<?xml version="1.0" encoding="ANSI_X3.4-1968" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=ANSI_X3.4-1968" /><title>Frame format</title><meta name="generator" content="DocBook XSL Stylesheets V1.75.2" /><link rel="home" href="index.html" title="The mac80211 subsystem for kernel developers" /><link rel="up" href="ch04.html" title="Chapter 4. Receive and transmit processing" /><link rel="prev" href="ch04.html" title="Chapter 4. Receive and transmit processing" /><link rel="next" href="ch04s03.html" title="Packet alignment" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Frame format</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04.html">Prev</a> </td><th width="60%" align="center">Chapter 4. Receive and transmit processing</th><td width="20%" align="right"> <a accesskey="n" href="ch04s03.html">Next</a></td></tr></table><hr /></div><div class="sect1" title="Frame format"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="id2707460"></a>Frame format</h2></div></div></div><p> </p><p> As a general rule, when frames are passed between mac80211 and the driver, they start with the IEEE 802.11 header and include the same octets that are sent over the air except for the FCS which should be calculated by the hardware. </p><p> There are, however, various exceptions to this rule for advanced features: </p><p> The first exception is for hardware encryption and decryption offload where the IV/ICV may or may not be generated in hardware. </p><p> Secondly, when the hardware handles fragmentation, the frame handed to the driver from mac80211 is the MSDU, not the MPDU. </p><p> Finally, for received frames, the driver is able to indicate that it has filled a radiotap header and put that in front of the frame; if it does not do so then mac80211 may add this under certain circumstances. </p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch04.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="ch04.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch04s03.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 4. Receive and transmit processing </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Packet alignment</td></tr></table></div></body></html>
