Computer networks--introduction computer-networking

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Varna Free University “Chernorizec Hrabar”
-------------------------------------------------------------------------
Institute of Technology
Introduction to
Computer Networking
Prof. Teodora Bakardjieva

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1.0 Introduction
The purpose of the networking guidelines are as follows:
 to assist students in understanding the benefits of networking
 to help students place in context their current stage of networking
development in their school.
 to assist students in planning the next stage of network development
in their school.
 to provide standard networking ‘models’ and best practice to students
that will assist students in their network planning.
This document includes information under the following main headings:
 Introduction to Networking
 Advantages of Networking
 Types of Networks
 Models of networking appropriate to students
 NCTE recommendation to students
 Some relevant terms.
1.1. Basic of Networking
A computer network consists of a collection of computers, printers and other
equipment that is connected together so that they can communicate with
each other. Fig 1 gives an example of a network in a school comprising of a
local area network or LAN connecting computers with each other, the
internet, and various servers.

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Fig 1: Representation of Network in a school.
Broadly speaking, there are two types of network configuration, peer-to-peer
networks and client/server networks.
Peer-to-peer networks are more commonly implemented where less then
ten computers are involved and where strict security is not necessary. All
computers have the same status, hence the term 'peer', and they
communicate with each other on an equal footing. Files, such as word
processing or spreadsheet documents, can be shared across the network and
all the computers on the network can share devices, such as printers or
scanners, which are connected to any one computer.
Fig 2: Peer to Peer Networking
Client/server networks are more suitable for larger networks. A central
computer, or 'server', acts as the storage location for files and applications
shared on the network. Usually the server is a higher than average
File and Print Server
CD or Multimedia
Servers
Other users,
computers
Users
computers
Cache, Proxy,
Filtering, Firewall
Server
Access to:
Internet content &
learning resources,
Scoilnet etc
Email communication
Modem or Router
School ‘Local Area
Network’ (LAN)
Peer to Peer
Network

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performance computer. The server also controls the network access of the
other computers which are referred to as the 'client' computers. Typically,
teachers and students in a school will use the client computers for their work
and only the network administrator (usually a designated staff member) will
have access rights to the server.
Fig 3: Client - Server Networking
Table 1 provides a summary comparison between Peer-to-Peer and
Client/Server Networks.
Peer-to-Peer Networks vs Client/Server Networks
Peer-to-Peer Networks Client/Server Networks
 Easy to set up  More difficult to set up
 Less expensive to install  More expensive to install
 Can be implemented on a wide
range of operating systems
 A variety of operating systems can
be supported on the client computers,
but the server needs to run an
operating system that supports
networking
 More time consuming to
maintain the software being used
 Less time consuming to maintain
the software being used (as most of
Other
equipment
File Server

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(as computers must be managed
individually)
the maintenance is managed from the
server) 
 Very low levels of security
supported or none at all. These
can be very cumbersome to set
up, depending on the operating
system being used
 High levels of security are
supported, all of which are controlled
from the server. Such measures
prevent the deletion of essential
system files or the changing of
settings
 Ideal for networks with less
than 10 computers
 No limit to the number of
computers that can be supported by
the network
 Does not require a server
 Requires a server running a server
operating system
 Demands a moderate level of
skill to administer the network
 Demands that the network
administrator has a high level of IT
skills with a good working knowledge
of a server operating system
Table 1: Peer-to-Peer Networks vs Client/Server Networks
Components of a Network
A computer network comprises the following components:
 A minimum of at least 2 computers
 Cables that connect the computers to each other, although wireless
communication is becoming more common (see Advice Sheet 20 for
more information)
 A network interface device on each computer (this is called a network
interface card or NIC)
 A ‘Switch’ used to switch the data from one point to another. Hubs
are outdated and are little used for new installations.
 Network operating system software
Structured Cabling
The two most popular types of structured 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 Video Recorder to a TV.

