Computer Fundamentals
Instructor: Jun Yan
Thursday (3, 4), N229, South Campus
Lecture 10: Computer Networks and
Internet Service
张毅斌
2015050536
Welcome to the class.
This lecture covers the following topics:
Search engine basics
Formulating searches
E-mail overview
FTP
Virtual private networks
Review
(1) Web base:
The Web is a collection of document, image, video and sound files that can be
linked and accessed over internet using a protocol called HTTP.
(Clients communicate with servers by using http techniques)
A Web server is an internet-based computer that accepts requests from
browsers
A Web page is the product or output of one or more Web-based files displayed
in a format similar to a page in a book
④A Wed browser is a client software that displays Web page elements and
handles links between pages
(2) HTTP (HTTP messages flow between a browser and a Web server.)
Every Web Page has a unique address called a URL(uniform resource locator)
E.g.
http://
Web protocol standard
www.cnn.com/
web server name
showbiz/
folder name
movies.htm
file name and file extension
HTML is a set of specifications for creating documents that a browser can
display as a Web page. It is a markup language because authors mark up
documents by inserting special instructions, called HTML tags. And these
tags are instruction for the browser.
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Computer Fundamentals
Instructor: Jun Yan
Thursday (3, 4), N229, South Campus
(3) HTML Scripts
HTML scripts can perform specific actions or respond to specific user actions.
(4) Web browser
A kind of application that help you access web pages.
Browser’s ability can be extended by using some Plug-in, add-on, or extension.
(5) Cookies
Small chunk of data, which collect some personal information, generated by a
Web server and stored in a text file on computer’s hard disk.
(6) Web page authoring
The web page should be due on Dec. 31 as a final project if you choose to do it
The new lecture
Internet Services including real-time messaging, voice over IP (VOI), search,
E-mail, FTP and VPN. We are familiar with the former two. We use QQ or WeChat
almost every day. They are what we call the Real-Time Messaging. Most of us have
ever used Skype or other internet telephone, and they are what we call the Voice
over IP. So, we begin with search.
(1) Search Engine Basics
A Web search engine is a program designed to help people locate information
on the web by formulating simple keyword queries.
Take Google as an example (www.google.com is a web site that offers access to
google search engine), if you type some key words in the blanket and click the
Search button, it will show you millions of relevant sites in a very short time. For
economic purpose, sometimes the first site that existed in the results is an
advertisement, but usually the most relevant or the most useful site will followed.
Just click an underlined link, it will connect you to the web page. With the engine,
it’s easy to get some information we need in the net.
(We have other search engine like Bing from Microsoft, Baidu from baidu
cooperation and so on.)
Usually speaking, a search engine including web crawler, indexer, query processor
and pagerank algorithm.
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Computer Fundamentals
Instructor: Jun Yan
Thursday (3, 4), N229, South Campus
·A Web crawler is a computer program that is automated to methodically visit
Web sites and gather data. And these data will be formed as a database which
will be used when responding user’s search requirement.
·A search engine indexer is software that pulls keywords from a web page and
stores them in a database. It is noteworthy that the database will increase
continuously.
·A search engine’s query processor looks for your search terms in search engine’s
indexed database and returns a list of relevant web sites.
·Pagerank algorithm. Link popularity is measured by quantity and quality of links
from one web page to others.
How can a web sites be added to a search engine?
1. Discovered by web crawler. Usually it takes a long time, but if the web site is
popular, which means that many people visit the website, the time it took is
much shorter. Maybe within few days a new but hot website will be found by
web crawler.
2. Submitted by web masters. Search engine will pay more attention to web
masters because they play an important role in the net. Their websites
usually have great influence.
3. Submitted for a paid placement. For economic purpose, most search engines
will have a paid placement for those website which want to exist in the front.
If you search something in baidu, you may easily see this paid placement.
4. Submitted as banner or pop-up ads. In this case, the owner of the ads should
pay a great amount of money to the owner of search engine. This is the
important way for google to earn its income.
(2) Formulating Searches
·Most search engines work with keyword queries in which you enter one or
more words, called search terms.
·A Boolean operator is a word or symbol that describes a relationship between
keywords, helping you create a more focused query.
AND
When two search terms are joined by AND, both terms must appear
on a webpage before it can be included in the search results.
OR
When two search terms are joined by OR, either one or both of the
search words could appear on a page.
NOT
The keyword following NOT must not appear on any of the pages
found by the search engine.
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Computer Fundamentals
Instructor: Jun Yan
Thursday (3, 4), N229, South Campus
Then, we watch a video called How To Google Like A Pro! It tells about the top 10
google search tips & tricks. This video may be found in our course website.
(3)E-mail Overview
·Any person with an e-mail account can send and receive e-mail messages.
Usually speaking, an E-mail contains recipient’s name or e-mail address,
subject line, file attachment and message body.
·Basic e-mail activities
--Writing
--Reading
--Replying to
--Forwarding
Local E-mail
·E-mail systems based on local client software, such as outlook, are referred
to as local e-mail.
·An internet-based e-mail server stores your incoming messages until you
launch your e-mail client and get your mail. This is referred to as
store-and-forward technology.
·Three protocols:
--POP3 (Post Office Protocol version 3)
--IMAP (Internet Message Access Protocol)
Recommended, because it is suitable for multiple computers /
smartphones to access a single mail server.
--SMTP (Simple Mail Transfer Protocol)
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Computer Fundamentals
Instructor: Jun Yan
Thursday (3, 4), N229, South Campus
Webmail
·Web-based e-mail accounts allow you to use a browser to access your e-mail
messages.
HTML mail
·E-mail messages containing HTML tags that produce various texts, fonts,
graphics, and so on.
·You can choose HTML or plain, unformatted ASCII text
More about HTML mail please visit: https://en.wikipedia.org/wiki/HTML_email
Spam
·spam is unwanted electronic junk mail about medical products, low-cost loans,
and fake software upgrades that arrive in your online mailbox.
·A spam filter is a type of utility software that captures unsolicited e-mail
messages before they reach your inbox. It works by checking the text of
e-mail headers and messages against a series of rules.
·But the spam is not smart enough, sometimes some useful mail will be filtered
also, so you had better search your spam in a regular time.
(3) FTP
· FTP clients such as FileZilla make it easy to upload and download files from
an FTP server
·There are so many resources (such as movies, ppt, doc and so on) in FTP
servers, you may almost find everything in FTP servers.
Steps:
Open a FTP link in the browser → click the file you want to download
→ click download or yes in the pop-up windows.
E.g. ftp://ftp.jnu.edu.cn
(4) Virtual Private Networks (VPN)
·It is possible to secure remote connections by setting up virtual in the
corporate office.
·Employees who need to access a VPN are given the necessary instructions,
addresses, and passwords to make connections.
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Computer Fundamentals
Instructor: Jun Yan
Thursday (3, 4), N229, South Campus
Nowadays, we usually use this way to bypass the GFW.
That’s all.
Thanks.
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