Subject: [multimob] Comments on draft-schmidt-multimob-pmipv6-mcast-deployment-01

From: "Luis M. Contreras" <[email-masked]>
Date: Mon, 05 Oct 2009 23:47:40 +0200

Hi,

I would like to share some comments/doubts regarding 
draft-schmidt-multimob-pmipv6-mcast-deployment-01.

1/ On the event of handover, the new MAG sends a MLD Query over the 
radio interface to the attaching MN (see figure 2 of the draft) to 
obtain active membership information. What about if the MN connecting 
to new MAG has not an active multicast session? Is that query sent 
anyway in all handover processes?

2/ Due that a MAG could have association with more than one LMA, a 
distinct MLD proxy instance is needed for each LMA. Probably, two 
different MNs attached to the same MAG, each one associated to 
different LMA, can be suscribed to the same content. Would be feasible 
some kind of internal MLD proxy coordination to avoid multiple 
suscriptions to the same content through different LMA connections?

Thanks in advance,

Regards,

Luis

---

From: "Thomas C. Schmidt" <[email-masked]>
Date: Tue, 06 Oct 2009 00:02:17 +0200

Hi Luis,

thanks for looking over our draft.

Luis M. Contreras wrote:

> obtain active membership information. What about if the MN connecting to 
> new MAG has not an active multicast session? Is that query sent anyway 
> in all handover processes?
>
Yes, in a multicast-enabled domain the MAG has to query (one could 
aggregate queries in a domain of frequent & diverse handovers). There 
are no other generic means to learn about a group under subscription of 
a newly attached mobile node.

> different MNs attached to the same MAG, each one associated to different 
> LMA, can be suscribed to the same content. Would be feasible some kind 
> of internal MLD proxy coordination to avoid multiple suscriptions to the 
> same content through different LMA connections?
> 

Yes, you are right: a MAG hosts MLD Proxy instances for each uplink with 
an LMA. Two different MNs associated with two different LMAs could 
initiate the identical multicast traffic to traverse the same MAG and 
the same wireless link.

We believe, there is no way around this redundancy unless one defines 
dedicated multicast mobility protocols at the MAGs/LMAs.

The objective of this draft however was to define a minimal protocol 
solution for multicast that does not alter any of the existing protocol 
standards, but just combines them in a proper way (targeting at a 
BCP-type of solution).

There are many clever ways to eliminate this redundancy - however, it 
should be noted that the pure combination of  unaltered protocols 
already gives rise to a solution that is non-optimal, but in many cases 
efficient.

Best regards,

Thomas
-- 

Prof. Dr. Thomas C. Schmidt
° Hamburg University of Applied Sciences                   Berliner Tor 7 °
° Dept. Informatik, Internet Technologies Group    20099 Hamburg, Germany °
° http://www.haw-hamburg.de/inet                   Fon: +49-40-42875-8452 °
° http://www.informatik.haw-hamburg.de/~schmidt    Fax: +49-40-42875-8409 °