1.3 Exchanging Data Flashcards
1
Q
What does compression do?
A
Reduce requirements on file storage
Reduce download times
Make best use of bandwidth
2
Q
What are the two types of compression?
A
Lossy
Lossless
3
Q
What is lossy compression?
A
Type of compression that removes data to reduce the file size, stripping out the least important data
4
Q
Can the original be recreated in lossy compression?
A
No because detail is removed
5
Q
What is lossy compression typically used for?
A
Multimedia files
6
Q
What are examples of lossy compression?
A
JPEG
MP3
MPEG
GIF
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
8
Q
Can the original be recreated with lossless compression?
A
Yes
9
Q
What is lossless compression used for?
A
Essential for file types like computer programs
10
Q
What are some examples of lossless compression?
A
ZIP
PNG
11
Q
What are two methods of lossless compression?
A
Run Length Encoding (RLE)
Dictionary Based Encoding
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
13
Q
Is a real-life image suitable for RLE?
A
No because the image has too much detail
14
Q
Does RLE have to be used on image data?
A
No
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
16
Q
What is a disadvantage of RLE?
A
Only achieves significant reductions in file size if there are long runs of data
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
18
Q
What is plaintext?
A
The data that is being stored or is going to be transferred
The data to be encrypted
19
Q
What is ciphertext?
A
The encrypted text
20
Q
What is a cipher?
A
Algorithm used to encrypt the data
21
Q
What is a key?
A
Data that is used within the cipher
22
Q
What is decryption?
A
Converting the ciphertext back into the original plaintext
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
24
Q
How does symmetric encryption work?
A
Sender and receiver use the same key to encrypt and decrypt data
25
Is symmetric encryption faster than asymmetric encryption?
Yes because it uses less complex mathematical operations
26
What is a disadvantage of symmetric encryption?
Key has to be exchanged across a network, which could be intercepted by an attacker
27
What is asymmetric encryption?
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
28
How does asymmetric encryption work?
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
29
What are the problems with asymmetric encryption?
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)
30
How does authentication work?
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
31
What does SSL stand for?
Secure Sockets Layer
32
What is the SSL handshake?
HTTPS protocol encrypts communication between web browser and web server in both directions
Creates encrypted link between server and a client
33
How does the SSL handshake work?
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
34
What is a hash function?
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
35
What is a hash value?
A string of characters of a fixed size which is different for each key
36
What is a collision?
When two different keys produce the same hash value
37
How can hashing algorithms be used for integrity validation?
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
38
How can hashing algorithms be used?
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
39
What is a database?
Persistent organised store of data
40
What does a persistent database mean?
Data stored on secondary storage device and is non-volatile
41
What does an organised database mean?
Data organised into records and fields
42
What is a relational database?
A database with multiple tables linked by primary key-foreign key relationships
43
What is a flat file database?
A database with a single table with information about a single entity
44
What is a primary key?
Unique identifier for each record in a table
45
What is a foreign key?
Non-primary key field in a table that links to primary key field in another table
46
What is an attribute in a database?
The different fields within a database
47
What is a record in a database?
A row within a database
48
What is a composite key?
Use multiple (two or more) fields to create a unique identifier for a record
49
What is data integrity?
The accuracy of the data within the database
50
What is data redundancy?
Duplicating data in multiple places in the database
51
What is a secondary key?
A field that will be used to search the table often
52
What is an entity?
Category of object, person, event or thing of interest about which data needs to be recorded
53
What is SQL?
Structured Query Language
Standard language used to query a relational database
54
How do you SELECT from a database?
SELECT field1, field2
FROM table_name
WHERE filtering criteria
ORDER BY fields ASC/DESC
55
How do you INSERT INTO a database?
INSERT INTO table_name (field1, field2)
VALUES (value1, value2)
56
How do you UPDATE a database?
UPDATE table_name
SET field1 = value1, field2 = value2
WHERE filtering criteria
57
How do you DELETE from a database?
DELETE
FROM table_name
WHERE filtering criteria
58
How do you create a table in a database?
CREATE TABLE IF NOT EXISTS table_name
(field1 TEXT NOT NULL PRIMARY KEY,
field2 INTEGER NOT NULL, field3 FLOAT)
59
How do you create a table with a foreign key and a composite key? (using the example of student, course, enrolled)
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)
60
How do you SELECT data from three tables? (using an example of appointment, doctor, patient)
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
61
What are the different relationships between two entities?
