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Manual Chapter: Establishing Additional TCP Connections with MultiConnect
Manual Chapter
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Establishing Additional TCP Connections with MultiConnect

Overview: Accelerating requests and responses with MultiConnect

Most web browsers create a limited number of persistent TCP connections when requesting data, which restricts the amount of content a client can receive at one time. You can provide faster data downloads to your clients using the BIG-IP® device's MultiConnect feature.

The MultiConnect feature enables you to specify unique subdomains that prompt the browser to open more persistent TCP connections (up to five per HTTP subdomain and five per HTTPS subdomain generated by the BIG-IP device). The origin web servers never get a request from these additional subdomains; they are used exclusively on externally linked URLs or links that request images or scripts and are only for requests or responses between the client and the BIG-IP device. If the BIG-IP device needs to send a request to the origin server, it removes the subdomain prefixes before sending the request.

The BIG-IP device uses the MultiConnect feature only on the following types of links:

  • Image tags: <img src="...">
  • Script tags: <script src="...">
  • Forms whose input type is an image: <form><input type="image” src="..."></form>

Optimization of TCP connections

The BIG-IP® application acceleration provides MultiConnect functionality that decreases the number of server-side TCP connections required while increasing the number of simultaneous client-side TCP connections available to a browser for downloading a web page.

Decreasing the number of server-side TCP connections can improve application performance and reduce the number of servers required to host an application. Creating and closing a TCP connection requires significant overhead, so as the number of open server connections increases, maintaining those connections while simultaneously opening new connections can severely degrade server performance and user response time.

Despite the ability for multiple transactions to occur within a single TCP connection, a connection is typically between one client and one server. A connection normally closes either when a server reaches a defined transaction limit or when a client has transferred all of the files that are needed from that server. The BIG-IP system, however, operates as a proxy and can pool TCP server-side connections by combining many separate transactions, potentially from multiple users, through fewer TCP connections. The BIG-IP system opens new server-side connections only when necessary, thus reusing existing connections for requests from other users whenever possible.

The Enable MultiConnect To check box on the Assembly screen of BIG-IP applies MultiConnect functionality to image or script objects that match the node. The Enable MultiConnect Within check box, however, applies MultiConnect functionality to image or script objects that are linked within HTML or CSS files for the node.

MultiConnect example

For this example, your site serves a simple page (http://www.siterequest.com/index.htm) that consists of several image files. The page that your site serves appears as follows:

   <html>
     <head><title>example page</title></head>
     <body>
      <p>The images that your site serves:</p>
      <p><img src=”myImages/image1.jpeg”></p>
      <p><img src=”myImages/image2.jpeg”></p>
      <p><img src=”myImages/image3.jpeg”></p>
      <p><img src=”myImages/image4.jpeg”></p>
     </body>
   </html>
  

An additional subdomain prefix of wa is configured for the host map and the MultiConnect feature enabled, so the BIG-IP® device modifies the page and serves it as follows:

    <html>
      <head><title>example page</title></head>
      <body>
        <p>The images that your site serves:</p>
        <p><img src=”http://wa1.www.siterequest.com/myImages/image1.jpeg”></p>
        <p><img src=”http://wa2.www.siterequest.com/myImages/image2.jpeg”></p>
        <p><img src=”http://wa2.www.siterequest.com/myImages/image3.jpeg”></p>
        <p><img src=”http://wa1.www.siterequest.com/myImages/image4.jpeg”></p>
      </body>
   </html>   
  
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