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EMTM 553: E-commerce Systems Lecture 2: The Internet and the Web

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Title: EMTM 553: E-commerce Systems Lecture 2: The Internet and the Web


1
EMTM 553 E-commerce SystemsLecture 2 The
Internet and the Web
  • Insup Lee
  • Department of Computer and Information Science
  • University of Pennsylvania
  • lee_at_cis.upenn.edu
  • www.cis.upenn.edu/lee

2
Computer Networks
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

4
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

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., 123.45.678.0 in dotted
    quad form)
  • 128-bit address for replacement
  • End-to-end protocols
  • The network needs to know only the destination
    address for delivering a packet.

6
Layering of Internet Protocols
Application (Email, Web Browser)
End-to-End Protocol (TCP/UDP)
Host-to-Host Protocol (IP)
Physical Layer
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)

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

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. 158.130.64.176)

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

11
Packet-Switched Network and Message Packets
Source Schneider and Perry
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, email

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.

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 (158.130.64.176)

edu
upenn
cmu
washington
cis
seas
clapton
rice
red
blue
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 e-mail from a mail
    server

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

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

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 pages worldwide name.

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)

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

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 pages actual content, unlike HTML
  • Data-tracking capability

22
Traditional vs. Hyperlinked Document Pages
Source Schneider and Perry
23
HTML
  • HTML tags
  • lttagname propertiesgtDisplayed information
    affected by taglt/tagnamegt
  • ltBgtbestlt/Bgt - Bolds the word best
  • ltP alignrightgt - Aligns text to the right
  • HTML code defines the formatting of the page, but
    a page may look different on two different
    browsers

24
HTML Codes to Format Memo Page
Source Schneider and Perry
25
Internet Explorer Display of Memo Page
Source Schneider and Perry
26
More about HTML
  • HTML Links
  • Anchor tags used to link to text within the same
    document, or on a distant computer
  • ltA HREFaddressgtVisible link textlt/Agt
  • ltA HREFhttp//www.upenn.edugtUniversity of
    Pennsylvanialt/Agt
  • ltA HREFreferencesgtReferences are found
    herelt/Agt
  • Text between the anchors appears as a hyperlink

27
Hyperlink Structures
Source Schneider and Perry
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

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

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

31
Client/Server Structure of the WWW
Source Schneider and Perry
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

33
Web Browser
URL Uniform Resource Locator Ex. www.google.com
HTTP HyperText Transport Protocol Request/Reply
pages
HTML HyperText Markup Language Ex.
Graphic,colorful page
34
Web Server Software
  • Capabilities/Features
  • Support HTTP protocol
  • Support Secure Sockets Layer (SSL)
  • File Transfer Protocol (FTP)
  • Search engines and indexing
  • Data Analysis

35
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)

36
Message Flow Between Web Client and Server
Source Schneider and Perry
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

38
Basic Web application architecture
Database
Web Server
Programs
requests
downloads
Web Browser
39
Two-Tier Client/Server
Tier 1
Tier 2
Network
DMS
Client
Server
  • Web Server
  • Database Server
  • Application Server
  • User Interface
  • Web Applications

40
Three-Tier Client/Server
Tier 1
Tier 3
Tier 2
Network
Network
DMS
Client
Server
Database Server
  • User Interface
  • Web Applications
  • Web Server
  • Application Server

41
N-Tier Client/Server
Tier 1
Tier 3
Tier 2
Tier N
DMS
Client
Application Server
Database Server
Web Server
42
QA
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