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 over a billion people use it The Internet Really a hierarchy of networks Covered in the Communications and Networks lecture Internet Communication Several problems must be solved to transmit data over the Internet On the most basic level, connect devices Transmit data efficiently within a local network Uniquely identify all devices on the Internet Efficiently move data around the Internet Avoid congestion Allow transmission on any type of network Avoid centralization Keep Internet communication error-free Design software to communicate among devices 1

2 Internet Communication Solving all these problems is a complex process We need a model to help us reduce the complexity One model: TCP/IP protocol suite TCP/IP Model Transfer Control Protocol/Internet Protocol Model for Internet communication Simplified compared to some models, but sufficient for our purposes Includes five functions TCP/IP Model TCP/IP: Physical Equipment Network hardware The physical equipment needed to connect networked devices together Cables (e.g., fiber, copper) Switches, hubs, etc. Cable modems, wireless APs, etc. 2

3 TCP/IP: Physical Equipment TCP/IP Model Networks and Communications lecture Reading LANs & Home Networks Network Architecture Network Cabling Network Hardware Connecting to the Internet TCP/IP: LAN Communication Protocols for communication among devices in a LAN or other local network Standards for communication so devices talk the same language Also need to avoid collisions of data within the LAN Wired network: Ethernet protocol is the most common Wireless network: standard is most common TCP/IP: LAN Communication Networks and Communication lecture Reading: WiFi Wireless Networks Protocols: Ethernet and LocalTalk 3

4 TCP/IP Model TCP/IP: Internet Routing Two problems: How can we identify different nodes, such as computers, on the Internet? What is best way to route information between nodes? TCP/IP: IP Addresses Nodes identified by a unique Internet Protocol (IP) address Example: is server housing Wofford web pages Hyperlink: Routers Located at junction points of Internet Choose best path in which to route packets Based on dynamic routing tables maintained by router 4

5 TCP/IP: Internet Routing TCP/IP Model Networks and Communication lecture Reading TCP/IP Protocol Routers TCP/IP: Internet Transport How will information be moved around? How will we maintain connections? How will we ensure that data has been transmitted with no errors? TCP/IP: Packet Switching Computers on both ends run TCP program TCP on sending computer breaks information into packets before sending Packets sent separately over Internet TCP on receiving computer verifies that the packets are error-free TCP on receiving computer reassembles packets 5

6 Why Packet Switching? More efficient transmission Packets are sent independently Can move by any route Reduces effects of service disruptions or congestion Lessens congestion Routers move packets along most efficient paths Splitting large set of information up doesn t choke one line Why Packet Switching? Decentralized Packets broken out and reassembled by clients and servers. No central management needed. Allows transmission on a variety of networks Network only carries the packets Any kind of network will work (fiber, copper, microwave, etc.) TCP/IP: Internet Transport TCP/IP Model Networks and Communication lecture Reading: TCP/IP Protocol Routers 6

7 TCP/IP: Internet Applications There are many examples of application layer protocols. Three common ones are: DNS: Domain Name Service Find out IP address for a server HTTP: Hypertext Transfer Protocol Communicate on the WWW TLS or SSL: Transport Layer Security or Secure Socket Layer Provide secure communication on the Internet Client-Server Strategy Internet communication generally uses the Clientserver strategy Clients Individual computers request web pages from a web server Servers Web server sends information back to the clients Domain Name System (DNS) IP addresses are difficult to remember Associate a text name with an IP address = Top-level domain names.edu (educational institution).gov.com.org (government) (commercial) (organization) DNS Servers How does a computer learn the IP address of the web server it wants? Computer learns domain name from URL in web browser Computer supplies domain name to a DNS server, which returns the corresponding IP address Actually several layers of DNS servers 7

