Transmission Impairment
Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received.
The three different causes of impairment are attenuation, distortion, and noise.
Add a commentPerformance of the Network
One important issue in networking is the performance of the network. The different factors which effects performance of the Network are as follows:
One characteristic that measures network performance is bandwidth. However, the term can be used in two different contexts with two different measuring values: bandwidth in hertz and bandwidth in bits per second.
Line Coding and Its Characteristics
Line coding is the process of converting digital data to digital signals.
The data may be in the form of text, numbers, graphical images, audio, or video, are stored in computer memory as sequences of bits.
Line coding converts a sequence of bits to a digital signal. At the sender, digital data are encoded into a digital signal; at the receiver, the digital data are recreated by decoding the digital signal.
Different Line-Coding Techniques
The Line Coding schemes are categorized as shown in the following figure:
Different Block Coding Techniques
We need redundancy to ensure synchronization and to provide some kind of inherent error detecting. Block coding can give us this redundancy and improve the performance of line coding.
Block coding changes a block of m bits into a block of n bits, where n is larger than m. Block coding is referred to as an mB/nB encoding technique.
Block coding normally involves three steps: division, substitution, and combination. In the division step, a sequence of bits is divided into groups of m bits.
Add a commentDifferent Scrambling Techniques for Data Transfer:
Biphase schemes that are suitable for dedicated links between stations in a LAN are not suitable for long-distance communication because of their wide bandwidth requirement. The combination of block coding and NRZ line coding is not suitable for long-distance encoding either, because of the DC component. Bipolar AMI encoding, on the other hand, has a narrow bandwidth and does not create a DC component. However, a long sequence of Os upsets the synchronization. If we can find a way to avoid a long sequence of Os in the original stream, we can use bipolar AMI for long distances. One solution to this is called as scrambling.
If we can find a way to avoid a long sequence of Os in the original stream, we can use bipolar AMI for long distances. One solution to this is called as scrambling.
Add a commentAnalog to Digital Conversion Techniques
If we have an analog signal such as one created by a microphone or camera. To change an analog signal to digital data we use two techniques, pulse code modulation and delta modulation. After the digital data are created (digitization) then we convert the digital data to a digital signal.
Different Transmission Modes
The primary concern in the transmission of data from one device to another is the wiring and how to send the data stream. Do we send 1 bit at a time or group bits into larger groups. The transmission of binary data across a link can be accomplished in either parallel or serial mode. In parallel mode, multiple bits are sent with each clock tick. In serial mode, 1 bit is sent with each clock tick. The different transmission modes are as shown in the following figure.
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