Re: [Q] General Question on Multicast and its simulation

[Lloyd Wood <L.Wood@surrey.ac.uk>]

On Fri, 22 Oct 1999, Lee Jiwoong wrote:

> After the general multicast simulation result of ns-2, 
> I became curious the general mechanism of dynamic join/leave 
> and multicast routing/forwarding.
> 
> 1. In NS-2, when I start the multicast sender, it distributes its packets 
> throughout the whole topology even though none of potential receivers
> have not joined yet. 

This is correct behaviour for distance-vector multicast (DM), which
your script is using.

> What I guess is that the simulation result as correct solution,
> should show no multicast packet transmission even though the sender start
> , until  at the moment when one receiver joins that multicast session.

How would the sender know?


> 2. Therefore, my question is this: In the real world, how the multicast works ?

You can answer that question by doing some reading, e.g.:

Steve Deering, "Scalable Multicast Routing Protocol", Ph.D. Thesis,
Stanford University, 1989.

for DVMRP, and

Ballardie's thesis:
http://www.cs.ucl.ac.uk/staff/J.Crowcroft/paststudents.html

Ordered Core based tree protocol:
http://www.cse.ucsc.edu/~clay/ocbt/ocbt.html

for an idea of shared trees etc.

L.

<L.Wood@surrey.ac.uk>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>