Unit 5 Networks and Web Technologies Flashcards
What is the largest Network in the world?
The Internet
What is the Internet?
A network of inter-connected networks
What is the World Wide Web?
A collection of resources accessed via the Internet
What is the main part of the Internet known as?
The backbone
What is the Backbone of the Internet?
A set of dedicated connections that connect several large networks at various points on the globe. Each of these points are then connected to other regional networks, usually controlled by Internet Service Providers
What does an ISP do?
Internet Service Providers
Provides access to individual end-users
What is an Internet Address?
Each device on a network needs to be uniquely identified so that data can be sent to the correct destination, much like an address on a letter
What is a URL stand for?
Uniform Resource Locator
What does a URL do?
Specifies the means of accessing a resource across a network and its location
The protocol and the domain name of the resource together form the URL
What is a DNS?
Domain Name System
Servers are dedicated computers with an index of domain names and their corresponding IP addresses
How many DNS servers work together to catalogue every domain name
13
Why do we not use IP addresses directly in a browser?
Because URLs are much more user friendly and easier to remember
What could happen when the DNS Server does not have a record for a specific domain? (2)
- It could recursively handle the request so that it can eventually deliver an IP address or print an error message
- It could refer to a DNS server authoritative
Why must Domain Names be unique?
Because otherwise the DNS request could be confused
What are Internet Registries?
Organizations that control the allocation of domain names and IP addresses
How many global Internet Registries are there?
5
Who issues available Domain Names?
Internet Registries
What is a LAN?
Local Area Network
Two or more computers connected together within a small geographical area
What is a WAN?
Wide Area Network
A large network of information that is not tied to a single location
What is a Network Topology?
The arrangement of the various computing devices which make up a computer network
What is a Bus Topology?
An arrangement where nodes are connected in a daisy chain by a single central communications channel
What are the advantages of a Bus Topology? (3)
- Inexpensive to set up
- Devices can be easily added
- Good for small networks
How does a Bus Topology work? (5)
- All nodes are connected to a single backbone cable
- Each end of the backbone is connected to either a terminator or a computer which stops signals ‘bouncing back’
- Each node is passive
- Data is sent in one direction at a time only
- Only one computer can transmit successfully at any one time
What the disadvantages of a Bus Topology? (4)
- Main cable is a point of failure
- Limited cable length
- Performance degrades with heavy use because of data collisions
- Poor security
What is a Star Topology?
An arrangement where a central node or hub provides a common connection point for all other nodes
What are the advantages of a Star Topology? (3)
- Easy to isolate problems
- Good performance
- More secure if a switch is used because data is only sent to recipient
How does a Star Topology work? (2)
- Computers are connected to a central node. This is often a switch
- A switch sends each communication to the specific computer it is intended for
What are the disadvantages of a Star Topology? (2)
- Can be expensive to set up because of the length of cable required
- Central device is point of failure
What is a Physical Topology?
How the devices are physically connected
What is a Logical Topology?
How the devices communicate across the physical topologies
What is Wifi?
A wireless networking technology providing high-speed Internet and network connections
What does WAP stand for?
Wireless network Access Point
What happens in Circuit Switching?
A communication connection is created between 2 endpoints for the duration of a phone call or transfer of data
What happens in Packet Switching?
Packets are often sent across networks that have multiple connections with multiple routes through a destination
What does a Router do?
Forwards data packets from one network to another
How to Routers work? (4)
- Each router stores data about the available routes to the destination node
- Looks up the destination IP address in its routing table to find the best router to forward the packet to
- Each transfer between routers is known as a hop
- Routers continue to forward the packet until it reaches its destination node
What is a Packet Split into? (3)
- Trailer
- Payload
- Header
What does a Packet Header Contain? (4)
- The recipient’s address so that it can be directed appropriately across the network
- Senders address so that replies can be sent appropriately
- The packet number and overall number of packets in the transmission to assist in reassembling the data
- The Time To Live (TTL) or hop limit is also included
What does a Packet Trailer Contain?
Error checking components to verify the data received in the payload has not been corrupted on transfer
What is a Protocol?
A set of rules, or a formal description, of the format of a digital transmission. It will cover, for example, the size of the packets, the contents and format of the header, the error detection and correction procedure
When is a Gateway required?
When data is travelling from one network to another that use different protocols
Why are Protocols important?
They make sure that all data being transfered in consistent which is needed for communication to work
What is a TCP/IP Stack?
A set of rules used in turn, to format a message so it can be sent over a network. Each layer provides a specific function within the transmission of the message
What are the layers of a TCP/IP Stack? (4)
- Application layer
- Transport layer
- Internet layer
- Link layer
What is the Application Layer used for?
