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Concept
Node-to-node data transfer
Summary
In telecommunications, node-to-node data transfer is the movement of data from one node of a network to the next. In the OSI model it is handled by the lowest two layers, the data link layer and the physical layer.
In most communication systems, the transmitting point applies source coding, followed by channel coding, and lastly, line coding. This produces the baseband signal. The presence of filters may perform pulse shaping. Some systems then use modulation to multiplex many baseband signals into a broadband signal. The receiver un-does these transformations in reverse order: demodulation, trellis decoding, error detection and correction, decompression.
Some communication systems omit one or more of these steps, or use techniques that combine several of these steps together. For example, a Morse code transmitter combines source coding, channel coding, and line coding into one step, typically followed by an amplitude modulation step. Barcodes, on the other hand, add a checksum digit during channel coding, then translate each digit into a barcode symbol during line coding, omitting modulation.
See main article Data compression
Source coding is the elimination of redundancy to make efficient use of storage space and/or transmission channels.
Examples of source coding are:
Huffman coding
Morse code
Binary coding
See main article Error correction and detection.
In digital telecommunications, channel coding is a pre-transmission mapping applied to a digital signal or data file, usually designed to make error-correction (or at least error detection) possible.
Error correction is implemented by using more digits (bits in cases of binary channel) than the number strictly necessary for the samples and having the receiver compute the most likely valid message that could have resulted in the received one.
Types of channel coding include:
Parity checks
Hamming code
Reed-Muller code
Reed-Solomon code
Turbo coding
See main article Line code
Line coding consists of representing the digital signal to be transported, by an amplitude- and time-discrete signal, that is optimally tuned for the specific properties of the physical channel (and of the receiving equipment).
Official source
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