203 lines
8.3 KiB
HTML
203 lines
8.3 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>Sat (Satellite Technology) HOWTO: Background Knowledge</TITLE>
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<LINK HREF="Sat-HOWTO-3.html" REL=next>
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<LINK HREF="Sat-HOWTO-1.html" REL=previous>
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<LINK HREF="Sat-HOWTO.html#toc2" REL=contents>
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<A HREF="Sat-HOWTO-3.html">Next</A>
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<A HREF="Sat-HOWTO-1.html">Previous</A>
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<A HREF="Sat-HOWTO.html#toc2">Contents</A>
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<HR>
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<H2><A NAME="s2">2. Background Knowledge</A></H2>
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<H2><A NAME="ss2.1">2.1 What about satellite</A>
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</H2>
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<P>In the last few years satellite began to be applied in Internet networking,
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mainly by medium-big ISPs and we have seen it diffused between users. Sat connections
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are a very different kind of networking than terrestrial ones, with different
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timing such as higher RTT (round trip time), but also with different bandwidth
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value, up to 2 Mbps or more.
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<H2><A NAME="ss2.2">2.2 How does it work?</A>
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</H2>
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<P>We can imagine a path like this:
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<P>
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<PRE>
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|||||| S A T E L L I T E ||||||||
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/ /|\
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Downl / | Uploading
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load / | from
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to /(4) | (3) server
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client / |
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/ |
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SatCard(parabolic antenna) |
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\|/ |
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USER PC ----make request-----> SAT-SERVER <---retrieving---> INTERNET
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(1) (2)
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</PRE>
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<P>So first we make the request (1) (using our Internet connection) to the
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Sat-Server, after it will retrieve out info from Internet (2) and it will send
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it to Satellite (3); in the end we would receive data from the it (4) to our
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home using a parabolic antenna and a Sat Card.
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<P>Typically exist 2 kinds of request :
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<P>
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<UL>
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<LI>Http</LI>
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<LI>Ftp</LI>
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</UL>
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<P>Both of them have a little request data and a much bigger answer size,
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so satellite works very well with it, but with a big time of answer, this is
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the biggest problem of satellite connection (consider a typical Sat distance,
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like 36.000 km, so you would have a time access of [ 36000 km / 300.000
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km/s = 0.120 s = ] 120 ms you have to add (2 times, cause first ISPs server
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send it to, then you download it from) to classical Internet time access.
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<P>Recently ISP allows their clients to use also other kind of service, like
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<P>
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<P>
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<UL>
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<LI>Chat </LI>
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<LI>Email </LI>
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<LI>News </LI>
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</UL>
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<P>and many others.
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<P>There exist also services called "one-way", which consist in mail service
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, download on-demand (where you make a file reservation to be scheduled at
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some time) and site download: these services are offline, so you can access
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to them without modem (or other kind of) connection.
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<H2><A NAME="ss2.3">2.3 Other technologies</A>
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</H2>
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<P>We have to report another satellite technology: the 2-way sat connection.
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It uses only the parabolic antenna to contact Internet in both 2 directions.
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Its cost is much higher that 1-way connection. We expect something from it
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for immediate future, for now it allows a bandwidth of 4 Mbit/s in download
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and 256Kbit/s in upload.
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<H2><A NAME="ss2.4">2.4 What is the max bandwidth?</A>
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</H2>
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<P>It depends on many factors: ISP purpose, TCP window used, applications
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used by the client and the more important of all, "Internet congestion".
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<P>You can expect a max bandwidth of 1-4 Mbps and a average of about 10-30
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KBytes/s, but I repeat, it depends on many factors.
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<P>Anyway some ISPs tell you they give you a "Max" bandwidth, while the average
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bandwidth could be very lower, due to intra-ISP congestion.
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<P>Some other ISPs guarantees you to have a "Minimal" bandwidth, which is more
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meaningful than "MAX", cause it is available all the time.
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<P>Please see Appendix A for more about get downloading performance better.
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<H2><A NAME="ss2.5">2.5 How much does it cost?</A>
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</H2>
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<P>We have to distinguish between hardware costs and account costs, the first
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are known, while the second depend on which service you choose ("guaranteed"/"not
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guaranteed", what bandwidth).
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<H3>Hardware costs</H3>
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<P>To install our little satellite system we need:
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<P>
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<OL>
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<LI>Sat card</LI>
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<LI>Parabolic antenna</LI>
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<LI>one or more feed (converter)</LI>
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</OL>
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<P>Noticed that we need a digital converter to use Internet via satellite.
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<P>Sat card costs depends on brand you choose, about 200US$-300US$.
