Computer Science E-1: Understanding Computers and the
Internet
Harvard University Extension School
Fall 2005
Lecture 4: The Internet
Instant Messenging (IM)
We demonstrated the extended capabilities of today's IM programs by holding two live conversations with E-1's distance students.
(1) A conversation with video (the class was able to see the distance student):
Brian Thomas: iChat @ Phoenix, AZ
David Malan: AIM @ Cambridge, MA
(2) An audio conversation via GoogleTalk:
We spoke with Ken Williams in Alexandria, VA
GoogleTalk:
works incredibly well for audio
avoids many firewall isues
available for free to anyone who has a Gmail account
if you need a Gmail account, send us email
Email
Email Protocols:
Outgoing mail server (Client --> Server):
SMTP (Simple Mail Transfer Protocol)
Incoming mail servers (Server --> Client):
POP (Post Office Protocol)
IMAP (Internet Message Access Protocol)
IMAP is more flexible because it maintains synchronization between the client and the server, i.e. you can read your messages on the server from several clients.
Web-based mail (Gmail, Hotmail, Yahoo, etc) is completely server-based. You only use a Web browser to display your messages temporarily: they are not stored on your computer.
Email Security:
Email Scams & Phishing:
example: fake email from PayPal
a link points to http://62.111.138.7/... (instead of www.paypal.com)
a perfect copy of PayPal’s website
the hacker can use username and password to log into the real PayPal and steal money
Electronic chain letters:
ask users to add their name to the list and forward it to all of their friends
create unnecessary traffic on the Internet and waste people’s time
Some emails ask you to install software on your computer. Never do so!
Addressing:
Canonical email address forms:
username@domain.tld
username@subdomain.domain.tld
Only valid domain and tld sequences are allowed in the portion of the address after the ‘@’ character. It does not matter if letters in this portion are upper-case or lower-case.
Only alphanumeric characters (i.e. letters and digits), hyphens (-), underscores (_), and dots (.) are allowed in the username portion. It does matter if the letters are upper- or lower-case.
World Wide Web (WWW)
What is the distinction between the Internet and the World Wide Web?
The Internet is the physical network infrastructure that connects computers all over the world.
World Wide Web is the collection of computers that serve Web pages (i.e. actual content) to other computers, which runs on top of the Internet.
Other services, such as email and IM, run over the Internet as well.
What do you need to have your own website?
Get your own domain name from a 3rd-party provider (e.g. godaddy.com – checking first that the domain has not been taken already
Get someone to host your website, i.e. to provide the server to serve your Web pages (e.g. www.e-rice.net)
Create the content for your website (i.e. write your Web pages): we will teach you to do so later in the course!
Protocol is a "language" that the computers "speak" to communicate information over a network.
The most commonly found protocol is HTTP (Hyper Text Transfer Protocol), which allows to transfer HTML documents that comprise Web pages. In fact, most browsers automatically append the “http://” portion to an address you type in.
Other protocols include FTP, SSH, and Telnet (and are used independently of WWW).
Domain names in URLs are not case-sensitive, i.e. fAs.hArvArd.EDU is the same as fas.harvard.edu
Paths, however, are case-sensitive.
The default path on a particular domain is a top-level index.html file.
Other Internet-related Topics
SSH (Secure Shell): A protocol that allows encrypted exchange between a client and a server.
We will be using an SSH program to access content in your own directories on fas.harvard.edu
SFTP (Secure File Transfer Protocol): A protocol that allows encrypted file download and upload from and to a server.
We will be using an SFTP program to move content between your own computer and your directories on fas.harvard.edu
Blogging
Instant Messanging (Client – Server – Client)
Netiquette
Emoticons
TLDs (Top Level Domains)
Usenet: yesteryear's newsgroups and bulletin boards.
Google Groups largely replaced Usenet.