diff --git a/bindings/python/ns3/__init__.py b/bindings/python/ns3/__init__.py
index 943a01575..cd1f9ec82 100644
--- a/bindings/python/ns3/__init__.py
+++ b/bindings/python/ns3/__init__.py
@@ -1,4 +1,7 @@
 
 from _ns3 import *
 
+import atexit
+atexit.register(Simulator.Destroy)
+del atexit
 
diff --git a/bindings/python/wscript b/bindings/python/wscript
index 69825e2b6..403cbca07 100644
--- a/bindings/python/wscript
+++ b/bindings/python/wscript
@@ -70,12 +70,21 @@ def configure(conf):
         conf.report_optional_feature("python", "Python Bindings", False, str(ex))
         return
 
-    ## Check for pybindgen
+    # Check for the location of pybindgen
+    if Options.options.with_pybindgen is not None:
+        if os.path.isdir(Options.options.with_pybindgen):
+            conf.check_message("pybindgen location", '', True, ("%s (given)" % Options.options.with_pybindgen))
+            conf.env['WITH_PYBINDGEN'] = os.path.abspath(Options.options.with_pybindgen)
+    else:
+        pybindgen_dir = os.path.join('..', "pybindgen")
+        if os.path.isdir(pybindgen_dir):
+            conf.check_message("pybindgen location", '', True, ("%s (guessed)" % pybindgen_dir))
+            conf.env['WITH_PYBINDGEN'] = os.path.abspath(pybindgen_dir)
+        del pybindgen_dir
+    if not conf.env['WITH_PYBINDGEN']:
+        conf.check_message("pybindgen location", '', False)
 
-    no_net = False
-    if Options.options.with_pybindgen:
-        conf.env['WITH_PYBINDGEN'] = os.path.abspath(Options.options.with_pybindgen)
-        no_net = True
+    # Check for pybindgen
 
     set_pybindgen_pythonpath(conf.env)
 
@@ -100,10 +109,9 @@ def configure(conf):
             Logs.warn("pybindgen (found %s) is too old (need %s)" %
                     (pybindgen_version_str,
                      '.'.join([str(x) for x in REQUIRED_PYBINDGEN_VERSION])))
-            if no_net or not fetch_pybindgen(conf):
-                conf.report_optional_feature("python", "Python Bindings", False,
-                                             "PyBindGen too old and newer version could not be retrieved")
-                return
+            conf.report_optional_feature("python", "Python Bindings", False,
+                                         "PyBindGen too old and newer version could not be retrieved")
+            return
 
     ## If all has gone well, we finally enable the Python bindings
     conf.env['ENABLE_PYTHON_BINDINGS'] = True
diff --git a/doc/WifiArchitecture.dia b/doc/WifiArchitecture.dia
new file mode 100644
index 000000000..71deb6830
Binary files /dev/null and b/doc/WifiArchitecture.dia differ
diff --git a/doc/WifiArchitecture.png b/doc/WifiArchitecture.png
new file mode 100644
index 000000000..3bed78bce
Binary files /dev/null and b/doc/WifiArchitecture.png differ
diff --git a/doc/manual/Makefile b/doc/manual/Makefile
index 7dc11ceef..6775f1f7a 100644
--- a/doc/manual/Makefile
+++ b/doc/manual/Makefile
@@ -7,6 +7,7 @@ CSS = --css-include=manual.css
 SPLIT = --split section
 
 FIGURES = figures
+DOC_FIGURES = ..
 VPATH = $(FIGURES)
 
 IMAGES_EPS = \
@@ -18,7 +19,8 @@ IMAGES_EPS = \
 	$(FIGURES)/sockets-overview.eps \
 	$(FIGURES)/testbed.eps \
 	$(FIGURES)/emulated-channel.eps \
-	$(FIGURES)/snir.eps
+	$(FIGURES)/snir.eps \
+	$(DOC_FIGURES)/WifiArchitecture.eps
 
 IMAGES_PNG = ${IMAGES_EPS:.eps=.png}
 IMAGES_PDF = ${IMAGES_EPS:.eps=.pdf}
diff --git a/doc/manual/wifi.texi b/doc/manual/wifi.texi
index cd200f4d1..29f1e451e 100644
--- a/doc/manual/wifi.texi
+++ b/doc/manual/wifi.texi
@@ -83,6 +83,11 @@ is no model for cross-channel interference or coupling.
 The source code for the Wifi NetDevice lives in the directory
 @code{src/devices/wifi}.
 
+@float Figure,fig:WifiArchitecture
+@caption{Wifi NetDevice architecture.}
+@image{../WifiArchitecture,5in}
+@end float
+
 @node Using the WifiNetDevice
 @section Using the WifiNetDevice
 
diff --git a/regression.py b/regression.py
index 037c8d96e..d92683af1 100644
--- a/regression.py
+++ b/regression.py
@@ -9,6 +9,7 @@ import urllib
 import Build
 import Options
 import Utils
+import Task
 
