Docs: Added efficient downloads Android U class

        </ul>

      </li>

      <li class="toggle-list">

        <div><a href="<?cs var:toroot ?>training/efficient-downloads/index.html">

            <span class="en">Transferring Data Without Draining the Battery</span>

          </a> <span class="new">new!</span></div>

        <ul>

          <li><a href="<?cs var:toroot ?>training/efficient-downloads/efficient-network-access.html">

            <span class="en">Optimizing Downloads for Efficient Network Access</span>

          </a>

          </li>

          <li><a href="<?cs var:toroot ?>training/efficient-downloads/regular_updates.html">

            <span class="en">Minimizing the Effect of Regular Updates</span>

          </a>

          </li>

          <li><a href="<?cs var:toroot ?>training/efficient-downloads/redundant_redundant.html">

            <span class="en">Redundant Downloads are Redundant</span>

          </a>

          </li>

          <li><a href="<?cs var:toroot ?>training/efficient-downloads/connectivity_patterns.html">

            <span class="en">Modifying Patterns Based on the Connectivity Type</span>

          </a>

          </li>

        </ul>

      </li>

      <li class="toggle-list">

        <div><a href="<?cs var:toroot ?>training/search/index.html">

            <span class="en">Adding Search Functionality</span>

page.title=Modifying your Download Patterns Based on the Connectivity Type

parent.title=Transferring Data Without Draining the Battery

parent.link=index.html

trainingnavtop=true

previous.title=Redundant Downloads are Redundant

previous.link=redundant_redundant.html

@jd:body

<div id="tb-wrapper">

<div id="tb">

<h2>This lesson teaches you to</h2>

<ol>

  <li><a href="#WiFi">Use Wi-Fi</a></li>

  <li><a href="#Bandwidth">Use greater bandwidth to download more data less often</a></li>

</ol>

<h2>You should also read</h2>

<ul>

  <li><a href="{@docRoot}training/monitoring-device-state/index.html">Optimizing Battery Life</a></li>

</ul>

</div>

</div>

<p>When it comes to impact on battery life, not all connection types are created equal. Not only does the Wi-Fi radio use significantly less battery than its wireless radio counterparts, but the radios used in different wireless radio technologies have different battery implications.</p>

<h2 id="WiFi">Use Wi-Fi</h2>

<p>In most cases a Wi-Fi radio will offer greater bandwidth at a significantly lower battery cost. As a result, you should endeavor to perform data transfers when connected over Wi-Fi whenever possible.</p>

<p>You can use a broadcast receiver to listen for connectivity changes that indicate when a Wi-Fi connection has been established to execute significant downloads, preempt scheduled updates, and potentially even temporarily increase the frequency of regular updates as described in <a href="{@docRoot}training/monitoring-device-state/index.html">Optimizing Battery Life</a> lesson <a href="{@docRoot}training/monitoring-device-state/connectivity-monitoring.html">Determining and Monitoring the Connectivity Status</a>.</p>

<h2 id="Bandwidth">Use Greater Bandwidth to Download More Data Less Often</h2>

<p>When connected over a wireless radio, higher bandwidth generally comes at the price of higher battery cost. Meaning that LTE typically consumes more energy than 3G, which is in turn more expensive than 2G.</p>

<p>This means that while the underlying radio state machine varies based on the radio technology, generally speaking the relative battery impact of the state change tail-time is greater for higher bandwidth radios.</p>

<p>At the same time, the higher bandwidth means you can prefetch more aggressively, downloading more data over the same time. Perhaps less intuitively, because the tail-time battery cost is relatively higher, it's also more efficient to keep the radio active for longer periods during each transfer session to reduce the frequency of updates.</p>

<p>For example, if an LTE radio is has double the bandwidth and double the energy cost of 3G, you should download 4 times as much data during each session&mdash;or potentially as much as 10mb. When downloading this much data, it's important to consider the effect of your prefetching on the available local storage and flush your prefetch cache regularly.</p>

<p>You can use the connectivity manager to determine the active wireless radio, and modify your prefetching routines accordingly:</p>

<pre>ConnectivityManager cm =

 (ConnectivityManager)getSystemService(Context.CONNECTIVITY_SERVICE);

TelephonyManager tm =

  (TelephonyManager)getSystemService(Context.TELEPHONY_SERVICE);

NetworkInfo activeNetwork = cm.getActiveNetworkInfo();

int PrefetchCacheSize = DEFAULT_PREFETCH_CACHE;

switch (activeNetwork.getType()) {

  case (ConnectivityManager.TYPE_WIFI): 

    PrefetchCacheSize = MAX_PREFETCH_CACHE; break;

  case (ConnectivityManager.TYPE_MOBILE): {

    switch (tm.getNetworkType()) {

      case (TelephonyManager.NETWORK_TYPE_LTE | 

            TelephonyManager.NETWORK_TYPE_HSPAP): 

        PrefetchCacheSize *= 4;

        break;

      case (TelephonyManager.NETWORK_TYPE_EDGE | 

            TelephonyManager.NETWORK_TYPE_GPRS): 

        PrefetchCacheSize /= 2;

        break;

      default: break;

    }

    break;

  }

  default: break;

}</pre>

 No newline at end of file