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Today’s Labs are moved to Tuesday … join any
section: 8:30, 9:30, 1:30, 2:30 |
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Office hours have been posted on the class Web
Page |
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More than just a social interaction |
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Computers are useful alone, but are better when
connected (networked) |
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Access more information and software than is
stored locally |
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Help users to communicate, exchange information
… changing ideas about social interaction |
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Perform other services -- printing, Web,... |
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The Internet is making fundamental changes … The
FIT text gives 5 ways |
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Nowhere is remote -- access to info is no longer
bound to a place |
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Connecting with others -- email is great |
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Revised human relationships -- too much time
spent online could be bad |
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English becoming a universal language |
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Enhanced freedom of speech, assembly |
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Networks are structured differently based
(mostly) on how far apart the computers are |
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Local area network (LAN) -- a small area such as
a room or building |
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Wide
area networks (WAN) -- large area, e.g. distance is more than 1 Km |
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To communicate computers need to know how to
set-up the info to be sent and interpret the info received |
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Communication rules are a protocol |
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Example protocols |
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EtherNet for physical connection in a LAN |
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TCP/IP -- transmission control protocol /
internet protocol -- for Internet |
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HTTP -- hypertext transfer protocol -- for Web |
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EtherNet is a popular LAN protocol |
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Recall, it’s a “party” protocol |
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The campus subnetworks interconnect computers of
the UW domain which connects to Internet via a gateway |
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Information is sent across the Internet using IP
-- Cerf uses postcard analogy |
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Break message into fixed size units |
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Form IP packets with destination address,
sequence number and content |
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Each makes its way separately to destination,
possibly taking different routes |
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Reassembled at destination forming msg |
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A packet sent from UW to ETH (Swiss Fed. Tech.
University) took 21 hops |
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People name computers by a domain name -- a
hierarchical scheme that groups like computers |
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.edu
All educational computers |
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.washington.edu All computers at UW |
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dante.washington.edu A UW computer |
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.ischool.washington.edu iSchool computers |
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.cs.washington.edu CSE computers |
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june.cs.washington.edu A CSE computer |
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Computers are named by IP address, four numbers
in the range 0-255 |
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cse.washington.edu: 128.95.1.4 |
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ischool.washington.edu: 128.208.100.150 |
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Remembering IP addresses would be brutal for
humans, so we use domains |
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Computers find the IP address for a domain name
from the Domain Name System -- an IP address-book computer |
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.edu .com .mil .gov .org .net domains are “top
level domains” for the US |
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Recently, new TLD names added |
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Each country has a top level domain name: .ca
(Canada), .es (Spain), .de (Germany), .au (Australia), .at (Austria), .us |
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There are 2 ways to view the Internet |
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Humans see a hierarchy of domains relating
computers -- logical network |
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Computers see groups of four number IP addresses
-- physical network |
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Both are ideal for the “users” needs |
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The Domain Name System relates the logical
network to the physical network by translating domains to IP |
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The Internet computers rely on the client/server
protocol: servers provide services, clients use them |
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Sample servers: email server, web server, ... |
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UW servers: dante, courses, www, student,… |
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Frequently, a “server” is actually many
computers acting as one, e.g. dante is a group of more than 50 servers |
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World Wide Web is the collection of servers
(subset of Internet computers) & the information they give access to |
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Clearly, WWW ¹ Internet |
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The “server” is the web site computer and the
“client” is the surfer’s browser |
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Many Web server’s domain names begin with www by
tradition, but any name is OK |
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Often multiple server names map to the same
site: MoMA.org and www.MoMA.org |
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Web surfers are not “connected” to a server, but
interact briefly: Browser (client) sends a request for a page, the server
replies; it’s 2 transmissions |
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This is a smart scheme: clients can flit from
site to site; servers handle other requests |
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This scheme is part of the hypertext transfer
protocol, http |
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Web addresses are URLs, uniform resource locator,
an IP address+path |
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URLs are often redirected to other places;
e.g. http://www.cs.washington.edu/100/ goes to |
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Networking is changing the world |
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Internet: named computers using TCP/IP |
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WWW: servers providing access to info |
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Principles |
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Logical network of domain names |
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Physical network of IP addresses |
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Domain Name System connects the two |
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Client/Server, fleeting relationship on WWW |
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Notes
