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Computer Science > Unit 5 Networks > Flashcards

Unit 5 Networks Flashcards

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1
Q

What is the Internet?

A
  • A group of inter-connected networks
  • Many services use the Internet such as the web and email
  • No one person or organization owns the Internet, this is known as collective or distributed ownership
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2
Q

How is the Internet different from World Wide Web?

A
  • The World Wide Web is one service that makes use of the Internet
  • The World Wide Web is the information system of interlinked web pages and other resources
  • It is accessed from a web browser
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3
Q

What is the World Wide Web?

A
  • The World Wide Web is the information system of interlinked web pages and other resources
  • It is accessed from a web browser such as Chrome, Safari, Edge or Firefox
  • It makes use of HTTP to send and receive data
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4
Q

Wide Area Networks

A
  • Any network in which computers communicate using resources supplied by a ‘third party carrier’ such as BT, is a Wide Area Network (WAN)
  • A WAN uses cables, telephone lines, satellites or radio waves to connect two or more remote locations
  • The Internet is the largest WAN in the world
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5
Q

Name three organisations that may be using a WAN to connect locations

A
  • Organisations such as universities and schools may have a number of geographical locations
  • Each one will have its own network. When these networks are joined together they will create a WAN

Other organisations may use WANs including:
- Large companies with many offices such as banks
- Governments which have employees in many locations
- Research organisations which are located in more than one place

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6
Q

IP addresses

A
  • Every computer in the world has an IP (Internet Protocol) address
  • IP addresses are four 8-bit numbers (0-255) separated by dots
  • Where packets of data are sent to or received from
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7
Q

A circuit switching network

A
  • When you make a telephone call, a dedicated connection is set up between you and the person you are calling for the duration of the call
  • This is called ‘circuit switching’
  • It works fine for phone calls, but there could never be enough lines for all the billions of people sending data across the Internet
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8
Q

What works in place of a circuit switching network for the Internet?

A

Packet switching

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9
Q

What is contained in the header given to each packet?

A
  • The IP address it is going to
  • The IP address it has come from
  • The sequence number of the packet
  • The number of packets in the whole communication
  • Error checking data
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10
Q

Data packets

A
  • Each data packet will contain the same number of bytes, usually a data packet is 512 bytes
  • The packets may flow through the Internet via different routes
  • Each packet is marked with the packet number so that the packets can be put back together by the receiver
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11
Q

Reassembling the data packets

A
  • The recipient computer re-orders the packets into the correct order
  • Each packet is checked for errors
  • Corrupt packets are requested to be resent
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12
Q

Moving packets on the net

A
  • Points on a network diagram are called nodes
  • Routers are any node that can route packets from one place to another
  • Your home router, routes packets to the different devices on you home-network
  • Internet routers route packets around the world like a mail sorting office
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13
Q

Network Interface Cards (NIC)

A
  • A Network Interface Card (NIC) is built into every networked device
  • It may be wireless with an antenna or wired with a network cable socket
  • Most modern computers and phones incorporate the NIC into the motherboard
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14
Q

MAC addressing

A
  • A Media Access Control (MAC) Address is assigned to each NIC by the manufacturer
  • A smartphone will have two different MAC addresses: one will be for Wi-Fi and one for Bluetooth
  • A computer may have more than one MAC address if it has both and Ethernet and Wi-Fi connection
  • Every networked device in the world has a unique MAC address
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15
Q

Why doesn’t the Internet use a MAC address instead of an IP address to locate a web address?

