send these unsolicited responses to the multicast group or the single controller. Again the syntax of the commands are most likely defined by legacy standards. Assuming the DALI standard, the command PUT //blue-lights.bu036.floor1/DALI/OnOff=on leads to the following packet lay-out: - dest multicast IP address determined by: //blue- lights.bu036.floor1 - T bits to 1: Non Confirmable message - Code = 2, PUT method - OC bits set to 1 (for one Mime option) - Transaction ID set, for prevention of double messages - Option type= 1, content type: /application/DALI - DALI command: set OnOff attribute to on 7. Discovery At a high level the the discovery strategy can be introduced with an example to create a group "DALI/lights" in a given building domain. - The building domains can be resolved according to a domain specification which is consistent over a set of buildings maintained by a building control provider - A query over a specified domain returns the IP addresses of all nodes in this domain with the reource DALI/lights - The IP address of multicast group "DALI/lights" is defined - The multicast group can be realized in two alternative ways: - A list of IP addresses invoked by unicast. - Each member allocates the IP multicast address, and receives all messages sent to this IP address. van der Stok & Lynn Expires January 10, 2011 [Page 12] Internet-Draft CoAP Utilization for Building Control July 2010 - Messages can be multicast to the group DALI/lights. This implies a consistent naming scheme within each node. The above group definition can be done on-line and off-line. Service or resource discovery is often scoped according to the building structure. For example, BACnet defines "Who-Is" and "Who- Has" functions to locate nodes and resources, respectively, that match specified criteria (filters) in a defined network scope. CoAP defines a resource discovery capability, but it is limited to link- local scope; examples may be found in [I-D.ietf-core-coap]. A service discovery capability is required to extend discovery to other subnets. DNS-based Service Discovery [I-D.cheshire-dnsext-dns-sd] defines a conventional way to configure DNS PTR, SRV, and TXT records to enable enumeration of services such as CoAP nodes within subdomains. A service is specified by a name of the form Instance.Type.Domain, where the type for CoAP nodes is _coap._udp and the domain is a DNS domain name that identifies a building zone as in the examples above. For each CoAP end-point in the zone, a PTR record with the name _coap._udp is defined and it points to an SRV record having the Instance.Type.Domain name. All CoAP nodes in a given subdomain may be enumerated by sending a DNS query to the authoritative server for that zone for PTR records named _coap._udp. A list of SRV records is returned. Each SRV record contains the port and host name of a CoAP node. The IP address of the node is obtained by resolving the host name. DNS-SD also specifies an optional TXT record, having the same name as the SRV record, which can contain "key=value" attributes. This can be used to store information about the device, e.g. schema=DALI, type=switch. Another feature of DNS-SD is the ability to specify service subtypes using PTR records. For example, a CoAP node that supports BACnet commands might be represented with a PTR record having the name _bacnet._sub._coap._udp. In this way, all BACnet nodes in a subdomain might be enumerated more efficiently. This technique for node enumeration can be used to emulate BACnet's "Who-Is" function. With an enumerated list of nodes, a management workstation may then perform unicast resource discovery as described in [I-D.ietf-core-coap]. Alternately, the group multicast addressing described earlier can be used to scope queries for specific resources to different subdomains. This technique effectively emulates BACnet's "Who-Has" function. van der Stok & Lynn Expires January 10, 2011 [Page 13] Internet-Draft CoAP Utilization for Building Control July 2010 When for example a lamp wants to discover the controller, it is only interested in the controllers located in the same office (area) as itself. Consequently, the service discovery is related to the groups defined according to the building structure. It is advisable to send a discovery message to a given group. Also the packet does not need the complete URI in the URI option. In conformance with RFC 5785 [RFC5785], a packet from a controller with the request to return the device types of all DALI devices within the office bu036 can look like: - dest multicast IP address defined by: //bu036.floor1 - T bits to 0: Confirmable messages - Code 0: GET method - OC bits set to 2 (for Mime and URI option) - Transaction ID set - Option type= 9, uri-path: LEN=13, ".well-known/r" - Option type= 1, content type: /application/DALI - DALI command: "return device type" The responses from the DALI nodes may look like: - dest IP address of controller - T bits to 2: Acknowledgement messages - CODE = 0, OK - OC bits set to 1 (for Mime option) - Transaction ID identical - Option type= 1, content type: /application/DALI - DALI command: "type = Lamp" The rest of the protocol is dictated by the legacy standard in use but encapsulated within the CoAP discovery messages as shown above. van der Stok & Lynn Expires January 10, 2011 [Page 14] Internet-Draft CoAP Utilization for Building Control July 2010 8. Conclusions This I-D explains how building control is based on a hierarchical structure of the building areas, and that the logical scope of control and discovery messages is determined by the building structure. It is shown that DNS subdomain delegation and naming can be used to express this