Title: EMTM 553: E-commerce Systems Lecture 2: The Internet and the Web
1EMTM 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
2Computer Networks
3Development 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
4Uses 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
5Design 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.
6Layering of Internet Protocols
Application (Email, Web Browser)
End-to-End Protocol (TCP/UDP)
Host-to-Host Protocol (IP)
Physical Layer
7Internet 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)
8Physical 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
9Internet 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)
10Packet-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
11Packet-Switched Network and Message Packets
Source Schneider and Perry
12TCP 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
13UDP 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.
14Domain 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
15Other 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
16Other 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
17Other 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
18The 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.
19Advantages 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)
20Markup 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
21Markup 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
22Traditional vs. Hyperlinked Document Pages
Source Schneider and Perry
23HTML
- 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
24HTML Codes to Format Memo Page
Source Schneider and Perry
25Internet Explorer Display of Memo Page
Source Schneider and Perry
26More 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
27Hyperlink Structures
Source Schneider and Perry
28HTML 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
29HTML 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
30Web Clients and Servers
- Client computers typically request services,
including printing, information retrieval, and
database access - Servers are responsible for processing the
clients requests
31Client/Server Structure of the WWW
Source Schneider and Perry
32Web 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
33Web Browser
URL Uniform Resource Locator Ex. www.google.com
HTTP HyperText Transport Protocol Request/Reply
pages
HTML HyperText Markup Language Ex.
Graphic,colorful page
34Web Server Software
- Capabilities/Features
- Support HTTP protocol
- Support Secure Sockets Layer (SSL)
- File Transfer Protocol (FTP)
- Search engines and indexing
- Data Analysis
35Uniform 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)
36Message Flow Between Web Client and Server
Source Schneider and Perry
37Hypertext 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
38Basic Web application architecture
Database
Web Server
Programs
requests
downloads
Web Browser
39Two-Tier Client/Server
Tier 1
Tier 2
Network
DMS
Client
Server
- Web Server
- Database Server
- Application Server
- User Interface
- Web Applications
40Three-Tier Client/Server
Tier 1
Tier 3
Tier 2
Network
Network
DMS
Client
Server
Database Server
- User Interface
- Web Applications
- Web Server
- Application Server
41N-Tier Client/Server
Tier 1
Tier 3
Tier 2
Tier N
DMS
Client
Application Server
Database Server
Web Server
42QA