[Asterisk-Users] How many FXS/FXO ports do I need?

[Aaron O'Hara]

All,

I'm new to phone systems and phone wiring and I couldn't find an answer
to this question on the wiki or google.

My understanding is that a standard residential/business phone line
carries the signal over 2 wires. Your 4-wire RJ11 wiring supports 2
phone lines. Given that each line takes 2 wires, and there are 8 wires
in an FXO port, can I conceivably support 4 phone lines on one FXO port?

On the phone/FXS side of things, can you also have multiple lines per
FXS port?

If I want to hookup 5 phones to my residential phone service with 2
lines, what # of FXO & FXS ports do I need?

Thanks for your clarification...

-- Aaron

[Kerry Garrison]

For your configuration you should get two X100P cards (compatible cards are
$6.95 on eBay). That's all you would need. The 5 phones connect to the
Asterisk server over an ethernet connection.

Kerry Garrison
http://www.geekgazette.com


-----Original Message-----
From: asterisk-users-***@lists.digium.com
[mailto:asterisk-users-***@lists.digium.com] On Behalf Of Aaron O'Hara
Sent: Friday, April 08, 2005 5:31 PM
To: Asterisk Mailing List
Subject: [Asterisk-Users] How many FXS/FXO ports do I need?

All,

I'm new to phone systems and phone wiring and I couldn't find an answer to
this question on the wiki or google.

My understanding is that a standard residential/business phone line carries
the signal over 2 wires. Your 4-wire RJ11 wiring supports 2 phone lines.
Given that each line takes 2 wires, and there are 8 wires in an FXO port,
can I conceivably support 4 phone lines on one FXO port?

On the phone/FXS side of things, can you also have multiple lines per FXS
port?

If I want to hookup 5 phones to my residential phone service with 2 lines,
what # of FXO & FXS ports do I need?

Thanks for your clarification...

-- Aaron


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[Andrew Kohlsmith]

Post by Aaron O'Hara
My understanding is that a standard residential/business phone line
carries the signal over 2 wires. Your 4-wire RJ11 wiring supports 2
phone lines. Given that each line takes 2 wires, and there are 8 wires
in an FXO port, can I conceivably support 4 phone lines on one FXO port?

No; the FXO ports only have the middle two pins wired to anything. One port =
one line.

Post by Aaron O'Hara
On the phone/FXS side of things, can you also have multiple lines per
FXS port?

See above; only the middle two are wired. The TDM400P uses RJ45 because they
can use the same backplate with the TE4xxP cards. :-)

Post by Aaron O'Hara
If I want to hookup 5 phones to my residential phone service with 2
lines, what # of FXO & FXS ports do I need?

if you want each of the 5 phones on their own 'extension' then you need 5 FXS
ports. Irrespective of that, you need two FXO ports.

I'd say get a TDM22P; that gives you two internal extensions (say 3 phones on
one, and 2 on the other), and access to your two lines.

I'd recommend against the X101Ps; not only will you have double the interrupts
of a single TDM that can handle twice the number of ports, but you will also
have a poorer hybrid interface to the PSTN; the TDM4xxP's FXO modules can be
tuned much better.

-A.

[Rich Adamson]

Post by Aaron O'Hara
I'm new to phone systems and phone wiring and I couldn't find an answer
to this question on the wiki or google.
My understanding is that a standard residential/business phone line
carries the signal over 2 wires. Your 4-wire RJ11 wiring supports 2
phone lines. Given that each line takes 2 wires, and there are 8 wires
in an FXO port, can I conceivably support 4 phone lines on one FXO port?
On the phone/FXS side of things, can you also have multiple lines per
FXS port?
If I want to hookup 5 phones to my residential phone service with 2
lines, what # of FXO & FXS ports do I need?
Thanks for your clarification...

Others have already addressed most of your questions.

You have lots of different choices on how you address 5 phones and
2 lines. A couple choices include:

- use the digium TDM card with two fxo modules (to connect to the
two pstn lines), and one fxs module (to ring all of the five phones)

- use two Sipura spa-3000 adapters (each adapter can support one pstn
line and one fxs port, and you decide whether the two fxs ports
provided on the adapters have one or more of the five phones
attached to them. eg, business vs home phones.

- replace all of your analog phones with voip sip phones (and ethernet
wiring). No need for fxs ports.

I kind of like the spa-3000 approach since those adapters allow
you to make a decision on how you want your system to function,
while also allowing you to change your mind and support your phones
in a different way at some later date. Lots of little features built
into those boxes.

If you use the TDM card approach, any time your asterisk system is
down (for any reason), your phones are all down. That will likely be
a problem for you as you learn how to do things with asterisk, and
some of those "things" require you to stop asterisk & restart it.

If you use the spa-3000 approach, you can configure the boxes to
have all incoming pstn calls ring through to your phones (even when
asterisk is down, or AC power is down).