Communication Systems Revision Set 2

The range of frequencies a transmission channel occupies is known as its bandwidth. Bandwidth refers to the amount of data that can be transmitted through a channel in a given amount of time. It represents the capacity of the channel to carry information and is typically measured in hertz (Hz). Symbol rate refers to the number of symbol changes per second, baud refers to the number of signal elements per second, and speed is a general term that can refer to various aspects of a transmission channel.

The baud rate refers to the number of signal events that occur in one second. It is a measure of the signaling speed or the rate at which data is transmitted. The term "baud" is often used interchangeably with "bits per second," but they are not the same. Baud rate specifically refers to the number of signal events, while bits per second refers to the number of bits transmitted per second. Therefore, the correct answer is baud rate.

TCP (Transmission Control Protocol) and IP (Internet Protocol) are both network protocols that are widely used in computer networks. TCP is responsible for establishing and maintaining a reliable connection between two devices, ensuring that data is transmitted accurately and in the correct order. IP, on the other hand, is responsible for addressing and routing packets of data across the network. Both TCP and IP include checksums as a way to detect errors in the data transmission. The checksum is a value calculated from the data being transmitted, and it is compared at the receiving end to ensure that the data arrived intact.

CRCs are better at detecting commonly occurring types of transmission errors compared to checksums. CRCs use polynomial division to generate a unique check value for the data being transmitted. This check value is appended to the data and sent along with it. At the receiving end, the same polynomial division is performed on the received data, and if the check value obtained does not match the one sent, it indicates that errors have occurred during transmission. CRCs have a higher probability of detecting errors such as single bit flips, burst errors, and most common types of transmission errors.

An 8-bit checksum is a simple error detection technique in which a sum of all the data bits is calculated and appended to the data packet. When the packet is received, the sum is recalculated and compared to the appended checksum. If they match, it is assumed that no errors occurred during transmission. However, if they don't match, it indicates that an error has occurred. Therefore, the statement "Approximately 99.6% of errors are detected" is true because the checksum has a high probability of detecting errors, but it cannot correct them.

Ethernet and ISDN are both examples of baseband communication links. Baseband communication refers to the transmission of digital signals without modulation, where the entire bandwidth of the communication medium is used for a single channel. Ethernet is a standard for local area networks (LANs) that uses baseband communication over twisted pair or fiber optic cables. ISDN (Integrated Services Digital Network) is a telecommunications standard that uses baseband communication over digital lines to transmit voice, video, and data. Therefore, the correct answer is Ethernet, ISDN.

The communication channel is using 256 QAM modulation, which means it can transmit 8 bits per symbol. Since there are 8 million symbols transmitted each second, the channel has a data rate of 8 million symbols/second * 8 bits/symbol = 64 million bits/second. To transfer 10MB, we need to convert it to bits, which is 10MB * 8 bits/byte * 1024 kilobytes/MB * 1024 bytes/kilobyte = 83,886,080 bits. Dividing this by the data rate gives us 83,886,080 bits / 64 million bits/second = 1.31 seconds. Rounded to the nearest tenth, the answer is 1.3 seconds. Therefore, the closest option is 1.25 seconds.

When a parity bit is added to each byte of data sent, it helps in detecting errors in the transmission. However, if all data bits are reversed, the parity bit will also be reversed along with the data bits. As a result, the transmitted data will still have the correct number of 1s and 0s, and the parity bit will still match the data. Therefore, no error will ever be detected in this scenario.

In odd parity, the number of 1s in a byte should be odd. If the received data contains errors, it is most likely that an even number of bits in some bytes were corrupted. This would result in an incorrect number of 1s in those bytes, causing the parity check to fail.

When using parity bits, checksums, and CRCs, these error detection techniques rely on the assumption that an odd number of bits will be corrupted. This is because these techniques are designed to detect errors, and an odd number of bit errors will result in a change in the parity bit, checksum, or CRC value. However, if an even number of bits within the message are corrupted, the error detection mechanism will not be able to detect the error, as the parity bit, checksum, or CRC value will remain unaltered.