VoIP Gateway: What’s the Difference between FXS and FXO?

The analog phone system or POT (Plain Old Telephone Service) is the service provided by the telecom company. The telecom company connects the phones with twisted pair wires.

To increase the distance of signal transmission and management, there are also many communication network devices, such as PBX, VoIP gateway, and routers.

Switching to a VoIP phone system has become a popular choice for many small and medium businesses due to better connectivity, expanded calling features and tools, and the possibility to make and receive local and international calls.

Before VoIP, analog phone systems were mostly adopted, which used FXO (Foreign Exchange Office) and FXS (Foreign Exchange Station) ports to establish connections.

Read on to learn how to use FXO and FXS to connect analog phones and PBXs to VoIP systems to build hybrid communications infrastructure and modernize business communications.

fxs vs fxo

Part I. Difference Between FXS and FXO

1. What Are FXS and FXO Ports?

FXS is a port for conveying the internal connection to office devices like fax machines or phones. In other words, it aims to deliver dial tone, battery current, and ringing voltage.

FXO is a port that connects an FXO device to an outside telephone line. It can be a jack on a telephone or fax machine, or an analog telephone system, which is used to transmit on-hook/off-hook indications (loop closed).

2. How Do FXS and FXO Ports Work?

To establish a call, the FXS and FXO ports must be connected. This applies to outbound and inbound calls. When you pick up an analog phone (FXO device) connected to an FXS port, you dial a number and connect to the other end using PSTN service. The numbers you dial on your office phone are encoded as DTMF or DTMF digits and passed to the FXS port.

If there is an incoming call, the FXS interface will transmit the ringing voltage to the connected FXO device and start ringing. Once the phone is picked up, the line is established. However, connecting two FXO or two FXS ports will result in unsuccessful communication. Even if you want to connect two internal FXO devices, no dial tone will be transmitted.

When it comes to equipment over the Internet to connect an analog phone line to a VoIP network phone system, or to connect a traditional enterprise communications switch to an IP network service provider, FXS gateway and FXO gateway are needed.

3. What Are FXS Gateway and FXO Gateway?

FXS Gateway

FXS gateways are required to connect analog telephones, fax machines and PABXs to IP telephony networks and VoIP systems. These devices connect to the ports of the FXS gateway, which converts the line to a VoIP provider.

VSOL provides a series of FXS VoIP gateways for small and medium enterprises to ensure an easy and smooth transition to VoIP.

FXO Gateway

FXO gateways are used to connect VoIP systems with analog lines and convert analog lines to establish VoIP.

4. Conclusion

Connect foreign exchange users and foreign exchange bureau ports to make or receive calls. An FXS port is a wall plug, and an FXO port is a plug on an office phone or fax machine. When a call is made, the FXO device sends a signal to the FXS port.

To answer a call, the FXS port sends a ringing voltage to the FXO port of the device. However, when adding another network, such as a VoIP system, the process is different. An FXS gateway is required to connect FXO devices for VoIP calls. An FXO gateway is required to connect the analog phone line to the VoIP.

Part II. Related Products: VSOL FXS VoIP Gateway

VSOL provides a series of FXS VoIP Gateway IAD30xx, including 4/8/16/32/64 FXS ports. The IAD30xx series products are designed based on VSOL’s many years of experience in FTTx. They support SIP protocol and plenty of speech coding technology.

VSOL IAD30XX Port Expanding Function

The VoIP gateway has different numbers of FXS and FXO ports. For example, the 32 FXS VoIP Gateway IAD3032 has 16 FXS ports, 16 FXO ports, and 2 FE ports. Therefore, it depends on the exact demand for different ports to choose the devices.

Features of VSOL VoIP Gateway Devices:

1. Advanced Technology

It’s compatible with the mainstream IMS platform and adopts advanced SIP protocol, supporting calling control, VoIP gateway, and telecom supplementary service.

2. Great Value-added Service

It provides PSTN additional services and value-added services, increasing clients’ business efficiency and promoting VoIP system value.

3. Easy Management and Maintenance

Graphic Web management and devices support remote configuration maintenance and online updates. The logging is conducive to fault analysis and troubleshooting.


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