FXS vs FXO: What’s the Difference and How It Works

Switching to a VoIP phone system has been a popular choice for many small and medium-sized businesses for obvious reasons. The most common ones are better connections, extended call functions and tools, and the possibility to make and receive calls locally and internationally.

Before VoIP, analog phone systems were commonly adopted and they used FXO and FXS ports to establish connections. Read on to learn the differences between FXO and FXS and how you can use them to connect analog phones and PBX to VoIP systems to build a hybrid communication infrastructure and modernize business communications.

Table of Contents

• What Is FXO? →
• What Is FXS? →
• FXS vs. FXO: What’s the Difference? →
• How Do FXS and FXO Ports Work? →
• What FXO Port and FXS Port Are Used For? →
• Conclusion →

What Is FXO?

FXO, Foreign Exchange Office, is a port that connects an FXO device to an outside telephone line. FXO port is a plug on the office phone, analog fax machine, or modem. So, the FXO interface receives the POTS service from the Central Office of the Public Switched Telephone Network (PSTN) and generates a loop closure. This allows the device to communicate with the PSTN, enabling voice and data transmission over traditional phone lines. FXO ports are essential for integrating analog devices with digital communication systems like PBX or VoIP gateways.

What Is FXS?

FXS, Foreign Exchange Subscriber, is a port conveying the internal connection to office devices like fax machines or phones. Wall jack or FXS interface delivers dial tone, ringing voltage, and battery power to FXO devices. This interface connects to the end-user equipment, enabling these devices to communicate with the telephony network. By providing the necessary electrical signals, FXS ports allow traditional analog devices to function seamlessly within modern telecommunication systems.

FXS vs. FXO: What’s the Difference?

FXO and FXS are the ports used by POTS (Plain Old Telephone Service) or an analog phone line. The two ports are always paired together to make a call.

An FXO port connects to the PSTN and receives the line, while an FXS port connects to end-user devices and provides the necessary signals like dial tone and ringing. Essentially, the FXO port plugs into the FXS port, creating a complete communication loop that allows analog devices to operate within telephony networks. This pairing is crucial for establishing and maintaining voice communication over traditional phone lines.

How Do FXS and FXO Ports Work?

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

In case of incoming calls, an FXS interface will transmit the ring voltage to the attached FXO device, and it will 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, the dial tone will not be transmitted.

What FXO Port and FXS Port Are Used For? (FXO vs. FXS)

FXO and FXS ports are used when a company wants to introduce an additional network. Such network systems can be Voice over IP or Private Branch Exchange (PBX). The connection procedure is slightly more complex and requires new lines attached to another network provider.

What Is a Voice Over IP Phone System?

The VoIP system stands for Voice over Internet Protocol and allows companies to make calls over Internet connections. It provides many more advanced call-handling features than analog phone systems. Traditional phone systems use FXO and FXS ports while IP phone systems require additional gateways.

FXS and FXO Ports With VoIP Phone System

FXS Gateway
FXS gateway is required when connecting analog phones, fax machines, and PABX with IP telephony networks and VoIP systems. These devices are connected to the ports of an FXS gateway which translates the lines to the VoIP provider.

At Yeastar, we offer a cost-effective TA Series FXS VoIP Gateway for small and medium enterprises to ensure an effortless and smooth transition to VoIP. By integrating traditional phone systems into IP-based systems, you can provide employees with a robust IP telephony feature set and will not have to allocate huge investment on new VoIP phones but, instead, continue using the existing analog phones as extensions of the IP-PBX.

FXO Gateway
An FXO gateway is used when you want to connect a VoIP system with analog lines and translate analog lines to establish a VoIP call.

Yeastar TA Series FXO VoIP Gateway provides an affordable and reliable solution that can connect analog lines and PABX extension interface to SIP trunks, enabling calls to be made over the Internet.

When connected to a headquarters IP PBX system, FXO gateways can use the local landlines of your remote sites to avoid long-distance rates. Besides, FXO Gateway can offer a failover or fallback solution by connecting your PBX to an outside telephone line if the network crashes or SIP trunking to IP-PBX fails.

Conclusion

Foreign Exchange Subscriber and Foreign Exchange Office ports are connected to make or receive a call. An FXS port is a plug on the wall, and an FXO port is a plug on your office phone or fax machine. When making a call, an FXO device sends a signal to an FXS port. And to answer a call, an FXS port sends a ring voltage to an FXO port to a device.

However, the process is different when adding another network, like a VoIP system. An FXS gateway is required to connect an FXO device for a VoIP call. An FXO gateway is necessary to connect analog phone lines to VoIP.

Yeastar has provided solutions to this transition for small and medium-sized companies with a limited budget. VoIP can offer a much better performance rate and significantly save on communication costs in the long run. Contact us for more details here.