Have done a search here and elsewhere and didn't find what I needed answer-wise:

If I have an ATA, something/somewhere has to match the inbound number to my IP address. How is this done with a dynamic IP address from my ISP?

Similarly, how is this accomplished if I use an ATA while traveling?

Thanks in advance.

Whenever your ATA is turned on, it needs to log on or re-register a "session" with your VOIP provider, with your IP address an attribute persisted accordingly.

Use a dynamic DNS service, like http://www.no-ip.com/services/manage...namic_dns.html

These services function by mapping your current IP address to a static one. Packets inbound to your static IP are redirected to the current one. There is software in your computer that notifies the service when your IP changes, so it can update its tables.

Somewhere Over the Atlantic's answer is correct. There is absolutely no need for any kind of a dynamic DNS service when using an ATA device, unless the OP also intends to run their own VOIP PBX system.

I don't think that's how DDNS works. Client-side software appears to be responsible for updating the IP address associated with the DNS name provided by the DDNS service. If a DHCP renewal causes my router's address to change, the router firmware automatically contacts my DDNS provider to update the DNS "A" (Address) record for my DNS host name.

At least that seems to be how it works . . .

And, of course, this is all irrelevant to the subject of the OP

For inbound VOIP calls it is essential to have your ATA "register" with the VOIP provider. You'll probably see settings on how long to keep a registration before renewing it. Depending on how often your IP address changes would be an important thing to determine how often to renew the registration. Also your VOIP provider may restrict how often you are able to register. I use 30-45 minutes personally.

For outbound calls, it doesn't matter as your ATA is contacting the VOIP company. With this information sent out is your IP number so that the VOIP company knows how to send the audio back to you.

Does this make sense? Don't worry anything about the dynamic DNS services (DDNS). It doesn't apply to you unless you are trying to do something semi-complicated.

Thanks for this excellent response. It suggests the method I would have come up with if I were blank-sheeting a design. I'm assuming the renewal process is very short, otherwise there is a window of missed-call possibility. It also suggests that a static IP address is indeed a (perhaps only slightly) better way to go.

No, you can ignore the posts here that refer to Dynamic DNS - this is not relevant to what you are asking.

ATA devices generally use a protocol called SIP. When you plug the device in, regardless of your IP address, the ATA will contact a registration server, tell it who you are and what your phone number is. It periodically performs this process, and the server can see what IP address the messages are coming from. This is what forms the phone number <-> IP address matching.

Generally, the only time your IP address changes (if it does at all) is when the Internet connection is dropped or re-established. In these situations the SIP device just re-registers itself from the new address and works as normal.

You should have no issue using the device when traveling, provided it is connected to an "open" Internet connection. If you have to perform some sort of authentication first (like on a hotel Internet connection for example) then you may find it more tricky to get working.

Bottom line - Plug-in and Talk.

I have used my Vonage ATA all over the world to give me a US telephone number (in and out bound) wherever I am. I really don't care what my IP address is, and the ATA handles telling the Vonage servers. (otherwise it wouldn't work, right?)

I carry a small travel router so I can use both my PC and phone in the hotel room at the same time. This way if there is some sign-on required to the hotel internet, it can be done on the PC. You want your phone plugged in all the time if you want inbound calls.