Download Server-Based Networks

A network consist of two computers or more that connected
“linked” together in order and they can share resources (
e.g. data, printers or CD-ROMs), exchange files, and allow
electronic communication. Networking arose from the need
to share data in a timely fashion. The computers on the
network may be connect through cables, telephone lines,
radio waves, satellites, or infrared light beams. We know
that the personal computer is wonderful to produce Data,
Spreadsheet, Graphics and other kinds of information. From
that we can define network as a group of computers that
connected together to sharing data.
Computers connect to each other via cable
to share resources
1.Data.
2.E-mail, messages,scheduling
3.Graphics.
4.Printers.
5.Fax machines.
6.Modems.
7.Applications.
8.Other hardware resources.
The benefits of networks:1-File and programs sharing.
2-Resources sharing such as printer.
3-sharing data messages, printers…etc
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***Types of networks***
There are basically two types of network:local-area network "LAN" and wide-area network "WAN" , the main
difference between the two is the way in which they are geographically
distributed.
 Local-area networks (LAN): LAN are usually designed to cover a small geographical area (such as
a single building or afew adjacent buildings) and are generally used in an
office environment.
 Wide-area network (WAN):
WAN ara usually distrbuted over a large geographical
area (such as the United States).
Classification of networks by Scale :
Distance
1m
example
Multicomputer
10 - 1km
Local Area
Network (LAN)
Wan
100km
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***Network design***
Data Networking :
Transmission technology:• Broadcast
• Point to point
Broadcast :
 Single channel shared by all the machines
 Messages (packets) sent by one machine is
seen by all
 Broadcasting messages is simple
Point-to-point :
 Also called store and forward or
packet switched subnet.
 Impractical (costly) for all communication
devices to be point-to-point connected.
 Devices are typically connected to a
communications network .
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Example of Point-to-Point Subnet Topologies
Transmission Mode:Transmission Mode Defines the direction of the signal
between linked devices.
• Half duplex - Can transmit or receive, but not at the same
time.
• Full duplex - Each can transmit or receive simultaneously.
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*There are two kinds of topology physical and logical :The physical topology of a network refers to the configuration of
cables, computers, and other peripherals.
The logical topology is the method that used to pass the information.
Main types of physical topologies :The following parts are discussing the physical topologies
used in network and other related topics:o Star brunch from hub.
o Ring or loop.
o Bus or row. Linear bus.
o Tree .
1-Star networks:A network with radial topology in which a central
the point to which all other nodes join. "control" node is
And we can say from this topology as the following, cable
segments to a centralized component connect computers is
called a hub.
Signals are transmitted from the sending computer through
the hub to all computers on the network. In the previously the
computers are connected with mainframe computer as alternative
the hub.
The star network offers centralized resources and
management. However, because each computer is connected to a
central point, this topology requires a great deal of cable in a
large network installation. Also, if the central point fails, the
entire network goes down.
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Star
Topology
If one computer, or the cable that connects it to the hub, fails
on a star network,only failed computer will not be able to send
or receive network data. The rest of the network continues
to function normally.
We can summarization advantages and disadvantage as
following for this topology.

Advantages of a star topology:• Easy to install and wire.
• No disruptions to the network 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.
2-Ring networks:Ring architecture connects each node in a closed loop, Signals
ravel from one node to the next in a single direction around the
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loop. The server in a ring is just one of several
nodes.
Advantages of a ring topology:• It is more scalable because the point-to-point links between
nodes dose not limit the number of nodes in the ring.
Point-to-point: - A direct link between two objects in a network.

