Knowledgebase
DrVoIP Support > DrVoIP Network, VoIP, Security & AWS Cloud! > Knowledgebase

FXS/ FXO procedures – how it technically works

Solution

 

What do the terms FXS and FXO mean?

 

FXS and FXO are the name of ports used by Analog phone lines (also known as POTS - Plain Old Telephone Service) or phones.

 

FXS - Foreign eXchange Subscriber interface is the port that actually delivers the analog line to the subscriber. In other words it is the ‘plug on the wall’ that delivers a dialtone, battery current and ring voltage.

 

FXO - Foreign eXchange Office interface is the port that receives the analog line. It is the plug on the phone or fax machine, or the plug(s) on your analog phone system. It delivers an on-hook/off-hook indication (loop closure). Since the FXO port is attached to a device, such as a fax or phone, the device is often called the ‘FXO device’.

 

FXO and FXS are always paired, i.e similar to a male / female plug.

 

Without a PBX, a phone is connected directly to the FXS port provided by a telephone company.

fxs/fxo without a pbx
FXS / FXO without a PBX

 

If you have a PBX, then you connect the lines provided by the telephone company to the PBX and then the phones to the PBX. Therefore, the PBX must have both FXO ports (to connect to the FXS ports provided by the telephone company) and FXS ports (to connect the phone or fax devices to).

fxs/fxo with a pbx
FXS / FXO with a PBX

 

FXS & FXO & VOIP

You will come across the terms FXS and FXO when deciding to buy equipment that allows you to connect analog phones to a VOIP Phone System or traditional PBXs to a VOIP service provider or to each other via the Internet.

 

An FXO gateway

 

To connect analog phone lines to an IP phone system you need an FXO gateway. This allows you to connect the FXS port to the FXO port of the gateway, which then translates the analog phone line to a VOIP call. There are a number of different FXO gateways available. 

FXO gateway

 

An FXS gateway

 

An FXS gateway is used to connect one or more lines of a traditional PBX to a VOIP phone system or provider. Alternatively, you can use it to connect analog phones to it and re-use your analog phones with a VoIP phone system. You need an FXS gateway because you want to connect the FXO ports (which normally are connected to the telephone company) to the Internet or a VOIP system.

FXS gateway

 

An FXS adapter a.k.a. ATA adapter

 

An FXS adapter is used to connect an analog phone or fax machine to a VOIP phone system or to a VOIP provider. You need this because you need to connect the FXO port of the phone/fax machine to the adapter.

FXS (ATA) adaptor

 

FXS/ FXO gateways are widely available.

 

 
Was this article helpful? yes / no
Related articles How does FAX work in VOIP environments?
What is DID?
Understanding SIP Firewall Configuration
CISCO dial peer Translation Rule - Quick Summary Guide
Setup Paging on ShoreTel
Article details
Article ID: 9
Category: Knowledgebase
Rating (Votes): Article rated 2.9/5.0 (33)

 
« Go back