1.3 Exchanging data Flashcards
What is the purpose of compression?
- Reduce the size of a file
- Reduce download times
- Reduce storage needed
- Make best use of bandwidth
What are the 2 methods of compression?
- Lossy
- Lossless
How does lossy compression work on images?
- Stores a lower number of colours or stores larger areas of pixels as a single colour
- As a result, reduces the quality of the image.
- A small reduction is barely noticeable, at least by the human eye.
How does lossless compression works?
- Compresses an image to the point where it doesn’t lose quality, as it best works on images where there is a continuous area of the same colour
- Most effective on vector- style images such as logos and icons
What compression type should you use on text files and executables and why?
- Lossless
- Because we must not lose any of the data during compression
What are the characteristics of lossy compression?
- Some data is lost when the file is compressed
- Slightly reduces quality but significantly reduces file size
- Suitable for images, audio and video
What are the characteristics of lossless compression?
- None of the original data is lost
- The original file can be recreated when it is uncompressed
- Suitable for executable files and documents
What is a database?
- An organised collection of data
What is a flat file database?
- A database that contains only a single table, often saved as a CSV file.
What are the benefits of a flat file database?
- Simple to understand
- Quick to set up
- Requires little expertise to maintain
Why can flat files become inefficient?
- Repetitive data
- Repeating data takes up more space in the database, and as the database grows, the situation will get worse
- If you only used flat file databases, they would soon become difficult to maintain, slow to query and take up unnecessary space
What do 2 tables need to be turned into a relational database?
- A common field
What is a primary key?
- A field in a record that is unique
- Primary keys serve as unique identifiers for each row in a database table
What are the 3 possible relationships in linking tables?
- One to one
- One to many
- Many to many
What is a ERD?
- Entity relationship diagram
- A sketch of the relationships between databases tables
What is a foreign key?
- Foreign keys link data in one table to the data in another table
How can you capture data?
- Using paper-based data capture form
- Optical character recognition (OCR)
- Optical mark recognition (OMR)
How can we design a data capture form to avoid errors and make it as fast as possible?
- Every part of the form labelled clearly
- Instruction to complete the form in a black pen
- Instruction to complete the form in capital letters
- Use of tick boxes
- Squares for entering each letter separately
How does OCR work?
- Reads text by interpreting the shape of the letters, it works better with printed text rather than handwriting
How does OMR work?
- Often used for multiple-choice tests and lottery tickets
- Very fast and efficient for collecting data and inputting it in a database
What are examples of selecting data?
- SQL
- Query by example (QBE)
What do both SQL and QBE allow you to do?
- Specify tables, fields, criteria, output sorting
- Use boolean expressions
What does a DBMS provide?
- Hides the underlying structure of the data and ensures it remains integral by:
- Preventing the creation of duplicate primary keys
- Enforcing validation rules
- Providing secure access
- Providing encryption
- Providing program data independence
- Managing multiple users
What are the 2 common formats of exchanging data?
- CSV
- XML
- JSON
What is EDI?
- Electronic Data Interchange
- A protocol between 2 systems to facilitate exchange of data
What is a standalone machine?
- A single computer not connected to anything else
What are some advantages of a network?
- Users can share files
- Users can access files from any computer on the network
- Users can share peripherals and connections to other networks such as the Internet
- Communication with other people
- Servers can control security, software updates and backups of data
What are some disadvantages of a network?
- Increased security risk to data
- Malware and viruses spread very easily between computers
- If a server fails, the computers connected to it may not work
- Computers may run slower if there is a lot of data travelling on the network
What are standards?
- Set of hardware and software specifications that allow manufacturers to create products and services that are compatible with each other
What are some examples of standards?
- HTML
- Character sets
What is a protocol?
- A set of rules for communication over a network
What are the 3 types of protocol used for communication over LAN/WAN?
- TCP
- IP
- UDP
What are the 2 types of protocols used for Web Page requests?
- HTTP
- HTTPS
What is the protocol used for file transfers?
- FTP
What are the 3 protocols used for sending/receiving email?
- POP
- MAP
- SMTP
What do the TCP and IP protocols do?
- The TCP protocol provides error free transmission between two routers
- The IP protocol routes packets across a WAN
What does the UDP protocol do?
- Uses a simple connectionless transmission model
- It’s an alternative to TCP but has no error checking
- Used to send short messages using datagrams, where speed is more important than accuracy
What do the HTTP/HTTPS protocols do?
- HTTP is a way for a client and server to send and receive requests and deliver HTML web pages
- HTTPS is the same as HTTP, but it adds in encryption and authentication
What does the FTP do?
- Used for sending files between computers, normally on a WAN
What do the POP/IMAP/SMTP do?
- Used in conjunction with mail servers to deal with email
- SMTP transfers ongoing emails between servers and from email clients to servers
- POP retrieves emails from a mail server and transfers them to your device, and it removes the email from the server
- IMAP keeps email on the mail server, maintaining synchronicity between devices
What is the concept of layers?
- Divide the complex task of networking into smaller, simpler tasks that work in tandem with each other
What are the advantages of layering?
- Reduces complex problem into smaller sub-problems
- Devices can be manufactured to operate at a particular layer
- Products from different vendors will work together
What is the TCP/IP stack?
- Refers to a set of networking protocols consisting of four layers working together
What are the 4 layers of the TCP/IP stack?
