FXS or FXO?

VOIP setup and troubleshooting
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austdata
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Location: Melbourne

FXS or FXO?

Post by austdata » Sat Feb 16, 2008 1:39 am

G'day All,
I'm still having trouble working out the difference between FXS and FXO.

What I think they are, is the FXS is a PSTN to PSTN equipment and FXO is IP to PSTN equipment. Is that correct?

Cheers,

Mike

ymo
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Location: Wollongong NSW

Post by ymo » Sat Feb 16, 2008 10:17 am

From Wikipedia http://en.wikipedia.org/wiki/Foreign_exchange_office & http://en.wikipedia.org/wiki/Foreign_exchange_station
An FXO is any device that, from the point of view of a telephone exchange, seems to be a regular telephone. As such, it should be able to accept ringing signals, go on-hook and off-hook, and send and receive voice signals.

FXS is any device that, from the point of view of a telephone, seems to be a telephone exchange. As such, it should be able to supply power to the connected telephone, provide ringing signals and dialtone, understand when phone goes on-hook or off-hook, and send and receive voice signals.
It looks to me as if a VOIP ATA is an FXS but if it can connect to a regular phone line for fallback then it is also an FXO.

Here is another explanation: http://www.dceexpress.com/FXS_FXO_Discussion.htm

austdata
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Location: Melbourne

Post by austdata » Sat Feb 16, 2008 1:21 pm

G'day Ymo,
Thanks for the information. I've read the "The Difference Between FXS and FXO" web page before and it still doesn't seem, to me at least, to say what each one is.

I read the Wikiepeadia reference and near the top it describes FXO as an IP Phone and a little further down it describes it as a "regular phone" which is confusing.

Perhaps I'll just stick with the one explanation it makes clear:
Analogue telephone handsets, fax machines and (analogue) modems are FXO devices
Then just assume that FXS is for IP Telephony. That leaves me with only one problem, is this FKX/FSO stuff what external to the building or is it internal.

Cheers,

Mike

GaryG
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Location: Melbourne

Post by GaryG » Sat Feb 16, 2008 6:33 pm

On my modem (Billion 7404VGP) I have two FXS and one FXO port.

You plug the handsets into the FXS ports and connect the FXO to the phone socket (via an ADSL2 filter).

If you using PSTN (normal phone) this will connect your phones straight from FXS to FXO (or vice versa).

If you using VOIP the call goes via the modem but the FXO provides fallback, ie if the VOIP fails you still get connected to PSTN.

austdata
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Joined: Wed Apr 25, 2007 12:38 am
Location: Melbourne

Post by austdata » Sat Feb 16, 2008 10:22 pm

GaryG wrote:You plug the handsets into the FXS ports and connect the FXO to the phone socket.

If you using PSTN this will connect your phones straight from FXS to FXO (or vice versa).

If you using VOIP the call goes via the modem but the FXO provides fallback, ie if the VOIP fails you still get connected to PSTN.
G'day Gary,
Okay I think I've got it. The FXO is line in (hence it can also be used for fall back) and FXS is line out but usually for VoIP. If VoIP fails and if configured correctly it can be line-out for PSTN.

How's that?!

Mike

GaryG
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Location: Melbourne

Post by GaryG » Sat Feb 16, 2008 10:37 pm

austdata wrote:
GaryG wrote:You plug the handsets into the FXS ports and connect the FXO to the phone socket.

If you using PSTN this will connect your phones straight from FXS to FXO (or vice versa).

If you using VOIP the call goes via the modem but the FXO provides fallback, ie if the VOIP fails you still get connected to PSTN.
G'day Gary,
Okay I think I've got it. The FXO is line in (hence it can also be used for fall back) and FXS is line out but usually for VoIP. If VoIP fails and if configured correctly it can be line-out for PSTN.

How's that?!

Mike
Sort of. But it is a 2 way process.

FXS connects your phones to the modem.
FXO connects your modem to the PSTN to give you access if VOIP fails or if you want to override VOIP and use PSTN instead.

So FXO only gets used when you connect to PSTN.

FXS gets used all the time.

austdata
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Location: Melbourne

Post by austdata » Sat Feb 16, 2008 10:54 pm

Thanks Gary,
I get it now. In most cases (a one phone line home) one FXO port would do and one or more FXS ports for all the VoIP phones. :D

So a Netcomm V431 SmartVoice 3FXS, 1FXD would be adequate for my home office.

NOTE: I reckon the FXD on the Netcomm web site is a typo. Either that or I'm way more confused than even I thought. :shock:

Cheers,

Mike

GaryG
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Post by GaryG » Sat Feb 16, 2008 10:59 pm

Happy to help.

And yes, 1 FXO is usually plenty.

With multiple FXS, you could have different VOIP numbers on each for example.

If you don't need 3 FXS, a much cheaper option (going by the RRP on that website, is the Billion that I use.

austdata
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Post by austdata » Sat Feb 16, 2008 11:12 pm

The V431 can be bought for $542. It has the advantage of have T.38 for fax over IP, not that I really need it.

Mainly it's because I'm lead to believe it delivers a noticeable improvement to VoIP being a commercial VoIP Gateway.

Cheers,

Mike

GaryG
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Location: Melbourne

Post by GaryG » Sat Feb 16, 2008 11:19 pm

The Billion has T.38 as well - not that you need it. :D

It would have to offer a lot of improvement in VOIP for me to speed an extra $350 for that improvment so it is hard for me to see it but your choice in the end.

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