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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.
Fig 4a shows a Cat5e cable, with a standard connector, known as an RJ-45
connector.
Fig 4b shows a standard Cat5e Wall Outlet socket which the cables are
connected to.
Fig 4c shows a standard Cat5e Patch Panel Wall Outlet socket which is used
to terminate the cables from various points in the school bank to a central
point.
Fig 4d shows a wall mounted cabinet used to house and protect patch panel
cables and connectors.
Fig 4a: Cat5e Cable and a close up of RJ-45 connector
Fig 4b: Cat5e Wall Outlets
Fig 4c: Cat5e Patch Panel

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Fig4d: Wall Mounted Cabinet
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. All new
networks use a minimum of standard unshielded twisted-pair (UTP)
Category 5e 10BaseT cabling because it offers a performance advantage
over lower grades.
Network Interface Card (NIC)
A NIC (pronounced 'nick') is also known as a network card. It connects the
computer to the cabling, which in turn links all of the computers on the
network together. Each computer on a network must have a network card.
Most modern network cards are 10/100 NICs and can operate at either
10Mbps or 100Mbps.
Only NICs supporting a minimum of 100Mbps should be used in new
installations students.
Computers with a wireless connection to a network also use a network card
(see Advice Sheet 20 for more information on wireless networking).
Fig 5: Network Interface Cards (NICs)
Hub and Switch
A hub is a device used to connect a PC to the network. The function of a hub
is to direct information around the network, facilitating communication
between all connected devices. However in new installations switches

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should be used instead of hubs as they are more effective and provide better
performance. A switch, which is often termed a 'smart hub'.
Switches and hubs are technologies or ‘boxes’ to which computers, printers,
and other networking devices are connected. Switches are the more recent
technology and the accepted way of building today's networks. With
switching, each connection gets "dedicated bandwidth" and can operate at
full speed. In contrast, a hub shares bandwidth across multiple connections
such that activity from one PC or server can slow down the effective speed
of other connections on the hub.
Now more affordable than ever, Dual-speed 10/100 autosensing switches are
recommended for all school networks. Students may want to consider
upgrading any hub based networks with switches to improve network
performance – ie speed of data on the network.
Fig 6a: An 8 port Hub
Fig 6b: 2 Examples of 24 port Switches
Wireless Networks
The term 'wireless network' refers to two or more computers communicating
using standard network rules or protocols, but without the use of cabling to
connect the computers together. Instead, the computers use wireless radio
signals to send information from one to the other. A wireless local area

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network (WLAN) consists of two key components: an access point (also
called a base station) and a wireless card. Information can be transmitted
between these two components as long as they are fairly close together (up
to 100 metres indoors or 350 metres outdoors).
Fig 7a: Wireless Access point or Wireless Basestation
Suppliers would need to visit the students and conduct a site survey. This
will determine the number of base stations you need and the best place(s) to
locate them. A site survey will also enable each supplier to provide you with
a detailed quote. It is important to contact a number of different suppliers as
prices, equipment and opinions may vary. When the term 'wireless network'
is used today, it usually refers to a wireless local area network or WLAN. A
WLAN can be installed as the sole network in a school or building.
However, it can also be used to extend an existing wired network to areas
where wiring would be too difficult or too expensive to implement, or to
areas located away from the main network or main building. Wireless
networks can be configured to provide the same network functionality as
wired networks, ranging from simple peer-to-peer configurations to large-
scale networks accommodating hundreds of users.
Fig 7b: Desktop PC Wireless LAN card Fig 7c: Laptop PC
Wireless LAN card
What are the advantages and disadvantages of a Wireless LAN?
Wireless LANs have advantages and disadvantages when compared with
wired LANs. A wireless LAN will make it simple to add or move

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workstations, and to install access points to provide connectivity in areas
where it is difficult to lay cable. Temporary or semi-permanent buildings
that are in range of an access point can be wirelessly connected to a LAN to
give these buildings connectivity. Where computer labs are used in students,
the computers (laptops) could be put on a mobile cart and wheeled from
classroom to classroom, providing they are in range of access points. Wired
network points would be needed for each of the access points.
A WLAN has some specific advantages:
 It is easier to add or move workstations
 It is easier to provide connectivity in areas where it is difficult to lay
cable
 Installation can be fast and easy and can eliminate the need to pull
cable through walls and ceilings
 Access to the network can be from anywhere in the school within
range of an access point
 Portable or semi-permanent buildings can be connected using a
wireless LAN
 Where laptops are used, the ‘computer suite’ can be moved from
classroom to classroom on mobile carts
 While the initial investment required for wireless LAN hardware can
be similar to the cost of wired LAN hardware, installation expenses
can be significantly lower
 Where a school is located on more than one site (such as on two sides
of a road), it is possible with directional antennae, to avoid digging
trenches under roads to connect the sites
 In historic buildings where traditional cabling would compromise the
façade, a wireless LAN can avoid drilling holes in walls
 Long-term cost benefits can be found in dynamic environments
requiring frequent moves and changes
 They allows the possibility of individual pupil allocation of wireless
devices that move around the school with the pupil.
WLANs also have some disadvantages:
 As the number of computers using the network increases, the data
transfer rate to each computer will decrease accordingly
 As standards change, it may be necessary to replace wireless cards
and/or access points

