BASIC NETWORKING
Khalid
A network is a group of computers, printers, and other devices that are
connected together with cables. Information travels over the cables,
allowing network users to exchange documents & data with each other,
print to the same printers, and generally share any hardware or
software that is connected to the network.
Each computer, printer, or other peripheral device that is connected to
the network is called a node. Networks can have tens, thousands, or
even millions of nodes.
Like most things, networks are are assembled according to certain
rules. Cabling, for example, has to be a certain length, each cabling
strand can only support a certain amount of network traffic, etc.
The rules that govern how a network is set up is called its topology.
The most popular topology in use today is called Ethernet, which
consists of computers and peripherals cabled together in specific ways.
Ethernet is relatively inexpensive, easy to set up and use, and very,
very fast.
Ethernet networks are categorized by how fast they can move
information. Speed is expressed in megabits per second (or Mbps), where
one "bit" is equal to 1/8th of a character, letter, or number.
There are currently two Ethernet speed categories. Standard Ethernet
operates at a fast 10Mbps, which is quick enough for most networking
tasks. Fast Ethernet, by contrast, races along at a blistering 100Mbps,
making it ideal for desktop video, multimedia, and other speed-hungry
applications. The new technology behind Fast Ethernet, which was
introduced in the beginning of 1995, is not readily compatible with
standard Ethernet.
Making the two "talk" with each other requires special equipment and
some knowledge of internetworking. If you're building your first
network, decide whether to go with standard or Fast Ethernet before you
begin shopping around for network hardware and software. Unless you
plan on using video, multimedia, or heavy graphics software, plan on
using standard Ethernet.
Cabling Basics
The two most popular types of network cabling are twisted-pair (also
known as 10BaseT) and thin coax (also known as 10Base2). 10BaseT
cabling looks like ordinary telephone wire, except that it has 8 wires
inside instead of 4. Thin coax looks like the copper coaxial cabling
that's often used to connect a VCR to a TV set.
Which type of cabling is best for you? Thin coax and 10BaseT can both
be used exclusively or together, depending on the type of network that
you're putting together.
Small networks, for example, may want to use 10BaseT cabling by itself,
because it's inexpensive, flexible, and ideal for going short
distances. Larger networks (usually with 10 or more computers) may use
a thin coax backbone with small clusters of 10BaseT cabling that branch
off from it at regular intervals.
Network Adapters
A network computer is connected to the network cabling with a network
interface card, (also called a "NIC", "nick", or network adapter. Some
NICs are installed inside of a computer: the PC is opened up and a
network card is plugged directly into one of the computer's internal
expansion slots. 286, 386, and many 486 computers have 16-bit slots, so
a 16-bit NIC is needed. Faster computers, like high-speed 486s and
Pentiums, often have 32-bit, or PCI slots.
These PCs require 32-bit NICs to achieve the fastest networking speeds
possible for speed-critical applications like desktop video,
multimedia, publishing, and databases. And if a computer is going to be
used with a Fast Ethernet network, it will need a network adapter that
supports 100Mbps data speeds as well.
Hubs
The last piece of the networking puzzle is called a hub. A hub is a box
that is used to gather groups of PCs together at a central location
with 10BaseT cabling. If you're networking a small group of computers
together, you may be able to get by with a hub, some 10BaseT cables,
and a handful of network adapters.
Larger networks often use a thin coax "backbone" that connects a row of
10BaseT hubs together. Each hub, in turn, may connect a handful of
computer together using 10BaseT cabling, which allows you to build
networks of tens, hundreds, or thousands of nodes.
Like network cards, hubs are available in both standard (10Mbps) and
Fast Ethernet (100Mbps) versions.
As companies rely on applications like electronic mail and database
management for core business operations, computer networking becomes
increasingly more important. This tutorial helps to explain Ethernet
and Fast Ethernet, which are two of the most popular technologies used
in networking.
LANs (Local Area Networks)
A network is any collection of independent computers that communicate
with one another over a shared network medium. LANs are networks
usually confined to a geographic area, such as a single building or a
college campus.
LANs can be small, linking as few as three computers, but often link
hundreds of computers used by thousands of people. The development of
standard networking protocols and media has resulted in worldwide
proliferation of LANs throughout business and educational
organizations.
WANs (Wide Area Networks)
Often a network is located in multiple physical places. Wide area
networking combines multiple LANs that are geographically separate.
