[ns] werid delay between enqueue and dequeue

[Bo Wen <bowen@mail.wsu.edu>]

Hi, can anyone help me figure out this problem? 

The following is "grepped" trace file for a particular packet.
Why is there a small delay between enqueue and dequeue 
(0.012394-0.0115 = 0.000894)?  Where is it from?  From queue delay?

I used droptail queue, but traffic rate did not exceed the link
bandwidth.  however, when I test some small simulation scenario,
the enqueue and dequeue time are exactly same.  Why?

Thanks a lot.

+ 0 0 3 cbr 500 ------- 2 0.3 6.0 0 2 
- 0.001 0 3 cbr 500 ------- 2 0.3 6.0 0 2 
r 0.0115 0 3 cbr 500 ------- 2 0.3 6.0 0 2 
+ 0.0115 3 4 cbr 500 ------- 2 0.3 6.0 0 2 
^^^^^^^^^
- 0.012394 3 4 cbr 500 ------- 2 0.3 6.0 0 2 
^^^^^^^^^^
r 0.022894 3 4 cbr 500 ------- 2 0.3 6.0 0 2 
+ 0.022894 4 6 cbr 500 ------- 2 0.3 6.0 0 2 
- 0.023394 4 6 cbr 500 ------- 2 0.3 6.0 0 2
r 0.033894 4 6 cbr 500 ------- 2 0.3 6.0 0 2