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 Lower wireless bandwidth means some applications such as video
streaming will be more effective on a wired LAN
 Security is more difficult to guarantee, and requires configuration
 Devices will only operate at a limited distance from an access point,
with the distance determined by the standard used and buildings and
other obstacles between the access point and the user
 A wired LAN is most likely to be required to provide a backbone to
the wireless LAN; a wireless LAN should be a supplement to a wired
LAN and not a complete solution
 Long-term cost benefits are harder to achieve in static environments
that require few moves and changes
 It is easier to make a wired network ‘future proof’ for high data
transfer.
Wireless Network Components
There are certain parallels between the equipment used to build a WLAN
and that used in a traditional wired LAN. Both networks require network
interface cards or network adapter cards. A wireless LAN PC card, which
contains an in-built antenna, is used to connect notebook computers to a
wireless network. Usually, this is inserted into the relevant slot in the side of
the notebook, but some may be internal to the notebook. Desktop computers
can also connect to a wireless network if a wireless network card is inserted
into one of its internal PCI slots.
In a wireless network, an 'access point' has a similar function to the hub in
wired networks. It broadcasts and receives signals to and from the
surrounding computers via their adapter card. It is also the point where a
wireless network can be connected into an existing wired network.
The most obvious difference between wireless and wired networks,
however, is that the latter uses some form of cable to connect computers
together. A wireless network does not need cable to form a physical
connection between computers.
Wireless Network Configurations
Wireless networks can be configured in an ad hoc/peer-to-peer arrangement
or as a local area network.
Ad Hoc/Peer-to-Peer Configuration
This is the most basic wireless network configuration. It relies on the

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wireless network adapters installed in the computers that are communicating
with each other. A computer within range of the transmitting computer can
connect to it. However, if a number of computers are networked in this way,
they must remain within range of each other. Even though this configuration
has no real administration overhead, it should only be a consideration for
very small installations.
Benefits and Educational Uses
The installation of cables is time consuming and expensive. The advantages
of not doing so are apparent:
the amount of work required and the time taken to complete it are
significantly reduced
the network is accessible in places where wiring would have been difficult
or impossible with no cables linking computers together, cable-related faults
and network downtime are minimized.
Where a wireless network is in place, teachers or students can have
continuous access to the network, even as they move with their equipment
from class to class.
The space over which a wireless network operates is not planar but
spherical. Therefore, in a multi-level site, network access is available in
rooms above or below the access point, without the need for additional
infrastructure.
In a location within a school where network access is required occasionally,
desktop computers fitted with wireless network cards can be placed on
trolleys and moved from location to location. They can also be located in
areas where group work is taking place. As they are connected to the
network, documents and files can be shared, and access to the Internet is
available, enhancing group project work.
As the range of the wireless network extends outside the building, students
and teachers can use wireless devices to gather and record data outside, e.g.,
as part of a science experiment or individual performance data as part of a
PE class.
Technical and Purchasing Considerations
Network interface cards for wireless networks are more expensive than their
wired counterparts. The cost of the access points has also to be considered.
Wireless networks work at up top 54Mbps, whereas wired networks
normally work at 100Mbps (Fast Ethernet). This data transmission rate is
dependant on the number of users, the distance from the access point and the
fabric of the building (metal structures in walls may have an impact). A

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wireless network will be noticeably slow when a group of users are
transferring large files. This should be considered if multimedia applications
are to be delivered over the network to a significant number of users.
As the range of the network may extend beyond the walls of the building, it
can be accessed from outside. Consideration should be given to what
security features the equipment provides to ensure that only valid users have
access to the network and that data is protected.
1.2. Advantages of Networking students
Speed.
Networks provide a very rapid 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 in this manner is very time-consuming.
Cost.
The network version of most 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 the program. The changes have to be done only once, on the file server,
instead of on all the individual workstations.
Centralized Software Management.
One of the greatest benefits of installing a network at a school is the fact that all
of the software can be loaded on one computer (the file server). This eliminates
that need to spend time and energy installing updates and tracking files on
independent computers throughout the building.
Resource Sharing.
Sharing resources is another area in which a network exceeds stand-alone
computers. Most students 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 network, they can be shared by many users.
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

