Computer Network Questions and Answers

Answer: D

Correct answer: 2000 m

Fibre carries a signal furthest of the media in the list - 2000 m per segment for the 100Base-FX and 10Base-FL standards - because glass attenuates light far less than copper attenuates a current.

Answer: A

Correct answer: equilizer

In a synchronous modem the digital-to-analog converter's output goes to the equalizer, which compensates for the distortion the telephone line will impose before the signal is put on the line.

Answer: C

Correct answer: simplify Boolean expressions

A Karnaugh map is a graphical method of minimising a Boolean expression. It arranges the cells of a truth table so that any two adjacent cells differ in exactly one variable, which lets a redundant variable be spotted and cancelled by grouping. That adjacency is achieved by labelling the axes in Gray code - 00, 01, 11, 10 rather than 00, 01, 10, 11 - and the map wraps at its edges, so the leftmost and rightmost columns are also adjacent. Groups must contain a power of two cells: 1, 2, 4, 8. Each doubling of a group removes one variable from the resulting term, so the aim is to cover every 1 with as few and as large groups as possible. Overlapping is allowed. Cells marked as don’t care may be treated as 1 or 0, whichever makes the groups larger. The map is practical up to four variables; beyond that the Quine–McCluskey algorithm is used instead.

Answer: B

Correct answer: selects one of several inputs and routes it to a single output

A multiplexer, or data selector, has several data inputs, one output, and a set of select lines that decide which input reaches the output. A multiplexer with \( n \) select lines can choose among \( 2^{n} \) inputs, so a 4-to-1 multiplexer needs two select lines and an 8-to-1 needs three. Its inverse is the demultiplexer, described by the second option, which takes one input and routes it to one of several outputs. The two are used together to send many signals over a single shared line and separate them again at the far end - the principle behind time-division multiplexing in communications. A decoder, the third option, converts an \( n \)-bit code into one of \( 2^{n} \) active outputs and is used for address decoding in memory; an encoder does the reverse. Multiplexers can also implement arbitrary logic functions directly, which makes them useful beyond data routing.

Answer: C

Correct answer: Go-back-N has better line utilization

Selective repeat retransmits only the frame that failed, whereas go-back-N retransmits it and everything sent after it, so selective repeat makes the better use of the line. It pays for that with more buffering at the receiver and more complex logic, which is what the other statements record.