 # local modules
 import wutils
@@ -21,106 +22,6 @@ def dev_null():
         return open("/dev/null", "w")
 
 
-### Regression testing
-class Regression(object):
-    def __init__(self, testdir, reference_traces):
-        self.testdir = testdir
-        self.reference_traces = reference_traces
-        self.env = Build.bld.env
-
-    def run_test(self, verbose, generate, testName, arguments=[], pyscript=None, refTestName=None):
-        """
-        @param verbose: enable verbose execution
-
-        @param generate: generate new traces instead of comparing with the reference
-
-        @param testName: name of the test
-
-        @arguments: list of extra parameters to pass to the program to be tested
-
-        @pyscript: if not None, the test is written in Python and this
-        parameter contains the path to the python script, relative to
-        the project root dir
-
-        @param refTestName: if not None, this is the name of the directory under refDirName
-        that contains the reference traces. Otherwise "refDirname/testName + .ref" is used.
-
-        """
-        if not isinstance(arguments, list):
-            raise TypeError
-        
-        if refTestName is None:
-            refTestDirName = os.path.join(self.reference_traces, (testName + ".ref"))
-        else:
-            refTestDirName = os.path.join(self.reference_traces, refTestName)
-
-        if not os.path.exists(self.reference_traces):
-            print"No reference trace repository"
-            return 1
-
-        if generate:
-            if not os.path.exists(refTestDirName):
-                print "creating new " + refTestDirName
-                os.mkdir(refTestDirName)
-
-            if pyscript is None:
-                tmpl = "%s"
-                for arg in arguments:
-                    tmpl = tmpl + " " + arg
-                wutils.run_program(testName, tmpl, cwd=refTestDirName)
-            else:
-                argv = [self.env['PYTHON'], os.path.join(Options.cwd_launch, *os.path.split(pyscript))] + arguments
-                wutils.run_argv(argv, cwd=refTestDirName)
-            print "Remember to commit " + refTestDirName
-            return 0
-        else:
-            if not os.path.exists(refTestDirName):
-                print "Cannot locate reference traces in " + refTestDirName
-                return 1
-
-            if refTestName is None:
-                traceDirName = testName + ".ref"
-            else:
-                traceDirName = refTestName
-            traceDirName = os.path.join('regression', 'traces', traceDirName)
-
-            try:
-                shutil.rmtree(traceDirName)
-            except OSError:
-                pass
-            os.mkdir(traceDirName)
-
-            if pyscript is None:
-                wutils.run_program(testName,
-                                   command_template=wutils.get_command_template(*arguments),
-                                   cwd=traceDirName)
-            else:
-                argv = [self.env['PYTHON'], os.path.join('..', '..', '..', *os.path.split(pyscript))] + arguments
-                wutils.run_argv(argv, cwd=traceDirName)
-
-            if verbose:
-                #diffCmd = "diff traces " + refTestDirName + " | head"
-                diffCmd = subprocess.Popen([self.env['DIFF'], traceDirName, refTestDirName],
-                                           stdout=subprocess.PIPE)
-                headCmd = subprocess.Popen("head", stdin=diffCmd.stdout)
-                rc2 = headCmd.wait()
-                diffCmd.stdout.close()
-                rc1 = diffCmd.wait()
-                rc = rc1 or rc2
-            else:
-                rc = subprocess.Popen([self.env['DIFF'], traceDirName, refTestDirName], stdout=dev_null()).wait()
-            if rc:
-                print "----------"
-                print "Traces differ in test: test-" + testName
-                print "Reference traces in directory: regression/" + refTestDirName
-                print "Traces in directory: traces"
-                print "Rerun regression test as: " + \
-                    "\"./waf --regression --regression-tests=test-" + testName + "\""
-                print "Then do \"diff -u regression/" + refTestDirName + " regression/" + traceDirName +\
-                    "\" for details"
-                print "----------"
-            return rc
-
 def _find_tests(testdir):
     """Return a list of test modules in the test directory
 
@@ -136,7 +37,161 @@ def _find_tests(testdir):
     tests.sort()
     return tests
 
