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Lesson 1 Introduction to Networking

At the end of Lesson 1, the student will be able to:



Define Networking Terminologies



Illustrate the difference between a LAN, MAN and a WAN.



Describe the topologies used in local area, wide area, and metropolitan area
ne
tworks.



Demonstrate proficiency in the use of networking terminology by providing
accurate definitions of terms and examples on how these terms apply in common
usage.


1.1

Definition of Terms


What is a Network?


A network consists of two or more computers tha
t are linked in order to share
resources (such as printers and CD
-
ROMs), exchange files, or allow electronic
communications. The computers on a network may be linked through cables, telephone
lines, radio waves, satellites, or infrared light beams.



Some
of components which are the constituents of a network are:



One or more servers



Workstation



Peripheral devices



Network board



Communication media



Network administrator


What is a Workstation?


Workstation is a client, more specifically it is a standalone co
mputer of the
network. It has its own software, data files and does its own processing to expand its
resources and knowledge, it m
ay get connected to a network.



A typical workstation is a computer that is configured with a network interface
card, networ
king software, and the appropriate cables. It does not necessarily need
floppy disk drives because files can be saved on the file server.



What is a Client?


It is a computer system that accesses a (remote) service on another computer by
some kind of net
work. The term was first applied to devices that were not capable of
running their own stand

alone programs, but could interact with remote computers via
a network. These dumb terminals were clients of the time
-
sharing mainframe computer.


What is a serve
r?


A server is a computer that performs a service for other computers on the
network.
W
hen using a standalone computer, the computer handles all processing
.

I
n a
network
,

the server may handle some processing.





Different types of Servers



File server



Pr
int server



Communication server



Disk Server



Non
-
dedicated Server


File Server


It is a program that provides to the user the disks or other mass storage devices
for storing and retrieving files as specified by the users. The program provides
protection fro
m unauthorized reading and writing.



File servers store the files that are created by the network users. They also store
applications such as word processing programs, spreadsheets etc. Users can access
parts of a file server’s hard disk which will appea
r as an extra drive on their own
computer. Applications can either be run from the file server, or they can be downloaded
to the user’s workstation.


Print Server


It is a combination of hardware and software package which allows anyone on
the network to h
ave access to printing services. The hardware includes an ordinary line
printer and the software receives and buffers a file of information, which may come from
a personal computer with its own disk.



When a file is printed, the file is sent to the print
server which assigns it to the
printer that has been requested by the user.


Communication Server


This server provides communications links external to the LAN
-

that is,
micro/mainframe links to other networks. To accomplish this service, the communicati
on
server controls one or more modems.


Disk Server


It primarily functions to achieve economy of scale by dividing a large disk into
sections to which individual users have to access.


Dedicated Server


A
computer without a human operator, whose only job
is to share data and
printers for others to use
,

is called a “dedicated server”.


Non
-
dedicated Server


A
computer that both runs standard programs and lets other users see its data at
the same time is said to be a “non
-
dedicated server”.




What is a Peri
pheral device?


They are computer related devices, such as local printers, disk drivers and
modems
.
Some of the most popular devices are listed below:




RAM
-

expands memory, usually in increments of 256KB or 1MB (1KB is roughly
1000 characters and 1mb is 1,
000,000 characters).




Modem
-

permits communication with remote computers via telephone link.




Serial port
-

Installation of this board provides access to the bus via another serial
port. It receives or sends information over a single wire.




Parallel port
-

s
ends or receives information over eight wires at a time and is very
fast.




Printer spooler
-

enables data to be printed while the user continues with other
processing activities. Data are transferred at a high speed from RAM to a print
buffer and then route
d to the printer from the buffer.




Accelerator



the accelerator board gives the user the flexibility to upgrade a
micro’s processor.


What is a Netwok Board?


A network board is a circuit board installed in each computer to allow servers and
workstation
to communicate with each other.


What is a Network interface Card?


The Network Interface Card (NIC) facilitates and controls the exchange of data
between the micros in a PC network (several micros linked together).

