Internetworking Communications - PowerPoint PPT Presentation

Internetworking Communications

Introduction

• Communication refers to the transfer of information from one place to another
• The simplest communication system consists of the following:

Message

Receiver

Sender

Medium

Voice

TelephoneSet

TelephoneSet

Telephone Line

In order to allow 2 computers at different location to communicate over a telephone line, a modem is needed to change the data from digital to analog signal and vice versa.

Encode

Transmission

Decode

010110

Receiving device receive analog signal

Sending device send digital signal

• Information (e.g. data, text, voice or video) from the sending device is converted into signals which the communication medium can carry

• The signals are transmitted through the medium to the receiving device

Signal transmitted

by telephone line

Sending device

Receiving device

010110

Receiving device receive digital signal

Sending device send analog signal

• The signals are converted back into the information in its original form in the receiving device

• One drawback of PC is that it is standalone computer primarily designed for single users.
• Information is therefore cannot be shared or transmitted easily and effectively between computer.
• The solution is to link up computers to form a computer network.

A Network is a collection of

computers

and

peripherals

via communication media such as cable and telephone line.

Benefits of using network:

• Efficient sharing of resources
• Centralized control
• Communication
• Easier software management
• Flexibility of location

OK! I give it to you.

• Sharing data or program

I want your file.

Thank you!

OK! I let you print.

• Sharing of hardware resources such as printer

I want to print.

• Sharing : data, programs and hardware
• Data and software can be centrally storedin a computer acting as the file server and accessed by any computer in the network
• An expensive laser printer can be connected to a computer which serves as a print server and processing printing jobs from other computers

The network supervisor

better security

measures

centralized

control over all

facilities and

resources

• The network supervisor can have a centralized control over the use of all facilities and resources
• including all data, programs, disk spaces and other hardware
• better security measures can be applied

Mac

IBM PS/2

• Different types of computers store data files using different internal representation methods.
• A network operation system can automatically convert the files into the required representations before they are transferred.

Server

Install

new

software

Use new software

Use new

software

Use new

software

• When a new applications is developed and installed in the server, workstation canimmediately use it from any computer
• upgrading or changing software is simpler because it is now stored in the single file server but not distributed among different computers

• Any computer on the network can be used to access the centralized database or the software and data in the file server
• it is fairly easy to add a workstation anywhere, relocate a computer to another site, to add a new printer or any other resources

Types of Network

• Network that connects computer in a limited area, such as an office, a school or group of buildings is called LAN.

• Within a large city
• Optical fibers as media

LAN

LAN

LAN

• link small networks in different geographic area

Network Topology

It refers to the way by which the network hardware (called nodes) are arranged and the means if data flow.

Star architecture

Workstation

Workstation

Server

Workstation

Workstation

????

I can’t work!

Hello?

Host

Node

Yes, I can hear you

Transferring

Hello?

Host

Node

whole network breaks down

Node fails,

network not affected

Configuration is simple

Ring architecture

Workstation

Workstation

Server

Workstation

Workstation

PC1, I love U!

I know u love me,

but I hate u !

Oh, not for me, I will

pass the message

All Computer are nodes

PC1, I love U!

????

Oh, I can’t transfer

your message!!

Nodes

If any node fails,

whole network break down

Bus architecture

Workstation

Workstation

Server

Bus

Workstation

Workstation

What! The deadline

has changed??

Not my message,

I won’t pick up

Not my message,

I won’t pick up

It’s my message,

I will pick it up

Node

BUS

Not my message,

I won’t pick up

You have to hand

in your homework

today!

What! The deadline

has changed??

Not my message,

I won’t pick up

It’s my message,

I will pick it up

Node

What will happen?

BUS

Not my message,

I won’t pick up

You have to hand

in your homework

today!

BUS

If any node fails,

network not affected

Bridge

Gateway

• Bridge
• responsible for connecting LANs of the same type
• Gateway
• responsible for connecting LANs of different type

Both computer networks and mainframes allow users to communicate and share data and resources. Why computer networks still supersede Mainframes?

It is because computer networks have higher reliability and performance over price ratio. It is also much easier to expand a computer network than a mainframe.

Means of Communication

1. Direct Mode Transmission

Signals are transmitted to a particular receiver

Signals are transmitted to all directions

• Twisted Pair
• Cheapest & therefore most common
• Susceptible to local electrical noises
• Usually used for short distance connections such as telephone line

• single wire surrounded by a tube-shaped conductor of solid copper
• can support very high speed data transfer
• used for long distance communication (e.g. TV system)
• moderate cost

• a popular high bandwidth (can carry thousands of channels) transmission medium

• small size,light weight
• provide little interference (noise) and highest transmission rate
• Suited for long distances communication in high data rate

• Ground station send the data and beam to the satellite by microwave

• Satellite will re-transmit data to another ground station

Understanding Internet

• The Internet is a loose association of thousands of networks and millions of computers across the world that all work together to share information.
• “Network of Networks”
• The Internet now serves approximately 50 million users!
• It is a living entity and is ever growing!

