The IP over ATM Mailing List Archive by date

[Luca.Fantolino@CSELT.STET.IT (Luca Fantolino - CSELT - Italy)]

Raif, Bert

Why mpt-pt (or mpt-mpt) ATM connections are required?
In my understanding the reason is that you want to avoid that every
station set-up a connection to every other station in the cloud. Note
that setting-up such a connection mesh is bad thing due to
scalability, resource allocation, continuous changing of the
configuration caused by power up/down of the station, etc.
So you have a couple of alternatives:

VCI multiplexing. You can set up a mpt-mpt VP connection and assign a
unique VCI to each sender station. In that case the network does not
support VC connection, but only VP connections. When a station is
powered up/down no action is required but the notification of the VCI
to be used to that station only (note that this identifier might also
be locally derived, e.g from the less significant bit of the IP
address). A receiver can demultiplex concurrent incoming packets which
may be tranported using normal AAL5.
The main disadvantage of this solution is that it is not applicable if
you use the ATM sub-layering for other purpose. For example, if you
create a private ATM network joining ATM LAN through a ATM VP pubblic
service (WAN) you cannot apply VCI multiplexing.

AAL multiplexing. You have to provide demultipling information inside
the cell. AAL 3/4 MID is an example, but in my understanding AAL 3/4
has not been considered suitable for our purposes because of its
complexity (e.g. CRC computation for each cell). Shall we need an
AAL5+? [E.g: the first 32 word provides MID (maybe derived from the IP
address) and packet Begin/End indication].