Peer-to-Peer Networks
In a peer-to-peer network, a group of PCs are hooked together, with each PC, having the same (peer) status in the network. There's no " boss" PC that regulates network traffic or acts as a hub for managing the network. All the PCs can share files, send each other messages, and share a printer or two. Microsoft Windows NT Workstation and Microsoft Windows 95 can be configured in a peer-to-peer LAN. You may already have a peer-to-peer network in your office.
Small businesses often choose to install a peer-to-peer network because it is inexpensive and relatively easy to set up and maintain. However, while this kind of network may be a good solution for very small offices, a peer-to-peer network has significant disadvantages:
- It lacks dial-in support for shared files and services for employees on the road.
- It lacks central control. Each person has to administer his or her own computer in terms of granting access to certain people for certain files.
- It lacks overall system security and backup for the files and databases on your network.
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A Small Business Server Network
Small Business Server runs on a central, dedicated computer (the server computer) where applications, files, and e-mail messages are stored. This server is like a server in a cafe, but instead of serving up eggs and toast to customers, it can serve up applications such as your company's accounting system, your customer database, or a word processor, as well as data files and e-mail messages. It also acts as the central hub for sharing, printers, doing global backup, providing network security, providing access to the Internet, and performing general management of the network.
A number of PCs, known as client computers, are physically connected to the server computer, using the same methods you use to hook up a peer-to-peer network (network cards in PC clients and the server, and one of several kinds of network cable setup).
Most small businesses install Small Business Server. or move from peer-to-peer LANs to Small Business Server for four primary reasons: Software Consistency, Hardware Flexibility
When you run your applications from a server, you know that everyone in the business has the same versions of the word processor, spreadsheet, graphics package, or database, so they can easily share files. When you upgrade the server software, everybody gets upgraded automatically. In terms of hardware, you have more flexibility in the individual workstation computers you have. Unlike computers on a peer-to-peer network, the individual PCs don't have to be sufficiently powerful to handle the network traffic-the server does that.
Central Storage of Data
On a peer-to-peer network, when one machine goes down, all the information on that
machine is inaccessible to the rest of the network. This can happen even when
someone goes home for the night, turns off his or her computer, and has it password-
protected so no one else can gain access to it. When you have a central server,
authorized users can get at data when they need it.
Security
When you have a dedicated server, one person can administer and oversee the
network, and the company can apply standards, passwords, and procedures that keep
unauthorized people from gaining access to the company's data. It's also much easier
to keep viruses (software programs that tamper with your data) from infecting your
company from outside sources like shareware or the Internet.
Backup
Because your company's important information, such as financial reports and
customer lists, is kept on a central server, it's much easier to back up that data than it
is to rely on individuals to regularly back up their individual computers. With Small
Business Server, you can even "mirror" a disk drive. Information is instantly copied to
a second disk drive, so that if the first drive in your system goes down, you cm switch
over and keep working.
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What Hardware Does a Network Require?
There are several pieces of hardware you'll need for your network. Some of it you can
buy and have ready, and some of it you'll probably want to leave to a consultant or
network installer to buy and install for you. First we'll cover the hardware you can
buy and have ready.
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Server Computer
For your Small Business Server computer, you need:
- A Pentium-based computer with at least 64 megabytes (MB) of RAM
- A 2-gigabyte (GB) hard disk drive, or several hard disk drives assembled in an
array in the server
- You can add modems and printers your users can share and a tape backup system
for doing backups of both the server and the client computers on the network.
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Client Computers
A client computer is the personal computer that serves as the user's connection to the
network. If you have the option, it's better to have at least a 486/33 processor in the
computers you use as clients on the network. That's because Windows client
computers have to do a certain amount of processing on the client end to be "good"
clients to the network.
Most commonly, the clients on your LAN will be Intel-based machines, such as a 486
or Pentium processor running the Windows 95 or Windows NT Workstation operating
system. However, you can use 386-based computers running Windows for
Workgroups, Reduced Instruction Set Chip (RISC) machines running a version of
LTNIX or Microsoft Windows NT Workstation, or Apple Macintosh computers.