• The Internet is growing because the no. of people participating in it is increasing rapidly.
• It is so large and complex that no one can control it, or just be able to understand all of it.

In the late 1960s, the U.S. Defense Department began the Internet as a military research project. The government created a network that covered a large geographic area and could withstand nuclear attack. If part of the network failed, information could still find new route around the disabled computers.

B

C

A

D

H

E

G

F

Suppose A, B, C, D, E, F, G and H are LANs in different geographic area.They are connected together to form a larger computer system

B

C

A

D

H

E

G

F

If someone wants to send a message from A to H, it can go through the following path:

However, if LAN B breaks down in case of bomb attack ….

B

C

A

D

H

E

G

F

The message can still go to the destination through the path A -> E -> D -> G -> H.

C

A

D

H

E

G

F

• The network quickly grew to include scientists and researchers across the U.S.
• Eventually, school, businesses and libraries around the world were on the Internet.

• The name “Internet” is derived from the word “inter-networking” for it is a collection of tens of thousands of networks.

• The secret of the Net is a network protocol called TCP/IP.
• TCP/IP is a kind of coding system that lets computers electronically describe data to each other over the network. (similar to the language & grammar we use everyday)

• The term actually refers to two separate parts: the transmission control protocol(TCP) and the Internet protocol (IP).
• Every computer that hooks to the Internet understands these two protocols and uses them to send and receive data from the next computer along the network.

• First, TCP breaks down every piece of data-- such as an email message or instructions from a Java applet - into small chunks called packets, each of which is wrapped in an electronic envelope with Web addresses for both the sender and the recipient.
• The IP protocol then figures out how the data is supposed to get from point A to point B by passing through a series of routers - sort of like regular mail passes through several post offices on its way to a remote location.

• If your email was broken into ten packets, then each of those may have traveled a completely separate route. But you'll never know it, because as the packets arrive, TCP takes over again, identifying each packet and checking to see if it's intact. Once it has received all the packets, TCP reassembles them into the original.

1.Makes messages of different sizes to become packets of standard size --> standard size buffer can be used in transmitting the packets.

2.Packets of the same message can take different route to the destination --> increase flexibility of the network

3.When a transmission error occurs, only the contaminated packet needs to be re-transmitted.

• Hypertext Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• File Transfer Protocol (FTP)
• Telnet protocol.

• It is a measurement of capacity of the communication channel
• 10Mbps = transferring 10Mbits per second
• How long will it take to transfer a 1MB file on a 6Mbps bandwidth?

• The Internet is extremely large.
• How can the network provide facilities to the users and how can the users get access to the facilities of the network?

Client

Server

• Users can use a client programs to talk to a server programs that provide facilities/services
• Example:

Web Server in SLCSS

Http:/www.slcss.edu.hk

Computer at home

• MS Internet Explorer (installed in the client computer)
• Plug-ins (e.g. Realplayer, flash player)
• Server Program:
• MS IIS (installed in the web server)

Internet Resources

• Also know as “Email”
• One of the most popular internet services.
• Send and receive messages from anyone on the Internet.
• Advantages of using email:
• Fast
• cheap

• Most e-mail systems include a text editor for composing messages.
• You then send the message to the recipient by specifying the recipient's address.
• You can also send the same message to several users at once. This is called broadcasting.

Let’s try your email account provided by HKedCity!

MS Outlook

Hotmail (Web-Mail)

• WWW  Internet
• WWW is only one of the many services available on the Internet
• WWW is a large system of server that offers all kinds of information to anyone on the Internet.
• WWW is stored in the form of pages and you use browser to view the pages.

• Graphics (圖片)
• Animation (動畫)
• Audio (聲音)
• Video (電影)

DEMO: http://www.scsite.com/dc2000/

• Web site designed to offer a variety of internet services from a single and convenient location.
• Examples
• http://www.yahoo.com.hk
• http://www.netvigator.com
• http://www.hutchcity.com
• http://www.show8.com
• http://www.renren.com

• Similar to the WWW, provide information to Internet users - gopherspace.
• The different between gopherspace and WWW lies in the organization of information.
• In gopherspace, the information is presented as a series of simple menus
• Text-based only

• Helps you to copy files from one computer to another in a network.
• For security, you can copy files between 2 computers only if you can log in both computers.
• You can use a ftp client to connect to te remote computer. You will then be asked to enter a userid and password.

