Re: [ssm] Re: last call comments on ssm-arch doc

[Daniel Zappala <zappala@cs.uoregon.edu>]

On Wed, 2003-01-15 at 07:50, Toerless Eckert wrote:
> On Wed, Jan 15, 2003 at 04:38:01PM +0100, Rolland Vida wrote:
> > Toerless,
> > 
> > > If you're building the white board application as pure peer to peer,
> > > each peer has to become a SSM channel source. If you implement the
> > > application as a client/server system, the clients could unicast to
> > > the server, and the server would have one SSM channel to all clients.
> > > Advantages: Easier model for access control, session management
> > > and ressource allocation then in a full peer to peer model.
> > 
> > This is a nice trick to provide a multi-source service through SSM. However,
> > there are also some drawbacks: no source filtering, no shortest path
> > delivery. It is basicly like standard PIM-SM: everybody sends to the RP
> > (server), which forwards then on the shared tree (here the SSM channel). And
> > as in PIM-SM already the shared tree is switched for a source-specific tree
> > (to optimize delivery), why should it be now acceptable to use such a shared
> > tree just to enable multi-source SSM?
> 
> Because in SSM the reflection is done at application level, so the
> reflecting server can do a lot of useful stuff like source filtering
> (access control), (re-)encoding/fec, (re-)encryption, filtering,
> synchronization, buffering, shaping, adding coffee. And security 
> of the applications data flow is now completely under the control of
> the application.

Well put.  I'd also like to add that you can get around the delay
penalty (because shortest paths are no longer used if all data is
relayed through a single source).  You just use the primary source (the
application-level relay) to bootstrap other relays.  See:

	D. Zappala, and A. Fabbri, Using SSM Proxies to Provide 
	Efficient Multiple-Source Multicast Delivery. IEEE Globecom,
	Sixth Global Internet Symposium, November, 2001.

at

	http://www.cs.uoregon.edu/~zappala/uo/uo.publications.html
or
	http://www.nrg.cs.uoregon.edu/pubs/ssm_gis01.pdf

-- 
======================================================================
Daniel Zappala                                    Computer Science
Assistant Professor                               University of Oregon

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