Cambridge A Level IT Chapter 13.01 Network Components

1. Chapter 13
Networks
anjan.mahanta@satreephuketipc.com
Cambridge A Level IT
13.01 Network Components

2. 13.1 Network components
Data Packet
● An Internet Protocol (IP) data packet will include header information and the data that is
being sent.
● With the header information will be the source address, destination address, IP version
being used (e.g. IP V4), the length of the data packet and an identification number to
enable packets to be sequenced.
● The source and destination addresses will both be 32 bit IP addresses (IP V4) for
example 212.35.0.89 and they don’t change during transmission.
https://www.youtube.com/watch?v=nomyRJehhnM
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3. SWITCH
● Switches are used to join computers and other
devices together in a network.
● Switches are able to inspect packets of data so that
they are forwarded appropriately to the correct
computer.
● Because a switch sends a packet of data only to the
computer it is intended for, it reduces the amount
of data on the network, thus speeding up the
network.
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4. HUB
● A hub is a simple device that does not manage
any of the data traffic through it.
● lt is simply used to enable computers on the
network to share files and hardware such as
scanners and printers.
● Data is transferred through networks in
packets. A hub contains multiple ports
(connection points).
● A hub can also be classed as a multi-port
repeater. 4

5. HUB
● When a packet arrives at one port, it is
transferred to the other ports so that all
network devices of the LAN can see all
packets.
● Every device on the network will receive the
packet of data,which it will inspect to see if it
is intended for that device or not.
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6. Wireless access point
● A wireless access point connects Wi-Fi (wireless)
enabled devices to a network.
● It uses radio waves at frequencies of 2.4 GHz or 5
GHz to transmit data.
● A wireless access point is usually connected to a
switch by a cable, although it is possible in the
home to have a combined wireless access
point/switch/router.
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7. Network Interface Card (NIC)
● Before a computer can be connected to a
network, it will need to have a network
interface card.
● Most modern computers have these when you
buy the computer. These cards connect directly
to the motherboard of the computer and have
external sockets so that the computer can be
connected to a network via cables.
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8. Network Interface Card (NIC)
Basically a NIC does the following:
● lt prepares the data for sending.
● lt sends the data.
● lt controls the flow of data from the computer
to the transmission media (metal wire, optical
fibre, etc.).
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9. Wireless Network Interface Card (WNIC)
● A wireless NIC (WNIC) makes a device “wireless
enabled” meaning that it can connect to a
network wirelessly through a wireless access
point.
● It is most often part of the motherboard circuitry
of a laptop, printer, tablet or smartphone.
● However, it is also possible to to add a wireless
NIC to a non-wireless enabled device.
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10. Routers
● Each computer linked to the internet is given a
number which is called its lP(Internet Protocol)
address.
● An lP address looks like this: 123.456.1.98 and is
unique for each device while linked to the internet.
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11. Routers
● When data is transferred from one network to another the data is put into
packets.
● The packets contain details of the destination address of the network it is
intended for.
● Computers on the same network all have the same first part of the Internet
Protocol address and this is used to locate a particular network.
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12. Routers
● Routers are hardware devices that read the
address information to determine the final
destination of the packet.
● From details stored in a table in the router,
the router can direct the packet onto the
next network on its journey.
● The data packet is then received by routers
on other networks and sent on its way until
finally ending up at the final destination
network.
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13. Repeater
● A repeater is another name for an active
hub. It boosts the signals along a network
cable.
● This is necessary when long cable lengths are
required (typically over 100 m) and the
signal won’t be strong enough to reach the
destination.
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14. Gateway
● A gateway connects two networks of a different type. It is typically used as a
router to connect a LAN to a WAN.
● When data leaves one network to move onto another network, it must pass
through the gateway. 14

