[Article] How does multiplexing in HTTP/2 work?

[admin]

Let's consider a Web page test.html located at https://example.com/test.html which uses a CSS sheet style.css and includes 3 images a.jpg, b.jpg and c.jpg.

If a HTTP/1.1 browser visits https://example.com/test.html, it will:

• Open a TCP/IP connection to example.com
  
• Negociate an SSL/TLS session
  
• Send a request for virtual path /test.html
  
• Receive the reply and parse the page
  
• Reuse the same connection to send a new request for /style.css
  
• Receive the reply
  
• Open a TCP/IP connection to example.com
  
• Negociate an SSL/TLS session
  
• Use the new connection to request /a.jpg
  
• Reuse the new connection to request /b.jpg
  
• Reuse the first connection to request /c.jpg
  
• Close both connections

If a HTTP/2 browser visits https://example.com/test.html, it will:

• Open a TCP/IP connection to example.com
  
• Negociate an SSL/TLS session
  
• Send a request for virtual path /test.html
  
• Receive the reply and parse the page
  
• Send a request for /style.css
  
• Send a request for /a.jpg
  
• Send a request for /b.jpg
  
• Send a request for /c.jpg
  
• Receive the replies for all requested files
  
• Close the connection

In this small example, HTTP/2 has used a single TCP/IP connection with a single SSL/TLS negociation while HTTP/1.1 required two of each.
The total time to load the page with its dependencies is also shorter.
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