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Computer Science > 1.3 Exchanging Data > Flashcards

1.3 Exchanging Data Flashcards

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1
Q

What does compression do?

A

Reduce requirements on file storage

Reduce download times

Make best use of bandwidth

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2
Q

What are the two types of compression?

A

Lossy

Lossless

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3
Q

What is lossy compression?

A

Type of compression that removes data to reduce the file size, stripping out the least important data

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4
Q

Can the original be recreated in lossy compression?

A

No because detail is removed

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5
Q

What is lossy compression typically used for?

A

Multimedia files

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6
Q

What are examples of lossy compression?

A

JPEG

MP3

MPEG

GIF

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7
Q

What is lossless compression?

A

Type of compression to reduce the file size where data is not lost

Typically less effective at reducing file size

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8
Q

Can the original be recreated with lossless compression?

A

Yes

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9
Q

What is lossless compression used for?

A

Essential for file types like computer programs

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10
Q

What are some examples of lossless compression?

A

ZIP

PNG

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11
Q

What are two methods of lossless compression?

A

Run Length Encoding (RLE)

Dictionary Based Encoding

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12
Q

How does RLE work?

A

Finds runs of repeated binary pattern and replaces them with a single instance of the pattern and a number that specifies how many times the pattern is repeated

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13
Q

Is a real-life image suitable for RLE?

A

No because the image has too much detail

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14
Q

Does RLE have to be used on image data?

A

No

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15
Q

How are runs typically encoded with RLE?

A

Two bytes

One byte for the pattern, one byte for the number of repetitions in a run

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16
Q

What is a disadvantage of RLE?

A

Only achieves significant reductions in file size if there are long runs of data

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17
Q

How does dictionary based encoding work?

A

Searching for matches between the text to be compressed and a set of strings contained in a data structure (dictionary) maintained by the coder

When encoder finds a match, substitutes a reference to the string’s position in the data dictionary

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18
Q

What is plaintext?

A

The data that is being stored or is going to be transferred

The data to be encrypted

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19
Q

What is ciphertext?

A

The encrypted text

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20
Q

What is a cipher?

A

Algorithm used to encrypt the data

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21
Q

What is a key?

A

Data that is used within the cipher

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22
Q

What is decryption?

A

Converting the ciphertext back into the original plaintext

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23
Q

What is encryption?

A

Process of converting a message into plaintext into ciphertext using a cipher so it cannot be understood if the message is intercepted

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24
Q

How does symmetric encryption work?

A

Sender and receiver use the same key to encrypt and decrypt data

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25
Q

Is symmetric encryption faster than asymmetric encryption?

A

Yes because it uses less complex mathematical operations

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26
Q

What is a disadvantage of symmetric encryption?

A

Key has to be exchanged across a network, which could be intercepted by an attacker

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27
Q

What is asymmetric encryption?

A

A different key is used to encrypt and decrypt the data (public and private key pair)

Public key used to encrypt the message, which can be known by anyone, but cannot be used to decrypt the message

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28
Q

How does asymmetric encryption work?

A

Public key is used to encrypt the message, which can be known to anyone. Therefore recipient can send their public key to a device that wants to send them data, which is used to encrypt the data

Public key CANNOT be used to decrypt the message so can therefore be sent over the internet

Private key is NOT transferred over the internet and is only known by the recipient and is used to decrypt the message

Two keys cannot be used to determine the other and together are known as a key pair

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29
Q

What are the problems with asymmetric encryption?

A

Public key is widely known by any device so any device can use it to encrypt the data and pretend to be the sender (useful, therefore, to authenticate)

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30
Q

How does authentication work?

A

Sender encrypts the data using their PRIVATE key then encrypts that ciphertext using the recipients PUBLIC key

Data is then sent

Recipient decrypts the ciphertext using their PRIVATE key, leaving the ciphertext

Recipient decrypts the data using the senders PUBLIC key

Data can now be read and transfer has been authenticated

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31
Q

What does SSL stand for?

A

Secure Sockets Layer

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32
Q

What is the SSL handshake?

A

HTTPS protocol encrypts communication between web browser and web server in both directions

Creates encrypted link between server and a client

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33
Q

How does the SSL handshake work?

A

Browser sends HTTPS request to web server it wants to communicate with

Web server transfer back a digital certificate with its public key

Symmetric session key generated on browser and encrypted using the key received

This key sent to the server

Server retrieves symmetric session key by decrypting the data received using its private key

Symmetric session key is key that will be used to encrypt and decrypt data during the transfer

Symmetric session key cannot be decrypted during transfer by anyone that intercepts it

Allows for fast data transfer over the internet

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34
Q

What is a hash function?

A

Generates an output (hash value) for an input (key), which is always the same for each key

With the key, you can calculate the hash value

With a hash value, you can’t calculate the key

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35
Q

What is a hash value?

A

A string of characters of a fixed size which is different for each key

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36
Q

What is a collision?

A

When two different keys produce the same hash value

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37
Q

How can hashing algorithms be used for integrity validation?

A

Generate a hash called a checksum that’s appended to the end of the message being set

Makes sure that the message has been issued by the right person and not tampered with before reaching its destination

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38
Q

How can hashing algorithms be used?

