Bug 1798 – Changing the rate of onOffApplication might stop transmission

Bug 1798 - Changing the rate of onOffApplication might stop transmission


Summary:	Changing the rate of onOffApplication might stop transmission

Status:	RESOLVED FIXED

Product:	ns-3
Classification:	Unclassified
Component:	applications
Version:	ns-3-dev
Hardware:	PC Linux

Importance:	P1 major
Assigned To:	George Riley

URL:
Keywords:

Depends on:
Blocks:
	Show dependency tree / graph

Reported:	2013-11-12 10:57 UTC by Ra
Modified:	2013-11-23 09:08 UTC (History)
CC List:	3 users (show)

See Also:

Attachments
place the file in scratch folder and run "./waf --run onOff-datarateChangeBug" to reproduce the bug. (7.84 KB, text/x-c++src) 2013-11-12 10:57 UTC, Ra	Details
bugfix (1.94 KB, patch) 2013-11-14 16:03 UTC, Tommaso Pecorella	Details \| Diff
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Description Ra 2013-11-12 10:57:24 UTC

Created attachment 1704 [details]
place the file in scratch folder and run "./waf --run onOff-datarateChangeBug" to reproduce the bug.

Changing the rate of onOffApplication at 5.0 seconds into the simulation results in no packets transmitted. However changing the rate at 5.001 seconds into the simulation seems to work OK. Please see line 204 in the attached file and change the value "5.0" to "5.001" to see the problem go away. You may run the attached file in the scratch folder with default values to reproduce the bug.

Comment 1 Tommaso Pecorella 2013-11-14 16:03:00 UTC

Created attachment 1711 [details]
bugfix

The bug is here:
void OnOffApplication::CancelEvents ()
{
  NS_LOG_FUNCTION (this);

  if (m_sendEvent.IsRunning ())
    { // Cancel the pending send packet event
      // Calculate residual bits since last packet sent
      Time delta (Simulator::Now () - m_lastStartTime);
      int64x64_t bits = delta.To (Time::S) * m_cbrRate.GetBitRate ();
      m_residualBits += bits.GetHigh ();
    }
  Simulator::Cancel (m_sendEvent);
  Simulator::Cancel (m_startStopEvent);
}

If m_cbrRate is changed at the wrong moment, m_residualBits can become larger than m_pktSize * 8. Hence the ScheduleNextTx will schedule the next transmission to an extremely large time.
And the application will seems to stop.

The patch fixes the bug in a rather dirty (but effective) way

Comment 2 Brian Swenson 2013-11-20 14:56:44 UTC

This looks good to me.  Ignoring residual bits immediately after cbr change seems to be the best approach.

Comment 3 Tommaso Pecorella 2013-11-23 09:08:15 UTC

Closed in changeset: 10438:32b7a66dbe7f