This is accomplished by connecting the different LANs using services
such as dedicated leased phone lines, dial-up phone lines (both
synchronous and asynchronous), satellite links, and data packet carrier
services.
Wide area networking can be as simple as a modem and remote access
server for employees to dial into, or it can be as complex as hundreds
of branch offices globally linked using special routing protocols and
filters to minimize the expense of sending data sent over vast
distances.
Internet
The Internet is a system of linked networks that are worldwide in scope
and facilitate data communication services such as remote login, file
transfer, electronic mail, the World Wide Web and newsgroups.
With the meteoric rise in demand for connectivity, the Internet has
become a communications highway for millions of users.
The Internet was initially restricted to military and academic
institutions, but now it is a full-fledged conduit for any and all
forms of information and commerce. Internet websites now provide
personal, educational, political and economic resources to every corner
of the planet.
Intranet
With the advancements made in browser-based software for the Internet,
many private organizations are implementing intranets. An intranet is a
private network utilizing Internet-type tools, but available only
within that organization. For large organizations, an intranet provides
an easy access mode to corporate information for employees.
Ethernet
Ethernet is the most popular physical layer LAN technology in use
today. Other LAN types include Token Ring, Fast Ethernet, Fiber
Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM) and
LocalTalk. Ethernet is popular because it strikes a good balance
between speed, cost and ease of installation.
These benefits, combined with wide acceptance in the computer
marketplace and the ability to support virtually all popular network
protocols, make Ethernet an ideal networking technology for most
computer users today.
The Institute for Electrical and Electronic Engineers (IEEE) defines
the Ethernet standard as IEEE Standard 802.3. This standard defines
rules for configuring an Ethernet network as well as specifying how
elements in an Ethernet network interact with one another. By adhering
to the IEEE standard, network equipment and network protocols can
communicate efficiently.
Fast Ethernet
For Ethernet networks that need higher transmission speeds, the Fast
Ethernet standard (IEEE 802.3u) has been established.
This standard raises the Ethernet speed limit from 10 Megabits per
second (Mbps) to 100 Mbps with only minimal changes to the existing
cable structure. There are three types of Fast Ethernet: 100BASE-TX for
use with level 5 UTP cable, 100BASE-FX for use with fiber-optic cable,
and 100BASE-T4 which utilizes an extra two wires for use with level 3
UTP cable.
The 100BASE-TX standard has become the most popular due to its close
compatibility with the 10BASE-T Ethernet standard. For the network
manager, the incorporation of Fast Ethernet into an existing
configuration presents a host of decisions.
Managers must determine the number of users in each site on the network
that need the higher throughput, decide which segments of the backbone
need to be reconfigured specifically for 100BASE-T and then choose the
necessary hardware to connect the 100BASE-T segments with existing
10BASE-T segments. Gigabit Ethernet is a future technology that
promises a migration path beyond Fast Ethernet so the next generation
of networks will support even higher data transfer speeds.
Token Ring
Token Ring is another form of network configuration which differs from
Ethernet in that all messages are transferred in a unidirectional
manner along the ring at all times. Data is transmitted in tokens,
which are passed along the ring and viewed by each device.
When a device sees a message addressed to it, that device copies the
message and then marks that message as being read. As the message makes
its way along the ring, it eventually gets back to the sender who now
notes that the message was received by the intended device. The sender
can then remove the message and free that token for use by others.
Various PC vendors have been proponents of Token Ring networks at
different times and thus these types of networks have been implemented
in many organizations.
Protocols
Network protocols are standards that allow computers to communicate. A
protocol defines how computers identify one another on a network, the
form that the data should take in transit, and how this information is
processed once it reaches its final destination.
Protocols also define procedures for handling lost or damaged
transmissions or "packets." TCP/IP (for UNIX, Windows NT, Windows 95
and other platforms), IPX (for Novell NetWare), DECnet (for networking
Digital Equipment Corp. computers), AppleTalk (for Macintosh
computers), and NetBIOS/NetBEUI (for LAN Manager and Windows NT
networks) are the main types of network protocols in use today.
Although each network protocol is different, they all share the same
physical cabling. This common method of accessing the physical network
allows multiple protocols to peacefully coexist over the network media,
and allows the builder of a network to use common hardware for a
variety of protocols.
This concept is known as "protocol independence," which means that
devices that are compatible at the physical and data link layers allow
the user to run many different protocols over the same medium.
