Re: Can't multicast w/simplex links?

[Lloyd Wood <eep1lw@surrey.ac.uk>]

On Tue, 9 Mar 1999, Daniel Friedman wrote:

> My ns version is 2.1b4a.
> 
> I'm trying to "broadcast" a message from one node to several others,
> using simplex links.  I tried to take ~ns/tcl/ex/newmcast/mcast1.tcl and
> change the duplex-links to simplex-links.  For example, I changed
> 	$ns duplex-link $n0 $n1 1.5Mb 10ms DropTail
> to 
> 	$ns simplex-link $n0 $n1 1.5Mb 10ms DropTail
> and similarly elsewhere. (I also commented-out the duplex-link-op
> lines.)
> 
> Why do I find no traffic is sent after making these changes?

because the join-group messages sent at specific times can never reach
the source. You've just broken the only paths they had. 

If you're using simplex links, the multicast should work with
asymmetrical topologies, but you still need bidirectional
communication overall between nodes and sources for
flooding/reverse-path forwarding or to allow join/leave messages to
reach the source, depending on the multicast paradigm chosen. 

If you were using a DVMRP tree, you might get away with it, because
flooding ought to work in this case and pruning messages never get
received. But this script is using centralised multicast... 

cheers,

L.

and this is where I recommend Huitema's 'Routing in the Internet'.

>  Daniel Friedman    danielf@isr.umd.edu    http://www.isr.umd.edu/~danielf

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