The IP over ATM Mailing List Archive by date

[Rick Bubenik <rick@stl.nexen.com>]

> From: Tim Dwight <0006078043@mcimail.com>
> Subject: Re: Multicasting with ATM - a concern
> 
> Rick Bubenik writes:
> 
> > There is an alternative that allows AAL5 to be used for mpt-to-mpt
> > connections.  Namely, set up the connection as a switched VP and
> > either: 1) allocate a unique VCI to each transmitter or 2) set aside
> > a block of VCIs and have each transmitter randomly select a value
> > prior to sending a packet.  The first approach guarantees no
> > interleaving, but requires a VCI assignment protocol (relatively
> > simple, but not trivial).  The second approach allows occasional
> > interleaving, with an interleave probability that can be controlled
> > (based on the range of VCIs set aside and the number of expected
> > simultaneous transmitters).
> > 
> > The advantage of using a true mpt-to-mpt ATM level service is that
> > only one connection need be set up to each participant and there is
> > no single point of failure.  Also, this solution scales to very
> > large multicasts.
> 
> I am confused.  pt-mpt VPC's, like pt-mpt VCC's, are unidirectional.
> That is, they have one root (sender) and multiple leaves (receivers).
> 
> To my knowledge there is no 'true mpt-to-mpt ATM level service'.
> mpt-mpt connectivity is a concept, not a service, whose most direct
> analogue at the ATM layer will be a mesh of pt-mpt connections.  The
> difficulty in supporting true mpt-mpt is in bandwidth allocation (i.e.,
> in the connection-oriented nature of ATM).

I'm aware of several ATM switches that support a true mpt-to-mpt
(bidirectional) ATM level service.  The degree to which they solve
the traffic problem varies, where some are better than others.
The ideal building block would be a switch that can support (true)
mpt-to-mpt connections for ABR.  However, I'm not sure whether
the Forum's ABR mechanism is amenable to this.

	rick

> It seems to me that servers like the MARS are going to be needed 
> indefinitely, to provide mpt-mpt emulation by magically adding a user
> to or removing a user from, multiple pt-mpt VCC's.
> 
> The existing MARS can likely be improved through the use of Leaf Initiated
> Join and Proxy Signaling (2 features of ATM Forum UNI 4.0).  Rick was one
> of the authors of this work;  perhaps he'd care to rough out the changes
> required to pick it up?
> 
> Tim Dwight
> MCI
> 
>