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Cable
When it comes to cable selection and installation, it's probably smart to call a network
consultant or service provider who specializes in providing and setting up cable for
networks, unless you enjoy-and can get permission for-crawling around in duct
work over the ceilings or under the floors of your office building. Although you may
install Microsoft BackOffice Small Business Server software yourself (because it's
easy and so you understand the process later), these service providers can help with
this key component of the network.
Consultants or service providers are often listed in the classified telephone directory
under Computers or Networks. In this section, we'll discuss cable on a fairly technical
level, just so that you know some of the options you have. For most small-business
networks, there are typically two cable alternatives to consider-twisted pair cable
and coaxial cable.
Twisted Pair Cable
Twisted pair cable is made from insulated strands of wire twisted together inside a
sheath that may or may not be shielded. Unshielded Twisted Pair (UTP) is the most
commonly used cable for small LANs and therefore will be the only type discussed
here. It is often referred to as 10BaseT because the most popular size of this cable
transmits 10 megabits of data per second. It comes in different categories that carry
between 4 megabits/second and 100 megabits/second of data and can carry a signal
about 300 feet before the signal starts to suffer from loss of strength.
To connect to the wall and to the computer, twisted pair cable requires a connector that looks like a standard phone-cord connector, but larger. It has the advantage of being easy to install, since it's light and thin like the wire that connects your phone to the wall. Another advantage is the way you configure a twisted pair cabled network-if it breaks, it doesn't bring the entire network down. Twisted pair cable is also less expensive than coaxial cable.
The disadvantages of twisted pair cable include the fact that you need hubs to Jay out
your network, and you also need 10BaseT network hubs to connect the wire to the
network interface cards in the PCs. You'll need one 10BaseT box for every 10 users
on the network. This initial expense at installation will provide you with substantial
flexibility and protection against downtime as your company grows and uses your
network.
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Coaxial Cable
Coaxial cable is similar to your TV cable-it looks much the same and has the same
characteristics. It has a core of solid or braided copper wire surrounded by insulation,
braided metal shielding, and an outer cover. The thinner coaxial cables can carry a
signal about 600 feet before the signal starts to suffer from loss of strength. The thick
coaxial cables can carry a strong signal for about 1,600 feet-
The advantages of coaxial cable are that it doesn't need hub connectors, as does
twisted pair cable, and you can run it long distances through your building without
having the signal strength deteriorate. The disadvantages are that it goes into your
network in a "daisy-chain" loop, so if it breaks anywhere (mice have been known to
chew through it) your entire, network goes down. It's also harder to install than twisted
pair cable, and it's more susceptible to electrical interference from appliances such as
fluorescent lights. Unless you get strong, specific advice from your installer, stick
with twisted pair.
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Network Adapter Cards
Network adapter cards are hardware boards or cards that you put into empty slots in
the back of your client computers and the server. The cards physically connect to the
cable that links your network together. Network adapter cards can also be attached to
your client computers by using the serial ports. In addition to providing the physical
connection, these cards:
- Prepare the data so it can go through the cable. The network adapter card
translates the data bits back and forth as they go from the computer to the cable
and back again.
- Address the data Each network adapter card has its own unique address,
which it imparts to the data stream. The card provides the data with an identifier
when it goes out onto the net and enables data seeking a particular computer to
know where to hop off the cable.
- Control the data flow The card has RAM on it to help it pace the data so that
it doesn't overwhelm the receiving computer or the cable.
- Make (and agree on) the connection to another computer Before it
actually sends the data, the network adapter card starts an electronic dialog with
the other PC on the network that wants to communicate, in much the same way
that two jugglers have to work things out in advance so that their act goes
smoothly. They agree on things like the maximum size of the data groups that will
be sent, the total amount of the data, the time interval between data chunks, the
amount of time that elapses before confirmation that the data arrived successfully,
and how much data each card can hold before it overflows.
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Hubs and Routers
You'll probably need hubs and routers for your network-if not now, then perhaps in
the future as your network grows. When it comes to these components, the advice is
the same as it was for the cable-unless you have just a handful of client PCs and
they are all reasonably close together, get someone who does cable installation and
network setup for a living to help with this part of the network. Here's a summary of
hub and router functions:
-
Hubs - Let you concentrate the signals from several PCs into a single point of entry
to the network.