• allows the public to log in their guest account (userid = anonymous; password = email address)
• Distribute program or data files to the public. (e.g. Hardware Drivers)

• Telnet is an internet service letting people to log in and use remote computers.
• A telnet can only be made if an account exists in the remote computer and a connection is made through Internet with the provision of correct username and password
• Use a Telnet client to make connection to a remote host.
• Example: telnet://ihome.slcss.edu.hk:21

• An electronic message center. Most bulletin boards serve specific interest groups.
• They allow you to dial in with a modem, review messages left by others, and leave your own message if you want.
• Example:
• telnet://amtigers.adsldns.org/

• Usenet is a system of discussion groups
• You can join the Usenet for
• reading & responding articles
• seeking for advise of certain problems
• Usenet is free of charge

• A newsgroup is a discussion group that allows people with common interests to communicate with each other
• There are thousands of newsgroups on every subject imaginable.
• Each newsgroup discusses a particular topic such as hardware, software, music, games and movies etc.

• A newsgroup name consists of two or more words, separated by dot (.)
• The first name describe the main topic. Each of the following words narrows the topic.

• Instant communication tools allow us to communicate with our friends and make new friends from different parts of the world.

Yahoo! Messenger ICQ

• An easy-to-use online instant messaging program. Pronounced as separate letters, so that it sounds like "I-Seek-You,"
• It is used as a conferencing tool by individuals on the Net to chat, e-mail, perform file transfers, play computer games, and more.

• Once you have downloaded and installed ICQ onto your PC, you can create a list of friends, family, business associates, etc. (who also have ICQ on their PC's).
• ICQ uses this list to find your friends for you, and notifies you once they have signed onto the Net. You can then send messages, chat in real time, play games, etc.

Internet Addressing

• Web Internet
• The Internet is the global association of computers that carries data and makes the exchange of information possible.
• The World Wide Web is only a subset of the Net -- a collection of inter-linked documents that work together using a specific Internet protocol called HTTP

• Web pages are written in HTML, or Hypertext Markup Language, which tells the Web browser how to display the page and its elements.
• The defining feature of the Web is its ability to connect pages to one another -- as well as to audio, video, and image files -- with hyperlinks. Just click a link, and suddenly you're at a Web site on the other side of the world.

<strong>This is a Test!</strong>

• The Web is based on a set of rules for exchanging text, images, sound, video, and other multimedia files, which is collectively known as HTTP, or hypertext transfer protocol.
• Web pages can be exchanged over the Net because browsers (which read the pages) and Web servers (which store the pages) both understand HTTP.

• A computer in the Internet must have an unique identification - IP address.
• An IP address is a 12-digit number. The digits are organized in four groups of numbers (which can range from 0 to 255) separated by periods.

http://206.16.0.204/ is the same as http://www.cnet.com/.

• Internet domain names are the next level of Internet addressing, just as the street name is followed by the city and state.
• Domain names create a single identity for a series of computers used by a company or an institution.

While there may be 38 servers at a given company, each with its own IP address, they all share a common domain name, such as CNET.COM.

Computer Name

Domain Name

• The domain name of our school is
• slcss.edu.hk
• There are several web servers in our school network, for example:
• www.slcss.edu.hk (210.0.197.34)
• ihome.slcss.edu.hk (210.0.197.39)
• intranet.slcss.edu.hk (210.0.197.36)

Top-level Domain

• Considering the following domain
• microsoft.com
• There are 2 parts for the domain name
• microsoft: Company Name
• com: Organization Name

• Example
• www.slcss.edu.hk

Geographical Domain Name

(means the organization is located in HK)

• Stand for Domain Name Server
• an Internet service that translates domain names into IP addresses.
• Because domain names are alphabetic, they're easier to remember.
• The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

http://www.dmedia.com.hk/edu/flash/3_4_a_4a.htm

• Let’s try the following command in DOS Prompt:
• PING www.yahoo.com.hk
• The IP address of the HK Yahoo will be resolved:
• 202.1.233.111

• The domain name identifies all the computers in a group. But if you want to get to a specific page stored on any of those computers, you'll need an even more precise address.
• Each web page has its own unique address, known as a Uniform Resource Locator (URL), which tells your browser exactly where to go on the server to find a page.

Http://www.cnet.com/Content/Features/Techno/Networks/index.html

• Part of it is the Internet's fault: its ability to handle an enormous amount of data every day trades flexibility for speed.
• Everyone who uses the Net shares bandwidth--the data-carrying capacity of a network.
• Every time you send an email or download a file, you're contributing to the load. Web pages are particularly bad bandwidth hogs because they are loaded down with graphics and multimedia.

