Re: Message pools _are_ in use today!

[jim bell <jimbell@pacifier.com>]

At 05:25 PM 7/3/96 -0700, Timothy C. May wrote:

>Someone mentioned the Ku-band dishes that are used by PageSat (or whatever
>it is now called....). My DSS system, which is technically a Ku-band
>receiver, has a digital i/o connector of some sort on the back, and it is
>rumored that this will someday be available for PageSat-like uses. (I have
>a feeling this may be years off, for admin reasons if not technical
>reasons.)

As I understand it, the DSS broadcast (unlike older C-band units) consists 
of a single digital stream which contains the highly compressed (MPEG?) data 
representing all channels.  Being compressed, the data rate needed per 
channel varies  with the scene and the rate it changes.  Even if you add up 
a large number of these statistically-varying channels, you'll still get a 
fairly wide variation in the needed bit rate per second.   The system must 
have a substantial amount of headroom to protect against occasional times 
when many channels need a lot of bits, headroom that is mostly not being 
used, most of the time.  If this is correct, then most of this headroom 
should be available to piggybacked data traffic on a "space-available" 
basis.  Probably tens of megabits per second.

Jim Bell
jimbell@pacifier.com