[6lowapp] Multicast support in CoAP

Forwarding Guido's question to the list.

----- Forwarded Message ----
> From: Guido Moritz <guido.moritz@uni-rostock.de>
> To: Behcet Sarikaya <sarikaya@ieee.org>
> Sent: Tue, January 26, 2010 2:20:08 PM
> Subject: AW: [6lowapp] draft-shelby-6lowapp-coap-00
> 
> Please can you go more into detail why IP layer multicast is too
> expensive/more expensive than application layer multicast?
> 
> IP layer implies further efforts for group membership management and
> multicast routing. But if IP layer routing is used, it is the most energy
> efficient way for data dissemination for the overall sensor network. Indeed,
> problem is group management through routers.
> 
> In contrast, application layer multicast needs single unicast connections to
> every endpoint. This has a significant influence on energy consumption of
> the originator and even for 'routing' intermediate nodes in scenarios with
> many endpoints. However, application layer multicast requires group
> membership managements as well, but require no specific routing effort
> because only unicast messages are assumed.
> 
> Thank you for clarification in advance,
> Guido
> 
> > -----Ursprüngliche Nachricht-----
> > Von: 6lowapp-bounces@ietf.org [mailto:6lowapp-bounces@ietf.org] Im
> > Auftrag von Behcet Sarikaya
> > Gesendet: Dienstag, 26. Januar 2010 20:23
> > An: Zach Shelby; d.sturek@att.net
> > Cc: 6LoWAPP
> > Betreff: Re: [6lowapp] draft-shelby-6lowapp-coap-00
> > 
> > 
> > 
> > 
> > 
> > ----- Original Message ----
> > > From: Zach Shelby 
> > > To: d.sturek@att.net
> > > Cc: 6LoWAPP <6lowapp@ietf.org>
> > > Sent: Tue, January 26, 2010 8:46:31 AM
> > > Subject: Re: [6lowapp] draft-shelby-6lowapp-coap-00
> > >
> > >
> > > On Jan 26, 2010, at 15:43 , Don Sturek wrote:
> > >
> > > > Hi Zach,
> > > >
> > > > I agree we need to keep CoAp a simple REST implementation.
> > Reviewing DPWS
> > > > and other OASIS protocols is fine as long as we keep CoAp simple.
> > > >
> > > > We have done our job correctly if something like DPWS over CoAp
> > becomes a
> > > > reality and we haven't if we find CoAp now is an annex of the OASIS
> > WS
> > > > specifications.
> > >
> > > Exactly. CoAP's goal is to support very light-weight RESTful
> > interactions for
> > > constrained device environments. Just as HTTP can be used for WS
> > purposes, CoAP
> > > should also be useful. There are a bunch of shortcomings in HTTP such
> > as the
> > > lack of multicast and subscribe/notify - by fixing those in CoAP will
> > enable
> > > simple REST applications, which also benefits use for e.g. DPWS or
> > other WS-* if
> > > they so wish to bind to CoAP.
> > 
> > I agree that application layer multicast is better for constrained
> > device environments as IP multicast would be too costly.
> > 
> > Regards,
> > 
> > Behcet
> > 
> > 
> > 
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