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AT&T iP5 switches to 4G from LTE when placing a phone call

S

soulvoid

macrumors member
Original poster
Sep 5, 2007
39
0
Please explain why this happens. I know Verizon and sprint can't handle voice and data at the same time on LTE but AT&T can. So why the switching? Is the 4G network handling all the voice calls for now until the LTE network is mature or what?

I can't be the only one this affects either. Please chime in. Thanks
 
soulvoid said:
Please explain why this happens. I know Verizon and sprint can't handle voice and data at the same time on LTE but AT&T can. So why the switching? Is the 4G network handling all the voice calls for now until the LTE network is mature or what?

I can't be the only one this affects either. Please chime in. Thanks
Click to expand...

Both versions can only support one type of a connection at a time. Neither Verizon nor ATT support VoLTE yet so each drop down to the GSM or CDMA network for calls. GSM then supports data over the same connection as it always has.
 
soulvoid said:
Please explain why this happens. I know Verizon and sprint can't handle voice and data at the same time on LTE but AT&T can. So why the switching? Is the 4G network handling all the voice calls for now until the LTE network is mature or what?

I can't be the only one this affects either. Please chime in. Thanks
Click to expand...

No carrier in the world supports voice over LTE. Voice over LTE is a new thing that is being prototyped to send higher quality voice signals over LTE, but until that's implemented in 1-2 years LTE is only for data period for everyone worldwide.
 
Shaddow825 said:
Both versions can only support one type of a connection at a time. Neither Verizon nor ATT support VoLTE yet so each drop down to the GSM or CDMA network for calls. GSM then supports data over the same connection as it always has.
Click to expand...

That's all fine and dandy but... Is the reason LTE doesn't support VoLTE currently because the network infrastructure isn't robust enough or the specification doesn't handle it period? Before I posted and ran across something pertaining to this about Verizon's LTE but not AT&T.
 
Radiating said:
No carrier in the world supports voice over LTE. Voice over LTE is a new thing that is being prototyped to send higher quality voice signals over LTE, but until that's implemented in 1-2 years LTE is only for data period for everyone worldwide.
Click to expand...

Actually MetroPCS has rolled it out in some markets and will be networkwide in the next few months.
 
Radiating said:
No carrier in the world supports voice over LTE. Voice over LTE is a new thing that is being prototyped to send higher quality voice signals over LTE, but until that's implemented in 1-2 years LTE is only for data period for everyone worldwide.
Click to expand...

Ahh ok. So disregard my last post then. So the spec support it but not for mass market yet. Gotcha.
 
soulvoid said:
That's all fine and dandy but... Is the reason LTE doesn't support VoLTE currently because the network infrastructure isn't robust enough or the specification doesn't handle it period? Before I posted and ran across something pertaining to this about Verizon's LTE but not AT&T.
Click to expand...

Neither have rolled out support for in in their switches. And I do not know for certain that the software in the iphone 5 supports it even in the future when it is rolled out.
 
Pretty much all of these answers are wrong. That said, here is why it switches to "4G""

It's called Circuit Switched Fallback", and it's a normal behavior of a GSM/HSPA/LTE network when calls are made/received. LTE doesn't support voice at the moment, it's data only, that should change maybe in a year or so with VoLTE (once VoLTE codecs and fallback is standardized), but each time you make a call the baseband chipset has to fallback to HSPA to prioritize Voice. This is the only possible way to do it. The benefit is that you're still able to talk+surf at the same time, just not on LTE.

CDMA networks behave similar except that you fallback to 1XRTT where talk+Surf isn't supported at the same time. A complete extra set of antenna setup would've been needed to achieve talk+surf on CDMA network.

Hope this helps.
 
I use AT&T. My current iPhone 4 can make calls and surf the internet simultaneously on 3G. Why doesn't the iPhone 5 send voice over 3G and keep the data flowing through LTE?
 
milan03 said:
Pretty much all of these answers are wrong. That said, here is why it switches to "4G""

It's called Circuit Switched Fallback", and it's a normal behavior of a GSM/HSPA/LTE network when calls are made/received. LTE doesn't support voice at the moment, it's data only, that should change maybe in a year or so with VoLTE, but each time you make a call the baseband chipset has to fallback to HSPA to prioritize Voice. This is the only possible way to do it. The benefit is that you're still able to talk+surf at the same time, just not on LTE.

CDMA networks behave similar except that you fallback to 1XRTT where talk+Surf isn't supported at the same time. A complete extra set of antenna setup would've been needed to achieve talk+surf on CDMA network.

Hope this helps.
Click to expand...

I appreciate the technical answer. And commend you for doing so :)
 
soulvoid said:
Ahh ok. So disregard my last post then. So the spec support it but not for mass market yet. Gotcha.
Click to expand...

Actually my mistake I checked up on the issue:

They've already gone past the prototype stage and are starting very very early adoption in select markets with specially designed devices.

Long story short:

In August 2012 VoLTE (Voice over LTE) has been activated in South Korea.

In August 2012 Metro PCS has activated VoLTE AND has released a phone which works with it: LG Connect 4G in Texas
 
xak said:
I use AT&T. My current iPhone 4 can make calls and surf the internet simultaneously on 3G. Why doesn't the iPhone 5 send voice over 3G and keep the data flowing through LTE?
Click to expand...