-def run_regression(reference_traces):
+
+class regression_test_task(Task.TaskBase):
+    after = 'cc cxx cc_link cxx_link'
+    color = 'BLUE'
+
+    def __init__(self, env, test_name, test_scripts_dir, build_traces_dir, reference_traces):
+        super(regression_test_task, self).__init__()
+        self.env = env
+        self.test_name = test_name
+        self.test_scripts_dir = test_scripts_dir
+        self.build_traces_dir = build_traces_dir
+        self.reference_traces_dir = reference_traces
+
+    def __str__(self):
+        return 'regression-test (%s)\n' % self.test_name
+
+    def run(self):
+        """Run a single test"""
+        sys.path.insert(0, self.test_scripts_dir)
+        try:
+            mod = __import__(self.test_name, globals(), locals(), [])
+        finally:
+            sys.path.remove(self.test_scripts_dir)
+
+        assert self.test_name.startswith('test-')
+        short_name = self.test_name[len('test-'):]
+
+        trace_dir_name = getattr(mod, "trace_dir_name", None)
+        if trace_dir_name is None:
+            trace_dir_name = "%s.ref" % short_name
+        trace_output_path = os.path.join(self.build_traces_dir, trace_dir_name)
+        reference_traces_path = os.path.join(self.reference_traces_dir, trace_dir_name)
+
+        if hasattr(mod, 'get_arguments'):
+            arguments = mod.get_arguments(self.env, '..')
+        else:
+            arguments = getattr(mod, "arguments", [])
+
+        pyscript = getattr(mod, "pyscript", None)
+        if pyscript:
+            is_pyscript = True
+            program = pyscript
+        else:
+            is_pyscript = False
+            program = getattr(mod, "program", short_name)
+
+        if hasattr(mod, 'may_run'):
+            reason_cannot_run = mod.may_run(self.env)
+        else:
+            reason_cannot_run = None
+        if reason_cannot_run:
+            print "SKIP %s (%s)" % (self.test_name, reason_cannot_run)
+            self.result = None
+            return 0
+
+        if Options.options.regression_generate:
+            # clean the target dir
+            shutil.rmtree(reference_traces_path, ignore_errors=True)
+            os.makedirs(reference_traces_path)
+            result = self.run_reference_generate(reference_traces_path, program, arguments, is_pyscript)
+            if result == 0:
+                print "GENERATE " + self.test_name
+            else:
+                print "GENERATE FAIL " + self.test_name
+        else:
+            # clean the target dir
+            shutil.rmtree(trace_output_path, ignore_errors=True)
+            os.makedirs(trace_output_path)
+            # run it
+            result = self.run_reference_test(reference_traces_path, trace_output_path, program, arguments, is_pyscript)
+            if result == 0:
+                print "PASS " + self.test_name
+            else:
+                print "FAIL " + self.test_name
+        self.result = result
+        return 0
+
+    def run_reference_test(self, reference_traces_path, trace_output_path, program, arguments, is_pyscript):
+        if not os.path.exists(reference_traces_path):
+            print "Cannot locate reference traces in " + reference_traces_path
+            return 1
+
+        if is_pyscript:
+            script = os.path.abspath(os.path.join('..', *os.path.split(program)))
+            argv = [self.env['PYTHON'], script] + arguments
+            wutils.run_argv(argv, cwd=trace_output_path)
+        else:
+            wutils.run_program(program,
+                               command_template=wutils.get_command_template(self.env, arguments),
+                               cwd=trace_output_path)
+
+        if Options.options.verbose:
+            #diffCmd = "diff traces " + refTestDirName + " | head"
+            diffCmd = subprocess.Popen([self.env['DIFF'], trace_output_path, reference_traces_path],
+                                       stdout=subprocess.PIPE)
+            headCmd = subprocess.Popen("head", stdin=diffCmd.stdout)
+            rc2 = headCmd.wait()
+            diffCmd.stdout.close()
+            rc1 = diffCmd.wait()
+            rc = rc1 or rc2
+        else:
+            rc = subprocess.Popen([self.env['DIFF'], trace_output_path, reference_traces_path], stdout=dev_null()).wait()
+        if rc:
+            print "----------"
+            print "Traces differ in test: ", self.test_name
+            print "Reference traces in directory: " + reference_traces_path
+            print "Traces in directory: " + trace_output_path
+            print "Run the following command for details:"
+            print "\tdiff -u %s %s" % (reference_traces_path, trace_output_path)
+            print "----------"
+        return rc
+
+
+    def run_reference_generate(self, trace_output_path, program, arguments, is_pyscript):
+        if is_pyscript:
+            script = os.path.abspath(os.path.join('..', *os.path.split(program)))
+            argv = [self.env['PYTHON'], script] + arguments
+            retval = wutils.run_argv(argv, cwd=trace_output_path)
+        else:
+            retval = wutils.run_program(program,
+                                        command_template=wutils.get_command_template(self.env, arguments),
+                                        cwd=trace_output_path)
+        return retval
+
+
+class regression_test_collector_task(Task.TaskBase):
+    after = 'regression_test_task'
+    color = 'BLUE'
+
+    def __init__(self, test_tasks):
+        super(regression_test_collector_task, self).__init__()
+        self.test_tasks = test_tasks
+
+    def __str__(self):
+        return 'regression-test-collector\n'
+
+    def run(self):
+        failed_tests = [test for test in self.test_tasks if test.result is not None and test.result != 0]
+        skipped_tests = [test for test in self.test_tasks if test.result is None]
+        print "Regression testing summary:"
+        if skipped_tests:
+            print "SKIP: %i of %i tests have been skipped (%s)" % (
+                len(skipped_tests), len(self.test_tasks),
+                ', '.join([test.test_name for test in skipped_tests]))
+        if failed_tests:
+            print "FAIL: %i of %i tests have failed (%s)" % (
+                len(failed_tests), len(self.test_tasks),
+                ', '.join([test.test_name for test in failed_tests]))
+            return 1
+        else:
+            print "PASS: %i of %i tests passed" % (len(self.test_tasks) - len(skipped_tests),
+                                                   len(self.test_tasks))
+            return 0
+
+def run_regression(bld, reference_traces):
     """Execute regression tests.  Called with cwd set to the 'regression' subdir of ns-3.
 
     @param reference_traces: reference traces directory.
@@ -148,57 +203,18 @@ def run_regression(reference_traces):
         print "Tests directory does not exist"
         sys.exit(3)
 
-    sys.path.append(testdir)
-    sys.modules['tracediff'] = Regression(testdir, reference_traces)
-
     if Options.options.regression_tests:
         tests = Options.options.regression_tests.split(',')
     else:
         tests = _find_tests(testdir)
 
-    print "========== Running Regression Tests =========="
-    env = Build.bld.env
-
     if not os.path.exists(reference_traces):
         print "Reference traces directory (%s) does not exist" % reference_traces
         return 3
     