- Application
- Transport
- Internet
- Link
What protocol rules are part of the application layer? What happens at this layer?
- FTP, HTTP, HTTPS, SMTP, IMAP
- Network applications such as web browsers or email programs operate at this layer
What protocol rules are part of the transport layer? What happens at this layer?
- TCP, UDP
- Sets up communication between 2 hosts - they agree settings such as language and packet size
What protocol rules are part of the Internet layer? What happens at this layer?
- IP
- Addresses and packages data for transmission. Routes packets across the network
What protocol rules are part of the link layer? What happens at this layer?
- Copper twister pair, fibre, Wi-Fi
- Network hardware and connection port standards. OS device drivers also sit there. Facilitates the transmission of binary via any media
What is the TCP stack responsible for?
- Establishing an end-to-end connection and maintaining conversations between application processors
How do TCP/IP protocols track sessions?
- By using port numbers
What happens at the transport layer once the connection is made?
- It splits the data into packets, then it adds to each packet:
- Its number/sequence
- The total number of packets
- The port number that the packet should use
What part of the TCP/IP stack does the Internet Layer use?
- IP
What does the IP part of the stack add to each packet?
- Source IP address
- Destination IP address
What is a socket?
- IP address + port
What happens once data reaches the link layer?
- This layer is responsible for adding the unique MAC address of the source device an destination device
- When transmitting data between routers over a WAN, the MAC address is changed at each hop on the route
What does communication between 2 devices on the same LAN require in terms of layers?
- Link layer which creates a frame using MAC addresses
What does communication between 2 devices on the different devices (WAN) require in terms of layers?
- Network layer (which uses IP addresses to create a packet) and link layer frame
What do switches do in terms of MAC addresses?
- They learn and store MAC addresses for connected LAN devices only.
What do routers do in terms of IP addresses?
- Cache some IP addresses
Why do we need both an IP address and a MAC addresses to route traffic over a WAN?
- Because the MAC address is used to show what is needed to be transmitted and the IP address shows where it needs to go roughly
How does the DNS work in the context of accessing a website?
- User requests a URL via a browser
- The browser sends the domain name to a DNS
- the DNS maps the domain name to an IP address and returns it to the browser
- A GET request is sent to the web server using the IP address
- The requested web page is returned to the web browser
What is a LAN?
- Any network that covers a small geographical area, typically located on a single site
Who owns the hardware in a LAN?
- Owned and controlled by the organisation using it
What are LANs typically connected with?
- UTP cables
- Fibre Optic
- Wi-Fi
What is a WAN?
- Any network that covers a large geographical area
- Could also be defined as multiple LAN’s connected together
What are WANs typically connected by?
- Telephone lines
- Fibre Optic Cables
- Satellite links
What is circuit switching?
- It provides the basis for traditional telephone networks
- Circuit switching creates a temporary and dedicated link of fixed bandwidth between source and destination that lasts only until the transmission is complete
Why can circuit switching be a good choice?
- Guarantees quality of the transmission through dedicated bandwidth, making it excellent for data that needs a constant link end-to-end such as real-time video
Why can circuit switching be a bad choice?
- A lot of the potential bandwidth can be wasted
What is packet switching?
- Breaks streams of data into smaller blocks, each sent independently of one another
- At each node, packets are sent via whichever node is the least congested - which maximises bandwidth but doesn’t guarantee the quality of the transmission
- It also means that packets can take different routes to their destination and may arrive out of order
What are the benefits of packet switching over circuit switching?
- Packet switching is more affordable and efficient as all bandwidth can be used at once.
- It also requires less complex infrastructure and can easily respond if parts of the network fail
What are the characteristics of circuit switching?
- It has a physical path between source and destination
- All packets use the same path
- Reserves bandwidth in advance
- Can cause a lot of bandwidth wastage
- No store and forward transmission
What are the characteristics of packet switching?
- It has no physical path
- Packets travel independently
- Does not reserve bandwidth
- No bandwidth wastage
- Supports store and forward transmission
What does a server do in a client-server network?
- Controls access and security for a shared file store
- Manages access to the Internet
- Manages printing jobs
- Provides email services
- Runs regular backups of data
What does a client do in a client-server network?
- Makes requests to the server for data, connections and other services
What are some advantages of a client-server model?
- Easier to manage file security
- Easier to back up shared data
- Easier to install software updates to all computers
What are some disadvantages of a client-server model?
- Can be expensive to set up and maintain
- Requires IT specialists to maintain
- The server is a single point of failure
- Users will lose network access if the server fails
What are client-server networks best suited to?
- Organisations with a large number of computers or situations where many computers need access to the same information
How does a peer-to-peer model work?
- A peer is a computer connected to the network
- A peer is equal to all other peers
- Peers serve their own files to each other
- Each peer is responsible for its own security and data backups
- Peers usually have their own printers
- Peers can send print jobs to another peer to process, but that peer must be switched on to communicate with the printer
What are some advantages of a peer-to-peer model?
- Very easy to maintain
- Specialist staff are not required
- No dependency on a single computer
- Cheaper to set up
- No expensive hardware
What are some disadvantages of a peer-to-peer model?
- The network is less secure
- Users will need to manage their own backups
- Can be difficult to maintain a well-ordered file store
What are peer-to-peer networks best suited for?
- Smaller organisations with fewer computers or where fewer users need access to the same data
