[Asterisk-Users] FAQ...FXS...LAN...FXO

[Jim Fleming]

----- Original Message ----- 
From: "Stefano Finetti Lynx Automotive srl" <ssfinetti at lynxautomotive.it>
> >
> > Phone===FXS(PC)====LAN=====[Asterisk]FXO===[wall]]======{Phone Company}
> > Phone===FXS(PC)====LAN
> > IP-Phone===========LAN
> > Headset===(PC)=====LAN
> 
> According to your scheme, FXS card should be installed on PCs in order to
> have an analog phone working with them and making them ring when called?
> 

Correct...
One popular way to turn a PC into an IP-Phone (or add that capability) is with an FXS card....$109 per PC...
http://www.quicknet.net
http://www.linuxjack.com
...it is non-trivial to ring a standard phone...
...the FXS devices do that...and have to make themselves look like a phone company (central office)...

The FXO cards come from the low-cost (commodity) modem industry. They have to look like a phone
which is much easier to do, for less money. The software modem cards (internal PCI) are very dumb and
push all of the processing into the C at T Litter Box (Asterisk/Linux). That allows the box to do all of the
LAN to WAN processing. With a DSL arrangement, the box also has another LAN to map the local
LAN (Intranet) to the InterNAT.

As for connecting 4 telephones (FXS), one can assume that you mean as 4 independent stations. Obviously,
connecting 4 telephones on the same wires works, but they can not each be used at the same time, for
intercom and other uses. For 4-ports, there are many options...in some cases, they support 24 ports on
one PCI interface. You quickly move from the consumer realm to the higher-cost commercial realm.

If you look at the small PBX and Key-Telephone market place, historically, 4x16 is the basic building block.
That is 4 lines and 16 stations. If you assume that a DSL comes in on a phone line, and presents the user
with a working line as well as an Ethernet LAN connection, then, you have a starting point for the typical
home, small office. A 2-slot PCI Uni* (Linux) box, with the LAN interface on the motherboard, can do the
entire job, with one FXO (modem card) and a LAN card for the internal intranet. Each PC owner on the
internal LAN can then decide how they want to handle the FXS interface.

One catch is that $50 ADSI phones, are handy when one just needs a low-cost LCD display. The architecture
and protocols have to be arranged to make sure those phones are properly managed. If they are connected
to the FXS cards in the PCs, then that is different from being connected directly to FXS ports on the Asterisk box.
(ADSI = Analog Display Services Interface...not Active Directory Services Interface from M$)

...to summarize, you have to have some idea of the market or application you are addressing...
...the C at T Litter boxes are for the home (SOHO) market...not for a major call center...

Jim Fleming
http://IPv8.iscool.net