More packet departures than arrivals?

[Christoph Haenle <chris@cs.vu.nl>]

Hello,

I'm using the latest ns (ns-2.1b2) and encounter a surprise when looking
at the queuemonitor statistics. In particular, it seems that there are more 
packet departures than packet arrivals on a normal duplex link (for the one 
direction monitored).

While the simulation was in action, I took some snapshots, generated with

     puts stdout "[_o269 set parrivals_] [_o269 set pdepartures_] [_o269 set
     pdrops_]"

where _o269 was the relevant QueueMonitor instance.
Shown below are three snapshots:

     3718 3741 0
     6034 6057 0
     12383 12406 0

As can be seen, the link produced more (23 packets) departures than arrivals.

Though the difference is always 23, another test yielded increasing values for 
the difference, even more than to the maximum number of packets for the output 
buffer (default=50 packets?).

Am I missing something or is this wrong in ns-2?

     -Chris.