| More than just a social interaction |
| Computers are useful alone, but are better when connected (networked) | ||
| Access more information and software than is stored locally | ||
| Help users to communicate, exchange information … changing ideas about social interaction | ||
| Perform other services -- printing, Web,... | ||
| The Internet is making fundamental changes … The FIT text gives 5 ways | |||
| Nowhere is remote -- access to info is no longer bound to a place | |||
| Connecting with others -- email is great | |||
| Revised human relationships -- too much time spent online could be bad | |||
| English becoming a universal language | |||
| Enhanced freedom of speech, assembly | |||
| Networks are structured differently based (mostly) on how far apart the computers are | ||
| Local area network (LAN) -- a small area such as a room or building | ||
| Wide area networks (WAN) -- large area, e.g. distance is more than 1 Km | ||
| To communicate computers need to know how to set-up the info to be sent and interpret the info received | |||
| Communication rules are a protocol | |||
| Example protocols | |||
| EtherNet for physical connection in a LAN | |||
| TCP/IP -- transmission control protocol / internet protocol -- for Internet | |||
| HTTP -- hypertext transfer protocol -- for Web | |||
| EtherNet is a popular LAN protocol | |||
| Recall, it’s a “party” protocol | |||
| The campus subnetworks interconnect computers of the UW domain which connects to Internet via a gateway |
| Information is sent across the Internet using IP -- Cerf uses postcard analogy | |||
| Break message into fixed size units | |||
| Form IP packets with destination address, sequence number and content | |||
| Each makes its way separately to destination, possibly taking different routes | |||
| Reassembled at destination forming msg | |||
| A packet sent from UW to ETH (Swiss Fed. Tech. University) took 21 hops |
| Interested? | ||||
| Find software called Visual Routes (personal evaluation copies are free) | ||||
| at http://www.visualroute.com | ||||
| Download a copy of the software | ||||
| Install software and type in foreign URLs | ||||
| Switzerland eth.ch | ||||
| Australia www.usyd.edu.au | ||||
| Japan kyoto-u.ac.jp | ||||
| South Africa www.uct.ac.za | ||||
| People name computers by a domain name -- a hierarchical scheme that groups like computers | |||
| .edu All educational computers | |||
| .washington.edu All computers at UW | |||
| dante.washington.edu A UW computer | |||
| .ischool.washington.edu iSchool computers | |||
| .cs.washington.edu CSE computers | |||
| june.cs.washington.edu A CSE computer | |||
| Computers are named by IP address, four numbers in the range 0-255 | |||
| cse.washington.edu: 128.95.1.4 | |||
| ischool.washington.edu: 128.208.100.150 | |||
| Remembering IP addresses would be brutal for humans, so we use domains | |||
| Computers find the IP address for a domain name from the Domain Name System -- an IP address-book computer | |||
| .edu .com .mil .gov .org .net domains are “top level domains” for the US | ||
| Recently, new TLD names added | ||
| Each country has a top level domain name: .ca (Canada), .es (Spain), .de (Germany), .au (Australia), .at (Austria), .us | ||
| There are 2 ways to view the Internet | |||
| Humans see a hierarchy of domains relating computers -- logical network | |||
| Computers see groups of four number IP addresses -- physical network | |||
| Both are ideal for the “users” needs | |||
| The Domain Name System (DNS) relates the logical network to the physical network by translating domains to IP addresses | |||
| The Internet computers rely on the client/server protocol: servers provide services, clients use them | |||
| Sample servers: email server, web server, ... | |||
| UW servers: dante, courses, www, student,… | |||
| Frequently, a “server” is actually many computers acting as one, e.g. dante is a group of more than 50 servers | |||
| World Wide Web is the collection of servers (subset of Internet computers) & the information they give access to | |||
| Clearly, WWW ¹ Internet | |||
| The “server” is the web site computer and the “client” is the surfer’s browser | |||
| Many Web server’s domain names begin with www by tradition, but any name is OK | |||
| Often multiple server names map to the same site: MoMA.org and www.MoMA.org | |||
| For Web pages, the client requests a page, the server returns it: there’s no connection, just two transmissions |
| Web addresses are URLs, uniform resource locator, an IP address+path | |||
| URLs are often redirected to other places; e.g. http://www.cs.washington.edu/100/ goes to | |||
| Networking is changing the world | |||
| Internet: named computers using TCP/IP | |||
| WWW: servers providing access to info | |||
| Principles | |||
| Logical network of domain names | |||
| Physical network of IP addresses | |||
| Protocols rule: LAN, TCP/IP, http, ... | |||
| Domain Name System connects the two | |||
| Client/Server, fleeting relationship on WWW | |||