Download WWW slides

World Wide Web
and E-Commerce
Internet and WWW
Basics
Fall 2000
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Objectives
• What is the World Wide Web (web or WWW)?
• How does the web use HTTP and TCP/IP?
• How do the URLs work?
• What’s the problem that IPv6 is a solution for?
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So, what is the web?
The Web is a protocol that uses the Internet
as the communication structure
The Web links documents stored in
computers that communicate on the Internet
Informal sort of arrangement!
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Internet
• Hosts
Web
• web pages
– 80 million
• Servers
– 1 billion
• Web databases
– 80 million x ?
– Terabytes x ?
delivery
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Internet
• TCP/IP protocol for passing data between
nodes on the Internet
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Intranet
• Corporate network using Internet
technology but secured behind a firewall
• Use TCP/IP like the Internet
• Operate as a private network
• Connected to the Internet thru firewall
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An Intranet
Servers
ERP
Clients
Legacy
systems
Public/External
Internet Users
Intranet
E-mail
servers
Web
servers
Firewalls
Databases
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© Prentice Hall, 2000
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Intranet Examples
• Often on a LAN (local Area Network) or
WAN (Wide Area Network)
• Your department is no doubt on an Intranet!!
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Extranet
• An extended intranet that connects remote
intranets
• Uses TCP/IP Internet protocols
• Employs secure channels between the
intranets
• VPN is technology that provides this
virtual private network on the Internet
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An Extranet
Extranet
Suppliers
Intranet
Firewall
VPN
Distributors
VPN
Tunneling Internet
Intranet
VPN
Firewall
Customers
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© Prentice Hall, 2000
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Virtual Private
(VPN)
Virtual
PrivateNetwork
Network
(VPN)
• VPN is a secure network on the Internet using
tunneling schemes
• The major objective of a VPN is to use the
Internet rather than a private line ($$)
• When two sites are connected across a VPN, each
must have a VPN-capable router, firewall, or VPN
access device installed
• When VPN is used to link mobile clients with
Internet dial-up connections, the laptops must be
equipped with VPN client software equipped with
the addresses and associated encryption keys for
corporate host sites
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Extranet Cases
• Reduced Product Development Cycle Time:
Caterpillar, Inc.
– Customers can use the extranet to retrieve and
modify detailed order information while the
vehicle remains on the assembly line
• Sears
– Suppliers for just-in-time production
• Govt. select suppliers and govt. procurement
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The Internet
•
•
•
•
•
•
No quality control
No central control
No guarantees of delivery
No guarantees of security
No guarantees of privacy
No place where the “buck stops”
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The WEB
Communication protocol using the Internet
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Search Engine Sizes (800M)
Feb2000
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Basics
• Web server - machine that services internet request
• Web client - machine that initiates internet request
• Browser - software to interact with web data at the
client
•
•
•
•
TCP/IP - internet data transfer protocol
FTP - internet file transfer protocol
HTTP - hypertext transfer protocol
HTML - hypertext display markup language
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1. Client-Server & Web
• Cloud model
• Based on TCP/IP
• HTTP and MIME types
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Client-Server Model
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HTTP
HyperText Transport Protocol
• Native protocol for WWW
• sits on top of internet’s TCP/IP protocol
• HTTP is a 4 step process per transaction
• uses a predefined set of document formats
from MIME
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MIME defines data types
• MIME - multipurpose internet mail extensions
– defines file formats (images, video, text, etc)
– e.g. Content-type: text/html
– Data type/subtype
»
text/html
»
text/plain
»
image/gif
»
video/mpeg
» application/msword
» etc!!!
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HTTP Connection
• 1. Client
– makes an HTTP request for a web page
– makes a TCP/IP connection
• 2. Server accepts request
– sends page as HTTP
• 3. Client downloads page
• 4. Server breaks the connection
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HTTP is Stateless!!!!
• Each operation or transaction makes a new
connection
• each operation is unaware of any other
connection
• each click is a new connection
• So how do they do those shopping carts??
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What does HTTP look like?
