[Ns-bugs] [Bug 255] New: Deterministic Behavior May Cause Problems

[bugzilla-daemon@nsnam-www.ece.gatech.edu]

http://www.nsnam.org/bugzilla/show_bug.cgi?id=255

           Summary: Deterministic Behavior May Cause Problems
           Product: ns-3
           Version: pre-release
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: minor
          Priority: P4
         Component: internet-node
        AssignedTo: ns-bugs at isi.edu
        ReportedBy: craigdo at ee.washington.edu


Consider:
   - Two applications are started at precisely t seconds;
   - Applications generate packets that require arp at precisely the same time;
   - LOOP:
   - Both arp protocols schedule retransmission for precisely t+timeout
seconds;
   - Generated arp packets are sent at precisely t seconds;
   - Device/channel mechanism causes arp packets to collide and be 
discarded;
   - At t+timeout seconds, arp protocols retry on both nodes (at precisely the
same simulation time);
   - t = t+timeout;
   - goto LOOP.

The result is that ARP retransmissions happen at precisely the same time and
collide over and over again.

Our models may be "too deterministic" in some cases.  Should models such as arp
be configurable to add a random "fuzz" to their timeouts to simulate real
timing uncertainties?


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