Computer Network Questions and Answers

Answer: C

Correct answer: 16

Hexadecimal is base 16, using the digits 0 to 9 followed by the letters A to F for the values 10 to 15. It is used because each hexadecimal digit corresponds to exactly four bits, so binary can be written compactly and converted by inspection rather than by arithmetic. The byte 11010110 splits into 1101 and 0110, which are D and 6, giving D6. Octal, base 8, works the same way with three bits per digit, and was common in the era of 12-, 24- and 36-bit machines; hexadecimal took over once 8-, 16- and 32-bit words became standard, since those divide evenly by four. Hexadecimal is written with a prefix to avoid ambiguity: 0x in C and its descendants, or a trailing H in assembly. It appears throughout computing - memory addresses, colour codes such as #FF0000 for red, and MAC addresses are all hexadecimal.

Answer: B

Correct answer: True

The statement is true. A NOR gate is an OR gate followed by an inverter, so its output is the complement of OR: since OR gives 0 only when every input is 0, NOR gives 1 only in that case. Its truth table for two inputs runs: 0,0 gives 1; 0,1 gives 0; 1,0 gives 0; 1,1 gives 0. NOR is a universal gate: every logic function can be built from NOR gates alone. Tying both inputs together makes an inverter; a NOR followed by an inverting NOR makes an OR; and by De Morgan’s theorem a NOR fed by two inverters makes an AND. NAND is universal for the same reason. The first integrated circuit computer, the Apollo Guidance Computer, was built almost entirely from three-input NOR gates - a practical demonstration of universality. Two cross-coupled NOR gates also form the simplest SR latch, the basic one-bit memory element.

Answer: D

Correct answer: NAK

Stop-and-wait ARQ has only one frame outstanding at a time, so a negative acknowledgement needs no sequence number: there is only one frame it could refer to. Numbered NAKs belong to the sliding-window protocols.

Answer: D

Correct answer: half duplex

Half duplex allows both directions but only one at a time, so the line must be turned round between transmissions. Full duplex allows both at once and simplex only one direction ever.

Answer: D

Correct answer: Three

A full adder takes three inputs - the two bits being added and a carry-in from the previous stage - and produces a sum and a carry-out. That carry-in is exactly what a half adder lacks, which is why half adders cannot be chained.

Answer: A

Correct answer: First three

The first three digits of the DNIC are the country code; the fourth distinguishes networks within that country.

Answer: A

Correct answer: E-mail

A mail message is small and its delivery is not time-critical, so it travels perfectly well over a slow link. Bulk file transfer and the traffic between nodes of a LAN both need the bandwidth.

Answer: A

Correct answer: less power than a TTL IC

CMOS draws significant current only while switching, so its static dissipation is minute compared with TTL, which draws current continuously through its output stage. Lowering the supply to 3 V reduces it further still, since dynamic power varies with the square of the supply voltage.

Answer: A

Correct answer: 2 (m - 2)

In a binary tree of \( 2^{m}-1 \) nodes the path from a leaf to the root has \( m-1 \) hops, so a message going up and back down again traverses about \( 2(m-2) \) links on average once the shared part of the two paths is discounted.

Answer: A

Correct answer: successive values differ in exactly one bit

Gray code is an ordering of binary values in which each differs from the next in exactly one bit. For three bits it runs 000, 001, 011, 010, 110, 111, 101, 100. That single-bit property solves a real problem. When several bits change at once in ordinary binary - 0111 to 1000, for instance - they will not switch at precisely the same moment, and a reading taken during the transition can be wildly wrong. With Gray code only one bit ever changes, so the worst error is one count. It is therefore used in shaft encoders and position sensors, where a mechanical brush or optical reader may sample mid-transition. It is also why the axes of a Karnaugh map are labelled in Gray code: adjacent cells then differ in one variable, which is what makes grouping valid. Conversion from binary is simple: the first bit is copied, and each later bit is the XOR of the corresponding binary bit with the one before it.