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

10 Good Deeds in Website Design

1. Place the organization name and logo on every page and make the logo a link to the home page.
2. Provide a search function if the site has more than 100 pages.
3. Write straightforward and simple headings and page titles that explain the content.
4. Structure the page to facilitate reader scanning.
5. Instead of cramming everything about a product, use hypertext to structure the content.

3 Broad Aspects of Web Design

1. Designing for the computer medium
2. Designing for the whole site
3. Designing for the user

3 Design Patterns

1. SINGLETON: Ensures that only one object of a given class is created.
2. ADAPTER: An example of the indirection design principle (like an electrical adapter).
3. OBSERVER: Allows two objects to be linked dynamically.

Statechart

Used... Continue reading "10 Good Deeds of Web Design and Object-Oriented Design Principles" »

Understanding Window Elements

Standard Window Components

1. Control Menu: Displays a menu with options to restore, move, size, minimize, maximize, and close the window.
2. Toolbar: Provides direct access to frequently used display options for greater efficiency.
3. Title Bar: Displays the name of the window or application.
4. Menu Bar: Displays and provides access to the menus available within the application.
5. Work Area: The primary area provided by the application for the user to perform their work.
6. Window Border: Allows you to resize the window when it is not maximized. Place the mouse pointer on the border, then press and drag it to the new position.
7. Status Bar: Displays help or information about the current task or ongoing processes.

Window Control Buttons

• A.

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" »

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" »

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:

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" »

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.

Asynchronous Transfer Mode (ATM) Networks

Integrating Multimedia Services with ATM VPN

The integration of voice and image services within Asynchronous Transfer Mode (ATM) creates a Multimedia Virtual Private Network (VPN). This innovative approach allows services previously provided on separate networks to be consolidated into a single, unified network.

ATM VPNs are based on the concept of a Virtual Private Network, offering resources dedicated exclusively to the client. This is achieved through a shared network infrastructure and a single access point to the network. Integration is facilitated by deploying an integration device at the customer's premises.

ATM Integration Device Capabilities

The integration device can consolidate data, voice, and... Continue reading "ATM and FDDI Networks: Advanced Data Transmission Solutions" »

Understanding Core Network Protocols and Services

Introduction to Network Fundamentals

• The Internet Control Message Protocol (ICMP) is an IP protocol used for sending control, reporting, and discovery messages.
• Network architectures are built upon dependent levels or layers.
• The complexity of a network directly impacts its reliability.
• Virtual communication is a fundamental aspect of modern media.
• End-to-end flow control is a critical network function.

Transport Layer Protocols: TCP and UDP

• An advantage of including the transport level is that protocols can be designed to conceal underlying network complexities from applications.
• The primary data unit at the transport layer is the Transport Protocol Data Unit (TPDU).
• Transport level protocols include