[Ns-bugs] [Bug 1133] New: DSDV: Possible bug in settling time calc

[code@nsnam.ece.gatech.edu]

https://www.nsnam.org/bugzilla/show_bug.cgi?id=1133

           Summary: DSDV: Possible bug in settling time calc
           Product: ns-3
           Version: ns-3-dev
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P5
         Component: dsdv
        AssignedTo: hemanthnarra222 at gmail.com
        ReportedBy: tommaso.pecorella at unifi.it
                CC: ns-bugs at isi.edu
   Estimated Hours: 0.0


in RoutingProtocol::GetSettlingTime (Ipv4Address address) the weightedTime is
calculated as:

weightedTime = Time ((m_weightedFactor * mainrt.GetSettlingTime () + 1.0 -
m_weightedFactor)
                                * mainrt.GetLifeTime ());

To be honest this calc seems all but right to me. According to DSDV
documentation (I'm not a full expert on that tho), the weightedTime should be
updated according to a EWMA smooth function, as is:

WTnew = k WTold + (1-k) NewSample. Thus the "right" calc should be:


weightedTime = Time ((m_weightedFactor * mainrt.GetSettlingTime ()) +
                                (1.0 - m_weightedFactor) *  mainrt.GetLifeTime
());

I found it because the previous expression goes to infinity, raising a
multiplication overflow on some machines.

Check it and in case update please.

T.

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