The Internet and the World Wide Web

Review From Week 1 Overview of eCommerce History of the Internet Definition Components Comparison to Traditional Commerce Why eCommerce: Unique features Appropriateness of eCommerce History of the Internet

Week Two Topics Technology Components Packet Switching Protocols: TCP/IP, FTP, HTTP, eMail Purpose, use of various protocols TCP/IP Architecture IP Addresses, URLs, Domains Publishing on the Web: In Depth File Transfer Protocol

What is the Internet? A loosely configured global wide-area network. Loosely configured = open architecture, no single control Network = connection of computers Wide Area = large geographical coverage

Factors Behind Growth Primary technology factors behind growth discussed tonite: The TCP/IP standard and packet switching. The web-like ability to link from site to site enabled through HTML and HTTP.

A Model for Networking The world’s telephone companies were the early models for networked computers because the networks used leased telephone company lines. Telephone companies at the time established a single connection between sender and receiver for each telephone call. Once a connection was established, data traveled along that path.

Circuit switching Telephone company switching equipment (both mechanical and computerized) selected the phone lines, or circuits, to connect in order to create the path between caller and receiver. This centrally controlled, single connection model is known as circuit switching. Using circuit switching does not work well for sending data across a large network. Point-to-point connections for each sender/ receiver pair is expensive and hard to manage.

A Different Approach The Internet uses a less expensive and more easily managed technique than circuit switching. Files and messages are broken down into packets that are labeled with codes that indicate their origin and destination. Packets travel from computer to computer along the network until they reach their destination. The destination computer reassembles the data from the packets it receives. This is called a packet switching network.

View of Packet Switching

Packet switching In a packet-switched network, each computer that an individual packet encounters determines the best way to move the packet to its destination. Computers performing this determination are called routers. The programs that the computers use to determine the path are called routing algorithms. Utilizes Transmission Control Protocol/Internet Protocol TCP/IP

Routing Messages

Benefits of Packet Switching There are benefits to packing switching: Long streams of data can be broken down into small manageable data chunks, allowing the small packets to be distributed over a wide number of possible paths to balance traffic. It is relatively inexpensive to replace damaged data packets after they arrive, since if a data packet is altered in transit only a single packet must be retransmitted.

Protocols A protocol is a set of rules for the exchange of data across communication lines. Protocols need to handle the following tasks: Format messages Order Data in message Compress message Provide Error checking on message

Most Popular Internet Protocols The most popular Internet protocols include: TCP/IP: Transmission Control Protocol/Internet Protocol FTP: File Transfer Protocol HTTP: Hypertext Transfer Protocol E-mail protocols: SMTP, POP, IMAP Each protocol is used for a different purpose, but all of them are important.

TCP/IP The protocols that underlie the basic operation of the Internet are TCP (transmission control protocol) and IP (Internet protocol). Establish rules about how data are moved across networks and how network connections are established and broken.

Purposes of Each TCP controls the assembly of a message into smaller packets before it is transmitted over the network. It also controls the reassembly of packets once they reach their destination. The IP protocol includes rules for routing individual data packets from their source to their destination. It also handles all addressing details for each packet. More on addressing later.

TCP/IP Architecture

General Layer Properties Full discussion of the TCP/IP Architecture beyond the scope of this class. Useful to understand where each protocol resides: TCP operates in the transport layer. IP operates in the Internet layer. HTTP, SMTP, POP, IMAP and FTP operate in the application layer.

File transfer protocol FTP (file transfer protocol) is a part of TCP/IP that allows files to be transferred between computers connected using TCP/IP. It uses the client/server model. FTP permits files to be transferred in both directions, that is, from the client to the server or from the server to the client. It can transfer files one at a time or many files simultaneously.

Files types and FTP FTP allows the transfer of two types of files: ASCII text: files containing only characters available through the keyboard and containing no formatting information. Example: Files created using Notepad Binary data: files containing word processed documents, worksheets, graphics, etc.

Other Functions of FTP FTP has other useful functions: Displaying remote and local computers’ directories Changing the current client’s or server’s active directories Creating and removing local and remote directories.

Accessing with FTP There are two ways to access remote machines: Full privilege FTP access: This requires that you have an account on the remote computer and that you supply your username and password. Anonymous FTP: If you do not have an account on the remote computer, you can type anonymous as the username and your e-mail address as the password and obtain limited access to the remote computer. You can use an FTP client program or Web browser interface for FTP.

Browsing Through Files Once you have logged into your account using FTP you can browse through the files located in your account. You do this by double clicking on the folders that appear.

FTP with a Browser To use a browser as an interface with FTP: Type ftp://yourlogin@students.comsats.edu.pk This will bring up a window that prompts you for your password. Type in your password (being careful to type it correctly) and hit enter. The files in your main directory will appear. Note: Be sure to check that browser doesn’t store password. Look at Tools/Internet Options/Content/AutoComplete.

