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The translation used by some ISPs to calculate MAC address (which need
to have your DVB card to receive their packets) is:
00 : 01 : IP[0] : IP[1] : IP[2] : IP[3]
where
IP[0].IP[1].IP[2].IP[3] is your
dynamic IP address.
This feature is used, for example, by EON.
Satellite connections are an interesting example of very high RTT (round
trip time, access time): another example is the Mars - Earth communication
or also the Moon - Earth one.
These connections have a very bad feature: very low interactively.
Typical network (or digital, generally) connections use the so called transmission
"window", which represents the data buffer can be sent before waiting for an
answer. In TCP/IP protocol stack this is the TCP Window.
----------------------
| - - - - - - - > can continue |-|-|-|---->
| ----------------------
| Buffer sendable before confirm
|
| - - - - - - - <----------------------
Confirmation Answering
Now, if our communication has an high access time and if we had a little
TCP Window we would lose very much time only waiting for the data confirmation
(ACK), so the real bandwidth would decrease (for example if you have a 16KB
TCP window, typical of Windows systems and a RTT of 400 ms, you cannot overcome
16KB/0.4 = 40 KB/s)
Solution is to use a very high TCP Window (such as 256 KB or some MB).
Unfortunately, under many systems, is not so simple to have a great TCP
Window, so, in latest years, it starts to appear new applications ("download
accelerators" described in next section) that split in many pieces a file and
download all them in the main time: this is just equivalent to download only
one file with a single piece size, avoiding the RTT problem.
We report here some useful link to so called "download accelerator" which
is an application that does 2 things:
- resuming session management, it allows stopping downloading and restarting
later (this can be done thanks to "resuming feature" introduced in Http and Ftp
server, which allows you to specify at what byte number start to download).
- splitting, divide the file in many pieces and let them start in a multithreaded
fashion.
As we saw in the previous section, a download accelerator allows us to
increase satellite bandwidth.
Under Linux
Under Windows
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