Chris,
I believe the University of Maryland event was held at U of M - College Park
at the end of April and was our (ACT Conferences) 4th annual event. If I'm
wrong about the event Aaron was referencing, my apologies to all. I was told
the event was incorrectly listed in an industry pub. as the University's 2nd
annual event, so the confusion is understandable. Actually, Aaron may be
amazingly prescient -- the director of the University's center for Satellite &
Hybrid Networks has approached us about producing the event next year
with the University.
Our main URL is www.actconferences.com which should have a link to past
conferences-I'm on the road otherwise I'd get you the specific URL. Also,
look for a similar conf. in Nov. on the west coast.
Regards,
Robert Dean
VP, Program Development
ACT Conferences
417.865.7500
From: "Falk, Aaron" <[email protected]>
To: "'Chris Metz'" <[email protected]>
Copies to: [email protected]
Subject: RE: IP over Satellite Questions/References
Date sent: 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 protected] * http://www.net-36.com
This archive was generated by hypermail 2b29 : Tue Jun 06 2000 - 18:07:43 EDT