Data Representation & Communication Essentials

Representation of Data

  • General Idea
    • All data types (text, numbers, images, audio, video) are ultimately converted into a pattern of bits (0s and 1s) before being transmitted or stored.
    • The specific conversion method depends on the nature of the data.

Text

  • Represented as a bit pattern whose length is determined by the number of symbols in the language set.
  • Example: For the English alphabet (26 uppercase letters A–Z), each letter is mapped to a unique bit pattern.
  • Industry-standard mappings include ASCII, Unicode, etc.
  • Key takeaway: the mapping table (e.g., ASCII) is required so both sender and receiver agree on which bit pattern represents which letter.

Numbers

  • Numbers are not mapped with character tables like ASCII.
  • Instead, the numeric value is directly converted to its binary equivalent.
    • Example: 13{10}=1101{2}.
  • Eliminates the need for a lookup table, saving overhead.

Images

  • An image is logically sliced into a matrix of pixels (picture elements).
    • Each pixel is a tiny dot carrying color or grayscale information.
  • Resolution refers to the number (and size) of pixels. Higher resolution ⇒ more pixels ⇒ more detailed image.
  • Resulting pixel values (intensity or RGB triplets) are then turned into bit patterns for storage/transmission.

Audio

  • Audio is a continuous (analog) representation of sound waves.
    • Even when captured with a microphone and turned into an electrical signal, the original signal remains continuous.
  • To transmit/store digitally, analog audio must be sampled and quantized; however, the transcript only stresses its inherent continuity.

Video

  • Video may originate in two ways:
    1. As a single continuous signal (e.g., live TV camera).
    2. As a rapid sequence of discrete images/frames stitched together to create motion.
  • Both analog and digital conversions are possible.
  • Digital video essentially becomes a time-ordered collection of image frames, each frame itself a pixel matrix.

Data Communication: Definition

  • “Telecommunication” literally means communication at a distance.
  • “Data” = information in any agreed-upon form.
  • Data Communication = exchange of data between two or more devices via some transmission medium (cable, fiber, air, etc.).
  • Successful communication requires both hardware (physical equipment) and software (protocols/programs).

Characteristics of an Effective Data-Communication System

  • Accuracy
    • Delivered data must be free from uncorrected errors; otherwise, it is unusable.
  • Delivery
    • Data must reach the correct destination (right device/user).
  • Timeliness
    • Data must arrive on time.
    • For real-time media (audio/video) the data has value only if delivered at the rate it is produced.
    • This on-the-fly requirement is called real-time transmission.

Components of a Data-Communication System

  1. Sender
    • Device that originates the message.
    • Examples: computer, workstation, telephone handset, video camera.
  2. Receiver
    • Device that accepts the message.
    • Can be identical categories as the sender (workstation, phone, camera, etc.).
  3. Transmission Medium
    • Physical path carrying the data from sender to receiver.
    • Two broad classes: guided (coaxial cable, fiber-optic, twisted pair) and unguided (radio waves, microwaves, infrared).
  4. Message
    • The actual information: text, numbers, images, sound, video, or any mixture thereof.
  5. Protocol
    • A formal set of rules that govern the communication process.
    • Ensures both devices “speak the same language,” analogous to two human speakers agreeing on French, Japanese, etc.
    • Without protocol, connected devices may still be unable to understand one another.

Directions of Data Flow (Modes of Transmission)

Simplex

  • Unidirectional — data flows in one direction only.
  • Device roles are fixed: one always transmits, one always receives.
  • Metaphor: one-way street.
  • Examples:
    • Keyboard → computer (keys only send).
    • Traditional monitor ← computer (screen only receives).

Half-Duplex

  • Devices can both transmit and receive, but not simultaneously.
  • At any given moment, the entire channel capacity belongs to whichever side is sending.
  • Metaphor: single-lane, two-direction road where cars in one direction must wait while the other direction uses the lane.
  • Examples: walkie-talkies, citizens-band (CB) radios.

Full-Duplex (Duplex)

  • Both devices transmit and receive simultaneously.
  • Metaphor: two-way street with lanes for each direction.
  • Example: standard telephone conversation (both parties speak and listen concurrently).

Practical / Real-World Relevance & Connections

  • Choosing simplex vs. half-duplex vs. full-duplex affects bandwidth utilization, hardware complexity, and user experience.
  • Real-time requirements (timeliness) dominate modern applications: streaming, VoIP, telemedicine, online gaming.
  • Protocol agreements (e.g., TCP/IP, HTTP, RTP) build on the basic definition in the transcript, ensuring global interoperability.
  • Error-control mechanisms (
    \text{Parity},\;\text{CRC},\;\text{ARQ}) directly target accuracy, while quality-of-service (QoS) techniques address timeliness.

Ethical & Philosophical Considerations (Implied)

  • Ensuring accurate and timely delivery has societal implications: misinformation or delayed emergency data can have real consequences.
  • Open, standardized protocols promote accessibility and fairness, preventing vendor lock-in and fostering innovation.