Internet and WWW CS216

Open System Interconnection (OSI)

OSI

TCP/IP The Internet is the communications medium that uses the TCP/IP protocol. The World Wide Web (WWW) is a service that uses the Internet. The Internet had its beginnings around 1969 with work done by the defense department to establish a reliable communications network.

World Wide Web The WWW began in Europe, as an effort of the European Laboratory for Particle Physics (CERN) as a method for researchers to share results. The WWW is an architected way to send and receive web pages of information. Each user has a browser program. From the browser you can request web pages. The web page uses the Hyper Text Markup Language (HTML) language. The browser gets a file of data containing HTML keywords and data and other files (for example graphics files), and displays the web page. The user can send data back to the sender of the web page, request other web pages (via its Uniform Resource Locator or a hyperlink). Web pages are requested by their Uniform Resource Locator (URL).

URL The URL has the format: – scheme://internet-address/resource The scheme describes the protocol used to access the resource. It is usually the protocol used by the World Wide Web (WWW). The internet address is the node where the resource (usually a file) is located. The resource name follows the slash. This may be just a file name, or it may contain directory information for the server to locate it on the node. For the WWW, the protocol is hypertext transfer protocol (http). Some other Internet protocols are:

Other protocols news (newsgroups) ftp (file transfer protocol) telnet https You can create one yourself

Domain names Web_page_name.domain name is the symbolic name of the page (for example In the U.S., the highest level domain names [top level domain], furthest on the right) are: com - businesses edu - educational institutions gov - government organizations mil - military organizations org - nonprofit organizations net - network resources

ICANN Other countries have their own domain names, for example, uk for England. Because of the overuse of the.com domain name, the governing body for the Internet the governing organization for the Internet (Internet Corporation for Assigned Names and Numbers – ICANN) has created other domain names that are not country specific.

DNS URLs are a human convenience. All Internet addresses are (for now) four byte addresses called IP addresses. They are expressed as four decimal numbers separated by periods: This is the IP address for the CS server. Besides URLs, browsers will accept IP addresses. A hyperlink is a shortcut to a URL. A hyperlink to another web page is highlighted in some manner (usually a different color and underlined) on the page. By clicking on the hyperlink, your browser requests that web page. This is done by HTML tags.

Connecting to the Internet In homes, you can connect to a network via a digital subscription line (DSL), a TV cable company, or a phone line. DSL and cable connections are high speed (also called broad band) connections. The phone line is much lower speed, but you do not pay any extra charges over the cost of your phone connection.

Modem The modem (modulator/demodulator) converts the serial digital bits of information into analog information that can be sent across the lines. This modulation process is accomplished by varying the amplitude or frequency of a carrier tone transmitted on the phone line. Standard modems advertise 56,000 bits per second transmission capability. However because of the errors in data transmission (phone lines werent designed for transmission of bits of information) causing retransmission of data, plus the added bits needed for control, error detection, and framing data into packets, the effective rate of transmission is perhaps half that. DSL overcomes that problem by superimposing higher frequency signal on low frequency carrier

LAN In offices and schools, the medium is usually a cable, and the connection of workstations together into a network is called a local area network (LAN)

LAN

Wide Area Networks A network (such as the Internet) that covers a wide geographical area is called a Wide Area Network (WAN). Besides the Internet, businesses or government organizations may have their own WANs.

WAN The computer at each end of a communications link must follow the same rules. These communications rules are called protocols. The protocol followed for the Internet is called TCP/IP. When accessing a website via URL addresses, DNS is used for conversion to TCP/IP addresses and a connection is made to the destination. User communications programs (like Internet browsers, programs) use the operating system communication services. If you know the operating system interface for TCP/IP, or FTP (the file transfer program) you can use them directly from the command line, however using the communications programs (such as a browser) is much easier. If you have to develop a web server application to respond to web page requests, you would have to learn more about the underlying TCP/IP protocol. Common terms used in a TCP/IP connection are sockets, ports, and the secure shell.

TCP / IP TCP – Transfer Control Protocol IP – Internet Protocol Key concept: they are two distinct protocols that coexist – Each machine (for practical purposes) has one IP address – However, it can have many ports (TCP address)

TCP Ports Addressing on top of IP so that multiple communication channels can exist simultaneously Common port assignments: – Port 23 is TELNET – Port 25 is SMTP – Port 80 is HTTP – Port 8080 is also used for HTTP sometimes so that two servers can live together on the same machne