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Internetworking Communications

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Title: Internetworking Communications


1
Internetworking Communications
2
Introduction
3
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
4
Example
Voice
TelephoneSet
TelephoneSet
Telephone Line
5
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
6
Encode
  • Information (e.g. data, text, voice or video)
    from the sending device is converted into signals
    which the communication medium can carry

7
Transmission
  • The signals are transmitted through the medium to
    the receiving device

Signal transmitted by telephone line
Sending device
Receiving device
8
Decode
  • The signals are converted back into the
    information in its original form in the receiving
    device

9
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.

10
Computer Network
A Network is a collection of
and
computers
peripherals
via communication media such as cable and
telephone line.
11
The need for networking
  • Benefits of using network
  • Efficient sharing of resources
  • Centralized control
  • Communication
  • Easier software management
  • Flexibility of location

12
1. Sharing of resources
OK! I give it to you.
  • Sharing data or program

I want your file.
Thank you!
13
1. Sharing of resources
OK! I let you print.
  • Sharing of hardware resources such as printer

I want to print.
14
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

15
2. Centralized Control
The network supervisor
better security measures
centralized control over all facilities and
resources
16
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

17
3. Communication
Mac
IBM PS/2
18
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.

19
4. Easier Software Management
Server
Install new software
Use new software
Use new software
Use new software
20
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

21
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

22
Types of Network
23
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.

24
Metropolitan Area Network (MAN)
  • Within a large city
  • Optical fibers as media

25
Wide Area Network (WAN)
  • link small networks in different geographic area

26
Network Topology
  • It refers to the way by which the network
    hardware (called nodes) are arranged and the
    means if data flow.

27
Star architecture
Workstation
Workstation
Server
Workstation
Workstation
28
Star architecture
Host
Node
29
Star architecture
Host
Node
30
Star architecture
  • Host fails,
  • whole network breaks down
  • Node fails,
  • network not affected
  • Configuration is simple

31
Ring architecture
Workstation
Workstation
Server
Workstation
Workstation
32
Ring architecture
I know u love me, but I hate u !
Oh, not for me, I will pass the message
All Computer are nodes
33
Ring architecture
????
Oh, I cant transfer your message!!
34
Ring architecture
  • All computers are
  • Nodes
  • If any node fails,
  • whole network break down

35
Bus architecture
Workstation
Workstation
Server
Bus
Workstation
Workstation
36
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!
37
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!
38
Bus architecture
  • All Nodes connected to
  • BUS
  • If any node fails,
  • network not affected

39
Interconnection of LANs
Bridge
Gateway
40
Interconnection of LANs
  • Bridge
  • responsible for connecting LANs of the same type
  • Gateway
  • responsible for connecting LANs of different type

41
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.
42
Means of Communication
43
Two ways of Transmitting Signal
  • 1. Direct Mode Transmission

Signals are transmitted to a particular receiver
44
  • 2. Broadcast Mode Transmission

Signals are transmitted to all directions
45
Direct Mode Transmission
  • Twisted Pair
  • Cheapest therefore most common
  • Susceptible to local electrical noises
  • Usually used for short distance connections such
    as telephone line

46
  • 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

47
  • 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

48
Broadcast Mode Transmission
Ground station send the data and beam to the
satellite by microwave
Satellite will re-transmit data to another ground
station
49
Understanding Internet
50
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!

51
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.

52
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.

53
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
54
If someone wants to send a message from A to H,
it can go through the following path
55
However, if LAN B breaks down in case of bomb
attack .
B
C
A
D
H
E
G
F
56
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
57
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.

58
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)

59
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.

60
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.

61
  • 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.

62
(No Transcript)
63
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.

64
Other Important Protocols
  • Hypertext Transfer Protocol (HTTP)
  • Simple Mail Transfer Protocol (SMTP)
  • File Transfer Protocol (FTP)
  • Telnet protocol.

65
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?

66
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
67
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
68
  • 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)

69
Internet Resources
70
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

71
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!
72
MS Outlook
Hotmail (Web-Mail)
73
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.

74
Multimedia on the Web
  • Graphics (??)
  • Animation (??)
  • Audio (??)
  • Video (??)

DEMO http//www.scsite.com/dc2000/
75
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

76
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

77
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.

78
File Transfer Protocol (FTP)
79
File Transfer Protocol (FTP)
80
  • 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)

81
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

82
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/

83
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

84
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.

85
  • Http//news.newsgroup.com.hk

86
  • 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.

87
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
88
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.

89
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.

90
Internet Addressing
91
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

92
  • 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.

93
(No Transcript)
94
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.

95
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/.
96
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.
97
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)

98
Dissecting Domain
  • Considering the following domain
  • microsoft.com
  • There are 2 parts for the domain name
  • microsoft Company Name
  • com Organization Name

99
  • 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)
100
(No Transcript)
101
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
102
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

103
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
104
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.

105
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.

106
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.

109
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.

110
Accessing Internet
111
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

112
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

113
Internet access via a phone line
Internet
ISP
Public Phone Line
ISP Organization or company that offers access
to the Internet
114
Internet Access via cable modem
  • I-Cable Setting

115
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.
116
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.

117
Hardware Requirements
  • Computer
  • Modem (Modulator-Demodulator)
  • Encoding (digital --gt analog)
  • Transmission
  • Decoding (analog --gt digital)
  • Phone Line

118
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

119
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?
  • ..

121
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).

125
  • This is why you need to specify both the POP or
    IMAP server and the SMTP server when you
    configure your e-mail application.

126
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.

127
Email Structure
  • A email consists of 2 parts
  • Header
  • From
  • Cc
  • To
  • Subject
  • Date
  • Body

128
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
129
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
131
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/
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