-    bad = []
-
+    test_scripts_dir = bld.path.find_dir('regression/tests').abspath()
+    build_traces_dir = bld.path.find_or_declare('regression/traces').abspath(bld.env)
+    tasks = []
     for test in tests:
-        try:
-            result = _run_regression_test(test)
-            if result == 0:
-                if Options.options.regression_generate:
-                    print "GENERATE " + test
-                else:
-                    print "PASS " + test
-            else:
-                bad.append(test)
-                print "FAIL " + test
-        except NotImplementedError:
-            print "SKIP " + test            
-
-    return (len(bad) > 0)
-
-
-def _run_regression_test(test):
-    """Run a single test.
-
-    Arguments:
-    test -- the name of the test
-    """
-    traces_dir = os.path.join("regression", "traces")
-    if os.path.exists(traces_dir):
-        files = os.listdir(traces_dir)
-        for file in files:
-            if file == '.' or file == '..':
-                continue
-            shutil.rmtree(os.path.join("traces", file), ignore_errors=True)
-    else:
-        os.mkdir(traces_dir)
-    
-    mod = __import__(test, globals(), locals(), [])
-    return mod.run(verbose=(Options.options.verbose > 0),
-                   generate=Options.options.regression_generate)
-
+        tasks.append(regression_test_task(bld.env, test, test_scripts_dir, build_traces_dir, reference_traces))
+    regression_test_collector_task(tasks)
diff --git a/regression/tests/test-csma-bridge.py b/regression/tests/test-csma-bridge.py
index 67a1b4475..e0905d33e 100644
--- a/regression/tests/test-csma-bridge.py
+++ b/regression/tests/test-csma-bridge.py
@@ -2,15 +2,13 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import sys
-import tracediff
+import os.path
 
-def run(verbose, generate):
-    """Execute a test."""
-    if tracediff.env['ENABLE_PYTHON_BINDINGS']:
-        return tracediff.run_test(verbose, generate,
-                                  "csma-bridge", pyscript=os.path.join('examples', 'csma-bridge.py'))
+def may_run(env):
+    """Returns 0 when it can run, return non-zero or string (reason) when it cannot run"""
+    if env['ENABLE_PYTHON_BINDINGS']:
+        return 0
     else:
-        print >> sys.stderr, "Skipping csma-bridge: Python bindings not available."
-        raise NotImplementedError
+        return "Python bindings not available."
+
+pyscript = os.path.join('examples', 'csma-bridge.py')
diff --git a/regression/tests/test-csma-broadcast.py b/regression/tests/test-csma-broadcast.py
index b34d136dc..4c77bc125 100644
--- a/regression/tests/test-csma-broadcast.py
+++ b/regression/tests/test-csma-broadcast.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "csma-broadcast")
diff --git a/regression/tests/test-csma-multicast.py b/regression/tests/test-csma-multicast.py
index c128f273b..b8afea9f8 100644
--- a/regression/tests/test-csma-multicast.py
+++ b/regression/tests/test-csma-multicast.py
@@ -1,12 +1,3 @@
 #! /usr/bin/env python
 
 """Generic trace-comparison-type regression test."""
-
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "csma-multicast")
diff --git a/regression/tests/test-csma-one-subnet.py b/regression/tests/test-csma-one-subnet.py
index b5d4645fc..4c77bc125 100644
--- a/regression/tests/test-csma-one-subnet.py
+++ b/regression/tests/test-csma-one-subnet.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "csma-one-subnet")
diff --git a/regression/tests/test-csma-packet-socket.py b/regression/tests/test-csma-packet-socket.py
index ca71d7b9d..4c77bc125 100644
--- a/regression/tests/test-csma-packet-socket.py
+++ b/regression/tests/test-csma-packet-socket.py
@@ -2,12 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate,
-        "csma-packet-socket")
diff --git a/regression/tests/test-csma-ping.py b/regression/tests/test-csma-ping.py
index 4cae6945f..4c77bc125 100644
--- a/regression/tests/test-csma-ping.py
+++ b/regression/tests/test-csma-ping.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "csma-ping")
diff --git a/regression/tests/test-csma-raw-ip-socket.py b/regression/tests/test-csma-raw-ip-socket.py
index 3c45b023d..4c77bc125 100644
--- a/regression/tests/test-csma-raw-ip-socket.py
+++ b/regression/tests/test-csma-raw-ip-socket.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "csma-raw-ip-socket")
diff --git a/regression/tests/test-csma-star.py b/regression/tests/test-csma-star.py
index 4e39f0443..4c77bc125 100644
--- a/regression/tests/test-csma-star.py
+++ b/regression/tests/test-csma-star.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "csma-star")
diff --git a/regression/tests/test-dynamic-global-routing.py b/regression/tests/test-dynamic-global-routing.py
index 9a7ff13a3..4c77bc125 100644
--- a/regression/tests/test-dynamic-global-routing.py
+++ b/regression/tests/test-dynamic-global-routing.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "dynamic-global-routing")
diff --git a/regression/tests/test-global-routing-slash32.py b/regression/tests/test-global-routing-slash32.py
index bf613b6e1..4c77bc125 100644
--- a/regression/tests/test-global-routing-slash32.py
+++ b/regression/tests/test-global-routing-slash32.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "global-routing-slash32")
diff --git a/regression/tests/test-ns2-mob.py b/regression/tests/test-ns2-mob.py
index 6f5503590..7ed54ce01 100644
--- a/regression/tests/test-ns2-mob.py
+++ b/regression/tests/test-ns2-mob.py
@@ -2,11 +2,12 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
+import os.path
 
