Ask Mr. Andrews: How Do I Select the Right ATA?

October 7, 2008 by Garrett Smith

Q: My VoIP Service Provider Allows Me to Bring My Own ATA, Which One is the Best?

A: Thanks for the question, but your questions should really be,

“What is the Right ATA For My Situation?”

Most VoIP service providers do a poor job of explaining the differences and benefits of the different types of analog telephone adapters (ATA). Many take your level of knowledge as it pertains to telephone adapters for granted; assuming you fully understand each feature/ functionality of an ATA, and that you understand how these features/ functionalities relate to your calling situation.

What follows is a quick guide to selecting the proper ATA for your VoIP Service.

What is An ATA?

An Analog Telephone Adapter (ATA) is a device that converts analog telephone signals into digital packets for transfer across an IP network. Analog Telephones (small office key systems can also can access to VoIP through an ATA) connect to the the ATA via an FXS port and the ATA connects to the IP network via an RJ45 port. Some ATA’s also have an FXO port for connectivity to the PSTN. ATA’s also convert digital packets back into analog voice streams.

So an ATA is a device that sits between your router or modem and your home phone, that takes your speech and converts it into digital packets to be sent over the internet by your VoIP service provider, and vice versa.

What is an FXS Port?

FXS stands for Foreign Exchange Station. An FXS port is an interface on that connects station devices such as phones or a PBX to the ATA. An FXS port would be where you plug your home phone into an ATA. The number of FXS ports dictates the number of phones that can be plugged into an ATA.

What is an FXO Port?

FXO stands for Foreign Exchange Office. An FXO port is an interface that receives your home land-line telephone service connection. An FXO port would be where you plug your home telephone line into an ATA. An FXO port allows you to use both VoIP calling and traditional PSTN calling. This is often referred to as a “life-line”.

What is an RJ45 Port?

An RJ45 port is an interface that connects your ATA to your home data network. An RJ45 is where you would plug your CAT5 cabling coming from your modem or router in order to give the ATA access to the Internet. The number of RJ45 ports on an ATA is important as you may need a certain ATA if you do or do not have a home router.

Which ATA is Right For Me?

Here is How Your Select the Right ATA For Your Situation:

  1. How Many Home Phones Do You Need to Connect? – The number of home phones that you would like to connect to your ATA will dictate the number of FXS ports. If you want to connect one home phone, you will need an ATA with one FXS port. If you want to connect two home phones, you will need an ATA with two FXS ports. Most service providers only offer ATA’s with 2 FXS ports, so if you are planning on connecting more than two home phones, you will need to get more than one ATA. Contact your VoIP service provider for more information on how to connect more than one ATA device to their service.
  2. Are You Going to Keep Your PSTN Phone Line? – If you plan on keeping your PSTN line, as a life-line in case your network connection goes down, then you will need an ATA with an FXO port. Now, if you decide that you want this functionality, first make sure that your VoIP service provider supports this type of functionality as some do not. Most ATA’s only come with one FXO port, so you will only be able to connect your ATA to one PSTn phone line.
  3. Do You Have A Home Router? – The existence of a home router will be a big factor in the number of RJ45 ports you will need your ATA to have. The reason? If you do not have a router for your home, that means your computer is connected directly to your cable/dsl modem. Without a router, only your ATA or computer to could be connected to the Internet at any given time. That sucks. If you do not have a home router, your home router has no more open ports, or your phone is near your computer, you want an ATA with 2 RJ45 ports, so that you connect your ATA and your computer to the Internet.


  • Ali

    Truly appreciated your guide. Simple, Sweet yet digestive language about VoIP. Thank You very much.


  • Garrett Smith


    No problem! Look for more post like this each and every week.

  • Profk

    I am a Skype user, and am converting to Verizon FIOS from Comcast cable (which was too unreliable for VOIP). I have a 2-line Siemens Gigaset 8825 multihandset system with 7 handsets and a superb answering system, and want to keep it. I plan to keep one copper phone line for reliability. I’ll use the copper line 1 for incoming calls, faxes, my burglar alarm, and 911. I want to use Skype on line 2 for outgoing calls.