A

Barcodes and ISBN book numbers use a similar approach called check digit

CSV number of a credit card is form of checksum used to validate credit cards

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39
Q

What is a database?

A

Persistent organised store of data

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40
Q

What does a persistent database mean?

A

Data stored on secondary storage device and is non-volatile

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41
Q

What does an organised database mean?

A

Data organised into records and fields

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42
Q

What is a relational database?

A

A database with multiple tables linked by primary key-foreign key relationships

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43
Q

What is a flat file database?

A

A database with a single table with information about a single entity

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44
Q

What is a primary key?

A

Unique identifier for each record in a table

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45
Q

What is a foreign key?

A

Non-primary key field in a table that links to primary key field in another table

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46
Q

What is an attribute in a database?

A

The different fields within a database

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47
Q

What is a record in a database?

A

A row within a database

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48
Q

What is a composite key?

A

Use multiple (two or more) fields to create a unique identifier for a record

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49
Q

What is data integrity?

A

The accuracy of the data within the database

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50
Q

What is data redundancy?

A

Duplicating data in multiple places in the database

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51
Q

What is a secondary key?

A

A field that will be used to search the table often

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52
Q

What is an entity?

A

Category of object, person, event or thing of interest about which data needs to be recorded

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53
Q

What is SQL?

A

Structured Query Language

Standard language used to query a relational database

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54
Q

How do you SELECT from a database?

A

SELECT field1, field2
FROM table_name
WHERE filtering criteria
ORDER BY fields ASC/DESC

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55
Q

How do you INSERT INTO a database?

A

INSERT INTO table_name (field1, field2)
VALUES (value1, value2)

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56
Q

How do you UPDATE a database?

A

UPDATE table_name
SET field1 = value1, field2 = value2
WHERE filtering criteria

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57
Q

How do you DELETE from a database?

A

DELETE
FROM table_name
WHERE filtering criteria

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58
Q

How do you create a table in a database?

A

CREATE TABLE IF NOT EXISTS table_name
(field1 TEXT NOT NULL PRIMARY KEY,
field2 INTEGER NOT NULL, field3 FLOAT)

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59
Q

How do you create a table with a foreign key and a composite key? (using the example of student, course, enrolled)

A

CREATE TABLE IF NOT EXISTS enrolled_table
(date_started TEXT NOT NULL, student_id INTEGER NOT NULL, course_code INTEGER NOT NULL,
PRIMARY KEY(student_id, course_code),
FOREIGN KEY(student_id) REFERENCES student_table(student_id) ON DELETE CASCADE,
FOREIGN KEY(course_code) REFERENCES course_table(course_code) ON DELETE CASCADE)

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60
Q

How do you SELECT data from three tables? (using an example of appointment, doctor, patient)

A

SELECT patient_table.firstname, patient_table.surname, patient_table.contact, doctor_table.firstname, doctor_table.surname
FROM appointment_table
JOIN patient_table
ON patient_table.patient_id = appointment_table.patient_id
JOIN doctor_table
ON doctor_table.doctor_id = appointment_table.doctor_id
WHERE appointment_table.appointment_id = 1

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61
Q

What are the different relationships between two entities?

A

One-to-one

One-to-many/many-to-one

Many-to-many

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62
Q

What is an example of a one-to-one relationship?

A

Husband — Wife

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63
Q

What is an example of a one-to-many relationship?

A

Mother —<- Child

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64
Q

What is many-to-many relationship?

A

Not allowed

Have to be split up using additional entity

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65
Q

What does a split up many-to-many relationship look like?

A

Patient —<- Appointment ->— Doctor

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66
Q

Are entities singular or plural?

A

Singular

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67
Q

What does ERD stand for?

A

Entity Relationship Diagram

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68
Q

What is an ERD?

A

Represents all the entities/tables with their attributes/fields and the relationships between entities

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69
Q

What should a structure of a database enable a user to do?

A

Enable a user to enter as many or as few records as required so make sure there are no many-to-many relationships

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70
Q

What is normalisation?

A

Splitting up data in databases and arranging the data to be in 1st, 2nd and 3rd normal form

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71
Q

What is the purpose of normalisation?

A

To design a database more efficient and easier to maintain

Removing unneeded and redundant data - as redundant data takes up storage and may make searching longer

Organising the data in a logical structure so all data in tables is related

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72
Q

What is 1st normal form?

A

Each data item cannot be broken down any further (ATOMIC)

Each row is unique (has a primary key)

Should be no repeating groups of attributes

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73
Q

What is 2nd normal form?

A

Be in 1NF

Each non-key attributes must depend fully on the primary key (depend on each part of the primary key) - NO PARTIAL DEPENDENCIES

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74
Q

What is 3rd normal form?

A

Be in 2NF

All non-primary key attributes must be dependent on only the primary key (must not be dependent on any other non-key attributes)

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75
Q

What is data integrity?

A

Accuracy and reliability of data

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76
Q

What is data redundancy?

A

Where data is stored multiple times

May happen in a flat file database but shouldn’t happen in a relational database that’s correctly designed

More redundant data had, more memory used and more chance there is a lack of data integrity

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77
Q

What is referential integrity?

A

Adds constraints to the data updated, deleted and entered into a relational database to ensure the data is as accurate as possible

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78
Q

How can referential integrity affect when data is entered into a database?

