Networking

What is networking? Definition: In the world of computers, networking is the practice of interfacing two or more computing devices with each other for the purpose of sharing data. Computer networks are built with a combination of hardware and software.

Area Networks

Computer networks can be categorized in several different ways. One approach defines the type of network according to the geographic area it spans. Local area networks (LANs), for example, typically span a single home, school, or small office building, whereas wide area networks (WANs), reach across cities, states, or even across the world. The Internet is the world's largest public WAN.

Network Design

Computer networks also differ in their design approach. The two basic forms of network design are called client/server and peer-to-peer. Client-server networks feature centralized server computers that store email, Web pages, files and or applications. On a peer-to-peer network, conversely, all computers tend to support the same functions. Client-server networks are much more common in business and peer-to-peer networks much more common in homes.

A network topology represents its layout or structure from the point of view of data flow. In so-called bus networks, for example, all of the computers share and communicate across one common conduit, whereas in a star network, all data flows through one centralized device. Common types of network topologies include bus, star, ring networks and mesh networks.

Network Protocols

Communication languages used by computer devices are called network protocol. Yet another way to classify computer networks is by the set of protocols they support. Networks often implement multiple protocols with each supporting specific applications.

Popular protocols include TCP/IP, the mostcommon protocol found on the Internet and in home networks.

Home Networking

While other types of networks are built and maintained by engineers, home networks belong to ordinary homeowners, people often with little or no technical background. Various manufacturers produce broadband routerhardware designed to simplify home network setup. Home broadband routers allow devices in different rooms to efficiently share a broadband Internet connection, enable people to more easily share their files and printers within the network, and help with overall network security.

Home networks have increased in capability with each generation of new technology. Years ago, people commonly set up their home network just to connect a few PCs, share some documents and perhaps a printer. Now its common for households to also network game consoles, digital video recorders, and smartphones for streaming sound and video.Home automation systems have also existed for many years, but these too have grown in popularity more recently with practical systems for controlling lights, digital thermostats and appliances.

Business Networks

Small and home office (SOHO) environments use similar technology as found in home networks. Businesses often have additional communication, data storage, and security requirements that require expanding their networks in different ways, particularly as the business gets larger. Whereas a home network generally functions as one LAN, abusiness network tends to contain multiple LANs. Companies with buildings in multiple locations utilize wide-area networking to connect these branch offices together. Though also available and used by some households, voice over IP communication and network storage and backup technologies are prevalent in businesses. Larger companies also maintain their own internal Web sites, called intranets to help with employee business communication.

Networking and the Internet

The popularity of computer networks sharply increased with the creation of the World Wide Web (WWW) in the 1990s. Public Web sites, peer to peer (P2P) file sharing systems, and various other services run on Internet servers across the world.

Wired versus  Wireless Networking

Many of the same network protocols, like TCP/IP, work in both wired and wireless networks. Networks with Ethernet cables predominated in businesses, schools, and homes for several decades. More recently, however, wireless alternatives have emerged as the premier technology for building new computer networks, in part to support smartphones and the other new kinds of wireless gadgets that have triggered the rise of mobile networking.







                                          Physical Topology

What is a Topology?

The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter.

Main Types of Physical Topologies

The following sections discuss the physical topologies used in networks and other related topics.

Linear Bus
Star
Tree (Expanded Star)
Considerations When Choosing a Topology
Summary Chart

Linear Bus

A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable.

Advantages of a Linear Bus Topology

Easy to connect a computer or peripheral to a linear bus.
Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology


Entire network shuts down if there is a break in the main cable.
Terminators are required at both ends of the backbone cable.
Difficult to identify the problem if the entire network shuts down.
Not meant to be used as a stand-alone solution in a large building.

Star

A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator (See fig. 2).

Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

Advantages of a Star Topology

• Easy to install and wire.
• No disruptions to the network when connecting or removing devices.
• Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

Requires more cable length than a linear topology.
If the hub, switch, or concentrator fails, nodes attached are disabled.
More expensive than linear bus topologies because of the cost of the hubs, etc.

Tree or Expanded Star

• A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 3). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantages of a Tree Topology

• Point-to-point wiring for individual segments.
• Supported by several hardware and software venders.

Disadvantages of a Tree Topology

• Overall length of each segment is limited by the type of cabling used.
• If the backbone line breaks, the entire segment goes down.
• More difficult to configure and wire than other topologies.

5-4-3 Rule

A consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule. One aspect of the Ethernet protocol requires that a signal sent out on the network cable reach every part of the network within a specified length of time. Each concentrator or repeater that a signal goes through adds a small amount of time. This leads to the rule that between any two nodes on the network there can only be a maximum of 5 segments, connected through 4 repeaters/concentrators. In addition, only 3 of the segments may be populated (trunk) segments if they are made of coaxial cable. A populated segment is one that has one or more nodes attached to it . In Figure 4, the 5-4-3 rule is adhered to. The furthest two nodes on the network have 4 segments and 3 repeaters/concentrators between them.

NOTE: This rule does not apply to other network protocols or Ethernet networks where all fiber optic cabling or a combination of a fiber backbone with UTP cabling is used. If there is a combination of fiber optic backbone and UTP cabling, the rule would translate to a 7-6-5 rule.The speed of networking switches is vastly improved over older technologies, and while every effort should be made to limit network segment traversal, efficient switching can allow much larger numbers of segments to be traversed with little or no impact to the network.

Considerations When Choosing a Topology

• Money. A linear bus network may be the least expensive way to install a network; you do not have to purchase concentrators.
• Length of cable needed. The linear bus network uses shorter lengths of cable.
• Future growth. With a star topology, expanding a network is easily done by adding another concentrator.
• Cable type. The most common cable in schools is unshielded twisted pair, which is most often used with star typologies.

