Hypertexttransferprotocolhttp 131012171813-phpapp02

HyperText Transfer
Protocol (HTTP)
GURJOT SINGH REVTI RAMAN SINGH
UG201113013 UG201110026
1

WHAT IS A PROTOCOL AND HTTP?
• Protocol: A Protocol is a standard procedure for
defining and regulating communication. For
example TCP, UDP, HTTP etc.
• HTTP is the foundation of data communication for
the World Wide Web.
• The HTTP is the Web’s application-layer protocol
for transferring various forms of data between
server and client like plaintext, hypertext, image,
videos and sounds .
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TERMINOLOGY
• IP Address: An Internet Protocol address (IP address) is a numerical label assigned to each
device (e.g., computer, printer) participating in a computer network that uses the Internet
Protocol for communication.
• TCP :Transmission Control Protocol (TCP) is one of the two original core protocols of
the Internet Protocol Suite (IP), and is so common that the entire suite is often called TCP/IP.
TCP provides reliable, ordered, error-checked delivery of a stream of octets between
programs running on computers connected to an intranet or the public Internet.
• Port Number : A port number is a 16 bit number which when associated with IP address ,
completes the destination address for a communications session.
• Socket : A socket is nothing but a combination of IP address and port number. It is simply an
end while communication. 3

HOW HTTP WORKS?
• HTTP is implemented in two programs: a client
program and a server program, executing on
different end systems, talk to each other by
exchanging HTTP messages.
• The HTTP client first initiates a TCP
connection with the server. Once the
connection is established, the browser and the
server processes access TCP through their
socket interfaces.
4

HOW HTTP WORKS?
5
Suppose client wants to visit www.yahoo.com

PERSISTENT AND NON-PERSISTENT CONNECTIONS
• In non-persistent connection each request/response pair are sent over a
separate TCP connection.
• In persistent connections all of the requests and their corresponding responses
are sent over the same TCP connection.
10

HTTP REQUEST MESSAGE
• The first line of an HTTP request message is
called the request line; the subsequent lines are
called the header lines. The request line has
three fields: the method field, the URL field, and
the HTTP version field. The method field can take
on several different values, including GET, POST,
HEAD, PUT, and DELETE etc. The great majority
of HTTP request messages use the GET method.
The GET method is used when the browser
requests an object, with the requested object
identified in the URL field.
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REQUEST METHODS
• GET: Retrieve Document identified in URL
• HEAD: Retrieve meta information about document identified in URL
• DELETE: Delete specified URL
• OPTIONS: Request information about available options
• PUT: Store document under specified URL
• POST: Give information to server
• TRACE: Loopback request message
• CONNECT: For use by Proxies
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HTTP RESPONSE MESSAGES
• It has three sections: an initial status line,
header lines, and then the entity body. The
entity body contains the requested object
itself. The status line has three fields: the
protocol version field, a status code, and a
corresponding status message.
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SOME COMMON STATUS CODES AND
ASSOCIATED PHRASES
• Some common status codes and associated phrases
include:
• 200 OK: Request succeeded and the information is
returned in the response.
• 301 Moved Permanently: Requested object has been
permanently moved; the new URL is specified in Location:
header of the response message. The client software will
automatically retrieve the new URL.
• 400 Bad Request: This is a generic error code indicating
that the request could not be understood by the server.
• 404 Not Found: The requested document does not exist
on this server.
• 505 HTTP Version Not Supported: The requested HTTP
protocol version is not supported by the server.
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15
An HTTP request using telnet

HTTP: A STATELESS PROTOCOL
• HTTP is a stateless protocol, because an HTTP server maintains no information
about the clients.
• If a particular client asks for the same object twice in a period of a few
seconds, the server does not respond by saying that it just served the object to
the client; instead, the server resends the object, as it has completely forgotten
what it did earlier.
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USER-SERVER INTERACTIONS: COOKIES
• HTTP server being stateless, simplifies server design and has permitted engineers to
develop high-performance Web servers that can handle thousands of simultaneous
TCP connections. However, it is often desirable for a Web site to identify users, either
because the server wishes to restrict user access or because it wants to serve content
as a function of the user identity. For these purposes, HTTP uses cookies. Cookies
allow sites to keep track of users.
• The cookie technology has four components:
• a cookie header line in the HTTP response message
• a cookie header line in the HTTP request message
• a cookie file kept on the user’s end system and managed by the user’s browser
• a back-end database at the Web site
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WEB CACHING
• Also called proxy server, is a network entity that
satisfies HTTP requests on the behalf of an origin Web
server.
• The Web cache has its own disk storage and keeps
copies of recently requested objects in this storage.
• A Web cache can substantially reduce the response
time for a client request, particularly if the bandwidth
between the client and the origin server is much less
than the bandwidth between the client and the cache.
• Web caches can substantially reduce traffic
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