A

Could not add a record with a foreign key where the primary key it links to doesn’t have a record with that

pragma foreign_keys = ON

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79
Q

How does referential integrity affect when data is deleted from a database?

A

Deletes all records with that primary key

ON DELETE CASCADE

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80
Q

How does referential integrity affect when a primary key of a record is updated in a database?

A

Changes all instances of that primary key in all tables

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81
Q

What are the problems with carrying out operations on a database?

A

Multiple users trying to change data at the same time

A transaction being part completed by not fully completed

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82
Q

What is ACID?

A

Rules that should be followed to maintain consistency within a database

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83
Q

What does ACID stand for?

A

Atomicity

Consistency

Isolation

Durability

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84
Q

What is atomicity?

A

All or nothing

Requires that a transaction is processed in its entirety or not at all

In any situation, including power cuts or hard disk crashes, it is not possible to process only partly of a transaction

If any part of the transaction fails, roll it back and don’t complete any of it

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85
Q

What is an example of atomicity?

A

Bank transfers

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86
Q

What is consistency?

A

Ensures that no transaction can violate any of the defined validation rules

Referential integrity, specified when the database is set up, will always be upheld

Cannot process a transaction that would break the rules we’ve set up on the database

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87
Q

What is an example of consistency?

A

Referential integrity

Validation
- length check
- NOT NULL
- range check
- type check
- format check

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88
Q

What is isolation?

A

Ensures that concurrent execution of transaction leads to the same result as if transactions were processed one after the other

Crucial in a multi-user database

IF PROCESSING INSTRUCTIONS CONCURRENCTLY, THE OUTCOME SHOULD BE THE SAME IF WE WERE PROCESSINGN THEM SEQUENTIALLY

Record locking and time stamping

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89
Q

What is an example of isolation?

A

If two people are booking tickets for a show at the same time, the outcome should be the same if they were doing it one after another

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90
Q

What is record locking?

A

Prevents simultaneous access to records in a database in order to prevent updates being lost or inconsistences in the data arriving

Using record locking, a record is locked when a user retrieves it for editing or updating

Anyone else attempting to retrieve it is denied access until the transaction is completed or cancelled

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91
Q

What is deadlock?

A

Problem with record locking

If two users are attempting to update two records, a situation can arise in which neither can proceed

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92
Q

What is serialisation?

A

Ensures transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost

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93
Q

What is timestamp ordering?

A

Serialisation technique

Every record in the database has a READ TIMESTAMP and a WRITE TIMESTAMP

These are updated whenever an object is read or written

When a user tries to save an update, if the READ TIMESTAMP is not the same as it was when they started the transaction, the DBMS knows another user has accessed the same object

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94
Q

What is durability?

A

ENSURES THAT ONCE A TRANSACTION HAS BEEN COMMITTED, IT WILL REMAIN SO, EVEN IN THE EVENT OF A POWER CUT

As each part of a transaction is completed, it is held in a buffer on a disk until all elements of the transaction are completed

Only then will the changes to the database tables be made

Ensures that if the user is told a transaction is successful then the changes will actually be committed to the database

Redundancy

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95
Q

What is redundancy?

A

Many organisations have built-in redundancy in their computer systems

Duplicate hardware, located in different geographical areas, mirrors every transaction that takes place on the main system

If this fails, backup system automatically takes over

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96
Q

What are some examples of redundancy?

A

RAID setup mirroring data

Having redundant backup hardware

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97
Q

What does DBMS stand for?

A

Database Management System

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98
Q

What is the DBMS?

A

Software application that allows a database administrator to maintain one or more relational databases

Hides the complexity of the physical implements, allowing the administrator to define the database structures at a conceptual or logical level

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99
Q

What are examples of methods of capturing data?

A

Input forms

Barcodes

Magnetic strip readers

OMR (Optical Mark Reader)

ANPR (Automatic Number Plate Recognition)

OCR (Optical Character Recognition)

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100
Q

Are input forms automatic or manual?

A

Manual

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101
Q

What are the benefits of input forms?

A

Can use drop-down lists, checkboxes etc can be used to reduce data entry errors

If well designed can be clear to the end user what data they are expected to enter

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102
Q

What are the drawbacks of input forms?

A

Can be slow to enter large amounts of data

If poorly designed may result in the end user know being clear on what is expected

If suitable validation not in place then error in data can occur

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103
Q

Are barcodes automatic or manual?

A

Automatic

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104
Q

What can barcodes be used for?

A

Shopping items

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105
Q

What are the benefits of barcodes?

A

Faster and easier to ring up items

More accurate

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106
Q

What are the drawbacks of barcodes?

A

No read/write capabilities

Can be slow as have to scan individually

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107
Q

Are magnetic strip readers automatic or manual?

A

Automatic

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108
Q

What are the uses of magnetic strip readers?

A

Bank cards

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109
Q

What are the benefits of magnetic strip readers?

A

Low costs

Rewriteable data

Quick and easy to use

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110
Q

What are the drawbacks of magnetic strip readers?

A

Tape can be damaged

Special equipment has to purchased

Limited storage capacity

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111
Q

Are OMRs automatic or manual?

A

Automatic

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112
Q

What are the uses of OMRs?

