Parallel vs. Serial Data Transmission: Types & Channels
Parallel vs. Serial Data Transmission
Parallel Transmission:
In parallel transmission, all bits are transmitted simultaneously, followed by a brief pause before the next set of bits. This type of transmission typically occurs inside a machine or between machines when the distance is very short.
The main advantage of parallel transmission is its high transmission rate. The biggest disadvantage is the cost.
Data multiplexing can also be considered a form of parallel transmission, where data is transmitted on a single line, with different data streams interleaved during transmission.
Parallel Transmission
Serial Transmission
In serial transmission, the ‘n’ bits comprising a message are transmitted one after another over the same line.
Serial data
When data exits a machine in parallel format, it is converted into serial data for transmission. At the receiving end, the reverse process takes place, converting the serial data back into parallel format. The sequence of bits transmitted is in order of increasing weight, and usually includes a parity bit as the last bit. An important aspect of serial transmission is synchronous transmission, which refers to the process by which the transmitter and receiver recognize the zeros and ones of the bits in the same way.
Timing can be at the bit level, byte level, or block level, where each level identifies the beginning and end of the data unit. Within serial transmission, there are two main methods:
Asynchronous Transmission
Asynchronous transmission, also known as start/stop transmission, requires a start bit to signal the beginning of a character and a stop bit to indicate the completion of the character or block.
Format character
Typically, when there is no transmission, the line is at a high level. Both the transmitter and the receiver know the number of bits that make up the character (e.g., 7 bits in the example). Stop bits specify the number of bits per character, and a start bit exists between different characters after the stop bit. Despite being commonly used, asynchronous transmission has a disadvantage: low performance. For example, if a character is 7 bits, the transmission requires 10 bits (including start and stop bits). Thus, only 70% of the transmitted bits belong to the actual data.
Synchronous Transmission
In synchronous transmission, the transmitter and receiver must use the same clock frequency. Transmission is done in blocks, which are defined by two groups of bits called delimiters. These delimiters indicate the beginning and end of each block. This method is more effective because the flow of information occurs uniformly, enabling higher data rates. To achieve synchronization, the transmitter sends a signal through the start bit, which activates the receiver clock. From that moment on, the transmitter and receiver are synchronized. Another way to achieve synchronization is by using self-synchronizing codes, which can identify the beginning and end of each bit.
Communication Channel
A communication channel refers to the physical resource that must be established between various means of transmission to communicate.
The communication channel is also called a link.
Types of Communication
Simplex
In simplex communication, the transmitter and receiver are clearly defined, and communication is unidirectional. Such communications are generally used in broadcast networks, where recipients do not need to send any data back to the transmitter.
Duplex or Semi-Duplex
In duplex or semi-duplex communication, both ends of the communication system can act as both transmitter and receiver. Data moves in both directions, but not simultaneously. This type of communication is commonly used in the interaction between terminals and a central computer.
Full Duplex
Full-duplex communication is similar to duplex, but data moves in both directions simultaneously. To achieve this, both transmitters have different transmission frequencies or two separate communication paths, while half-duplex communication normally requires only one. For the exchange of data between computers, full-duplex communications are more efficient than half-duplex transmissions.