A

MAC addresses do not change with location, but IP addresses do. The actual geographical location of a networked device can be determined by its IP address

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16
Q

The role of the MAC address

A

When you request a web page, each router along the way uses the MAC address of the next router to send the data packet on the next leg of its journey

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17
Q

Routers

A
  • Looks at the destination of packets of data and sends them to the network that is closer towards their destination
  • A home router will route packets between the home local area network (LAN) and the Internet
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18
Q

Switches

A
  • Switches connect each node (computer) in a network
  • They know the MAC address of all connected computers and devices
  • When a packet of data arrives, they can send it to the correct computer
  • Hubs, by comparison will send the data to all connected networks
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19
Q

Wireless networks

A
  • Connect using Wi-Fi
  • Broadcast using radio waves, these are part of the microwave spectrum
  • Wi-Fi networking protocols, Wi-Fi is a family of related protocols, it is a trademark used to describe a Wireless LAN or WLAN
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20
Q

Wireless transmission

A
  • Commonly uses radio waves for communication
  • Susceptible to interference from objects and other nearby electronics or other wireless devices
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21
Q

Wireless access point

A
  • A wireless Access Point (AP) is a device that allows wireless devices to connect to a wired network using Wi-Fi
  • The AP usually connects to a router via a wired network
  • Home Wi-Fi routers often combine the functions of a switch, router and wireless access point in one box
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22
Q

Wireless NICs

A

A wireless NIC is built into every networked device capable of connecting to a wireless network

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23
Q

Examples of wireless devices

A
  • PCs
  • Smartphones
  • Wireless speakers
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24
Q

Packet

A

One unit of data sent through an IP network

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25
Q

Wireless and wired network

A

Wireless network - a network using radio waves
Wired network - a network using cables

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26
Q

What is a LAN?

A
  • LAN stands for Local Area Network
  • Operates on a single site such as a school, hotel or business using their own cabling systems
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27
Q

What is the difference between LAN and WAN?

A
  • LANs are local and located within one location such as a building
  • WANs connect networks at remote locations via leased lines
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28
Q

Advantages of LANs

A
  • Computers can share resources such as printers
  • Files can be accessed through any computer in the network
  • Data is easy to back up as it is stored centrally on the server
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29
Q

Disadvantages of LANs

A
  • Purchasing the network hardware is expensive
  • Managing a large network is complicated
  • Viruses may be able to infiltrate the network and infect every computer
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30
Q

What is a topology?

A

The way in which parts of a system are connected

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31
Q

Network topologies

A

There are many topologies for setting up networks and LANs. Two of these topologies are:
- Star
- Bus

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32
Q

Example of network topologies

A

The London Underground network has a topology that shows where connections, and lines are

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33
Q

Star topology

A

In a star topology, computers and other devices (known as nodes) are all connected to a central switch

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34
Q

Advantages of star topology

A
  • Fast data transfer to the hub as each wire isn’t shared with other computers
  • If one cable fails the other computers are not affected
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35
Q

Disadvantages of star topology

A
  • Requires additional hardware such as the central switch and network cables
  • If the central switch fails the whole network goes down
36
Q

Bus topology

A
  • In a bus topology, computers and other devices are all connected to a central coaxial cable
  • Terminators are placed at each end of the cable to absorb signals and prevent them reflecting down the cable
37
Q

Advantages of bus topology

A
  • Less cable so cheaper to install the network
  • Easier to add more devices as they only need to connect to a central cable
38
Q

Disadvantages of bus topology

A
  • The single cable is shared by many devices so there will be many ‘collisions’ of data if data is sent at the same time, which slows down data transfer
  • If the cable is damaged, the whole network fails
  • Any device can view all data on the cable creating a security risk
39
Q

Why does star topology not have a security risk?

A
  • All connected devices pass through a switch/hub
  • The switch/hub implements safety features
40
Q

Network security methods

A
  • Authentication
  • Encryption
  • Firewall
  • MAC address filtering
41
Q

Authentication

A
  • Authentication is checking that the computer and the user are allowed to access content
  • This is most commonly done using a username and password
42
Q

Intercepting data

A
  • Data that is transmitted over a network can be intercepted
  • Any intercepted data can be read and understood unless measures are taken to prevent it from being interpreted
  • These measures are known as encryption
43
Q

Encryption

A

Encryption is the encoding of data so that it can no longer be easily understood

44
Q

Plaintext

A

The original message to be encoded

45
Q

Ciphertext

A

The encrypted message

46
Q

Key

A

A sequence of numbers used to encrypt or decrypt, often data using a mathematical formula

