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Local Area Networks


Local Area Networks (LANS) allow for computers which are in relatively close
proximity (say within the same building or group of buildings) to quickly
communicate and transparently share resources. The major benefits of LANs over
unconnected (or free standing) micro-computers are easier management, cost
savings brought about by the ability to share otherwise expensive resources,
improved security as well as the provision of communications services (such as
electronic mail or file transfer: see below).

LANs are composed of several elements, typically including cabling,
communications devices (hubs, bridges and routers which link different cable
segments), file servers (and other types of servers such as print servers),
shared peripheral devices (such as printers and modems), and the client
microcomputers. LANs may use one of several different cabling schemes. Options
include shielded and unshielded twisted pair cable (similar to, or some cases
identical to, telephone cable), coaxial cable or optical fibre. The most
popular choices for new installations are unshielded twisted pair (UTP) for
connecting workstations and coaxial cable or optical fibre for network
backbones. Information is passed around the network as a set of packets. A
packet is composed of a header (where the packet came from and where it is
going to), and a body (the data itself). Several protocols specify the packet
format, the cabling scheme and electronic signalling requirements of devices
on the network. The most popular standard is Ethernet (IEEE 802.3). It uses a
signalling rate of 10Mbps and runs over a variety of cable types. Other
standards include Token Ring (IEEE 802.5, used primarily with IBM equipment,
running at 4 or 16Mbps), AppleTalk (used by Apple micro-computers) and the
relatively new FDDI (100Mbps over optical fibre).

File servers are used to store files for access by client               [PP23]
workstations. They differ from conventional multi-user systems
in that their main task is simply to provide clients with shared
access to files. They are generally not responsible for any client
related computation - this takes place on the workstations. There are
several standards and protocols for communicating with file servers. One of
the most popular microcomputer file server operating systems is Novell's
NetWare. Other common systems include Microsoft's Lan Manager, Apple's
Appleshare and the Unix file sharing standard (NFS).

The importance of creating flexible LANs within a court complex is difficult
to overstate. Such LANs ought to employ a standard cabling scheme and support
standard low and high level protocols. Although it is not possible to list all
of the potential uses of a court-room LAN, some obvious ones include:
providing access to data for presentation purposes, allowing access to
computerised exhibits and providing access to litigation support facilities.
Such uses and others are discussed in Seaman (1992) and Jacobsen et al (1992).
The development of a LAN is considered a 'fundamental building block' of the
Western Australian Judicial Support System.



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