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Internetworking Communications Introduction 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 Example Voice Telephone Set Telephone Set Telephone Line

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introduction3
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

example
Example

Voice

TelephoneSet

TelephoneSet

Telephone Line

computer communication
Computer Communication

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

encode

010110

Receiving device receive analog signal

Sending device send digital signal

Encode
  • Information (e.g. data, text, voice or video) from the sending device is converted into signals which the communication medium can carry
transmission
Transmission
  • The signals are transmitted through the medium to the receiving device

Signal transmitted

by telephone line

Sending device

Receiving device

decode

010110

Receiving device receive digital signal

Sending device send analog signal

Decode
  • The signals are converted back into the information in its original form in the receiving device
computer network
Computer Network
  • 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.
computer network10
Computer Network

A Network is a collection of

computers

and

peripherals

via communication media such as cable and telephone line.

the need for networking
The need for networking

Benefits of using network:

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

OK! I give it to you.

  • Sharing data or program

I want your file.

Thank you!

1 sharing of resources13
1. Sharing of resources

OK! I let you print.

  • Sharing of hardware resources such as printer

I want to print.

1 sharing of resources14
1. Sharing of resources
  • 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
2 centralized control
2. Centralized Control

The network supervisor

better security

measures

centralized

control over all

facilities and

resources

2 centralized control16
2. Centralized Control
  • 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
3 communication
3. Communication

Mac

IBM PS/2

3 communication18
3. Communication
  • 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.
4 easier software management
4. Easier Software Management

Server

Install

new

software

Use new software

Use new

software

Use new

software

4 easier software management20
4. Easier Software Management
  • 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
5 flexibility of location
5. Flexibility of location
  • 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
local area network lan
Local Area Network (LAN)
  • Network that connects computer in a limited area, such as an office, a school or group of buildings is called LAN.
metropolitan area network man
Metropolitan Area Network (MAN)
  • Within a large city
  • Optical fibers as media
wide area network wan

LAN

LAN

LAN

Wide Area Network (WAN)
  • link small networks in different geographic area
network topology

Network Topology

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

slide27

Star architecture

Workstation

Workstation

Server

Workstation

Workstation

star architecture

????

I can’t work!

Hello?

Star architecture

Host

Node

star architecture29

Yes, I can hear you

Transferring

Hello?

Star architecture

Host

Node

star architecture30
Host fails,

whole network breaks down

Node fails,

network not affected

Configuration is simple

Star architecture
slide31

Ring architecture

Workstation

Workstation

Server

Workstation

Workstation

ring architecture

PC1, I love U!

Ring architecture

I know u love me,

but I hate u !

Oh, not for me, I will

pass the message

All Computer are nodes

ring architecture33

PC1, I love U!

Ring architecture

????

Oh, I can’t transfer

your message!!

ring architecture34
All computers are

Nodes

If any node fails,

whole network break down

Ring architecture
slide35

Bus architecture

Workstation

Workstation

Server

Bus

Workstation

Workstation

bus architecture
Bus architecture

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!

bus architecture37
Bus architecture

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 architecture38
All Nodes connected to

BUS

If any node fails,

network not affected

Bus architecture
interconnection of lans40
Interconnection of LANs
  • Bridge
    • responsible for connecting LANs of the same type
  • Gateway
    • responsible for connecting LANs of different type
question
Question

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.

two ways of transmitting signal
Two ways of Transmitting Signal:

1. Direct Mode Transmission

Signals are transmitted to a particular receiver

slide44
2. Broadcast Mode Transmission

Signals are transmitted to all directions

direct mode transmission
Direct Mode Transmission
  • Twisted Pair
    • Cheapest & therefore most common
    • Susceptible to local electrical noises
    • Usually used for short distance connections such as telephone line
slide46
Coaxial Cable
    • 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
slide47
Optical Fibre
    • 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
broadcast mode transmission
Broadcast Mode Transmission
  • Ground station send the data and beam to the satellite by microwave
  • Satellite will re-transmit data to another ground station
what is internet
What is 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!
what is internet51
What is Internet?
  • 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.
history of internet
History of Internet

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.

slide53

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

slide54

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:

internet
Internet
  • 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.
how does the networks
How does the 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)
tcp ip
TCP/IP
  • 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.
mechanism of tcp ip
Mechanism of TCP/IP
  • 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.
slide61
Each router examines the destination addresses of the packets it receives and then passes the packets on to another router as they make their way to their final destination.
  • 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.
why breaking down message into packets
Why breaking down message into packets?

