[Ns-bugs] [Bug 438] New: csma helper hooks the transmit queue enqueue operation for pcap tracing

[code@nsnam.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=438

           Summary: csma helper hooks the transmit queue enqueue operation
                    for pcap tracing
           Product: ns-3
           Version: ns-3-dev
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P3
         Component: devices
        AssignedTo: ns-bugs at isi.edu
        ReportedBy: craigdo at ee.washington.edu
   Estimated Hours: 0.0


Hooking the transmit queue enqueue is not what I would have expected at all. 
That makes it appear that the packet went on the wire when the packet was
enqueued.  The packet is actually sent after it is dequeued.

I think the helper should hook the dequeue trace hook for pcap tracing since
there can be a significant delta-t between the enqueue and the dequeue.

Perhaps even better, there should be a new low-level trace hook Tx that
corresponds to a packet being sent out to the channel.  Right now there is a
hole where a packet can be dequeued from the transmit queue and subsequently
silently dropped.  This makes it appear as if the packet was transmitted
successfully.

I think it would be better to have upper level trace hooks into the transmit
queue, and lower level trace hooks at the device/channel interface.  Right now
things are mixed and somewhat confused/confusing.


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