[Click] Service Time Anomaly?

[Caroline Williams]

Hello,  I hope someone can explain either my misconception or tell me 
what I'm doing wrong.  I am trying to do a QOS project that needs to 
report queueing delay and system delay.  Using queueing theory, I 
created a table of expected values.  I run a simple Click script that 
reports system delay.  I have a dump file containing 60 seconds of 
traffic at 50% utilization.  The packets have a total length of 554 
bytes.  With a capacity set at 1.25MBps, I should have an average 
service delay of 0.00088640.  We know at the very least that it takes 
0.0004432 seconds to process 554 bytes at 1.25MBps.  This is the 
script:

a :: FromDump($dump, TIMING true);
d :: SetTimestamp( FIRST false );
q0 :: Queue(100000);
e :: TimestampAccum;
i :: BandwidthShaper( 1.25 MBps );
a -> CheckIPHeader2(14, VERBOSE true)
    -> d -> q0
    -> i -> e -> Discard;
Script( TYPE DRIVER,
    wait $secs,
    print >> $stats $percentage $(e.count) $(e.time) $(e.average_time) 
$(q0.highwater_length),
    stop
);

Running for only two seconds, I get these results from the Script 
print:
50 2116 0.020058 9.47920604915e-06 2

Clearly, the delay is too small.  To help understand the problem, I 
modified TimestampAccum to display the timestamp values it was using 
to do the accumulation.  Here is a small sample:
now: 1196627352.902001 pkt time: 1196627352.901996 diff: 5e-06
now: 1196627352.902049 pkt time: 1196627352.902041 diff: 8e-06
now: 1196627352.905707 pkt time: 1196627352.905702 diff: 5e-06
now: 1196627352.905727 pkt time: 1196627352.905723 diff: 4e-06

Your assistance is appreciated,
Caroline