Cell Relay Archive

[Teughels Michel <teughels@esat.kuleuven.ac.be>]

On Wed, 19 Aug 1998 albert.e.manfredi@boeing.com wrote:

> In article
> <Pine.WNT.3.96.980819154054.-208601A-100000@hamming.esat.kuleuven.ac.be>,
>   Michel Teughels <Michel.Teughels@esat.kuleuven.ac.be> wrote:
> > Hi,
> >
> > In Q.2971 (about signalling for point-to-multipoint connections)
> > they say a network has to reject a SETUP message if the Broadband
> > bearer capability IE indicates "point-to-multipoint" and
> > contains an ATM traffic descriptor IE with any backward cell rate
> > field specifying a non-zero value.
> >
> > Now why is this ?  Isn't the problem of sorting out which cells
> > were sent by which leaf a problem of the higher layers ?
> 
> Higher layers? The problem is that we're talking about cells here. Higher
> layers cannot differentiate between cells in a shared VC unless you have merge
> points packetize the different cell streams from the leaves. It's this merging
> that causes the problems for mpt-mpt comms over ATM. Packetizing the cells, of
> course, sort of defeats the whole purpose of ATM. So the "right" way to do it
> is to establish different return VCs for each leaf. Or to do something that
> emulates IP multicast.
> 
Thanks for your answers.  I was wondering weather the refusal of
bidirectional multicast connections was a problem at the ATM layer
(the forwarding of cells) or at the higher layers: to me, the AAL
layer is a higher layer.

Michel