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Re: [ns] M/M/1
Peter Rabinovitch wrote:
> This will be approximately correct (and is how Opnet does an M/M/1 example
> too), except that in a real M/M/1 queue, departures are a poisson process
> with departure rate the same as the arrival rate. In this approximation,
> departures will be at your service rate as long as there are bytes in the
> buffer.
The way I understand the queuing mechanism in ns is that it takes the whole
packet out of the buffer right away and computes the serialization time of this
packet. Then it adds the propagation delay of the link to the next node and puts
it into this node's buffer.
If the packet lengths are neg. exp. distributed, you should get a Markovian
service behavior.
> So, depending on the time resolution you need, this might/might not be
> sufficient. What I mean is if you soom in close enough, this approximation
> will show a continuous stream of chunks at your service rate, where as M/M/1
> would show nothing, followed by a packet sized chunk at one instant, which
> could be much different than the service rate.
I'm not totally sure, but I think ns does not let you zoom in close enough to
see the bit granularity. Packet times are all you get. Therefore, M/M/1 should
be observable exactly.
- Anton
>
> Clear as mud?
>
> > -----Original Message-----
> > From: Debojyoti Dutta [mailto:[email protected]]
> > Sent: Monday, March 12, 2001 12:53 PM
> > To: Lloyd Wood
> > Cc: Radhakrishna Sampigethaya; [email protected]
> > Subject: Re: [ns] M/M/1
> >
> >
> > Lloyd is right. I forgot to mention that the source needs to
> > be markovian.
> > To be precise droptail queueing is M/D/1. I think one can
> > change droptail
> > Qs and add some randomness to model M/M/1 more accurately.
> >
> > Debo
> >
> > On Mon, 12 Mar 2001, Lloyd Wood wrote:
> >
> > > On Mon, 12 Mar 2001, Debojyoti Dutta wrote:
> > >
> > > > It must be same / similar to drop tail.
> > >
> > > ..with arrivals from a single Poisson source, surely? Has to be
> > > memoryless.
> > >
> > > L.
> > >
> > > > On Wed, 7 Mar 2001, Radhakrishna Sampigethaya wrote:
> > > >
> > > > > Has anyone tried to implement an M/M/1 queue in ns-2?
> > >
> > >
> > <[email protected]>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>
> > >
> > >
> >