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Created: October 22, 2004.
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ASHRAE Releases BACnet Web Services Interface Specification for Public Review.

A public review draft has been released for the BSR/ASHRAE Web Services Addendum to the ANSI/ASHRAE Standard 135-2004 (BacNet). The Building Automation and Control Networks (BACnet) specification is an American national standard (ANSI), a European pre-standard, and an ISO global standard.

The BACnet data communication protocol provides a set of rules governing the exchange of data over a computer network. The rules govern, for example, "what kind of cable to use, or to how to form a particular request or command in a standard way. What makes BACnet special is that the rules relate specifically to the needs of building automation and control equipment, i.e., they cover things like how to ask for the value of a temperature, define a fan operating schedule, or send a pump status alarm."

According to the ASHRAE announcement, potential uses of the Addendum's Web Services technology include "simplifying access to building energy and performance data for inclusion in spreadsheets and other management reports; accessing equipment run-time data for use by maintenance management systems; allowing tenant control of space temperature setpoints; coupling of room scheduling with ventilation and comfort control, etc."

Creation of the new Web Services Interface Addendum was motivated by a recognition that Web services "is emerging as the predominant technology for the integration of a wide variety of enterprise information. The addendum therefore defines a standard means of using Web services to integrate facility data from disparate data sources, including BACnet networks, with a variety of business enterprise applications."

The BacNet Web Services Addendum reflects deliberations of the XML Working Group over two years, beginning with an initial meeting which discussed several XML spplications: "object profiles, EPICS documents, a Device Definition Language specification, protocol analyzer traces (i.e., what is seen on the wire, including timestamps, source and destination addresses), router configuration information, network topology information, and anything that can be extended by a vendor.

The BACnet XML Working Group "is working on defining applications of the Extensible Markup Language (XML) relevant to BACnet systems. It is also working on Web service definitions that will allow data exchange between building automation and control systems and various enterprise management systems. In June 2004, after months of intense effort by the Web Services Task Team of the BACnet/XML Working Group, SSPC 135 unanimously voted to recommend public review of the WS addendum to BACnet-2004.

The specification is composed of two parts: Part 1 (135-2004c-1) Normative Annex N defines "Adding BACnet/WS Web Services Interface." This interface "is intended to be communication protocol neutral in that the defined Web services can be used with any underlying protocol including BACnet, Konnex, MODBUS, LON or legacy proprietary protocols. This has been accomplished by defining how to read and write the common elements of all building automation and control systems such as values, schedules, trend logs and alarm information using services such as 'getValue' and 'setValue' that use a simple path to define the intended data source."

Addendum Part 1 also defines mechanisms for localization "where certain types of data such as time, date and numbers can be formatted according to local custom and language: A BACnet/WS server may support multiple locales simultaneously, and several of the attributes of a node are accessible for different locales. For example, in a server that supports multiple locales, the 'DisplayName' attribute can be used to get a user interface presentation name for the node in more than one language. Specifying a locale in a service also allows the client to request dates, times and numbers in a format appropriate to that locale."

Addendum Part 2 is the Normative Annex H, "Combining BACnet Networks with Non-BACnet Networks." It "prescribes how a gateway should be constructed that translates web service requests specifically to and from BACnet messages. The Annex M subclause (H.6 Using BACnet with the BACnet/WS Web Services Interface) "provides examples of the correspondence between BACnet/WS node attributes to specific properties of BACnet Objects. For some nodes and attributes, mapping may not be to any BACnet property but rather to a static value or to a function that transforms internal information to a BACnet datatype or concept."

The modifications of the BACnet/WS Web Services Interface Addendum are the result of change proposals made pursuant to the ASHRAE continuous maintenance procedures and of deliberations within Standing Standard Project Committee 135. SSPC is a "Standing Standard Project Committee" as defined and authorized by the ASHRAE Standards Committee. SSPC 135 participants, according to the published roster, include representatives from Novar, Automated Logic, Delta Controls, VVS Tekniska, ABOK, Siemens Building Technologies, Kyoritsu Kiden Co., Ltd., SIA, Sebesta Blomberg, NAVFAC, Cimetrics, Tridium, NIST, Siemens, Lithonia Lighting, JDL Business Services, University of Cincinnati, ESS Engineering, Montgomery College Maryland, and Andover Controls.

The BSR/ASHRAE Addendum c to ANSI/ASHRAE Standard 135-2004 approved for review by the ASHRAE Standards Committee will be open for comment during 45-day period October 22, 2004 through December 6, 2004.

Related standards work is being done within the OASIS Open Building Information Exchange (oBIX) Technical Committee, chartered to "define a standard web services protocol to enable communications between building mechanical and electrical systems, and enterprise applications. This protocol will enable facilities and their operations to be managed as full participants in knowledge-based businesses. The oBIX specification will utilize web services for exchange of information with the mechanical and electrical systems in commercial buildings."

Bibliographic Information

Proposed Addendum c to Standard 135-2004, BACnet — A Data Communication Protocol for Building Automation and Control Networks. Public Review Draft, ASHRAE Standard. BSR/ASHRAE Addendum c to ANSI/ASHRAE Standard 135-2004. First Public Review. Released: October 22, 2004. 32 pages. Copyright (c) American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. August 30, 2004. This draft shows proposed changes to the current standard.