One-to-one
One-to-many/many-to-one
Many-to-many
62
What is an example of a one-to-one relationship?
Husband --- Wife
63
What is an example of a one-to-many relationship?
Mother ---<- Child
64
What is many-to-many relationship?
Not allowed
Have to be split up using additional entity
65
What does a split up many-to-many relationship look like?
Patient ---<- Appointment ->--- Doctor
66
Are entities singular or plural?
Singular
67
What does ERD stand for?
Entity Relationship Diagram
68
What is an ERD?
Represents all the entities/tables with their attributes/fields and the relationships between entities
69
What should a structure of a database enable a user to do?
Enable a user to enter as many or as few records as required so make sure there are no many-to-many relationships
70
What is normalisation?
Splitting up data in databases and arranging the data to be in 1st, 2nd and 3rd normal form
71
What is the purpose of normalisation?
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
72
What is 1st normal form?
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
73
What is 2nd normal form?
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
74
What is 3rd normal form?
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)
75
What is data integrity?
Accuracy and reliability of data
76
What is data redundancy?
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
77
What is referential integrity?
Adds constraints to the data updated, deleted and entered into a relational database to ensure the data is as accurate as possible
78
How can referential integrity affect when data is entered into a database?
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
79
How does referential integrity affect when data is deleted from a database?
Deletes all records with that primary key
ON DELETE CASCADE
80
How does referential integrity affect when a primary key of a record is updated in a database?
Changes all instances of that primary key in all tables
81
What are the problems with carrying out operations on a database?
Multiple users trying to change data at the same time
A transaction being part completed by not fully completed
82
What is ACID?
Rules that should be followed to maintain consistency within a database
83
What does ACID stand for?
Atomicity
Consistency
Isolation
Durability
84
What is atomicity?
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
85
What is an example of atomicity?
Bank transfers
86
What is consistency?
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
87
What is an example of consistency?
Referential integrity
Validation
- length check
- NOT NULL
- range check
- type check
- format check
88
What is isolation?
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
89
What is an example of isolation?
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
90
What is record locking?
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
91
What is deadlock?
Problem with record locking
If two users are attempting to update two records, a situation can arise in which neither can proceed
92
What is serialisation?
Ensures transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost
93
What is timestamp ordering?
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
94
What is durability?
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
95
What is redundancy?
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
96
What are some examples of redundancy?
RAID setup mirroring data
Having redundant backup hardware
97
What does DBMS stand for?
Database Management System
98
What is the DBMS?
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
99
What are examples of methods of capturing data?
Input forms
Barcodes
Magnetic strip readers
OMR (Optical Mark Reader)
ANPR (Automatic Number Plate Recognition)
OCR (Optical Character Recognition)
100
Are input forms automatic or manual?
Manual
101
What are the benefits of input forms?
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
102
What are the drawbacks of input forms?
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
103
Are barcodes automatic or manual?
Automatic
104
What can barcodes be used for?
Shopping items
105
What are the benefits of barcodes?
Faster and easier to ring up items
More accurate
106
What are the drawbacks of barcodes?
No read/write capabilities
Can be slow as have to scan individually
107
Are magnetic strip readers automatic or manual?
Automatic
108
What are the uses of magnetic strip readers?
Bank cards
109
What are the benefits of magnetic strip readers?
Low costs
Rewriteable data
Quick and easy to use
110
What are the drawbacks of magnetic strip readers?
Tape can be damaged
Special equipment has to purchased
Limited storage capacity
111
Are OMRs automatic or manual?
Automatic
112
What are the uses of OMRs?
Multiple choice tests
Lottery tickets
Exam questions
113
What are the benefits of OMRs?
Fast and efficient way of collecting data and inputting it into a database
Significantly reduces human error
Accurate
114
What are the drawbacks of OMRs?
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
115
Are ANPRs automatic or manual?
Automatic
116
What are the uses of ANPRs?
Car parks
Toll gates
117
What are the benefits of ANPRs?
Efficient and reliable
Enhanced security
118
What are the drawbacks of ANPRs?
Privacy concerns
Bad weather can affect accuracy
119
Are OCRs automatic or manual?
Automatic
120
What are the uses of OCRs?
Reading postcodes and routine mail
121
What are the benefits of OCRs?
