Announcements
Today’s Labs are moved to Tuesday … join any section: 8:30, 9:30, 1:30, 2:30
Office hours have been posted on the class Web Page

Networking
More than just a social interaction

Networks...
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,...

Networking Changes Life
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

Network Structure
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

Protocol Rules!
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

LAN in the Lab
EtherNet is a popular LAN protocol
Recall, it’s a “party” protocol

Campus & The World
The campus subnetworks interconnect computers of the UW domain which connects to Internet via a gateway

IP -- Like Using Postcards
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 Trip to Switzerland
A packet sent from UW to ETH (Swiss Fed. Tech. University) took 21 hops

Naming Computers I
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

Naming Computers II
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

Domains
.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

Logical vs Physical
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 relates the logical network to the physical network by translating domains to IP

Client/Server Structure
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
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

Brief Encounter
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
This is a smart scheme: clients can flit from site to site; servers handle other requests
This scheme is part of the hypertext transfer protocol, http

Dissecting a URL
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

Summary
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
Domain Name System connects the two
Client/Server, fleeting relationship on WWW