15. BRIDGES
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16. BRIDGES
● Bridges are used to connect LANs together. When one of the LANs sends a
message, all the devices on the LAN receive the message.
● This increases the amount of data flowing on the LAN. Often a large LAN is
divided into a series of smaller LANs. If a message is sent from one computer in a
LAN to another computer in a different LAN then the message needs to pass
between the LANs using a bridge.
● The advantage in subdividing a larger network is that it reduces the total network
traffic as only traffic with a different LAN as its destination will cross over the
bridge. A bridge therefore usually has only two ports in order to connect one LAN
to another LAN. 16

17. FIREWALL
● A firewall prevents external users gaining unauthorised
access to a computer system. It is usually positioned at
the gateway to a network and will examine all incoming
data to determine if it should be allowed.
● Data that is not allowed will be prevented from gaining
access to the network.
● A firewall is often configured as part of a router but it
can also be software that is installed on a proxy server
or individual computers.
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18. SERVERS
● A server is a computer on a network which provides
resources that can be used by client devices.
● Individual servers or group of servers can perform a
variety of functions depending on how they are
configured.
● A file server’s role is to male files available for users
on the network. Depending on the permissions given
to each user or group of users, files can be created,
read, modified or deleted.
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19. SERVERS
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20. Print server
● A print server deals with all the print
jobs on a network.
● Each time a client computer sends a
request for printing, it will be added to
the queue on the print server.
● The print server will then deliver each
print job in turn to the printer.
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21. Mail server
● A mail server receives and sends all
emails for an organization.
● The mail server can be the part of a
LAN or WAN.
● Incoming emails are checked for
viruses, phishing or spam and then
sent to the user’s mailbox.
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22. Application server
● An application server delivers
software to client computers.
● This can be done by the clients
accessing the software direct from the
server or by the server managing the
installation of the software onto each
client computer.
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23. Proxy server
● A proxy server deals with all requests to the internet.
● It sits between the LAN and the gateway. It will check that each request is allowed
and filter out any undesirable requests such as pornographic websites.
● It will also store webpage in a cache which will speed up the time it takes for a user to
receive a webpage. It often includes firewall software.
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24. Bandwidth and bit rate
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25. Bandwidth and bit rate
● Bandwidth measures the range of frequencies available on a communication
channel. This defines its capacity.
● Bandwidth is measured as a frequency range in kilohertz (kHz) or as a transmission
rate in bits per second (bps).
● Although the bandwidth is often thought of as a speed, it’s actually the number of
bits per second the line is capable of transmitting.
● It is therefore the maximum possible speed to data transfer. The transmission speed
is often referred to as the bit rate.
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26. Bit streaming
● A bit stream is a series of bits which represent a stream of data transmitted at one
time.
● In networking, streaming takes place when video or audio files are sent to a
receiving device for viewing or listening to without downloading a file to save in
storage.
● With a video, the first few seconds consisting of several frames will be sent to fill a
buffer (a temporary area of storage) which can then be watched at the receiving
device.
● As the frames with the buffer are viewed, they are removed so that more frames can
be added to the buffer to keep it full.
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27. Bit streaming
● A buffer is used to keep the video running smoothly.
● Without a buffer, any data congestion would be
noticed by the video pausing, missing out frames or
pixelating until the full transmission rate was
available again.
● Data congestion can be caused by devices on the
same network using up so much bandwidth that there
isn’t enough left for the full video transmission.
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28. The importance of bandwidth and bit rate
when transmitting data
There are two main scenarios when bandwidth is important:
● accessing content within a time limit
○ If a user needs to download a 50Mb high quality photograph but doesn’t need to view it until several
minutes later, then bandwidth may not be a major issue.
● accessing content in real time
○ When a user needs to access streamed or live content in real time, it is essential that there is
sufficient bandwidth to stream the content without the buffer emptying at any point.
○ If the buffer empties due to the content not being streamed quickly enough, then the user will
experience pauses, pixelation or missing the video or sound.
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29. The importance of bandwidth and bit rate
when transmitting data
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30. Different types of communication/
transmission media govern bandwidth
Cables
● Copper cables are the main method used for connecting
devices in a LAN.
● The most common form of copper cable is unshielded
twisted pair (UTP) which is also known as an Ethernet cable.
● The cables consists of four twisted pairs of cables and are
protected by plastic tubes, but there is no earth wire, which
can result in the lost data packets at high frequencies.
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31. Different types of communication/
transmission media govern bandwidth
Cables
● Copper cables are suitable over distances up to 100 meters
but beyond that the signals weakens.
● The bandwidth available is governed by the the frequencies
that the copper cable can accommodate, and electrical
interference which can result in lost data packets that will
affect the transmission rate.
● When the higher bandwidths are required, shielded twisted
pair (STP) cables can be used. They include a metal shield
around each twisted pair and an earth wire. 31

