networking:) WWW AND HTTP

2.  When
a web address (or URL- Uniform
Resource Locator) is typed into a web
browser, the web browser establishes a
connection to the web service running
on the server using HTTP.
 URLs
and URIs (uniform resource
identifiers) are the names most people
associate with web addresses.

3. 
The URL http://www.cisco.com/index.html refers to a
specific resource—a web page named index.html on
a server identified as cisco.com.

Web browsers are the client applications computers
use to connect to the World Wide Web and access
resources stored on a web server.

As with most server processes, the web server runs as
a background service and makes different types of
files available.

4.  To
access the content, web clients make
connections to the server and request the
desired resources.
 The
server replies with the resources and,
upon receipt, the browser interprets the data
and presents it to the user.
 Browsers
can interpret and present many
data types, such as plain text or HTML, the
language in which web pages are constructed.

5.  Other
types of data, however, might require
another service or program, typically referred
to as a plug-in or add-on.
 To
help the browser determine what type
of file it is receiving, the server specifies what
kind of data the file contains.

6. consider the URL http://www.cisco.com/webserver.htm.
First, the browser interprets the three parts of the
URL:

■ http: The protocol or scheme
■ www.cisco.com: The server name
■ web-server.htm: The specific filename requested

The browser then checks with a name server to
convert http://www.cisco.com into a numeric
address, which it uses to connect to the server.

7.  Using
the HTTP requirements, the browser
sends a GET request to the server and asks for
the file web-server.htm.
 The
server in turn sends the HTML code for
this web page to the browser.
 Finally, the
browser deciphers the HTML code
and formats the page for the browser
window.

8.  HTTP,
one of the protocols in the TCP/IP
suite, was originally developed to
publish and retrieve HTML pages and is now
used for distributed, collaborative
information systems.
 HTTP is
used across the world wide web for
data transfer and is one of the most used
application protocols.

9.  HTTP
specifies a request/response protocol.
When a client, typically a web browser, sends
a request message to a server, the HTTP
protocol defines the message types the client
uses to request the web page and the
message types the server uses to respond.

10.  GET
is a client request for data.
A
web browser sends the GET message to
request pages from a web server.

When the server receives the GET request, it
responds with a status line, such as HTTP/1.1
200 OK, and a message of its own, the body
of which can be the requested file, an error
message, or some other information.

11.  The
are:
three common message types
■ GET
■ POST
■ PUT

12.  POST
and PUT are used to send messages
that upload data to the web server.

For example, when the user enters data into
a form embedded in a web page, POST
includes the data in the message sent to the
server.
 PUT
uploads resources or content to the web
server.

13. Looks up phone book
for the number
Example
Could have been also
POST/phonebook.cgi.HTTP/1.0 achieved by Get
Date:
But in that case number
User-Agent:
would have been in the
Accept Language: en-us
Resource URL
Content Length: 14
Which would have been
98490 55266
stored in the log

14.  Although
it is remarkably flexible, HTTP is
not a secure protocol.
 The
POST messages upload information to
the server in plain text that can be
intercepted and read.
 Similarly, the
server responses, typically HTML
pages, are unencrypted.

15.  For
secure communication across the Internet,
the Secure HTTP (HTTPS) protocol is used for
accessing and posting web server information.
HTTPS can use authentication and
encryption to secure data as it travels
between the client and server.
 HTTPS
specifies additional rules for passing
data between the application layer and the
transport layer.

16. HTTP Protocol
Using GET

17. Accessing Resources over the Web

<protocol>://<server>/<path>
Communication Protocol
between the client and
the server
Defines the address
(Uniform Resource Locator)

18. Hypertext Transport Protocol
(HTTP) characteristics

Request-response mechanism:

Resource Identification

Statelessness

Meta data support
◦ Transaction is initiated by a client sending a request
to server
◦ Server generates a response
◦ Each HTTP request includes a URI (Uniform Resource
Identifier)
◦ The server does not maintain any information about the
transaction
◦ Metadata about information can be exchanged in the
messages

19. HTTP Request Format
Request Line
Header Lines
GET /index.html HTTP/1.0
Specifies
resource via URI
& meta data
Host: www.content-networking.com
Date: BBBBBBBBBBBB
User-Agent: Mozilla/5.0 (en) (WINNT; U)
Accept-Language: en-us
Carriage Return/Line
Feed
Message Body
Specifies
request
method
Content-length:
(Message Payload)

20. HTTP Response Format
Status line
Header Lines
HTTP/1.0 200 OK
Date: BBBBBBBBBBBB
Server: Apache/1.3.12 (Unix)
Last-Modified: (date)
Content Type: text/html
Carriage Return/Line Feed
Message Body
Content-length:
(Message Payload)
Status line
with result
code and
phrase
Specifies
server &
resource meta
data

21. Result Code and Phrase





1xx: Informational – Not Done Yet
2xx: Success – You win
3xx:Redirection-You lose but try again
4xx:Client Error – You lose, your fault
5xx:Server Error – You lose, my bad
200
204
300
301
302
304
400
401
404
500
OK
No Content
Multiple Choices
Moved Permanently
Moved Temporarily
Not Modified
Bad Request
Unauthorized
Not Found
Internal Server Error

22. Improvements in HTTP/1.1

Persistent connections
◦ Keeps the connection open after the server
response
◦ Connection can be closed by either client or server

Request Pipelining
◦ Allows a client to send several requests without
waiting for a response
◦ Server responds in the same order

Chunked Encoding
◦ Allows sender to break a message into arbitrary
sized chunks
◦ Useful for dynamically created response messages

23. Cookies
HTTP is stateless protocol
Cookies manage state maintenance by shifting the
burden to client
• Cookies are transmitted in clear text (security issue)
•
•
Server
Client
Usual HTTP Request
1st client
request
2nd
client
request
Usual HTTP Response,
including header line Setcookie: <cookie>
Usual HTTP Request,
including header line
Set-cookie: <cookie>
Usual HTTP Response
Client does
not interpret
the cookie
string
Server is
presented
with the
previously
returned state
information

24. User Authentication
• Users browser information remembers
credentials and includes them in headers
for subsequent requests
• Browser typically deletes stored
authentication credentials once browser is
closed
• HTTP allows various authentication
mechanisms

25. Group 2
 John
Gabriel Javier
 Jenica Salmorin
 Enrefie Abuela
 Marilou Villanueva