-def run(verbose, generate):
-    """Execute a test."""
-    arguments = ["../../../samples/ns2-mob.tr", "out.tr"]
-    return tracediff.run_test(verbose, generate, "main-ns2-mob", arguments=arguments)
+program = "main-ns2-mob"
+
+def get_arguments(env, top_dir):
+    ns2_tracefile = os.path.abspath(os.path.join(top_dir, "samples", "ns2-mob.tr"))
+    return [ns2_tracefile, "out.tr"]
+
+trace_dir_name = "main-ns2-mob.ref"
diff --git a/regression/tests/test-realtime-udp-echo.py b/regression/tests/test-realtime-udp-echo.py
index b1344cdad..4c77bc125 100644
--- a/regression/tests/test-realtime-udp-echo.py
+++ b/regression/tests/test-realtime-udp-echo.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "realtime-udp-echo")
diff --git a/regression/tests/test-second.py b/regression/tests/test-second.py
index 56dd9b5e5..4c77bc125 100644
--- a/regression/tests/test-second.py
+++ b/regression/tests/test-second.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "second")
diff --git a/regression/tests/test-simple-error-model.py b/regression/tests/test-simple-error-model.py
index 6a9dece25..4c77bc125 100644
--- a/regression/tests/test-simple-error-model.py
+++ b/regression/tests/test-simple-error-model.py
@@ -2,12 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate,
-        "simple-error-model")
diff --git a/regression/tests/test-simple-global-routing.py b/regression/tests/test-simple-global-routing.py
index 271fb8f85..4c77bc125 100644
--- a/regression/tests/test-simple-global-routing.py
+++ b/regression/tests/test-simple-global-routing.py
@@ -2,12 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate,
-        "simple-global-routing")
diff --git a/regression/tests/test-simple-point-to-point-olsr.py b/regression/tests/test-simple-point-to-point-olsr.py
index b581b876f..4c77bc125 100644
--- a/regression/tests/test-simple-point-to-point-olsr.py
+++ b/regression/tests/test-simple-point-to-point-olsr.py
@@ -2,12 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate,
-        "simple-point-to-point-olsr")
diff --git a/regression/tests/test-static-routing-slash32.py b/regression/tests/test-static-routing-slash32.py
index 6ac8550cc..4c77bc125 100644
--- a/regression/tests/test-static-routing-slash32.py
+++ b/regression/tests/test-static-routing-slash32.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "static-routing-slash32")
diff --git a/regression/tests/test-tcp-large-transfer.py b/regression/tests/test-tcp-large-transfer.py
index 3078fa69d..4c77bc125 100644
--- a/regression/tests/test-tcp-large-transfer.py
+++ b/regression/tests/test-tcp-large-transfer.py
@@ -2,12 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate,
-        "tcp-large-transfer")
diff --git a/regression/tests/test-tcp-nsc-lfn.py b/regression/tests/test-tcp-nsc-lfn.py
index bff77dfd0..b58d4b227 100644
--- a/regression/tests/test-tcp-nsc-lfn.py
+++ b/regression/tests/test-tcp-nsc-lfn.py
@@ -2,32 +2,25 @@
 
 """Trace-comparison-type regression test for the Network Simulation Cradle."""
 
-import os
-import shutil
-import sys
-import tracediff
 import platform
 
 
-def run(verbose, generate):
-    """Run a Network Simulation Cradle test involving two TCP streams."""
-
-    if not tracediff.env['ENABLE_NSC']:
-        print >>sys.stderr, "Skipping tcp-nsc-lfn: NSC not available."
-        raise NotImplementedError
-
-    testName = "tcp-nsc-lfn"
-    arguments = ["--ns3::OnOffApplication::DataRate=40000", "--runtime=20"]
-    platform_bits = platform.architecture()[0]
-    
-    if platform_bits == "64bit":
-        traceDirName = testName + "_64bit.ref"
-    elif platform_bits == "32bit":
-        traceDirName = testName + "_32bit.ref"
+def may_run(env):
+    if not env['NSC_ENABLED']:
+        return "NSC not available"
     else:
-        # Something unexpected. How should we signal an error here? Rasing a
-        # string might not be the best idea?
-        raise "Unknown architecture, not 64 or 32 bit?"
+        return 0
+
+
+platform_bits = platform.architecture()[0]
+if platform_bits == "64bit":
+    trace_dir_name = "tcp-nsc-lfn_64bit.ref"
+elif platform_bits == "32bit":
+    trace_dir_name = "tcp-nsc-lfn_32bit.ref"
+else:
+    raise AssertionError("Unknown architecture, not 64 or 32 bit?")
+del platform_bits
+
+arguments = ["--ns3::OnOffApplication::DataRate=40000", "--runtime=20"]
+
 
-    return tracediff.run_test(verbose, generate,
-        testName, arguments=arguments, refTestName=traceDirName)
diff --git a/regression/tests/test-third.py b/regression/tests/test-third.py
index 582e8b44a..4c77bc125 100644
--- a/regression/tests/test-third.py
+++ b/regression/tests/test-third.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "third")
diff --git a/regression/tests/test-udp-echo.py b/regression/tests/test-udp-echo.py
index 6fe71055a..4c77bc125 100644
--- a/regression/tests/test-udp-echo.py
+++ b/regression/tests/test-udp-echo.py
@@ -2,11 +2,3 @@
 
 """Generic trace-comparison-type regression test."""
 