The NIC connects
information from the bu
sy microprocessor, stores it, and doles it out slowly onto the
network wires.



It 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.

The three most common network interface connections are Ethernet cards,
LocalTalk connectors, and Token Ring cards. According to an International Data
Corporation study, Ethernet is the most popular, followed by Token Ring and LocalTalk.


What is Communic
ation Media?


The communication media is basically the connection or link between different
devices of a network system which can allow communication to occur.

Ex. Coaxial cable, twisted pair for LAN, Satellite/microwave for WAN.





1.2

Strengths and Weakness
es of Networking



Strengths of networking:



Saving in host processing power



Independent stability of the client and server platforms



Code modularity through shared service as the process to code than can be
shared by multiple applications



The ability to us
e workstation, as well as user and development tools


Weaknesses of Networking



Performance overhead network cost



Complex information system management


man
a
ge concurrent access of data.


1.3

Advantages of Installing a Network




Speed
. Networks provide a very
r
apid method for sharing and transferring files.
Without a network, files are shared by copying them to floppy disks, then carrying
or sending the disks from one computer to another. This method of transferring
files (referred to as
sneaker
-
net
) is very tim
e consuming.




Cost
.

Networkable versions of many popular software programs are available at
considerable savings when compared to buying individually licensed copies.
Besides monetary savings, sharing a program on a network allows for easier
upgrading of t
he program. The changes have to be done only once, on the file
server, instead of on all the individual workstations.





Security
. Files and programs on a network can be designated as “copy inhibit”,
so that you do not have to worry about illegal copying of

programs. Also,
passwords can be established for specific directories tp restrict access to
authorized users.




Centralized Resource Management
.

All of the software can be loaded on one
computer (the file server). This eliminates that need to spend time an
d energy
installing updates and tracking files on independent computers throughout the
building.




Resource Sharing
-

most schools cannot afford enough laser printers, fax
machines, modems, scanners, and CD
-
ROM players for each computer.
However, if these or

similar peripherals are added to a networl, they can be
shared by many users.




Electronic Mail
.

The presence of a network provides the hardware necessary to
install an email system. E
-
mail aids in personal and professional communication
for all school per
sonnel, and it facilitates the dissemination of general information
to the entire school staff. Electronic mail on a LAN can enable students to
communicate with teachers and peers at their own school. if the LAN is
connected to the Internet, students can c
ommunicate with others throughout the
world.




Flexible Access
.

School networks allow students to access their files from
computers throughout the school. Students can begin an assignment in their
classroom, save part of it on a public access area of the ne
twork, and then go to
the media center after school to finish their work. Students can also work
cooperatively throughout the network.




Workgroup Computing
.

Workgroup software (such as Microsoft Back Office)
allows many users to work on a document or proje
ct concurrently. For example,
educators located at various schools within a county could simultaneously
contribute their ideas about new curriculum standards to the same document and
spreadsheets.


1.4

Disadvantages of installing a Network




Expensive to Insta
ll
-

although a network will generally save money over time,
the initial costs of installation can be prohibitive. Cables, network cards, and
software are expensive, and the installation may require the services of a
technician.




Requires Administrative Tim
e
-

proper maintenance of a network requires
considerable time and expertise. Many schools have installed a network, only to
find that they did not budget for necessary administrative support.




File Server May Fail
-

Although a file server is no more suscept
ible to failure than
any other computer, when the file server “goes down”, the entire network may
come to a halt. When this happens, the entire school may lose access to
necessary programs and files.




Cables May Break.

Network topology presents information

about the various
configurations of cables. Some of the configurations are designed to minimize
the inconvenience of a broken cable; with other configurations, one broken cable
can stop the entire network.


1.5

Network design



Computer networks also differ i
n their design.

The two types of high
-
level network
design are called
client
-
server

and
peer
-
to
-
peer
.



Client
-
server networks

feature centralized server computers that store email,
Web pages, files and or applications. Has at least one workstation which h
as configured
as a network server. The server is used as a computer running the network operating
system. The server controls the communication and shares the network resources. The
client workstations are the individual computer to the work.