Providing services for applications that want to communicate across a network, often the Internet
Does the Application Layer determine how data is transmitted?
No, it only specifies the rules of what should be sent
How does the Transport Layer work? (4)
- Uses the Transmission Control Protocol (TCP) to establish an end‐to‐end connection with the recipient computer
- Splits data into packets and numbers them sequentially
- Adds port number to be used based on HTTP protocol
- At the receiving end this layer confirms that packets have been received and requests any missing packets be resent
How does the Internet Layer work? (3)
- Uses the Internet Protocol (IP) to address packets with the source and destination IP addresses
- A router forwards each packet towards an endpoint called a socket, defined by the combination of IP address and port number
- Each router uses a routing table to instruct the next hop
How does the Link Layer work?
- Operates across a physical connection
- Adds the MAC address of the physical NIC that packets should be sent to based on the destination IP address
- MAC addresses change with each hop
Using the TCP/IP Stack Levels, how is data received? (4)
- The Link Layer removes the MAC address from each packet and passes it to the Internet Layer
- The Internet Layer removes the IP address from each packet and passes it to the Transport Layer
- The Transport Layer removes the port number f from each packet, reassembles the packets in the correct order and passes them to the Application Layer
- The Application Layer presents the image data for the user in a browser
What does TCP/IP stand for?
Transmission Control Protocol/Internet Protocol
What does a MAC address do?
Media Access Control addresses
Uniquely identifies a physical device with a NIC
What does NIC stand for?
Network Interface Card
What is a Port used for?
Alerting a specific application to deal with data sent to a computer. They are used by protocols to specify what data is being sent
What is Port 20 typically used for?
File Transfer Protocol (FTP) DATA
What is Port 21 typically used for?
File Transfer Protocol (FTP) CONTROL
What is Port 22 typically used for?
Secure Shell (SSH) Remote login
What is Port 23 typically used for?
Telnet (unencrypted) Remote login
What is Port 25 typically used for?
Simple Mail Transfer Protocol (SMTP)
What is Port 80 and 8080 typically used for?
HyperText Transfer Protocol (HTTP)
What is Port 110 typically used for?
Post Office Protocol v3 (POP3)
What is Port 143 typically used for?
Interim Mail Access Protocol (IMAP)
What is Port 443 typically used for?
HyperText Transfer Protocol Secure (HTTPS)
What does FTP stand for?
File Transfer Protocol
What is File Transfer Protocol?
An application level protocol used to move files across a network. FTP uses the client-server model with separate data and control channels operating on ports 20 and 21
What are Mail Servers?
Dedicated computers that are responsible for storing email, providing access to clients and providing services to send emails
What are the protocols of Mail Servers? (3)
- SMTP
- POP3
- IMAP
What does the SMTP protocol of Mail Servers do?
Used to send emails and forward them between mail servers to their destination
What does the POP3 protocol of Mail Servers do?
Downloads email stored on a remote server to a local client (removed after download)
What does the IMAP protocol of Mail Servers do?
Manages emails on a sever so multiple clients can access the same email account in synchronicity
What is a Firewalll?
Software or hardware that controls access to and from a network
What happens in Packet Filtering?
Packets of data are inspected by the firewall to check which port they are attempting to access. If this traffic is to be allowed through, the port must be opened for the duration of the connection, otherwise the firewall will automatically reject it
What does a Proxy Server do?
Makes a web request on behalf of your own computer, hiding the true request IP addresses from the recipient
What are the purposes of a Proxy Server?
- Enables anonymous surfing
- Can be used to filter undesirable online content
- Logs user data with their requests
- Provides a cache of previously visited sites to speed access
What is Encryption?
The act of encoding a plaintext message so that it cannot be deciphered unless you have a numerical key to decrypt it
What is Malware?
Malicious software that annoys users or damages their data
What is a Worm?
A standaloneprogram that does not require a user to run it in order for it to spread.
Worms exploit vulnerabilities in the destination system and spread automatically
What is a Trojan?
A programs that masquerades as innocuous or useful application. It cannot self-replicate and they often serve to open up back doors in your computer to the internet so that the processing power, internet bandwidth and data can be exploited remotely
What is Phishing?
Using an email to manipulate a victim into visiting a fake website and giving away personal information
When does Buffer Overflow Occur?
When a program accidentally writes data to a location too small to handle it
What is an SQL Injection?
When a malicious user enters SQL commands via online database forms to change the processing
What does HTML stand for?
Hyper Text Mark-up Language
What is HTML?
The language of the World Wide Web
HTML describes the content of Web Pages
What is the difference between HTML and CSS?
