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

Bit stuffing and destuffing are crucial techniques used in data link layer protocols to ensure reliable data transmission. They prevent sequences of data bits from being misinterpreted as control characters or flags, especially when the data itself contains patterns identical to these control sequences.

What is Bit Stuffing?

Bit stuffing is the process of adding one or more extra bits into a data stream to break up a sequence of identical bits that might otherwise be misinterpreted as a control signal. For example, in protocols like HDLC, a flag sequence (01111110) is used to mark the beginning and end of a frame. To prevent the actual data from containing this sequence, a '0' bit is stuffed after every five consecutive '1's in the data stream.... Continue reading "C Program for Bit Stuffing and Destuffing" »

Understanding Computer Networks

• A computer network is the interconnection of multiple devices, generally termed as hosts, connected using multiple paths for the purpose of receiving data or media.
• Connected devices share information and resources.
• The channel or line is where this information is transmitted.

Computer Network Classifications

Networks can be classified in several ways:

1. By Size: The most common classification.
2. By Property
3. By Connection Method
4. By Topology

1. Network Classification by Size

• LAN (Local Area Network): Maximum of a building. The most frequent type, common in most offices.
• MAN (Metropolitan Area Network): Maximum of a city, connecting different buildings.
• WAN (Wide Area Network): Connects devices from different cities or even countries.

Scene 1:

• Everyone shows up in a round table with computers thinking on what is the new game they will create.

• Poster: Brainstorm of ideas

• Carla: What game should we create now?

• Andrea: We can create a city!

• Bernardo: Yes! Let’s create a game that allows creating and simulating the life of your own avatar.

• Ines: That will be perfect! We can design clothes and accessories for the avatars

• Cuesta: That is a great idea, and it will not take too much time to code.

• Carla: We can also adapt the game so people can play using their smartphones.

• Everyone: Great let's call it... BIM’S!

Scene 2:

• Cuesta: You sit down in front of a computer and start typing codes. Let’s start with the coding

  • Question to Bernardo: Bernardo, do you remember the coding of how to make

CIA Triad

The CIA Triad consists of Confidentiality, Integrity, and Availability. Related concepts include Authentication, Accountability, and Auditability.

Types of Harm

• Interception
• Interruption
• Modification
• Fabrication

Web Technologies

HTML

• GET: Embeds parameters into the URL.
• POST: Sends data directly to the server; more secure.

PHP

• PUT: Used to create or replace a file at the specified URL. Sends data like POST, more suitable for uploading files.

Penetration Testing

5 Steps to Penetration Testing:

1. Reconnaissance
2. Scanning
3. Gaining Access
4. Maintaining Access
5. Clearing Tracks

Security Controls

• Prevention: Outright stopping an attack.
• Deterrence: Making an attack harder.
• Deflection: Making a target less attractive.
• Mitigation: Lessening the harm.
• Detection: Identifying

NETWORKING

1- Characteristics of Electronic Cables

Impedance, attenuation, and capacitance are crucial in electronic cables.

Impedance:

Resistance to electron movement in an AC circuit, measured in ohms (Ω).

Attenuation:

Resistance to electron flow, measured in db/m.

Capacitance:

Energy storage in a cable, measured in picofarads (pF).

2- Physical Description of Cables

Twisted Pair: Protects against crosstalk and noise.

Coaxial Cable: Consists of copper conductor, plastic insulation, and shielding.

Fiber-Optic Cable: Core, cladding, buffer, strengthening material, and outer jacket.

3- UTP vs. STP

Shielding reduces electrical noise in STP but makes installation complex.

4- Crimping RJ-45 UTP Cables

Creates straight-through and crossover cables for connecting... Continue reading "Understanding Networking: Cables, Protocols, and Topologies" »

Java Programming Fundamentals

This document provides a quick reference to fundamental Java programming concepts, including object-oriented programming basics, common data structures like ArrayLists, handling user input, string manipulation, type conversion, and file input/output operations.

Object-Oriented Programming: The Persona Class

Below is a basic definition of a Persona class, illustrating fields and a constructor. In a complete implementation, you would also include getter and setter methods for each field.

public class Persona {
    private String nombre;
    private int ojos;
    private int piernas; // Added for completeness based on constructor
    private int brazos; // Added for completeness based on constructor

    public Persona(

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Functions and Arguments

A function is a module of program code that takes input (arguments) and produces output (a return value).

• Arguments allow us to customize the operation performed by the function.
• The return value is often the result of executing the code.
• Calling a function causes the code in a function to execute. If called again, it will execute again.

To document a function, use a multi-line comment immediately after the def line.

Local Variables

Local variables are variables used inside functions.

• They are accessible/usable within that function only.
• This refers to the variable's scope.

Global Variables

Global variables are variables used outside of a function.

• Global variables' scope includes both inside and outside of functions.
• However, since

Understanding Computer Security

Common Threats

• Worm: Designed to replicate itself, a worm operates as a standalone application, unlike a virus.
• Trojan: Disguised as a legitimate program (e.g., a screensaver), a Trojan operates covertly to inflict damage.
• Phishing: Attackers impersonate trustworthy entities to steal sensitive information, exploiting social engineering tactics.

Network and Security Concepts

• Simple Mail Transfer Protocol (SMTP): A standard for email communication, SMTP is known for its lack of robust security.
• Sandboxes: Software environments that isolate programs to prevent them from harming the host system, commonly used in web browsers.

Wireless Security

• Wireless Internet (Wi-Fi): Enables wireless communication between devices, forming