47
Q

Encryption algorithm

A

The formula for encrypting the plaintext

48
Q

State the two encryption techniques

A
  • Private key (symmetric encryption)
  • Public key (asymmetric encryption)
49
Q

Private key

A
  • Symmetric encryption
  • A single key is used to encrypt and decrypt a message and must be given to the recipient of your message to decrypt the data
50
Q

Public key

A
  • Asymmetric encryption
  • Two keys are used, one (public key) to encrypt and the other (private key) to decrypt data
  • This is more secure as it means that you never have to send or reveal your decryption key
51
Q

Caesar shift cypher

A
  • The earliest known substitution cipher was invented by Julius Caesar
  • Each letter is replaced by a n positions further on in the alphabet
  • n is the key and is used to encrypt and decrypt the message
  • This is an example of symmetric encryption
52
Q

State the two most common wireless security standards

A
  • WEP (Wired Equivalent Privacy)
  • WPA (Wi-Fi Protected Access)
53
Q

WEP

A
  • Older method of encryption
  • Can be cracked in seconds
  • This standard should no longer be used to protect a home
54
Q

Strong and weak encryption

A
  • Encryption can be considered to be ‘strong’ when the useful lifetime of the encrypted data is less than the time taken to break the code
  • With weak encryption, the code may be broken in time to use the information, but it wouldn’t be worth the effort trying
55
Q

What is a protocol?

A

A set of rules

56
Q

HTTP and HTTPS protocol

A
  • HTTP (hypertext transfer protocol) is used for accessing and receiving web pages via the Internet
  • These are written in HTML (Hypertext mark-up language)
  • The protocol requests a web page from the web server
  • The server then sends its response which contains the web page
  • HTTPS (secure HTTP) encrypts the information so that it cannot be understood by an eavesdropper
57
Q

Specific types of sites that use HTTPS

A
  • Banks, to prevent theft
  • Online shops, for bank and log in details
  • Social networks, for log in details and personal data
58
Q

FTP

A
  • File Transfer Protocol (FTP) is used for sending or retrieving files to or from a FTP server
  • A graphical interface will allow files to be dragged from your computer to the server
59
Q

How email works

A
  • When an email is sent from a computer it will first be sent to a mail server using the SMTP protocol
  • It is then forwarded on by other SMTP servers
  • When it reaches the destination mail server it is stored
  • The user’s computer uses POP or IMAP to access the email
60
Q

What are POP and IMAP?

A

Email retrieval protocols that fetch message data and attachments from your remote mail server

61
Q

POP

A
  • POP (Post-Office Protocol) will download every new message to your local device and with them no longer being available on the server
  • This is similar to the protocol of sending a letter through a post office
62
Q

IMAP

A
  • IMAP (Internet Message Access Protocol) will leave the messages on a server
  • They can be accessed by multiple devices and they only are removed if the user deletes them
63
Q

SMTP

A
  • Simple Mail Transfer Protocol (SMTP) is an email protocol used for sending email
  • Email software, such as Outlook, sends the email to the SMTP server used by the company or individual
  • The mail server then relays the message through various other servers known as mail relays
  • Finally, the email arrives at the destination mail server
64
Q

TCP

A

Transmission Control Protocol (TCP)
- Breaks up messages sent over the Internet into data packets
- Reassembles the packets at the other end
- Detects errors
- Resends lost messages

65
Q

IP

A

Internet Protocol (IP) routes the individual packets from one IP address to another

66
Q

The TCP/IP protocol stack

A
  • The protocol stack defines four layers that enable communication on the Internet
  • This is a modular design with each layer being responsible for a small part of the communication process
  • The four layers are divisions of network functionality, each carrying out different roles:
  • application layer
  • transport layer
  • internet layer
  • link layer
67
Q

Application layer

A
  • Applications such as email clients and web browsers create data to send in this layer
  • SMTP, FTP and HTTP operate in this layer
68
Q