A

Multiple choice tests

Lottery tickets

Exam questions

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113
Q

What are the benefits of OMRs?

A

Fast and efficient way of collecting data and inputting it into a database

Significantly reduces human error

Accurate

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114
Q

What are the drawbacks of OMRs?

A

If marks aren’t dark enough or in the right space, won’t be read correctly

Not suitable for text input

Needs the answers on a prepared form

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115
Q

Are ANPRs automatic or manual?

A

Automatic

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116
Q

What are the uses of ANPRs?

A

Car parks

Toll gates

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117
Q

What are the benefits of ANPRs?

A

Efficient and reliable

Enhanced security

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118
Q

What are the drawbacks of ANPRs?

A

Privacy concerns

Bad weather can affect accuracy

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119
Q

Are OCRs automatic or manual?

A

Automatic

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120
Q

What are the uses of OCRs?

A

Reading postcodes and routine mail

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121
Q

What are the benefits of OCRs?

A

Automatically reads texts by interpreting shape of letters

Fast and efficient

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122
Q

What are the drawbacks for OCRs?

A

Doesn’t work as well with handwriting

Sometimes inaccurate

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123
Q

What does JSON stand for?

A

JavaScript Object Notation

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124
Q

What is JSON?

A

Open source and language independent

Text-based

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125
Q

What are the two structures of JSON?

A

An ordered list of values

A collection of name/value pairs

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126
Q

What are the advantages of JSON?

A

Easy for humans to understand

Easy for computers to parse so quick to process

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127
Q

What are the disadvantages of JSON?

A

Supports limited types of data

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128
Q

What does XML stand for?

A

Extensible Markup Language

129
Q

What is XML?

A

Allows a schema to be written (type of metadata that specifies and constrains the structure of the XML file)

130
Q

What is a schema?

A

Defines elements and attributes that must be included in the file

Data types, attributes and order

131
Q

What is a standalone computer?

A

A computer that’s unable to communicate with other devices

132
Q

What is a computer network?

A

Joining two or more computers together so they can communicate, share resources or be centrally managed

133
Q

What are the advantages of networks?

A

Computers can share resources such as storage, and peripherals

Data can be shared between computers

Enables different types of computers to communicate (phones, tablets, laptops, etc)

Allows for communication (VOIP, email and video conferencing)

Backing up data can be completed centrally

134
Q

What are the disadvantages of networks?

A

More difficult to keep secure from hackers

Expensive to set up

Need a network manage in place and if this person is not good, network may not be good

If part of network breaks, may affect all computer

Viruses can spread easily

As amount of data/usage increases, performance may degrade

135
Q

What does LAN stand for?

A

Local Area Network

136
Q

What is a LAN?

A

Devices in network in same geographical location

Doesn’t make use of 3rd party infrastructure

137
Q

What does WAN stand for?

A

Wide Area Network

138
Q

What is a WAN?

A

Devices on network connected across wide geographical location

Makes use of 3rd party infrastructure

Two or more LANs connected together

139
Q

What is a standard?

A

Set of specifications for hardware or software agreed upon by academic and industry contributes that make it possible for many manufacturers to create products that are compatible with one another

140
Q

What is a de jure standard?

A

Standards set by official organisation

141
Q

What is a de facto standard?

A

Standards unofficially set, established by common use

142
Q

What are the advantages of standards?

A

Prevent confusion between end-user and manufacturer

Makes it easier for people to build software and programs that work on different systems in different countries

Makes programs/products more widely compatible

Easier to work with other people

143
Q

What are some common standards?

A

MP3 - file format for audio files supported by most media-playing software

HTML - markup language for creating websites

Unicode - form of representing text

144
Q

What is a network protocol?

A

Set of rules or standards that all devices need to follow when transferring data on a network

145
Q

What happens if devices don’t follow the same protocols?

A

They won’t be able to communicate

146
Q

What does TCP stand for?

A

Transmission Control Protocol

147
Q

What does TCP do?

A

Splits data up into packets

Orders data packets

Adds error-checking before sent

Checks for errors when data packets are received

Reassembles packets into correct order when received

148
Q

What does IP stand for?

A

Internet Protocol

149
Q

What does IP do?

A

Directs data packets to the correct destination using the IP address

150
Q

What does FTP stand for?

A

File Transfer Protocol

151
Q

What does FTP do?

A

Used to transfer files between computers

Operates on the application layer of the TCP/IP stack

Used when uploading and downloading files from the internet

152
Q

What does SMTP stand for?

A

Simple Mail Transfer Protocol

153
Q

What does SMTP do?

A

Used to send emails between servers

154
Q

What does POP3 stand for?

A

Post Office Protocol 3

155
Q

What does POP3 do?

A

Used to receive emails

Emails REMOVED from the server when they are read on a device

156
Q

What does HTTP stand for?

A

Hyper Text Transfer Protocol

157
Q

What does HTTP do?

A

Used to transmit web pages

158
Q

What does HTTPS stand for?

A

Hyper Text Transfer Protocol Secure

159
Q

What does HTTPS do?

A

Used to transmit web pages

Data encrypted

160
Q

What does IMAP stand for?

A

Internet Message Access Protocol

161
Q

What does IMAP do?

