Client Server vs. Peer-to-Peer
Every network requires special software to control the flow of information
between users. A Network Operating System, or NOS, is installed onto each PC
that requires network access. The NOS is like a traffic cop that monitors
the exchange and flow of files, electronic mail, and other network
information.
Network Operating Systems are usually classified according to whether they
are peer-to-peer or client-server NOSs. Peer-to-peer NOSs like Windows 98,
98se, ME, 2000, or XP are best for home & small office use--they're great
for sharing applications, data, printers, and other localized resources
across a handful of PCs. Client-server NOSs like Windows .NET, 2000 & NT are
ideal for large-scale organizations that require fast network access for
video, publishing, multimedia, spreadsheet, database, and accounting
operations.
Peer-to-Peer Networks
A peer-to-peer network allows two or more PCs to pool their resources
together. Individual resources like disk drives, CD-ROM drives, and even
printers are transformed into shared, collective resources that are
accessible from every PC.
Unlike client-server networks, where network information is stored on a
centralized file server PC and made available to tens, hundreds, or
thousands client PCs, the information stored across peer-to-peer networks is
uniquely decentralized. Because peer-to-peer PCs have their own hard disk
drives that are accessible by all computers, each PC acts as both a client
(information requestor) and a server (information provider).
 In the
diagram, three peer-to-peer workstations are shown. Although not capable of
handling the same amount of information flow that a client-server network
might, all three computers can communicate directly with each other and
share one another's resources.
A peer-to-peer network can be built with either 10BaseT cabling and a hub or
with a thin coax backbone. 10BaseT is best for small workgroups of 16 or
fewer users that don't span long distances, or for workgroups that have one
or more portable computers that may be disconnected from the network from
time to time.
After the networking hardware has been installed, a peer-to-peer network
software package must be installed onto all of the PCs. Such a package
allows information to be transferred back and forth between the PCs, hard
disks, and other devices when users request it. Popular peer-to-peer NOS
software includes Windows 98, 98se, ME, 2000, XP, Artisoft LANtastic, and
NetWare Lite.
Most NOSs allow each peer-to-peer user to determine which resources will be
available for use by other users. Specific hard & floppy disk drives,
directories or files, printers, and other resources can be attached or
detached from the network via software. When one user's disk has been
configured so that it is "sharable", it will usually appear as a new drive
to the other users. In other words, if user A has an A and C drive on his
computer, and user B configures his entire C drive as sharable, user A will
suddenly have an A, C, and D drive (user A's D drive is actually user B's C
drive). Directories work in a similar fashion. If user A has an A and C
drive, and user B configures his "C:\WINDOWS" and "C:\DOS" directories as
sharable, user A may suddenly have an A, C, D, and E drive (user A's D is
user B's C:\WINDOWS, and E is user B's C:\DOS). Did you get all of that?
Because drives can be easily shared between peer-to-peer PCs, applications
only need to be installed on one computer - not two or three. If users have
one copy of Microsoft Word, for example, it can be installed on user A's
computer - and still used by user B.
The advantages of peer-to-peer over client-server NOSs include:
- No need for a network administrator
- Network is fast/inexpensive to setup & maintain
- Each PC can make backup copies of its data to other PCs for security.
By far the easiest type of network to build, peer-to-peer is perfect for
both home and office use.
Client-Server Networks
In a client-server environment like Windows NT or Novell NetWare, files are
stored on a centralized, high speed file server PC that is made available to
client PCs. Network access speeds are usually faster than those found on
peer-to-peer networks, which is reasonable given the vast numbers of clients
that this architecture can support. Nearly all network services like
printing and electronic mail are routed through the file server, which
allows networking tasks to be tracked. Inefficient network segments can be
reworked to make them faster, and users' activities can be closely
monitored. Public data and applications are stored on the file server, where
they are run from client PCs' locations, which makes upgrading software a
simple task - network administrators can simply upgrade the applications
stored on the file server, rather than having to physically upgrade each
client PC.
In the client-server diagram, the client PCs are shown to be separate and
 subordinate to
the file server. The clients' primary applications and files are stored in a
common location. File servers are often set up so that each user on the
network has access to his or her "own" directory, along with a range of
"public" directories where applications are stored. If the two clients below
want to communicate with each other, they must go through the file server to
do it. A message from one client to another is first sent to the file
server, where it is then routed to its destination. With tens or hundreds of
client PCs, a file server is the only way to manage the often complex and
simultaneous operations that large networks require.
Network Printing
In client-server networks, network printing is normally handled by a print
server, a small box with at least two connectors: one for a printer, and
another that attaches directly to the network cabling. Some print servers
have more than two ports - they may, for example, support 2, 3, or 4
printers simultaneously. When a user sends a print job, it travels over the
network cabling to the file server where it is stored. When the print server
senses that the job is waiting, it moves it from the file server to its
attached printer. When the job is finished, the print server returns a
result message to the file server, indicating that the process is complete.
In the diagram, the laptop client PC sends a
 job to the file
server. The file server, in turn, forwards the job to the print server,
which sends it to the laser printer when it's available. Any client on the
network can access the printer in this fashion, and it's quite fast. The
print server can be placed anywhere on the network, and a network can have
more than one print server - possibly one in an office's accounting
department, another in marketing, and so on.
Print Servers are available for both client-server and peer-to-peer
networks. They're incredibly convenient because they let you put a printer
anywhere along your network even if there isn't a computer nearby. However,
users often opt not to use a print-server with their peer-to-peer network.
Why? Because every computer's resources are available to everyone on the
network, Sally can print a job on John's printer - just as if Sally had a
printer attached to her computer.
In this example, the printer
 is attached to
the computer on the right. When the PC on the left sends a job, it "thinks"
that it is printing to a printer of its own. In actuality, the job travels
over the network cables to the PC on the right, which stores and prints the
job in the background. The user at the PC with the printer is never
interrupted while his computer processes and prints the job transparently.
Remote Access & Modem Sharing
When a client-server network needs a gateway to the world, the network
administrator usually installs a remote-node server, which serves up two
functions: remote access and modem sharing. Most remote-node servers attach
directly to the network cabling; they provide a bridge between the network,
a modem, and a telephone line.
Remote access allows users to dial into their home networks from anywhere in
the world. Once a connection has been established over ordinary phone lines
by modem, users can access any programs or data on the network just as if
they were seated at one of its local workstations. Some remote access
servers only provide access to a file server's disk drives. Others can
provide access to both the file server and direct access to any PC's hard
disk on the network. This saves time because it allows a remote user to
communicate directly with any network user without having to go through the
file server.
Modem sharing lets local network users dial out from their individual
network computers to access the Internet, bulletin boards, America On-Line,
and more. After firing up their favorite communications software, local
users establish a link with the remote-node server over the network, which
opens up an outgoing telephone line. Users' individual PCs don't need
modems, which is a big money saver - only a single modem & phone line are
required for tens or hundreds of users. In the case of peer-to-peer
networks, by contrast, every PC requires its own modem for access to the
outside world.
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