Both MSN and AOL will use MPEG-2 encapsulation of the IP data to make the receiver as cheap as possible. MPEG is easy to look at if you know the multiplexing scheme but the IP addressing will be NATted over the bird. MSN uses a further layer called DVB (http://www.dvb.org/resources/pdf/dvb_cook.pdf) which can provide "conditional access."
DVB is the same format that EchoStar Dish DBS uses for their Digital TV signals. It is possible to use IPSec to encrpyt the IP payload but it takes dedicated hardware in the user terminal and slows the user speed down substantially. It is very unlikely any encryption will be used except there is some "scrambling" associated with the modulation scheme but this is not random...just there to keep from harming other (terrestrial) signals when the radio frequency energy is concentrated in a very small bandwidth.
The return from the user will be on a seperate channel from the first and takes a big dish (maybe 12 feet in diameter) to receive it so sniffing will be a pretty sophisticated (and unesthetical) operation.
You are wrong by twice. 250 milliseconds is the "air time" round trip delay. There is also the "processing delay", the modulation and demodulation and that adds roughly 100 ms so the ping shouldn't be more than 350 ms...still sucks for gaming but doesn't add up to much when waiting for html or ftp.
There are tons of problems with this delay over TCP. TCP is looking for a reply much quicker than 350 ms so it assumes the link is errored and halves the session transmission rate. This continues down to about 200 Kbps (depending on your TCP window size) where it stabilizes. To make the session speed higher, the satellite operator "spoofs" the TCP both at the uplink and the consumer's box. With this technique (described in an RFC) single session speeds can reach many, many megabits per second.
As far as filling the pipe, both systems mentioned in the post use a shared~27 Mbps carrier on the forward channel (to the subscribers... like cable modem). The return channel (back to the ISP) is also shared but at a much lower rate (128 - 150 Kbps) and it can be "hogged" for short periods.
MSN originally though they could get by with 20,000 subscribers per satellite transponder ($2,000,000/year) but after beta testing they are going to have to back it down to below 7,000 subs (and IMHO below 2,500) to get acceptable performance.
The real satellite broadband will NOT happen because of the economics mentioned above until Ka-Band satellites such as WildBlue or Cyberstar get launched beginning in late 2001. Then the bandwidth costs will drop by 4 or 5 times making it reasonable to offer a $20-$30 per month price.
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Both MSN and AOL will use MPEG-2 encapsulation of the IP data to make the receiver as cheap as possible. MPEG is easy to look at if you know the multiplexing scheme but the IP addressing will be NATted over the bird. MSN uses a further layer called DVB (http://www.dvb.org/resources/pdf/dvb_cook.pdf) which can provide "conditional access."
DVB is the same format that EchoStar Dish DBS uses for their Digital TV signals. It is possible to use IPSec to encrpyt the IP payload but it takes dedicated hardware in the user terminal and slows the user speed down substantially. It is very unlikely any encryption will be used except there is some "scrambling" associated with the modulation scheme but this is not random...just there to keep from harming other (terrestrial) signals when the radio frequency energy is concentrated in a very small bandwidth.
The return from the user will be on a seperate channel from the first and takes a big dish (maybe 12 feet in diameter) to receive it so sniffing will be a pretty sophisticated (and unesthetical) operation.
You are wrong by twice. 250 milliseconds is the "air time" round trip delay. There is also the "processing delay", the modulation and demodulation and that adds roughly 100 ms so the ping shouldn't be more than 350 ms...still sucks for gaming but doesn't add up to much when waiting for html or ftp.
There are tons of problems with this delay over TCP. TCP is looking for a reply much quicker than 350 ms so it assumes the link is errored and halves the session transmission rate. This continues down to about 200 Kbps (depending on your TCP window size) where it stabilizes. To make the session speed higher, the satellite operator "spoofs" the TCP both at the uplink and the consumer's box. With this technique (described in an RFC) single session speeds can reach many, many megabits per second.
As far as filling the pipe, both systems mentioned in the post use a shared~27 Mbps carrier on the forward channel (to the subscribers... like cable modem). The return channel (back to the ISP) is also shared but at a much lower rate (128 - 150 Kbps) and it can be "hogged" for short periods.
MSN originally though they could get by with 20,000 subscribers per satellite transponder ($2,000,000/year) but after beta testing they are going to have to back it down to below 7,000 subs (and IMHO below 2,500) to get acceptable performance.
The real satellite broadband will NOT happen because of the economics mentioned above until Ka-Band satellites such as WildBlue or Cyberstar get launched beginning in late 2001. Then the bandwidth costs will drop by 4 or 5 times making it reasonable to offer a $20-$30 per month price.