A

Used to receive and access stored emails

Emails REMAIN ON the server when read on a device

Suit emails read on multiple devices

More advanced protocol than POP

162
Q

What is a single stack protocol?

A

Single protocol that takes data from one computer application and sends it to an application on another computer

Inflexible as any changes require changing entire application and protocol software

163
Q

Where are layered protocol stacks used?

A

Networking

164
Q

What are layered protocol stacks?

A

Each level of the stack perform a particular function and communicates with the levels above and below it

Data is passed down the stack, transferred then passed up the stack

165
Q

What is the TCP/IP stack?

A

Collection of protocols used to send data on an IP network

166
Q

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

A

Application
↓ ↑
Transport
↓ ↑
Internet
↓ ↑
Link

167
Q

What are the protocols used on the application layer?

A

Web browser - HTTP, HTTPS

Emails - POP3, IMAP, SMTP

Transferring files - FTP

168
Q

What are the protocols used on the transport layer?

A

TCP - establishes end-to-end connection with recipient

UDP - faster connectionless protocol

169
Q

What protocols are used on the internet layer?

A

IP

170
Q

What protocols are used on the link layer?

A

Wi-Fi

Ethernet

171
Q

What happens in the down application layer?

A

Uses protocols relating to the application being used to transmit data

172
Q

What happens on the down transport layer?

A

Data split into packets

Each packet given a number (the order) and a port number to ensure its handled by the correct application when received

Add data to be able to check for errors

173
Q

What happens on the down internet layer?

A

Adds sender’s and recipient’s IP address to packet

Routers operate on this layer (look at IP address and move data one hop closer)

Addition of IP address to port numbers form a socket (device and application that will use it)

174
Q

What happens on the down link layer?

A

Physical connection between devices

Adds MAC address to data packet which identifies correct piece of hardware

MAC address points to next router whereas IP address remains the destination address

175
Q

What happens in the up link layer?

A

Physically sends the data packets

176
Q

What happens in the up internet layer?

A

Checks if destination is reached

177
Q

What happens in the up transport layer?

A

Checks for errors

Reorders packets

178
Q

What happens on the up application layer?

A

Depends on task being performed

Displays data, downloads files

179
Q

What are the layers of the OSI model?

A

Application

Presentation

Session

Transport

Network

Data link

Physical

180
Q

What is encapsulation (in relation to the TCP/IP stack)?

A

As data sent between layers in TCP/IP stack, additional data is added onto the packet

May be result of processing or encrypting data

Added then the new data packet is sent to the next layer

When data received, reverse happens and data packets are unpaked

181
Q

How are packets routed on a LAN?

A

Switch using MAC address

182
Q

How are packets routed on a WAN?

A

Router using IP address

183
Q

What is an IP address?

A

Unique address

184
Q

What is a static IP address?

A

Cannot change

185
Q

What is a dynamic IP address?

A

Assigned by network they connect to so change over time

186
Q

What does DHCP stand for?

A

Dynamic Host Configuration Protocol

187
Q

What does a DHCP do?

A

Allocates IP address to device when it connects to the Internet

188
Q

What is circuit switching?

A

Reserve direct path/connection between devices

Data packets travel along the SAME path (IP)

Data packets travel in their CORRECT ORDER (TCP)

No other data can be sent until all packets have been sent

189
Q

What are the advantages of circuit switching?

A

Quicker to transfer data

190
Q

What are the disadvantages of circuit switching?

A

Less secure as data all travelling together

Ties up the network cables for other data

191
Q

What is packet switching?

A

Data travels along DIFFERENT paths (IP)

Router determines these routes

Data packets PUT BACK into correct order when they reach the destination (TCP)

192
Q

When is packet switching used?

A

Internet traffic

193
Q

What are the advantages of packet switching?

A

More secure as data not all travelling together

Does not tie up the network cables for other data

194
Q

What are the disadvantages of packet switching?

A

Slower than circuit switching

195
Q

What are the factors determining the different routes that a packet may take?

A

Amount of traffic

Fault in network

196
Q

What are the steps for packet switching?

A
  1. data split into data packets
  2. each packet includes a header with the IP address of the source, IP address of the destination and position of the packet
  3. packets sent across the network and redirected from one router to another till they reach their destination
  4. receiving device checks if all packets have arrived
  5. if packet missing or corrupted, receiving device automatically asks sending device to resend lost packet
  6. once all packets arrived, receiving computer rearranges them in correct order (sequencing)
  7. receiving computer then processes the data
197
Q

What does URL stand for?

A

Uniform Resource Locator

198
Q

What is a URL?

A

Address of an internet resource

199
Q

What is a domain name?

A

Identifies area/domain internet resources reside in

Has IP address

In a hierarchy of small domains which follow rules of the DNS

200
Q

What does DNS stand for?

A

Domain Name System

201
Q

What does a DNS do?

A

Stores all IP addresses paired with domain name

202
Q

What does TLD stand for?

A

Top Level Domain

203
Q

What does a TLD hold?

A

.org

.com

.co.uk

204
Q

What are the stages of loading a website?

