A local area network (LAN) connects personal computers,
printers, and other computer resources together within a building
or campus. Many schools, offices, and even homes now have LANs.
These networks allow printers, as well as documents and projects,
to be shared. LANs also enable computers to talk to one another
and are often used to share Internet access across all of the computers
in a building or school.
Most LANs use wires, or cables, to connect computers and other peripheral devices. In most networks, a network cable (which generally looks like an oversized telephone cord) connects a computer to a network jack in the wall. Sometimes, in classrooms or business offices, many computers are connected to an intermediate hub or switch, not directly to the network jack. The hub or switch into which all of the computers are plugged is the device that is connected to the network jack. In both cases, the network jack is connected to a small router by another cable. Printers are also often shared using this method of hubs and switches.
Some LANs are now wireless. Wireless LANs are fundamentally the same as wired LANs, but the cabling is replaced by small "radios" that are contained inside the computers. Wireless LANs are generally somewhat slower than the wired networks, but they are much easier to set up and allow users to move their machines around without having to reconnect network cables.
Wireless LANs have moved into the mainstream in schools and
classrooms during the last few years; however, it is important
to note that security is much more difficult when using a wireless
network (see chapter 6 of this guidebook
for security recommendations). Additionally, the adoption of competing
protocols is creating some confusion in the marketplace. Agencies
need to select a wireless protocol with care, considering how
the network can be upgraded and whether it is compatible with
existing wireless protocols.
Where a LAN may connect all of the computers within a building or campus, a wide area network (WAN) connects multiple LANs. Many districts now have WANs connecting all of the schools within the district for the sharing of Internet access, selected files, or other resources.
What Are Servers, Routers, and Firewalls?
LANs often involve a number of different components, including a
dizzying variety of servers, switches, routers, firewalls, and the
like. This section provides descriptions of many of these items.
While servers often are spoken of in almost mystical tones, they are really just powerful computers running specialized software designed to share files, manage printers, or perform any other specialized task assigned. Most of these computers are powerful enough to do more than one thing at a time; for example, a single network server might be a file server, a print server, and a mail server simultaneously.
A file server is essentially the computer equivalent of a filing cabinet. Documents, spreadsheets, and other (computer) files are stored on a file server, just as paper documents are stored in a filing cabinet. The file server's job is to make those files available to computer users on the LAN and, when appropriate, allow the users to update the files.
A print server is a piece of software or hardware that manages print jobs submitted by users. When a document is sent to a networked printer, the print server receives the job and queues it (puts it in line behind previously submitted jobs). When a job gets to the front of the queue, the print server sends it to the printer. It is not necessary to buy an individual printer for each personal computer. Users in classrooms or offices often share printers, since not everyone is typically printing at the same time. This option can save an agency a great deal of money.
- Mail server. The third common type of server is a
mail server. The mail server acts as the conduit to the outside
world as messages are sent and received. Some servers are set
up so that all of the mail stays on the mail server until a
user actively deletes it. In other configurations, the user
is able to move the mail from the server to the desktop computer.
This process, called "downloading," uses less space on the mail
A router is a piece of equipment that acts as the interface between a local network and the Internet, by routing traffic from one to the other. A router may be a computer dedicated to managing the traffic of a WAN, or it may be a piece of software running on a computer that is configured for other tasks as well. Routers also may be used in LANs to route internal traffic.
A critical component of any network is a firewall. A firewall in layman's terms is a wall that acts as a firebreakit keeps a fire from spreading. In this sense, a computer firewall keeps a network secure from hackers (the "arsonists" of the Internet) by denying access to all or part of the network. Management of firewalls requires a great deal of expertise. While the network administrator must ensure that no unwanted traffic can enter the network from outside, a level of access to and from the Internet must be created that will permit authorized users to conduct their business safely and efficiently.
A solid, well-designed firewall is critical to ensure that only
authorized users have access to a restricted network. Like routers
and servers, firewalls are available as either hardware or software.
Choosing a firewall for a particular network is an issue best
addressed at the local level, after reviewing the options available.
Firewalls and network security in general are discussed at length
in chapter 6 of this guidebook.
Advances in technology have blurred the distinctions between the
computer on the desktop and a network server. Computing power has
continued to grow exponentiallyin fact, most users do not
need all the computing power available to them (at least for now).
The same is true of network servers, which have become so powerful
that some network administrators run applications, in addition to
the server software, from the network server, rather than installing
applications directly on each of the computers connected to the
network. Servers are capable of managing a much greater workload
today than they were in past years.
Running Applications: Server vs. Desktop Computer
Running applications from a server has a number of advantages. One key advantage is in licensing, since it is much easier to track usage. Another is that local users are prevented from altering the configuration of applications, which can create software failure and cause problems for other users. In addition, it is much easier to upgrade software since only one copy needs to be upgraded, instead of upgrading one copy for each personal computer. Applications run from a network server, however, are often comparatively slower than applications running directly on a desktop computer.
Another benefit to server-run applications is the cost-saving
use of thin clients. Thin clients are basic, low-cost
computers with insufficient power to run sophisticated software
applications, but with enough power to access applications installed
on the server. By purchasing a single copy of an application that
can run on a network, with licenses for multiple users, the organization
can save the cost of multiple software copies and can purchase
less powerful computers at a much lower cost.
In addition, by instituting a thin client environment, older
computers in schools have longer useful lives. In recent years,
more and more LANs have incorporated thin clients for a variety
of purposes. In addition, more and more computer applications
are written to take advantage of the web to run remotely. The
user's desktop computer essentially acts as a "dumb" terminal,
simply displaying the web pages broadcast by the server. The computing
actually takes place on an Internet server, and users transmit
their commands via the web page. This web-based model works best
when users have high-speed Internet connections, as described
in appendix C.
Computing today occurs on the desktop, on network servers, and Internet servers alike. The distinctions between the various types of computers and servers, in many cases, matter less and less. As computer and network transmission speeds improve, the differences will be even harder to grasp. The increasing complexities of computing and networking reinforce the need for agencies to employ the services of a qualified network administrator.