Subject: RE: IP over Satellite Questions/References

From: "Falk, Aaron" <[email-masked]>
Date: Tue, 6 Jun 2000 09:05:31 -0400

Chris-

> - IP/MPEG/DVB? So are IP packets carried in the MPE 
> capabilities of MPEG 
> for transmission over DVB systems?

Yes.

> 
> - What about special satellite-specific link layers? Are MPEG frames 
> carried inside these L2 protocols?

The one I'm familliar with (HNS) is an alternative to MPEG/DVB rather than
just DVB. So, IP goes directly into their link layer. So, no MPEG. 

> 
> - How is the satellite uplink for a bidirectional system done? 

The primary difference is that the RF electronics has the capacity to
transmit rather than just receive. This increases the user equipment cost
significantly since the transmission tube is the most expensive part of a
VSAT terminal (and a receive-only terminal doesn't need one). In the
simplest form, you could do PPP over a fixed bandwidth RF link. Most
services do (& will) use something more sophisticated since (a) the duty
cycle for a single terminal is usually low and (b) satellite bandwidth is
expensive. The operators want to share the bandwidth across as many users as
possible (while still providing acceptable service). 

> I am 
> familiar with the DirecPC approach of using a terrestrial 
> (dial, ISDN) 
> uplink from the home. Is the bandwidth symmetrical or asymmetrical?

Since most of these systems are designed for web access, the bandwidth will
almost always be asymmetrical. But in some designs, particularly the Ka-band
systems in development, that's a matter of provisioning rather than the
architecture. Meaning that if you had a user that needed symmetric access
(or, rather, was willing to pay for it), you could set up channels with the
same rates in both directions. Nevertheless, the majority of these systems
are designed expecting that most users will want to consume more data than
they generate.

> 
> - How much bandwidth is possible? I see that DirecPC 
> advertises 400Kb. What 
> are the issues that affect how much bandwidth one can use?
> 

Sharing satellite bandwidth is a zero-sum game. If your transponder can
handle 45Mbps (a typical value), you can share that across all the users you
want but it has to add up to 45Mbps. If you've ever studied communications
channels, you know you can trade channel utilization (percentage of time
that the channel is not idle) for data delay. In other words, you make users
wait in queues so they can transmit at the most convenient time. However, if
you make them wait too long, they get annoyed. There can be significant
overhead in these channel sharing (DAMA, Bandwidth on Demand) schemes since
you have to tell users when to transmit.

> Any conferences/tutorials/whitepapers/books that people can 
> recommend to 
> learn about this stuff?

Lots of conferences:
  -) University of Maryland has an annual Internet over satellite conference

     (I couldn't find a URL)
  -) The annual Ka-utilization conference talks about new Ka-band (duplex)
systems
  -) MOBICOM
  -) 'Internet Via Satellite,' marketing oriented but useful if you want to
find
     out what people are doing,
http://www.actconferences.com/Satv4/index.htm
  -) IEEE Communication Society usually has some sessions at ICC, 
     http://www.icc00.org/technic/pglance.htm

  ...Hopefully, folks on the mail list can contribute additional ones.

Hope this helps,

--aaron

---
Aaron Falk
NET/36 Network Architect
PanAmSat Corporation
Greenwich, Connecticut, USA
*	Phone: 	203.861.8326
*	Mobile: 	203.912.5689
*	Fax: 		203.861.8677
*	mailto:[email-masked] 
*	http://www.net-36.com

---

From: "Bo Ryu" <[email-masked]>
Date: Tue, 6 Jun 2000 15:45:45 -0700

While we are at it, there is WOSBIS (Workshoop in Satellite Based
Information and Services). WOSBIS was with Mobicom for '96, '97, and '98,
and last year, it was with Globecom. I recall there was one paper on IP over
DVB from Europe in '98 WOSBIS. Check out
http://www.wins.hrl.com/conferences/WOSBIS98/advprog.html

If you like, I will send you a copy of that paper. :-)

-Bo

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On
> Behalf Of Falk, Aaron
> Sent: Tuesday, June 06, 2000 6:06 AM
> To: 'Chris Metz'
> Cc: [email-masked]
> Subject: RE: IP over Satellite Questions/References
>
>
>
>
> > ----------
> > From: 	Falk, Aaron[SMTP:[email-masked]]
> > Sent: 	Tuesday, June 06, 2000 6:05:31 AM
> > To: 	'Chris Metz'
> > Cc: 	[email-masked]
> > Subject: 	RE: IP over Satellite Questions/References
> > Auto forwarded by a Rule
> >
> Chris-
>