Something about the number of antennas and radios it can use at the same time. Hey technical answer guy. Chime in on this one eh?
 
Radiating said:
Actually my mistake I checked up on the issue:

Long story short:

VoLTE (Voice over LTE) has been activated in Korea since August 2012, but there are no devices that actually work with it.

Metro PCS has activated VoLTE AND has released a phone which works with it: LG Connect 4G in Texas

So actually they've already gone past the prototype stage and are starting very very early adoption in select markets with specially designed devices.
Click to expand...

So will this be enabled for us AT&T ip5 guys with a software/baseband update or the iphone5S or 6? What's the tech tell us...
 
soulvoid said:
Something about the number of antennas and radios it can use at the same time. Hey technical answer guy. Chime in on this one eh?
Click to expand...
That would require a whole other radio and it wouldn't be efficient at all. Battery would suffer and also i doubt FCC would allow that to happen due to the increased radiation SAR level. You're basically broadcasting voice + data on HSPA and on top of that LTE.
 
soulvoid said:
So will this be enabled for us AT&T ip5 guys with a software/baseband update or the iphone5S or 6? What's the tech tell us...
Click to expand...

The iPhone 5 already has HD Voice from the factory which is another name for Voice Over LTE. This was discussed on a slide in the keynote.

As soon as the carriers support it it will work. No update nessesary.
 
Radiating said:
The iPhone 5 already has HD Voice from the factory which is another name for Voice Over LTE. This was discussed on a slide in the keynote.

As soon as the carriers support it it will work. No update nessesary.
Click to expand...

Word. I like this :)
 
Every other LTE device on Verizon supports simultaneous voice + data with LTE coverage, the iPhone is the only device that does not. I was hoping I would be able to make the switch from android to iphone this time, but sadly I cannot, and only for a small decrease in form factor. Currently I can work remote and take work calls simultaneously with my android device, and this should have been possible with the LTE iPhone but they screwed it up. As you can see I'm a little butthurt.

(In fact there is one device (Thunderbolt) that supports voice+data with Verizon 3G coverage.)
 
Radiating said:
The iPhone 5 already has HD Voice from the factory which is another name for Voice Over LTE. This was discussed on a slide in the keynote.

As soon as the carriers support it it will work. No update nessesary.
Click to expand...
HD Voice isn't VoLTE. HD Voice is the wideband codec made for WCDMA networks. 20 European GSM/HSPA carriers will be using this.
It's a completely different thing.
 
shaddix said:
Every other LTE device on Verizon supports simultaneous voice + data with LTE coverage, the iPhone is the only device that does not. I was hoping I would be able to make the switch from android to iphone this time, but sadly I cannot, and only for a small decrease in form factor. Currently I can work remote and take work calls simultaneously with my android device, and this should have been possible with the LTE iPhone but they screwed it up. As you can see I'm a little butthurt.

(In fact there is one device (Thunderbolt) that supports voice+data with Verizon 3G coverage.)
Click to expand...

That's because they use two chips, which uses a ton of battery power. The iPhone 5 uses 1 chip, and a lot of effort went into making it this way. Just wait until Voice over LTE is turned on.

milan03 said:
HD Voice isn't VoLTE. HD Voice is the wideband codec made for WCDMA networks. 20 European GSM/HSPA carriers will be using this.
It's a completely different thing.
Click to expand...

Interesting, I read on a blog otherwise, but I guess they were definetly missinformed after reading some more. well regardless the iPhone 5 supports VoLTE, which is where the voice information is sent as a data packet through the LTE data connection.
 
Radiating said:
Interesting, I read on a blog otherwise, but I guess they were definetly missinformed after reading some more. well regardless the iPhone 5 supports VoLTE, which is where the voice information is sent as a data packet through the LTE data connection.
Click to expand...
Well the interesting thing is MDM9615 Baseband chipset in the iPhone 5 supports VoLTE, but according to FCC testing, it's not actually active in iPhone 5. So it really doesn't support, and if they're to update it, it would've required another trip to FCC.

VoLTE in the U.S. is still far from being a wide spread solution. Verizon announced VoLTE deployment once they completely blanket their existing 3G footprint with LTE, and AT&T didn't even announce any VoLTE path. The problem they're facing is that codec isn't really standardized globally so they're not commiting, and also calls made from VoLTE solution to regular landline or GSM/CDMA would need to scale and that's still not ironed out from the technical standpoint.

MetroPCS on the other hand already has VoLTE deployed in one market, but it's a poor narrowband codec that doesn't do much. They just like to be first lol :)
 
It's so they can throttle you and give you an explanation why throttling you saves you battery.
 
shaddix said:
Every other LTE device on Verizon supports simultaneous voice + data with LTE coverage, the iPhone is the only device that does not. I was hoping I would be able to make the switch from android to iphone this time, but sadly I cannot, and only for a small decrease in form factor. Currently I can work remote and take work calls simultaneously with my android device, and this should have been possible with the LTE iPhone but they screwed it up. As you can see I'm a little butthurt.

(In fact there is one device (Thunderbolt) that supports voice+data with Verizon 3G coverage.)
Click to expand...

Time to switch to AT&T:D
 
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