Standard 135-2004 — BACnet — A Data Communication Protocol for Building Automation and Control Networks. ANSI approved. Published by ASHRAE. 2004. ISBN/ISSN: 1041-2336. 611 pages. The purpose of this ANSI approved standard is "to define data communication services and protocols for computer equipment used for monitoring and control of HVAC&R and other building systems and to define an abstract, object-oriented representation of information communicated between such equipment, thereby facilitating the application and use of digital control technology in buildings. This standard is under continuous maintenance, which is a process ASHRAE uses to keep standards current through the issuance of addenda, or revisions."

Excerpts from BSR/ASHRAE Addendum c to ANSI/ASHRAE Standard 135-2004 Public Review Draft

This annex [N - BACnet/WS Web Services Interface] "defines a data model and Web service interface for integrating facility data from disparate data sources with a variety of business management applications. The data model and access services are generic and can be used to model and access data from any source, whether the server owns the data locally or is acting as a gateway to other standard or proprietary protocols.

Implementations of the services described in this annex shall conform to the Web Services Interoperability Organization (WS-I) Basic Profile 1.0, which specifies the use of Simple Object Access Protocol (SOAP) 1.1 over Hypertext Transfer Protocol — HTTP/1.18 (RFC2616) and encodes the data for transport using Extensible Markup Language (XML) 1.0 (Second Edition), which uses the datatypes and canonical encodings defined by the World Wide Web Consortium XML Schema..."

Data model: "A node is the fundamental primitive data element in the BACnet/WS data model. Nodes are arranged into a hierarchy in the data model... A path is a character string that is used to identify a node or an attribute of a node. The hierarchy of nodes is reflected in a path as a hierarchy of identifiers arranged as a delimited series, similar to the arrangement of identifiers in a Uniform Resource Locator (URL) for the World Wide Web. A path like '/East Wing/AHU #5/Discharge Temp' identifies a node, and a path like '/East Wing/AHU #5/Discharge Temp:InAlarm' identifies the InAlarm attribute of that node..."

Security (N6): "BACnet/WS does not define its own authentication mechanism; rather, this annex specifies the use of a transport authentication defined by other standards. Authentication may be provided by a simple HTTP username and password, or may be secured through SSL/TLS certificates or more advanced options such as WS-Security/SAML and others yet to be defined. To ensure a base level of interoperability, this annex requires that all servers be capable of supporting the HTTP 'basic' authentication, which is supported by all major Web services toolkits and application servers. Once a user is authenticated to a server, the authorization as to what that user can access and/or modify is according to authorization policies in the server. The configuration of these authorization policies is a local matter..."

Normalized Points: "Most building automation protocols, both standard and proprietary, have the concept of organizing data into 'points' that have 'values.' In addition to their values, points often contain data such as 'point description' or 'point is in alarm.' But these data may be named, structured, and/or accessed differently in different protocols. To ensure that a Web service client can retrieve data without knowing these naming and access-method details, this annex defines 'normalized points.' This means that the common attributes of points available in the majority of building data models are exposed using a common set of names..."

Extending BACnet/WS (N.13) "The data model defined by this annex can be extended in the following ways: (1) extended information that might be considered to be a property of a node may be modeled by adding children nodes with a NodeType of 'Property'. This allows for the extended property data to be arbitrarily complex; (2) Node classification can be extended by local application of the NodeSubtype attribute; (3) The Units enumeration may be extended by configuring the Units attribute to the canonical value of 'other', and setting a localized value of the Units attribute to the new units string..."

List of added entries for BACnet Standard 135-2004 Clause 25, pages 448-449:

About BACnet and ASHRAE

BACnet — A Data Communication Protocol for Building Automation and Control Networks has been developed under the auspices of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), BACnet is an American national standard, a European pre-standard, and an ISO global standard. The protocol is supported and maintained by ASHRAE Standing Standard Project Committee 135..."

"BACnet is a Data Communications Protocol for Building Automation and Control Networks. It is an ASHRAE, ANSI, and ISO standard protocol... BACnet became an ASHRAE/ANSI standard in 1995, and an ISO standard in 2003. BACnet is under continuous maintenence by the ASHRAE Standing Standard Project Committee 135. The BACnet protocol defines a number of services that are used to communicate between building devices. The protocol services include Who-Is, I-Am, Who-Has, I-Have, which are used for Device and Object discovery. Services such as Read-Property and Write-Property are used for for data sharing. The BACnet protocol defines a number of Objects that are acted upon by the services. The objects include Analog Input, Analog Output, Analog Value, Binary Input, Binary Output, Binary Value, Multi-State Input, Multi-State Output, Calendar, Event-Enrollment, File, Notification-Class, Group, Loop, Program, Schedule, Command, and Device. The BACnet protocol defines a number of data link / physical layers, including ARCNET, Ethernet, BACnet/IP, Point-To-Point over RS-232, Master-Slave/Token-Passing over RS-485, and LonTalk..." [see the BACnet entry from Wikipedia]

The goal of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) is to "advance the arts and sciences of heating, ventilation, air conditioning, refrigeration and related human factors to serve the evolving needs of the public and ASHRAE members. ASHRAE has some 87 active standards and guideline project committees, addressing such broad areas as indoor air quality, thermal comfort,energy conservation in buildings, reducing refrigerant emissions, and the designation and safety classification of refrigerants..."

"ASHRAE, founded in 1894, is an international organization of 55,000 persons. Its sole objective is to advance through research, standards writing, publishing and continuing education the arts and sciences of heating, ventilation, air conditioning and refrigeration to serve the evolving needs of the public..." [ASHRAE web site]

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