Media
An important part of designing and installing an Ethernet is selecting
the appropriate Ethernet medium. There are four major types of media in
use today: Thickwire for 10BASE5 networks, thin coax for 10BASE2
networks, unshielded twisted pair (UTP) for 10BASE-T networks and fiber
optic for 10BASE-FL or Fiber-Optic Inter-Repeater Link (FOIRL)
networks.
This wide variety of media reflects the evolution of Ethernet and also
points to the technology's flexibility. Thickwire was one of the first
cabling systems used in Ethernet but was expensive and difficult to
use. This evolved to thin coax, which is easier to work with and less
expensive.
The most popular wiring schemes are 10BASE-T and 100BASE-TX, which use
unshielded twisted pair (UTP) cable. This is similar to telephone cable
and comes in a variety of grades, with each higher grade offering
better performance.
Level 5 cable is the highest, most expensive grade, offering support
for transmission rates of up to 100 Mbps. Level 4 and level 3 cable are
less expensive, but cannot support the same data throughput speeds;
level 4 cable can support speeds of up to 20 Mbps; level 3 up to 16
Mbps.
The 100BASE-T4 standard allows for support of 100 Mbps Ethernet over
level 3 cable, but at the expense of adding another pair of wires (4
pair instead of the 2 pair used for 10BASE-T); for most users, this is
an awkward scheme and therefore 100BASE-T4 has seen little popularity.
Level 2 and level 1 cables are not used in the design of 10BASE-T
networks.
For specialized applications, fiber-optic, or 10BASE-FL, Ethernet
segments are popular. Fiber-optic cable is more expensive, but it is
invaluable for situations where electronic emissions and environmental
hazards are a concern.
Fiber-optic cable is often used in interbuilding applications to
insulate networking equipment from electrical damage caused by
lightning. Because it does not conduct electricity, fiber-optic cable
can also be useful in areas where large amounts of electromagnetic
interference are present, such as on a factory floor.
The Ethernet standard allows for fiber-optic cable segments up to 2
kilometers long, making fiber optic Ethernet perfect for connecting
nodes and buildings that are otherwise not reachable with copper media.
Topologies
A network topology is the geometric arrangement of nodes and cable
links in a LAN, and is used in two general configurations: bus and
star. These two topologies define how nodes are connected to one
another. A node is an active device connected to the network, such as a
computer or a printer. A node can also be a piece of networking
equipment such as a hub, switch or a router.
A bus topology consists of nodes linked together in a series with each
node connected to a long cable or bus. Many nodes can tap into the bus
and begin communication with all other nodes on that cable segment. A
break anywhere in the cable will usually cause the entire segment to be
inoperable until the break is repaired. Examples of bus topology
include 10BASE2 and 10BASE5.
10BASE-T Ethernet and Fast Ethernet use a star topology, in which
access is controlled by a central computer. Generally a computer is
located at one end of the segment, and the other end is terminated in
central location with a hub. Because UTP is often run in conjunction
with telephone cabling, this central location can be a telephone closet
or other area where it is convenient to connect the UTP segment to a
backbone.
The primary advantage of this type of network is reliability, for if
one of these 'point-to-point' segments has a break, it will only affect
the two nodes on that link. Other computer users on the network
continue to operate as if that segment were nonexistent.
Collisions
Ethernet is a shared media, so there are rules for sending packets of
data to avoid conflicts and protect data integrity. Nodes determine
when the network is available for sending packets. It is possible that
two nodes at different locations attempt to send data at the same time.
When both PCs are transferring a packet to the network at the same
time, a collision will result.
Minimizing collisions is a crucial element in the design and operation
of networks. Increased collisions are often the result of too many
users on the network, which results in a lot of contention for network
bandwidth.
This can slow the performance of the network from the user's point of
view. Segmenting the network, where a network is divided into different
pieces joined together logically with a bridge or switch, is one way of
reducing an overcrowded network.
Ethernet Products
The standards and technology that have just been discussed help define
the specific products that network managers use to build Ethernet
networks. The following text discusses the key products needed to build
an Ethernet LAN.
Transceivers
Transceivers are used to connect nodes to the various Ethernet media.
Most computers and network interface cards contain a built-in 10BASE-T
or 10BASE2 transceiver, allowing them to be connected directly to
Ethernet without requiring an external transceiver. Many Ethernet
devices provide an AUI connector to allow the user to connect to any
media type via an external transceiver.
The AUI connector consists of a 15-pin D-shell type connector, female
on the computer side, male on the transceiver side. Thickwire (10BASE5)
cables also use transceivers to allow connections.
