Monday, April 22, 2013

Basics of Data Communication

By the help of direct, two-level electrical signals over simple copper conductors, the digital data can be transmitted. These types of transmission are needed as the distance over which data moves within a computer may vary from a few thousandths of an inch. In this case within a single IC chip, to as much as several feet along the backplane of the main circuit board, the help of copper conductors are utilized. The circuit designers are not concerned about the shape of the conductor or the analog characteristics of signal transmission except for the fastest computers.

The data should be sent beyond the local circuitry that constitutes a computer. The distances involved may be enormous in many applications. As the distance between the source of a message and its destination increases, efficient transmission of data becomes increasingly difficult. This is mainly due to the electrical distortion of signals occurs while traveling through long conductors and from noise added to the signal as it propagates through a transmission medium, which is generally called as the Channel in a communication network. The biggest challenge occurs when the data is transferred to devices outside the computer's circuitry. In such applications, the distortion and noise influenced through the channel can become so severe that information may be lost.

The transmission of digital messages to devices external to the message source, Data Communications is mainly concerns. The maximum permissible transmission rate of a message is directly proportional to the signal power and is inversely proportional to channel noise. The aim of any communications system is to provide the highest possible transmission rate at the lowest possible power and with the least possible noise. In other words, the task of a communication is to increase the data (signal) strength and to minimize the noise content. This can be represented by the Signal to Noise ratio (SNR). The aim of any communication network should be to maximize the SNR strength. Here Maximizing the SNR will leads to the minimization of the noise content.

Serial Communications:

Most digital messages are greatly longer than just a few bits. Since it is neither practical nor financial to exchange all bits of a long data at the same time, the data is broken into smaller parts and passed on sequentially. Bit-serial transmitting provides a one bit data at some point through a route in transmitter-receiver link. Each bit symbolizes a part of the data. The individual pieces are then put back together at the destination to restore the data. In general, one route will pass only one bit at some point. Bit-serial transmitting is usually called serial transmitting and is the most chosen transmission method in many computer peripheral devices.

The byte-serial transmitting provides eight pieces at some point through eight similar channels. Although the raw exchange rate is eight periods faster than in bit-serial transmitting, eight channels are needed, and the cost may be as much as eight periods higher to deliver the data. When ranges are short, it may however be both feasible and financial to use similar programs in return for high information rates. The popular Getronics printer interface is a case where byte-serial transmitting is used. As another example, it is common practice to use a 16-bit-wide information bus to exchange information between a micro-processor and memory chips; this provides the equivalent of 16 similar programs. On the other hand, when interacting with a time period discussing system over a computer, only one route is available, and bit-serial transmitting is required.

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