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Computer science > Communication and Internet technologies > Flashcards

Communication and Internet technologies Flashcards

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1
Q

What is an example of short distance data transmission?

A

Computer to printer

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2
Q

What is an example of long distance data transmission?

A

Telephone network

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3
Q

What are the factors that affect data transmission?

A
  1. The direction of the data transmission (in one direction or both)
  2. The method of data transmission (how many bits are sent at a time)
  3. The method of synchronisation between two devices
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4
Q

What is simplex data transmission?

A

The data is only sent in one direction (sender to reciever) , an example of this is computer to a printer

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5
Q

What is half-duplex data transmission?

A

The data is sent in both directions but not at the same time, an example of this is a conversation on a phone where only one person speaks at a time or radio transmissions

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6
Q

What is full-duplex data transmission?

A

The data is sent in both directions at the same time, an example of this is texting one another or a broadband connection on a phone line

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7
Q

What is serial data transmission?

A

It is when data is sent one bit at a time, over a single wire or channel (bits are sent one after the other in a single stream)

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8
Q

What distance is serial data transmission most effective?

A

Long distance, because the data has less chance of being lost seeming only one wire is being used

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9
Q

What is the problem with serial data transmission?

A

It can be quite slow, that’s why it isn’t used for short distances

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10
Q

What is Parallel Data Transmission?

A

It i when several bits of data (ussually 1 byte) are sent down several wires or channels at the same time; one wire or channel is used to transmit each bit.

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11
Q

What distance is parralel data transmission most effective?

A

Over short distances, but over long distances the data can be skewes - which means the data will no longer be synchronised

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12
Q

What is a common use for serial data transmission?

A

USB (Universal serial bus)

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13
Q

What is parralel data transmission used for?

A

It is used in the internal electronics of the computer system. The pathways between the CPU and the memory all use this method of data transmission. Integrated circuits, buses and other internal components all use parralel data transmission because of the need for high speed data transmission

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14
Q

What is Asynchronous Data Transmission?

A

It refers to data being transmitted in an agreed bit pattern.

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15
Q

What is the use for start and stop bits?

A

The receiver of the data knows when the data starts and ends, which prevents data becoming mixed up. Without these bits it would impossible to split groups of data as they arrive.

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16
Q

What is Synchronous Data Transmission?

A

It is a continuous stream of data (unlike asynchronous data which is sent in groups). This data is accompanied by timing singals generated by an internal clock, which ensures that the sender and the reciever are synchronised with each other.

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17
Q

Why is timing so important in Synchronous Data Transmission?

A

The timing must be accurate seeming there are no control bits in this type of data.

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18
Q

Is Synchronous or Ansynchronous data transmission faster?

A

Synchronous

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19
Q

What does USB stand for?

A

Universal Serial Bus

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20
Q

Does USB use Ansychronous or Synchronous?

A

Ansychronous

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21
Q

What does the USB cable consist of?

A
  1. A four-wire shielded cable
  2. Two of the wires are used for power and the earth
  3. Two of the wires are used in the data transmission
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22
Q

What happens when you plug the usb in your device?

A
  1. The computer automatically detects that a device is present (due to a small change in the voltage level on the data signal wires in the cable)
  2. The devic is automatically recognised, and the appropriate device driver is loaded up so that computer and the usb can communicate effectively
  3. If a new device is detected, the computerwill look for the device driver which matches the device; if this is not available, the user is promted to donwload the appropriate software
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23
Q

What are the four methods of error-checking?

A
  1. Parity checking
  2. Automatic repeat request
  3. Checksum
  4. Echo checking
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24
Q

In parity checking what is added to a byte of data?

A

A parity bit

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25
Q

What does Even parity do?

A

It checks if there’s an even number of 1s, if it isn’t even then a 1 is added and if it is then a 0 is added.

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26
Q

What does Odd parity do?

A

It checks if there’s an odd number of 1s, if it isn’t odd then a 1 is added to the piece of data vice verca.

