back to article WTF is... VoLTE

How are the UK's mobile network operators going to handle voice calls when they switch on their 4G LTE networks? Possibly not very well. LTE is a purely IP network, so ordinary phone calls need to carried using voice-over-IP (VoIP) technology. That ought to be straightforward: VoIP has been around for years, the principles are …


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  1. Anonymous Coward
    Anonymous Coward

    I missed article ratings for the first time I rather liked this article, and wanted to click the "chapeau!" button. Very good, quite a nice summary of what's going on for the faint of heart. Thanks for that, good work.

    (OK, so my inner pedant wanted to correct a couple of prose trainwrecks, but it was otherwise very enjoyable)

  2. nsld


    Given that everything everywhere blocks the use of VoIP on its data connections if you use a mobile dongle will this mean that over the top VoIP will now work on 4G?

    1. Mage Silver badge

      Re: Interesting

      Good try, but an operator can tell the difference between their overpriced VOIP and your VOIP application.

    2. MrXavia

      Re: Interesting

      Doesn't it work now? I use voip on my phone all the time with 3G?

      or is is the meanie US networks doing this limitation?

  3. Lee Dowling Silver badge

    Is it just me thinking that yet-another-technology will be destroyed by commercial interests, deliberate incompatibilities, differing pricing structures and lack of co-operation?

    What if one network charges all things through it's net per second and another per kilobyte? Are we then just going to raise prices for everyone to make up the shortfall of costs to/from the differing network?

    Someone needs to step in, even in the 3G days, and say that you can bill per kilobyte. Differing prices for "prioritised" data if you like, but that's all you can do. Then we get to use things like Skype (whereas currently its use is artificially restricted because it would do a better and cheaper job over their own network than the networks can provide themselves), data-downloads, etc. and not have this sort of hassle.

    I predict yet-another-mess. We're already in a mess with spectrum licensing with it, we're in a mess with some networks getting to run trials that others can't, and now we're seriously suggesting all these companies to get together and decide what to charge the end users and how and do it fairly and consistently (even while roaming). It's not going to happen. It's a train-wreck waiting to happen.

    Yet-another-technology thrown to the dogs because commercial interests can't deploy it in co-operation with each other.

    1. HMB

      I just don't agree and with good reason.

      Circuit switching is a lot less efficient than packet switching, that's why it's not the best for data and ultimately why it's not best for voice either. When some technical person hands their boss a piece of paper in the future indicating that they can support 10-20% more users by going entirely to packet switched VoLTE they'll see savings and do it.

      New technology throws off mobile operators, happens all the time.

      How companies bill is up to them, whether we buy it or not is up to us, the public. The only time authorities should ever step in is for price fixing and the like.

    2. Roland6 Silver badge

      re: Lee 2-Oct-12 11:15

      Yes, it does seem that charging based on content type and traffic priority is a potential billing elephant for the telco's, particularly with respect to voice where all mobile networks still need to connect to well established fixed networks.

      I however don't see it as such a big problem, given that with 3G the operators are already doing mixed billing.

      For example, with Three UK: use their voice service (calls routed over voice priority infrastructure) and pay per minute, use Skype for 3 and just pay for data - but voice is still routed over 3's voice infrastructure to Skype, use native (data service) Skype and pay just for data. However, in both of the Skype cases if the user wishs to call outside of the Skype walled garden then there is a time-based additional call cost.

  4. Anonymous Coward
    Anonymous Coward

    Erm, like, who cares???

    Who on earth cares about voice quality these days? It's all about Facebook and twitter for me and my tech savvy friends now, and rightly so. By facebooking them, I have a permanent, searchable record of our interactions and can easily find out who said what to whom, and it's allowed us to resolve many disputes that, if we had to have relied upon memory, would have led to acrimony and sniping. My facebook profile is open and free to the world - I have nothing to hide and only those who have something to be ashamed about can be concerned as to the demise of voice calling these days.

    The only voice calls I receive these days are from someone trying to scam me for Payment Protection Insurance - thanks, but I can live without that.

    1. Captain Hogwash

      Re: Erm, like, who cares???

      AC? Nothing to hide? Irony or idiocy?

      1. Dazed and Confused

        Re: Erm, like, who cares???

        I rather liked the idea that the AC thinks he has friends

    2. TeeCee Gold badge

      Re: Erm, like, who cares???

      How weird, my experience is the opposite.

      My tech-savvy friends all avoid Faceberk and Tw@ter like the plague. Too full of bloody sheep. I tried FB for a while and just got deluged with trivial crap from extended family members. There may have been something interesting in there somewhere, but I couldn't be arsed wading through the crap to find it.

      You can replicate the Facebook/Twitter experience by standing in a Mancunian Bingo hall and listening to the conversations going on around you.

      1. HMB

        Re: Erm, like, who cares???