 Programming

 

Computer programming (often shortened to programming) is a process that leads from an original formulation of a computing problem to executable computer programs. Programming involves activities such as analysis, developing understanding, generating

algorithms, verification of requirements of algorithms including their correctness and resources consumption, and implementation (commonly referred to as coding) of algorithms in a target programming language. Source code is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate performing a specific task or solving a given problem. The process of programming thus often requires expertise in many different subjects, including knowledge of the application domain, specialized algorithms and formal logic.
Related tasks include testing, debugging, and maintaining the source code, implementation of the build system, and management of derived artifacts such as machine code of computer programs. These might be considered part of the programming process, but often the term "software development" is used for this larger process with the term "programming", "implementation", or "coding" reserved for the actual writing of source code. Software engineering combines engineering techniques with software development practices.

Flowchart

A flowchart is a graphical representation of decisions and their results mapped out in individual shapes that were first developed by Herman Goldstine and John von Neumann in the 1940's. Flowcharts can provide a step-by-step diagram for mapping out complex situations, such as programming code or troubleshooting problems with a computer. The picture to the right shows an image from Microsoft Visio, a popular program used to design and create flowcharts and diagrams.

Below is an example of a basic flowchart created in Visio that gives a good representation of their layout. As can be seen, you have several steps that may be followed systematically to help determine the cause of computer problem. Of course, this is just an example and not the full set of steps required to troubleshoot computer issues.

Other examples of how flow charts are used

• Flowcharts can also be created for any of the situations below.
• Algorithm - List the steps of how an algorithm works.
• Audit - Give the steps required to test a system or process with steps on handle any problems.
• Procedure - List the steps for completing any procedure to help verify everything is done right the first time and every time.
• Program - Steps on how to create or use a program.
• Projects - Give an overview of the steps required for creating a new project or the steps on how to complete the project.
• Troubleshooting - List the steps involved for troubleshooting a problem, like the example listed earlier.
  

 

 

Pseudocode

INTRODUCTION

For getting the turtle to draw simple things, like a box, you can just enter Logo instructions in TG's CommandCenter and most of the time your program just works.  It does what you wanted it to, what you thought it would do.  However, when you write any non-trivial program, this will rarely be the case.  The more instructions you include in your programs, the more you need to keep in your head, in your working memory, about what you're doing.  The more instructions, the more typing you will do; so, the more chances or a typo.  And finally, the more instructions, the more chances to make a mistake.In this lesson you will learn how to write computer programs in steps.The first step will be to just think about what you need to do.In the next step you will write what you want the program to do in pseudocode.
    Pseudocode (derived from pseudo and code) is a description    of a computer programming algorithm that uses the structural    conventions of programming languages, but omits detailed    subroutines or language-specific syntax.  ( WikipediA )
    ...written in a pseudo-code that resembles a computer language but    avoids excessive detail by lapsing from time to time into ordinary    English. This lets us specify quite a bit of the program before we    have worked out all aspects of it.  On larger programs, it is    valuable to begin with pseudo-code and refine it in stages until    it is all executable.  This way you can revise and improve the    design at a high level without writing any executable code, yet    remain close to a form which can be made executable.  (Software Tools, Kernighan, Plauger) A third step is the conversion of the pseudocode into properly formed instructions that are available in the programming language you are using, Logo in our case.

JavaScript

 

 
JavaScript (/ˈdʒɑːvəˌskrɪpt/) is a high level, dynamic, untyped, and interpreted programming language. It has been standardized in the ECMAScript language specification. Alongside HTML and CSS, it is one of the three essential technologies of World Wide Web content production; the majority of websites employ it and it is supported by all modern web browsers without plug-ins. JavaScript is prototype-based with first-class functions, making it a multi-paradigm language, supporting object-oriented, imperative, and functional programming styles. It has an API for working with text, arrays, dates and regular expressions, but does not include any I/O, such as networking, storage or graphics facilities, relying for these upon the host environment in which it is embedded.
Despite some naming, syntactic, and standard library similarities, JavaScript and Java are otherwise unrelated and have very different semantics. The syntax of JavaScript is actually derived from C, while the semantics and design are influenced by the Self and Scheme programming languages.
JavaScript is also used in environments that are not web-based, such as PDF documents, site-specific browsers, and desktop widgets. Newer and faster JavaScript virtual machines (VMs) and platforms built upon them have also increased the popularity of JavaScript for server-side web applications. On the client side, JavaScript has been traditionally implemented as an interpreted language, but more recent browsers perform just-in-time compilation. It is also used in game development, the creation of desktop and mobile applications, and server-side network programming with runtime environments such as Node.js.

HTML

HyperText Markup Language, commonly referred to as HTML, is the standard markup language used to create web pages. Web browsers can read HTML files and render them into visible or audible web pages. HTML describes the structure of a website semantically along with cues for presentation, making it a markup language, rather than a programming language.
HTML elements form the building blocks of all websites. HTML allows images and objects to be embedded and can be used to create interactive forms. It provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items.
he language is written in the form of HTML elements consisting of tags enclosed in angle brackets (like <html>). Browsers do not display the HTML tags and scripts, but use them to interpret the content of the page.HTML can embed scripts written in languages such as JavaScript which affect the behavior of HTML web pages. Web browsers can also refer to Cascading Style Sheets (CSS) to define the look and layout of text and other material. The World Wide Web Consortium (W3C), maintainer of both the HTML and the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997^.

HTML Example

A small HTML document:

<!DOCTYPE html>
<html>
<head>
<title>Page Title</title>
</head>
<body>

<h1>My First Heading</h1>
<p>My first paragraph.</p>

</body>
</html>