Data Transmission Fundamentals

Representing Images

• A bitmap image consists of pixels arranged in a grid
• Each pixel is represented by a binary code
• The resolution refers to the number of pixels in the image.
• A higher resolution results in a sharper, more detailed image
• Higher resolutions require more storage space.
• Colour depth is the number of bits used to represent each colour.
• A higher colour depth means that more colours can be represented
• Higher colour depths result in more realistic images.
• Higher colour depths also require more storage space.
• An 8-bit colour depth allows for 256 different colours to be represented.
• A 24-bit colour depth allows for over 16 million different colours to be represented.
• The file size of an image increases as the resolution and colour depth increase
• More pixels and colours require more binary data to represent them.
• The quality of an image increases as the resolution and colour depth increase
• It is important to balance the desired quality with the practical limitations of storage space.

Representing Sound

• Sound is a type of analog signal that is captured and converted into digital form for processing
• Converting sound into digital form requires using a process called sampling
• Sampling involves taking measurements of the sound wave at regular intervals
• Sampling also means converting these measurements into binary data
• The quality of digital sound depends on the sample rate
• Sample rate refers to the number of samples taken per second
• A higher sample rate results in a more accurate representation of the original sound wave
• A higher sample rate increases the file size of the digital sound

Sample Rate

• A typical CD-quality digital sound has a sample rate of 44.1 kHz, meaning 44,100 samples are taken per second.
• Sample resolution affects the quality of digital sound
• Sample resolution refers to the number of bits per sample, determining the level of detail and accuracy.
• A higher sample resolution results in a more accurate representation of the sound wave
• A higher sample resolution increases the file size of the digital sound.
• A CD-quality digital sound typically has a sample resolution of 16 bits
• Each sample is represented by a 16-bit binary number with 16 bit resolution

Choosing Sample Rate

• It's important to choose the appropriate sample rate and resolution
• Sample rate and resolution are chosen based on the specific requirements of the digital sound application.
• High-quality music recordings need higher sample rate and resolution
• Voice recordings for podcasts need a lower sample rate and resolution

Sound Files

• MIDI and MP3 are two examples of sound files

MIDI

• MIDI stands for Musical Instrument Digital Interface file
• MIDI files store a set of instructions for how the sound should be played.
• MIDI files do not store the actual sounds
• The data in MIDI files has been recorded using digital instruments.
• MIDI files specify the note to be played.
• MIDI files specify when each note starts and stops playing
• MIDI files specify the duration of the note.
• MIDI files specify the volume of the note.
• MIDI files specify the tempo of the note.
• MIDI files specify the type of instrument.
• Individual notes in MIDI files can be edited.

MP3 Format

• MP3 is a format for digital audio
• MP3 is an actual recording of the sound
• MP3 is a lossy compression format.
• MP3s are recorded using a microphone

Character Sets

• Text is a collection of characters that can be represented in binary.
• Binary is the language that computers use to process information
• To represent text in binary, a computer uses a character set
• A character set is a collection of characters and the corresponding binary codes that represent them
• ASCII stands for American Standard Code for Information Interchange
• ASCII is one of the most commonly used character sets
• ASCII assigns a unique 7-bit binary code to each character, including uppercase and lowercase letters, digits, punctuation marks, and control characters.
• The ASCII code for the uppercase letter "A" is 01000001
• The ASCII code for the character "?" is 00111111
• ASCII has limitations in terms of the number of characters it can represent
• ASCII does not support characters from languages other than English
• Unicode was developed to address the limitations of ASCII.
• Unicode allows for a greater range of characters and symbols than ASCII, including different languages and emojis.
• Unicode uses a variable-length encoding scheme
• Unicode assigns a unique code to each character, which can be represented in binary form using multiple bytes
• The Unicode code for the heart symbol is U+2665, represented in binary as 11100110 10011000 10100101.
• Unicode requires more bits per character than ASCII
• Unicode results in larger file sizes and slower processing times when working with text-based data.