-import os
-import shutil
-import tracediff
-
-def run(verbose, generate):
-    """Execute a test."""
-    #print tracediff.env
-    return tracediff.run_test(verbose, generate, "udp-echo")
diff --git a/regression/tests/test-wifi-wired-bridging.py b/regression/tests/test-wifi-wired-bridging.py
index 9ff8ae0e5..263c2c892 100644
--- a/regression/tests/test-wifi-wired-bridging.py
+++ b/regression/tests/test-wifi-wired-bridging.py
@@ -2,11 +2,5 @@
 
 """Compare that Wifi-Wired Bridging generates correct traces."""
 
-import os
-import shutil
-import tracediff
+arguments = ["--SendIp=0"]
 
-def run(verbose, generate):
-    """Execute a test."""
-
-    return tracediff.run_test(verbose, generate, "wifi-wired-bridging", ["--SendIp=0"])
diff --git a/samples/wscript b/samples/wscript
index 5286f56c9..deba5598e 100644
--- a/samples/wscript
+++ b/samples/wscript
@@ -19,7 +19,7 @@ def build(bld):
     obj = bld.create_ns3_program('main-test')
     obj.source = 'main-test.cc'
 
-    if bld.env['ENABLE_THREADING']:
+    if bld.env['ENABLE_THREADING'] and bld.env["ENABLE_REAL_TIME"]:
         obj = bld.create_ns3_program('main-test-sync')
         obj.source = 'main-test-sync.cc'
 
diff --git a/src/core/wscript b/src/core/wscript
index cdcd0bc31..a15b6fee6 100644
--- a/src/core/wscript
+++ b/src/core/wscript
@@ -1,6 +1,6 @@
 ## -*- Mode: python; py-indent-offset: 4; indent-tabs-mode: nil; coding: utf-8; -*-
 import sys
-
+import Options
 
 def configure(conf):
     if conf.check(header_name='stdlib.h'):
@@ -9,9 +9,33 @@ def configure(conf):
 
     conf.check(header_name='signal.h', define_name='HAVE_SIGNAL_H')
 
-    conf.check(lib='rt', uselib='RT', define_name='HAVE_RT')
+    # Check for POSIX threads
+    test_env = conf.env.copy()
+    if Options.platform != 'darwin':
+        test_env.append_value('LINKFLAGS', '-pthread')
+        test_env.append_value('CXXFLAGS', '-pthread')
+        test_env.append_value('CCFLAGS', '-pthread')
+    fragment = r"""
+#include <pthread.h>
+int main ()
+{
+   pthread_mutex_t m;
+   pthread_mutex_init (&m, NULL);
+   return 0;
+}
+"""
+    have_pthread = conf.check(header_name='pthread.h', define_name='HAVE_PTHREAD_H',
+                              env=test_env, fragment=fragment,
+                              errmsg='Could not find pthread support (build/config.log for details)',
+                              mandatory=False)
+    if have_pthread:
+        # darwin accepts -pthread but prints a warning saying it is ignored
+        if Options.platform != 'darwin':
+            conf.env['CXXFLAGS_PTHREAD'] = '-pthread'
+            conf.env['CCFLAGS_PTHREAD'] = '-pthread'
+            conf.env['LINKFLAGS_PTHREAD'] = '-pthread'
 
-    conf.env['ENABLE_THREADING'] = conf.check(header_name='pthread.h', define_name='HAVE_PTHREAD_H')
+    conf.env['ENABLE_THREADING'] = have_pthread
 
     conf.report_optional_feature("Threading", "Threading Primitives",
                                  conf.env['ENABLE_THREADING'],
@@ -55,7 +79,6 @@ def build(bld):
         'callback.cc',
         'names.cc',
         ]
-    core.uselib = 'RT'
 
     headers = bld.new_task_gen('ns3header')
     headers.module = 'core'
@@ -117,6 +140,7 @@ def build(bld):
             'unix-system-mutex.cc',
             'unix-system-condition.cc',
             ])
+        core.uselib = 'PTHREAD'
         headers.source.extend([
                 'system-mutex.h',
                 'system-thread.h',
diff --git a/src/devices/emu/wscript b/src/devices/emu/wscript
index 8400d1288..53761d516 100644
--- a/src/devices/emu/wscript
+++ b/src/devices/emu/wscript
@@ -1,11 +1,16 @@
 ## -*- Mode: python; py-indent-offset: 4; indent-tabs-mode: nil; coding: utf-8; -*-
 
 def configure(conf):
-    conf.env['ENABLE_EMU'] = conf.check(header_name='linux/if_ether.h',
-                                        define_name='HAVE_IF_ETHER_H')
-    conf.report_optional_feature("EmuNetDevice", "Emulated Net Device",
-                                 conf.env['ENABLE_EMU'],
-                                 "<linux/if_ether.h> include not detected")
+    if conf.env['ENABLE_THREADING']:
+        conf.env['ENABLE_EMU'] = conf.check(header_name='linux/if_ether.h',
+                                            define_name='HAVE_IF_ETHER_H')
+        conf.report_optional_feature("EmuNetDevice", "Emulated Net Device",
+                                     conf.env['ENABLE_EMU'],
+                                     "<linux/if_ether.h> include not detected")
+    else:
+        conf.report_optional_feature("EmuNetDevice", "Emulated Net Device",
+                                     False,
+                                     "needs threading support which is not available")
 
