Precisions about loss insertion

[Biaz Saad <saadb@cs.tamu.edu>]

Hi everybody,

	I would like to explain why the error module should be inserted
after link delay element.

	Suppose that the error module is inserted just after the queue
(as it is now).
	Let us consider two packets P1 and P2 which get to the queue back to back
in the order P1 first, P2 second.
	Normally, P2 cannot be sent until P1 is completely transmitted,
(whether P1 is lost or not.
	With inserting the error module just after the queue, if P1 is
lost, then P2 is sent right after : This is not the real behavior of any
transmission module.
	Putting the error module just after the queue of after deqt_ does
not reflect a real network.

	Unfortunately, modifying Haobo's script does not work. 
Here is Haobo's script with my modifications:

SimpleLink instproc add-loss { ns em } {
$self instvar queue_ head_ link_ isLossy_ deqT_ lossModule_

# --- ORIGINAL --------                  ---- MODIFIED -------

if [info exists deqT_] {    -----------> if [info exists link_] {
$em target [$deqT_ target]  -----------> $em target [$link_ target]
$deqT_ target $em           -----------> $link_ target $em
} else {                    ---- NOT MODIFIED ----
$em target [$queue_ target] ---- NOT MODIFIED ----
$queue_ target $em          ---- NOT MODIFIED ----
}                           ---- NOT MODIFIED ----
                            ---- NOT MODIFIED ----
set isLossy_ 1              ---- NOT MODIFIED ----
set lossModule_ $em         ---- NOT MODIFIED ----
}                           ---- NOT MODIFIED ----


	Maybe am I missing something. Your comments and your help will
highly appreciated.
	
					Saad.

___________________________________________________________________
Saad Biaz (Abou Youssef)		Graduate Research Assistant	
Texas A&M University			Office : (409) 845-5007
Department of Computer Science		Home   : (409) 862-9135
College Station, TX, 77843-3112         Fax    : (409) 847-8578
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