Notes, summaries, assignments, exams, and problems for Computer science

Network Architectures and Technologies

According to the architecture: Arcnet, Ethernet, Token Ring, FDDI, ATM, ISDN, Frame Relay, DSL, and X.25.

Geographic Extent of Networks

• PAN (Personal Area Network): Home networks covering nearby areas within the same environment, such as the dependencies of a house (living room, bedroom, office, etc.). Example: Home Office.
• LAN (Local Area Network): Covers areas around local area networks within the same environment, such as offices, condominiums, schools, or a university campus.
• MAN (Metropolitan Area Network): Networks covering the metropolitan area of a large city or between nearby cities. Example: Speedy, Virtua.
• WAN (Wide Area Network): Long-distance networks connecting computers located in different cities,

Understanding DNS: Domain Name System

DNS is the translation mechanism that converts domain names into IP addresses. A domain is the name that identifies a website. Common top-level domains include:

• .com: Commercial organizations
• .edu: Educational organizations
• .net: Internet-related organizations
• .org: Non-commercial organizations
• .gov: Government organizations

When to Use a DNS Server

A DNS server is necessary when maintaining the /etc/hosts file is no longer feasible due to the volume of entries.

What is DNS Delegation?

Delegation is a mechanism that allows for the decentralization of database administration by dividing DNS domains into subdomains.

Network Example

Consider a Class C network (192.168.100.0) with subnet numbering determined by a mask,...

Digital Counters (Sequential Circuits)

Counters are sequential circuits whose output represents the number of clock pulses applied to the input. They consist of interconnected bistables (flip-flops).

Counters can operate in ascending mode (content increases with each pulse) or descending mode (content decreases).

Applications of Digital Counters

• Watches and Timers
• Frequency Dividers
• Frequency Meters (Frecuencímetro)

The maximum number of states a counter passes through is called the Modulus.

Asynchronous (Ripple) Counters

In asynchronous counters, the external clock signal is connected only to the first flip-flop. The clock input of subsequent flip-flops is connected to the output of the previous flip-flop.

This configuration causes all flip-flops...

Test Strategy

• Test Planning
• Design test cases
• Test Run
• Collection and evaluation

The software is tested to discover errors made inadvertently when carrying out their design and construction.

The tests are a set of activities you can plan ahead and carry out systematically. For this reason, you must define the process of software engineering template for software testing.

A software testing strategy should include: evidence of low-level, high level evidence.

Verification: a set of activities to ensure that software correctly implements a specific function.

Validation: different set of activities to ensure that software built is consistent with customer requirements.

Only once the software architecture comes into play is completed Independent Test Group.

User Accounts: To use the Unix operating system you must have a user account that consists of user name (login) and password (password). User accounts are created by the administrator in Unix is a special user called root.
User Groups: All users belong to at least one group that is the main user group, also called user's primary group but can belong to more groups. If you belong to more groups, these are secondary groups.
Root: The root user, sometimes called root, is the user administrator. Is identified with the user number zero (uid = 0) and has permissions on the entire system without any restrictions. The root user can access any file, run, install and uninstall any application, modify the system configuration files and manage users.

...

Networking Essentials: TCP/IP Concepts

TCP Flow Control Purpose

Why is flow control used for TCP data transfer?

• To synchronize the speed of data sent.
• To synchronize and order sequence numbers so data is sent in complete numerical order.
• To prevent the receiver from being overwhelmed by data.
• To synchronize window size on the server.
• To simplify data transfer to multiple hosts.

Analyzing Network Output: Key Information

Refer to the exhibit. What two pieces of information can be determined from the output shown? (Choose two.)

• The local host is using well-known port numbers to identify the source ports.
• A request for termination has been sent to 192.135.250.10.
• Communication with 64.100.173.42 is using secure HTTP.
• The local computer is accepting HTTP requests.

Microprocessors

The microprocessor is the device responsible for processing the data received. It is able to perform arithmetic operations and transfer blocks of information. The increase in processing power allows for faster and faster PCs. This is mainly due to improvements in architecture, microcode, and operating speeds.

Overclocking

Overclocking is a method used to obtain faster processing speed by increasing the domestic multiplier value of the microprocessor. It is not advisable because it causes overheating of the processor. Besides the increased frequency, it may result in errors of "timing" and then produce erroneous results or hang the system. You can also overclock the system clock speed, which will affect the overall team bus. This...

Semaphores: Synchronization Tool

Semaphores are a synchronization tool designed to solve critical section and synchronization problems. A semaphore is an integer variable accessed only through two atomic operations: Wait and Signal. When a process modifies the semaphore's value, no other process can simultaneously modify that same semaphore value. The semaphore is initialized to a non-negative value.

Wait and Signal Operations

• Wait (P): Decrements the semaphore's value. If the value becomes negative, the process is blocked.
• Signal (V): Increments the semaphore's value. If the value is not positive, a blocked process waiting on this semaphore is unblocked.

The definitions are:

P(s):

while (s <= 0)
s--;

V(s):

s++;

Operating System Usage

Operating...

Grammar and Phrasing Corrections

Adjective Replacement Example

Original: It is a swan around the house.
Corrected: It is a calm swan.

Grammatical Correction Example

Original: Gradually have damaged the work of humans.
Corrected: They gradually damaged the artwork.

What is a Text?

A text is a group of sentences that constitute a coherent, autonomous, and communicative unit.

Digital Communication Concepts

Chat

An electronic discussion, essentially a conversation conducted over a network.

Email

Email allows users to compose, send, and receive messages via electronic communication systems. Each email message typically has two main components: the header and the body.

Instant Messaging

Instant messaging is a system for exchanging messages between two or more people...

Wide Area Networks (WAN)

A Wide Area Network (WAN) spans a large geographic area, such as a country or continent. Its primary function is to connect networking and terminal equipment located at great distances. These networks rely on an infrastructure of powerful switching nodes to facilitate the continuous flow of significant amounts of information. WANs are considered public networks because they handle traffic from diverse locations, enabling users worldwide to transmit data across vast distances.

Network Protocols

A network protocol is a set of rules specifying the exchange of data or commands for communication between systems. These rules allow information to flow between computers that might otherwise handle different languages. If two computers...