Automatically reads texts by interpreting shape of letters
Fast and efficient
122
What are the drawbacks for OCRs?
Doesn't work as well with handwriting
Sometimes inaccurate
123
What does JSON stand for?
JavaScript Object Notation
124
What is JSON?
Open source and language independent
Text-based
125
What are the two structures of JSON?
An ordered list of values
A collection of name/value pairs
126
What are the advantages of JSON?
Easy for humans to understand
Easy for computers to parse so quick to process
127
What are the disadvantages of JSON?
Supports limited types of data
128
What does XML stand for?
Extensible Markup Language
129
What is XML?
Allows a schema to be written (type of metadata that specifies and constrains the structure of the XML file)
130
What is a schema?
Defines elements and attributes that must be included in the file
Data types, attributes and order
131
What is a standalone computer?
A computer that's unable to communicate with other devices
132
What is a computer network?
Joining two or more computers together so they can communicate, share resources or be centrally managed
133
What are the advantages of networks?
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
What are the disadvantages of networks?
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
What does LAN stand for?
Local Area Network
136
What is a LAN?
Devices in network in same geographical location
Doesn't make use of 3rd party infrastructure
137
What does WAN stand for?
Wide Area Network
138
What is a WAN?
Devices on network connected across wide geographical location
Makes use of 3rd party infrastructure
Two or more LANs connected together
139
What is a standard?
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
What is a de jure standard?
Standards set by official organisation
141
What is a de facto standard?
Standards unofficially set, established by common use
142
What are the advantages of standards?
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
What are some common standards?
MP3 - file format for audio files supported by most media-playing software
HTML - markup language for creating websites
Unicode - form of representing text
144
What is a network protocol?
Set of rules or standards that all devices need to follow when transferring data on a network
145
What happens if devices don't follow the same protocols?
They won't be able to communicate
146
What does TCP stand for?
Transmission Control Protocol
147
What does TCP do?
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
What does IP stand for?
Internet Protocol
149
What does IP do?
Directs data packets to the correct destination using the IP address
150
What does FTP stand for?
File Transfer Protocol
151
What does FTP do?
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
What does SMTP stand for?
Simple Mail Transfer Protocol
153
What does SMTP do?
Used to send emails between servers
154
What does POP3 stand for?
Post Office Protocol 3
155
What does POP3 do?
Used to receive emails
Emails REMOVED from the server when they are read on a device
156
What does HTTP stand for?
Hyper Text Transfer Protocol
157
What does HTTP do?
Used to transmit web pages
158
What does HTTPS stand for?
Hyper Text Transfer Protocol Secure
159
What does HTTPS do?
Used to transmit web pages
Data encrypted
160
What does IMAP stand for?
Internet Message Access Protocol
161
What does IMAP do?
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
What is a single stack protocol?
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
Where are layered protocol stacks used?
Networking
164
What are layered protocol stacks?
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
What is the TCP/IP stack?
Collection of protocols used to send data on an IP network
166
What are the layers in order of the TCP/IP stack?
Application
↓ ↑
Transport
↓ ↑
Internet
↓ ↑
Link
167
What are the protocols used on the application layer?
Web browser - HTTP, HTTPS
Emails - POP3, IMAP, SMTP
Transferring files - FTP
168
What are the protocols used on the transport layer?
TCP - establishes end-to-end connection with recipient
UDP - faster connectionless protocol
169
What protocols are used on the internet layer?
IP
170
What protocols are used on the link layer?
Wi-Fi
Ethernet
171
What happens in the down application layer?
Uses protocols relating to the application being used to transmit data
172
What happens on the down transport layer?
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
What happens on the down internet layer?
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
What happens on the down link layer?
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
What happens in the up link layer?
Physically sends the data packets
176
What happens in the up internet layer?
Checks if destination is reached
177
What happens in the up transport layer?
Checks for errors
Reorders packets
178
What happens on the up application layer?
Depends on task being performed
Displays data, downloads files
179
What are the layers of the OSI model?
Application
Presentation
Session
Transport
Network
Data link
Physical
180
What is encapsulation (in relation to the TCP/IP stack)?
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
How are packets routed on a LAN?
Switch using MAC address
182
How are packets routed on a WAN?
Router using IP address
183
What is an IP address?
Unique address
184
What is a static IP address?
