"Dana" <raff242@yahoo.com> wrote:
>"Andrew Swallow" <am.swallow@btopenworld.com> wrote:
>> Dana wrote:
>>
>>> As for the delay, that will still be there, as you have to get up and
>>> back to the satellite, On VSATS in the field and my own satellite
>>> connection at the house here in Alaska, I have seen delays up to 2 doing
>>> ping.
>>
>> If done properly routing in the satellite will half the delay.
>>
>> Previous systems did it one of two ways.
>>
>> 1. Subscribe A to satellite and the satellite broadcast the data to
>> everyone.
>> 2. Or Subscriber A to satellite, satellite forwards data to a military
>> base somewhere. The routing computer at the military base decides
>> which one of its satellites to send the data to. Base sends data
>> to satellite and the satellite forwards data to Subscriber B.
>> This requires four 36,000 mile hops and 4 radio frequencies.
>>
>> The new satellite appears to contain its own routing computer.
>> New way. Subscriber A to satellite. Satellite examines the Call
>> Request and looks in its data base for Subscriber B. If B is
>> within the foot print then the satellite calls Subscriber B.
>> This requires two 36,000 mile hops and 2 radio frequencies.
>>

This is the IP equivalent of DAMA (Demand Access Multiple
Assignment) for switched circuit networking (the PSTN).

Subscriber A now is talking to a ground based router via one
satellite link, and Subscriber B is talking to the same ground
based router via a different satellite link. Two hops to the
satellite are used for A and B to communicate. Each hop adds
approximately 400-500ms of latency, even though A and B could
literally be in adjacent buildings.

The "new" idea is to have a router in the satellite, there will
be only one hop, as each subscriber still has a link to the
satellite, but no second link to a ground station is required
(for the data path, at least, but I would expect that most of
the router's smarts will be ground based, and only the switching
fabric will be in the satellite).

That has practical application in Alaska, just the same as DAMA
used for voice switched networking for the PSTN. Using DAMA
reduces the use of very expensive satellite bandwidth almost
half, and provides the customer with a significantly higher
quality service.

Consider the problems that state agencies, schools, and health
care organizations all have with existing private networking.
For example, one network based in Bethel (the Yukon/Kuskokwim
Delta region of southwestern Alaska) had to put their main
network routing center in Seattle just because it would have
been a killer to double hop all traffic that did connect
outside, whereas there is much less traffic between the
villages, so village-to-village traffic had to tolerate the
higher latency.

With a router in the satellite, they would be able to move the
main operation to their building in Bethel and have much better
administrative control and at the same time provide better
technical service to their end users in each village.

>> The is only a small advantage in having tactical routers but big
>> advantages in strategic and logistics routers. The front line
>> Lieutenant can send an email back to the USA.

But that is *not* significant for email! That's a store and
forward system that might have hours of latency! But video
conferencing, or even just voice calls/conferencing, would be
significantly better with lower latency. Schools and health
care providers in particular would find it useful.

Of course the military would also be able to deploy a much more
effective remote controlled tactical battle team, with the
remote control being in the field and mobile. With low latency
between each user the Command Post could actually be dispersed,
with potentially each user participating.

>They are doing that with VSATS, and have been for years.

Where? I thought all of them were using common base to
subscriber links and multiple subscriber to base links. That
requires a ground based router, and communications between any
two satellite subscribers requires a double hop.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com