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.

other important protocols
Other Important Protocols
  • Hypertext Transfer Protocol (HTTP)
  • Simple Mail Transfer Protocol (SMTP)
  • File Transfer Protocol (FTP)
  • Telnet protocol.
bandwidth
Bandwidth
  • 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?
client servers
Client & Servers
  • 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

clients servers
Clients & Servers
  • 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

slide68
Client Program:
    • MS Internet Explorer (installed in the client computer)
    • Plug-ins (e.g. Realplayer, flash player)
  • Server Program:
    • MS IIS (installed in the web server)
electronic mail
Electronic Mail
  • 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
electronic mail71
Electronic Mail
  • 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!

slide72

MS Outlook

Hotmail (Web-Mail)

world wide web www
World Wide Web (WWW)
  • 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.
multimedia on the web
Multimedia on the Web
  • Graphics (圖片)
  • Animation (動畫)
  • Audio (聲音)
  • Video (電影)

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

portals
Portals
  • 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
gopher
Gopher
  • 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
file transfer protocol ftp
File Transfer Protocol (FTP)
  • 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.
slide80
Anonymous FTP:
    • 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
Telnet
  • 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
slide82
BBS
  • 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
Usenet
  • 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
newsgroup
Newsgroup
  • 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.
slide86
The name of a newsgroup describes the type of the information discussed.
  • 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
Instant Communication Tools
  • Instant communication tools allow us to communicate with our friends and make new friends from different parts of the world.

Yahoo! Messenger ICQ

slide88
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.
slide89
ICQ
  • 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.
world wide web www91
World Wide Web (WWW)
  • 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
slide92
The Web uses a metaphor of individual pages, usually combined to make up sites.
  • 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.
how does the web works
How does the Web works?
  • 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.
ip address
IP Address
  • 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/.

domain name
Domain Name
  • 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.

examples

Computer Name

Domain Name

Examples
  • 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)
dissecting domain

Top-level Domain

Dissecting Domain
  • Considering the following domain
    • microsoft.com
  • There are 2 parts for the domain name
    • microsoft: Company Name
    • com: Organization Name
slide99
As the internet expanded internationally, a more specific top-level showing the geographical location is needed:
  • Example
    • www.slcss.edu.hk

Geographical Domain Name

(means the organization is located in HK)

slide101
DNS
  • 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

example102
Example
  • 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
slide103
URL
  • 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

why the internet is so slow
Why the Internet is so slow?
  • 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.
what is intranet
What is Intranet?
  • 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.
firewall
Firewall
  • 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

proxy server
Proxy Server
  • 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

extranet
Extranet
  • 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.
what is java activex
What is Java & ActiveX?
  • 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 the intenet
Accessing the Intenet
  • 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
what do you need to get connected
What do you need to get connected?
  • A computer
  • A phone line
  • A modem (or NIC for faster digital connection)
  • An ISP (Internet Service Provider)
  • Browser software
internet access via a phone line

modem

Internet access via a phone line

Internet

ISP

Public Phone Line

  • ISP = Organization or company that offers access to the Internet
after successfully apply an account from the isp you will receive
After Successfully apply an account from the ISP, you will receive:
  • 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.

two types of internet accounts
Two types of Internet accounts
  • 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.
hardware requirements
Hardware Requirements
  • Computer
  • Modem (Modulator-Demodulator)
    • Encoding (digital -->analog)
    • Transmission
    • Decoding (analog --> digital)
  • Phone Line
modem
Modem
  • 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”
choosing an isp
Choosing an ISP
  • 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.
questions to be asked in choosing isp
Questions to be asked in choosing ISP:
  • 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?
  • …..
introduction122
Introduction
  • 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.
slide123
SMTP
  • 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.
slide124
POP3
  • 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).
slide125
This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
email address
Email Address
  • 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.
email structure
Email Structure
  • A email consists of 2 parts:
    • Header
      • From
      • Cc
      • To
      • Subject
      • Date
    • Body
receiving email

Mail

modem

Receiving Email

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

receiving email129

Mail

modem

Receiving Email

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

Internet

ISP

MailBox

receiving email130

Mail

modem

Receiving Email

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

smileys
Smileys

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/