Page 232 - Handbook of Electronic Assistive Technology

Chapter 8 • Assisted Living 221

to changes in topology once installed. It developed from a focus on building automation
associated with regulatory requirements within Europe for management of services such as
lighting and blind control, and so concentrates on obtaining a highly consistent standard of
operation and interoperability in that sphere. The American home automation market his-
torically had a primary focus on home entertainment and communication, and has a clear
split between very low cost and high-end implementation, so has evolved slightly differently.

LonWorks
LonWorks is a sophisticated field bus system that has many applications, including home
automation and such diverse implementations as high-speed trains. It was created by the
Echelon Corporation in 1988 from a vision to make sophisticated control systems avail-
able to all. Lon is an acronym for local operating network and the system has many of the
properties of a LAN, and can be considered an intelligent control network. The system is
based around a LonWorks device called a node that includes a Neuron chip manufactured
under licence, and a transceiver with a range of transceiver types being available for dif-
ferent media. Communication between nodes is achieved using the LonTalk protocol, the
protocol being held as firmware on the chip, which can itself also execute applications and
includes 11 input/output pins. The Neuron chip remains the primary method of imple-
mentation, but the protocol has been available for general-purpose processors since 1999.
The system can communicate over a large range of speeds up to the Mbits/s range, but the
most common data rate is 78 kbits/s, which is used by the free topology twisted pair trans-
ceiver. A segment refers to the longest piece of uninterrupted wire and a segment can con-
tain up to 64 nodes. The network can be split into many segments, each operating over its
own medium at its own speed, making it a very powerful and adaptable system, which can
be achieved because a LonWorks router can be fitted with any two transceivers. The unique
48-bit Neuron ID is also a three part address consisting of logical domain, subnet and node.
The most important communication object of the LonTalk protocol is the network
variable, which is the data item that a device expects to get or make available on a net-
work. LonWorks implements the full functionality of the OSI model and a variable may
be an environmental variable such as a temperature or a switch status. Interoperability is
achieved by defining standard network variable types, which is achieved under the aus-
pices of the LonMark Organisation. LonMark interoperability was introduced in 1994 and
LonMark International, a nonprofit unincorporated organisation, was created in 2003. It
has been adopted as the basis for a number of standards and in 2005 it was adopted as EN
14908 (European building automation standard).

BACnet

BACnet is a protocol that was developed by the American Society of Heating, Refrigeration
and Air-Conditioning Engineers (ASHRAE), beginning in 1987 and being adopted
as a standard as ASHRAE/ANSI Standard 135 in 1995 and in 2003. The BACnet protocol
defines a number of data link/physical layers, including ARCNET, Ethernet, BACnet/IP,