1. EMTM 553: E-commerce Systems Lecture 2: The Internet and the Web
Insup Lee
Department of Computer and Information Science
University of Pennsylvania
10/13/2018
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2. Computer Networks
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3. Development of the Internet
A network of networks, or an “inter-network”
ARPA Net in 1960s
1980s, NSF Net to connect universities and research labs
1991, NSF allowed commercial traffic onto the Internet
1995, Internet Service Providers (ISP): companies that provide and charge a fee for connections to the Internet
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4. Uses of the Internet E-mail File Transfer Protocol (FTP) Telnet
to send messages to one or many across the Internet
File Transfer Protocol (FTP)
to transfer data files from one computer to another
Telnet
to remotely logon to another computer
World Wide Web (WWW)
to access information using a common interface
Videoconferencing
to use video across the Internet for conferencing purposes
Multimedia
to use video, audio, and animations across the Internet
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5. Design Principles of the Internet
Interoperability
Independent implementations of Internet protocols actually work together.
Layering and Simplicity
IP itself is simple.
Below IP, IP hides the complexity of many different kinds of network hardware.
Above IP, higher-level protocols offer services abstractions that are easy to use and understand for application programs.
Uniform naming and addressing
IP address: 32-bit (e.g., in dotted quad form)
End-to-end protocols
The network needs to know only the destination address for delivering a packet.
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6. Layering of Internet Protocols
Application ( , Web Browser)
End-to-End Protocol (TCP/UDP)
Host-to-Host Protocol (IP)
Physical Layer
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7. Internet protocols Host computers and routers Computers form networks
Routers connect networks
Each host has a unique address
Internet protocol (IP)
IP addressing
IP datagram
Ports: (IP address, Port number)
Transmission Control Protocol (TCP)
Unreliable Datagram Protocol (UDP)
Domain Name System (DNS)
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8. Physical Layer No single technology:
Ethernet, token ring, FDDI (Fiber Distributed Data Interconnect), ATM (Asynchronous Transfer Mode), etc.
ARP (Address Resolution Protocol) to translated IP addresses (32-bit) into Ethernet addresses (48-bit)
Routing protocols
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9. Internet Protocol (IP)
Protocol that supports the interconnection of multiple networking technologies into a single, logical inter-network.
IP specifies the format of packet or datagrams.
IP provides the addressing scheme: global, unique, hierarchical. (ex )
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10. Packet-Switched Networks
The Internet uses Packet switching
Files and messages are broken down into packets, which are electronically labeled with their origin and destination
The destination computer collects the packets and reassembles the data from the pieces in each packet
Each computer the packet encounters decides the best route towards its destination
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11. Packet-Switched Network
and Message Packets
Source: Schneider and Perry
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12. TCP: Transmission Control Protocol
End-to-End protocol on top of IP
TCP provides a reliable, in-order delivery of packets using acknowledgements, checksums and sequence number.
Flow control, congestion control
Suitable for file transfer,
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13. UDP: Unreliable Datagram Protocol
End-to-End protocol on top of IP.
It does multiplexing/demultiplexing and ensures the correctness by using checksum.
UDP is used for small/real-time packet delivery such as voice data.
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14. Domain Name System (DNS)
IP addresses are difficult for human to remember.
Mapping IP to readable host names.
For example: red.seas.upenn.edu ( )
edu
cmu
upenn
washington
cis
seas
clapton
rice
red
blue
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15. Other Internet Protocols
Hypertext Transfer Protocol (HTTP)
Responsible for transferring and displaying Web pages
Simple Mail Transfer Protocol (SMTP)
Specifies the exact format of a mail message
Post Office Protocol (POP)
Responsible for retrieving from a mail server
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16. Other Internet Protocols
Interactive Mail Access Protocol (IMAP)
Latest protocol, may replace POP
Defines how a client program asks a mail server to present available mail
Download only selected messages, instead of all messages
View headers only
Create and manipulate mailboxes on the server
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17. Other Internet Protocols
File Transfer Protocol (FTP)
Transfers files between TCP/IP-connected computers
Uses client/server model
Transfers both binary and ASCII text
Displays and manipulates remote and local computer file directories
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18. The World Wide Web
In 1992, Tim Berners-Lee at CERN released the first implementation of the WWW.
A global hypertext network of Web servers and Web browsers connected by HTTP (Hypertext Transfer Protocol).
The Web is a collection of “pages” located on “servers” all over the world.
Servers store HTML (Hypertext Markup Language) files and respond to request.
A browser provides a point-and-click user interface to access pages in HTML.
