Yesterday a friend of mine sent me this text message:
So, I spoke to two separate AT&T representatives, one on Tuesday and the other yesterday, and they both said that VoLTE calls when available will subtract from monthly cellular data.
Well, I can’t well ignore that. I reached out to AT&T via Twitter for comment:
@ATT @ATTCares Can you comment on VoLTE data usage?
Not receiving a response, I decided to do some ballparking on my own. I wanted a rough estimate of the peak usage that VoLTE could use under any circumstances, because, what if it’s true?
So, first thing to note is that under AT&Ts roll-out of VoLTE, they’re introducing HD Voice. HD Voice is also being rolled out on other carriers, some possibly independent of a VoLTE roll-out, but since I’m focusing on bandwidth utilization, that difference is not applicable to this.
Now, for the purposes of VoLTE, there are two codecs in play here. AMR-NB (for narrowband, normal calls), and AMR-WB (for wideband, HD Voice calls) [source]. AMR-WB will naturally have the higher bandwidth utilization of the two.
The AMR-WB codec uses, at peak, a 23.85kbps (kilobits) codec [source]. That’s one-way, making it 47.7kbps peak for both ways. I’ll say 48kbps to add a little overhead. This number is in line with an article at NetworkWorld, which states that VoLTE calls come out to about 30-40kbps at peak. That comes out to 6kBps (kilobytes), both ways, at peak. Roughly speaking. It’s possible for the codec to shift to a lower bandwidth during silences and lower frequency-range conversations, or during network congestion, and that’s important to understand.
So, doing the math on a 15-minute phone call will give you a peak usage of 6kB/sec, 360kB/min, and 5.4MB/15min (1MB=1000kB). That’s absolute peak. All other usage not withstanding, that’s [very] roughly at least 92.5 hours or 5,550 minutes of talking on your 2GB plan.
And that’s if VoLTE calls bill against your data plan.
UPDATE: A reader has sent me the following from Verizon’s website, which specifically mentions HD Voice, but not VoLTE:
HD Voice is available at no additional charge and is included in existing plans.
HD Voice calls are billed as standard voice calls according to your plan. No data charges apply.Mobile-to-Mobile calls that happen to be HD Voice calls are charged just like traditional Mobile-to-Mobile calls and are billed against your monthly minute allowance according to your plan.
A video call is an HD Voice call combined with real-time video. The voice portion is billed as a standard voice call, according to your plan. The video portion is billed as data, according to your data plan. No data charges apply to video calls transmitted over Wi-Fi.
Note: An average 1-minute video call uses about 6 – 8 MB of data. The actual data consumption of your video call may vary. You can estimate your data usage using our online Data Usage Calculator.
Source: https://www.verizonwireless.com/support/advanced-calling-faqs/
Thoughts on this? Corrections on my math? Please feel free to comment below.
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