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Sat (Satellite Technology) HOWTO: Background Knowledge Next Previous Contents

2. Background Knowledge

2.1 What about satellite

In the last few years satellite began to be applied in Internet networking, mainly by medium-big ISPs and we have seen it diffused between users. Sat connections are a very different kind of networking than terrestrial ones, with different timing such as higher RTT (round trip time), but also with different bandwidth value, up to 2 Mbps or more.

2.2 How does it work?

We can imagine a path like this:

              |||||| S A T E L L I T E  ||||||||
                   /                       /|\                   
Downl             /                         |      Uploading
load             /                          |      from 
to              /(4)                        | (3)  server
client         /                            |     
              /                             |     
SatCard(parabolic antenna)                  |                                      
             |                              |
            \|/                             |        
       USER PC ----make request-----> SAT-SERVER <---retrieving---> INTERNET
                         (1)                               (2)

So first we make the request (1) (using our Internet connection) to the Sat-Server, after it will retrieve out info from Internet (2) and it will send it to Satellite (3); in the end we would receive data from the it (4) to our home using a parabolic antenna and a Sat Card.

Typically exist 2 kinds of request :

  • Http
  • Ftp

Both of them have a little request data and a much bigger answer size, so satellite works very well with it, but with a big time of answer, this is the biggest problem of satellite connection (consider a typical Sat distance, like 36.000 km, so you would have a time access of [ 36000 km / 300.000 km/s = 0.120 s = ] 120 ms you have to add (2 times, cause first ISPs server send it to, then you download it from) to classical Internet time access.

Recently ISP allows their clients to use also other kind of service, like

  • Chat
  • Email
  • News

and many others.

There exist also services called "one-way", which consist in mail service , download on-demand (where you make a file reservation to be scheduled at some time) and site download: these services are offline, so you can access to them without modem (or other kind of) connection.

2.3 Other technologies

We have to report another satellite technology: the 2-way sat connection. It uses only the parabolic antenna to contact Internet in both 2 directions. Its cost is much higher that 1-way connection. We expect something from it for immediate future, for now it allows a bandwidth of 4 Mbit/s in download and 256Kbit/s in upload.

2.4 What is the max bandwidth?

It depends on many factors: ISP purpose, TCP window used, applications used by the client and the more important of all, "Internet congestion".

You can expect a max bandwidth of 1-4 Mbps and a average of about 10-30 KBytes/s, but I repeat, it depends on many factors.

Anyway some ISPs tell you they give you a "Max" bandwidth, while the average bandwidth could be very lower, due to intra-ISP congestion.

Some other ISPs guarantees you to have a "Minimal" bandwidth, which is more meaningful than "MAX", cause it is available all the time.

Please see Appendix A for more about get downloading performance better.

2.5 How much does it cost?

We have to distinguish between hardware costs and account costs, the first are known, while the second depend on which service you choose ("guaranteed"/"not guaranteed", what bandwidth).

Hardware costs

To install our little satellite system we need:

  1. Sat card
  2. Parabolic antenna
  3. one or more feed (converter)

Noticed that we need a digital converter to use Internet via satellite.

Sat card costs depends on brand you choose, about 200US$-300US$.

Parabolic antenna is about 50 US$.

Converter is about 50US$.

So we have about 3-400 US$ of hardware cost (maybe you still have to add installation cost!!).

If you want also receiver Crypt service:

  1. CI is about 100 US$.
  2. CAM is about 100 US$-250 US$.

Account costs

Here costs depend on what ISPs give you access, what's peak bandwidth, if there is a guaranteed bandwidth (which is more important than peak one), what kind of service they give you and so on.

Also some ISP gives you free access in change of viewing an always foreground spot banner (you cannot iconize it!!): in this case you will pay when you'll go to buy something showed in banner!!

Typically account costs are about 100-150 US$ at year for "not guaranteed" services and 4-600 US$ or more for guaranteed ones (they guarantee you a minimal bandwidth you can use also under congestion moments, obviously intra Sat-ISP congestion!! When you go out to Internet nobody can guarantee you anything!!).

2.6 What are the satellites used?

When we speak about satellites we mean: Astra (19.2 degree SE), Hotbird (13.2 degree SE), new Europestar (45 degree SE), Eutelsat (8 degree SW), Astra (26E), ArabSat 3A (26E).

2.7 What ISPs give Sat Internet Access?

In Europe we know about 8 ISPs giving Sat access for Internet:

  1. EuropeOnLine - EON
  2. Netsystem
  3. Starspeeder
  4. Sat Node
  5. Eliosat
  6. Falcon Stream
  7. SkyDSL
  8. OpenSky
  9. DirecPC but this use a proprietary sat card (this is a first Sat ISP )
  10. http://www.xanticbroadband.com/

EON gives access for about 150 US$ at year without guaranteed bandwidth.

Netsystem offers its services at "null cost", you just have to see its banner.

Starspeeder gives access ???

Eliosat costs 350 US$ at year with a 128 Kbps guaranteed (minimal service, see web site for more);in addition it gives 2-way technology access for either receive and transmit.

SkyDSL gives access full-time and it costs about 15 US$ at month with 128Kbit/s bandwidth, but it allows a bigger bandwidth where you pay each Mb downloaded (you can select from 256Kbit/s up to 4Mbit/s), for more you can visit its web site.

IMPORTANT : before subscribing some satellite account, please verify "foot of Satellite" and diameter of parabola.

OpenSky started before summer 2001 in its "beta test": it allows you to try the sat service downloading at maximum 300 MB at month (free). To register you need to go at OpenSky registration procedure (which is in italian language!).

2.8 What else?

With every kind of DVB card you can also receive TV digital channels (free channels only) and some cards have support for common interface to watch encrypted channel.

Follows the schema:

Smart-Card -> CAM -> Common Interface -> Sat Card (with support C.I.)

CAM Card (there are many standards used for decryption: SECA, IRDETO, VIACCESS and others) is the hardware allowing decryption (for TV, Radio and Data) while the Common Interface or C.I. (ETSI EN 50221) allow connection between CAM and Sat Card.

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