Hello all, as a relative newbie I obediently ordered the recently recommended "Newton's Telecom Dictionary" but it did not provide the answer to one of my question. Perhaps one of you can do so. What is the difference in functionality between an FXO and an FXS port? I know that the line from telco goes into an FXO and standard POTS phone goes into an FXS, but since both types of ports must be able to both make and answer calls, what is the actual functional difference? Or in other words, what does an FXO to FXS converter do (I have seen some mention but no explanation of those)? Thanks. Wolf Paul
The way I explain the difference between fxo and fxs, is electrically... The telco lines, PROVIDES voltage and current to makes the telephone ring, so the FXO is a device, adapted to recive this voltage an current. The phone, NEEDS voltage and current, to ring, so the FXS is a device, adapted to provide this voltage and current. So, if you plug an FXS to a Telco Line, both equiments PROVIDE voltage and current, so... what you have? Sparks and a short cut, and at least like 75usd of the fxs module or even worst, like 100usd for iaxy or fxs card :( Wolf Paul wrote:> Hello all, > > as a relative newbie I obediently ordered the recently recommended > "Newton's Telecom Dictionary" but it did not provide the answer to one > of my question. Perhaps one of you can do so. > > What is the difference in functionality between an FXO and an FXS port? > I know that the line from telco goes into an FXO and standard POTS phone > goes into an FXS, but since both types of ports must be able to both > make and answer calls, what is the actual functional difference? > > Or in other words, what does an FXO to FXS converter do (I have seen > some mention but no explanation of those)? > > Thanks. > > Wolf Paul > > _______________________________________________ > Asterisk-Users mailing list > Asterisk-Users@lists.digium.com > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users >
On Sat, 16 Oct 2004, Wolf Paul wrote:> What is the difference in functionality between an FXO and an FXS port? > I know that the line from telco goes into an FXO and standard POTS phone > goes into an FXS, but since both types of ports must be able to both > make and answer calls, what is the actual functional difference?An Asterisk FXO interface connects to a phone line. So it has to detect ringing voltage, answer (take the "phone off hook", ie loop the line) and so on. An Asterisk FXS interface has to connect to a phone. So it has to make ringing voltage, detect if the phone is taken off hook or put on hook, detect tone or pulse dialling and so on. Steve
Benjamin on Asterisk Mailing Lists
2004-Oct-16 10:20 UTC
[Asterisk-Users] FXO vs FXS question
On Sat, 16 Oct 2004 19:05:34 +0200, Wolf Paul <wnp@doulos.at> wrote:> What is the difference in functionality between an FXO and an FXS port? > I know that the line from telco goes into an FXO and standard POTS phone > goes into an FXS, but since both types of ports must be able to both > make and answer calls, what is the actual functional difference?An FXS port provides voltage to the phone, it also provides a dialtone. An FXO port does none of that. Apart from that, the signalling is different. rgds benjk -- Sunrise Telephone Systems, 9F Shibuya Daikyo Bldg., 1-13-5 Shibuya, Tokyo, Japan. NB: Spam filters in place. Messages unrelated to the * mailing lists may get trashed.
Andres Tello Abrego wrote:> The way I explain the difference between fxo and fxs, is electrically... > > The telco lines, PROVIDES voltage and current to makes the telephone > ring, so the FXO is a device, adapted to recive this voltage an current. > > The phone, NEEDS voltage and current, to ring, so the FXS is a device, > adapted to provide this voltage and current. > > So, if you plug an FXS to a Telco Line, both equiments PROVIDE voltage > and current, so... what you have? Sparks and a short cut, and at least > like 75usd of the fxs module or even worst, like 100usd for iaxy or > fxs card :(When I designed line cards for the PSTN we specifically tested that this sort of thing would not happen. Phone lines are handled in a pretty sloppy way. If a line card in an exchange blew up every time someone shorted two lines together they would be replacing cards all day. Regards, Steve
I have blown one fxs module in that way :( It?s a warning, and you MUST be careful of tring no to do so. Steve Underwood wrote:> Andres Tello Abrego wrote: > >> The way I explain the difference between fxo and fxs, is electrically... >> >> The telco lines, PROVIDES voltage and current to makes the telephone >> ring, so the FXO is a device, adapted to recive this voltage an current. >> >> The phone, NEEDS voltage and current, to ring, so the FXS is a device, >> adapted to provide this voltage and current. >> >> So, if you plug an FXS to a Telco Line, both equiments PROVIDE voltage >> and current, so... what you have? Sparks and a short cut, and at least >> like 75usd of the fxs module or even worst, like 100usd for iaxy or >> fxs card :( > > > When I designed line cards for the PSTN we specifically tested that this > sort of thing would not happen. Phone lines are handled in a pretty > sloppy way. If a line card in an exchange blew up every time someone > shorted two lines together they would be replacing cards all day. > > Regards, > Steve > > _______________________________________________ > Asterisk-Users mailing list > Asterisk-Users@lists.digium.com > http://lists.digium.com/mailman/listinfo/asterisk-users > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-users >
> as a relative newbie I obediently ordered the recently recommended > "Newton's Telecom Dictionary" but it did not provide the answer to one > of my question. Perhaps one of you can do so. > > What is the difference in functionality between an FXO and an FXS port? > I know that the line from telco goes into an FXO and standard POTS phone > goes into an FXS, but since both types of ports must be able to both > make and answer calls, what is the actual functional difference? > > Or in other words, what does an FXO to FXS converter do (I have seen > some mention but no explanation of those)?A box/adapter that has a FXS port must be capable of "ringing" the attached phone, and support other supervisory functions as though it were the controlling interface to that attached phone. A box/adapter that has a FXO port must be capable of receiving ringing and other types of signaling, answer that incoming call, etc. In addition, most FXO ports are capable of sending calls to the pstn line, etc. FXO ports have no need for a ringing generator.
