and the World Wide Web

Transcription

1 The Internet 1 The Internet and the World Wide Web The Internet is a global collection of interconnected networks Originally ARPNET had only four host computers on the network. Now tens of millions 1 The Internet Really a hierarchy of networks Start with a LAN, like at Wofford Connect to an Internet Service Provider s Point of Presence (POP) Dedicated line owned by the ISP Many LANs connected to one POP The Internet A POP is connected to a Network Access Point (NAP) by a high capacity line Many POPs connected to one NAP NAP connected to Internet s backbone 1

2 The Internet The Internet backbone is made of many huge corporate networks All agree to intercommunicate at network access points Backbone made of high capacity cable Routers 2 Computers located at junction points on Internet Direct flow of information so it gets to right place. 2 Internet Communication Client-server Most common strategy Clients Individual computers request web pages Servers Web server sends information Internet Communication Must connect many different networks of different designs Must not require central management Must be able to identify a large number of nodes Must be done without errors One solution: TCP/IP protocol 2

3 TCP/IP Protocol Transfer Control Protocol/Internet Protocol Standard protocol on the Internet Also used as a protocol for LANs IP Responsible for moving data from node to node on a network TCP Responsible for verifying that data is delivered correctly TCP/IP: IP Addresses Nodes identified by a unique Internet Protocol (IP) address Example: Originally connections were made by supplying IP address Manageable when only a few computers on internet Unwieldy if there are many Domain Name System (DNS) Associates a text name with an IP address = Top-level domain names.edu (educational institution).gov (government).com (commercial).org (organization) And others Uniform Resource Locator: URL Domain name entered in a browser as a URL Hypertext transfer protocol Client-server protocol for moving text over the Internet name Example: 3

4 Uniform Resource Locator: URL Most web browsers assume that you are using HTTP Entering only the domain name in the browser will bring you to a page. DNS Servers How does your computer learn the IP address of the web server it wants. DNS Servers Actually many layers of DNS servers Example: Root servers Know IP addresses for top-level DNS servers Top-level servers.edu,.gov,.com,.....edu server knows DNS server handling Finally, this DNS server furnishes the IP TCP/IP: TCP Information, such as web pages, broken into packets by TCP program when sent by server Packets sent separately over Internet Reassembled at destination by TCP program at client 4

5 TCP: Verifies Delivery of Data TCP detects errors and lost data Retriggers transmission until data is correctly and completely received. TCP: Packets Avoid Congestion Packets are sent independently Can move by any route Not affected by service disruptions or congestion Avoids congestion Splitting large set of information up doesn t choke one line TCP: Packets Network-Independent Packets broken out and reassembled by clients and servers Network only carries the packets Advantage any kind of network will work (fiber, copper, microwave, etc.) World Wide Web Question: Is the WWW the same as the Internet? 5

6 World Wide Web Combination of four basic ideas 1 Resource identifiers (URLs & IP addresses) Client-server model Hypertext (links between documents) HTML (Hypertext markup language) HTML Hypertext Markup Language is text sent to your computer from the web server Your computer translates the code into a web page 1 HTML Hypertext Markup Language Language for writing web pages Chapter 4 in fluency text Uses tags Words or abbreviations surrounded by <> HTML: Formatting Tags <h1> </h1> largest heading <h2> </h2> next largest heading <p> </p> paragraph <b> </b> bold <i> </i> italics 6

7 HTML: Miscellaneous Tags <hr> </hr> horizontal rule Straight line HTML: Anchor Tags <a href= > </a> Adds a link to a web page <a href= > Wofford Web Page </a> This creates a link to the web site HTML: White Space White space in HTML code has no effect on appearance of web page. Example: Addition of blank lines does not change appearance of web page shown below. HTML Example Open FrontPage Choose Create a new page or site Choose Blank page You should see a blank web page 7

8 HTML Choose Split View Shows both the HTML code and the web page Title Enter Example between title tags. No effect on web page Title will show in tab if page is saved. Body The HTML text is entered between the body tags. Headings Headings have different sizes <h1> </h1> is the largest 8

9 Headings <h2> </h2> is next largest Paragraphs Paragraphs are enclosed in <p> </p> tags. Bold and Italics Phrases enclosed in <b> </b> will show in bold. Phrases enclosed in <i> </i> will show in italics. Horizontal Line <hr> adds a horizontal line 9

10 Anchors Anchor tags <a> </a> enclose a hyperlink Anchors The link is enclosed in the quotes: The web page text that is linked is enclosed between the <a> tags. Anchors In the above, if you click on Wofford on the web page you will be linked to the web page. 10