WiFi Calling and the MicroCell - Some Answers

The following is basically a summary of what AT&T had to say about WiFi calling (WiFi-C) in response to my questions and questions that were posted/sent to me. There is nothing earth shattering here and is pretty much what everyone expected.

WiFi-C is essentially offered for the same reason that the MicroCell is. It is intended to patch holes in coverage, primarily in your home. It is not intended to replace cellular. The phone should attach to WiFi-C whenever cellular strength is weak/unsteady and a strong WiFi connection is present.

HD Voice only matters for the purposes of handing-off to a tower. However, a 2G/3G device (i.e. the MicroCell) isn’t capable of HD Voice so calls will not hand off from WiFi-C to the MicroCell (or a 3G connection) because the 3G tower cannot “see” the WiFi call. This is due to network/technology structuring.

So, if you are in a mixed environment and want to use WiFi-C in home, your only option is to enable Airplane Mode to turn off the cellular radio and force the phone to connect to your WiFi network. AT&T will probably not change the preference for cellular over WiFi because they are selling a cellular service, not a WiFi-C service. If there is anyway to change the preference it will have to come from Apple. Personally I don’t think Apple will change it either because it’s just not a priority for them.

According the AT&T, if you have wireless access points in your house and move from point A to point B, the WiFi-C call will drop because your wireless access points don’t have handing off protocols between them. Towers can hand off to each other because they are connected to each other by a base controller. I’m not convinced that this is true in all cases of WiFi-C. Even though your wireless access points don’t communicate (hand off) directly with each other, they do go thru your router, which to me, would act as a base controller. My guess is that your mileage will vary on this one depending on how you have your wireless network setup, distance between access points, and other wifi-related issues.

The strength of the WiFi signal needed for successful calls is probably close to the same as it is for cellular calls. If the signal strength gets close to -90dBm calling may be iffy. At -95dBm to -100dBm or lower you will probably start to drop calls or lose them altogether. Any issues that affect your WiFi will affect WiFi-C so keep that in mind.

WiFi-C for Apple devices use ports 500 and 4500. Those are two of the same four ports that are required for the MicroCell. When there have been port issues with the MicroCell, port 4500 seems to be the culprit in a lot of cases. So, if you experience MicroCell issues and port 4500 is blocked or is having issues, you may have WiFi-C issues as well. Unfortunately, port issues can only be corrected by your hardware and/or the ISP. AT&T has no control over that.

Will WiFi-C come to Android devices? That’s a good question. The challenges to implementing WiFi-C on the multitude of Android-based devices and mfrs is daunting at best. The iPhone was easy because it’s only one device and OS. Android is a bit more difficult so it’s anybody’s guess as to if, and when, it will be offered. iPhone models earlier than the iPhone 6 will not be able to take advantage of WiFi-C either because they can’t be provisioned for VoLTE (Voice over LTE) which is a base requirement for HD Voice. Both terms have been used interchangeably so the distinction between the two is probably only minor, if at all.

Of course all of the above is from AT&T so it can change without notice, and I’m sure there are going to be instances where actual experiences will differ.

So for now, if you want to use WiFi-C in home you need to either;

1. Disable the MicroCell altogether and sell it.
2. Enable Airplane Mode so that your phone can only connect to your WiFi network.
3. Remove your phone number from the MicroCell. If the phone number used to register the MicroCell is the same as the WiFi-C capable phone, then the MicroCell will probably have to be deactivated and then re-registered to another non-WiFi-C capable phone on the same account. There is some disagreement on whether this works easily or not. I haven’t actually tested that myself so if anyone else has, please let me know.

Remember, you cannot hand off from WiFi-C to cellular (2G/3G) and vice versa, and

cellular will always be the preferred connectivity protocol when the signal is stronger and/or more stable.