Transport layer

A
  • The Transport layer creates the connection between two computers, or ‘hosts’
  • The two computers agree the communication settings and the size of the packets they will send and receive
  • Data is then divided up into packets and given a packet number
  • Packets are reassembled by the recipients Transport layer
  • Lost packets are resent
  • This layer uses the TCP (Transmission Control Protocol) or the UDP (User Datagram Protocol)
69
Q

Receiving data

A
  • Data packets move back up the layers on arrival
  • The link layer removes the MAC address and passes packets up to the Internet layer
  • The Internet layer removes the IP addresses and passes packets up the Transport layer
  • The Transport layer reassembles the packets and passes the data to the Application layer
  • The Application layer uses the correct protocol to correctly display the data, web page or email for the user
70
Q

The advantages of layers

A
  • Layers are self-contained, the functionality of one layer can be changed without affecting the functionality of other layers
  • Different hardware or software operates on a particular layer providing interoperability between providers and systems
71
Q

UDP

A
  • The User Datagram Protocol (UDP) maintains an open data connection to send a stream of packets without checking they are received correctly
  • UDP is unreliable as it isn’t known if a packet was received
  • UDP makes most sense to use when it doesn’t make sense to wait and fill in gaps left by lost packets: online gaming, video streaming
72
Q

What is a PAN?

A
  • Personal Area Network
  • A computer network used for data transmission among devices such as computers, laptops, phones
  • A PAN can be used for communication between the devices themselves or for connecting to the Internet
73
Q

What is a firewall?

A

A network security device that monitors incoming and outgoing network traffic and decides whether to allow or block specific traffic based on a defined set of security rules

74
Q

Advantages of using fibre optic cables

A
  • Not affected by electromagnetic interference
  • Greater bandwidth
  • Do not break as easily as copper cables
  • Faster transmission
75
Q

Disadvantage of fibre optic cables

A

More expensive than using copper cables

76
Q

What is a network?

A

A group of devices connected together, wirelessly or using cables, so that they can communicate with each other and share resources

77
Q

What are the four layers of the TCP/IP stack (in order)?

A
  • Application layer
  • Transport layer
  • Internet layer
  • Link layer
78
Q

Explain the function of the application layer

A
  • Where data is sent from software applications into the protocol stack
  • At the other end of the communications link, the application layer passes the data to the receiving application
  • The data is encoded so that it will be understandable by the recipient
  • The protocols used in the application layer are: HTTP, HTTPS, FTP, SMTP AND IMAP
79
Q

Explain the function of the transport layer

A
  • Breaks the application data into data packets
  • Adds packet information to the header: sequence numbers, source and destination
  • TCP and UDP operate in this layer
  • Data sent using the TCP protocol will be resent if there are any missing data packets
  • Data sent using the UDP protocol will not be resent if there are any missing data packets
  • Passes the data down to the Internet layer
80
Q

Explain the function of the internet layer

A
  • Addresses and packages data for transmission and routes the packets across the network
  • Attaches the IP address of the sender and destination
  • IP operates on this layer
  • The internet layer passes the data down to the link layer
81
Q

Explain the function of the link layer

A

Attaches the MAC addresses of the sender and recipient, allowing the packet to be directed to a specific device

82
Q

What are the advantages of using a wired network?

A
  • Connection speeds are typically faster
  • They typically have higher bandwidth
  • They typically have better security
83
Q

What are the advantages of using a wireless network?

A
  • Typically have lower setup costs as there is no need to lay cables
  • Easier to connect more devices
  • Devices can be portable within the range of the access point
84
Q

What are the disadvantages of using a wired network?

A
  • Can be expensive to setup
  • Not all devices can connect via cable
  • Cables can be hazardous and unsightly
85
Q

What are the disadvantages of using a wireless network?

A
  • Can be less reliable than wired networks
  • If many devices try to use the same access point at the same time, the connection can be very slow
  • Connection speed reduces the further the device is from the access point

Computer Science (9 decks)

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