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Write short notes on: (i) TCP Timers (ii) HTTP

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(i) TCP Timers:

a. Time-Out Timer:

  • The Time-Out Timer in TCP (Transmission Control Protocol) is used to manage the retransmission of data in case of lost or delayed packets.
  • When a sender transmits a segment, it starts the timer. If an acknowledgment is not received before the timer expires, the sender assumes that the segment was lost and retransmits it.

b. Time Wait Timer:

  • The Time Wait Timer is associated with the TCP connection termination process.
  • After a connection is closed, the socket pair enters the TIME_WAIT state to ensure that any delayed packets are not misinterpreted in subsequent connections.
  • The Time Wait Timer ensures that the TIME_WAIT state does not last indefinitely, preventing resource exhaustion.

c. Keep Alive Timer:

  • The Keep Alive Timer is designed to prevent idle connections from being terminated by routers or firewalls.
  • Periodic keep-alive messages are sent over the connection, and if no response is received within a specified time (determined by the timer), the connection may be considered as idle and subject to termination.

d. Persistent Timer:

  • The Persistent Timer is related to the handling of the TCP Persist Timer event.
  • It is used to prevent a sender from being stuck in a transmit window when the receiver's window size is zero. The Persistent Timer triggers the retransmission of small segments to probe for changes in the receiver's window size.

(ii) HTTP (Hypertext Transfer Protocol):

  • Overview:

    • HTTP is a protocol for communication on the World Wide Web.
    • It is the foundation for data communication on the web and facilitates the transfer of hypertext documents, which can contain text, images, multimedia, etc.
  • Key Features:

    • Stateless Protocol: Each request from a client to a server is independent, and the server doesn't retain information about the client's state between requests.
    • Request-Response Model: Clients (e.g., browsers) send HTTP requests to servers, and servers respond with the requested information.
    • Uniform Resource Identifiers (URIs): Used to identify resources on the web, such as web pages or images.
  • Versions:

    • HTTP/1.0: The initial version.
    • HTTP/1.1: Improved performance through persistent connections, caching, and other enhancements.
    • HTTP/2: Major improvements in speed and efficiency, with features like multiplexing and header compression.
  • Methods:

    • GET: Retrieve data from the server.
    • POST: Send data to be processed to a specified resource.
    • PUT: Update a resource on the server.
    • DELETE: Request the removal of a resource.
  • Status Codes:

    • Examples include 200 OK (successful), 404 Not Found (resource not found), and 500 Internal Server Error (server error).
  • Headers:

    • Used for passing additional information in both requests and responses.
    • Examples include "Content-Type" indicating the type of data being sent and "User-Agent" identifying the client application.
  • Connection Types:

    • Persistent (Keep-Alive): Multiple requests and responses can be sent over a single connection, reducing latency.
    • Non-Persistent: A new connection is established for each request-response pair.
  • Security:

    • HTTPS (HTTP Secure) is a secure version of HTTP that uses encryption (SSL/TLS) to protect data during transmission.

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