    Vendors seem reluctant to state which providers their ATAs are compatible with. I read somewhere that the Linksys PAP2T-NA can work on Skype. Can you confirm that?

    If you don’t carry a Skype-compatible ATA, which uinits offer the broadest compatibility? I understand Vonage is having problems (who isn’t?), and don’t want to be locked into a single service.


  • Cory Andrews

    Bob, you might take a look the Dlink DPH-50U or the Radian RST401

  • Debra W

    I love the skype service, fees and versatlity. I have been using the netgear cordless 2-line phone system. Other than some sound quality issues and i don’t have the ability to pick up an extension i want to go back to a 2 line cordless phone system with a base unit, much like the set-up i had with vonage 2 years ago.

    I plan on keeping my PSTN line, so then I will need an ATA with an FXO port… Correct?

    I have a zoom series 1058 combo wireless router-modem . Am I correct in understanding – once I find the right adapter I will be able to use the VOIP line plugged into the internet without the computer?

    In your blog 4. answer, to try the Dlink DPH-50u i would still need the computer link 24-7. I work off of a laptop so i am in search of a Vonage like configuration using skype.

    Which ATA Would you suggest in your product line?

  • Cory Andrews

    Debra – the DualPhone 3088 looks really promising. You can take a look at it here

  • Debra W

    Thank You!

    I am reviewing your recommendation and
    reading through the installation and user guide.

    I am a little hesitant as the resource to purchase is from the skype shop.

    The 1st phillips phone i purchased lacked quality and a bit of hassle sending it back.

    I’m just not sure on the sound quality of this type of phone.

    All and all – not too concerned that i have the skype contact list availability- just really like having a second line as the source for making long distance calls as a business line for myself and my friend who does not use computers period and has trouble hearing.

    I have since been scouring the net , i am still confused on gateways and adapters thinking i would like to research a little more down that path than be subject to another test round form the skype shop.

    is that viable or am i going down a dead end?

  • Cory Andrews

    Debra – I am fairly certain there are some companies that make Skype compatible ATA devices that would have both what we can an FXS (RJ11 port into which you plug your analog phone or fax machine) as well as a PSTN (FXO) port to allow you to toggle between the PSTN and Skype, and use the 5.8GHz wireless analog phone of your choice. I will do a bit more research, we don’t have such an animal in our product catalog, but I have very little doubt that it exists.

    It’s too bad VTech or Uniden don’t take one of their slick 5.8GHz or DECT wireless phones and put an ethernet in the back and bundle in Skype service. You could build some simply diaplan routing intelligence into the device, have it default to SkypeOut service on outbound, long distance and international calls, and use the PSTN for inbound calls and local outbound calls.

    I’ll let you know what I dig up!

  • Debra W

    Wow, you have been very helpful!

    i was really hoping to use one of your products and work with one of your consultants for purchase and installation

    i did some reading on the dual phone- it did not list anything specific on the use of picking up an extension, so do know that it is going to be any better than what i have

    I stumbled on a couple of other interesting products:
    FRITZ!Box Fon WLAN 7270
    …but it is not listed for use in the US and i don’t know what they mean by annex A or B

    then i stumbled on this Phone Adapter for Skype – Model 5900

    but i have to have it plugged into a usb hub- one extra piece of hardware- just not sure it will work

    and finally (Single Analog FXS/FXO Gateways )
    … not to sure on the reliability of these vendors?

    anyways i really appreciate your input – alot of this language is over my head!
    Thanks again Corey

  • Debra W

    Hey Corey, just checking in to see if you have found anything else out since the email i last sent 9. Debra W

  • VOIP India

    Hello, I found it very informative, all my technicality solutions was well discribed in your article. I am reading it again to make my self aware of the information to provide to my customers.


  • George Pal

    When we were setting up our VoIP on a LinkSys ATA we use this guide and we were able to do it without problems. This could help you as well.

    I hope you can find it useful.


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