32. Different types of communication/
transmission media govern bandwidth
Wireless
● Less frequencies are available to wireless communication methods than to copper
cable, which means there is less bandwidth available.
● Wireless transmission is also susceptible to interference from other wireless
devices and wireless access points.
● This interference causes lost data packets which reduces the transmission rate.
● Obstacles such as walls and ceilings can reduce the strength of a wireless signal,
which means there is even less bandwidth available the further away a device is
from a wireless access point. 32

33. Different types of communication/
transmission media govern bandwidth
Optical
● As fibre optics are not susceptible to electrical interference, it is far less likely that
data packets will be lost.
● So, the total bandwidth available is considerably higher than with copper cables.
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34. Circuit switching
● Traditional voice telephone calls using the Public Switched Telephone Network
(PSTN) are transmitted using circuit switching.
● This method of data communication sets up physical network path from the sender
to the receiver before any communication starts.
● All the data is then transmitted using this single path.
● While the circuit is open, no other devices can transmit data using that path.
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35. Packet switching
● This method of data communication splits the
data to be transmitted into packets, which are
groups of bits.
● Packets will include header data which identifies
the source and destination, some of the data and
error control bits.
● Each packet can take its own route from source to
destination.
● As each packet is received by a network node,
such as a switch or router, it will be routed to the
next node. 35

36. Message switching
● Message switching transmits the whole set of data together from source to destination.
● It doesn’t have a predefined route. The data is sent to one network node at a time and is
temporarily stored there before being passed to the next node. This is known as store and
forward.
● Each message includes a header which contains the source and destination.
● This method is quite slow because it depends processing taking place at each node and also
requires network nodes with adequate storage capacity. 36

37. Optical communication method
● Optical communication method make use of light to transmit
data. The big advantage of this is that the speed of light is far
faster than any other method.
● Light travels at 300 million m/s. That means it can travel
around the whole earth 7.5 times every second or that it only
takes 0.065 seconds to travel halfway around the world.
● This means that there is negligible latency (delay) between
sending and receiving data, which makes it suitable for
real-time applications.
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38. Infrared
● Infrared is the communication method used by most remote
control devices.
● It is cheap to produce and a well-recognised standard method
of transmitting simple commands.
● It works by transmitting electromagnetic radiation that is just
past the red end of the visible light spectrum, so it can’t be
seen by the human eye.
● It does not have a very high bandwidth and so is only suitable
for transmitting small amounts of data.
● Infrared will only work for short distances.
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39. Fibre optic
● Fibre optics are fine strands of glass that transmit data as
light.
● As the strands are very fine, a large number can be fitted into
a small space, meaning that it is possible to transmit a lot of
data at once.
● The fine strands are also flexible, which means that the cables
can be used in buildings and around corners.
● Fibre optic have very large bandwidths. A single fibre optic
strand used in an internal network can easily carry 1 Gbps of
data.
● Security is another advantage of fibre optics.
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40. Fibre optic
● The main disadvantages of fibre optics are that if they are
broken they can be complicated to repair, especially if there
are several hundred strands to fix, and they are more costly to
produce than copper cables.
● Because they suffer hardly any degradation of signal, they can
be used over large distances, including in LANs where copper
cable limits are typically 100m.
● They are also used in aircraft where weight is an important
factor, because they are lighter than copper cables.
● ISPs often use a method called fibre to the cabinet (FTTC) to
provide internet connectivity to homes. 40

