15.1 BACKGROUNDThe variety of appli

15.1 BACKGROUND
The variety of applications for LANs is wide. To provide some insight into the types
of requirements that LANs are intended to meet, this section provides a brief discussion
of some of the most important general application areas for these networks.
Personal Computer LANs
A common LAN configuration is one that supports personal computers. With the
relatively low cost of such systems, individual managers within organizations often
independently procure personal computers for departmental applications, such as
spreadsheet and project management tools, and Internet access.
But a collection of department-level processors will not meet all of an organization’s
needs; central processing facilities are still required. Some programs,
such as econometric forecasting models, are too big to run on a small computer.
Corporate-wide data files, such as accounting and payroll, require a centralized
facility but should be accessible to a number of users. In addition, there are other
kinds of files that, although specialized, must be shared by a number of users. Further,
there are sound reasons for connecting individual intelligent workstations
not only to a central facility but to each other as well. Members of a project or
organization team need to share work and information. By far the most efficient
way to do so is digitally.
Certain expensive resources, such as a disk or a laser printer, can be shared by
all users of the departmental LAN. In addition, the network can tie into larger corporate
network facilities. For example, the corporation may have a building-wide
LAN and a wide area private network. A communications server can provide controlled
access to these resources.
LANs for the support of personal computers and workstations have become
nearly universal in organizations of all sizes. Even those sites that still depend heavily
on the mainframe have transferred much of the processing load to networks of
personal computers. Perhaps the prime example of the way in which personal computers
are being used is to implement client/server applications.
For personal computer networks, a key requirement is low cost. In particular,
the cost of attachment to the network must be significantly less than the cost of the
attached device.Thus, for the ordinary personal computer, an attachment cost in the
hundreds of dollars is desirable. For more expensive, high-performance workstations,
higher attachment costs can be tolerated.
Backend Networks and Storage Area Networks
Backend networks are used to interconnect large systems such as mainframes,
supercomputers, and mass storage devices. The key requirement here is for bulk
data transfer among a limited number of devices in a small area. High reliability is
generally also a requirement. Typical characteristics include the following:
• High data rate: To satisfy the high-volume demand, data rates of 100 Mbps or
more are required.