The use of c
lient/server systems also offers key technological advantages.
Keeping data on the server can help enforce data security and business rules with
centralized and coordinated features such as:




Log
-
in control



Centralized backup



A single uninterruptable powe
r supply



Stored procedures that follow required company business rules


On the other hand;




Usually more than 10



Need server



Central administration



Need Admin



Complex to implement


In the Client
-
Server setup, client sometimes acts as server when it provid
es
service to the other unit in the network
.



On a
peer
-
to
-
peer network
, conversely, all computers tend to support the same
functions. Client
-
server networks are much more common in business and peer
-
to
-
peer
networks much more common in homes.

The simples
t of this kind of network has at
least two workstations connected together, each enabling them to use the resources of
the others. All
workstations on a peer
-

to
-

peer network are equal and no one is
designated as the main or host computer or centralized

point of control.



An exciting development for cost
-
conscious individuals has been the creation of
peer
-
to
-
peer networks. These networks are on one step above zero slot LANs, which
are system that forgo the use of network cards, and one step below a full

network.
These system are both less expensive to install and maintain than the full networks, but
do offer file
-
transfer and printer
-
sharing capabilities.




Usually less than ten in number



No central administration



Need no Admin



No security



Easy to implem
ent


1.6

Network System


What is a Network System?


It is a n
etwork
that
consists of two or more computers that are conne
cted
together, usually by cable and

running software, which allows them to communicate with
one
another,

share resources
,

and access remote

hosts or other network
. Users on a
network can share computer resources such as hard drives
, printers
, modems, CD
-
ROM, and Processors.

1.7

Types of Network


Local Area Network

(LAN)


A Local Area Network (LAN) is a network that is confined to a relatively sma
ll
area. It is generally limited to a geographic area such as a writing lab, school, or
building. Rarely are LAN computers more than a mile apart.



In typical LAN configuration, one computer is designated as the file server. It
stores all of the software

that controls the network, as well as the software that can be
shared by the computers attached to the network.



Computers connected to the file server are called workstations. The workstations
can be less powerful than the file server, and they may have

additional software on their
hard drives. On most LANs, cables are used to connect the network interface cards in
each computer.



It is a LAN w
hen the
computers
connected to a network are all close together,
such as in the same building or campus
.


Wide
area Network (WAN)


Wide area Networks (WANs) connect larger geographic areas, such as Florida,
the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may
be used to connect this type of network.


A WAN is complicated. It uses

multiplexers to connect local and metropolitan
networks to global co
mmunications networks like the I
nternet.

To users, however, a
WAN will not appear to be much different than a LAN or a MAN.


Other Types of Area Networks


While LAN and WAN are by far th
e most popular network types mentioned, you
may also commonly see references to those others:



Wireless Local Area Network (WLAN)
-

a LAN based on WiFi wireless network
technology.


Metropolitan Area Network (MAN)
-

a network spanning a physical area larger

than a LAN but smaller than a WAN, such as a city.
It i
s a connection of networks in the
same city.
A MAN is typically owned an operated by a single entity such as a
government body or large corporation.


Campus Area Network
-

a network spanning multiple L
ANs but smaller than a
MAN, such as on a university or local business campus.


Storage Area Network
-

c
onnects servers to data storage devices through a
technology
like Fibre Chann
el.


System Area Network
-
links high performance computers with high speed
con
nections in a cluster configuration. Also known as Cluster Area Network.




1.8

Network Topologies



Topology

refers to arrangement or physical layout of computer cables and other
components on the network. It can also be called the physical layout, diagram or

map of
the network.



The physical topology of a network refers to the configuration of cables,
computers, and other peripherals.



Physical topology should not be confused with logical topology which is the
method used to pass information between worksta
tions.



Main types of Physical Topologies



Linear Bus



Star



Ring



Tree



Mesh


Linear Bus











A linear bus c
onnects each computer to a single cable, usually a coaxial cable.
Data passes back and forth to cable until it reaches the receiving station
.