41. Laser
● Laser is an intense beam of light that can be used to transmit
data.
● Like infrared, line of sight is necessary, but, unlike infrared,
laser beams can cover large distances.
● Laser still travels at the speed of light, but it doesn’t require a
physical connection like fibre optics.
● Lasers can be used to connect LANs between buildings. They
are suitable for this because very few data packets are lost as
there is little interference in normal atmospheric conditions.
● It is quick to set up and can be portable, making them suitable
for live events such as sports and music concerts.
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42. Wireless communication/transmission
methods
Bluetooth
● Bluetooth is a wireless communication method used for the transfer of data between
devices.
● It uses wireless frequencies between 2402 and 2480 MHz.
● It splits transmission of data into packets which can be transmitted on 1 to 70 channels,
each with a bandwidth of 1 MHz.
● It is typically used with mobile phone devices to connect to a range of equipments -
headsets, smartwatch, transferring files between phones, etc.
● It requires very less power to operate. 42

43. Wi-Fi
● Wi-Fi enables computers and other devices to communicate wirelessly with
each other. It operates in the 2.4 GHz and 5 GHz frequencies.
● Areas where the internet can be accessed wirelessly using Wi-Fi are called
access points or hotspots and they can be found in many public places, such as
coffee bars, hotels, airports, etc.
● The range of a Wi-Fi depends on the type of wireless router being used and also
if there are obstacles such as walls in the way of the signal.
● For a home network, the range of Wi-Fi are typically 50m indoors and lOOm
outdoors.
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44. Wi-Fi
● There have been many Wi-Fi standards
that have evolved over the years and they
are all referred by the number 802.11
followed by a letter.
● The 802.11ac standard supports speeds
of upto 1.3 Gbps, compared to just 450
Mbps (0.45 Gbps) on the previous
802.11n standard.
● The 2.4 GHz spectrum in 802.11n was
too crowded reducing connection speed. 44

45. Wi-Fi
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46. Wi-Fi
Wi-Fi is used in a range of applications including:
● Connection to portable devices such as laptops, tablets and mobile phones to a
network, which could be a corporate LAN, a home LAN or a wireless hotspot.
● “Smart” televisions which use services from the internet and so require a
connection to a LAN that is connected to the internet.
● Printers that can be located anywhere in a room, without having to run
additional cables.
● ‘Casting’ of a devices screen to another device wirelessly.
● Smart home devices. 46

47. Radio
● Bluetooth and Wi-Fi both use radio waves.
● Another transmission method that uses radio waves is
radio-frequency identification (RFID).
● RFID uses electromagnetic fields to identify and track small RFID
chips.
● One use of RFID is to monitor the location of parcels from a
distribution warehouse to the delivery point. Each parcel can have a
RFID tag that is unique to the parcel. As it moves through the tag is
read by the RFID reader and the location gets updated in the
database. 47

48. Radio
● Another use of RFID is for wireless key cards that are used to
unlock doors.
● These close proximity RFID chips are known as near field
communication (NFC).
● NFC is also used by mobile phones to emulate a NFC tag on a
credit or debit card and make contactless payments.
● The mobile phone can also read NFC tags, which can be used
to activate an application, change phone settings or open a
web page.
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49. Task
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50. Protocol
● A communication protocol is a set of rules that ensure data is transmitted
between devices correctly.
● These rules are required so that a variety of devices and applications can
communicate together successfully.
● A protocol defines
○ the method of addressing to use
○ type of error checking to be used
○ how sending devices will indicate the start and end of a message
○ how a receiving device will confirm it has received a message
○ any data compression methods to be used
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51. Types of protocol
The International Organization of
Standardardization (ISO)
published a layered model in
1983 known as Open System
Interconnection (OSI) model.
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52. Abstraction layers
The Open System Interconnection (OSI) model is a framework that put protocols into seven
different layers with each layer being an abstraction of communication.
1. The physical layer of communication deals with electrical and mechanical operations.
2. The data link layer deals with data packets.
3. The network layer deals with how data is switched, routed and addressed.
4. The transport layer ensures data flows correctly without errors.
5. The session layer defines protocols between applications during a communication session.
6. The presentation layer ensures that data is in a format that can be recognized such as
types of image, types of video file and the text encoding method to use.
7. The application layer deals with specific types of communication application such as file
transfer or email. 52

