Data transmission methods
Transmission is the act of transporting information from one location to another via a signal. The signal may be analog or digital, and may travel in different media. Transmission: Communication of data by propagation and processing of signals. Signal processing is the representation, transformation and manipulation of signals plus the information they contain. Signal Types
Signals: An electric or electromagnetic representations of data by which data is propagated (transmitted). All signals are either analog or digital. An analog signal: is one in which information appears as a continuous variation of some property. Human speech is an example: it produces a continuous variation of air pressure. Examples of media: Copper wire media, (twisted pair and coaxial cable), fiber optic cable and atmosphere or space propagation. Analogue signals represent some physical quantity and they are a ‘MODEL’ of the real quantity and can propagate analogue and digital data. A digital signal: is one in which information appears as a sequence of binary values 0 and 1. Digital signals have two amplitude levels called nodes. The value of which are specified as one of two possibilities such as 1 or 0, HIGH or LOW, TRUE or FALSE and so on. Digital signals can propagate analogue and digital data To represent these two values, a signal is used in which only two wave shapes are allowed, one representing the binary value 0 and the other representing the binary value 1. By definition, therefore, a digital signal is a restricted form of an analog signal. A human speaker who only utters the two words zero and one is a crude example of a digital signal. The difference between digital signals and analog signals:
Analog signal is a continuously varying signal while digital signal has discrete values 2.
Analog signal has many issues of intensity over a period of time while a digital signal has only a limited number of defined values. 3.
Since digital computers play a central role in data communication, in nearly all cases, digital signals are used. Analog signals are used in cases of equipment which date back to before the advent of digital technology. Existing analog telephone networks are a good example of the latter.
continuous (e.g., voice)
discrete (e.g., text)
continuous electromagnetic waves
Used mainly for transmitting data across a network.
sequence of voltage pulses
Used mainly internally within computers.
1. Transmission of analog signals without regards to their content (the data may be analog or binary). 2. The signals become weaker (attenuated) with the distance. 3. Amplifiers may be used to strengthen the signals, but as side effect they also boost the noise. 4. This might not be a problem for analog data, such as voice, but is a problem for digital data.
1. Transmission that is concerned with the content of the signal. 2. Repeaters are used to overcome attenuation.
3. A repeater recovers the digital pattern from the signal it gets, and resubmits a new signal.
Analog and Digital Data Transmission
Digital and Analog transmission have more to do with the way in which data is conveyed between point A and point B than with whether the data is digital or analog. Analog data can be transmitted using analog transmission or digital transmission techniques. Likewise, digital data can be conveyed using either digital or analog transmission. Before data is transmitted over a network, it must be encoded depending on what type it is. For example: Audio, text, video or graphical giving it its computer representation. This encoding depends basically on the physical medium used to transfer the data, the guaranteed data integrity and transmission speed. Data transmissions depend on the characteristics of the signal and of the medium. •
For guided media, the medium is the dominant factor
For unguided media, the bandwidth of the signal...
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