Data Transmission, Error Detection, Encryption, and Computer Architecture

Question-and-Answer flashcards covering packet structure, transmission methods, error detection, encryption, CPU architecture, performance factors, instruction sets, and embedded systems.

What are the three main sections of a typical data packet?

Header, payload, and trailer.

What information is normally stored in the header of a packet?

Destination IP address, sender IP address, and packet (sequence) number.

What is the purpose of the trailer in a packet?

It marks the end of the packet.

List the five stages of packet switching.

1) Break data into packets. 2) Assign sequence numbers. 3) Each packet chooses a route based on congestion. 4) Routers control the routing. 5) Packets are reordered at the destination.

In simplex transmission, how does data travel?

In only one direction along a single cable.

How does half-duplex transmission differ from full-duplex transmission?

Half-duplex sends data both directions but not simultaneously; full-duplex sends data both directions at the same time using two channels.

What is serial data transmission?

Sending data one bit at a time over a single cable.

Give two advantages of serial transmission.

Minimal interference and simple, low-cost cabling with better reliability over long distances.

What is the main disadvantage of serial transmission?

Lower transmission speeds compared to parallel transmission.

What is parallel data transmission?

Sending multiple bits simultaneously across multiple wires.

State one advantage and one disadvantage of parallel transmission.

Advantage: very high speed. Disadvantage: limited to short distances and susceptible to interference/skew.

Which transmission type does USB use?

Serial transmission that supports both half- and full-duplex modes.

How many wires are in a standard USB cable and what are they for?

Four: black (ground), red (+5 V), green (Data +), white (Data –).

Give two advantages of using USB.

Automatic device detection/driver loading and backward compatibility (plus most devices do not need extra power).

Name one disadvantage of USB compared with Ethernet.

Short maximum cable length (~5 m) and generally slower data transfer on newer versions compared to Ethernet.

What are two common causes of data corruption during transmission?

Electrical interference (noise) and problems during packet switching.

How does an even parity bit detect errors?

The MSB is set so the total number of 1-bits (including the parity bit) is even; a mismatch on arrival signals an error.

What extra benefit does a parity block check provide over a single parity bit?

By checking rows and columns, it can locate (and therefore correct) the specific bit in error.

Describe how a checksum is used to detect errors.

Sender runs an algorithm to produce a checksum, appends it, receiver recalculates and compares; mismatch implies error.

What is an echo check?

The receiver sends an exact copy of the received data back to the sender for comparison; differences trigger a resend.

Outline the basic steps of Automatic Repeat reQuest (ARQ).

Receiver tests data with an error code; if errors or no acknowledgment within a time-out, sender retransmits until positive acknowledgment or max attempts reached.

Where are check digits commonly used?

Barcodes, ISBN numbers, and Vehicle Identification Numbers (VINs).

Briefly describe how to calculate a modulus-11 check digit.

Weight each digit, multiply, add, divide by 11, subtract the remainder from 11; result is the check digit.

How is a check digit validated on receipt?

Repeat the weighted sum (including the check digit); if the remainder when divided by 11 is zero, the number is valid.

What is encryption?

Encoding a message so only the sender and intended recipient can read it.

How does symmetric encryption work?

The same pre-shared private key is used for both encryption and decryption.

What is a weakness of symmetric encryption?

The shared key must be transmitted and can be intercepted, reducing security.

How does asymmetric encryption maintain security?

A public key (shared) encrypts the message; only the matching private key (kept secret) can decrypt it.

What are the three primary functions of a CPU?

Accept data/instructions, process them, and output results.

Name three main internal components of a CPU.

Arithmetic Logic Unit (ALU), Control Unit (CU), and registers (with buses connecting components).

What is the role of the ALU?

It performs arithmetic calculations and logical comparisons.

What does the Control Unit (CU) do?

Directs data flow by sending control signals within the CPU.

What is held in the Program Counter (PC)?

The address of the next instruction to be executed.

Which register temporarily stores data fetched from or to be written to memory?

Memory Data Register (MDR).

What is the purpose of the Accumulator?

It stores the results of ALU operations temporarily.

In the von Neumann architecture, where are instructions and data stored?

Together in the same main memory (RAM) in binary form.

Name the three buses in a typical CPU and their directionality.

Address bus (unidirectional), Data bus (bidirectional), Control bus (bidirectional).

What are the three stages of the fetch-decode-execute cycle?

Fetch the instruction from memory, decode it to determine action, and execute it.

How does clock speed influence CPU performance?

Higher clock speed means more cycles per second, allowing potentially more instructions to be processed each second.

Why doesn't doubling the number of cores always double performance?

Cores must communicate and many programs cannot use multiple cores efficiently, so gains are less than linear.

Why does larger CPU cache improve performance?

It stores recently used data/instructions closer to the CPU, reducing time-consuming accesses to main memory.

What is an instruction set?

The complete list of machine code commands that a specific processor can execute.

Which low-level language uses mnemonics to represent machine code?

Assembly language.

What is an embedded system? Give one example.

A computer system with a dedicated function within a larger device, e.g., traffic lights, washing machines, or engine management systems.

List two typical properties of embedded systems.

Low power consumption and small size (also rugged operating ranges and low cost per unit).