HTML is used to define the page content and structure
CSS are used to define page styles and appearance
What does CSS stand for?
Cascade Style Sheets
What can CSS be used to change? (4)
- The style of an entire website
- A single web page
- A section of a webpage define by a <div> tag or
- A single occurrence of an element, for example:
What are the ways that Styles can be applied to HTML content? (3)
- Inline styling to apply a unique style within an HTML element
- Internal, embedded styles defined within <style> tags in the <head> section of a single HTML file</style>
- Using an external style sheet and linking to it from any HTML files that may be created for an entire website
What is the benefit of using External CSS Files?
Enables you to apply styles on a single CSS stylesheet to multiple HTML files throughout an entire website.
This also removes the CSS from the HTML pages making them easier to read
What is the difference between Identifiers and Classes
Identifiers are unique to one element per web page. Classes can identify more than one element per page
What is Javascript used for?
Used to program the behavior of web pages and add interactivity between the user and a web page
What is a Function?
A block of code that is designed to be repeatedly called. They perform specific tasks that the user may wish to carry out multiple times. Functions are executed once they are invoked and are otherwise idle in the background
Why would a website want an Alert Box? (2)
- Sometimes it is an effective way of making sure the user conveys a piece of information
- The alert box will often ask for confirmation and will not allow the user to continue interacting with the webpage
What can an Array do?
Store multiple pieces of data under a single variable assignment
What is a Web Crawler?
An Internet bot that continuously crawls the web to discover and record publicly available web pages
What does a Meta Tag do?
Describes the content of a web page through HTML tags to make the page more likely to be found
Can Meta Tags be seen by users?
No, only by web crawlers
What is the PageRank algorithm specifically?
PR(A) = (1-d) + d [PR(Ti)/C(Ti) + … + PR(Tn)/C(Tn)]
What is PR(Ti)?
The PageRank of Ti
What is C(Ti)?
The number of outlinks on Ti
What Factors affect PageRank? (6)
- Domain name – relevance to the search item
- Frequency of search term in web page
- Age of web page
- Frequency of page updates
- Magnitude of content updates
- Keywords in <H1> tags
What is the Damping Factor?
The probability of a random web browser reaching a page. This value is usually set to 0.85
What are the features of Client-Server Networking? (6)
- A central server is used to manage security
- Some files are held on the central server
- Some processing tasks are performed by the server
- Clients issue requests to the server for services such as email, file storage, backup and printing
- Suitable for many different types of organization, small and large
- Can require specialist IT staff to administer the network
Does a Peer-to-Peer Model have a Central Server?
No
What are the features of Peer-to-Peer Networking? (5)
- They are suitable for a small company or home network with a few computers
- No central server controls files or security
- All computers can see files on all other computers
- All computers can communicate with each other without going through a server
- If a computer is switched off, data cannot be retrieved from it
What are the other features of Client-Server Networking? (5)
- User IDs, passwords and access levels centrally controlled
- Used in many small, medium-size and large organisations
- Can be expensive to set up and to manage
Backup is centralised and usually automated - No access to other users’ files
What are the other features of Peer-to-Peer Networking? (5)
- Files and programs stored on individual computers
- Suitable for a home computer network
- Cheap to set up and maintain
- Each computer on the network can act as both client and server
- Can be used for sharing of music and streaming coverage of live events
What are the advantages of Client Processing? (4)
- Allows for more interactivity by immediately responding to a users’ action
- Quick execution as no communication with the server is required
- Removes potentially unnecessary processing from the server
- Data cannot be intercepted on the way to the server, increasing security for the user
What are the disadvantages of Client Processing? (4)
- Not all browsers support all scripts (although most modern browsers support an overwhelming majority)
- Because the scripts are processed by the client, they are dependent on the performance of the clients’ machine
- Different browsers process scripts in slightly different ways, so the web page owner cannot be certain how the end-product will look to the user
What are the disadvantages of Client Processing? (4)
- Not all browsers support all scripts (although most modern browsers support an overwhelming majority)
- Because the scripts are processed by the client, they are dependent on the performance of the clients’ machine
- Different browsers process scripts in slightly different ways, so the web page owner cannot be certain how the end-product will look to the user
What are the disadvantages of Client Processing? (4)
- Not all browsers support all scripts (although most modern browsers support an overwhelming majority)
- Because the scripts are processed by the client, they are dependent on the performance of the clients’ machine
- Different browsers process scripts in slightly different ways, so the web page owner cannot be certain how the end-product will look to the user
What is an API?
Application Programming Interface
A set of tools that can be used for building software applications. API requests are processed by the client and responded to by the relevant server
What are examples of Server Programming Languages? (3)
- Python
- PHP
- ASP