A
linear bus
topology consists of a main run of cable with a terminator at each end (See fig. 1). All
nodes (file server, workstations, and peripherals) are connected to the linear cable.
Ethernet and LocalTalk networks use a linear bus topology
.












Fig. 1
.1

Linear Bus Topoloogy

Advantages of a Linear Bus Topology



Easy to connect a computer or peripheral to a linear bus.



Requires less cable length than a star topology.


Disadvantages of a Linear Bus Topology



Entire network shuts down if there i
s a break in the main cable.



Terminators are required at both ends of the backbone cable.



Difficult to identify the problem if the entire network shuts down.



Not meant to be used as a stand
-
alone solution in a large building.


Star



A star topology i
s designed with each
node

(file server, workstations, and
peripherals) connected directly to a central network hub or
concentrator (See figure 2).
The hub or concentrator manages and controls all functions of the network. It also acts
as a repeater for the

data flow. This configuration is common with twisted pair cable;
however, it can also be used with coaxial cable or fiber optic cable.














Fig. 1.2 Star Topology



Each computer is connected by a hub. Signals from a computer passes through
the h
ub to all the computers on the network. It uses more cable and failure lies on hub.


Advantages of a Star Topology



Easy to install and wire.



No disruptions to the network then connecting or removing devices.



Easy to detect faults and to remove parts.


Disadvantages of a Star Topology



Requires more cable length than a linear topology.



If the hub or concentrator fails, nodes attached are disabled.



More expensive than linear bus topologies because of the cost of the
concentrators.



The protocols used w
ith star configurations are usually Ethernet or LocalTalk.
Token Ring uses a similar topology, called the star
-
wired ring.

Ring


In a ring network, every device has exactly two neighbors for communication
purposes.

All messages travel through a ring in th
e same direction (either "clockwise" or
"counterclockwise").

A failure in any cable or device breaks the loop and can take down
the entire network.












Fig. 1.3 Ring Topology

Tree


A tree topology combines characteristics of linear bus and star top
ologies. It
consists of groups of star
-
configured workstations connected to a linear bus backbone
cable

(See fig. 1.4)
.

Tree topologies allow for the expansion of an existing network, and
enable schools to configure a network to meet their needs.


Advantag
es



Point
-
to
-
point wiring for individual segments.



Supported by several hardware and software venders.

Disadvantages



Overall length of each segment is limited by the type of cabling used.



If the backbone line breaks, the entire segment goes down.



More
difficult to configure and wire than other topologies.

















Fig. 1.4 Tree Topology

Mesh


A Mesh topology consists of a network where every device on the network is
physically connected to every other device on the network.

This provides a grea
t deal of
performance and reliability, however the complexity and difficulty of creating one
increases geometrically as the number of nodes on the network increases.












Fig. 1.5 Mesh Topology


Star Ring Topology


It is sometimes called star
-
wired
ring and is similar to star bus centered in a hub,
which contain the actual ring. Star rings are connected in a star pattern by the main hub.


Considerations When Choosing a Topology:



Money
. A linear bus network may be the least expensive way to install a
network;
you do not have to purchase concentrators.



Length of cable needed
. The linear bus network uses shorter lengths of cable.



Future growth
. With a star topology, expanding a network is easily done by
adding another concentrator.



Cable type
. The mos
t common cable in schools is unshielded twisted pair, which
is most often used with star topologies.


Advantages



BUS


Less cable, Inexpensive
media and easy to install,
simple, reliable, easy
t
o extend,

less component requirement.



RING


Even computer ac
cess as well as performance even in
the presence of
many
users.



STAR


Centralized management and monitoring of network, easy addition and
modification of computer, independence of each other in case of breakdown.


Disadvantages



BUS



Heavy traffic can slo
w down the network, difficult to isolate problems,
break in cable will affect many users.



RING



Breakdown of a computer will affect the rest of the user in the network,
difficult to isolate problems, changes in network configurations will disrupt user
ope
ration.