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on a public access area of the network, then go to the media center after school
to finish their work. Students can also work cooperatively through the network.
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 to restrict access to authorized users.
Main challenges of installing a School Network
Costs
Although a network will generally save money over time, the initial costs can
be substantial, and the installation may require the services of a technician.
Requires Administrative Time.
Proper maintenance of a network requires considerable time and expertise.
Many students have installed a network, only to find that they did not budget
for the necessary administrative support.
File Server May Fail.
Although a file server is no more susceptible to failure than any other computer,
when the files 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.

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1.3. Networking Models: Towards a Networked School
This model shows a diagram of a networked school indicating the various
types of networking models used. These include computer rooms, networked
classrooms, networked specialist rooms for specific subjects. Mobile
solutions are shown in the Resource room, the General Purpose room and
Building # 2. Note: To improve readability only network points are shown,
rather than cabling itself. Refer to Fig 8.
Main Building

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Fig 8: Representation of a Typical Network Model
Resource
Room
Specialist
Room
Post
Primary
Wireless link to
Building 2
Staff Room
Building 3
Building 2
Temporary Pre-Fab
- Wireless Network
Specialist
Room
Post
Primary
Standard
Classroom
Standard
Classroom
Standard
Classroom
Standard
Classroom
Standard
Classroom
Standard
Classroom
Standard
Classroom
Standard
Classroom
Store
Room
ICT
Server &
Equipment
Room
General Purpose Room
Computer room
with 15-30 computers
Standar
d
Classro
oms
School
Admin
Office
Principals
Office
Science
Labs
Post
Primary
Technology
Room
Post
Primary

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Fig 9: Typical Network Model for a Special school.
Figure 9 shows a model for a Primary or Special school. This includes
connectivity to all classrooms back to a central network. The network
connects to a File and Print Server. Internet access is handled via a modem
or router, while internet Filtering , Proxy and Web Caching are all handled
via a dedicated server.
Fig 10: Server Functionality Model
Access to:
Internet content &
learning resources,
Scoilnet etc
Email communication
Modem or Router
Cache, Proxy,
Filtering, Firewall
Server
File & Print Server
Principal/Office
Staffroom
# of computers
School ‘Local Area
Network’ (LAN)
Resource room
# of computers
3rd Class
# of computers
4th Class
# of computers
5th Class
# of computers
6th Class
# of computers
2nd Class
# of computers
Junior Infants
# of computers
Senior Infants
# of computers
1st Class
# of computers
Main Servers &
Internet Access
Network
Scanner
Printer
Multimedia or
CD Server
Access to:
Internet content &
learning resources,
Scoilnet etc
Email communication
Modem or Router
Cache/Proxy,
Filtering/Firewall
Server
File & Print Server

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Server Functionality
The network connects to a File and Print Server, Fig 10. The File server
stores common files, The Print Server manages the different requests for
printing. A Multimedia or CD server is used to store and distribute
Multimedia - Sound, Video, Text , applications etc . Internet access is
handled via a modem or router, while internet Filtering , Proxy and Web
Caching are all handled via a dedicated server.
Example network configurations:
Models for Networking
First let’s review some simple models where no networking exits and
computers are used in standalone or ad-hoc mode. The following represent
some simple models representing classrooms.
Model 1a: One computer in a classroom with its own private printer. It is
recommended that students with computers in this situation would network
the classrooms in question as shown. Networking will more effectively make
use of commonly shared resources such as file servers and school printers,
internet , email etc. When a mobile PC or PC with projector is require in a
room the network points are already present.
In this scenario, there could be a single LAN-connected point for the teacher
and an additional LAN connection to allow for a portable switch. Refer to
diagram 11a
Model 1a
Fig 11a: From single PC to networked LAN Points

