Asynchronous Data Transmission
Asynchronous transmission is so named because the timing of the signal is unimportant. Instead, information is received and translated by agreed upon patterns. As long as those patterns are followed, the receiving device can retrieve the information without regard to rhythm in which it is sent. Pattern is based on grouping the bit stream into bytes. Each group, usually bits is along the link as a unit. The sending system handles each group independently, relaying it to the link whenever ready without regard to timer.
Without synchronization, the receiver cannot use timing to predict when the next group will arrive. To alert the receiver to the arrival of a new group, therefore, an extra bit is added to the beginning of each byte. This bit, usually a zero, is called start bit. To the receiver know that the byte is finished, I or additional bits are appended to the end of byte. These bits, usually 1s, are called stop bits. By this method each method byte is increased in size to at least 10 bits, of which information and 2 bits or more are signals to the receiver. In addition, the transmission of each byte may then be followed by a gap of varying duration. This gap can be represented either by an idle channel or by a stream of additional stop bits.
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| Asynchronous Data Transmission |
The start and stop bits and the gap alert the receiver to the beginning and end of each byte and allow it to synchronize with the data stream. This mechanism is called asynchronous because, at the byte level, the sender and receiver do not to be synchronized. But within each byte, the receiver must still be synchronized with the incoming bit stream. That is, some synchronization is required, but only for the duration of a single byte. The receiving device synchronizes at the onset of each new byte. When the receiver detects a start bit, as soon as it detects the stop bit, it waits until it detects the next start bit. The addition of stop and start bits and the insertion of gaps into the stream make asynchronous transmission slower than forms of transmission that can operate without the addition of control information. But it is cheap and effective, two advantages that make it an attractive choice for situations such as low speed communication.
Keywords: data transmission network, data transmission, cellular data transmission, fiber optic data transmission, types of data communication, synchronous
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