Integrator question.

[Frank Solensky <solensky@TopLayer.com>]

I'm attempting to use an integrator to determine the average link utilization
in my script and am missing something in my script.

============

set r1 [$ns node]
set r2 [$ns node]
set rcv [$ns simplex-link $r1 $r2 1.544Mb 20ms DropTail]
set xmt [$ns simplex-link $r2 $r1 1.544Mb 20ms DropTail]

set rcvqm [$ns monitor-queue $r1 $r2 "" 0.1]

# set up various traffic flows..

proc bwupdate {} {
    global dt bw rcvqm ns weight

    set rcvin [$rcvqm get-pkts-integrator]
    #
    # Update the estimated bandwidth utilization
    #
    set x [$ns now]
    set y [$rcvqm set bdepartures_]
    set xa [$rcvin set lastx_]
    set ya [$rcvin set lasty_]

    set dt [expr $dt * (1.0 - $weight) + \
            ($y - $ya) / (($x - $xa) * 1930.0) * $weight]

    puts $bw [list $x $y $xa $ya $dt]
    $ns at [expr $x + 0.1] "bwupdate"
}

$ns at  0.1 "bwupdate"

============
The file that "dt" writes to indicates that the lastx_ values are increasing
over time but the lasty_ values are not.  If I change the script around so
that I'm not using the integrator object -- saving the last values of 'now'
and 'bdepartures_' in globals -- it works fine.  The fact that I'm saving 'x'
but not 'y' suggests to me that a periodic measurement of the queue is
occuring but the integrator is either looking at something else or that the
'y' values may be a current rather than a cumulative total?