I would have said that the satellite is a wireless router. It takes a stream sent up from the ground station and broadcasts it to all the End Users.

I think we're a bit at cross-purposes- I was including the end user as a ground station, I'll separate the two terms from now on .

The satellite isn't a router, it's just part of a radio link. It can handle multiple inputs from end users and squirt them to a "proper" ground station connected to the internet, but stuff coming the other way is only routed to the satellite if it's addressed to an end user, and then it's broadcast to all of them within its footprint. Bit of a security/privacy risk, actually.

The sat is acting more like a multiplexer in one direction and a simple repeater in the other, all the routing is done in the ground station.

In reply to a post by billford:

I would have said that the satellite is a wireless router. It takes a stream sent up from the ground station and broadcasts it to all the End Users.

I think we're a bit at cross-purposes- I was including the end user as a ground station, I'll separate the two terms from now on .

The satellite isn't a router, it's just part of a radio link. It can handle multiple inputs from end users and squirt them to a "proper" ground station connected to the internet, but stuff coming the other way is only routed to the satellite if it's addressed to an end user, and then it's broadcast to all of them within its footprint. Bit of a security/privacy risk, actually.

The sat is acting more like a multiplexer in one direction and a simple repeater in the other, all the routing is done in the ground station.

Fair enough. Actually I wonder how it handles inputs for 2-way BB? Does it rely on collision detection (seems unlikely with 120ms latency) or assigned frequencies? Seems like another potential bottleneck with large numbers of users.

Edited by Andrue (Tue 05-May-09 13:30:09)

In essence the whole satelite link replaces a single cable - that from you to your nearest point of presence (pop). Just with satelite the pop may be hundreds of miles away rather than the nearest exchange.

Everything else in the network is just the same.

In reply to a post by Andrue:

I wonder how it handles inputs for 2-way BB?

I have absolutely no idea .

With modern clocks it could be done with TDM, but it's getting complicated...

In reply to a post by billford:

In reply to a post by Andrue:

I wonder how it handles inputs for 2-way BB?

I have absolutely no idea .

With modern clocks it could be done with TDM, but it's getting complicated...

No kidding.

http://en.wikipedia.org/wiki/Time-division_multiplexing

And today's new word is:

http://en.wikipedia.org/wiki/Plesiochronous

brought to you by the letter 'P'

Edited by Andrue (Tue 05-May-09 14:11:26)

The laws of physics mean that 240ms gets added to your pings

and again. Two way satellite adds 480ms

you - sat - ground station - sat - you

on top of standard network latency.

On commercial data sat providers. Your looking at 500ms round trip. This is usually over come back wan/bandwidth mangement device i.e. PacketShapers Riverbeds etc etc.

Therefore the ammount of data on demand would not be small beer.

Also, the Hotbird/Eurobird does not provide data service on 19o East transponder.

In reply to a post by Anonymous:

The laws of physics mean that 240ms gets added to your pings

and again. Two way satellite adds 480ms

you - sat - ground station - sat - you

on top of standard network latency.

Yes but I'm assuming it'll be one-way. I believe that's what's most likely in the UK. Two way seems like rather a specialised option.

In reply to a post by Anonymous:

I've often wondered why Sky doesn't offer there broadband over there satellite network doing away with BT and getting coverage to most of the UK, can anyone tell me why?

Because it's not their satellite network.

</thread>

In reply to a post by billford:

In reply to a post by Andrue:

I wonder how it handles inputs for 2-way BB?

I have absolutely no idea .

With modern clocks it could be done with TDM, but it's getting complicated...

Here you go: http://www.satsig.net/vsat-equipment/tdma-explanatio...

EDIT: Could also use a flavour of CDMA, all depends on the implementation.

Edited by deleted (Tue 05-May-09 16:13:39)