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    <title>Optimizing For Bandwidth</title>
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<h1>Optimizing For Bandwidth</h1>    <p>
      PageSpeed's default <code>RewriteLevel</code> of
      <a href="config_filters#level">CoreFilters</a>
      is designed to reduce latency, incurring a small risk of page breakage.
      A related goal, bandwidth reduction, can be achieved with close to zero
      risk of web-site breakage:</p>
    <dl>
      <dt>Apache:<dd><pre class="prettyprint">
ModPagespeedRewriteLevel OptimizeForBandwidth</pre>
      <dt>Nginx:<dd><pre class="prettyprint">
pagespeed RewriteLevel OptimizeForBandwidth;</pre>
    </dl>
    <p>
      This option is suitable for use in a root configuration at a
      hosting service, CDN, or multi-site setup, in conjunction with
      <a href="configuration#virtual-hosts">InheritVhostConfig</a>.
      In this mode, PageSpeed does not alter HTML at all.  It compresses
      and transcodes images <a href="system#ipro">in place</a>, and minifies
      JavaScript and CSS. By avoiding changes to URL syntax and to HTML, the
      potential problem of user-written JavaScript encountering unexpected
      DOM elements is elimimated.  There is still latency benefit due to the
      reduced size of resources, as well as substantial bandwidth reduction.
    </p>
    <h2 id="savings">Bandwidth Savings</h2>
    <p>
      The bandwidth savings resulting from this option are, of course,
      dependent on the source site.  Our tests with the default
      settings for OptimizeForBandwidth indicate an average bandwidth
      reduction of roughly 37% over the content of 1000 large web sites with
      a client that is capable of displaying webp images, and 25% improvement
      with older clients.
    </p>
    <h2 id="adding_options">Adding Additional Options</h2>
    <p>
      Additional latency optimizations that modify HTML can be layered on
      top of <code>OptimizeForBandwidth</code> by enabling additional
      filters, and altering the <a href="config_filters#preserveurls">Preserve
        URL settings</a> for CSS, images, or JavaScript.  For example, to set
      up a shared hosting server with OptimizeForBandwidth in the root, but
      where individual sites have added
      <a href="filter-js-inline">inline_javascript</a>,
      <a href="filter-lazyload-images">lazyload_images</a> and
      <a href="filter-prioritize-critical-css">prioritize_critical_css</a>,
      or simply turned on <a href="config_filters#level">CoreFilters</a>,
      the following pagespeed.conf fragment may be used:
    </p>
    <dl>
      <dt>Apache:</dt>
      <dd>
        <pre>
ModPagespeedInheritVHostConfig on
ModPagespeedRewriteLevel OptimizeForBandwidth
&lt;VirtualHost *:80&gt;
  ServerName prioritize_above_the_fold.example.com
  ModPagespeedEnableFilters inline_javascript,prioritize_critical_css,inline_preview_images
&lt;/VirtualHost&gt;
&lt;VirtualHost *:80&gt;
  ServerName preserve_css_urls_off.example.com
  ModPagespeedCssPreserveURLs off
&lt;/Directory&gt;
&lt;VirtualHost *:80&gt;
  ServerName core.example.com
  ModPagespeedRewriteLevel CoreFilters
&lt;/Directory&gt;</pre>
      </dd>
      <dt>Nginx:</dt>
      <dd>
        <pre>
pagespeed RewriteLevel OptimizeForBandwidth;
server {
  server_name prioritize_above_the_fold.example.com
  pagespeed EnableFilters inline_javascript,prioritize_critical_css,inline_preview_images
}
server {
  server_name preserve_css_urls_off.example.com
  pagespeed CssPreserveURLs off
}
server {
  server_name core.example.com
  pagespeed RewriteLevel CoreFilters
}</pre>
      </dd>
    </dl>
    <p>
      In version 1.9.32.1 and later, <a href="system#ipro">In Place
      Resource Optimization</a> is enabled by default.  In earlier versions,
      turning on OptimizeForBandwidth automatically enables In Place
      Resource Optimization to optimize the resources without needing
      to change their URLs.  In these earlier versions, when a VirtualHost
      overrides the <code>RewriteLevel</code> to <code>CoreFilers</code>, that
      turns off In Place Resource Optimization, but it can be re-enabled
      explicitly:</p>
<dl>
  <dt>Apache:<dd><pre class="prettyprint"
     >ModPagespeedInPlaceResourceOptimization on</pre>
  <dt>Nginx:<dd><pre class="prettyprint"
     >pagespeed InPlaceResourceOptimization on;</pre>
</dl>
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