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27
Q

How does Parity Checking detect an error?

A

If a byte has been transmitted from ‘A’ to ‘B’,
and an even parity has been agreed on, an error would be flagged if the byte now had an odd number of 1 bits at the reciever end.

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28
Q

What happens before the data is transferred in parity checking?

A

Before data is transferred, an agreement is made between sender and reciever regarding which of the two types of parity are used. This is an example of Protocol

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29
Q

What is the problem with parity checking?

A

Even if an error is detected, you can’t determine which bit is in error

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30
Q

What is away around the problem with parity checking?

A

Seeming you can’t tell which bit is in error, you use a parity block.

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31
Q

What is a parity block?

A

In this methd, a block of data is sent and the number of 1-bits are totalled horizontally and vertically.

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32
Q

Using a parity block how can you determine where the error is?

A

With the intersection of the errored row and column, that is the part of the data that need to be changed, so if the data on the block shows 1 then change it to 0 vice verca.

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33
Q

Even with parity blocks what is the problem with parity checking?

A

The data may have been scrambled so there are the same amount of 1s and 0s but just in the wrong pattern meaning that they pass the parity check but mean a totally different thing. So, you would need to use a different form of error checking

34
Q

What does ARQ stand for?

A

Automatic repeat request

35
Q

What does Automatic repeat request use?

A

I uses an Acenknowledgement (a message sent by the reciever indicating that the data has been recieved correctly). It also uses TImeout (this is the time allowed to elapse before an acknowledgement is recieved)

36
Q

What does Automatic repeat request use?

A

I uses an Acenknowledgement (a message sent by the reciever indicating that the data has been recieved correctly). It also uses TImeout (this is the time allowed to elapse before an acknowledgement is recieved)

37
Q

What happens if the Acknowledgement isn’t sent before the timeout occurs?

A

Then the message is sent back automatically

38
Q

What is checksum?

A

It is a calculation made by the sender and reciever, if the calculation of the data (checksum) done by the reciever is different then the data has to be resent.

39
Q

What is the maximum value of a block of data that is 1 byte in length (checksum)

A

255

40
Q

What happens if the sume of the <= 255

A

Then the value is the checksum

41
Q

What happens if the value is >255

A

Then the checksum is found using this simple algorithm: Divide the sum(X) of the bytes by 256, then round down to the nearest whole number (Y), Z = Y*256, Calculate the differentce (X-Z), This value gives the checksum.

42
Q

Give an example of the simple algorithm used in checksum

A

X = 1185
1. 1185/256 = 4.629
2. Round down Y=4
3. Multiply by 256 Z = Y*256 = 1024
4. The difference (X-Z), (1185 - 1024) = 161
5. Checksum = 161

43
Q

What happens before and after the data is sent (checksum)?

A

The checksum is calculated then transmited with the block of data, the reciever calculates the checksum and compares it with the value sent with the block of data, if it doesn’t match then the data is resent

44
Q

What happens with echo check?

A

When data is sent to another device, this data is sent back again to the sender. The sender compares the two sets of data to check if any errors occur.

45
Q

What is the disadvantage with echo check?

A

If there is an error there is no way of telling if the error occured when sending it to the reciever or the reciever to the sender.

46
Q

What is the internet?

A

A globl communication infrastructure that links together computers and networks.
A collection of connected internent

47
Q

What does ISP stand for?

A

Internet Service Provider

48
Q

What is an Internet Service Provider?

A

The companies that provide the user with access to the internet. Amonthly fee is usually charged for this service. The ISP wukk set up a user account which will countain a username and password; most ISP’s also give the user an email address

49
Q

What does Ip stand for?

A

Internet Protocol Adress

50
Q

What is an ip?

A

Each device on the internet is given a unique address know as the IP. It is unique to a specific to the internet or a local network .This is a 32-bit number which i usually written as: 109.108.152.1.

51
Q

What does MAC stand for

A

Media access control

52
Q

What is a MAC address?