Cannot change
185
What is a dynamic IP address?
Assigned by network they connect to so change over time
186
What does DHCP stand for?
Dynamic Host Configuration Protocol
187
What does a DHCP do?
Allocates IP address to device when it connects to the Internet
188
What is circuit switching?
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
What are the advantages of circuit switching?
Quicker to transfer data
190
What are the disadvantages of circuit switching?
Less secure as data all travelling together
Ties up the network cables for other data
191
What is packet switching?
Data travels along DIFFERENT paths (IP)
Router determines these routes
Data packets PUT BACK into correct order when they reach the destination (TCP)
192
When is packet switching used?
Internet traffic
193
What are the advantages of packet switching?
More secure as data not all travelling together
Does not tie up the network cables for other data
194
What are the disadvantages of packet switching?
Slower than circuit switching
195
What are the factors determining the different routes that a packet may take?
Amount of traffic
Fault in network
196
What are the steps for packet switching?
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
What does URL stand for?
Uniform Resource Locator
198
What is a URL?
Address of an internet resource
199
What is a domain name?
Identifies area/domain internet resources reside in
Has IP address
In a hierarchy of small domains which follow rules of the DNS
200
What does DNS stand for?
Domain Name System
201
What does a DNS do?
Stores all IP addresses paired with domain name
202
What does TLD stand for?
Top Level Domain
203
What does a TLD hold?
.org
.com
.co.uk
204
What are the stages of loading a website?
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
What are the two models used to network computers?
Client server
Peer-to-peer
206
What is a server?
A computer dedicated to providing some kind of service to users across a network
207
What is a client server model?
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
What are the characteristics of a client server model?
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
What is a peer-to-peer model?
When two or more PCs are connected and share resources without going through a separate server
210
What are the characteristics of a peer-to-peer model?
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
What are the types of server?
Print server
Web server
Mail server
File server
Backup server
Application server
Proxy server
212
What does a print server do?
Schedules print jobs sent to it by device on the network
213
What does a web server do?
Hosts websites on the internet
214
What does a mail server do?
Stores emails ready to be sent to a user's inbox when they access their account
215
What does a file server do?
Stores user's documents which are then sent to user when they access file explorer
216
What does a backup server do?
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
What does an application server do?
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
What does a proxy server do?
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
What is a gateway?
Devices that can be used to transfer data between dissimilar networks (use different protocols)
220
What is a router?
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
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What is a switch?
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
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What type of network is a switch suitable for?
Larger networks
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What is a hub?
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
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What type of a network is a hub suitable for?
Smaller networks as there can be more data collisions
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What does WAP stand for?
Wireless Access Point
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What is a WAP?
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
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What does NIC stand for?
Network Interface Card
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What is a NIC
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
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What is a modem?
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
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What is transmission media?
Method a network uses to be able to transfer data
Provides wired connection and some wireless connection
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What is a wired connection?
Where it needs to be physically plugged in
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What are examples of transmission media?
UTP (Unshielded Twisted Pair)
Satellite
Fibre optic cable
Coaxial cable
Wi-Fi
Bluetooth
Infrared
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What is UTP?
Has different standards (Cat6, Cat5, Cat3)
Ethernet cables
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When is UTP used?
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
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What is satellite transmission media?
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
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When is satellite transmission media used?
Used to send data from remote locations (crossing the sea, mountain expeditions, army expeditions)
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What is fibre optic transmission media?
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)
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When is fibre optic transmission media used?
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
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What is Wi-Fi transmission media?
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
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What is Bluetooth transmission media?
Don't need to physically plugged into a device to send data
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What is infrared transmission media?
Don't need to physically plugged into a device to send data
Needs a clear line of sight to be able to send data
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What is a hacker?
An individual attempting to gain unauthorised access to a device
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What is malware?
Type of file that can harm your devices to the files in
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How can malware be prevented?
Regularly running anti-malware software
Regularly update software and apps
Education
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What is a virus?
Malicious software that spreads through a network by replicating itself on a host computer after the user has performed a particular action
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What are the consequences of viruses?
Destroy files
Open a backdoor
Send data back from the user
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How can viruses be prevented?
Education
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What is a worm?
Malicious software that replicates itself and infects other devices on the network
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What are the consequences of worms?
Destroy files
Open a backdoor
Send data back from the user
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How can worms be prevented?
Education
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What is a trojan?