8 Hypertext Transfer Protocol Transfer web page information on the WWW User enters URL (Uniform Resource Locator) for web site in a web browser name/folder/web page Hypertext Transfer Protocol The HTTP request is sent by the client computer to the web server The web server returns the requested information to the client computer http stands for Hypertext Transfer Protocol webs.wofford.edu is the domain name for the web server whisnantdm is a folder on the web server index.htm is a web page in this folder Security Protocols TLS and SSL are cryptographic protocols used for secure communications on the Internet Rely on public key encryption and certificate authentication In essence, computers send encrypted information to each other over the Internet They also exchange certificates that allow them to read the coded information See reading for description of PKI infrastructure Security Protocols Example: Click on the Banner Web link on the Wofford Note that the URL starts with rather than Web page information is being transmitted in encrypted form using a secure protocol 8

9 TCP/IP: Internet Applications Reading Client-server network strategy TCP/IP Protocol Computer and Network Security Internet Shortcomings The Internet was designed over 30 years ago It has been a tremendous success, but has some problems Researchers now are exploring ways to improve, or even replace, it. 1. Anick Jesdanun. Researchers explore scrapping Internet. Associated Press, April 13, Nick McKeown & Bernd Girod. Clean-Slate Design for the Internet. Stanford University. April 18, Internet: Current Shortcomings Security When Internet was designed all users were assumed to be trustworthy TCP/IP is not designed to authenticate users as trustworthy Makes it easy for spam, viruses, worms, etc. to exist and do damage Requires individual LANs and computers to filter messages for spam and viruses Definite problem: Wofford s network filters around 90% of the messages we receive Internet: Current Shortcomings Unreliability Communication on the Internet works well most of the time we cannot absolutely rely on it Time-critical communication not feasible because of unreliability Example: surgery in which robotic tools are controlled remotely by surgeon Need dedicated lines for time-critical communication 9

10 Internet: Current Shortcomings Mobility When the Internet was designed, computers seldom moved IP addresses are assigned to devices based on their locations Now many computers are mobile and connect through wireless APs When a laptop moves from one wireless AP to another it must reconnect Potentially disrupts data flow Internet: Current Shortcomings Ubiquity When the Internet was designed, there were few networked computers Now there are over a billion Internet users We eventually will run out of IP addresses One solution: IPv6 (see Communication and Networks lecture) Even if we move to IPv6, processing all the IP addresses may tax the system Internet: Current Shortcomings Ubiquity This problem will be exacerbated by new types of devices that are being connected to the Internet Telephone system (VoIP) Household sensors (lights, heating, toasters, etc.) Stand-alone sensors monitoring our everyday environment: parking, weather, safety, etc. Tackling Internet Shortcomings Several research projects that tackle Internet problems are in progress Clean Slate project Looking at a complete redesign of the Internet starting with a clean slate Knowing what we know now, how could we do better? NSF: Global Environment for Network Innovations (GENI) project Exploring both clean slate and evolutionary Internet projects 10

11 Tackling Internet Shortcomings Several research projects that tackle Internet problems are in progress European Union: Future Internet Research and Experimentation (FIRE) project These are long-term projects: probably 10 to 15 years Major changes in the Internet would be very expensive in the billions World Wide Web Question: Is the WWW the same as the Internet? 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) We have covered the first three need to have some understanding of how HTML works HTML Hypertext Markup Language is text sent to your computer from the web server Your computer translates the code into a web page

12 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 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 12

13 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 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. 13

14 Body The HTML text is entered between the body tags. Headings Headings have different sizes <h1> </h1> is the largest Enter <h1>this is First Heading</h1> Headings <h2> </h2> is next largest Enter <h2>your Name</h2> Paragraphs Paragraphs are enclosed in <p> </p> tags Enter <p>this is the first paragraph.</p> Enter <p>this is the second paragraph.</p> 14

15 Bold and Italics Horizontal Line Phrases enclosed in <b> </b> will show in bold. Phrases enclosed in <i> </i> will show in italics Enclose second paragraph with <b> </b> <hr> adds a horizontal line Enter <hr> below the second paragraph. 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. Below the horizontal line, enter the code shown in the picture above. 15

16 Anchors In the above, if you click on Wofford on the web page you will be linked to the web page. HTML Code You should be able to read HTML code and match it with a corresponding web page. 16