 def build(bld):
     module = bld.create_ns3_module('emu', ['node'])
diff --git a/src/devices/wifi/wifi.h b/src/devices/wifi/wifi.h
index 3ced79bf5..38df2a3a4 100644
--- a/src/devices/wifi/wifi.h
+++ b/src/devices/wifi/wifi.h
@@ -105,4 +105,7 @@
  * Finally, we provide access to the per-remote-station SLRC couter that
  * indications the number of retransmissions of data.  Changes to this 
  * counter are traced using the ns3::WifiRemoteStation::m_slrc source.
+ *
+ * \subsection wifil2stack Layer 2 Stack Overview
+ * \image html WifiArchitecture.png "Overview of the Wifi L2 sublayers traversed for transmitting and receiving a packet"
  */
diff --git a/src/internet-stack/wscript b/src/internet-stack/wscript
index 9f2ef127f..b2989d18e 100644
--- a/src/internet-stack/wscript
+++ b/src/internet-stack/wscript
@@ -29,16 +29,22 @@ def configure(conf):
     #    conf.check_tool('flex bison')
     #    conf.check(lib='fl', mandatory=True)
 
-    if not Options.options.with_nsc:
-        conf.report_optional_feature("nsc", "Network Simulation Cradle", False,
-                                     "--with-nsc configure option not given")
-	return
-
-    #check_nsc_buildutils()
+    # Check for the location of NSC
     if Options.options.with_nsc:
-        if not os.path.isdir(Options.options.with_nsc):
-            raise Utils.WafError("--with-nsc nsc path %r does not exist" % Options.options.with_nsc)
-        conf.env['WITH_NSC'] = Options.options.with_nsc
+        if os.path.isdir(Options.options.with_nsc):
+            conf.check_message("NSC location", '', True, ("%s (given)" % Options.options.with_nsc))
+            conf.env['WITH_NSC'] = os.path.abspath(Options.options.with_nsc)
+    else:
+        nsc_dir = os.path.join('..', "nsc")
+        if os.path.isdir(nsc_dir):
+            conf.check_message("NSC location", '', True, ("%s (guessed)" % nsc_dir))
+            conf.env['WITH_NSC'] = os.path.abspath(nsc_dir)
+        del nsc_dir
+    if not conf.env['WITH_NSC']:
+        conf.check_message("NSC location", '', False)
+        conf.report_optional_feature("nsc", "Network Simulation Cradle", False,
+                                     "NSC not found (see option --with-nsc)")
+	return
 
     arch = os.uname()[4]
     ok = False
diff --git a/src/simulator/wscript b/src/simulator/wscript
index 1824bd486..e4ae5c0b8 100644
--- a/src/simulator/wscript
+++ b/src/simulator/wscript
@@ -33,9 +33,14 @@ def configure(conf):
 
     conf.write_config_header('ns3/simulator-config.h')
 
-    conf.report_optional_feature("RealTime", "Real Time Simulator",
-                                 conf.env['ENABLE_THREADING'],
-                                 "threading not enabled")
+    if not conf.check(lib='rt', uselib='RT', define_name='HAVE_RT'):
+        conf.report_optional_feature("RealTime", "Real Time Simulator",
+                                     False, "librt is not available")
+    else:
+        conf.report_optional_feature("RealTime", "Real Time Simulator",
+                                     conf.env['ENABLE_THREADING'],
+                                     "threading not enabled")
+        conf.env["ENABLE_REAL_TIME"] = conf.env['ENABLE_THREADING']
 
 
 def build(bld):
@@ -101,7 +106,7 @@ def build(bld):
             'cairo-wideint-private.h',
             ])
 
-    if env['ENABLE_THREADING']:
+    if env['ENABLE_REAL_TIME']:
         headers.source.extend([
                 'realtime-simulator-impl.h',
                 'wall-clock-synchronizer.h',
@@ -110,4 +115,6 @@ def build(bld):
                 'realtime-simulator-impl.cc',
                 'wall-clock-synchronizer.cc',
                 ])
+        sim.uselib = 'RT'
+
 
diff --git a/src/wscript b/src/wscript
index df774e0e8..d91e6b8cc 100644
--- a/src/wscript
+++ b/src/wscript
@@ -9,10 +9,7 @@ import TaskGen
 import Task
 import Options
 import Build
-#import Action
-#import Common
-#import Object
-#import Params
+from Utils import md5
 
 
 all_modules = (
@@ -177,6 +174,21 @@ class gen_ns3_module_header_task(Task.Task):
         outfile.close()
         return 0
 
+    def sig_explicit_deps(self):
+        m = md5()
+        m.update('\n'.join([node.abspath(self.env) for node in self.inputs]))
+        return m.digest()
+
+    def unique_id(self):
+        try:
+            return self.uid
+        except AttributeError:
+            "this is not a real hot zone, but we want to avoid surprizes here"
+            m = md5()
+            m.update("ns-3-module-header-%s" % self.module)
+            self.uid = m.digest()
+            return self.uid
+
 
 class ns3moduleheader_taskgen(TaskGen.task_gen):
     """
diff --git a/wscript b/wscript
index 6197d4304..2c372ef1b 100644
--- a/wscript
+++ b/wscript
@@ -42,6 +42,14 @@ APPNAME = 'ns'
 wutils.VERSION = VERSION
 wutils.APPNAME = APPNAME
 