• Intranets work like the Web, with browsers, Web servers, and Web sites, but they're used internally by companies or organizations.
• Companies use them because they let employees share corporate data, but they're cheaper and easier to manage than most private networks -- no one needs any software more complicated or more expensive than a Web browser, for instance.
• They also have the added benefit of giving employees access to the Web.

• Intranets are closed off from the rest of the Net by firewall software, which lets employees surf the Web but keeps all the data on internal Web servers private.
• It refers to both hardware & software used to restrict access to data on the internal network.

http://www.dmedia.com.hk/edu/flash/3_4_a_7b.htm

• A proxy server stores web contents on local hard disks so that the next request for the same web page will be served faster from the hard disk, instead of getting it from the original web server.

http://www.dmedia.com.hk/edu/flash/3_4_a_7a.htm

• An extranet is formed when two companies connect their intranets or parts of the intranets to each other, using a private, leased telephone line or even the public Internet.
• A company's extranet could include shared content in the form of private newsgroups that let representatives from two or more companies hash out ideas and coordinate projects.

• Both Java and ActiveX are technologies that let programmers create animated and interactive Web pages--the kinds that move, flash, and play games.
• HTML is the language that describes all the basic elements of a page (such as text and graphics), but its current incarnation can't do much to make a page interactive; Java and ActiveX fill that void.

Accessing Internet

• Through campus computers
• computers in our school are connected to local network, which is connected to the Internet by leased line.
• Through Internet Service Provider (ISP)
• by connecting a modem to your computer at home and apply an account from an ISP

• A computer
• A phone line
• A modem (or NIC for faster digital connection)
• An ISP (Internet Service Provider)
• Browser software

modem

Internet

ISP

Public Phone Line

• ISP = Organization or company that offers access to the Internet

• I-Cable Setting:

• a user name
• a password
• a phone number your communication program should dial in order to connect to the Internet host provided by that ISP.

In return, you have to pay the necessary fees to the ISP.

• PPP account
• you computer will acts an Internet host during the period of connection.
• All the Internet clients run on your computer & your computer will do most of the work.
• The remote host acts as a pipe to the Internet
• Shell account
• your computer will emulate a terminal which allows you to work directly with the remote host.
• You actually do work in the remote host.

• Computer
• Modem (Modulator-Demodulator)
• Encoding (digital -->analog)
• Transmission
• Decoding (analog --> digital)
• Phone Line

• Internal Modem
• a circuit board plugged into an expansion slot inside the computer.
• External Modem
• circuit that fitted inside a box that is connected by cable to the serial port of the computer.
• has lights on it to show what is happening
• easy to move from one computer to another
• Speed
• measured in “bits per second” or “bps”

• Apart from Internet service, ISP may also provide
• Online Information Service
• Homepage storage space
• Email Account
• ISPs in Hong Kong
• Netvigator, I-Cable, HKNet, CTINet, iSmart, SuperNet, etc.

• How the Internet access fee is calculated?
• Are sufficient phone lines provided?
• Are fast lines provided?
• Is full Internet access offered?
• Are you allowed to put up your own homepage?
• …..

Using Email

• Most important Internet service
• Low price system for fast and reliable long distance communication
• Convenient and accessible:
• recipient can get the mail wherever the Internet is connected.

• Short for Simple Mail Transfer Protocol
• It describes how emails are to be sent from the client computer to email server
• Part of the TCP/IP family of protocols.

• Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server.
• Most e-mail client use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).

• Consists of a userid and a domain name. (e.g. contact@slcss.edu.hk)
• For sending email in local network, the email address can be simplified as contact@slcss.
• Most mail client program can figure out this is a local address and deliver the mail accordingly.

• A email consists of 2 parts:
• Header
• From
• Cc
• To
• Subject
• Date
• Body

Mail

modem

1. ISP is 24-hour a day connected to the Internet. Mails to you can always reach your ISP via the Internet.

Internet

ISP

MailBox

Mail

modem

2. Your mails are stored in your mailbox maintained by your ISP.

Internet

ISP

MailBox

Mail

modem

3. When you run your mail client, it contacts your ISP and your mails in your mail in your mailbox will be transmitted to your computer.

Internet

ISP

MailBox

A scheme for encoding and conveying one’s felling as small text “glyphs”

:-) happy

:-( disappointment

:-< really sad

%-( angry

:-X lips are sealed

The Unofficial Smiley Dictionary :

http://www.eff.org/papers/eegtti/eeg_286.htm/