title: Do USB Control Transfers guarantee delivery?
body: <p><a href="http://www.usb.org/developers/docs/usb20_docs/" rel="noreferrer">USB 2.0 specifies</a> 4 types of transfers (in section 5.4 Transfer Types):</p>
  
  <ul>
  <li>Control Transfers</li>
  <li>Isochronous Transfers</li>
  <li>Interrupt Transfers</li>
  <li>Bulk Transfers</li>
  </ul>
  
  <p>Section 5.8 says that Bulk Transfers provide:</p>
  
  <blockquote>
    <ul>
    <li>Access to the USB on a bandwidth-available basis</li>
    <li>Retry of transfers, in the case of occasional delivery failure due to errors on the bus</li>
    <li><strong>Guaranteed delivery of data</strong> but no guarantee of bandwidth or latency</li>
    </ul>
  </blockquote>
  
  <p>(Emphasis mine.)</p>
  
  <p>I don't see a similar statement for Control Transfers. Do they also guarantee delivery? If not, how are users expected to handle failures?</p>
  
  <p>Please provide a citation(s) to support your answer.</p>