hierarchy in the authority portion of the URI, down to the group or node level. The hierarchical naming scheme need not be standardized, but rather can be designed to suit the application. However, it is recommended that the scheme be employed consistently throughout the delegated subdomain(s). The authority portion of the URI is resolved by the client into the unicast or multicast IP address of the targeted node(s). Taking advantage of the CoAP design [I-D.ietf-core-coap], the uri-authority option need not be transmitted in requests to origin servers and thus there is no performance penalty for using descriptive naming schemes. The targeted resource is specified by the path portion of the URI. Again, this I-D does not mandate a universal naming standard for resources but uses examples to show how resources could be named for various legacy standards. An obvious requirement for resources that are accessed by multicast is that they MUST all share the same path, including short uri if used. It is shown that it is possible to transport legacy commands (e.g. expressed in BACnet, LON, DALI, ZigBee, etc.) inside a CoAP message body. This necessitates the definition of additional IANA mime codes, and the mapping of legacy specific discovery semantics to CoAP resource discovery messages or DNS-SD lookups. It is expected that many control messages are sent by battery-less sensors with their own specific sending intervals to a group of actuator nodes or controllers. Given the importance of groups and associated multicast messages to support legacy standard functions, the specification of a reliable multicast protocol with related multicast scope is needed in CoAP. 9. Security considerations TODO: The detailed CoAP security analysis needs to encompass scenarios for building control applications. Based on the programming model presented in this I-D, security scenarios for building control need to be stated. Appropriate methods to counteract the proposed threats may be based on the work done elsewhere, for example in the ZigBee over IP context. Multicast messages are, by their nature, transmitted via UDP. Any van der Stok & Lynn Expires January 10, 2011 [Page 15] Internet-Draft CoAP Utilization for Building Control July 2010 privacy applied to such messages must be block oriented and based on group keys shared by all targeted nodes. The CoRE security analysis must be broadened to include multicast scenarios. 10. IANA considerations This I-D proposes the following additions to the Media type identifiers in conformance with the proposals done in [I-D.ietf-core-coap]. Internet media type Code /application/BACnet xx /application/DALI xx+1 /application/ZDO xx+2 /application/LON xx+3 /application/KNX xx+4 /application/oBIX+exi xx+5 TODO: Investigate CoAP specific well-known multicast address assignment? 11. Acknowledgements This I-D has benefited from conversations with and comments from Andrew Tokmakoff, Emmanuel Frimout, Jamie Mc Cormack, Oscar Garcia, Dee Denteneer, Joop Talstra, Zach Shelby, Jerald Martocci, and Nicolas Riou. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. [RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast Addresses", RFC 3307, August 2002. [RFC3596] Thomson, S., Huitema, C., Ksinant, V., and M. Souissi, "DNS Extensions to Support IP Version 6", RFC 3596, October 2003. van der Stok & Lynn Expires January 10, 2011 [Page 16] Internet-Draft CoAP Utilization for Building Control July 2010 [RFC3956] Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, September 2007. [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known Uniform Resource Identifiers (URIs)", RFC 5785, April 2010. 12.2. Informative References [I-D.ietf-core-coap] Shelby, Z., Frank, B., and D. Sturek, "Constrained Application Protocol (CoAP)", draft-ietf-core-coap-01 (work in progress), July 2010. [I-D.cheshire-dnsext-dns-sd] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", draft-cheshire-dnsext-dns-sd-06 (work in progress), March 2010. [I-D.cheshire-dnsext-multicastdns] Cheshire, S. and M. Krochmal, "Multicast DNS", draft-cheshire-dnsext-multicastdns-11 (work in progress), March 2010. [I-D.martocci-6lowapp-building-applications] Martocci, J., Schoofs, A., and P. Stok, "Commercial Building Applications Requirements", draft-martocci-6lowapp-building-applications-01 (work in progress), July 2010. [BACnet] Bender, J. and M. Newman, "BACnet/IP", Web http://www.bacnet.org/Tutorial/BACnetIP/index.html. [ZigBee] Tolle, G., "A UDP/IP Adaptation of the ZigBee Application Protocol", draft-tolle-cap-00 (work in progress), October 2008. [LON] "LONTalk protocol specification, version 3", 1994. van der Stok & Lynn Expires January 10, 2011 [Page 17] Internet-Draft CoAP Utilization for Building Control July 2010 [DALI] "DALI Manual", Web http://www.dali-ag.org/c/manual_gb.pdf, 2001. [KNX] Kastner, W., Neugschwandtner, G., and M. Koegler, "AN OPEN APPROACH TO EIB/KNX SOFTWARE DEVELOPMENT", Web http:// www.auto.tuwien.ac.at/~gneugsch/ fet05-openapproach-preprint.pdf, 2005. [IEEE.802.15.4] "Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low Rate Wireless Personal Area Networks (LR-WPANs)", IEEE Std 802.15.4-2006, June 2006, . [oBIX] "oBIX working group", Web http://www.obix.org, 2003. [Mullender] Mullender, S., "Distributed Systems, Second Edition", Section 5 , Addison-Wesley Publishing Company, Inc. , ISBN 0-201-62427-3, 1995. Authors' Addresses Peter van der Stok Philips Research High Tech Campus Eindhoven, 5656 AA The Netherlands Email: peter.van.der.stok@philips.com URI: http://www.research.philips.com/ Kerry Lynn Consultant Phone: +1 978 460 4253 Email: kerlyn@ieee.org van der Stok & Lynn Expires January 10, 2011 [Page 18]