Malicious software that pretends to be legitimate to get the user to run it
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What are the consequences of trojans?
Data theft
Redirecting search requests
Installing further malware
Opening a backdoor
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How can trojans be prevented?
Education
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What is unauthorised access?
An individual gaining access to a computer that they should not have access to, using other user's details
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What does DoS stand for?
Denial of Service
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What is DoS attack?
Server is flooded with requests that it cannot handle, so it is prevented from functioning normally
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What is the consequence of a DoS attack?
Server won't work
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How can a DoS attack be prevented?
Firewall
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What does DDoS stand for?
Distributed Denial of Service
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What is a DDoS attack?
Using a botnet to perform a DoS
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What is the consequence of a DDoS attack?
Server won't work
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How can a DDoS attack be prevented?
Firewall
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What is social engineering?
Manipulating a user to hand over personal details
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What are the consequences of social engineering?
Account hacked
Personal details stolen
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How can social engineering be prevented?
Education
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What is phishing?
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
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What are the consequences of phishing?
Personal details stolen
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How can phishing be prevented?
Look out for blurry/pixelated images and spelling and grammar errors
Education
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What is pharming?
Redirecting website traffic to another fake website
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What are the consequences of pharming?
Personal details stolen
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How can pharming be prevented?
Check website URL
Education
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What is spyware?
Malicious software that installs itself on the user's computer without the user's knowledge, capturing data from the device
273
What are the consequences of spyware?
Gathers information on the user
Monitor internet usage
Send annoying but harmless adverts
Taking and reporting back screenshots
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How can spyware be prevented?
Education
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What is ransomware?
Holds files hostage until a ransom is paid
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What are the consequences of ransomware?
Can't access data
Encrypts user data
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How can ransomware be prevented?
Back up data regularly
Never pay for applications or add-ons on devices that aren't from reliable sources
Education
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What is botnet?
A collection of devices under the control of a single operator who can instruct the computers to do something at the same time
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What is the consequence of a botnet?
DDoS attack
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What is DNS spoofing?
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
What are the consequences of DNS spoofing?
Get personal details
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How can DNS spoofing be prevented?
Check website URL
Education
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What is a firewall?
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
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What are packet filters?
A set of rules that a data packet must meet
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What are some examples of packet filtering?
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
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What is another name for static filtering?
Stateless inspection
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What is static filtering?
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
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What are the problems with static filtering?
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
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What is another name for dynamic filtering?
Stateful inspection
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What is dynamic filtering?
CONTINUES to monitor incoming and outgoing data packets after a connection is established
Checks the PAYLOAD of the packet, not just the header
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What is the process of dynamic filtering?
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
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Where is a proxy server placed?
Between client machine's and a firewall
293
What is a proxy server?
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)
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What are the functions of a proxy server?
Anonymity for client devices
Web page filtering
Improved caching of web pages
295
What are the two types of web filtering?
BLOCK EVERYTHING - then add trusted websites
ALLOW EVERYTHING - then block certain websites
296
What is HTML?
Markup language for the formatting of a page
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What is CSS?
Changes look and feel of a webpage
298
What is JavaScript?
Adds functionality
299
How is CSS applied to a tag?
img {
}
300
How is CSS applied to an id?
#idName {
}
301
How is CSS applied to a class?
.className {
{
302
What is a search engine?
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
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What is a web crawler/spider?
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
What is an index?
A database of key terms and the web pages that are relevant to those key terms
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What is metadata?
Additional data attached to the web page, identifying the relevant key terms of that web page
306
What is the process of search engines?
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
6. 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
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Who is the PageRank algorithm used by?
Google Search to rank websites in their search engine results
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What is the PageRank algorithm?
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
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What is the underlying assumption of the PageRank algorithm?
More important websites are more likely to receive more links from other websites
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What is the PageRank algorithm formula?
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) )
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What is client side scripting?
Processing data on client machine in the browser
Front end
312
What is server side scripting?
Processing data on server
Back end
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What processing is done client side?
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
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What processing is done both client side and server side?
Validation to check against SQL injection attacks on the database
315
What processing is done server side?
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
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What are the advantages of client side scripting?
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
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What are the disadvantages of client side scripting?
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)
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What are the advantages of server scripting?
Hides source code from the user
Can keep data more secure
More powerful machine and so better for more complex calculation