A
  1. browser’s cache checked, if copy found, it’s quickly loaded
  2. client’s browser sends request to DNS resolver (recursive name server) and the location of this is usually set by ISP, and it requests IP address of URL entered
  3. recursive name server checks its cache to see if has copy of IP address for URL received
  4. if not, root server asked for address of relevant TLD server
  5. TLD server asked for and returns address of relevant authoritative name server
  6. authoritative name server asked for IP address for requested web server
  7. IP address returned to client and stored on recursive name server
  8. if IP address not found, error message returned (404 error)
205
Q

What are the two models used to network computers?

A

Client server

Peer-to-peer

206
Q

What is a server?

A

A computer dedicated to providing some kind of service to users across a network

207
Q

What is a client server model?

A

Client requests information from a dedicated server and server waits for requests from clients to provide its service

Uses one or more servers to supply resources to clients on the network

208
Q

What are the characteristics of a client server model?

A

Data on the network can be easily backed up

Network can be centrally managed

If the server breaks, all of the network will stop operating

Security can be done centrally and therefore one point to stop viruses from entering the network

Expensive to purchase hardware for this type of network

Usually requires a network manager or someone with experience

209
Q

What is a peer-to-peer model?

A

When two or more PCs are connected and share resources without going through a separate server

210
Q

What are the characteristics of a peer-to-peer model?

A

Files are stored on the individual machines

All print requests handled by individual computer

If one computer fails, it will not disrupt any other part of the network, it just means that those files aren’t available to other users at that time

Access rights are governed by setting sharing permissions on individual machines

No need for a network OS

Easier to set up this type of network

All nodes on the network are equal

211
Q

What are the types of server?

A

Print server

Web server

Mail server

File server

Backup server

Application server

Proxy server

212
Q

What does a print server do?

A

Schedules print jobs sent to it by device on the network

213
Q

What does a web server do?

A

Hosts websites on the internet

214
Q

What does a mail server do?

A

Stores emails ready to be sent to a user’s inbox when they access their account

215
Q

What does a file server do?

A

Stores user’s documents which are then sent to user when they access file explorer

216
Q

What does a backup server do?

A

Stores a copy of files on the network so that if files are deleted by mistake or a virus then the user’s files can be recovered

217
Q

What does an application server do?

A

Has all applications and software upgrade files so that they can be centrally managed and applied to all workstations that connect to server to recover and install latest upgrades when relevant

Applications can sometimes run directly from server, reducing need to install on each workstation

218
Q

What does a proxy server do?

A

Functions as an intermediatory between client and server

Monitors access to internet and applies necessary restrictions and filters to allow or block access to specific websites

219
Q

What is a gateway?

A

Devices that can be used to transfer data between dissimilar networks (use different protocols)

220
Q

What is a router?

A

Used to connect a LAN to a WAN and therefore used to connect to an external network

Scans data packets and redirects them towards the LAN or towards other routers depending on their origin and their destination

221
Q

What is a switch?

A

Used to connect multiple devices together in a star topology

Has number of Ethernet ports to connect to other devices (workstations, servers, WAPs, other hubs or switches, firewall, router)

Remembers the addresses of the devices connected to it

When directing data packets between devices, packets can be sent directly to intended recipients

222
Q

What type of network is a switch suitable for?

A

Larger networks

223
Q

What is a hub?

A

Used to connect multiple devices together in a star topology

Has number of Ethernet ports to connect to other devices (workstations, servers, WAPs, other hubs or switches, firewall, router)

Doesn’t remember the addresses of the devices connected to it

When directing data packets between devices, packets sent to all connected devices and recipient of packet then determines if it was the intended recipient

224
Q

What type of a network is a hub suitable for?

A

Smaller networks as there can be more data collisions

225
Q

What does WAP stand for?

A

Wireless Access Point

226
Q

What is a WAP?

A

Used to connect multiple devices together without using wires

Provides WiFi access to a network

Allows mobile phones and laptops to connect to a network without using wires

Fairly small coverage area (10-30m) so several may be required to cover large building

227
Q

What does NIC stand for?

A

Network Interface Card

228
Q

What is a NIC

A

To connect workstation to LAN, workstation needs to be equipped with this

Has wired connection (Ethernet port) and/or wireless connection to connect wirelessly to WAP

229
Q

What is a modem?

A

Used to convert data from digital signal (used within LAN) to analogue signal (one that can be sent along external cable)

Process called modulation and demodulation

230
Q

What is transmission media?

A

Method a network uses to be able to transfer data

Provides wired connection and some wireless connection

231
Q

What is a wired connection?

A

Where it needs to be physically plugged in

232
Q

What are examples of transmission media?

A

UTP (Unshielded Twisted Pair)

Satellite

Fibre optic cable

Coaxial cable

Wi-Fi

Bluetooth

Infrared

233
Q

What is UTP?

A

Has different standards (Cat6, Cat5, Cat3)

Ethernet cables

234
Q

When is UTP used?

A

Commonly used in LANs to send data

Not suitable for WANs as the data signal fades over distance and therefore needs a repeater to boost signal back to original strength

235
Q

What is satellite transmission media?

A

Don’t need to be physically plugged into a device to send data

Needs clear line of sight to be able to send data

Uses radio waves to transfer data without need to physically plug in devices

236
Q

When is satellite transmission media used?

A

Used to send data from remote locations (crossing the sea, mountain expeditions, army expeditions)

237
Q

What is fibre optic transmission media?

