E-commerce systems

							EMTM 553: E-commerce Systems

     Lecture 2: The Internet and the Web

                             Insup Lee

            Department of Computer and Information Science
                      University of Pennsylvania
                           lee@cis.upenn.edu
                        www.cis.upenn.edu/~lee
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            Computer Networks




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        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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               Uses of the Internet
• E-mail
     – 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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  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., 123.45.678.0 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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            Layering of Internet Protocols

                  Application (Email, Web Browser)




                  End-to-End Protocol (TCP/UDP)




                     Host-to-Host Protocol (IP)




                          Physical Layer


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                 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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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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            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. 158.130.64.176)




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            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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            Packet-Switched Network
             and Message Packets




                              Source: Schneider and Perry
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 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, email




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  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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            Domain Name System (DNS)

• IP addresses are difficult for human to remember.
• Mapping IP to readable host names.
• For example: red.seas.upenn.edu (158.130.64.176)


                                edu

             cmu             upenn                   washington

                       cis             seas
             clapton     rice         red     blue
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            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 e-mail from a mail server




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            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
        o Download only selected messages, instead of all
          messages
        o View headers only
        o Create and manipulate mailboxes on the server




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              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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            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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            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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 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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 Markup Languages and the Web
• Hypertext Markup Language (HTML)
     – Based on SGML
     – Easier to learn and support
     – Supports commonly used text markup features
        o Headings, title bars, bullets, lines, lists
        o 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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   Traditional vs. Hyperlinked Document Pages




                              Source: Schneider and Perry
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                          HTML
• HTML tags
     – <tagname properties>Displayed information affected by
       tag</tagname>
         o <B>best</B> - Bolds the word “best”
         o <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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       HTML Codes to Format Memo Page




                          Source: Schneider and Perry

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 Internet Explorer Display of Memo Page




                         Source: Schneider and Perry

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               More about HTML
• HTML Links
     – Anchor tags used to link to text within the same
       document, or on a distant computer
        o <A HREF=“address”>Visible link text</A>
        o <A HREF=http://www.upenn.edu>University of
          Pennsylvania</A>
        o <A HREF=“#references”>References are found
          here</A>
     – Text between the anchors appears as a hyperlink




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            Hyperlink Structures




                           Source: Schneider and Perry

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            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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                    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
        o Microsoft FrontPage
        o Dreamweaver




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            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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Client/Server Structure of the WWW




                       Source: Schneider and Perry
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                     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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                         Web Browser
HTTP: HyperText                         URL: Uniform
Transport Protocol                     Resource Locator

Request/Reply pages                    Ex. www.google.com




      HTML: HyperText
       Markup Language

  Ex. Graphic,colorful page

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                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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Uniform Resource Locators (URL)
• http://www.w3.org/example/index.html
• Protocol designator (http:)
• 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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   Message Flow Between Web Client
             and Server




                        Source: Schneider and Perry

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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.,
        o GET to retrieve document
        o PUT to upload files to the server
        o POST to send the results of a form filled out by the
          user
     – Responses from servers to browsers

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Basic Web application architecture

                                               Database




                   Web Server                  Programs


        requests                 downloads


                   Web Browser



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                   Two-Tier Client/Server
  Tier 1                           Tier 2



                     Network
                                                      DMS


     Client                       Server
• User Interface               • Web Server

• Web Applications             • Database Server
                               • Application Server

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                   Three-Tier Client/Server
  Tier 1                     Tier 2             Tier 3


                   Network            Network

                                                                DMS


     Client                  Server           Database Server
• User Interface       • Web Server
• Web Applications     • Application Server



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                N-Tier Client/Server

Tier 1         Tier 2      Tier 3        Tier N



                                                    DMS


 Client
              Web Server   Application   Database
                            Server        Server



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            Q&A

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