Packet Switching

• Sending packets over the internet is referred to as packer switching
• Packet switching is more efficient than circuit switching

Packet Switching Involves:

• Routers know which nearby router is closer to the destination device
• Like normal car traffic, data traffic may build up on the internet
• Routers may decide to send a packet down a different route that avoids traffic.
• Packets from the same message can take different routes
• Packets from the same message may arrive in different orders
• The receiver's computer reassembles the message by reordering the packets using the packet numbers
• Breaking down a file into packets and sending these packets down different routes over the internet (via routers) from a source to a destination will allow reassembling them at the end
• Packet numbers allow for the original message to be re-assembled in the correct order
• Routers contain routing tables which keep track of nearby routers like a map or contacts list
• If a packet does not reach its destination the receiver can send a resend request to the sender to resend the packet

Packet Advantages

• Interference and corruption are minimal where individual packets can be resent if they are lost or damaged
• The whole file doesn't need to be resent if a corruption occurs, only the individual packets that were corrupted need to be resent
• Internet bandwidth is saved by resending the entire information
• Packet switching is quicker than sending a large packet as each packet finds the quickest way around the network
• It's harder to hack an individual's data since each packet contains minimal data, and travels through the network separately

Data Transmission

• Compression is necessary to reduce the size of large files for storage, transmission, and faster processing
• The choice between lossy and lossless compression methods depends on the type of file and its intended use.
• Lossy compression is generally used for media files where minor data loss is acceptable, while lossless compression is used for text, code, and archival purposes.

Data Packets

• Information on the internet is broken down into packets and are created by TCP
• Transmitted over the internet
• Packets are small chunks of information/data
• TCP stands for Transmission Control Protocol which is used to organise data transmission over networks
• Small chunks of data are easier and quicker to route over the internet than big chunks of data
• Routing involves finding the most optimal path over a network
• Data in packets includes anything from text, images, audio, video, animations, etc, or any combination of these
• Packets contain chunks of information referred to as the "payload."
• Packets act like postage letters, having a delivery address, known as the destination IP address.

Packet Components

• Packets are split into three parts:
• Packet header
• Payload (the actual data)
• Trailer
• The header contains:
  • A return address (source IP address)
  • Source IP
  • Destination IP
  • Packet number
  • Error checker like a checksum or parity bit
• The trailer contains:
  • Additional error checks
  • End of packet notification
• A sample message "This is a message :)" is broken into 4 data packets for transmission, each representing a fragment of the message.
• Each packet figure contains a source IP address, destination IP address, payload (the data), and a packet number
• Individual packet structure depends on the protocol used to create them variations exist.
• Error checks ensure that a packet is received with minimal or no data corruption
• Corruption occurs when packet data is changed, lost, or added
• Parity bits check for bit flips from 0 to 1 or vice versa
• Checksums calculate and compare results to identify data corruption

Wired Connections

• Wires can be serial: where one bit is sent at a time across a single wire
• Wires can be parallel: where Multiple bits are sent at a time across several wires
• Transmission is asynchronous as some bits may arrive quicker than others
• Asynchronous transmission = skewing or skewed data that does not always arrive at the same time

Data Transmission Types

• Simplex Transmissions are a unidirectional transmission that only travels one direction
• Half-duplex transmissions are Bi-directional transmissions that travels in both directions but they can not transmit at the same time
• Full-duplex Transmission are bidirectional transmission that transmit signals in both direction at the same time
• Wires can be combination of serial, parallel, simplex, half-duplex, full-duplex

Advantage & Disadvantages: Serial

• Advantage: Data will arrive in the order it is sent, less likely to have errors and is cheaper over short and long distances where wire cost is fairly cheap
• Disadvantage: Data transmission is slow, especially over long distances with small quantities of data transmitted at a time
• Disadvantage: Serial transmission is expensive over very long distance as wire cost increases over distance

Advantage & Disadvantages: Parallel

• Advantage: Parallel transmission is fast, large quantities of data sent at one time
• Disadvantage: Parallel transmission is expensive over short distances as multiple wires need to be purchased
• Disadvantage: Parallel transmission is very expensive where long distances are incurred as wire costs increases with distance
• Disadvantage: Delays caused if data arrives asynchronously as receiver waits for all bits before accepting new data where this is true over longer distances