Although the wiki help topics seem to be quite extensive when it comes to the software side, there seems to be a serious dearth of information when it comes to setting up the hardware. I’m planning on purchasing a FreePBX appliance, but it would appear these don’t come with the interfaces necessary to connect to a phone line. I’ve hit a wall when it comes to researching whether I need FXO or FXS. I’ve read about the differences online but I still am not certain I have a solid grasp of which one I need. What do I need in order to connect the appliance to existing analog phone lines?

An FXO port is to connect a phone line, i.e. dial tone service from a phone company. An FXS port is used to connect a phone, the thing that touches your ear.

Unnecessary aside: an FXO port differs from FXO signalling, if you don’t know this fact, it is sometimes confusing when you are reading up on this stuff.

Thanks a lot. So, it sounds like an FXS port is only useful if you are supporting analog phones and devices rather than switching entirely to digital. If all of my phones will be digital, there is no need for any FXS ports, correct?

In other words, I need an FXO card to connect the FreePBX box to the phone lines and no FXS cards at all.

I was similarly confused when I first started looking at FreePBX. To add to Lorne’s explanation:

If you plan on using POTS lines, you’ll need an FXO port for each POTS line. So If you have 4 POTS lines, you’ll need 4 FXO ports. FXO ports are available as part of an analog interface card or gateway appliance.

Another option is to use a T1/E1 digital I/O card. A T1 has 24 channels and give you 23 “lines” (the 24th channel is used for signaling). Yet another option is to use SIP trunking.

In FreePBX. think of FXS ports as some thing that allows you to connect an analog phone to FreePBX. Most likely, this will be an Analog Telephone Adapter (ATA), an interface card, or a gateway appliance.

I would have to be pedantic here, a T1 means that the T stands for Telephony. The underlying transport is a DS1 (data service 1) the signalling over a T1 can be one of several things, only one of which is ISDN PRI (of which you speak) and does gives you 23 B (bearer) channels and one D (signaling) but equally acceptable is a traditional T1 using 24 channels of RBS (robbed bit signalling) (sometimes called a SuperTrunk) that has been around for 50 years.

If you run into any T1 , please ensure you follow what signalling it actually uses and NOT assume a PRI that can often BYITA . (The same situation (but less likely) can happen on E1 transports)


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