[Ns-developers] Ack Timeout bug

[kirillano]

Hi All,
I have tested multple queues (DcaTxops) in wifi and have faced with a bug:
  when MacLow sends a packet while ACK timeout has not expired (In 802.11 standard in chapter 9.2.8 was said, that we must wait ack timeout before next transmission).
I have added NS_ASSERT(false) after line, which cancels ACK timeout in CancelAllEvents () method in MacLow, which is called from StartTransmission () and my simulation has failed with tis assert.
When I have looked through output more detailed - I have seen that a packet from another queue (beacon queue) has accessed the medium before ACK timeout of data packet has expired after crash of ACK. I think, that the problem may be resolved by adding a moment of time when AckTimeout expires in DcfManager. Now DcfManager knows nothing about AckTimeout and can grant access before ACK timeout has expired.

This problem seems serious to me, because when AckTimeout is cancelled, the m_currentPacket in DcaTxop shall never be zero - so, the queue is blocked and no data packets can be sent.

Regards, Kirill Andreev
Wireless Software R&D Group,
IITP RAS