I. Networking Hardware

Networking hardware includes all computers, peripherals, interface

cards and other equipment needed to perform data-processing and

communications within the network.

File Servers

A file server stands at the heart of most networks. It is a very fast

computer with a large amount of RAM and storage space, along with a

fast network interface card. The network operating system software

resides on this computer, along with any software applications and data

files that need to be shared.

The file server controls the communication of information between

the nodes on a network. For example, it may be asked to send a word

processor program to one workstation, receive a database file from

another workstation, and store an e-mail message during the same time

period. This requires a computer that can store a lot of information and

share it very quickly. File servers should have at least the following

characteristics:

· 166 megahertz or faster microprocessor (Pentium, PowerPC)

· A fast hard drive with at least nine gigabytes of storage

· A RAID (Redundant Array of Inexpensive Disks) to preserve

data after a disk casualty

· A tape back-up unit (i.e. DAT, JAZ, Zip, or CD-RW drive)

· Numerous expansion slots

· Fast network interface card

· At least of 32 MB of RAM

Workstations

All of the computers connected to the file server on a network are

called workstations. A typical workstation is a computer that is configured

with a network interface card, networking software, and the appropriate

cables. Workstations do not necessarily need floppy disk drives or hard

drives because files can be saved on the file server. Almost any computer

can serve as a network workstation.

Network Interface Cards

The network interface card (NIC) provides the physical connection

between the network and the computer workstation. Most NICs are

internal, with the card fitting into an expansion slot inside the computer.

Some computers, such as Mac Classics, use external boxes that are

attached to a serial port or a SCSI port. Laptop computers can now be

purchased with a network interface card built-in or with network cards

that slip into a PCMCIA slot.

Network interface cards are a major factor in determining the

speed and performance of a network. It is a good idea to use the fastest

network card available for the type of workstation you are using.

The three most common network interface connections are

Ethernet cards, LocalTalk connectors, and Token Ring cards. According to

a International Data Corporation study, Ethernet is the most popular,

followed by Token Ring and LocalTalk (Sant'Angelo, R. (1995). NetWare

Unleashed, Indianapolis, IN: Sams Publishing).

(A) Ethernet Cards

Ethernet cards are usually purchased separately from a computer,

although many computers (such as the Macintosh) now include an option

for a pre-installed Ethernet card. Ethernet cards contain connections for

either coaxial or twisted pair cables (or both) (See fig. 1). If it is designed

for coaxial cable, the connection will be BNC. If it is designed for twisted

pair, it will have a RJ-45 connection. Some Ethernet cards also contain an

AUI connector. This can be used to attach coaxial, twisted pair, or fiber

optics cable to an Ethernet card. When this method is used there is

always an external transceiver attached to the workstation.

(B) LocalTalk Connectors

LocalTalk is Apple's built-in solution for networking Macintosh

computers. It utilizes a special adapter box and a cable that plugs into the

printer port of a Macintosh (See fig. 2). A major disadvantage of LocalTalk

is that it is slow in comparison to Ethernet. Most Ethernet connections

operate at 10 Mbps (Megabits per second). In contrast, LocalTalk operates

at only 230 Kbps (or .23 Mbps).

Fig.2. LocalTalk connectors

Token Ring network cards look similar to Ethernet cards. One

visible difference is the type of connector on the back end of the card.

Token Ring cards generally have a nine pin DIN type connector to attach

the card to the network cable.

Switch

A concentrator is a device that provides a central connection point

for cables from workstations, servers, and peripherals. In a star topology, twisted-pair wire is run from each workstation to a central switch/hub. Most switches are active, that is they electrically amplify the signal as it moves from one device to another. Switches no longer broadcast network packets as hubs did in the past, they memorize addressing of computers and send the information to the correct location directly. Switches are:

· Usually configured with 8, 12, or 24 RJ-45 ports

· Often used in a star or star-wired ring topology

· Sold with specialized software for port management

· Also called hubs

· Usually installed in a standardized metal rack that also may

store netmodems, bridges, or routers

Repeaters

Since a signal loses strength as it passes along a cable, it is often

necessary to boost the signal with a device called a repeater. The repeater

electrically amplifies the signal it receives and rebroadcasts it. Repeaters

can be separate devices or they can be incorporated into a concentrator.

They are used when the total length of your network cable exceeds the

standards set for the type of cable being used.

A good example of the use of repeaters would be in a local area

network using a star topology with unshielded twisted-pair cabling. The

length limit for unshielded twisted-pair cable is 100 meters. The most

common configuration is for each workstation to be connected by twistedpair

cable to a multi-port active concentrator. The concentrator amplifies

all the signals that pass through it allowing for the total length of cable on the network to exceed the 100 meter limit.

Bridges

A bridge is a device that allows you to segment a large network

into two smaller, more efficient networks. If you are adding to an older

wiring scheme and want the new network to be up-to-date, a bridge can

connect the two.

A bridge monitors the information traffic on both sides of the

network so that it can pass packets of information to the correct location. Most bridges can "listen" to the network and automatically figure out the address of each computer on both sides of the bridge. The bridge can inspect each message and, if necessary, broadcast it on the other side of the network.

The bridge manages the traffic to maintain optimum performance

on both sides of the network. You might say that the bridge is like a traffic cop at a busy intersection during rush hour. It keeps information flowing on both sides of the network, but it does not allow unnecessary traffic through. Bridges can be used to connect different types of cabling, or physical topologies. They must, however, be used between networks with the same protocol.

Routers

A router translates information from one network to another; it is

similar to a superintelligent bridge. Routers select the best path to route a message, based on the destination address and origin. The router can

direct traffic to prevent head-on collisions, and is smart enough to know

when to direct traffic along back roads and shortcuts.

While bridges know the addresses of all computers on each side of

the network, routers know the addresses of computers, bridges, and other routers on the network. Routers can even "listen" to the entire network to determine which sections are busiest -- they can then redirect data around those sections until they clear up.

If you have a school LAN that you want to connect to the Internet,

you will need to purchase a router. In this case, the router serves as the

translator between the information on your LAN and the Internet. It also

determines the best route to send the data over the Internet. Routers

can:

· Direct signal traffic efficiently

· Route messages between any two protocols

· Route messages between linear bus, star, and star-wired ring topologies

· Route messages across fiber optic, coaxial, and twisted-pair cabling