The term "FX" refers to an old telecom service that provided a "Foreign eXchange" circuit - basically an analog extension that the telco would terminate at a remote location and connect back into your PBX. The terms "FXS" and "FXO" came to refer to the respective ends of the circuit, where "O" stands for "Office", and "S" stands for station. The confusion that stems from all this is that cards which provide an "FX" interface (basically an analog telephone interface) are named by what they *connect* to, not by what they *do*. So, a card that you would plug an analog phone into would be an FXS card, because it is connected to a station. If you think about it, this can be confusing because an FXS card actually needs to exhibit the behaviour of a central *O*ffice. This is why, for example, a Zaptel FXS card uses FXO signalling. It *connects* to a station, but it must *behave* like (or provide the functions of) a central office. Obviously, an FXO card is the exact opposite. An FXO card needs to *connect* to a central office, but in order to successfully do so it will need to *behave* like a station. A modem is a classic example of an FXO device, so is a loop start trunk card in a PBX or KSU. To summarize: An FXS card emulates a central office. It: - *connects* to a *S*tation - provides dial tone - supplies ringing voltage, loop current, battery, etc. - receives touch tone digits - sends CLID - etc. An FXO card emulates a telephone. It: _ *connects* to an *O*ffice - requests dial tone - receives ringing voltage and is powered from the far end - generates touch tone - captures and interprets CLID - etc. The Terms FXS and FXO, when they refer to HARDWARE, always follow the above naming convention. Be forewarned, however, that various software may not follow this convention at all. In Asterisk, for example, an FXO card is controlled by signalling=fxS_ks (et al), and an FXS card is controlled by fxO_ks (et al). But other systems may not have such logic. In another device, you may have a bunch of FXO commands that do indeed program the FXO interface. The trick for Asterisk is to understand that an FXS (which connects to a *S*tation) needs to signal using FXO (because it needs to behave as an *O*ffice), and vice versa. Enjoy. Cheers, -- Jim> -----Original Message----- > From: asterisk-users-bounces@lists.digium.com > [mailto:asterisk-users-bounces@lists.digium.com] On Behalf Of > Wolf Paul > Sent: October 16, 2004 1:06 PM > To: asterisk-users@lists.digium.com > Subject: [Asterisk-Users] FXO vs FXS question > > > Hello all, > > as a relative newbie I obediently ordered the recently > recommended "Newton's Telecom Dictionary" but it did not > provide the answer to one of my question. Perhaps one of you > can do so. > > What is the difference in functionality between an FXO and an > FXS port? I know that the line from telco goes into an FXO > and standard POTS phone goes into an FXS, but since both > types of ports must be able to both make and answer calls, > what is the actual functional difference? > > Or in other words, what does an FXO to FXS converter do (I > have seen some mention but no explanation of those)? > > Thanks. > > Wolf Paul > > _______________________________________________ > Asterisk-Users mailing list > Asterisk-Users@lists.digium.com > http://lists.digium.com/mailman/listinfo/> asterisk-users > To > UNSUBSCRIBE or update options visit: >http://lists.digium.com/mailman/listinfo/asterisk-users --- Incoming mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.775 / Virus Database: 522 - Release Date: 08/10/2004 --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.775 / Virus Database: 522 - Release Date: 08/10/2004