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

Understanding the Data Link Layer

The MAC sublayer operates at the bottom of the Data Link Layer (OSI Layer 2).

MAC Sublayer: Core Functions

The Ethernet MAC sublayer has two primary responsibilities:

• Data Encapsulation
• Medium Access Control

Some key functions of the MAC sublayer include:

• Controlling access to the physical medium.
• Adding the MAC address to frames.
• Frame delimitation (determining the beginning and end of a data frame within a string of bits received by the physical layer).
• Performing transmission error detection.
• Discarding duplicate or erroneous frames.

LLC Sublayer: Data Transfer and Control

The LLC (Logical Link Control) sublayer defines how data is transferred on the physical environment, providing services to higher layers. The LLC... Continue reading "Data Link Layer Protocols: MAC, LLC, Token Ring, VLAN, STP Essentials" »

Welcome to Chops 6

This new version of Chops is full of exciting new features. Want to take a look?

New interface

Chops now has a more consistent, fast, and attractive interface. Also, the program windows are dockable, and you can customize the program in many different ways. Try the Options tab and the Window Layout button.

Edit several documents at once

Another key development in Chops is the ability to work with several documents at once. Now you can create a summary of a document in the same window or compare differences between two texts, for example. Try opening a new blank document and clicking the Options tab, or drag the open document tab to rearrange the desktop layout.

Live preview and contextual tabs

Try clicking the picture accompanying... Continue reading "Chops 6: New Interface, Multi-Document Editing & Live Preview" »

1.2. Organization of Memory

On Intel's 8051 family, program storage and data are physically separate. Both data and programs can be stored in internal or external memory devices. To identify external memory locations accessed during instruction execution, the microprocessor generates pulses on the ALE (Address Latch Enable) line and controls the PSEN (Program Store Enable) output state.

1.2.1. Program Memory

In 8051-based systems, the selection of program memory (internal and external) is determined by the hardware designer. The microprocessor accesses external memory only if the EA (External Access Enable) pin is connected to ground. If EA is high (connected to Vcc), the microprocessor uses its internal memory for low addresses and external memory... Continue reading "8051 Microcontroller: Memory Organization and ALU" »

Magnetic Storage Peripherals

Magnetic storage uses a ferromagnetic layer material (disks or hard drives).

Floppy Disk Drives

Floppy disks read and record information. Key parts include:

• Engine torque mechanism
• Shaft reading heads
• Ejecting mechanism and floppy connector

Hard Disk Drives (HDDs)

HDDs use tough aluminum platters that spin at high speed. The drive writes or reads data tracks.

Methods for Storing Information

• CHS (Cylinder, Head, Sector): Information is located by knowing the face, track, and sector.
• LBA (Logical Block Addressing): Data is accessed by calling a logical block number and searching for it.

HDD Physical Structure

The physical structure consists of:

• Platters (disks)
• Heads
• Spindle motor (engine torque)
• Head displacement mechanism (DLS heads)

Digital Sound Features

Sample Rate: The number of samples per second taken from a continuous analog signal to make a discrete digital signal. For example, CD-quality digital audio uses 44,100 Hz.

Channels: The number of audio channels in a sound recording. Mono = 1, Stereo = 2, 5.1 = 5 channels.

Sample Size: Indicates the number of bits of information in each sample. CD-quality audio uses 16 bits.

Formula: Size = Frequency x Sample Size x Number of Channels x Time (in seconds).

Audio Formats

WAV: A digital audio format without compression. It supports mono and stereo files, and its extension is .wav. It is seldom used on the internet. Microsoft and all programs recognize it.

MIDI: A protocol for communication between digital musical instruments and... Continue reading "Digital Sound and Video: Formats, Properties, and Tools" »

System Modeling Fundamentals

A model is an abstract representation of a real object. The first model developed is crucial as it defines the interfaces between the system and its environment. This initial model is known as the environmental model, describing the immediate context in which the system operates according to its objectives.

Components of the Environmental Model

1. Statement of Purpose (Objectives)

   This is a short and concise textual statement defining the system's purpose.

2. Context Diagram

   The Context Diagram graphically shows how the system interacts with the environment, making it easy for a user to interpret.

   It is a special case of a Data Flow Diagram (DFD), where a single bubble represents the entire system.

   Important Features Represented:

Domain Name System (DNS)

The DNS defines domain addresses (made up of character strings) and converts them to binary transport addresses (IP addresses). It identifies users and computers in the network using DNS server names.

DNS is composed of a distributed database (DB) on the network. Its tables contain correspondence between domain names and IP addresses.

Types of DNS Servers

• Cache Server

  Saves name information on domains, not zones.

• Primary Server

  Obtains information for its zones from its zone files. If data needs modification in a zone, it is done on the primary server. It is undesirable to have only a single primary server, as its failure may prevent resolving requests.

• Secondary Server

  Gets information from the primary server. Secondary servers

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.

... Continue reading "Content" »

Data

Data is the collection of facts considered in isolation. It describes an organization and carries meaning, but generally is not useful by itself.

Information

Information is data that has been manipulated and is useful to someone. Information must have value; otherwise, it would be considered just data. Information tells people something that confirms what they knew or suspected. (What, who, and when?)

Why? Because telecommunication networks transmit data, the networks do not identify meanings (information). The objective of networking is to take data from one place to another.

Data Types

• Analog: Continuous
• Digital: Discrete

Symbols limited by their use and origin:

• Alphanumeric
• Graphic
• Image
• Audio
• Video
• Multimedia

Model of a Basic Communication System

Components:... Continue reading "Data, Information, and Network Communication Essentials" »

DNS Protocols and Services

In data networks, devices are labeled with a numeric IP address so they can participate in sending and receiving network messages. However, most people spend much time trying to remember these numerical addresses. Therefore, domain names were created to convert the numeric addresses into a simple and recognizable name.

The DNS protocol defines an automated service that matches resource names with the numeric network address requested.

Top Level Domains (TLDs)

The different top-level domains represent the kind of organization or the country of origin. Examples of top-level domains are:

• .au: Australia
• .co: Colombia
• .com: A firm or industry
• .jp: Japan
• .org: A nonprofit organization

The Application Layer

The application layer is... Continue reading "Understanding DNS Protocols and Network Naming" »