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 10/13/2018 EMTM

Computer Networks 10/13/2018 EMTM

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 10/13/2018 EMTM

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 10/13/2018 EMTM

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. 10/13/2018 EMTM

Layering of Internet Protocols Application (Email, Web Browser) End-to-End Protocol (TCP/UDP) Host-to-Host Protocol (IP) Physical Layer 10/13/2018 EMTM

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) 10/13/2018 EMTM

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 10/13/2018 EMTM

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) 10/13/2018 EMTM

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 10/13/2018 EMTM

Packet-Switched Network and Message Packets Source: Schneider and Perry 10/13/2018 EMTM

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 10/13/2018 EMTM

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. 10/13/2018 EMTM

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 10/13/2018 EMTM

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 10/13/2018 EMTM

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 10/13/2018 EMTM

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 10/13/2018 EMTM

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. 10/13/2018 EMTM

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) 10/13/2018 EMTM

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 10/13/2018 EMTM

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 10/13/2018 EMTM

Traditional vs. Hyperlinked Document Pages Source: Schneider and Perry 10/13/2018 EMTM

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 10/13/2018 EMTM

HTML Codes to Format Memo Page Source: Schneider and Perry 10/13/2018 EMTM

Internet Explorer Display of Memo Page Source: Schneider and Perry 10/13/2018 EMTM

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=http://www.upenn.edu>University of Pennsylvania</A> <A HREF=“#references”>References are found here</A> Text between the anchors appears as a hyperlink 10/13/2018 EMTM

Hyperlink Structures Source: Schneider and Perry 10/13/2018 EMTM

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 10/13/2018 EMTM

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 10/13/2018 EMTM

Web Clients and Servers Client computers typically request services, including printing, information retrieval, and database access Servers are responsible for processing the clients’ requests 10/13/2018 EMTM

Client/Server Structure of the WWW Source: Schneider and Perry 10/13/2018 EMTM

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 10/13/2018 EMTM

Ex. Graphic,colorful page 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 10/13/2018 EMTM

Web Server Software Capabilities/Features Support HTTP protocol Support Secure Sockets Layer (SSL) File Transfer Protocol (FTP) Search engines and indexing Data Analysis 10/13/2018 EMTM

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) 10/13/2018 EMTM

Message Flow Between Web Client and Server Source: Schneider and Perry 10/13/2018 EMTM

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 10/13/2018 EMTM

Basic Web application architecture Database Web Server Programs requests downloads Web Browser 10/13/2018 EMTM

Two-Tier Client/Server Network DMS Client Server Web Server Database Server Application Server User Interface Web Applications 10/13/2018 EMTM

Three-Tier Client/Server Network Network DMS Client Server Database Server User Interface Web Applications Web Server Application Server 10/13/2018 EMTM

N-Tier Client/Server Tier 1 Tier 2 Tier 3 Tier N Client DMS Application Server Database Server Web Server 10/13/2018 EMTM

Q&A 10/13/2018 EMTM