VoIP Adaptor (ATA): What It Is and How to Use One

What Is a VoIP Adaptor?

A VoIP adaptor — formally known as an Analogue Telephone Adapter or ATA — is a small device that connects a traditional analogue phone to a VoIP network. It converts the analogue voice signals from your existing phone into digital packets that can be transmitted over the internet, and vice versa.

In simple terms, an ATA lets you keep your old phone but use it on a modern VoIP phone system. You plug your analogue phone into the ATA, connect the ATA to your network, and the phone works as though it were an IP device.

How Does an ATA Work?

An ATA sits between your analogue phone and your network router or switch. It performs the translation between two different technologies:

1. Outbound calls — when you pick up the phone and dial, the ATA converts your analogue voice signal into digital SIP packets and sends them to your VoIP platform over the internet
2. Inbound calls — when a call arrives from the VoIP platform, the ATA converts the digital packets back into an analogue signal and rings your phone

The ATA handles all the SIP signalling, codec negotiation, and packet assembly in the background. From the user's perspective, the phone simply works as it always has — you pick up, hear a dial tone, dial the number, and talk.

Why Would You Use an ATA?

There are several scenarios where an ATA makes practical and financial sense:

• Keeping existing analogue phones — if you have recently invested in analogue handsets or have specialist equipment (door entry phones, fax machines, franking machines), an ATA lets you integrate them into your new VoIP system without replacing them
• Phased migration — moving from a traditional phone system to VoIP in stages, converting extensions one at a time using ATAs before eventually replacing the hardware
• Lift and emergency phones — many buildings have analogue phones in lifts, reception areas, or fire panels that cannot easily be replaced with IP phones. An ATA bridges the gap.
• Fax machines — while fax over IP is unreliable with standard VoIP codecs, a T.38-compatible ATA can handle fax transmissions more reliably
• Cost savings — an ATA costs £30–£80, significantly less than replacing each phone with a new IP handset at £80–£200

What Does an ATA Look Like?

A typical ATA is a small box — roughly the size of a broadband router — with the following ports:

• FXS port(s) — one or two RJ11 phone ports where you plug in your analogue phone. A two-port ATA supports two separate phone lines.
• Ethernet port — an RJ45 network port that connects to your router or network switch
• Power port — a DC power input (or some models support PoE)

Some ATAs also include a WAN port for direct broadband connection, though in most business environments you will connect the ATA to your existing network switch.

Popular ATA Models

Several manufacturers produce reliable ATAs for business VoIP use:

• Grandstream HT801 / HT802 — single and dual-port ATAs, widely used and well-supported. The HT802 provides two independent FXS ports for two analogue phones.
• Cisco ATA 191 / 192 — enterprise-grade ATAs with robust SIP support and remote management capabilities
• Poly OBi302 — a dual-port ATA with T.38 fax support and a web-based configuration interface
• Patton SmartNode — higher-end ATAs with multiple FXS ports, suitable for connecting larger numbers of analogue devices

How to Set Up an ATA

Setting up an ATA involves connecting the hardware and configuring it to register with your VoIP platform. Here is the general process:

Step 1: Connect the Hardware

1. Plug the ATA's Ethernet port into your network switch or router
2. Connect your analogue phone to the ATA's FXS port using a standard phone cable
3. Power on the ATA

Step 2: Access the ATA's Configuration Interface

Most ATAs have a web-based admin panel. Find the device's IP address (check your router's DHCP table or press a code on the connected phone to hear it read aloud) and open it in a browser.

Step 3: Enter Your SIP Credentials

Your VoIP provider will supply the SIP registration details for the extension. Enter these in the ATA's configuration:

• SIP server / registrar — the address of your VoIP platform
• SIP user ID — the extension or account number
• Authentication password — the SIP password for that extension

Understanding how SIP trunking and SIP registration work will help you make sense of these settings.

Step 4: Configure Codec and Network Settings

Set the preferred audio codec (G.711a is standard in the UK) and ensure the ATA is configured for your network — VLAN tagging if required, DHCP or static IP, and any firewall-friendly settings your provider recommends.

Step 5: Test

Pick up the connected analogue phone. You should hear a dial tone. Make a test call to confirm inbound and outbound calls work correctly.

ATA vs IP Phone: When to Choose Each

• Choose an ATA when you want to keep existing analogue phones, connect non-phone analogue devices, or minimise upfront hardware costs
• Choose an IP phone when you want access to advanced features like BLF, colour displays, expansion modules, and built-in directory access that analogue phones cannot provide

ATAs are a bridge technology. They are ideal during a migration or for connecting legacy equipment, but for new desk deployments an IP phone will give you a better experience and more features.

Fax Over ATA

If your business still uses fax, an ATA with T.38 support provides the most reliable way to send and receive faxes over a VoIP connection. T.38 is a protocol specifically designed for fax transmission over IP networks, and it handles the timing-sensitive nature of fax signals better than standard voice codecs.

Ensure your VoIP provider supports T.38 on the hosted VoIP platform, as not all providers enable it by default.

Getting Started

If you are migrating to VoIP and want to keep some of your existing phones or connect analogue devices like fax machines, an ATA is the simplest and most cost-effective solution. We can help you choose the right model and get it configured on your VoIP platform.