STAR



When central hub fails, the rest of the network connection fails.

Best topology depends on the need and foreseeable growth of an organization.


1.9

Network Components



HUB
-

it is
a central component in a star
topology network that connects all

the
computers in the network. A hub is an
inexpensive way to

connect devices on a
network. The d
ata travels around a network in
'packets' and a hub forwards these data packets
out to all the devices connected to its ports.



New components are acting sim
ilarly and
better such as routers, bridges, repeaters, and
gateways.






Types of Hub



Active Hub


the usual type of hubs that regenerate and retransmit the signals in
the same way the repeater does.





Passive Hub


those hubs that act as connection points and do not amplify or
regenerate the signal as it just passes through the hub. Examples of these are,
wiring panels or punch
-
down blocks.












Hybrid Hub


special t
ype of hubs that can accommodate several different types
of cables. They are usually called stackable or cascadable hubs.


Hub & Topologies


There are many network topologies available:




Daisy Chain Hubs




Star
-

uses a hub



Tree
-

uses a hub



Bus
-

does

not use a hub



Ring
-

does not use a hub



Repeater


A device used to connect two segments of similar or dissimilar media and
regenerates a weakened signal to increase the distance it can travel.
It functions in the
physical layer of OSI model and passes
all traffic back and forth along the network.

It
doesn’t filter or restrict flow of problem traffic thus not advisable for network with heavy
traffic as well as for connection of segments that are using differen
t.




Network Switch


A switch is more sophi
sticated than a hub,
giving you more options for network management,
as well as greater potential to expand.





A switch filters the data packets, and only sends the packet to the port which is
connected to the destination address of that packet.

It does

this by keeping a table of
each destination address and its port. When the switch receives a packet, it reads the
destination address and then establishes a connection between the source port and the
destination port.

After the packet is sent, the connect
ion is terminated.




Switches also run in full duplex mode, which allows data to be sent and received
across the network at the same time. Switches can effectively double the speed of the
network when compared to a hub which only supports half duplex mod
e.


Packet


A packet consists of two kinds of data: control information and user data (also
known as
payload
). The control information provides data the network needs to deliver
the user data, for example: source and destination addresses, error detection
codes like
checksums, and sequencing information.



Typically, control information is found in packet headers and trailers, with user
data in between.


































Bridges



Having all the features of a repeater, it
can reduce ne
twork traffic bottlenecks by
splitting an overload network into two.

It can link
and expand distance of different network
segment and forward packets between them
even using different physical media. Bridges
caches source addresses as traffic passes on it
thus, it learns into which network segment a
data will be forwarded the next time.

Bridges are
not suited to WANs slower than 56K as it
passes all broadcast that could possibly create a
broadcast storm.















Fig. 1.8 Bridge

Routers


Better than br
idges, it interconnects networks and provides a filtering function to
determine the best route for a data to take thus limiting unnecessary network traffic.

It
can switch and route packet across multiple networks. It can however, works with
routable protoc
ols only.







Routers require specific network address only, not node addresses in its
communication to another routers and network adapter cards.

It also makes use of the
router
-
addressing scheme and does not pass or handle every packet thus, it cho
ose
among redundant path, eliminate bad data and greatly reduced network traffic.



















Fig. 1.9 Router


Types Routers:




Static Router

-
requires an administrator to manually set up and configure the
routing table and specify each route.




Dynam
ic Router
-
do an automatic discovery of routes and examines information
from other routers and made packet
-
by
-
packet decisions about how to send data
across the network.





















Static Router

Dynamic Router

Manual set up and configuration of all
routes

Manual configuration of the first route,
automatic discovery of additional networks
and routes

Always uses the same route which is
determined by a routing able entry

Can choose a
route based on factors such
as cost and amount of link traffic

The route used is hard coded and is not
necessarily the shortest route

Can decide to send packet over alternate
routes

Static routers are considered more secure
because he administrator speci
fies each
route

Security can be improved in dynamic router
by manually configuring the router to filter
out network addresses discovered and
prevent traffic from going there