N feeds may result in M UDL (M<=N)

[nghia PHAM <nghia_pham@CompuServe.COM>]

This to respond to Tim Woodall point posted to this list
on 23-March.

>Consider the case where a small set of receive sites may 
>also be acting as feeds, yet the underlying transport does 
>not support multiple feeds per UDL, so N feeds results in N
>distinct unidirectional links.

With traditional technology, the satellite acts as a bent pipe and
Tim Woodall's statement that satellite cannot support
multiple feeds per UDL is correct.

Not any more...

At EUTELSAT we have switch on this month Skyplex (TM).
Skyplex is an OBP (On-Board-Processing) based system. Basically,
we have put on our satellite a bank of demodulators (6 currently)
connected a to time-division mutiplexor and a modulator. Therefore, we 
can assemble in the sky up to 6 digital streams, transmitted from 6 
separated locations, at 6 different frequencies, into a single stream.
With only one demodulator, a receiver can take the traffic from 6 feeds
simultaneously.

Therefore the following topologies can exist:

1) N feeds connected to one UDL. This is the case when one single
(commercial) entity is operating Skyplex.

2) N feeds connected to M UDL's in a single physical link. This is the case
where the different streams from the feeds are segregated into M distinct
logical UDL's. In this situation a receiver must have M IP address to be
able
to receive all N feeds.

3) N feeds connected to N UDL's. A generalisation of Case 2 above.

On our next satellite we will have enhanced Skyplex (3 units, each being
able to demodulate up to 36 streams). The situation may exist that N feeds
belonging to the same commercial entity are spread over the 3 Skyplex
units.
Assuming that the receiver can be equiped with 3 demodulators, is there an 
elegant way to make the N feeds appear as if they were connected to the
same UDL?

Kind regards,

Nghia PHAM
EUTELSAT
European Telecommunication Organisation
70 rue Balard - PARIS 15
FRANCE
http://www.eutelsat.org
ph: 33-1 53 98 47 21, fax: 33-1 53 98 47 98
alternative email: npham@eutelsat.fr