Disadvantages of a ring topology:• A failure of any link between a node pair takes the bus down
and prevents communication by other nodes.
Ring
Topolpogy
*Linear Bus:Alinear bus topolgy consists of amain run of cable with a
terminator at each end.
all nodes have(fileserver,workstations,and peripherals)are
connected to the linear cable.
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Computer on the bus topology network
communication:by addresing data to aparticular computer and putting
that data on the cable in the form of electronic signal
To understand how computer communication on bus you
need to be familiar with three concepts:
 Sending the signal
 Signal bounce
 The terminator
Sending the signal:
Network data in the form of electronic signals is sent to
all of the computer on the network;however,the
information is accepted only by the computer whose
address matches the address encoded in the original
signal.only on computer at atime can send messages .
Because only one computer at atime can send data on
abus network,network performance is affected by the
number of computers attached to the bus,the more
computer there will be waiting to put data on the bus,and
the slower the network.
There is no standard measure for the imact of numbers of
computers on any given network.
The amount the network slows down is not solely related to
the number of computer on the network.
It depends on numerous factors including:
 Hardware capabilities of computer on the network.
 Number of times computer on the network transmit
data.
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 Type of applications begin run on the network.
 Types of cable used on the network.
 Distance between computers on the network.
The bus is apassive topology .computer on abus only
listen for data being sent on the network.there are not
responsible for moving data form one computer to the
next.
If one computer fails,it does not affect the rest of
network.in active toplogy.
Computer regenerate signals and move data along the
network.
signal bounce:-because the data,or electronic
signal,is sent to the entire network,it will travel from
one end of the cable to the other.
noise of the network communication.
Abreak in the cable will occur if the cable is physically cut
into tow pieces or if one end of the cable becomes
disconnected.in either case,one or more ends of the cable
will not have aterminateor,the signal will bounce,and all
network activity will stop.
this is referred to as the network being”down”.
Advantage of alinear bus topology: Easy to connect acomputer or peripheral to alinear bus.
 Requires less cable length than astar topology.
 The bus is simple,reiable in very small networks,easy
to use,and easy to understand.
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 The bus requires the least amount of cable to connect
the computers together and is therefore less expensive
than oyher cabling arrangment.
 It is easy to extend abus.
Disadvantages of alinear bus topology:
 Entire network shuts down if there is abreak in the
main cable.
 It difficult to troubleshoot the bus.
Tree topology:Atree topology combines characteristics of linear bus and
star topologies. It consists of groups of star- configured
workstation connected to a linear but backbone cable. Tree
topologies allow for the expansion of an existing network,
and enable schools to configure a network to meet their
needs.
Advantages of a tree toplogy: point-to point wiring for individual segments.
 Supported by several hardare and software venders.
disavantages of a tree topology: 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
topolgies.
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Parts of a Network: Servers: Provide shared resources to users
 Clients: Use the shared resources from servers
 Media: Device for connection
 Shared peripherals: Resources provided by servers
such as printers, modems
Wiring Concentrators, Hubs, and Switches :Wiring concentrators, hubs, and switches provide a
common physical connection point for computing devices.
Most hubs and all wiring concentrators and switches have
built-in signal repeating capability and thus perform signal
repair and retransmission.
In most cases, hubs, wiring concentrators, and switches are
proprietary, standalone hardware.
Occasionally, hub technology consists of hub cards and
software that work together in a standard computer.
Next figure shows one of common hardware-based
connection devices: a token-ring switch
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Hubs:One network component that is becoming standard
equipment in more and more networks is yhe hub.
Hub is the central component in astar topology.
Hub consideration:Hubs are versatile and offer several advantages over system
, In astandard linear bus topology ,abreak in the cable will
take the network down .with hubs,however,abreak in any of
the cables attached to the hub affect only the segment .
The rest of the network keeps functioning.
The benfits of hub-based topologyies include: Changing or expanding wiring as needed.simply plug
in another computer or another hub.
 Using different ports to accommodate avariety of
cabling types.
Modem : Modems convert digital (computer) signals to analog
(audio) signals, and vice versa, by modulating and
demodulating a carrier frequency. The most common
modems transmit and receive data across ordinary voicegrade telephone lines.
A transmitting modem converts (modulates) the encoded
data signal to an audible signal and transmits it. A modem
connected at the other end of the line listens to the audible
signal and converts it back into a digital signal
(demodulates it) for the computer on the receiving end of
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the communication link. Modems are commonly used for
inexpensive, intermittent communications between
geographically isolated computers and a main network.
Microwave Transmitters : -
Microwave transmitters and receivers, especially satellite
systems, are commonly used to transmit network signals
over great distances. A microwave transmitter uses the
atmosphere or outer space as the transmission medium to
send the signal to a microwave receiver. The microwave
receiver either relays the signal to another microwave
transmitter, which sends it to another microwave
receiver, or the receiving station translates the signal to
some other form, such as digital impulses,
and sends it along on some other suitable medium. Figure 4
shows a satellite microwave link.
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Internetworking Devices: Bridges and Routers
Bridges and routers are the devices used to interconnect
subnetworks. They can be either hardware or software
based. Software-based routers and bridges can be part of a
server's operating system or can at least run in the server
with the operating system. Hardware-based bridges and
routers can also be installed on standard computers to create
dedicated, standalone devices.
To understand internetworking, it is not essential that you
understand all the technical differences between a bridge
and router. In fact, without some study, this can be a
confusing area. For example, if you read about
multiprotocol Routers, you will find that these routers also
perform what is called source-route bridging.
However, without a basic understanding of bridging and
routing technology, you will find it difficult to understand
the capabilities of some products and the reasons such
capabilities are useful or important. Keep in mind that
bridges and routers have one important thing in
common: They both allow the transfer of data packets
(frames) between subnetworks with different network
addresses.
Bridges:A bridge operates at the data-link layer (layer two) of the
OSI model. A bridge acts as an
address filter; it relays data between subnetworks (with
different addresses) based on
information contained at the media access control level.
Simple bridges are used to connect networks that use the
same physical-layer protocol and the
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same MAC and logical link protocols (OSI layers one and
two). Simple bridges are not capable of translating between
different protocols.
Other types of bridges, such as translational bridges, can
connect networks that use different layer-one and MAClevel protocols; they are capable of translating, then
relaying, frames.
After a physical connection is made (at OSI layer one), a
bridge receives all frames from each of the subnetworks it
connects and checks the network address of each received
frame. The network address is contained in the MAC
header. When a bridge receives a frame from one
subnetwork that is addressed to a workstation on another
subnetwork, it passes the frame to the intended subnetwork.
Routers
Routers function at the network layer of the OSI model (one
layer above bridges). To communicate, routers must use the
same network-layer protocol. And, of course, the sending
and receiving workstations on different networks must
either share identical protocols at all OSI layers above layer
three, or there must be necessary protocol translation at
these layers.
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Like some bridges, routers can allow the transfer of data
between networks that use different protocols at OSI layers
one and two (the physical layer and the data-link layer,
which includes sublayers for media access control and
logical link control). Routers can receive, reformat, and
retransmit data packets assembled by different layer-one
and layer-two protocols. Different routers are built to
manage different protocol sets. Figure 11 illustrates how a
router transfers data packets.
Types of local area network(lAN)
 Peer-to-Peer Networks; Also Called Workgroups
1. Each computer acts as both a client and server
and is located in small area.
2. No dedicated or central server: no hierarchy
3. Each user determines the data to be shared
and is also responsible for the security of the
data.
4. Involves small groups, usually fewer than ten
computers
5. Peer-to-peer networking is built into operating
systems such as Microsoft Windows 3.11 (WFW),
Microsoft Windows 95, and Microsoft Windows
NT Workstation; no additional software is needed.

When to Use Peer-to-Peer Networks
 Ten or fewer users
 Limited growth expected for network
 Users clustered in same area
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 Security is not important
 Users can act as administrators and plan their
own security

Potential Limitations of Peer-to-Peer
Networks:1. Each user acts as his or her own administrator.
2. Users share their resources (printers, fax cards,
and so on) as they want.
3. Users must be knowledgeable in network
management (managing users and security,
making resources available, maintaining
applications and data, installing and upgrading
application software).
4. Requires CPU time to maintain the server
function
5. Limited to resource password security
6. Each resource has its own password.
7. Very little control over peer-to-peer networks.

1.
2.
3.
4.
Server-Based Networks
Dedicated server(s)
More servers can be added when necessary.
Users are grouped logically.
Servers can be specialized.
 Why server-based networking?
1.Centrally administered and controlled.
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2.Provides access to network resources without
compromising performace.
3.Security:Access to network resources can be limited to
specific users.
4.Backup and redundancy:All data backed up to one
location.
5.Data can be duplicated(fault tolerant)more users,larger
network.
Comparing peer-to-peer and server-based
networks:1. Multiple operating systems
can used
2.Peer-to-peer processor: Should
be at least a 486 33 or supported
RISC processor.
3.Hard disk requirements: Vary
with system; one GB or more is
recommended.
4.Multiple hard drives for super
servers.
Network Adapters :
A network adapter is the hardware installed in computers
that enables them to communicate on a network. Network
adapters are manufactured in a variety of forms. The most
common form is the printed circuit board, which is
designed to be installed directly into a standard
expansion slot inside a microcomputer. Other network
adapters are designed for mobile computing. They are small
and lightweight and can be connected to standard
connectors on the back of notebook computers so that the
computer and network adapter can be easily
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transported from network to network. Network adapters are
now being built into many computers, especially notebook
computers.
Network adapters are manufactured for connection to
virtually any type of guided medium, including twisted-pair
wire, coaxial cable, and fiber-optic cable. They are also
manufactured for connection to devices that transmit and
receive visible light, infrared light, and radio microwaves,
to enable wireless networking across the unguided media of
Earth's atmosphere and outer space.
The hardware used to make connections between network
adapters and different transmission media depends on the
type of medium used. For example, twist-on BNC
connectors are commonly used for connection to coaxial
cable, while snap-in telephone-type jacks are
ordinarily used for connection to twisted-pair wiring. The
figure below shows two different types of network adapters
connected to different computers and media, using different
types of connectors.
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Network cabling
Cable can be recovered in plastic rubber, be careful to get
the correct type of cable for the type of network card used.
1.





Primary cable types:Coaxial
Twisted pair
Shielded
Unsheilded
Fiber optic
 Twisted pair
The least_expansive and most widely_used guided
transmition medium is twisted pair.
cable
show
ing
vario
us
layer
s
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Physical description
A twisted pair consists of two insulated copper wires arranged
in a regular spiral pattern. wire pair acts as a single communication
link.
Typically,anumber of these pairs are bundled together into a
cable by wrapping them in a tought protictive sheath.
Cable may contain hundred of pairs .
The twisting tends to decrease the crosstalk interfrence between
adjacent pairs in acable .that links in the long _distance,the twist
length typically varies from two to six inches in apair have
thicknesses of from 0.016 to 0.036 inches.
Applications
That used in the telephone network as well as being the
workhorse for communication within building,for local area
network supporting personal computer.
Tisted pair is much less expensive than the other commonly used
guided transmission media(coaxial cable,optical fiber)and is easier
to work .it is more limited in terms of data rate and distance.
Transmittion characteristics
Twisted pair may be used to transmit both analog and
digital signals,for analog signal,amplifiers are required
about every 5 to 6 km,for digtal signal ,repeter are
required every 2 or 3 km.twisted pair is limited in distance.
The attenution for twisted is a very strong function of
fequency .
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Unshilded and shildeed twisted pair
Twisted pair comes in two varities:unshilded and shilded.
Unshilded twisted pair(utp)is ordinary telephone wire.office
buildings,by universal practice,this occur noise and
attenution also,this is the least expensive of all the
transmitiom media commonly used for local area networks
and asimple to insulate.
UTP
Unshielded twistedpair and shielded
twisted-pair cables
STP
Shielding
Recognises three categories of utp cabling:
 Category 3.utp cables and associated connecting
hardware whose transmition characteristics are specified
up to 16 MHZ.
 Category 4.utp cables and associated connecting
hardware whose transmition chracteristics are specified
up to 20MHZ.
 Category 5.utp cables ans associated connecting
hardware whose transmition charactrisics are specified
up to 100 MHZ.
The difference between category 3 and
category 5:The difference between category 3 and category 5 cable is the
number of twists in the cable per unit distance,category 5 is much
more tightly twisted typically 3 to 4 twists per inch,compared to 3
to 4 twists per foot for category 3,
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The tighter twisting is more expensive but provides much better
performance than category 3.
Coaxial cable
Physical description
Coaxial cable,like twisted pair ,consists of two conductors,it
consists of ahellow outer cylinderical conductor that surrounds
asingle inner wire conductor.
The inner conductor is held in place by either regularly spaced
insulating rings or a solid dielectric material.
The outer conductor is coverd with ajacet or shiled.
Coaxial cable has adiamter of from 0.4 to 1 inch.
Applications:Coaxial cable is perhaps the most veratile transmition medium
and is enjoying widespred use in a wide varietly of applications;
 Television distrbution
 Long_distance telephone transmition
 Short_run computer system links
 Local area networks
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Transmition chractristics
Coaxial cable is used to transmit both analog and digital
signals.
For long_distance transmition of analog signals,amplifirs
are needed every kelometers.
Outshield
Insulation (PVC,Teflon)
Coaxial cable showing various layersxial
Copper wire mesh or
aluminum sleeve
Conducting core
Optical fiber
*Physical description
An optical fiber is a thin(2 to 125 Mm).





Greater capacity
Smaller size and higter weight.
Lower attenution.
Electomagnatic isolation
Greater repeter spacing.
*Transmitiom chractrisics
Optical fiber system operate in the range of about 10^14 to
10^15 HZ.
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**Considerations when choosing a topology**
• Money. A linear bus network may be the least expensive way to
install 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, adding another concentrator
easily dose expanding a network.
• Cable type. The most common cable in schools is unshielded
twisted pair, which is most often used with star topologies.
SELECTING A TOPLOGY:There are many factors to consider when determining what
toplogy best suits the needs of an organization. The following
table provies some guidelines for selecting a topology.
Toplogy Advantages
Bus
Economical use of cable.
Media is inexpensive and
easy to work with simple,
reliable.
Easy to extend.
Ring
Equal access for all Computers.
Even Performance despite
many users.
Star
Easy to modify and add
New compters.
Disadvantages
Netwok can slow
Down in heavy traffic.
Problems are difficult
to isolate.
Cable break can affect
many users.
Failure one one
comupter can impact
the rest of the network.
Problems bard to
isolate.
Network
Reconfiguration
Disrupts operation.
If the centralized point
fails, the network fails
.
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