A

Send data using light where the light bounces off the walls repeatedly

Many beams of light can be transferred at once providing they all bounce at different points

Repeaters only needed after a distance of around 100km

Very high bandwidth

Can be difficult to work with (if cable breaks, cannot be fixed and whole cable needs to be replaced - expensive)

238
Q

When is fibre optic transmission media used?

A

Signal strength doesn’t fade quickly so can be used to transfer data a long distance

Often found installed under sea beds to transfer data between countries

239
Q

What is Wi-Fi transmission media?

A

Don’t need to physically plugged into a device to send data

Data transferred could be intercepted easily as no physical connection needed

Bandwidth not as high as wired connection

240
Q

What is Bluetooth transmission media?

A

Don’t need to physically plugged into a device to send data

241
Q

What is infrared transmission media?

A

Don’t need to physically plugged into a device to send data

Needs a clear line of sight to be able to send data

242
Q

What is a hacker?

A

An individual attempting to gain unauthorised access to a device

243
Q

What is malware?

A

Type of file that can harm your devices to the files in

244
Q

How can malware be prevented?

A

Regularly running anti-malware software

Regularly update software and apps

Education

245
Q

What is a virus?

A

Malicious software that spreads through a network by replicating itself on a host computer after the user has performed a particular action

246
Q

What are the consequences of viruses?

A

Destroy files

Open a backdoor

Send data back from the user

247
Q

How can viruses be prevented?

A

Education

248
Q

What is a worm?

A

Malicious software that replicates itself and infects other devices on the network

249
Q

What are the consequences of worms?

A

Destroy files

Open a backdoor

Send data back from the user

250
Q

How can worms be prevented?

A

Education

251
Q

What is a trojan?

A

Malicious software that pretends to be legitimate to get the user to run it

252
Q

What are the consequences of trojans?

A

Data theft

Redirecting search requests

Installing further malware

Opening a backdoor

253
Q

How can trojans be prevented?

A

Education

254
Q

What is unauthorised access?

A

An individual gaining access to a computer that they should not have access to, using other user’s details

255
Q

What does DoS stand for?

A

Denial of Service

256
Q

What is DoS attack?

A

Server is flooded with requests that it cannot handle, so it is prevented from functioning normally

257
Q

What is the consequence of a DoS attack?

A

Server won’t work

258
Q

How can a DoS attack be prevented?

A

Firewall

259
Q

What does DDoS stand for?

A

Distributed Denial of Service

260
Q

What is a DDoS attack?

A

Using a botnet to perform a DoS

261
Q

What is the consequence of a DDoS attack?

A

Server won’t work

262
Q

How can a DDoS attack be prevented?

A

Firewall

263
Q

What is social engineering?

A

Manipulating a user to hand over personal details

264
Q

What are the consequences of social engineering?

A

Account hacked

Personal details stolen

265
Q

How can social engineering be prevented?

A

Education

266
Q

What is phishing?

A

Emails sent to a large number of users to get them to click a link or download a file to place malware on the computer

267
Q

What are the consequences of phishing?

A

Personal details stolen

268
Q

How can phishing be prevented?

A

Look out for blurry/pixelated images and spelling and grammar errors

Education

269
Q

What is pharming?

A

Redirecting website traffic to another fake website

270
Q

What are the consequences of pharming?

A

Personal details stolen

271
Q

How can pharming be prevented?

A

Check website URL

Education

272
Q

What is spyware?

A

Malicious software that installs itself on the user’s computer without the user’s knowledge, capturing data from the device

273
Q

What are the consequences of spyware?

A

Gathers information on the user

Monitor internet usage

Send annoying but harmless adverts

Taking and reporting back screenshots

274
Q

How can spyware be prevented?

A

Education

275
Q

What is ransomware?

A

Holds files hostage until a ransom is paid

276
Q

What are the consequences of ransomware?

A

Can’t access data

Encrypts user data

277
Q

How can ransomware be prevented?

A

Back up data regularly

Never pay for applications or add-ons on devices that aren’t from reliable sources

Education

278
Q

What is botnet?

A

A collection of devices under the control of a single operator who can instruct the computers to do something at the same time

279
Q

What is the consequence of a botnet?

A

DDoS attack

280
Q

What is DNS spoofing?

A

Redirecting the DNS so that when it looks up the address for a certain website, it returns the wrong IP address and takes the user to a spoof/trick website

281
Q

What are the consequences of DNS spoofing?

A

Get personal details

282
Q

How can DNS spoofing be prevented?

A

Check website URL

Education

283
Q

What is a firewall?

A

Monitors data packets entering and leaving a network

Aims to prevent unauthorised access to a network

Examines data packets against a set of network rules

If packets break the rules, data packet is blocked

284
Q

What are packet filters?

A

A set of rules that a data packet must meet

285
Q

What are some examples of packet filtering?

A

Restricting access to certain destination IP addresses

Restricting access to certain source IP addresses

Restricting access to certain ports

Restricting data that uses certain protocols

286
Q

What is another name for static filtering?

A

Stateless inspection

287
Q

What is static filtering?

A

Checks information in the HEADER of the data packets and examines these against a set of rules

DOESN’T examine data in the payload

DOESN’T constantly monitor data packets once the connection has been established

288
Q

What are the problems with static filtering?