- Routers - Play "traffic cop" by ensuring that the message packets on your network are
routed to the correct network address.
If your network is connected to the Internet, you may need a router to get
packets from the Internet down the right cable to the right desktop, and from
desktops down the right cable to the Internet.
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What Software Does a Network Require?
To use a network, both your client computers and your server computer need to run
operating systems that are designed to run on a network.
The network operating system for the purposes of this book is Microsoft BackOffice
Small Business Server, which is based on the Windows NT Server operating system.
The network operating system controls the operations of the server, lets you decide
who can have access to it, and regulates information flowing from the various clients
on the network to each other; to the printers, modems, or CD-ROM drives that are
shared by the client computers, and from the client computer to itself. It's a big job.
Part of the software in the network operating system is the network redirector, so
named because it directs and redirects commands that are floating around on the
network. The redirector "grabs" all the commands that come onto the network and
looks them over to see whether a command is something the network server should
take care of or whether the command gets passed on to a client computer to carry out,
Protocols are also part of the network operating system. Protocols are essentially sets
of behavior rules that, if followed, let one database talk with another, let clients talk to
the server, and let e-mail messages make their way around the network to your PC.
Transports are one of the least important (to you at this stage) software components of
the operating system. Transports are the enabling network components that let clients
talk to the server and that let one network talk with another network of a different
brand. You may hear about the following transports in connection with small LANS:
NetBEUI and TCPIIP.
- NetBEUI stands for Network Basic End User Interface. It supports small LANs
and it serves the purpose of being fast and simple. However, it has an inherent
architectural structure that limits its effectiveness as your network grows.
- TCPIIP stands for Transfer Control Protocol/Internet Protocol. It was developed to
be a routable protocol, and it serves the purpose of being the standard for wide-
area networks and for access to the Internet. TCP/IP is used by default in Small
Business Server networks because it provides the best overall transport in terms of
flexibility, no matter how large your network gets.
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What Is Network Topology
The topology of a network is a fancy name for the cable pattern used to hook client
computers and servers together. How the computers are connected has some
implications for how the network operating system manages both the client computers
and the information flow on the network and for bow tolerant the system is to failure.
That's why topology is important. Two common topologies are the star and the bus.
Star Topology
+ Most fault-tolerant design- easy to modify and install
new clients; best for centralized management and
monitoring of network performance.
- Costs more initially because it requires more cable.
Bus Topology
+ Simple; easy to install; requires less cable than star or
ring- easy to extend.
- Network problems hard to isolate; the network slows
down during periods of heavy use.
The star topology is the most commonly used configuration for a network, and it's the
one we recommend that you use for yours. It consists of several cables radiating out in
a "star" pattern (more or less) from a central point (in this case, your server) to the rest
of the network-your PCs, printers, and any other peripherals, such as plotters, that
you might have. Although star topology costs more to initially install (because you
use more cable), it is the most fault-tolerant design and it is easy to modify and to
manage from a central location.
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Common Network Architectures
When you have a number of people working on their networked PCs, it's inevitable
that several are going to want to do the same thing on the network at the same time,
such as print a file or use a fax modem. Specific LAN architectures (or access
methods) are a-reed-upon standards for how to send signals and regulate network
traffic in the most effective way. These methods work in conjunction with both the
network and client operating systems and are installed as part of the network interface
card. Small Business Server supports an architecture called Ethernet.
Ethernet is perhaps the most popular LAN access method. It uses either coaxial cable
or UTP cable, transmits data at10megabits per second (new 100-megabit standards
are being developed), and it can be used in either the bus or the star topology (which
is most common for small-business- Ethernet networks).
The process works like this: on an Ethernet network, the client PCs each "listen" for
network traffic on the cable, and if they don't hear anything, they transmit their
information onto the network. Then, if two clients try to transmit information at the
same time, they are alerted to the conflict, stop transmitting, and wait for a
predetermined period of time before they try again.
Ethernet has some real advantages. It's been around for a long time, so it's well
understood and widely used. Forty percent of LANs use it, and the percentage is even
higher for small businesses. Ethernet also has a wide range of interface speeds and
formats, and it doesn't cost much.
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