A

It is a unique number that identifies a device connected to the internet.

53
Q

What is the difference between MAC addresses and IP addresses?

A

The IP address gives the location of a device on the internet, whereas the MAC addres indentifies the device connected to the internet. A good way of thinking of it is the IP is the location of the house (zip code) whereas the MAC is used to identify each person living in the house. It is possible to move house so IP can change but MAc doesn’t.

54
Q

In HTML what is structure and Presentation?

A

Sturcture: The essential part of HTML document; it includes the sematics and sturctural markup of the document.
Presentation: The style of the document; how the document will look for example.

55
Q

What should an author of a HTML file have?

A

The actuall code and seperate the CSS (Cascading Style sheet) file.

56
Q

What is a CSS file in HTML?

A

The CSS file will contain everything to control the actual presentation of the web page.

57
Q

What does HTTP stand for?

A

Hypertext-transfer-protocol

58
Q

What is HTTP?

A

It is a set of rules that must be obeyed when transferring files across the internet. When some form of security is used, then this changes to HTTPS.

59
Q

What does HTTPS stand for?

A

Hypertext-transfer-protocol-secure

60
Q

What is a web browser?

A

A web browser is software that allows a user to display a web page on ther computer screen.

61
Q

What do Web Browsers do?

A

They translate HTML code from websites and show the results of the translation.

62
Q

What features do Web Browsr share?

A
  1. They have a home page
  2. They have the ability to store a user’s favourite websites / pages
  3. They keep a history of the websites visited by the user
  4. They give the ability to go backward and forward to websites opened.
63
Q

What does URL stand for?

A

Uniform rescourse locator

64
Q

Break down HTTP://www.hodderededucation.co.uk/igcse_computer_science

A

HTTP is the protocol used
www.hodderededucation.co.uk is the web server’s name
igcse_computer_science is the file name

65
Q

What is a server?

A

A computer which provides the admin tools and resources which are shared by all computers on the network

66
Q

What kind of servers are there?

A

File server, Domain controller server, Email server, etc

67
Q

How does a client access apps and resources from the server?

A
  1. Client makes request
    2.Server processes request
  2. Server sends results back to client
68
Q

What are networks?

A

Connected computers or devices

69
Q

What are routers used for?

A

Used on packet switching networks
Each packet is given a destination address
Each device ginven an address

70
Q

What are Gateways?

A

Device that lets two networks, that use different protocols (languages), to communicate with eachother

71
Q

What are Dedicated lines

A

They are bought from the telephone company.
They have consisten data transfer speeds
High and consisten bandwidth
High data throughput and fast upload speeds
They allow for phone calls and video withoud buffering

72
Q

What main cables are there?

A

Copper and Coaxial. Uses iclude radio or tv computer network conections cable tv connections

73
Q

What are Fibre Optic Cables

A

Glass tubes
Light is transmitted down them
Used for Telephone comms, Internet comms, Networking

74
Q

What are USB-C cables?

A

They provide USB data transmission, but at the higher rates. Can be connected both ways up
USB-C can carry much more powern allowing larger powered without external power sources

75
Q

What are viruses and give an example

A

They are programs downloaded onto a users computer without them knowing about it.
STUXNET

76
Q

What is a firewall?

A

A system that protects unauthorised access to or from a computer or network. It monitors tansmissions coming into and out of a computer or network.

77
Q

What is a web Server?

A

A computer that hosts webpages
Can handle lots of requests
Data is sent using packets
Email, gaming, data storage
Can use just about anything as a server
DoS attacks - Lots of requests to a specific site in a very short period of time

78
Q

What doe TCP stand for?

A

Transmission Control Protocol

79
Q

What are Cookies?

A

Small pieces of data that are downloaded when you visit a website. Tracks if you have logged onto secure websites

80
Q

What is the difference between HTTP and HTTPS

A

HTTPS uses TLS to encrypt

Computer science (4 decks)

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