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<P>Parabolic antenna is about 50 US$.
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<P>Converter is about 50US$.
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<P>So we have about 3-400 US$ of hardware cost (maybe you still have
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to add installation cost!!).
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<P>If you want also receiver Crypt service:
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<P>
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<OL>
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<LI>CI is about 100 US$.</LI>
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<LI>CAM is about 100 US$-250 US$.</LI>
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</OL>
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<H3>Account costs</H3>
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<P>Here costs depend on what ISPs give you access, what's peak bandwidth,
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if there is a guaranteed bandwidth (which is more important than peak one),
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what kind of service they give you and so on.
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<P>Also some ISP gives you free access in change of viewing an always foreground
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spot banner (you cannot iconize it!!): in this case you will pay when you'll
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go to buy something showed in banner!!
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<P>Typically account costs are about 100-150 US$ at year for "not guaranteed"
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services and 4-600 US$ or more for guaranteed ones (they guarantee you
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a minimal bandwidth you can use also under congestion moments, obviously intra
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Sat-ISP congestion!! When you go out to Internet nobody can guarantee you anything!!).
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<H2><A NAME="ss2.6">2.6 What are the satellites used?</A>
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</H2>
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<P>When we speak about satellites we mean: Astra (19.2 degree SE), Hotbird
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(13.2 degree SE), new Europestar (45 degree SE), Eutelsat (8 degree SW), Astra
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(26E), ArabSat 3A (26E).
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<H2><A NAME="ss2.7">2.7 What ISPs give Sat Internet Access?</A>
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</H2>
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<P>In Europe we know about 8 ISPs giving Sat access for Internet:
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<P>
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<OL>
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<LI>
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<A HREF="http://www.europeonline.net">EuropeOnLine - EON</A></LI>
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<LI>
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<A HREF="http://www.netsystem.com">Netsystem</A></LI>
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<LI>
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<A HREF="http://www.starspeeder.com">Starspeeder</A></LI>
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<LI>
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<A HREF="http://www.satnode.com">Sat Node</A></LI>
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<LI>
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<A HREF="http://www.eliosat.com">Eliosat</A></LI>
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<LI>
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<A HREF="http://www.falconstream.com">Falcon Stream </A></LI>
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<LI>
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<A HREF="http://www.skydsl.com">SkyDSL</A></LI>
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<LI>
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<A HREF="http://www.opensky.it">OpenSky</A></LI>
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<LI>
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<A HREF="http://www.direcpc.com">DirecPC</A> but this use a proprietary sat card (this is a first Sat ISP )</LI>
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<LI>
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<A HREF="http://www.xanticbroadband.com/">http://www.xanticbroadband.com/</A></LI>
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</OL>
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<P>EON gives access for about 150 US$ at year without guaranteed bandwidth.
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<P>Netsystem offers its services at "null cost", you just have to see its banner.
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<P>
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<P>Starspeeder gives access ???
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<P>Eliosat costs 350 US$ at year with a 128 Kbps guaranteed (minimal
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service, see web site for more);in addition it gives 2-way technology access
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for either receive and transmit.
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<P>SkyDSL gives access full-time and it costs about 15 US$ at month
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with 128Kbit/s bandwidth, but it allows a bigger bandwidth where you pay each
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Mb downloaded (you can select from 256Kbit/s up to 4Mbit/s), for more you can
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visit its web site.
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<P>IMPORTANT : before subscribing some satellite account, please verify "foot
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of Satellite" and diameter of parabola.
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<P>OpenSky started before summer 2001 in its "beta test": it allows you to try
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the sat service downloading at maximum 300 MB at month (free). To register
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you need to go at
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<A HREF="http://www.opensky.it/cc/index.asp?f=registrazione.htm">OpenSky registration procedure</A> (which is in italian language!).
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<H2><A NAME="ss2.8">2.8 What else?</A>
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</H2>
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<P>With every kind of DVB card you can also receive TV digital channels (free
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channels only) and some cards have support for common interface to watch encrypted
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channel.
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<P>Follows the schema:
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<P>
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<PRE>
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Smart-Card -> CAM -> Common Interface -> Sat Card (with support C.I.)
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</PRE>
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<P>CAM Card (there are many standards used for decryption: SECA, IRDETO, VIACCESS
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and others) is the hardware allowing decryption (for TV, Radio and Data) while
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the Common Interface or C.I. (ETSI EN 50221) allow connection between CAM and
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Sat Card.
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<HR>
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<A HREF="Sat-HOWTO-3.html">Next</A>
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<A HREF="Sat-HOWTO.html#toc2">Contents</A>
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