Unit 5 Networks And Web Technologies Flashcards
Internet Service Providers
Connects directly to this backbone and distribute the Internet connection to smaller providers who in turn provide access to individual homes and business.
Uniform Resource Locators
A Uniform Resource Locators is the full address of an internet resource. URLs are used to specify 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
Domain Name System (DNS)
DNS servers are dedicated computers with an index of domain names and their corresponding IP addresses.
DNS server structure
- There are 13 root DNS servers that work together to catalogue every domain name
- These are segmented into geographical groupings or levels
- When the IP address of a given domain is not known it is referred to a related domain server that may know
Internet Register
Internet registrers hold records of all existing website names and the details of those domains that are currently available to purchase
Internet Protocol
IP address is a unique address that is assigned to a network device. It indicates where a packet of data is to be sent or has been sent from. Routers can use address to direct the data packet accordingly.
LAN
Local Area Network (LAN) is a network spread over a small geographical area
WAN
Wide Area Network (WAN) is a network spread over a large geographical area, that
typically requires extra hardware
DNS
● Domain Name System
● The system given to the method of naming internet resources
● A hierarchy where each smaller domain is separated from the larger domain by a
full stop
● DNS server translates domain names into IP addresses when we access a website.
Bus topology
Network topology where all terminals (devices) are connected to a
backbone cable
Advantages of Bus Topology
Cheaper to set up, doesn’t require any
additional hardware
Disadvantages of Bus Topology
If backbone cable fails, the entire network gets disconnected
As traffic increases, performance decreases
All computers can see the data transmission
Star Topology
Uses a central node (switch/computer) to direct the flow of data
Advantages of Star Topology
Performance is consistent even if network is being heavily used
If one cable fails, only that station is affected
Transmits data faster, so it gives better performance than bus topology
It’s easy to add new stations
No data collisions
Disadvantages of Star Topology
Expensive due to switch and cabling
If the central switch fails, the rest of the network fails
Mesh Topology
Every node is connected to every other node
Advantages of Mesh Topology
No cabling cost
As nodes increase, the reliability and speed of network becomes better Nodes automatically get incorporated
It’s faster since nodes don’t go through a central switch
Disadvantages of Mesh Topology
You have to purchase devices with wireless capabilities
Maintaining the network is difficult
Circuit switching
It involves creating a communication connection between two endpoints for the duration of a phone call or transfer of data
Packet switching
Packets are often sent across networks that have multiple connections with multiple routes through to a destination
Data packets
When sending across a network, data is broken into chunks (units) called data packets and assembled again at the receiving end
Routing
- Routers forward data packets from one network to another
- 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
Gateways
• A gateway is required where data is travelling from one network to another that use different protocols
Circuit Switching advantages
The data arrives in a logical order which results in a quicker reconstruction of the data.
This enables two uses to hold a call without delay in speech.
Circuit switching disadvantages
Bandwidth is wasted during periods of time where no data is sent.
The devices must transfer and receive data at the same rate.
Since switches are used, electrical interference is produced which can corrupt or lose data.
Packet Switching advantages
There are multiple methods to ensure data arrives (check Checksum and Cyclic Redundancy Check).
There is more than one method of getting to the other devices, so if one path breaks you can use another.
You can transfer packets over very large networks to allow communication globally.
Packet Switching disadvantages
Time is spent deconstructing and reconstructing the data packets.
Application Layer
. Based at the top of the stack
. Specifies what protocol needs to be used in order to relate the application that’s being sent
. Uses protocols relating to the application being used to transmit data over a network, usually the internet
. For example, if the application is a browser then it would select a protocol such as HTTP, POP3, FTP
Transport layer
- 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
Internet layer
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: 42.205.110.140:80
Link Layer
The connection between the network devices
Adds the MAC address identifying the Network Interface Cards of the source
and destination computers
On the recipient’s computer the layers occur again in reverse:
○ Link Layer ■ Removes the MAC addresses ○ Network Layer ■ Removes the IP addresses ○ Transport Layer ■ Removes the port number and reassembles the packets ○ Application layer ■ Presents the data to the recipient in the form it was sent
Firewalls
● Devices designed to prevent unauthorised access to a network
● Consist of two network interface cards (NICs), in-between the user and their internet connection.
