Networking (2)

Concepts of Networking

Standalone computer Single computer not attached to a network Cannot match power and convenience of network


What is a Network? A computer network, often simply referred to as a network, is a

collection of computers and devices interconnected by communications channels that facilitate communications and allows sharing of resources and information among interconnected devices.

A network consists of 2 or more computers connected together, and they can communicate and share resources (e.g. information)


Internet

External FirewallExternal Firewall

Router Internal Firewall Internal Firewall

Switch

Figure: Typical network


Node - Anything that is connected to the network. While a node is typically a computer, it can also be something like a printer or CD-ROM tower.

Backbone - The main cabling of a network that all of the segments connect to. Typically, the backbone is capable of carrying more information than the individual segments. For example, each segment may have a transfer rate of 10 Mbps (megabits per second: 1 million bits a second), while the backbone may operate at 100 Mbps.

Segment - Any portion of a network that is separated, by a switch, bridge or router, from other parts of the network.

Gateway - A gateway is a node that allows you to gain entrance into a network and vice versa. Hub - A common connection point for devices in a network. Hubs are commonly used to

connect segments of a LAN. A hub contains multiple ports. Router - A router is a device or, in some cases, software in a computer, that determines the

next network point to which a packet should be forwarded toward its destination. Switch - A network switch or switching hub is a computer networking device that connects

network segments. Bridge - The basic operation of a bridge is to join two or more network segments together. Topology - The way that each node is physically connected to the network.

Some Important Terms

IP Address (Internet Protocol Address): This number is an exclusive number all information technology devices (printers, routers, modems, et al)

use which identifies and allows them the ability to communicate with each other on a computer network. There is a standard of communication which is called an Internet Protocol standard (IP). In laymans terms it is the same as your home address. In order for you to receive snail mail at home the sending party must have your correct mailing address (IP address) in your town (network) or you do not receive bills, pizza coupons or your tax refund. The same is true for all equipment on the internet. Without this specific address, information cannot be received.

Domain Name System (DNS): This allows the IP address to be translated to words. It is much easier for us to remember a word than a series of numbers. The same is true for email addresses.For example, it is much easier for you to remember a web address name such as whatismyip.com than it is to remember 192.168.1.1 or in the case of email it is much easier to remember [email protected] than [email protected]

Bandwidth In computer networks, bandwidth is often used as a synonym for data transfer rate - the

amount of data that can be carried from one point to another in a given time period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps). Occasionally, it's expressed as bytes per second (Bps).


How many kinds of Networks? Depending on one’s perspective, we can classify networks in different ways

• Based on transmission media: Wired (Guided)(UTP, coaxial cables, fiber-optic cables) and Wireless (Unguided)

• Based on network size: LAN and WAN (and MAN)• Based on management method: Peer-to-peer and Client/Server• Based on topology (connectivity): Bus, Star, Ring …


Based on transmission media: Conducted or guided media

use a conductor such as a wire or a fiber optic cable to move the signal from sender to receiver

Wireless or unguided media use radio waves of different frequencies and do not need a wire or cable

conductor to transmit signals


Guided Transmission Media Transmission capacity depends on the distance and on whether the medium is point-to-point

or multipoint Examples

Twisted pair wires Coaxial cables Optical fiber


Twisted pair wires

Consists of two insulated copper wires arranged in a regular spiral pattern. Often used at customer facilities and also over distances to carry voice as well as data

communications Low frequency transmission medium

Twisted-Pair cables: Unshielded Twisted-Pair (UTP) cablesShielded Twisted-Pair (STP) cables


Unshielded Twisted-Pair (UTP) Typically wrapped inside a plastic cover (for mechanical protection) A sample UTP cable with 5 unshielded twisted pairs of wires

MetalInsulator


Shielded Twisted-Pair (STP)

STP cables are similar to UTP cables, except there is a metal foil or braided-metal-mesh cover that encases each pair of insulated wires


Twisted Pair Advantages

Inexpensive and readily available Flexible and light weight Easy to work with and install

Twisted Pair Disadvantages Susceptibility to interference and noise Distance increases signal quality decreases . Relatively low bandwidth (3000Hz)


