Message and Structured Data
The term data communication describes the transmission of computer related records, which have a structured format, from source to destination over transmission media like telephone line, optical fibre, microwave link, etc.
Other forms of digital transmission such as digitized voice, facsimile or video do not use structured data except in the case of telemetry, which can use fixed data field and formats.
Each record of a structured data type is identified by a transaction code; the data is organized into predefined fields, each of which contains a specified maximum number of characters.
Bits Streams and Symbols
The characters which make up a message are transmitted one after another as a bit stream, where a bit is the fundamental data unit represented as 1 or 0, mark or space in digital systems.
A symbol is the basic transmission element, which is used to transmit a group of bits.
Data Rate
Data Rate is measured as bits per second. When group of k bits is combined to form a transmission symbol which has a transmit duration T, then
Data Rate = k/T
Baud Rate
Baud rate is the transmit speed of a communication channel in bits per second. For example, 4800 baud is 4,800 bits/second of data transfer.
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