Internetworking Communications

1
Internetworking Communications
2
Introduction
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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
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Example
Voice
TelephoneSet
TelephoneSet
Telephone Line
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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
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Encode

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

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Transmission

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

Signal transmitted by telephone line
Sending device
Receiving device
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Decode

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

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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.

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Computer Network
A Network is a collection of
and
computers
peripherals
via communication media such as cable and
telephone line.
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The need for networking

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

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1. Sharing of resources
OK! I give it to you.

• Sharing data or program

I want your file.
Thank you!
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1. Sharing of resources
OK! I let you print.

• Sharing of hardware resources such as printer

I want to print.
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1. Sharing of resources

• Sharing data, programs and hardware
• Data and software can be centrally stored in 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

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2. Centralized Control
The network supervisor
better security measures
centralized control over all facilities and
resources
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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

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3. Communication
Mac
IBM PS/2
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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.

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4. Easier Software Management
Server
Install new software
Use new software
Use new software
Use new software
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4. Easier Software Management

• When a new applications is developed and
  installed in the server, workstation can
  immediately 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

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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

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Types of Network
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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.

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Metropolitan Area Network (MAN)

• Within a large city
• Optical fibers as media

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Wide Area Network (WAN)

• link small networks in different geographic area

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Network Topology

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

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Star architecture
Workstation
Workstation
Server
Workstation
Workstation
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Star architecture
Host
Node
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Star architecture
Host
Node
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Star architecture

• Host fails,
• whole network breaks down
• Node fails,
• network not affected
• Configuration is simple

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Ring architecture
Workstation
Workstation
Server
Workstation
Workstation
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Ring architecture
I know u love me, but I hate u !
Oh, not for me, I will pass the message
All Computer are nodes
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Ring architecture
????
Oh, I cant transfer your message!!
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Ring architecture

• All computers are
• Nodes
• If any node fails,
• whole network break down

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Bus architecture
Workstation
Workstation
Server
Bus
Workstation
Workstation
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Bus architecture
Not my message, I wont pick up
What! The deadline has changed??
Not my message, I wont pick up
Its my message, I will pick it up
Node
BUS
Not my message, I wont pick up
You have to hand in your homework today!
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Bus architecture
Not my message, I wont pick up
What! The deadline has changed??
Its my message, I will pick it up
Node
What will happen?
BUS
Not my message, I wont pick up
You have to hand in your homework today!
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Bus architecture

• All Nodes connected to
• BUS
• If any node fails,
• network not affected

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Interconnection of LANs
Bridge
Gateway
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Interconnection of LANs

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

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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.
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Means of Communication
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Two ways of Transmitting Signal

• 1. Direct Mode Transmission

Signals are transmitted to a particular receiver
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• 2. Broadcast Mode Transmission

Signals are transmitted to all directions
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Direct Mode Transmission

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

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• 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

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• 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

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Broadcast Mode Transmission
Ground station send the data and beam to the
satellite by microwave
Satellite will re-transmit data to another ground
station
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Understanding Internet
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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!

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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.

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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.

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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
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If someone wants to send a message from A to H,
it can go through the following path
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However, if LAN B breaks down in case of bomb
attack .
B
C
A
D
H
E
G
F
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The message can still go to the destination
through the path A -gt E -gt D -gt G -gt H.
C
A
D
H
E
G
F
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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.

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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)

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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.

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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.

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• 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.

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Why breaking down message into packets?

• 1.Makes messages of different sizes to become
  packets of standard size --gt standard size buffer
  can be used in transmitting the packets.
• 2.Packets of the same message can take different
  route to the destination --gt increase flexibility
  of the network
• 3.When a transmission error occurs, only the
  contaminated packet needs to be re-transmitted.

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Other Important Protocols

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

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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?

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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
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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
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• 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)

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Internet Resources
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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

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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.

Lets try your email account provided by HKedCity!
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MS Outlook
Hotmail (Web-Mail)
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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.

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Multimedia on the Web

• Graphics (??)
• Animation (??)
• Audio (??)
• Video (??)

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

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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

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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.

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File Transfer Protocol (FTP)
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File Transfer Protocol (FTP)
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• 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)

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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.hk21

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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/

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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

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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.

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• Http//news.newsgroup.com.hk

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• 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.

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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
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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.

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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.

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Internet Addressing
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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

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• 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.

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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.

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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/.
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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.
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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)

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Dissecting Domain

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

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• 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)
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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
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Example

• Lets 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

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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/Networ
ks/index.html
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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.

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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.

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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
107
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
108
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.

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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.

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Accessing Internet
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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

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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

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Internet access via a phone line
Internet
ISP
Public Phone Line
ISP Organization or company that offers access
to the Internet
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Internet Access via cable modem

• I-Cable Setting

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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.
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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.

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Hardware Requirements

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

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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

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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.

120
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?
• ..

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Using Email
122
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.

123
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.

124
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).

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• This is why you need to specify both the POP or
  IMAP server and the SMTP server when you
  configure your e-mail application.

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Email Address

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

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Email Structure

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

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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
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Receiving Email

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

Internet
ISP
MailBox
130
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
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Smileys

• A scheme for encoding and conveying ones felling
  as small text glyphs
• -) happy
• -( disappointment
• -lt really sad
• -( angry
• -X lips are sealed

The Unofficial Smiley Dictionary
http//www.eff.org/papers/eegtti/eeg_286.htm/