A

Hacker may ensure that all data meets the rules of the network

Suitable source and destination IP address

Suitable protocol

Acceptable port

May contain malicious code in the payload

289
Q

What is another name for dynamic filtering?

A

Stateful inspection

290
Q

What is dynamic filtering?

A

CONTINUES to monitor incoming and outgoing data packets after a connection is established

Checks the PAYLOAD of the packet, not just the header

291
Q

What is the process of dynamic filtering?

A
  1. data packets sent into a network and meet the rules of network so allowed
  2. however code inside payload then retrieves data from network and starts to send to destination IP away from network
  3. may be someone stealing information from the network
  4. however connection constantly monitored and payload inspected
  5. discovered that data shouldn’t be leaving the network and therefore blocked
292
Q

Where is a proxy server placed?

A

Between client machine’s and a firewall

293
Q

What is a proxy server?

A

Used to hide the client’s real IP address as the IP address of the proxy server is used

Keep a cache of web pages and therefore if it can it will load a web page from its cache rather than retrieving from the web server

May keep log of network user’s activity (what website they visited and for how long)

294
Q

What are the functions of a proxy server?

A

Anonymity for client devices

Web page filtering

Improved caching of web pages

295
Q

What are the two types of web filtering?

A

BLOCK EVERYTHING - then add trusted websites

ALLOW EVERYTHING - then block certain websites

296
Q

What is HTML?

A

Markup language for the formatting of a page

297
Q

What is CSS?

A

Changes look and feel of a webpage

298
Q

What is JavaScript?

A

Adds functionality

299
Q

How is CSS applied to a tag?

A

img {
}

300
Q

How is CSS applied to an id?

A

idName {

}

301
Q

How is CSS applied to a class?

A

.className {
{

302
Q

What is a search engine?

A

Used to help search information on the internet

Search engine provides build indexes and deploy very smart algorithms that allows them to provide more or less instant responses to requests for information

When we search, searches the index

303
Q

What is a web crawler/spider?

A

A program that a search engine uses to continuously visit all pages on the internet, following hyperlinks until it’s been to all pages on the internet, and collecting and analysing data from them to populate their index

304
Q

What is an index?

A

A database of key terms and the web pages that are relevant to those key terms

305
Q

What is metadata?

A

Additional data attached to the web page, identifying the relevant key terms of that web page

306
Q

What is the process of search engines?

A
  1. search engines make use of programs called SPIDERS or crawlers to continually search the internet
  2. start on a page and visit all HYPERLINKS from that page
  3. each page they study they gather data by analysing KEY TERMS and METADATA about the web page
  4. data used to build up an INDEX - database of pages and terms linked to a page
  5. when user then enters their SEARCH CRITERIA the search engine doesn’t search internet but instead searches their most recent index, finding WEB PAGES that include key terms user is searching for
  6. as internet constantly changing, crawlers continually search
  7. when reach the end, start again
  8. some SEARCH ENGINES make it so that their crawlers search commonly used pages more often so they can ensure data they store about these pages in their index is up to date
307
Q

Who is the PageRank algorithm used by?

A

Google Search to rank websites in their search engine results

308
Q

What is the PageRank algorithm?

A

Way of measuring the importance of web pages, by counting the NUMBER and QUALITY of links to a page to determine a rough estimate of how IMPORTANT the webpage is

309
Q

What is the underlying assumption of the PageRank algorithm?

A

More important websites are more likely to receive more links from other websites

310
Q

What is the PageRank algorithm formula?

A

PageRank of A = (1 - dampening factor) + dampening factor * ( (PageRank of first linked page / number of outbound links from that page) + (PageRank of second linked page / number of outbound links from that linked page) )

PR(A) = (1-d) + d( PR(T1)/C(T1) + … + PR(Tn)/C(Tn) )

311
Q

What is client side scripting?

A

Processing data on client machine in the browser

Front end

312
Q

What is server side scripting?

A

Processing data on server

Back end

313
Q

What processing is done client side?

A

Validation of data entered into a web form (e.g. presence check)

JavaScript scripting mainly used

Web browser games (e.g. flash games)

Storing and searching for cookies from previous visits to a website

Responsive design of a website (implements the CSS)

Interactivity on a web page

314
Q

What processing is done both client side and server side?

A

Validation to check against SQL injection attacks on the database

315
Q

What processing is done server side?

A

PHP, node.js and SQL scripting mainly used

Runs scripts before a page is loaded into the browser

Inserting/accessing/updating data from a database

Finding suitable search results from a Google Search

Used for more complex processing/calculation

316
Q

What are the advantages of client side scripting?

A

Quicker to perform simple validation

Reduces the load on the server

Code is more responsive as not being sent back and forth to server

Reduces the amount of data being transferred over the web

Quicker to perform non-complex processing as don’t need to transmit data

317
Q

What are the disadvantages of client side scripting?

A

Source code can be viewed and copied

Need correct interpreter installed to be able to run code

Code may not always be run if user has blocked (e.g. pop ups)

318
Q

What are the advantages of server scripting?

A

Hides source code from the user

Can keep data more secure

More powerful machine and so better for more complex calculation

Computer Science (8 decks)

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