Coaxial Cable (or Coax) Used for cable television, LANs, telephony Has an inner conductor surrounded by a braided mesh Both conductors share a common center axial, hence the term “co-axial”


Coaxial Cable Advantage Higher bandwidth Can be tapped easily Much less susceptible to interference than twisted pair

Coaxial Cable Disadvantage Expensive over long distance Bulky


Fiber Optic Cable Relatively new transmission medium used by telephone companies in place of

long-distance trunk lines Also used by private companies in implementing local data communications

networks


Fiber Optic Advantages

Greater capacity (bandwidth of up to 2 Gbps) Smaller size and lighter weight

Fiber Optic Disadvantages

Expensive over short distance Requires highly skilled installers Adding additional nodes is difficult


Wireless Examples Terrestrial microwave Satellite microwave Broadcast radio Infrared


Terrestrial microwave

Used for long-distance telephone service Uses radio frequency spectrum, from 2 to 40 Ghz Parabolic dish transmitter, mounted high Used by common carriers as well as private networks Requires unobstructed line of sight between source and receiver Curvature of the earth requires stations (repeaters) ~30 miles apart


Satellite Microwave Applications Television distribution Long-distance telephone transmission Private business networks


Microwave Transmission Disadvantages Line of sight requirement Expensive towers and repeaters Subject to interference such as passing airplanes and rain


Satellite Transmission Links Earth stations communicate by sending signals to the satellite on an uplink The satellite then repeats those signals on a downlink The broadcast nature of the downlink makes it attractive for services such as the distribution

of television programming


Radio Radio is omnidirectional and microwave is directional Radio is a general term often used to encompass frequencies in the range 3

kHz to 300 GHz. Mobile telephony occupies several frequency bands just under 1 GHz.


Based on network size: LAN and WAN (and MAN)• Local Area Network (LAN)• Small network, short distance

• A room, a floor, a building• Limited by no. of computers and distance covered• Usually one kind of technology throughout the LAN• Serve a department within an organization

• Examples: • Network inside the Student Computer Room• Network inside your home


• Wide Area Network (WAN)• A network that uses long-range telecommunication links to connect 2 or more

LANs/computers housed in different places far apart.• Towns, states, countries

• Examples:• Internet• ATM – Asynchronous Transfer Mode



Based on management method: Peer-to-peer and Client/Server

Peer-to-Peer Networks• Peer-to-peer network is also called workgroup• No hierarchy among computers all are equal• No administrator responsible for the network


• Advantages of peer-to-peer networks:• Low cost• Simple to configure• User has full accessibility of the computer

• Disadvantages of peer-to-peer networks:• May have duplication in resources• Difficult to uphold security policy• Difficult to handle uneven loading

• Where peer-to-peer network is appropriate:• 10 or less users• No specialized services required• Security is not an issue• Only limited growth in the foreseeable future


Clients and Servers

Network Clients Clients (WorkstationWorkstation)• Computers that request network resources or services

Network ServersServers• Computers that manage and provide network resources and services to clients

• Usually have more processing power, memory and hard disk space than clients

• Run Network Operating System that can manage not only data, but also users, groups, security, and applications on the network

• Servers often have a more stringent requirement on its performance and reliability


Advantages of client/server networks• Facilitate resource sharing – centrally administrate and control• Facilitate system backup and improve fault tolerance• Enhance security – only administrator can have access to Server• Support more users – difficult to achieve with peer-to-peer networks

Disadvantages of client/server networks• High cost for Servers• Need expert to configure the network• Introduce a single point of failure to the system


Based on topology (connectivity): Bus, Star, Ring …


Bus Topology• Simple and low-cost• A single cable called a trunk (backbone, segment)• Only one computer can send messages at a time• Passive topology - computer only listen for, not regenerate data


Star Topology• Each computer has a cable connected to a single point• More cabling, hence higher cost• All signals transmission through the hub; if down, entire network down• Depending on the intelligence of hub, two or more computers may send message

at the same time


Ring Topology• Every computer serves as a repeater to boost signals• Typical way to send data:

• Token passing• only the computer who

gets the token can send data• Disadvantages

• Difficult to add computers• More expensive• If one computer fails, whole network fails

Internet Explorer Usage

What is the Internet? The Internet is a network of computers around the world that are linked together by

telecommunications in order to share information. It is a network of networks. Different types of computers make up the network. Some computers contain information(host computers) or servers, others (clients) access the host or server to retrieve needed information.

