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The Internet & WWW 1 Internet Elements • The purpose of the Internet is to interconnect end systems, called hosts – Such as PCs, servers, notebooks, PDAs, smart phones, etc. • Most hosts that use the Internet are connected to a network, such as a LAN or a WAN • Networks are in turn connected by routers. Each router attaches to two or more networks. • A host may send data to another host anywhere on the Internet: – The source host breaks the data into a sequence of packets, called IP packets, or IP datagrams. – Each packet includes the unique numeric addresses of the source host and destination host, called IP addresses. – Based on the destination IP address, each packet travels through a series of routers and networks from source to destination. • Each router, upon receiving an IP packet, makes a routing decision and forwards the packet along its way to the destination. 3 Internet Elements 4 Internet Architecture • Today’s Internet is made up of thousands of overlapping hierarchical networks. • Individual hosts and LANs are connected to an Internet Service Provider (ISP) through a Point of Presence (POP). – Customer Premises Equipment (CPE): the communications equipment located onsite with the host, such as the modem. • Different levels of ISPs – Local ISP, Regional ISP, Backbone ISP • Backbone ISPs may be connected through the Network Access Point (NAP). 5 Internet Architecture 6 Universal Resource Locator http://www.leads.edu.pk/~ur5/tour/active.htm l http:// /~ur5/tour/active.html identifies type of transfer File Location on Remote Computer www.leads.edu.pk Domain Name name of remote computer What is WWW? • Via Internet, computers can contact each other • Public files on computers can be read by remote user – usually HyperText Markup Language (.html) • HTTP - HyperText Transfer Protocol • URL - Universal Resource Locator - is name of file on a remote computer • http://www.leads.edu.pk/~ur5/tour/active.html How to make a web page • Define the two basic steps required in making a web page. Two Basic Steps • Create an HTML File • Upload file to server – Saving to P: drive eliminates this step .html • Web documents are text files with .html extension • These text files have HTML “tags” in them HTML Tags • Each opening HTML tag has a closing HTML tag that matches it. – <P> for begin paragraph is followed by </P> for end paragraph – <P> goes at beginning of paragraph – </P> goes at end of paragraph Example of Tags • <P>Here is the paragraph about something</P><P>Here is the second paragraph</P> What it will look like: Here is the paragraph about something. Here is the second paragraph. Essential HTML Tags • • • • • • <HTML> begins HTML document <BODY> begins body of document <H1>Here’s a header in big type</H1> <P>Here’s a paragraph</P> </BODY> ends body </HTML> ends HTML document KEY POINTS • Data communications deals with the transmission of signals in a reliable and efficient manner. Topics covered include signal transmission, transmission media, signal encoding, interfacing, and data link control. • Networking deals with the technology and architecture of the communications networks used to interconnect communicating devices. This field is generally divided into the topics of local area networks (LANs) and wide area networks (WANs). 15