• Header data + object file
• Header
–
–
–
–
plain text
info about the object (MIME etc)
methods allowed
etc
• browser sends a header to server each time you
ask for information
• server sends a header and possibly content
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HTTP Header Example
GET /catalog/ip/ip.htm HTTP 1.0
Accept: text/html
Accept: image/gif
Referer: http://www.cs.dal.ca/catalog.html
User-Agent: Mozilla/2.0
<CR/LF>
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Side Effect of HTTP transfers
A record is left of all web transactions
Reside in Log files generated at the server
Good news: use-data galore
Bad news: what about user privacy
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Common Log File (CLF) Format
host identity Authuser
date
request
status
bytes
cast39.cs.dal.ca - - [12/Jan/2000:16:09:50 -0400]
"GET /~watters/webcourse/refSer.html HTTP/1.0"
304 -
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Footprints (clickprints)
• What can you do with this data
– Rearrange your site
– Change your marketing strategy
– Make a mailing list
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TCP/IP applications
• TCP/IP software usually includes:
– remote terminal client using TELNET protocol
for remote login
– electronic mail client using SMTP protocol to
transfer e-mail to remote system
– file transfer client using FTP protocol to
transfer files between 2 machines
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2. URLs: NAMES and ADDRESSES
What’s in a name, anyway?
www.abc.magic.ca
1011010011001110000111001100110
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Internet Node Addresses
• Each node has
– unique network name
• hierarchical composition based on name granting
authority
• www.cs.dal.ca
– unique network address
• hierarchical composition based on topographical
• 129.173.66.61
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What is the network IP address?
• 32 bits (4 bytes) per node (IPv4)
• schemes
– class-based addresses
– subnet addresses
– classless addresses
Is there a problem here?
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Class-based Addressing
IPv4
• General form network.host
• eg. UC Berkeley is 128.32.0.0
• eg. Borg 129.173.66.61
• large networks have few network bytes
– (more room for hosts on them)
• small networks have longer network address
hosts expected)
• What if the host addresses are not all used???
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That may be a big problem!
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IPv6 Features
•
•
•
•
•
•
128 bits address space
total 3.4 x 1038 addresses
Advanced Routing Capability
Better Options Support
Better Quality of service Support
Authentication and Security
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IPv6 Summary
•IPv6 simplifies packet header formats.
•IPv6 provides a much larger address space of 128
bits. This overhead in the header has been reduced
by simplifying the header formats.
•IPv6 supports authentication and encryption of
packet contents at the network layer.
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IPv4 address transits to IPv6
• IPv4-compatible IPv6 address
• 80 bits
16 bits
• 0000…000 0000
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32 bits
IPv4 address
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Transition Planning
• Maintain complete IPv4 routing system
until run-out
• Upgrade IPv4 router to IPv4/6 dual router
• Building up IPv6 only (6 bone)
• Shutdown IPv4 in areas where there is no
need for IPv4
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www.govcanada.ca
129.167.69.45
How do we get the network
address from network name?
• Domain name servers translate name to
network address
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Domain Hierarchy
• DNS hierarchy can be viewed as a tree
– Node in the tree corresponding to a domain.
– Leaves in the tree corresponding to the host
being named.
• DNS names are processed from right to left
and use period as separator.
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Name Servers do the work
Root name server
Dalhousie name
Gov. Canada
…...
server
name server
Cs name
server
IS2 name
server
–each name server contains IP addr for each lower level
server.
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Domain Hierarchy
edu
com
gov
mil
arizona….mit
cs ece
bas che
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acm
org
net
uk
ca
govcanada
dal
ieee
physics
cs
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Name Resolution
2
1
cheltenham.cs.arizona.edu
Client
192.12.69.60
8
Local
name
server
3
cheltenham.cs.arizona.edu
Cs.arizona.edu, 192.12.69.5
4
5
Root
name
server
Arizona
name
server
6
7
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server
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Recap
The World Wide Web (WWW or web) is a protocol
HTTP is the workhorse of WWW protocol
Every click on the web is recorded
URL’s need to be mapped into Internet addresses
We may run out of Internet addresses
IPv6
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