On Fri, Jan 31, 2003 at 12:38:56AM +0100, Torsten Schlabach wrote:
> >> Only their licence prohibits that.
>
> It prohibits to do what exactly?
>
> Internet downstream providers on Astra or Eutelsat are 10 a penny in the
> meanwhile, so if those folks don't want it, one could go for another. I
> am just not too sure to what extend we miss part of their business model
> here.
Read their agreement I've put at
http://www.miernik.ctnet.pl/sat/SATADSL350_abroad.txt
This was once on http://www.netsystem.com/eng/SATADSL350_abroad.pdf
but is gone. I've converted it to text, because the PDF was too big.
Now I have read it, and maybe it's not nessesairly that bad. I'll have
to read this, and also agreements of other operators more closely.
Please tell me if you can find/read agreements of the two german
providers, T-DSL and Strato. T-DSL had most info just in german which
I don't understand.
> In my understanding the transponder such a service uses is pretty much
> like an Ethernet collision domain and every subscriber is actually a
> node on that shared network. I always wondered that if they sell 300
> Kbit/s to 10.000 people that would make 3 Gbit/s they'd need on that
> network. Does a transponder on the satellite offer that much capacity?
There are 120 transponders on the Astra 19.2 degree fleet:
http://www.ses-astra.com/corporate/satellites/fleet/astra1.shtml
Transponders numbered 1 to 64 are 22.0 Msymbols/second
Transponders numbered 65 to 104 are 27.5 Msymbols/second
Transponders numbered 105 to 120 are 22.0 Msymbols/second
Total 80 of 22.0 Msyms/s transponders, and 40 of 27.5 Msyms/s ones.
Let me calculate the total bandwith of a single 22 Msymbol/s transponder:
Each symbol carries 2 bits of data: 2 * 22000000 = 44000000 bps
Of that only 188/204 is for data, rest is used for Reed
Solomon Forward Error Correction: 44000000 bps * 188 / 204 = 40549020 bps
Then comes viterbi Error Correction 5/6: 40549020 * 5 / 6 = 33790850 bps
That makes 32.225 Mibps of a single 22.0 Msysmbols/s Astra transponder.
Here goes for the newer 27.5 Msymbol/s transponders:
Each symbol carries 2 bits of data: 2 * 27500000 = 55000000 bps
Of that only 188/204 is for data, rest is used for Reed
Solomon Forward Error Correction: 55000000 bps * 188 / 204 = 50686275 bps
Then comes viterbi Error Correction 5/6: 50686275 * 5 / 6 = 42238562 bps
That makes 40.282 Mibps of a single 27.5 Msysmbols/s Astra transponder.
The whole bandwidth of Astra 19.2 degree fleet is:
80 * 32.225 Mibps + 40 * 40.282 Mibps =
= 2.5176 Gibps + 1.5735 Gibps = 4.0911 Gibps.
Of course most of it is "wasted" for TV channels.
Netsystem for example uses transponder 119, so they have 32.225 Mibps
in total. They sell 300 kibps per client. As I have seen, about half a
yer ago they had about 700 clinets (though they where just starting).
You can eaisly calculate the exact number of clients if you want. Just
watch with what different IP destination numbers do the packets from
their transponder come. Just set the dvb interface into promiscous
mode and watch it with iptraf -l. Half a yer ago I've only seen
clients at 172.23.139.0/24, 172.23.140.0/24 and 172.23.141/24 classes.
300 kibps * 700 = 205 Mibps. Over 6 times more then they have total bandwith.
The fact is, that 300 bips is not your guaranteed bandwith, it's only
your maximum bandwith (IF there is so much free bandwith at the
moment).
Another fact is, that noone usually uses the whole bandwith he can all
the time. I am working as a network administrator in a ISP in Poznan.
We have about 150 clients, to most of which we sell 64 kibps. That
theoretically means 9600 kibps. We have however only 2048 kibps
upstream link. In reality the whole used bandwith is most of the time
around 1 Mibps. Look at out bandwidth graphs at
http://www.ctnet.pl/mrtg/
When I look at the graphs of of individual clinets at
http://www.ctnet.pl/rrd/ I find out that out of these 150 clients,
only 25 of them use the link so much that I can notice it easily on
the graph. The remaining 85% of subscribers use maybe 1% of their link
most of the time.
That's why it's enough for an ISP to have an upstream link of about
10% of the bandwidth they have sold to clients.
> In Germany, Deutsche Telekom sells so called SkyDSL with 768 KBit/s and
> 10.000 subscribers is nothing to them. So where does the bandwidth come
> from. Or am I wrong? Is there anything I don't know?
P.S. ki, Mi and Gi mean 2^10, 2^20 and 2^30 respectively.
--
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