The Internet is a network of Computer Networks. Each computer on the network has a unique address, the Internet Protocol address (IP). It is made up of lots of servers and clients that hold and exchange information all over the world. The network is self organizing and self governing. There is no group that or individual that heads the network of net works. The computers are able to communicate with each other because they use a common set of rules or protocols

The protocols Transmission Control Protocol/Internet Protocol (TCP/IP) allows the connection and exchange of information between computers. There are a number of Internet protocols that make communication and information retrieval possible on the WWW.


Birth of the Net The Internet grew out of an experiment in the 1960s by the U.S. Department of

Defense. The DoD wanted to create a computer network that would continue to function in the event of a disaster, such as a nuclear war. If part of the network was damaged or destroyed, the rest ofthe system still had to work. That network was ARPANET, (Advanced Research Projects Agency Network) which linked U.S. scientific and academic researchers. It was the forerunner of today's Internet.

In 1985, the National Science Foundation (NSF), an American research organization, created NSFNET, a series of networks for research and education communication. Based on ARPANET protocols, the NSFNET created a national backbone service, provided free to any American research and educational institution. At the same time, regional networks were created to link individual institutions with the national backbone service.

NSFNET grew rapidly as people discovered its potential and as new software applications were created to make access easier.

Corporations such as Sprint and MCI began to build their own networks that they then linked to NSFNET. When commercial firms and other regional network providers took over the operation of the major Internet arteries, NSF withdrew from the backbone business.

NSF also coordinated a service called InterNIC that registered all addresses on the Internet so that data could be routed to the right system. This service has now been taken over by Network Solutions, Inc. and other Internet registration services in cooperation with NSF


Internet Protocols include:

E-mail (Simple Mail Transfer Protocol –SMTP) makes the distribution of electronic messages between computers possible.

TCP/IP - Transmission Control Protocol/Internet Protocol make the transmission of data through the network possible.

FTP( File transfer Protocol) Transfers texts between computers. HTML(Hypertext Markup Language) Used to create documents on the World Wide Web) HTTP(Hypertext Transfer Protocol) HTTP defines how messages are formatted and

transmitted, and what actions Web servers and browsers should take in response to various commands.

TELNET Make it possible to login to a host computer and execute instructions.

Internet uses The Internet is used by students, researchers and the general population to satisfy their

information needs. An Internet user has access to a wide variety of services such as: Electronic Mail

File Transfer News Services. Information Networks


Web Browser A web browser is the software program you use to access the World Wide Web, the graphical

portion of the Internet.

The first browser, called NCSA Mosaic, was developed at the National Center for Supercomputing Applications in the early 1990s. The easy-to-use point-and-click interface helped popularize the Web.

Microsoft Internet Explorer and Netscape Navigator are the two most popular ones.


Navigating the Web The Web is known as a client-server system. Your computer is the client; the remote

computers that store electronic files are the servers. To visit the website, enter the address or URL of the website in your web browser. Browser requests the web page from the web server that hosts the requested site. The server sends the data over the Internet to your computer. Your web browser interprets the data, displaying it on your computer screen.


Uniform Resource Locator (URL)

A Uniform Resource Locator (URL) is a Uniform Resource Identifier (URI) that specifies where a known resource is available and the mechanism for retrieving it. It is also referred to as a Universal Resource Locator and in many technical documents and verbal discussions it is often used .


Navigating the Web The "glue" that holds the Web together is called hypertext and hyperlinks. This feature allows

electronic files on the Web to be linked so you can jump easily between them. On the Web, you navigate through pages of information--commonly known as browsing or surfing--based on what interests you at that particular moment.

Web pages are written in a computer language called Hypertext Markup Language or HTML.


World Wide Web The World Wide Web (abbreviated as WWW or W3 and commonly known as the Web), is

a system of interlinked hypertext documents accessed via the Internet. The World Wide Web was originally developed in 1990 at CERN, the European Laboratory

for Particle Physics. The original idea came from a young computer scientist, Tim Berners-Lee. It is now

managed by The World Wide Web Consortium. The WWW Consortium is funded by a large number of corporate members, including AT&T, Adobe Systems, Inc., Microsoft Corporation and Sun Microsystems, Inc.


