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

Here's a breakdown of key characteristics and differences between TCP and UDP protocols:

• TCP and UDP sockets are created by the transport layer: False
• Before any data exchange takes place between two UDP applications, a logical connection must be established between them: False
• Both SMTP and POP3 are TCP based: True
• The UDP segment contains a checksum: True
• The TCP segment contains a checksum: True
• UDP makes use of the Selective Repeat protocol: False
• The Selective Repeat algorithm is used for congestion control: False
• HTTP uses TCP as its underlying transport protocol: True
• With POP3, the email message is always deleted from the mail server if the client downloads the email message to its local email client application: False
• Only TCP uses port numbers,

#!/bin/bash (Header .Sh)
echo"text" ("print()")
chmod u+x file.Sh
g++ add.Cpp -o name (compile)
./add < input.Txt > output.Txt
pet="dog" (variable)
echo "Hello $var" (access var)
read var (input())
echo "$x" ("" echo var echo '$x')
echo "\$x" (echo special char)
a="`cat fl.Txt`" (stores shell cmd output)
echo ${#var} (No. Char in var)
echo ${a:6:3} (return substring ${a:pos:len})
echo ${a/$from/$to} (replace 'from' to 'to)
let "b = $a + 9" (does math and ans strd in var)
var="$0" ("$0" cmd line arg, "$@", @:all)

if [ condition ] | [ "$string" ] True; length of $string is non-0 | [ -e $file ] True iff file exists
then | [ "$string1" == "$string2" ] True; strings are equal | [ -f $file ] True iff file is a file
some action | [ "$string1" != "$string2"

Computer Data Storage

Computer data storage, often called storage or memory, refers to computer components, devices, and recording media that retain digital data used for computing for some interval of time. Computer data storage provides one of the core functions of the modern computer: information retention. It is one of the fundamental components of all modern computers and, coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s.

In contemporary usage, memory usually refers to a form of semiconductor storage known as random access memory (RAM) and sometimes other forms of fast but temporary storage. Similarly, storage today more commonly refers to mass storage: optical discs, forms... Continue reading "Understanding Computer Data Storage: Memory and Mass Storage" »

What is the Internet?

The internet is a vast network of thousands of computers and devices worldwide, connected through various means like copper wires, fiber optics, and wireless connections.

Internet of Things

The Internet of Things (IoT) is a revolutionary concept that describes the connection of everyday objects to the internet. This interconnectedness allows us to interact with these objects remotely and seamlessly.

Web Browsers

A web browser is a software program that retrieves and displays the content of web pages. It acts as your gateway to accessing information and resources on the internet.

Search Engines

Search engines are sophisticated computer systems that index files stored on websites across the internet. They continuously crawl and... Continue reading "Internet Safety and Digital Responsibility Guide" »

It permits traffic from wireless clients in 10.10.10 y 10.10.20The solution must have active PEFNG licensesHave Radius server send different roles for users in different departments.Apply role-based firewall policiesChange user to any in the user any svc-dhcp permit ruleClientMatchAirwave combines information from more sources, such as Radius authenticating servers and APsWireless security camera operating on channel 8To support more POE devices directly connected to the MCSet the VLANs associated with desired subnets in the WLAN settingsRADIUS serverAddition of custom rules to control access for authenticated guestsIt removes any commands that are not supported on that MC or have dependency errorsMesh Portal APChoose ClearPass or the other

Java Socket Implementation

Client-Server Socket Class (`Misocket`)

Constructor for Server (`Misocket(int port)`):

• Initializes a `ServerSocket` with the specified port.
• Waits for and accepts a client connection using `serverSocket.accept()`.
• Obtains input and output streams from the accepted client socket.

Constructor for Client (`Misocket(String ip, int port)`):

• Creates a `Socket` to connect to the specified IP address and port.
• Obtains input and output streams for communication.

Core Functionality

Sending and Receiving Strings:

• `dos.writeUTF(cadena); dos.flush();` to send a string.
• `cadena = dis.readUTF(); return cadena;` to receive a string.

Sending and Receiving Integers:

• `dos.writeInt(tam);` to send an integer.
• `tam = dis.readInt(); return tam;` to receive

Four Servers Reside in the DMZ

• Mail
• WWW
• DNS
• Log Servers

DMZ Mail Server (a Separate Machine)

When an Email Message is Received from the Internet:

1. Reassembles the message.
2. Checks for malicious content.
3. Changes the addresses of the outer firewall (which is how the mail server is known to the outside world) to that of the internal mail server and forwards the mail to the internal mail server.

To Send a Message from the Internal Network to the Internet:

1. Reassembles the message.
2. Checks for malicious content (and maybe for proprietary information).
3. All internal addresses are replaced with "drib.org" (the name of the outside firewall).

DMZ WWW Server (a Separate Machine)

• Does not contact any servers or information sources on the internal network and it contains

Operating System Scheduling

1. The OS enables running multiple programs simultaneously. Several programs can reside in RAM concurrently, yet the CPU processes only one at a time. Only one process can be active at any given moment. CPUs are incredibly fast; even brief processing periods yield significant results. The OS determines the optimal method for switching between running, runnable, and waiting processes. It manages which process the CPU executes and distributes CPU access among processes. The task of determining when to switch processes is termed scheduling.

Disk Defragmentation

2. A disk defragmenter reorganizes files on a disk, ensuring they are stored contiguously. It arranges files on the disk into adjacent locations. This enhances... Continue reading "Understanding Operating Systems, Software, and Computer Hardware" »

Database Design Fundamentals

Key Concepts and Definitions

Data Type

The data type determines what field values are allowed and what other properties the field will have.

Saving a Table

You can specify a name for a table after you click the Save button on the Table Design toolbar.

Table Structure

The final step in the creation of a table is to save the table structure to disk.

Primary Key

A primary key uniquely identifies each record in a table.

Identifying Fields

When designing a database, you need to identify the fields that will be required.

Data Redundancy

Storing the same data field in multiple tables is called data redundancy.

Composite Key

A primary key that consists of more than one field is called a composite key.

Avoiding Data Redundancy

When designing... Continue reading "Database Design: Mastering Data Types, Keys, and Queries" »