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WHAT
IS IT MADE OF:
As
you can imagine it is not a very efficient solution and in fact
telephones have not been created for this purpose, but they are
used however because they are well spread and economical. Modems
are usually sent for less than 45 euros and telephone lines generally
cost around a hundred euros the year. The most common way to connect
some machines together and to create a LAN, is to use the cards
Ethernet. Different types of Ethernet exist (listed by the oldest
to the most recent):Thinwire/Coox/10base2,UTP (Unshield Twisted
Pair - duplex cable not screened) 10 baseT and UTP/100baseT.
The most recent gigabit Ethernet cards are available (the name
1000baseT started to be frivolous). The cable 10base2 are normally
coaxial and black, whoever can be connected to the line, provided
of a special terminal at the two extremes, through some connectors
to T-twist-on.
Instead UTP is generally a blue cable, with connectors "click"
as that normal telephones: every cable connects a knot to a central
HUB. The cable costs some euros for meter, while the cards 10baseT/10base2
(a lot of cards have grafts for both) cost about 27 euros. The
cards 100baseT, that are "compatible" with the 10baseT,
are ten times faster, and they cost about 90 Euros. On the other
hand of the ghost we find the fibre, a thin and continuous filament
of glass wound by a protective coverage, used for the connections
among continents. The fibres cost thousands of euros.
We will generally define every connection to a knot "interface
of net", or more simply interface. Linux assigns some names
as "ETH0" for the first interface Ethernet, and "FDDi0"
for the first interface that concerns the fibre. The command "/sbin/ifconfig"
shows a list of it.
PROTOCOL:
the most important thing to be known is which language is used by
the two connected parts. When two modems want to converse on a telephone
line, they have to agree on the different meanings of the signals,
otherwise they won't be understood. This convention is called "protocol".
New protocols are invented, as new methods of coding of the data
are discovered coming from the computer in always smaller signals.
For the modem exist at least a dozen all different ones and most
greater part of them try a certain number up to find that the other
modem includes. Another example is the 100baseT quotes before, it
uses the same type of physical connection (UTP) used by 10baseT,
but it is 10 times faster, these two protocols are known as protocols
of "level link" and they concern the management of the
individual connections of the net or of "one hop" (simple
jump). The term "protocol" also refers to other conventions
as we will subsequently see.
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