update CHANGES ns-3.7 to ns-3.8

CHANGES.html

@@ -43,6 +43,46 @@ the cracks, unfortunately.  If you, as a user, can suggest improvements
 to this file based on your experience, please contribute a patch or drop
 us a note on ns-developers mailing list.  </p>
 
+<hr>
+<h1>Changes from ns-3.7 to ns-3.8</h1>
+
+<h2>Changes to build system:</h2>
+
+<h2>New API:</h2>
+
+<h2>Changes to existing API:</h2>
+<ul>
+</pre>
+<li><b>Tracing Helpers</b>: The organization of helpers for both pcap and ascii
+tracing has been reworked.  Instead of each device and stack helper 
+re-implementing trace enable methods, classes have been developed to implement
+user-level tracing in a consistent way; and device and stack helpers use those
+classes to provide tracing functionality.<br>
+In addition to consistent operation across all helpers, the object name service
+has been integrated into the trace file naming scheme.<br>
+The primary user-visible results of this change are that trace-related functions
+have been changed from static functions to method calls; and a new object has
+been developed to hold streams for ascii traces.<br>
+The implementation of the helper code has been designed also to provide 
+functionality to make it easier for sophisticated users to hook traces of 
+various kinds and write results to (file) streams.
+Before:
+<pre>
+CsmaHelper::EnablePcapAll ();
+
+std::ofstream ascii;
+ascii.open ("csma-one-subnet.tr", std::ios_base::binary | std::ios_base::out);
+CsmaHelper::EnableAsciiAll (ascii);
+</pre>
+After:
+<pre>
+CsmaHelper csmaHelper;
+csmaHelper.EnablePcapAll ();
+
+AsciiTraceHelper ascii;
+csma.EnableAsciiAll (ascii.CreateFileStream ("csma-one-subnet.tr"));
+</pre>
+
 <hr>
 <h1>Changes from ns-3.6 to ns-3.7</h1>