Web Addresses

For example: www.mimranchi.comThe Home page of MIM


Domain Name Every computer that hosts data on the Internet has a unique numerical address. For example,

the numerical address for the White House is 198.137.240.100. But since few people want to remember long strings of numbers, the Domain Name System (DNS) was invented. DNS, a critical part of the Internet's technical infrastructure, correlates a numerical address to a word.

To access the White House website, you could type its number into the address box of your web browser. But most people prefer to use "www.whitehouse.gov." In this case, the domain name is whitehouse.gov.


The Structure of a Domain Name A domain name has two or more parts separated by dots and consists of some form of an

organization's name and a three letter or more suffix. For example, the domain name for IBM is "ibm.com"; the United Nations is "un.org." The domain name suffix is known as a generic top-leve domain (gTLD). It describes the type of organization.

Currently in use gTLDs: .aero--For the air-transport industry .biz--Reserved for businesses .com--For businesses, commercial enterprises .edu--For educational institutions and universities .gov--Reserved for United States government agencies .info--For all uses .mil--For the United States military .net--For networks; usually reserved for organizations such as Internet service providers .org--For non-commercial organizations


Search Engines To search the Internet you use what are called Internet search engines. These are easily accessed via your Internet browser (i.e. Microsoft Internet Explorer or

Netscape Navigator/Communicator). Within the search engine you enter a word or phrase and it will retrieve documents from the

Internet based on the information you typed in.









To Search a relevant document /Page in a website


Boolean Searching on the Internet The Internet is a vast computer database. As such, its contents must be searched according to

the rules of computer database searching. Much database searching is based on the principles of Boolean logic. Boolean logic refers to the logical relationship among search terms, and is named for the British-born Irish mathematician George Boole.

On Internet search engines, the options for constructing logical relationships among search terms often modify the traditional practice of Boolean searching. This will be covered in the section below, Boolean Searching on the Internet.

Boolean logic consists of three logical operators:

1. OR 2.AND 3.NOT


OR Logic

In this search, we will retrieve records in which AT LEAST ONE of the search terms is present. We are searching on the terms college and also university since documents containing either of these words might be relevant.


AND LOGIC

In this search, we retrieve records in which BOTH of the search terms are present


NOT LOGIC

In this search, we retrieve records in which ONLY ONE of the terms is present, the one we have selected by our search


Advanced Searching Techniques Truncation Proximity Searching

Phrase searching Near operator.

Case sensitivity


Truncation Truncation broadens your search by allowing you to retrieve all variant endings or

spellings of that word.

A particular character, like an asterisk (*) is used to truncate the END or MIDDLE OF A WORD. This is sometimes referred to as a WILDCARD. The truncation symbol and rules will depend on the database or search engine you are using.


Proximity Searching Refers to the ability to specify how close within a record multiple terms should be to each other.

The most commonly used proximity search option in Internet finding aids is a phrase search that requires terms to be in the exact order specified within the phrase markings. The default standard for identifying phrases is to use double quotes (" ") to surround the phrase.

1.Phrase Searching Example: "phrase searching is fun" Beyond phrase searching, other proximity operators can specify how close terms should be to each

other. Some will also specify the order of the search terms2. Near Operator What if you are looking for a sequence of words that are normally connected, but

that may be split by other words? If you were looking for information on the inventor Thomas Alva Edison, you could possibly search for a phrase, like this:

"Thomas Alva Edison" But this search would not bring you pages where the name is given as Thomas A.

Edison or Thomas Edison. You could solve this problem by entering "Thomas Alva Edison" OR "Thomas A. Edison" OR "Thomas Edison" or you could use the NEAR search operator. NEAR means "show me pages where

these words are near each other". Thomas NEAR Edison


Case Sensitive Search For instance, "Ram" is the name of a Hindu God while "RAM" is an abbreviation for Random

Access Memory. They both share the same spelling and it's the case that helps you understand the real context of the word. Unfortunately, Google searches are not case sensitive (or fold case) and hence most search results for Ram or RAM are about the "temporary" memory.