● Perform packet filtering / static filtering
○ Limit network access in accordance with administrator rules and policies
Client-Server
● Client-Server networks have terminals known as clients connected to a server
● The server is just a powerful central computer
● The server holds all of the important information and has extra processing power and the clients can request to use it
Advantages of Client-Server
● More secure
● Central backups eliminate the need for client backups
● Sharing data and resources between clients
Disadvantages of Client-Server
● Expensive to set up
● Staff with training are required to maintain the server
Peer-to-Peer networks
● Computers are connected to each other so that they can share files
● Inexpensive to set up
● Allow users to share resources
● Easy to maintain
Proxy Server
• A proxy server makes a web request on behalf of your own computer, hiding the true request IP addresses from the recipient
Functions 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
Encryption
The act of encoding a plaintext message so that it cannot be deciphered unless you have a numerical key to decrypt it
• If the message is intercepted it cannot be understood
• If the key can be intercepted, the encryption process is rendered useless
Worms
A worm is a standalone program 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
Trojans
Trojans are malicious software programs that masquerade as innocuous or useful applications
• They cannot self-replicate
• Often they 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
Phishing
Phishing is using email to manipulate a victim into visiting a fake website and giving away personal information
Code quality
- Improving code quality, together with monitoring attempts to gain unauthorised access and protection can significantly reduce threats from malware
- Measures include:
- Guarding against buffer overflow attack
- Guarding against SQL injection attack
- Use of strong passwords for login credentials
- Two-factor authentication
- Use of access rights (file system permissions)
Buffer overflow
- Buffer overflow occurs when a program accidentally writes data to a location too small to handle it
- As a result the overflowed data (written to location #3 below) may end up in a neighbouring instruction space
- Malware can deliberately cause and manipulate overflow data which may then be read as a malicious ‘instruction’
HTML
● HTML is the language/script that web pages are written in,
● It allows a browser to interpret and render a webpage for the viewer by describing
the structure and order of the webpage.
● The language uses tags written in angle brackets (, ) there are two
sections of a webpage, a body and head.
CSS
● CSS is a script/language like HTML except is used to describe the style of a
webpage.
● CSS can be used to specify the way HTML elements look, they can be applied to
whole tags such as <h1>, </h1><p> or </p><div>.
● CSS can be used using two different form, internal/embedded or external CSS the
internal CSS is when the style is placed.
● The internal/embedded CSS is placed inside the style tags and is entered directly
within the HTML document.</div>
JavaScript
● JavaScript is a language which has a similar layout to languages like python. The
main function of JavaScript is to add interactivity to websites.
● JavaScript isn’t compiled, instead it is interpreted, this is so it can be interpreted in
the browser every time the webpage is displayed.
● Javascript be used to input data on the client’s computer, this may change the local
page interactively or post data to a server. The advantages:
○ The local computer can fix invalid data before sending it off to the servers,
○ It can ease the traffic off of the busy servers,
Classes and Identifiers
● Class and identifier selectors are the names which you style, this means groups of items can be styled, the selectors for html are usually the div tags. ● Identifiers are defined with an initial hashtag, and must be unique to each webpage. ● Classes are defined with a full stop as a prefix to the class name, classes can be used multiple times on a webpage.
Network
A network is the name given to two or more computers connected together with the ability to transmit data between each other. There are two main types of networks: local area networks and wide area networks.
HTTP (Hypertext Transfer Protocol)
Used for web page rendering, an encrypted version, HTTPS (Secure), is becoming more common
TCP/IP (Transmission Control Protocol / Internet Protocol)
This is a networking protocol used in the routing of packets through networks
POP3 (Post Office Protocol) and IMAP (Internet Message Access Protocol)
Mailing protocols, used for email access.
FTP (File Transfer Protocol)
Used for the transmission of files over networks.
