Make sure that when multiple broadcast packets are queued on the same device in a short succession, that: 1) no backoff occurs if the frame arrives and the idle time >= DIFS or AIFSn (this is 'DCF immediate access', Figure 9-3 of IEEE 802.11-2012) 2) a backoff occurs for the second frame that arrives (this is clearly stated in Sec. More...

Inheritance diagram for DcfImmediateAccessBroadcastTestCase:

Collaboration diagram for DcfImmediateAccessBroadcastTestCase:

Public Member Functions
	DcfImmediateAccessBroadcastTestCase ()

virtual void	DoRun (void)
	Implementation to actually run this TestCase. More...

Public Member Functions inherited from ns3::TestCase
virtual	~TestCase ()
	Destructor. More...

std::string	GetName (void) const

Private Member Functions
void	NotifyPhyTxBegin (Ptr< const Packet > p)

void	SendOnePacket (Ptr< WifiNetDevice > dev)

Private Attributes
Time	m_firstTransmissionTime

ObjectFactory	m_mac

ObjectFactory	m_manager

unsigned int	m_numSentPackets

ObjectFactory	m_propDelay

Time	m_secondTransmissionTime

Additional Inherited Members
Public Types inherited from ns3::TestCase
enum	TestDuration { QUICK = 1, EXTENSIVE = 2, TAKES_FOREVER = 3 }
	How long the test takes to execute. More...

Protected Member Functions inherited from ns3::TestCase
	TestCase (std::string name)
	Constructor. More...

void	AddTestCase (TestCase *testCase, enum TestDuration duration)
	Add an individual child TestCase to this test suite. More...

TestCase *	GetParent () const
	Get the parent of this TestCsse. More...

bool	IsStatusFailure (void) const
	Check if any tests failed. More...

bool	IsStatusSuccess (void) const
	Check if all tests passed. More...

void	SetDataDir (std::string directory)
	Set the data directory where reference trace files can be found. More...

void	ReportTestFailure (std::string cond, std::string actual, std::string limit, std::string message, std::string file, int32_t line)
	Log the failure of this TestCase. More...

bool	MustAssertOnFailure (void) const
	Check if this run should assert on failure. More...

bool	MustContinueOnFailure (void) const
	Check if this run should continue on failure. More...

std::string	CreateDataDirFilename (std::string filename)
	Construct the full path to a file in the data directory. More...

std::string	CreateTempDirFilename (std::string filename)
	Construct the full path to a file in a temporary directory. More...

Detailed Description

Make sure that when multiple broadcast packets are queued on the same device in a short succession, that: 1) no backoff occurs if the frame arrives and the idle time >= DIFS or AIFSn (this is 'DCF immediate access', Figure 9-3 of IEEE 802.11-2012) 2) a backoff occurs for the second frame that arrives (this is clearly stated in Sec.

9.3.4.2 of IEEE 802.11-2012, (basic access, which applies to group-addressed frames) where it states "If, under these conditions, the medium is determined by the CS mechanism to be busy when a STA desires to initiate the initial frame of a frame exchange sequence (described in Annex G), exclusive of the CF period, the random backoff procedure described in 9.3.4.3 shall be followed." and from 9.3.4.3 "The result of this procedure is that transmitted frames from a STA are always separated by at least one backoff interval."

The observed behavior is that the first frame will be sent immediately, and the frames are spaced by (backoff + DIFS) time intervals (where backoff is a random number of slot sizes up to maximum CW)

The following test case should not generate virtual collision for the second frame. The seed and run numbers were pick such that the second frame gets backoff = 1 slot.

                 frame 1, frame 2
                 arrive                DIFS = 2 x slot + SIFS
                 |                          = 2 x 9us + 16us for 11a
                 |                    <----------->
                 V                                 <-backoff->

time |-----------—|----------------—|----------—|--------—> 0 1s 1.001408s 1.001442s |1.001451s ^ ^ ^ start TX finish TX start TX frame 1 frame 1 frame 2 ^ frame 2 backoff = 1 slot

The buggy behavior observed in prior versions was shown by picking RngSeedManager::SetRun (17); which generated a 0 slot backoff for frame 2. Then, frame 2 experiences a virtual collision and re-selects the backoff again. As a result, the actual backoff experience by frame 2 is less likely to be 0 since that would require two successions of 0 backoff (one that generates the virtual collision and one after the virtual collision).

See Bug 555 for past behavior.

Definition at line 380 of file wifi-test.cc.