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Model 1b: This scenario is similar to Model 1a, but where other equipment
such as printers, scanners are used in ad-hoc and inefficient configuration. It
is recommended that students with computers in this situation would
network the classrooms in question . Networking will more effectively make
use of commonly shared resources such as scanners, printers, internet , email
etc. In this scenario there may be a single LAN-connected point for the
teacher and a limited number of LAN connection points throughout the room
to allow students access to the school LAN. The connection points may be
situated as required around the room depending upon class learning
requirements and the availability of existing power outlets. Refer to diagram
11b
Model 1b:
Fig 12b: Networking other commonly used equipment
Networked Computer Room
Model 1c: A non networked computer room or resource area with an ad-hoc
and inefficient use of printers, scanners etc. Networking computer rooms is
essential so that all PCs can access printers, the internet, email etc. This
scenario represents a school computing room which can be timetabled for
classes, and with each computer networked to the LAN. There may be a
single LAN-connected presentation point for the teacher and LAN-
connected computers throughout the classroom. Traditionally, ICT in Irish
secondary students has been concentrated in dedicated computer rooms.
Primary students have more varied deployment. From an administrative
point of view, this setup is attractive. An entire class can be timetabled,
avoiding problems of extra teachers for split classes. Refer to diagram 12c
Model 1c:

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Fig 12c: Networked computer lab.
Media Bays (Ref Fig 13a)
Media bays, or data suites are clusters of perhaps four desktop computers, a
scanner and a printer.
Though self-sufficient in terms of peripherals, they would be connected to
the main school network and have Internet access. This is one reason why
they would be best sited in public areas around the school.
These suites would be used by students in small groups or individually and
could accommodate task-oriented activities and self-directed learning.
Advantages are easy access to staff and students alike, Utilise areas of
school without losing classrooms
Public supervision
Disadvantages are Open access means security issues must be addressed .
Fig 13a: Movable or mobile Media Bays
Laptop and data-projector (Ref Fig 13b)

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A combination of laptop and data-projector is a highly effective teaching
model where a teacher wants to provide the whole class with visual or
multimedia content . It can be used in conjunction with an existing LAN
point in the room for best effect.
Fig 13b: Movable or mobile Laptop PC with Digital Projector
Wireless LAN (Ref Fig 13c)
This scenario has the capability to connect multiple computers to the school
LAN without providing direct LAN connections. No LAN cabling is
required for the classroom; instead all computers are radio linked to the
LAN. Wireless LAN technology is relatively new and generally more
expensive and more limited than cabled LANs. There is the potential,
however, to save on extensive cabling work with this option.
Wireless connections allow a region to be connected to a network by
radiowaves, which link a wireless card in the computer to a wireless access
point. One should remember that the access point itself must be connected
by cable to the main network.
Advantages
 Flexibility of machines - usually laptops - linked even if students
break into small workgroups in different parts of room.
 Wireless networking means that large common areas such as canteens
or libraries can be easily connected to the network.
 Less unplugging of cables into sockets reduces wear and tear
Disadvantages
 Wireless networking may prove much more expensive if wiring large
numbers of machines close together.

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 Wireless hubs data rates (typically 11Mbps) are considerably less at
present than their cable equivalent. Thus is unsuitable for high data
volumes such as multimedia access by large numbers of machines.
 Manufacturers stated ranges of 100 - 300 metres is wildly optimistic.
Ranges of less than 18 metres are not uncommon, Data rates drop off
as distance increases.
While it is unlikely that wireless will replace data cables in the near
future they do provide a flexibility that can be harnessed creatively.
Fig 13c: Wireless LAN (WLAN)

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2.1. Some Relevant Terms
MDF Main Distribution Frame
IDF Intermediate Distribution Frame
Broadband Refers to a higher speed always on internet connection
Narrowband Refers to speeds of up to 128kbps
Dial up Refers to having to dial up the internet every time one
goes online.
Always On Refers to the nature of broadband, being ‘always on’ means a
dial up is not required.
Download speed The speed at which data is delivered to a school modem
from the internet
Upload speed The speed at which data is sent to the internet from a
school modem.
ISP Internet Service Provider
ISDN Integrated Services Digital Network (64kbps single
channel or 128kbps dual channel)
PSTN Public Switched Telephone Network (refers to an
ordinary telephone line)
ADSL Asymmetric Digital Subscriber Loop
Mbps Megabits per second (1,000,000 bits per second)
Kbps Kilobits per second (1,000 bits per second)
Ethernet Ethernet is a standard for transferring data over networks.
USB Universal Serial Bus
Modem A simple device used to access the internet
Router A more technically advanced device used to access the
internet

Computer networks--introduction computer-networking

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