Transcript Internet Technology

Lecture 3
The Internet: technology and services
Internet Technologies
9.2
The UNIX Connection
• The Internet has grown out of UNIX
Operating System
• Some Internet terms (email address)
and services (FTP) become more clear
after we cover UNIX
9.3
The Internet: A Network of
Networks
The Internet is an interconnected network
of thousands of networks linking
academic, research, government, and
commercial institutions.
9.4
Networks Near and Far
• There are two general types of
computer networks:
LAN
(Local Area
Network)
WAN
(Wide Area Network)
9.5
LAN (Local Area Network)
• A LAN is a network in which the
computers are physically close to each
other
– LAN networks are usually set up to share
peripherals, such as printers and network
servers
– Each computer and
shared peripheral is
a node on the LAN
9.6
WAN (Wide Area Network)
• A WAN is a network in which the
computers are a great distance from
one another
– Connections are made
via telephone lines,
satellites, and/or
microwave relay towers
– Each network site is a
node
9.7
WAN (Wide Area Network)
• WANs are often made up of LANs
9.8
Communication á la Modem
• A modem is needed to connect a
computer to a phone line
• The computer
communicates
with digital signals
• The telephone system
was designed to transmit voice signals
which are analog
9.9
Client/Server Model
9.10
Internet Protocols
TCP/IP (Transmission
Control
Protocol/Internet
Protocol) is the
protocol at the
heart of the
Internet.
9.11
Internet Protocols
• TCP/IP translates into:
– TCP (transmission control protocol) breaks
messages into packets.
– IP (Internet protocol) is the addressing for
the packets.
– computer in the Internet (host) is identified
by IP address (e.g. 128.214.9.225)
– IP addresses run out
9.12
Internet Addresses
An Internet address is made up of two
parts separated by the @ symbol:
• the person’s user name
• the host name
The host is named using DNS (domain
name system), which translates IP
addresses into a string of names.
9.13
Internet Addresses
An Internet address includes:
[email protected]
username is the person’s “mailbox”
hostname is the name of the host computer and is
followed by one or more domains separated by
periods:
•
•
•
•
host.subdomain.domain
host.domain
www.cs.helsinki.fi
[email protected] ([email protected] alias)
9.14
Internet Addresses
Top level domains
include:
–
–
–
–
–
.edu - educational sites
.com - commercial sites
.gov - government sites
.mil - military sites
.net - network
administration sites
– .org - nonprofit
organizations
9.15
Intranets
• Intranets – internal closed networks of
organizations that are designed using the
same technology as the Internet.
• Firewalls - used to prevent unauthorized
communication and secure sensitive internal
data.
• Virtual Private Networking (VPN) -- a way to
access intranets from public Internet
9.16
Internet Services
9.17
The World Wide Web:
Browsing the Web
WWW is a distributed
browsing and
searching systems
developed by
CERN.
Use hypertext links
and navigational
aids to explore
information on the
Internet.
9.18
Web Addresses
URL (Uniform
Resource Locator):
addresses for the
World Wide Web.
http (hypertext
transfer protocol):
the protocol of the
WWW
9.19
Searching the Web
• A directory (also an
index) is a
hierarchical catalog
of Web sites
compiled by
researchers.
9.20
Searching the Web
• A search engine
offers a more
complete database
of what is one the
WWW. A software
robot or spider
retrieves the entries
according to key
word queries.
9.21
Email on the Internet
• Email (one-on-one
communication).
• Pine - UNIX-based
mail program.
• MIME - Multipurpose
Internet Mail
Exchange - allows
you exchange files
through email.
Outlook express and Netscape
provide more advanced mail
readers
9.22
Disadvantages of Email
•
•
•
•
•
Works only if the recipient responds
Authentication is not ensured
Email is not private
Can be overwhelming (SPAM)
Both filter out many
human components
of communication
9.23
Mailing Lists and
Newsgroups
• Email is a valuable tool for one-to-one
communication
• Mailing lists allow you to participate in
email discussion groups on specialinterest topics.
• Usenet Newsgroups are virtual bulletin
boards that you access with a news
reader
9.24
Example of a mailing list
[email protected] is an
email list meant for distributing information
among foreign students at the University of
Helsinki.
Instructions on how to USE and LEAVE the
mailing list are available at the ESN website:
http://www.helsinki.fi/hyy/esn/eng/lists.html
Before posting mail to the mailing list, be sure
that you have read the NETIQUETTE of this
list:http://www.helsinki.fi/hyy/esn/eng/misc/fs_
netiquette.html
9.25
Mailing list (cont)
To subscribe mail [email protected] in
message body subscribe foreign-students
To unsubscribe mail [email protected] in
message body unsubscribe foreign-
students
Remember, the machine is stupid so write
exactly as above and try several times if it
fails
Never send these requests to the mailing list
itself
9.26
Mailing list (cont)
Contact the list administrator with related
problems at
[email protected]
Do not start or participate in flaming
• I.e. making offensive comments about
the person, spelling mistakes, etc.
• If you do, the administrator can remove
you from the list
9.27
Other email features
•
•
•
•
•
•
Attachments (one MB files are ok)
Filters
Ignore sender
Group by conversation
Work offline
Encryption and signature
9.28
News groups
• News (BBS) and web forums are an
alternative for mailing lists
• Most news groups maintain Frequently
Asked Questions (FAQ)
• Read FAQ before posting questions
• Web browsers like Netscape and IE
have tools for reading news
9.29
Remote Access and File
Transfer
The most popular use of the Internet is
information discovery and retrieval.
Because the Internet is unorganized,
you can use the following tools:
Telnet: for remote login to other computers.
FTP: file transfer protocol; transfer files
from remote computers.
SSH: secure remote login and file transfer
9.30
Paging and chatting
Talk is a UNIX program that allows you to
carry on a split-screen communication
Internet relay chat (IRC) allows several
users to type simultaneously
ICQ (I seek you): user-friendly messaging
system
– Microsoft Messenger is a similar tool
9.31
Streaming
• Listen to music from live radio stations
• Using RealPlayer or Microsoft Media
Player
• E.g. www.yle.fi provides links to several
life stations
• You can even find live air traffic control
– Pilots talking to a dispatcher
9.32
File sharing
• Search and download files like latest
hits (mp3), blockbuster movies (mpeg),
latest software packages (zip),pictures...
• Make your own files available to others
• Tools like Gnutella or Napster
• Difficult for authorities to snap these
systems to their distributed nature
9.33
Real-Time Communication
Video telephony
(see, hear, and type
to another person).
• MBONE - Multicast
Backbone –
centralized
distribution
• NetMeeting – works
over ”off-the-shelf”
Internet
9.34
E-Commerce
• Users connect (usually for a fee) to a
variety of on-line databases
• On-line databases include:
– current stock market status
– digital libraries
– banking
– shopping
9.35
Online banking
• Provided in Finland by all major banks
• E.g. in Leonia costs less than any other
service package
• You get a customer number and a PIN code
to log-in at their web site
• You get a challenge-response table of codes
• All connections are encrypted
• Within the same bank money are moved
instantly, otherwise it takes a couple of days
9.36
Rules of Thumb:
On-line Survival Tips
• Protect your privacy
• Cross-check on-line
information sources
• Netiquette
• Avoid information
overload
9.37