Notes, summaries, assignments, exams, and problems for Computers

Television Transmission and Reception

Analogue Television (TV)

Analogue TV signals are composed of video information, including synchronization and illumination lines, and the color of the points that form the images. Audio is also added. The video signal is modulated in AM, and the audio signal in FM.

Digital Television (DTV)

Digital TV signals are transmitted in binary form (digital).

Digital TV Service Models

• DVB Model: Developed for multimedia standard definition television.
• ATSC Model: Offers superior technical quality compared to traditional television services.
• ISDB Model: A combination of the DVB and ATSC models.

Digital TV Transmission Techniques

• Digital Terrestrial Television (DTT): Broadcasts over land-based transmitters.
• Satellite Television:

Users

• Creation

From the Partner's Computer

• Create user `Professor` @ '192.168.5.25' identified by 'Professor';

Local Access

• Administrative user `Create` @ 'localhost' identified by 'Administrative';

Access from Any Computer

• Create user `` @ '%' student identified by 'student';

• Deletion

• DROP

• Permissions

To Grant Permissions

• GRANT SELECT ON clase.cuidadores TO 'student'@'localhost';

SELECT * FROM carers;

• GRANT SELECT (name, currency) ON clase.cuidadores TO 'student'@'localhost';

SELECT name FROM currency carers;

• GRANT INSERT, SELECT, UPDATE ON IES.Curso TO 'Administrative'@'localhost';

• GRANT INSERT (IdCurso, DNI), SELECT (IdCurso, DNI), UPDATE (IdCurso, ID) ON IES.Matrícula TO 'Administrative'@'localhost';

With Update

• GRANT SELECT (name, currency), UPDATE (currency)

C Implementation of the Dining Philosophers Problem

This program simulates the Dining Philosophers problem using C and Pthreads to demonstrate concurrency and synchronization concepts.

Global Variables

• num_filosofos (int): Number of philosophers.
• seed (int): Seed for random number generation.
• holders (pthread_mutex_t*): Array of mutexes representing forks.
• timeIni (long): Initial time in milliseconds.

Functions

long dameTiempo()

Returns the current time in milliseconds.

int eat(int n)

Simulates a philosopher eating.

• TimeWait (long): Random wait time (0-500 ms).
• Prints a message indicating the philosopher is eating.
• Waits for TimeWait milliseconds.
• Releases the left and right forks (mutexes).

int sleep(int n)

Simulates a philosopher sleeping.

• TimeWait (long):

ADSL and DSL Technologies

ADSL (Asymmetric Digital Subscriber Line)

Advantages

• User: High-speed access, permanent connection, fast service provisioning.
• Telephone Company: Dual function of existing cable, no central office occupation, no risk of switched network collapse, service installed only on requested lines.

Disadvantages

• Service unavailability on certain lines (poor condition, distance from the central office).
• Potential for poor quality home cabling.
• Router cost.
• Requires a phone line.
• Cost in Spain.
• Theoretical limit for acceptable service at 5.5 km line length.

ADSL2+

Extends ADSL downstream capability with bit folding, achieving speeds of up to 24 Mbps downstream and 3.5 Mbps upstream. Doubles bandwidth from 1.1 MHz to 2.2 MHz.

ATM over ADSL

Allows... Continue reading "ADSL and DSL Technologies: A Comprehensive Overview" »

Relational Model: An In-Depth Look

The relational model allows users to obtain information from the database without needing assistance from information management professionals. The data is stored in a way that:

• Users understand it more easily.
• The data is stored as tables.
• Relationships between rows and tables are visible within the data.

Features of Relational Models

• It is important to know that the entries in the table are atomic.
• All entries in any column are of a single type. The table columns are called attributes.
• No two rows in the table are identical.

Structure of Relational Databases

At the conceptual level, the relational database model is represented by a collection of stored relations.

Submodel Data

External schemas of relational sub-models... Continue reading "Understanding Relational Database Models: Concepts and Operations" »

Understanding Network Communication Models

Client-Server Communication Model

In the Client-Server model, one process (the server) executes orders or commands requested by another process (the client).

Distributed Applications

Distributed applications consist of different programs that may be located on various machines, such as client and server machines, working together to achieve a common goal.

Network Communication Layers

Network communication can be conceptualized at different levels:

• Application Layer: Deals with the communication processes of application components.
• Physical/Architectural Layer: Focuses on the physical transmission of information.

Protocols and Services

• Protocol: A set of rules governing communication between two entities at a

This document presents a Java class named Student, demonstrating object-oriented programming principles. It includes attributes, constructors, getters, setters, and methods to calculate average grades and determine student status.

Test Class

import java.io.*;
public class Test {
    public static void main(String[] args) throws IOException {
        Student student = new Student("John", true, 3, 2, 5, 43);
        student.show();
    }
}

Student Class

import java.io.*;
public class Student {
    private int note1, note2, note3;
    private String name;
    private int age;
    private boolean sex; // attributes

    public Student() {
        this.name = "NN";
        this.sex = false;
        this.note1 = 0;
        this.note2 = 0;
        this.

Buttons in Java Applets

Introduction

Buttons are essential UI elements in Java applets, allowing user interaction and triggering specific actions. This guide explores various button types and their implementation.

Basic Buttons

Buttons can be created using the Button class. They are displayed on the screen and trigger events when clicked. Each button has an identifier used for event handling.

Example:

Button button;button = new Button("Button");

Button Events

When a user clicks a button, an event is generated. These events can be captured using the action() method:

public boolean action(Event evt, Object obj) {    if (evt.target instanceof Button) {        System.out.println((String) obj);    } else {        System.out.println("Event No-Button");

E1 Primary Access and Multiplexing

Multiplexing and Quantization

True or False: Multiframes are sent 500 per second in E1 primary access.

Plesiochronous multiplexers cause a loss of original formatting information.

CMI code requires greater bandwidth.

Question: What is the step size of a uniform quantizer with 2048 levels and a dynamic signal range of ±1V?

Answer: 0.977 mV

Question: How many quantization levels are in the second segment of a non-uniform quantizer using the A-law approach?

Answer: 16 levels

E1 Primary Access Characteristics

False Statement: In E1 primary access, the word alignment multiframe is transmitted every 15 frames.

True Statement: In E1 primary access, the word alignment multiframe is transmitted every 2 ms.

NFAS: Offers a speed... Continue reading "E1 Primary Access and Multiplexing in PDH and SDH Networks" »

Input/Output (I/O) Units

I/O units connect the system to the outside world, enabling the introduction and extraction of information. These units typically consist of registers operated by control buses, storing address information from the data bus. Their outputs are externally accessible for connecting to various devices.

Another crucial function of I/O units is to adapt:

• The format of signals from outside to the format of internal signals.
• Working speeds.
• Voltage levels.
• Binary codes.

System Buses

All elements of a programmable microsystem are interconnected by information channels, commonly known as buses. These buses are composed of multiple lines, each designed to transmit information of a specific type. The number of lines forming a bus determines... Continue reading "Computer System Components: I/O, Buses & Peripherals Explained" »