To solve this problem and help you conduct case sensitive searches on Google, someone has created a Google Appengine powered search engine at Case Sensitive Search - it scans through Google search results and filters out results that match the case of your search query.

Coming back to original example, here's is a comparison of case sensitive Google search results for "Ram" vs. "RAM".


More Search Techniques

Field Specific Searching Title Date URL

Language Restrictions


Bookmarks and Favorites save Web addresses so you can return to them quickly.

To save a web page, go to the Bookmarks or Favorites menu or click on its icon and select Add. When you click on the icon again, the title of the page you recorded will appear at the bottom of the list. To access the page, just double-click on the title.



E-mail Concepts

What is Email and Why is it Popular?

An electronic message sent from one computer to another. Email saves money and time compared to regular mail. An email message takes seconds to reach destination.

E-mail Concepts

How does Email Work?

Email travels via the Internet from one computer to another. Computers known as mail servers direct outgoing mail and store incoming the mail. Once email reaches your mail server, it waits in an electronic mail box, the "Inbox” for you to

collect it.

E-mail Concepts

Things You Can Do with Email

Compose and Send: write an email and send it to others.

Reply: reply to an email that you received.

Forward: pass on an email that you received to others.

Attachment: You can send files with your email such as: pictures, music, software and documents

E-mail Concepts

An email address consists of 3 parts:

E-mail Concepts

Two Ways to Get Email

1. Provided by your Internet Service Provider

Monthly fee for internet connection often includes email service. Aliant - [email protected] Eastlink - …@eastlink.ca

2. Free Web-Based Service Providers

Advertising on the site pays for the service. Gmail - …@gmail.com Hotmail - …@hotmail.com

E-mail Concepts

Two Ways People Check Email1. Web-Based Email Login to a web site Messages stay on the mail server Can be accessed from any computer with internet connection

2. Using Email Software Open and login to your email software application (e.g. Outlook) The application retrieves your messages from the mail server and saves them to your

computer’s hard drive

E-mail Concepts

How to Sign Up for a Gmail Email Account

1. Go to www.gmail.com

2. Click on “Sign Up for Gmail”

3. Fill in the Registration Form

E-mail Concepts

E-mail Concepts

E-mail Concepts

Signing In

1. Go to www.gmail.com 2. Type in your username

and password3. Click on the ‘sign in’

button

E-mail Concepts

To: contains the e-mail addresses of the recipients. This is a mandatory entry. CC: short for Carbon Copy. This is optional. BCC:, short for Blind Carbon Copy, contains the e-mail addresses of other recipients who

receive copies, but their names and addresses are hidden from the other recipients. This is optional.

E-mail Concepts

E-mail Concepts

Checking for New Email Messages

E-mail Concepts

E-mail Concepts

E-mail Concepts

E-mail Concepts

E-mail Concepts

Replying to a Message

“Replying” to a message sends it back to the person who sent it to you.

Forwarding a Message

By “forwarding” you can pass a message on to other friends.

E-mail Concepts

E-mail Concepts

The Trash Folder

Deleted messages go to the “Trash” folder.

If you delete something by accident, you can retrieve it from “Trash”.

If you delete a message in “Trash”, it is gone for good.

You can delete everything in the “Trash” folder by clicking on “Empty”

E-mail Concepts

E-mail can include a signature at the end of the message. An e-mail signature is not your hand-written signature.

Like a business card, an e-mail signature can include your name, title, telephone and fax numbers, street address, and e-mail address.

It saves time, you don’t have to retype the information each time you send a message. Clicking the feature automatically adds it to the message.

E-mail Concepts

Managing your Addresses With most software, you can create a set of e-mail addresses called a group. When you

address a message with a group, the message is automatically addressed to all the people in the group. This is sometimes referred to as a mailing list.

As your list grows, use the Search or Find function in the address book to locate an e-mail address based on a person's first or last name.

E-mail Concepts

Email Security

Always sign out, especially if you are using a public computer!

Never send your SIN or bank account number by email.

Beware of messages that: Ask for your bank account information, even if they say they want to put money into

your account (e.g. The Nigerian Scam) Ask you to click on a link, login and verify personal information (e.g. Phishing bank

scams) inform you that you have won a prize/money and ask for personal information in order

to give you your prize

E-mail Concepts

Education

Networking (2)