Notes

Outline

Networking At UW, The Internet And Beyond Various computers will be used in this class, so a quick introduction to their arrangement and networking is useful.  Along the way we answer the pressing question:  What is the difference between the Internet and the World Wide Web

Accomplishments To Date … You have a UWNetID that gives you access to the UW’s computers, but also access to the World Wide Web … your account is on Dante You have sent email, set up folders, set up an address book You have visited home pages for UW, CSE100, other sites You have tried out a search engine Other things you should find out about … Printing is possible for most computer applications … how do you use the printers at OUGL or MGH labs? In Pine, it is possible to “postpone” a mail message that you are writing -- that is, set it aside to use Pine in other ways and then return to it.  Try out “postpone” in your next mail.

Computers of the Realm... We will discuss how computers really work later, but for now think of them as having many forms Embedded -- processor, ROM, channels to sensor/actuators; m-wave oven Laptop -- processor, RAM, floppy disk, hard disk, LCD; mobility Desk Top -- processor, RAM, floppy, hard disk, CD, monitor; educational and office work Server -- processors (4-32), RAM, many hard disks, CD; services Supercomputer -- processors (16-1K), RAM, hard disks; big science

Class Computers FIT100 uses Laptop for lectures Desktop in Collabs, OUGL, MGH Dante server An unconnected computer can only access the data stored locally on its hard disk, run the software stored locally, read and write floppy disks, etc. The UW computers are connected, i.e. networked, together allowing us to send email and access the World Wide Web

Networks ... Networks connect computers, making them much more useful because Access more information and software Help users communicate, share information Perform services for one another UW’s networks ship ~1/2 trillion bytes of data per day Half this information goes to or comes from the Internet How are these networks arranged?

Ethernet … It’s Like Conversation Think of a dozen students sitting around the dorm telling stories … Everyone listens while one person tells his/her story When the story is finished, there is a pause A person with a story to tell starts talking, listening all the while If no one else started talking too, the person continues If others started talking, he/she stops and waits briefly before trying again In Ethernet, only the computers actually communicating listen to the transmission … the others simply wait for the break

UW Networks Connect To Internet The subnetworks of campus interconnect the computers of the UW domain (.washington.edu), which is connected to the Internet via a Gateway

How Are Computers Named Logically The logical way to name computers is using domains All educational institutions    .edu U Dub                 .washington.edu CSE               .cs.washington.edu Me           boris.cs.washington.edu This scheme is hierarchical Easier to remember names Names are associated with like units No limit to size or organizational depth

How Are Computers Named Physically The physical way to name computers is using an Internet protocol address, or IP address boris.cs.washington.edu’s IP address is:  128.95.2.227 cs.washington.edu’s IP address:            128.95.1.4 washington.edu’s IP address:                 140.142.15.163 The domain name system (DNS) associates human readable names with the physical IP addresses for use by the computers and routers of the Internet

Logical Network … Physical Network An important concept ... In computing it is common to separate the logical idea of something -- the way you think about it -- from the physical implementation -- how it’s actually built This is called a physical / logical separation In networking, the domain names make up our logical network, a hierarchical arrangement of names that tell us associations:   cs.washington.edu The computers actually use physical addresses The DNS enables the separation by making the correspondence between the two

How Is Information Sent? Sending information over the Internet works like this: Imagine sending the novel you wrote from Tahiti where you live to New York City where your publisher is using only postcards

The Internet Protocol How is the information sent? Information -- email, web pages, phone calls, everything sent over the internet -- is  broken up into small units, called packets Packets contain an IP address, a sequence number and some actual information, a part of the whole message This scheme is called the Transmission Control Protocol and Internet Protocol, or TCP/IP The packets are sent independently, usually taking different routes, and reassembled at the destination to reconstruct the original message

World Wide Web The world wide web is composed of those computers, called web servers, capable of sending information to your browser, e.g. Netscape or IE In most domains the computer that is the web server is called “www”, e.g. www.washington.edu But, a web server can have any name … your pages will be served by students.washington.edu The actual pages will be stored somewhere else, e.g. Dante There are different ways to connect to these servers Hyper-text transfer protocol, http for web pages File transfer protocol, ftp for files of information

Web Pages Web pages are just text files containing instructions to your browser on how to lay out the web page Web pages can be created with a text editor Web pages can be created with special tools, eg Adobe Page Mill The Web page instructions are written in a special language, hyper-text mark-up language, HTML It is possible to see the HTML that is producing the page you are looking at by selecting “source” from the View menu in your browser

HTML From CSE100 Home Page