For Fast Ethernet networks, a new interface called the MII (Media
Independent Interface) was developed to offer a flexible way to support
100 Mbps connections. The MII is a popular way to connect 100BASE-FX
links to copper-based Fast Ethernet devices.
Network Type
Max Nodes Per Segment
Max Distance Per Segment
10BASE-T
10BASE2
10BASE5
10BASE-FL
2
30
100
2
100m
185m
500m
2000m
All About Cabling
The two most popular types of network cabling are twisted-pair (also
known as 10BaseT) and thin coax (also known as 10Base2). 10BaseT
cabling looks like ordinary telephone wire, except that it has 8 wires
inside instead of 4. Thin coax looks like the copper coaxial cabling
that's often used to connect a VCR to a TV set.
10BaseT Cabling
When 10BaseT cabling is used, a strand of cabling is inserted between
each computer and a hub. If you have 5 computers, you'll need 5 cables.
Each cable cannot exceed 325 feet in length. Because the cables from
all of the PCs converge at a common point, a 10BaseT network forms a
star configuration, or geometric design, when viewed from above. In the
figure below, three computers are connected together with 10BaseT
cabling and a hub.
A 10BaseT hub is basically a box with a row of 10BaseT jacks. Most hubs
have 5, 8, 12, or 16 jacks, but some may have more. Most hubs also have
an uplink port, which is a special 10BaseT or thin coax port that
allows the hub to be connected to either (1) other hubs, or (2) a thin
coax backbone (see below for information on backbones). By uplinking
multiple hubs together, you can add additional computers to your
network whenever you need to.
10BaseT cabling is available in different grades or categories. Some
grades, or "cats", are required for Fast Ethernet networks, while
others are perfectly acceptable for standard 10Mbps networks--and less
expensive, too.
About 85% of the networks in the U.S. use standard unshielded
twisted-pair (UTP) Category 5 10BaseT cabling because it offers a
performance advantage over lower grades. If you are using a 10Mbps
network, category 3 is fine. If you plan on building a Fast Ethernet
network at some time in the future, it's best to install Category 5
cabling.
10BaseT
Category What It's Used For
5 Fast Ethernet (and everything below)
4 Networks other than Ethernet
3 10Mbps 10BaseT
2 Alarms, telephone voice lines
1 Unknown (not rated for anything specific)
If possible, decide whether you'll be using standard Ethernet or Fast
Ethernet technology before you begin building your network. If you're
not sure which technology you'll eventually use, choose to install
Category 5 cabling.
Remember, Fast Ethernet network adapters and hubs are not directly
compatible with each other. It is possible to have both 10Mbps and
100Mbps segments on the same network, provided you have a switching hub
between them that allows them to communicate.
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 95 and Windows for Workgroups 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 NT and NetWare 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). 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
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 & 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 below, 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.
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.
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.
BANDWIDTH
A capacity of the medium or channel. A range within a band of
frequencies or wavelengths.
The amount of data that can be transmitted in a fixed amount of time.
For digital devices, the bandwidth is usually expressed in bits per
second (bps) or bytes per second. For analog devices, the bandwidth is
expressed in cycles per second, or Hertz (Hz).
In computer networks, bandwidth is often used as a synonym for data
transfer rate. - the amount of data that can be carried from one point
to another in a given time period (usually a second). This kind of
bandwidth is usually expressed in bits (of data) per second (bps).
Occasionally, it's expressed as bytes per second (Bps). A modem that
works at 57,600 bps has twice the bandwidth of a modem that works at
28,800 bps. In general, a link with a high bandwidth is one that may be
able to carry enough information to sustain the succession of images in
a video presentation.
The bandwidth is particularly important for I/O devices. For example, a
fast disk drive can be hampered by a Bus with a low bandwidth. This is
the main reason that new buses, such as AGP, have been developed for
the PC..
In electronic communication, bandwidth is the width of the range (or
band) of frequencies that an electronic signal uses on a given
transmission medium. In this usage, bandwidth is expressed in terms of
the difference between the highest-frequency signal component and the
lowest-frequency signal component. Since the frequency of a signal is
measured in hertz (the number of cycles of change per second), a given
bandwidth is the difference in hertz between the highest frequency the
signal uses and the lowest frequency it uses. A typical voice signal
has a bandwidth of approximately three kilohertz (3 Khz); an analog
television (TV) broadcast video signal has a bandwidth of six megahertz
(6 MHz). Some 2,000 times as wide as the voice signal.