Communication protocols used in BAS

DeviceNet
SOAP
XML
BACnet
LonWorks
Modbus

DeviceNet

DeviceNet is a network protocol used in the automation industry to interconnect control devices for data exchange. It utilizes the Common Industrial Protocol over a Controller Area Network media layer and defines an application layer to cover a range of device profiles.

Typical applications include information exchange, safety devices, and large I/O control networks.

DeviceNet was originally developed by American company Allen-Bradley (now owned by Rockwell Automation). It is an application layer protocol on top of the CAN (Controller Area Network) technology, developed by Bosch.

DeviceNet incorporates a connection-based network.

SOAP

Simple Object Access Protocol (SOAP) is a lightweight XML-based protocol that is used for the exchange of information in decentralized, distributed application environments. You can transmit SOAP messages in any way that the applications require, as long as both the client and the server use the same method.

SOAP is the Simple Object Access Protocol, a messaging standard defined by the World Wide Web Consortium and its member editors. SOAP uses an XML data format to declare its request and response messages, relying on XML Schema and other technologies to enforce the structure of its payloads.

SOAP provides the Messaging Protocol layer of a web services protocol stack for web services. It is an XML-based protocol consisting of three parts an envelope, which defines the message structure and how to process it a set of encoding rules for expressing instances of application-defined datatypes a convention for representing procedure calls and responses

SOAP has three major characteristics

extensibility (security and WS-Addressing are among the extensions under development)
neutrality (SOAP can operate over any protocol such as HTTP, SMTP, TCP, UDP)
independence (SOAP allows for any programming model)

XML

The XML Protocol ("XMLP") is a standard being developed by the W3C XML Protocol Working Group to the following guidelines, outlined in the group's charter: An envelope for encapsulating XML data to be transferred in an interoperable manner that allows for distributed extensibility.

BACnet

BACnet is a network protocol used in building automation systems (BAS) to control the data exchange between different devices and components. BACnet stands for Building Automation and Control Network. It is a network standard developed by the American Heating Refrigerating and Air Conditioning Engineers.

It is a communication protocol standard designed specifically to provide a way to integrate building control products made by different manufacturers.

BACnet is "a data communication protocol for building automation and control networks." A data communication protocol is a set of rules governing the exchange of data over a computer network that covers everything from what kind of cable to use to how to form a particular request or command in a standard way.

Building Automation Controls Network (BACnet) is a network protocol specifically used for multiple devices to communicate across building automation systems by system users and building system manufacturers. It was developed by ASHRAE and is used for applications like boiler control and tank level measurements.

Advantages of BACnet

Scalability between cost, performance and system size
Endorsement and adoption by nearly every major vendor in North America and many other countries
Robust internetworking including multiple LAN types and dial-up
Unrestricted growth and the ability to add new innovations and new features anytime

Disadvantages of BACnet

Limited the number of field devices that can connect to a master station except Ethernet TCP/IP
MT/TP-Wire Length
Ethernet-Infrastructure
New standard has security standard but not implemented in all devices

key features of BACnet

Ethernet, IP, MS/TP, Zigbee transmission modes
Meets ANSI/ASHRAE Standard 185; ISO-16484-5; ISO-16484-6
Low cost; No charge for usage or licensing fees

LonWorks

LonWorks is a communication network protocol useful for building automation applications designed on a low bandwidth, for networking devices through power lines, fiber optics, and other media

It was designed by Echelon Corporation/ Motorola for Security, lighting systems, HVAC, machine control, manufacturing, and metering.

Advantages of LonWorks

Web based tool; saves time and cost
Numerous developers of Lonworks products in the market
Less Architecture at device level

Disadvantages of LonWorks

Outdated
Controlled devices & variables are connected to a separate control device. (Not recommended due to network interruptions producing system failures)
Extensions are allowed only through the LonMark Consortium.
Hardware specific, and requires the Neuron chip for network movement of the protocol.
Close to “plug & play” ability, yet still far from achieving interconnectivity using Microsoft Windows

key features of LonWorks

MS/TP, network, SNVT transmission modes
Meets ANSI/EIA 709.1; ISO/IEC 14908-1, 14908-2, 14908-3, 14908-4 standards
High cost; Limited users (exclusive to actual members; mostly manufacturers)

Modbus

Modbus is a network protocol best used for industrial automation systems specifically for connecting electronic equipment. Although Modbus is best for industrial applications, its simplicity allows it to be a useful tool for building automation as well. It was developed by Modicon Inc. for tasks such as request temperature reading, send status alarm, or fan schedule.

Advantages of Modbus

Easy connection to Modicon
Suitable for small/medium volumes of data (≤255 bytes)
Data transfer designed for industrial applications
Openly published and royalty-free
Easy to deploy and maintain
Moves raw bits or words without placing restrictions on vendors

Disadvantages of Modbus

Limited the number of data types; Large binary objects are not supported.
No standard method for a node to find the description of a data object, i.e. finding a register value represents a temperature between 30◦ and 175◦.
No security against unauthorized commands or interception of data
Transmissions must be contiguous which limits the types of remote communications devices to those that can buffer data to avoid gaps in the transmission.
Great amount of configuration and programming required
Protocol is not common in the SIMATIC family