I know this conversation could carry us away from the technical
issues, but...
I just want to add that even in North America and Europe satellite
service providers now target mass markets with low-cost (<$1000)
consumer-grade "truly" two-way "Internet access"-type of units with an
average link rates of ~384kbps - 2Mbps (I'm not talking about DirectPC
and other one-way systems!).
My point is that not only an "educational", but even a "business"
world is looking at <4Mbps links, where all the BER issues ARE
RELEVANT. I don't belive that in this particular market segment it
would be econimically feasible to implement "overwhelming" coding. So
rain (bird/basketball ;-)) fadings and congestions at the ISPs, IMHO,
will be major issues...
Again, my apologies for raising these non-technical issues here...
Regards,
Maxim Zakurdaev
NORTEL, Ottawa, Canada
---"Charles A. Ross" <[email protected]> wrote:
>
> Prague
> April 01, 1998
>
> Dear Colleagues,
> Mr. Fairhurst has written of an interesting point in suggesting the
impact
> of a small but friendly mass (ie., bird) perching & partially
obscuring a
> link such as, notably, a low power VSAT terminal(my addition),
particularly
> one of less than 2Mbps, and thereby signifcantly lowering the BER of
that
> VSAT link, albeit not for long. Hence the problem set instantly
develops of
> rapidly restoring TCP throughput over the degraded satellite link.
Other
> things, including passing aircraft or even a passing basketball, can
lower
> BER, too. Given the fact that international distance education
applications
> by satellite throughout the 2/3 of the planet not yet (nor soon to be)
> 'adequately' cabled, that they will undoubtedly be long done with RF
links
> of less than 2Mbps to geostationary satellites, obviously(!), and
> increasingly with the new low power/low cost VSAT terminals, it
would be a
> significant addition to the practical results of this group's
effort, I
> believe, to study and determine how best to manage this kind of
general
> transient situation inexpensively.
> This problem will become even more critical than it is today, as
people
> start to routinely install TCP/IP compression on framed IP links
before
> transmission into the satellite RF chain. The price of space segment
on a
> monthly basis will drive users to compress everything for the
comparably
> low cost of a one-time daughter-card-level hardware type purchase as
an add
> on to a framing unit. While it is very important to determine
> tcp-over-satellite solutions for larger links, such as >4Mbps,
tremendous
> numbers of schools around the planet will long depend on small, low
powered
> VSAT's with increasingly compressed IP links for voice, WWW,
interactive
> desktop video and database access, and we should today recognize
that fact
> ...now... while we are just beginning to implement and design
changes which
> incorporate these diverse user-driven traffic loading factors. Mr.
> Fairhurst is right in suggesting that there will be several ways to
do such
> work and I believe it would be useful to develop a series of
'guidance'
> solution sets-with commentaries(even signed, perhaps), more or less
> standardized and let operators chose what they want to work with on
a case
> by case basis. Different gear will lend itself differently and more
or less
> easily to known solution approaches, once explored and developped.
It would
> be a tremendous fallacy to assume that all implementions start with
the
> latest and best equipment....as many of these distance education
programs
> will be retrofits of older and donated equipment.
> This group's potential examination of such a low power, IP
transmission
> environment QOS problem would ultimately do countless people a great
public
> service if a way could be found to study and provide workable
guidance for
> these types of frankly low power VSAT applications needing to be
done with
> low budgets in less than perfect conditions. This does not have to be
> within the framework of a committee-type institutional document
process,
> but I feel strongly that the true obligations of such an ad hoc body
would
> suggest that reaseach along the lines that Mr. Fairhurst and I have
> outlined for links of <2Mbps is essential to the development of
globally
> usable TCP and generally speaking IP-over-satellite
solutions...which is
> what I believe to be the raison d'etre of such a prestigeous
gathering of
> experts as participate in this process. While some people will
complain
> that such additional work dillutes the 'thrust' of the body, I would
> counter that the sheer plethora of small VSAT links which can and
will be
> needed to be installed in coming years to the World's regions in rapid
> development -often almost exclusively for educational purposes, though
> increasingly I hope for mixed use in support of the entire rural
community
> environment, should indicate to any observant that the moral
implications
> of practicing professionally in this industry should suggest also
providing
> some attention to this 'less commercially attractive' sized link: that
> these implications are tremendous and hark to the now almost 'ancient'
> communications concept of universal, ubiquitous and I would add
<locally
> affordable telecommunications service>. Business users and rural
health
> care will benefit too, as their links are also of this size-and they
will
> use compression: guaranteed!