+#
+# The last part of the path name to use to find the regression traces.  The
+# path will be APPNAME + '-' + VERSION + REGRESSION_SUFFIX, e.g.,
+# ns-3-dev-ref-traces
+#
+REGRESSION_SUFFIX = "-ref-traces"
+
+
 # these variables are mandatory ('/' are converted automatically)
 srcdir = '.'
 blddir = 'build'
@@ -193,8 +201,19 @@ def configure(conf):
     variant_env = conf.env.copy()
     variant_name = Options.options.build_profile
 
+    # Check for the location of regression reference traces
     if Options.options.regression_traces is not None:
-        variant_env['REGRESSION_TRACES'] = os.path.abspath(Options.options.regression_traces)
+        if os.path.isdir(Options.options.regression_traces):
+            conf.check_message("regression traces location", '', True, ("%s (given)" % Options.options.regression_traces))
+            variant_env['REGRESSION_TRACES'] = os.path.abspath(Options.options.regression_traces)
+    else:
+        traces = os.path.join('..', "%s-%s%s" % (APPNAME, VERSION, REGRESSION_SUFFIX))
+        if os.path.isdir(traces):
+            conf.check_message("regression reference traces", '', True, ("%s (guessed)" % traces))
+            variant_env['REGRESSION_TRACES'] = os.path.abspath(traces)
+        del traces
+    if not variant_env['REGRESSION_TRACES']:
+        conf.check_message("regression reference traces", '', False)
 
     if Options.options.enable_gcov:
         variant_name += '-gcov'
@@ -242,6 +261,8 @@ def configure(conf):
     # we cannot pull regression traces without mercurial
     conf.find_program('hg', var='MERCURIAL')
 
+    conf.find_program('valgrind', var='VALGRIND')
+
     # Write a summary of optional features status
     print "---- Summary of optional NS-3 features:"
     for (name, caption, was_enabled, reason_not_enabled) in conf.env['NS3_OPTIONAL_FEATURES']:
@@ -407,7 +428,7 @@ def build(bld):
 
     if Options.options.run:
         # Check that the requested program name is valid
-        program_name, dummy_program_argv = wutils.get_run_program(Options.options.run, get_command_template())
+        program_name, dummy_program_argv = wutils.get_run_program(Options.options.run, wutils.get_command_template(env))
 
         # When --run'ing a program, tell WAF to only build that program,
         # nothing more; this greatly speeds up compilation when all you
@@ -415,26 +436,6 @@ def build(bld):
         if not Options.options.compile_targets:
             Options.options.compile_targets = os.path.basename(program_name)
 
-
-
-def get_command_template(*arguments):
-    if Options.options.valgrind:
-        if Options.options.command_template:
-            raise Utils.WafError("Options --command-template and --valgrind are conflicting")
-        cmd = "valgrind --leak-check=full %s"
-    else:
-        cmd = Options.options.command_template or '%s'
-    for arg in arguments:
-        cmd = cmd + " " + arg
-    return cmd
-
-
-def shutdown():
-    env = Build.bld.env
-
-    if Options.commands['check']:
-        _run_waf_check()
-
     if Options.options.regression or Options.options.regression_generate:
         if not env['DIFF']:
             raise Utils.WafError("Cannot run regression tests: the 'diff' program is not installed.")
@@ -443,15 +444,20 @@ def shutdown():
         if not regression_traces:
             raise Utils.WafError("Cannot run regression tests: reference traces directory not given"
                                  " (--with-regression-traces configure option)")
-        retval = regression.run_regression(regression_traces)
-        if retval:
-            sys.exit(retval)
+        regression.run_regression(bld, regression_traces)
+
+
+def shutdown():
+    env = Build.bld.env
+
+    if Options.commands['check']:
+        _run_waf_check()
 
     if Options.options.lcov_report:
         lcov_report()
 
     if Options.options.run:
-        wutils.run_program(Options.options.run, get_command_template())
+        wutils.run_program(Options.options.run, wutils.get_command_template(env))
         raise SystemExit(0)
 
     if Options.options.pyrun:
@@ -476,7 +482,7 @@ def _run_waf_check():
         out.close()
 
     print "-- Running NS-3 C++ core unit tests..."
-    wutils.run_program('run-tests', get_command_template())
+    wutils.run_program('run-tests', wutils.get_command_template(env))
 
     if env['ENABLE_PYTHON_BINDINGS']:
         print "-- Running NS-3 Python bindings unit tests..."
diff --git a/wutils.py b/wutils.py
index 9cebb2a5d..4e29cfd07 100644
--- a/wutils.py
+++ b/wutils.py
@@ -26,11 +26,13 @@ TRACEBALL_SUFFIX = ".tar.bz2"
 
 
 
-def get_command_template(*arguments):
+def get_command_template(env, arguments=()):
     if Options.options.valgrind:
         if Options.options.command_template:
             raise Utils.WafError("Options --command-template and --valgrind are conflicting")
-        cmd = "valgrind --leak-check=full %s"
+        if not env['VALGRIND']:
+            raise Utils.WafError("valgrind is not installed")
+        cmd = env['VALGRIND'] + " --leak-check=full --error-exitcode=1 %s"
     else:
         cmd = Options.options.command_template or '%s'
     for arg in arguments: