Today’s data is transfered over reliable communications. This is achieved by using error detection and control. There are different communications media with different quality of service (QOS). Consequently, there are several error detection and control schemes for different signal conditions. Some fundamental methods have existed for decades. In addition, there are also new methods that can take advantage of the nature of the signal type. These methods can be used to ensure reliable or adequate communications and faster data transfer rates which are used in today’s innovative applications.

1. Error sources

No errors can occur in the ideal transmission medium. However, none of the transmission media is ideal. The signal representing the data is always subject to various error sources. As the signal propagates along the transmission media its amplitude decreases. This phenomenon is called as the signal attenuation. The signal cannot be detected if it is too weak. In addition, as the length of the medium increases the waveform also changes during the transmission. This phenomenon is called as the delay distortion. The signal cannot be recognized if it is too distorted. Furthermore, the transmission media can also be a subject to interference resulting from other cables or signals caused by electromagnetic radiation. The medium itself may also cause constant white noise. All transmission errors increase as the length of the transmission medium inreases. [6]

2 Error bursts

In practice, data communications systems are designed so that the transmission errors are within acceptable rate. Under normal circumstanced there are only few errors. However, it is possible that the signal conditions can be sometimes so weak that sometimes the signal cannot be received at all. It is also possible that sometimes the interference signal is stronger than the signal to be transmitted. Consequently, the data sent during the break is lost. The contiguous blocks of data corrupted by the error signal are called error bursts. The length and frequency of the error bursts depend on the quality of the data link which in turn depends on the transmission medium and the signal conditions. Therefore, the error detection and control should be able to handle as many errors that possible. However, the applications limit which error detection and control schemes are suitable. All applications benefit from the effeciency of the sheme to be used. In addition, some applications may require short codeword length or low latency whereas some other applications might prefer extremere low error rate, for example.

3 Error detection

Error detection is a method that allows some sommunications erros to be detected. The data is encoded so that the encoded data contains additional redundant information about the data. The data is decoded so that the additional redundant information must match the original information. This allows some errors to be detected. Unfortunately, some error bursts may cause incorrectly received blocks which pass the error detection test. Therefore, good error detection schemes are designed so that this should occur as infrequently as possible.

4 Error Control

Error control is a method that can be used to recover the corrupted data whenever possible. There are two basic types of error control which are backward error control and forward error control. In backward error control, the data is encoded so that the encoded data contains additional redundant information which is used to detect the corrupted blocks of data that must be resent. On the contrary, in forward error control (FEQ), the data is encoded so that it contains enough redundant information to recover from some communications errors.

5 Conclusion

The conventional error detection and correction methods are still being used is conventional application. Today’s services can be implemented by using conventional methods. However, new methods have been discovered to increase the data transfer rate on some applications. These methods can certainly take advantage of the nature of the signal in a way that could not be achieved by using conventional methods. These new techniques are necessary for tomorrow’s multimedia applications especially as the amount of the IP-based and mobile network traffic increases.