> I believe strongly that a rigid standard-without guidance, and only
> looking at larger links >4Mbps will not be very useful in the real
world of
> practically building the essential and usually <2Mbps satellite links
> connecting to the places which the 'other 2/3' of this planet's
population
> call "home", too, in their own local language. After all, they are our
> neighbors on Earth and they need these links to work reliably at
what they
> consider <locally affordable costs>. Solution sets which count on
> Washington/New York, London, Paris, Berlin, and Tokyo ideas of 'what's
> affordable' won't be rapidly deployed, or at least not as rapidly as
> solutions where affordable basic connectivity is really what is
needed now.
> This kind of work will also be supportive of the ITU's thrust for
true
> universal service (and beyond telephony!) and will be welcomed in such
> circles, particularly among nation-members in the target populations
for
> increased basic connectivity such as I am discussing here, and
notably for
> the entire range of Voice and Video Over IP (VoIP) applications being
> developped for which TCP over satellite will become the long-haul
transport
> mode of choice for many regions, now with the ITU H.323 standard being
> accepted by equipment manufacturers everywhere.
> Once again, I would like to thank Mr. Fairhurst for his provocative
and
> constructive comments and examples.
>
> Respectfully,
> Charles A. Ross
>
> ------------------------------------
> Charles A. Ross
> President
>
> ACANTHUS Corporation
> &
> BEEDNET Group
>
> <[email protected]>
>
> replies to:
> Prague, Representative Office
> GSM mobile +420.(0)603.500.000 (voicemail)
> GSM mobile +420.(0)603.49.1000 (voicemail)
>
> +420.2.2421.9525 tel/fax/voicemail
> ------------------------------------
>
> At 11:00 AM 3/31/98 +0000, you wrote:
> >I read with interest the assertion that satellite links may be
> >"engineered" to give a BER of 10-9... Sure they can, the ways of
> >doing this are either lowering the bit rate (through FEC) or/and by
> >increasing the received energy per bit (i.e. utilising more
> >satellite transmit power). Both of these approaches are valid for
> >high bit rate systems > 4 Mbps, say, but for lower bit rate systems,
> >it may be the wrong solution, and providing error control techniques
> >in some way from the protocol is a very sound approach, providing it
> >is transparent enougth to TCP (Hmmmm.... this is tricky)
> >
> >Consider for example, the power budget required to overcome
> >interference from a noise source close to a satellite terminal, or
> >the potential for the satellite terminal to be obscured partially
> >(a friendly bird perched on the antenna feed?). If one chooses
> >to only optimise the bearer network by providing an error-free
physical
> >transmission path, then that's one way of building of network,
> >it is certainly NOT the only way.
> >
> >Is the group interested in 2 Mbps and lower data rates too?
> >
> >Gorry Fairhurst
> >Communication Group,
> >Dept Engineering
> >University of Aberdeen.
> >
> >
> ------------------------------------
> Charles A. Ross
> President
>
> ACANTHUS Corporation
> &
> BEEDNET Group
>
> <[email protected]>
>
> replies to:
> Prague, Representative Office
> GSM mobile +420.(0)603.500.000 (voicemail)
> GSM mobile +420.(0)603.49.1000 (voicemail)
>
> +420.2.2421.9525 tel/fax/voicemail
> ------------------------------------
>
>
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