VOIP gateway (or PSTN Gateway) is a device which converts telephony traffic into IP for transmission over a data network. By bridging the connection between analog and digital systems you can run a backup land line, fax machine, and credit cards lines through your VoIP system. Interactive Systems offers the best in gateway technology through Patton Technologies. They are used in 2 ways:

To convert incoming PSTN/telephone lines to VOIP/SIP:

In this manner the VOIP gateway allows calls to be received & placed on the regular telephony network. With the exponential increase in how business relies on the internet a VoIP system is necessary for any business trying to compete in todays market.

To connect a traditional PBX/Phone system to the IP network:

In this manner the VOIP gateway allows calls to be made via VOIP.  Calls can then be placed via a VOIP service provider, or in the case of a company with multiple offices, inter office calls costs can be reduced by routing the calls via the Internet. VOIP gateways are available as external units or as PCI cards. The vast majority of devices are external units. A VOIP gateway will have a connector for the IP network and one or more ports to connect the phone lines to it.




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.


FXS & FXO with 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.


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