Each page is assigned a URL (Uniform Resource Locator), which is the page’s worldwide name.
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19. Advantages of the Web
A global information sharing architecture that integrates online content and information servers in an easy-to-use manner.
Ease of navigation and use
Ease of publishing content
New distribution channel (of digital goods) such as software, documents, music, video, etc.
Enable a network-centric computing paradigm.
New business applications (e.g., auction of surplus capacity)
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20. Markup Languages and the Web
Standard Generalized Markup Language (SGML)
Regulated ISO standard since 1986
Nonproprietary
Supports user-defined tags
Costly to set up
Expensive compared to HTML
Steep learning curve
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21. Markup Languages and the Web
Hypertext Markup Language (HTML)
Based on SGML
Easier to learn and support
Supports commonly used text markup features
Headings, title bars, bullets, lines, lists
Precise graphic positioning, tables, and frames
Standard language for Web pages
Extensible Markup Language (XML)
Descendant of SGML
Defines which data to display, instead of how a page is displayed
Describes a page’s actual content, unlike HTML
Data-tracking capability
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22. Traditional vs. Hyperlinked Document Pages
Source: Schneider and Perry
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23. HTML
HTML tags
<tagname properties>Displayed information affected by tag</tagname>
<B>best</B> - Bolds the word “best”
<P align=“right”> - Aligns text to the right
HTML code defines the formatting of the page, but a page may look different on two different browsers
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24. HTML Codes to Format Memo Page
Source: Schneider and Perry
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25. Internet Explorer Display of Memo Page
Source: Schneider and Perry
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26. More about HTML HTML Links
Anchor tags used to link to text within the same document, or on a distant computer
<A HREF=“address”>Visible link text</A>
<A HREF= of Pennsylvania</A>
<A HREF=“#references”>References are found here</A>
Text between the anchors appears as a hyperlink
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27. Hyperlink Structures
Source: Schneider and Perry
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28. HTML Version History Version 1.0 appeared in the summer of 1991
Version 2.0 was released in September 1995
Internet Explorer 2.0 and Netscape Navigator 2.0 appeared
Version 3.2 was released in 1997
Provided support for tables, complex numbers, and text flow around images
Version 4.0 was released in December 1997
Support for OBJECT tag and Cascading Style Sheets (CSS)
Internationalization for various languages
Accessibility features
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29. HTML Editors Used to generate the HTML code
Simple text editors offer limited flexibility
Any word processor can be used
Web site builders offer more control
Microsoft FrontPage
Dreamweaver
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30. Web Clients and Servers
Client computers typically request services, including printing, information retrieval, and database access
Servers are responsible for processing the clients’ requests
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31. Client/Server Structure of the WWW
Source: Schneider and Perry
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32. Web Browser Implements HTTP (HyperText Transfer Protocol)
Interact with servers
Displays web pages
Caching, freshness control
Page rendering, font mapping
Compression, decompression
Handles multimedia, supports plug-ins
Interprets scripts
Executes Java applets
Maintains cache, history
Manipulates cookies
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33. Ex. Graphic,colorful page
Web Browser
URL: Uniform
Resource Locator
Ex.
HTTP: HyperText
Transport Protocol
Request/Reply pages
HTML: HyperText
Markup Language
Ex. Graphic,colorful page
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34. Web Server Software Capabilities/Features Support HTTP protocol
Support Secure Sockets Layer (SSL)
File Transfer Protocol (FTP)
Search engines and indexing
Data Analysis
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35. Uniform Resource Locators (URL)
Protocol designator (
Server name (servername.domain)
DNS name
The browser use the DNS to translate the name to an IP network address
Pathname (/path/name/of/object.html)
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36. Message Flow Between Web Client and Server
Source: Schneider and Perry
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37. Hypertext Transfer Protocol (HTTP)
The standard Web transfer protocol.
With HTTP, a client opens a TCP connection to the web server.
Two types of messages
Requests from browsers to servers; e.g.,
GET to retrieve document
PUT to upload files to the server
POST to send the results of a form filled out by the user
Responses from servers to browsers
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38. Basic Web application architecture
Database
Web Server
Programs
requests
downloads
Web Browser
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39. Two-Tier Client/Server
Network
DMS
Client
Server
Web Server
Database Server
Application Server
User Interface
Web Applications
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40. Three-Tier Client/Server
Network
Network
DMS
Client
Server
Database Server
User Interface
Web Applications
Web Server
Application Server
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41. N-Tier Client/Server Tier 1 Tier 2 Tier 3 Tier N Client DMS
Application Server
Database Server
Web Server
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42. Q&A
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