Features of the Internet

1
Features of the Internet WWW

• WWW uses the Internet to connect clients and
  servers using the HTTP protocol.
• The WWW is built on top of the Internet.
• The Internet has no central control.
• The Internet is a large WAN composed of backbones
  connecting privately-owned LANs
• Backbones are high-speed networks
• WANs are typically shared, public networks
• LANs span a small geographic area

2
Core Web Technologies

• HyperText Transfer Protocol (HTTP) allows web
  browsers to communicate with web servers
• Simple protocol to format a browser request and
  the server response
• HyperText Markup Language (HTML) encoding
  language used to create multimedia documents
  rendered by web browsers
• Uniform Resource Locators (URL) the address
  system for specifying the location of web
  documents
• First part of the URL indicates protocol to use
  (e.g. http//)
• Second part specifies the IP address or the
  domain name where the resource is located, (e.g.
  www.usouthal.edu)
• Last part specifies name of resource being
  requested including an optional path (optional)
  (e.g. /CIS/index.html)

3
Web Documents

• Web documents are composed of various media
  types
• ASCII Text Files includes HTML files that
  contain pointers (hyperlinks) to other documents
• Binary Files Images Audio Video Apps
• MIME Multipurpose Internet Mail Extensions
  rules allowing multimedia documents to be
  exchanged among different computer systems
• Uses 7 media types (application, audio, image,
  message, multipart, text and video) high level
  description of type of data.
• Uses subtypes to further describe data (ex. HTML
  is text media type, html is subtype so MIME is
  text/html. Plain text MIME text/plain, image
  image/gif)

4
Web Client/Server Basics

• Client/Server is a model for distributed
  applications.
• Server allows clients to access current data and
  to be geographically dispersed.
• server large computer capable of providing
  services to clients such as Web, FTP, email
• daemon a system process running in the
  background on the server such as print, email,
  web server, FTP
• In the Microsoft environment, daemons are
  referred to as services

5
Web Browsers

• Web browser clients on the web, used to format,
  display web content received from servers
• First graphical browser was NCSA Mosaic which was
  basis for Netscape browser
• Netscape Navigator and Microsoft Internet
  Explorer currently have about 15 and 81 (22
  and 75 in 11/2001) of the browser market share,
  respectively (source http//www.ews.uiuc.edu/bsta
  ts/latest-month.html)
• Browser Plug-ins extend capabilities of browser
  by allowing it to display more than just HTML
  documents
• Helper Applications separate programs that work
  with browser to display documents which browser
  cannot open

6
Web Servers

• Web server knows how to communicate with
  clients using HTTP
• main goal is to provide documents to clients
  including support for creation of dynamic
  documents
• HTTPD or HTTP daemon the web server process
• CERN HTTPD - 1st HTTPD
• NCSA HTTPD - popular from 1993-5
• Apache - developed from NCSA HTTPD
• Internet Information Server (IIS) Microsoft
• Others Zeus, Sunsite, etc.

7
Web Server Statistics 7/2006from
www.serverwatch.com/stats
Web Server
No. of Servers in Use
Market Share
No. of ServersWith .com domains
29,054,224
55,622,584
63.49
Apache
15,228,461
25,726,748
Microsoft-IIS
29.37
2,338,498
Unknown
2.67
1,751,706
Zeus
518,503
173,260
0.59
309,248
Netscape-Enterprise
0.35
144,393
8
Web Server Functions

• Accept HTTP Connections
• Retrieve Content from Disk
• Run Local CGI or Server-side Programs
• Generate dynamic content such as forms
• Transmit Data Back to Clients
• MIME type header informs client as to type of
  content
• Web server has little role in how data is
  displayed or usedthat is up to the browser

9
Web Server Non-Functions

• A web servers doesn't know
• about hyperlinks between documents
• web servers know nothing about the documents they
  deliver
• about inline images ltimg src"xxx.gif"gt
• browsers requests these images after seeing links
  in delivered document
• about links that point to a document it serves
• can result in "dangling" links if documents
  moved/deleted
• if MIME type assigned to document is correct
• author of document assigns MIME type

10
Internet Connections

• Protocol standard set of rules servers and
  clients use to communicate
• TCP/IP protocol suite computers connected to
  Internet use this protocol suite to exchange data
  
• TCP - allow two computers to exchange messages
• guarantees delivery of data and that packets will
  be delivered in same order in which they were
  sent
• IP - allow data packets to be routed across
  multiple routers from a source host to a
  destination host
• IP address generally each computer on internet
  has unique one maps to the second part of a URL
  (the machine domain)

11
Ports

• In TCP/IP and UDP networks, a port is an endpoint
  to a logical connection. The port number
  identifies what type of port it is.
• For example, port 80 is used for HTTP traffic.
• The destination computer specified by an IP
  address may have different services running on
  it. Specify a service using a unique, usually
  standard port number assigned to each service.
• Some default ports
• HTTP (80) Telnet (23)
• SMTP (25) FTP (20,21)
• You may set up other ports such as a second test
  server (HTTPD) on 8080, example URL
  http//www.test.com8080/index.html