Creating Directories To create a directory on students.depaul.edu using the browser interface: Select File Select New Select Folder Click on the folder and give it the name you wish it to have.

Moving Files Once you have created a public_html directory, you can move your HTML files into that directory. In order to do that: Open up the directory into which you wish to move the file. Open the folder where the file is located on your local machine. Select Edit/Copy or drag the file directly into the directory.

HTTP HTTP (hypertext transfer protocol) is the protocol responsible for transferring and displaying Web pages. It has continued to evolve since being introduced. Like other Internet protocols, HTTP uses the client/ server model of computing. Thus, to understand how HTTP works, we need to first discuss the client/server model.

Client/Server model In the client/server model there are two roles: the client and the server. The client process makes requests of the server. The client is only capable of sending a request to the server and then waiting for the reply. The server satisfies the requests of the client. It usually has access to a resource, such as data, that the client wants. When the resource that the client wants becomes available, it sends a message to the client. This model simplifies communication.

Client/Server Model

HTTP and Client/Server With HTTP the client is the user’s Web browser and the server is the Web server. To open a session, the browser sends a request to the server that holds the desired web page. The server replies by sending back the page or an error message if the page could not be found. After the client verifies that the response sent was correct, the TCP/IP connection is closed and the HTTP session ends. Each new page that is desired will result in a new HTTP session and another TCP/IP connection.

One Page, Multiple Requests If a Web page contains objects such as movies, sound, or graphics, a client must make a request for each object. For example, a Web page containing a back- ground sound and three graphics will result in five separate server request messages to retrieve the four objects plus the page itself.

Mail protocols Electronic mail is managed and stored by programs and hardware collectively known as mail servers. It is displayed and created using mail programs such as Eudora, Pine, Unix mail, Outlook, Web interface mail programs. Protocols are necessary for the mail programs to construct requests to receive e-mail and for the mail servers in downloading and/or deleting e-mail. The e-mail protocols we will discuss use the client/ server model.

SMTP SMTP (simple mail transfer protocol) is used by client mail programs to make requests about mail delivery. A wide variety of mail programs such as Eudora, Unix mail, and PINE, use SMTP to send mail to a mail server. The SMTP specifies the exact format of a mail message and describes how mail is to be administered.

POP POP is responsible for retrieving e-mail from a server. It requests that the mail server either retrieve mail from the mail server and then delete it, retrieve mail from the server without deleting it, or simply ask whether new mail has come but not retrieve it. When e-mail is read, POP specifies that it must be downloaded to your computer from the server. Read e-mail is not kept on the server.

IMAP IMAP (Internet Message Access Protocol) is a newer protocol that, like POP, can ask if there is new mail, download e-mail, and delete e-mail. IMAP has capabilities that POP does not: It defines how a client program asks a mail server to present available mail. It can allow you to manipulate and manage e-mail without downloading it from the server.

Internet Addresses Internet addresses are represented in several ways, but all the formats are translated to a 32-bit number called an IP address; a function of Internet Protocol (IP) The increased demand for IP addresses will soon make 32-bit addresses too small, and they will be replaced with 128-bit addresses (IP v6.0) in the near future. How does increasing the number of bits in the address help with increasing demand?

Dotted Quads IP numbers appear as a series of up to 4 separate numbers delineated by a period. Examples: 140.192.1.100 140.192.1.6 140.192.33.6 Each of the four numbers can range from 0 to 255, so the possible IP addresses range from 0.0.0.0 to 255.255.255.255

Elements of Internet Addressing

Domain Names Since IP numbers can be difficult for humans to remember, domain names are associated with each IP address. Examples: 140.192.1.100 140.192.33.6 A domain name server is responsible for the mapping between domain names and IP addresses. Domain names and IP addresses are registered separately. Registering domain name doesn’t imply getting an IP address. IP address is from hosting service.

Uniform Resource Locator People on the Web use a naming convention called the uniform resource locator (URL). A URL consists of at least two and as many as four parts. A simple two part URL contains the protocol used to access the resource followed by the location of the resource. Example: www.google.com A more complex URL may have a file name and a path where the file can be found.

Anatomy of an eMail Address abc @ yahoo . com Handle Domain Type Host/Server

Domain types .com .edu .gov .mil .net .org .biz .info .aero .coop Commercial organizations or businesses .edu Educational institutions .gov U.S. government agencies .mil U.S. military .net Network computers .org Nonprofit organizations and foundations .biz business firms .info information providers .aero Air transport industry .coop Cooperatives .museum Museums .name Individuals .pro Professionals

HTML HTML – Hypertext Markup Language One of the languages with the parent SGML – Standard Generalized Markup Language HTML provides Web page designers with a fixed set of markup “tags” that are used to format a Web page

HTML Example

HTML TOOLS