09 Mar 10 Data Communication Characteristics
Data communication is characterized by the number of bits transmitted at a time, the direction of communication and the synchronization.
Serial and Parallel Transmission
Data can be transferred serially or in parallel. Serial transmission occurs when one bit is transferred at a time. When 8 bits are received, it is interpreted as one symbol. Parallel transmission sends 8 bits all at once over different wires. Parallel transmission is faster than serial transmission. Parallel transmission is often used between a computer and a printer. When two computers communicate over analog telephone lines, there is only a single wire available; so serial communication is used.
Synchronous and Asynchronous Transmission
Data transmission could be either synchronized or asynchronized. Synchronous transmission is based on time. With synchronous transmission, bits are transmitted at specific time intervals. For example, the transmitting device will send one bit every 125 ms, and the receiving device will receive a bit every 125 ms. These devices need to be synchronized for this type of transmission.
Asynchronous transmission is not based on time. Digital data is transmitted with varying intervals between characters. Start and stop bits flag the beginning and end of each character. Asynchronous transmission is usually the method for data communication over analog telephone lines.
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