53. POP
● Post office protocol (POP) defines the rules for email client software to retrieve emails.
● The main method that is applied is to connect to an email server, download all messages
and store them on the client computer and then delete the messages from the server.
● POP also supports encrypted transmission of emails.
● POP is a part of the application layer of the OSI model.
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54. IMAP
● Internet message access protocol (IMAP) is an
alternative method for email client software to
retrieve emails.
● Instead of downloading the email and then deleting it
from the server, its default mode is to leave the email
on the server and download a copy to the client.
● This means the emails can still be accessed from a
remote location. IMAP also supports multiple folders
on a server whereas POP only supports a single folder
on the server.
● IMAP is part of the application layer of the OSI model.
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55. TCP/IP
● Transmission Control Protocol / Internet Protocol (TCP/IP) is the basic communication
protocol used on the Internet and in most LANs and WANs.
● TCP/IP consists of two layers.
● TCP deals with breaking a message down into small data packets that are transmitted and
then reassembled at the receiving end.
● IP deals with the address to ensure that each packet reaches the correct destination.
● The address will be checked each time a packet reaches a gateway and routed towards the
destination.
● The IP protocol uses addresses which consist of four numbers between 0 and 255 separated
by dots. e.g. 212.58.246.90. There are approximately 4 billion of these IP addresses.
● In 2011 a new version of IP v6 was introduced which has 3.4 x 10 ^ 38 addresses.
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56. FTP
● File transfer protocol (FTP) is part of the TCP/IP suite
and is used to define how computer files should be
transferred from one location to another.
● FTP allows for users to be authenticated by username
and password but also has an option for anonymous
connectivity.
● This protocol sets the rule for how a server should
respond using ASCII codes, the data format to use and
the mode of data transfer (stream, block or
compressed).
● FTP is the part of the application layer of the OSI model.
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57. HTTP
● Hypertext transfer protocol (HTTP) is also part of
TCP/IP suite and is used by web browsers to send
requests to a web browser to view a web page.
● When the request is received by the web server it sends
the web page information back to the web browser.
● HTTP is insecure and so HTTPS is a secure version that
encrypts the transmission.
● HTTP is part of the transport layer of the OSI model.
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58. BitTorrent Protocol
● The BitTorrent protocol specifies how multiple
downloads can take place from the same file source
concurrently.
● Several clients (peers) download portions of the file.
The peers that connect to each other directly to send
and receive those portions of the file between
themselves.
● This reduces the bandwidth required by the original
host of the file and can increase download speeds for
clients downloading large files.
● The protocol only works effectively if there are lots of
peers downloading the same file, as without lots of
peers there are less opportunities to receive portions
of the file. 58
https://skerritt.blog/bit-torrent/

59. BitTorrent Protocol
● A torrent is a metadata file which identifies the locations
(Uniform Resource Locators (URLs)) or trackers which
coordinate communication between the peers that are
downloading parts of the file and uploading parts for each
other to download on a peer-to-peer basis.
● When a peer wants to start downloading a file, it
announces that it wants to join the swarm.
● Peers will periodically report information on the tracker
regarding their download status and receive in exchange
information about other peers to which they can connect.
● Peers will eventually become seeders, which are clients
that have a full download of the torrent and are still making
it available to upload to other peers.
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https://www.youtube.com/watch?v=MMnsBJeb0IQ

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