Data Transmission Definition Data Transmission Data transmission occurs between transmitter (sender) and receiver over some transmission medium. This transfer of data takes place via some form of transmission medium (for example, coaxial cable, fiber optics etc.) The successful transmission of data depends principally on two factors: the quality of the signal being transmitted and the characteristics of the transmission medium Analog Transmission Analog signal transmitted without regard to content The signals may represent analog data (e.g. voice) or digital data (e.g. binary data pass through modem) The analog signal will become weaker (attenuate) over distance To achieve longer distances, analog transmission use amplifiers to boost the energy in the signal. Also amplifies noise - With cascaded amplifiers, the signal becomes more and more distorted. Digital Transmission Concerned with content The integrity of the data endangered by noise, attenuation and other impairments. Use a repeater for recovery or replication to be obtained. From the properties of the repeater. Making digital data received at the destination without noise accumulation. Because noise can be solved by using digital repeater is being rebuilt, the repeater itself. Noise is not amplified
Advantages of Digital Transmission: reasons of preferring digital transmission Digital technology - Drop in cost and size of digital circuitry because of the advent of LSI/VLSI technology. Data integrity - With the use of repeaters rather than amplifiers, it is possible to transmit data longer distances over lower quality (less cost) lines. Capacity utilization - High bandwidth links economical. Easier and more efficient multiplexing with digital techniques (time division) Security & Privacy - Encryption techniques can be easily applied to digital data. Integration - Can treat analog and digital data similarly, integration of voice, video, and digital data on the same transmission system is possible. Data transmission Parallel Serial Synchronous Asynchronous Digital Transmission
Parallel Transmission Advantages and Disadvantages of parallel transmission Advantages Speed, Because of the many bits can be transmitted bits to the destination simultaneously. Disadvantages 1. High cost, Because the channels are equal to the number of bits sent. 2. Appropriate for the data transmission short distance because if there is distance risk of error signal. Because each data bit signals sent simultaneously. In long distances, there may be an overlap between the target and not simultaneously.
Serial Transmission Advantages and Disadvantages of Serial Transmission Advantages 1. Saving communication line Using a single communication line. 2. Can transmit data from short distance to long distances. Disadvantages Slow, Because there is only one channel only Chanel.
Serial Transmission can be Asynchronous Transmission or Synchronous Transmission Asynchronous Transmission In asynchronous transmission, As a way to send information to the media by generally without clock signal. Each data character is preceded by a start-bit and is followed by an end-bit to inform the receiving equipment where the character begins and ends. To indicate the extent of data This may be a Gap between bytes but also add a bit used to check the accuracy with the Parity bit we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte. It also adds a bit used to check the accuracy with the Parity bit. Asynchronous here means asynchronous at the byte level, but the bits are still synchronized; their durations are the same. Example:
Advantages of Asynchronous Transmission The addition of stop and start bits and the insertion of gaps into the bit 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. Synchronous Transmission In synchronous transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits. Timing becomes very important, therefore, because the accuracy of the received information is completely dependent on the ability of the receiving device to keep an accurate count of the bits as they come in. Example: The advantage of synchronous transmission is speed. With no extra bits or gaps, synchronous transmission is faster than asynchronous transmission. As a way to deliver better performance asynchronous. Because the signal is actually a lot. Compared to the signal sent out to all. Present in signaling methods are used to transfer large amounts of data is widely used on mainframe computers. Applied to Wide Area Network (WAN). For this reason, it is more useful for high-speed applications such as the transmission of data from one computer to another. Byte synchronization is accomplished in the data link layer.
The difference between asynchronous transmission and synchronous transmission. Is a continuation of the transmitted data. In synchronous sent out continuous no-start bit or stop bit. Or even Parity bit. protocol used to send synchronous so different from asynchronous. Transmission Impairments Signal received may differ from signal transmitted For analog signal these impairments can degrade the signal quality For digital signals bit errors may be introduced, a binary 1 can be transformed into a binary 0 and vice versa. The most significant impairments are: - Attenuation and attenuation distortion - Delay distortion - Noise Attenuation means a loss of energy. When a signal, simple or composite, travels through a medium, it loses some of its energy in overcoming the resistance of the medium. To compensate for this loss, amplifiers are used to amplify the signal. Signal strength falls off with distance Attenuation depends on medium: - For guided media: it is exponential and expressed as a constant number of decibels per unit distance. - For unguided media: it is a complex function of distance and makeup of the atmosphere. The received signal strength must be: - enough to be detected by the electronic circuitry in the receiver. - sufficiently higher than noise to be received without error It is important to know that attenuation is an increasing function of frequency
Delay Distortion: means that the signal changes its form or shape. Distortion can occur in a composite signal made of different frequencies because: Only occurs in guided media Propagation velocity varies with frequency Hence various frequency components arrive at different times Each frequency signals, An Attenuation by the transmission medium with different rates. Noise : will be inserted. During the wave travels from the transmitter (sender). To the receiver Effect of noise