Data Communication Concepts and Transmission Methods
Data Communication Fundamentals
Core Concepts in Data Communication
Data Communication: The process of communicating information in binary form between two or more points. It requires four basic elements:
- Transmitter: A device that transmits data.
- Message: The data to be transmitted.
- Medium: The path data takes from source to destination.
- Receiver: The device receiving the data.
Bit: The smallest unit of information and the base unit for communications.
Byte: The minimum continuous set of bits that enables routing information within a computer system. It consists of 8 bits.
Frame: A sequence of bits with a predefined format used in bit-oriented protocols.
Packet: Pieces of a message with a predefined size, where each part or packet contains information on origin and destination, as well as information required for the reassembly of the message.
Interface: A connection that enables communication between two or more devices.
Code: An agreement on a set of meanings defining a series of symbols and characters. Any combination of bits represents a character within the code table. The most recognized code tables are the ASCII code and the EBCDIC code.
Parity: A technique that involves adding a bit to a character or a block of characters to force the collection of ones (1) to be even or odd. It is used for error checking to validate data. The parity bit can be zero (0 = SPACE) or one (1 = MARK).
Modulation: The process of manipulating the properties of a carrier signal in a controlled way to encode the information to be transmitted.
DTE (Data Terminal Equipment): Equipment that acts as the source or destination of data. Examples include computers (Hosts, Microcomputers, and Terminals).
DCE (Data Communications Equipment): Equipment that handles the conversion between the DTE and the transmission channel; essentially, the equipment connecting the DTE to communication lines.
Transmission Resources, Forms, and Types
Transmission Media
- Air: Based on radio-electric signals (using the atmosphere as the transmission medium), laser beams, or infrared rays.
- Solid: Primarily copper (twisted-pair or coaxial cable) and fiber optics.
Transmission Forms
Serial Transmission: Bits are transmitted one by one over a single line. It is used for transmitting over long distances.
Parallel Transmission: Bits are transmitted simultaneously in groups over multiple lines at the same time. Used primarily within computers.
Parallel transmission is faster than serial transmission. However, as the distance between equipment increases (should not exceed 100 feet), cables become more expensive, and the complexity of transmitters and line receivers increases due to the difficulty of transmitting and receiving pulse signals over long cables.
Transmission Types
Simplex Transmission: Data transmission occurs in only one direction. The sending and receiving nodes always maintain their respective functions.
Half-Duplex Transmission: Data transmission occurs in both directions, but only one direction at a time (alternating). If a device is receiving data, it cannot transmit simultaneously.
Full-Duplex Transmission: Data transmission occurs in both directions simultaneously. One end receiving data can simultaneously be transmitting other data.
Asynchronous Transmission: Each byte of data includes start and stop signals at the beginning and end. The purpose of these signals is to:
- Notify the recipient that data is arriving.
- Provide sufficient time for the receiver to perform synchronization functions before receiving the next byte.
Synchronous Transmission: Uses separate clock channels to manage the timing of data receipt and transmission. At the beginning of each transmission, specific preliminary signals are used:
- Sync bytes for byte-oriented protocols.
- Flags for bit-oriented protocols.
Their primary purpose is to alert the receiver about the incoming data.
Note: Clock signals determine the speed of transmission and reception.