Persistent vs Non-Persistent HTTP Connections
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Persistent vs Non-Persistent HTTP Connections

Learn about the differences between persistent and non-persistent HTTP connections in this quiz. Explore how maintaining the past history (state) is crucial, and how to reconcile inconsistent views of 'state' when servers or clients crash.

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Questions and Answers

What HTTP response status code indicates that the requested object has been moved to a new location?

301 Moved Permanently

In the context of HTTP, what does a 404 status code signify?

Requested document not found on this server

When establishing a TCP connection to an HTTP server, what is the default port used?


What does a 400 status code signify in the context of HTTP?

<p>Request message not understood by server</p> Signup and view all the answers

Which HTTP version is mentioned in the request message 'GET /fee/NewsDetails/142317/en HTTP/1.1'?

<p>HTTP/1.1</p> Signup and view all the answers

What does sending a minimal GET request involve in terms of communication with an HTTP server?

<p>Sending a minimal but complete request via port 80</p> Signup and view all the answers

Which status code indicates that the HTTP version used in the request is not supported?

<p>505 HTTP Version Not Supported</p> Signup and view all the answers

'ncat 80' is an example of what kind of connection in the context of HTTP?

<p>'Persistent' connection</p> Signup and view all the answers

'GET /fee/NewsDetails/142317/en HTTP/1.1' is an example of what part of an HTTP transaction?

<p>'Request message'</p> Signup and view all the answers

'Host:' is typically found in which part of an HTTP request message?

<p>'Request header'</p> Signup and view all the answers

Study Notes

HTTP Protocol

  • Past history (state) must be maintained, and reconciled in case of server/client crashes
  • HTTP connections have two types: non-persistent and persistent

Non-Persistent HTTP

  • One TCP connection is opened and closed for each object
  • Example: user enters URL containing text and references to 10 jpeg images
  • Steps:
    • HTTP client initiates TCP connection to HTTP server at port 80
    • HTTP client sends HTTP request message containing URL
    • HTTP server receives request message, forms response message, and sends message into its socket
    • HTTP server closes TCP connection
  • This process is repeated for each of the 10 jpeg objects
  • RTT (Round Trip Time) is the time for a small packet to travel from client to server and back
  • HTTP response time per object: 2RTT + file transmission time

Issues with Non-Persistent HTTP

  • Requires 2 RTTs per object
  • OS overhead for each TCP connection
  • Browsers often open multiple parallel TCP connections to fetch referenced objects in parallel

Persistent HTTP (HTTP 1.1)

  • Server leaves connection open after sending response
  • Subsequent HTTP messages between same client/server are sent over open connection
  • Client sends requests as soon as it encounters a referenced object
  • Response time is reduced to as little as one RTT for all referenced objects

HTTP Request and Response Messages

  • Two types of HTTP messages: request and response
  • HTTP request message:
    • ASCII (human-readable format)
    • Request line (GET, POST, HEAD commands)
    • Header lines
  • HTTP response message:
    • Status codes (e.g. 200 OK, 301 Moved Permanently, 400 Bad Request, 404 Not Found, 505 HTTP Version Not Supported)

Trying out HTTP (Client Side)

  • Use ncat tool to connect to a web server (e.g.
  • Type in a GET HTTP request message (e.g. GET /fee/NewsDetails/142317/en HTTP/1.1)
  • Observe the response message sent by the HTTP server

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