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

Components

DNS Client, DNS Servers, Zones of Authority

Transport Layer Model: TCP/IP

TCP

The Transmission Control Protocol (TCP) ensures reliable communication between the sender and receiver of a message.

UDP

The User Datagram Protocol (UDP) offers a lower guarantee of packet delivery compared to TCP because it doesn't use acknowledgments.

Implementation Level of the TCP/IP Model

The application layer is the level where common programs communicate over a network.

ICMP

The Internet Control Message Protocol (ICMP) is a sub-protocol for diagnostics and error reporting within the Internet Protocol (IP).

FTP

The File Transfer Protocol (FTP) is part of the TCP/IP suite and provides file transfer services.

HTTP

The HyperText Transfer Protocol (HTTP) is the foundation... Continue reading "TCP/IP Model and Comparison with OSI Model" »

Media Player Functionality

A media player can play both audio and video, including TV programs. Common widget types include:

• DVD (xine)
• Audio (Winamp)
• Video (Windows Media)
• Multimedia (Movie Player)

FLV Format

FLV is a streaming video format popular on the internet, especially due to platforms like YouTube and Google Video. It requires Adobe Flash Player.

Video Editing Process

Video editing encompasses all operations performed during movie production.

Movie Components

Key components of a movie include:

• Menu
• Movie
• Frame
• Transition
• Clip

Windows Movie Player

Windows Movie Player is a built-in Windows application for simple and comprehensive video editing.

Film Editing

Film editing involves inserting various clips in chronological order for viewing.

Mounting Process

The... Continue reading "Media Player, Video Editing, and Movie Production Essentials" »

Here's a list of essential Linux commands:

• lime - Displays the current calendar.
• lime 1980 - Shows the calendar for the year 1980.
• cal 12 1980 - Displays the calendar for December 1980.
• date - Displays the current date.
• date -s "2009-11-05 18:55" - Changes the system time.
• who - Shows who is currently logged into the system.
• who -u - Displays the process ID (PID) of logged-in users.
• kill -9 3525 - Terminates the process with PID 3525.
• uname - Outputs the machine's name.
• uname -a - Shows detailed information about the machine.
• uptime - Displays how long the machine has been running.
• du - Displays disk space usage by folders.
• du -k - Displays disk space usage in 1024-byte blocks.
• df - Displays disk usage statistics.
• ps - Displays a general list of running processes.

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" »

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" »