Principles and technologies of local area networks - Intelligent Buildings and Building Automation - page 43

4 Principles and technologies of

local area networks

Integration is one of the main features of modern building automation systems
and intelligent building systems. This integration is of the digital stations or
devices (system integration) and the integration of control and management
functions (function integration), while system integration provides a basis.
In a modern building, there might be a large number of digital stations
or devices to be integrated. Local area networks are the primary choice for
the integration of such large numbers of stations or devices in a building or
within a short distance (say, a few kilometres). LANs have been used for
data transmission among the stations or devices in the networks. However,
it is also normal nowadays to transmit (digitalized) image signals and voice
signals over a LAN.
This chapter introduces the basic principles of LAN, LAN topologies, the
OSI reference model, LAN protocols, medium access methods and some
typical LAN technologies for BAS/IB applications.

4.1 LAN characteristics

4.1.1 Wide area network (WAN) and local area network

WANs and LANs are distinguished on the basis of geographical distribution
of the devices in the networks.
WANs provide communications over a long distance and have no geo-
graphical boundary. They rely upon the infrastructure, such as telephone
networks and Internet backbone, which has already been installed and there-
fore provides worldwide coverage. Users do not therefore own their links, but
instead pay a time-based charge to the services providers when using them.
WANs and LANs are used to link networks and digital devices separated
by long or short distances together, but it is in fact hard to distinguish an
exact geographic boundary between them. Typically, a LAN will be over a
small geographic distance, normally a single building, or at most a campus.
It will usually be privately owned (as opposed to being leased from telecom-
munication service providers) and these days it will normally have a data
rate (measured in bits per second) of somewhere between a few Kbps and