        BINGO :P

        Oh, and when I'm on the phone with my friend from up north and I'm having to ask her to repeat what she just said because of the voice quality popping and smudging the sound, I bloody do care about voice quality. When I think about how good it could be, but isn't, I get even more annoyed. I had an HD Voice call once and it was fantastic, but completely took me by surprise.

    3. Natalie Gritpants Silver badge

      Re: Erm, like, who cares???

      > By facebooking them, I have a permanent, searchable record of our interactions

      How permanent is your facebook page?

    4. Simon Rockman

      Re: Erm, like, who cares???

      Voice is still the major use case. Indeed I use skype at home BECAUSE of the call quality. I like big old-fashioned phones that have a big enough speaker cavity for the audio to sound decent.

    5. Ilgaz

      Re: Erm, like, who cares???

      Mobile voice and sms (yea,sms!) is a trillion (that is thousand billions) industry.

    6. John H Woods Silver badge

      Re: Erm, like, who cares???

      Poe's Law in action?

  5. TeeCee Gold badge


    All well and good, but this imposes a short but potentially noticeable delay - from two to four seconds, according to insiders - when a voice call is initiated by an LTE handset or a call is routed to one.

    A two to four second delay on call setup could be considered a minor annoyance. I'd have thought that the elephant in the room here is what happens when your LTE handset moves out of LTE coverage and is forced to negotiate a slower connection and fallback mid-call? There doesn't seem to be any mention of how that would be handled and it would seem to be a basic requirement to me.

    Forcing calls to initiate on 2g or 3g might be the sensible move here.

    1. skipper

      Re: Fallback.

      Given that LTE coverage is expected to be very patchy at the start, then CSFB seems to be the only viable route if indeed you'd experience a big pause while your phone failed back to 2G/3G.

      That said an additional 2 - 4 seconds on making a call will seem like an age. I find the amount of time it takes my phone (Galaxy S2 on Orange) to initiate a call far too long (my old Blackberry, on Orange, was fairly instant). If this was to get any longer I know I'd be returning my new handset to Something Somewhere very quickly.

      But then would this be any different with VoLTE - is it just a case of waiting until the hardware and software can manage it instantaneously?

      1. JimiJoe

        Re: Fallback.

        The 2 - 4 second CSFB delay is also there on receiving a call so lots of 'Hello, who's there??? Hello, who's there???' when someone calls you on your shiny new 4G mobe. The CSFB delay is also present with SMS for the same reasons but not as noticeable.

        As for handover between cells mid-call; 2G - 3G cell handovers are hard enough, so 'good luck' with VoLTE - 2G/3G!

      2. Roland6 Silver badge

        Re: Fallback.

        I'll like to see fallback to 2G/GSM when the 4G networks occupy the UK GSM radio bands ...

        I don't see there being a user problem with a few extra seconds being added to call initiation. However, how call delivery is handled could be problemmatic as the reception radio negotiation will need to happen during the connection phase that occurs prior to the phone ringing, otherwise the caller might be tempted to disconnect.

    2. Anonymous Coward
      Anonymous Coward

      Re: Fallback.

      'There doesn't seem to be any mention of how that would be handled and it would seem to be a basic requirement to me.'


  6. Lis 0r

    "She was born in the 80s, she still uses her phone as a phone!"

  7. Patrick Evans

    Bye bye battery

    "It's like the early days of 3G. Back then, the new network was criticised for hammering handset batteries. Chipset and handset technology has solved that problem"

    Really? I must have missed that one - if I need more than a day of battery life for some reason, I ditch 3G and drop back to 2G only and *that* solves the problem.

    Or is a battery that gets me through til a teatime topup considered good enough these days?

    1. Anonymous Coward
      Anonymous Coward

      Re: Bye bye battery

      Clearly you need a better phone, if yours dies come teatime just because 3G is enabled.

    2. Steve Evans

      Re: Bye bye battery

      Coverage has a huge impact here.

      I spend 99% of the time with my phone on 2G. I only switch to 3G when I need to, which is very rare as I switch on wifi first.

      Where I live 3G will murder the battery. The 3G signal here is very weak (or just MIA!). 2G isn't much better, but at least it exists.

      This causes a problem for the phone in that it will ramp up the radio to higher power in an attempt to contact a tower. If the tower is uncontactable (as 3G is for me most of the time), the phone remains on high power trying negotiate a 3G link.

      The phone will always use the lowest power it can to talk to a mast, so having a mast it can talk to is far better than trying to contact one that just isn't there.

      If you don't believe me, get on the underground (assuming your chosen line has no coverage) and see how long your battery lasts. I forgot to put my phone into flight mode once, and it was a painfully slow trip (breakdown)... Result, 50% battery gone in 40 minutes. On the surface I rarely do 50% during the entire working day.

  8. Anonymous Custard Silver badge

    You have to wonder...

    If some of the unwillingness or inability for a cross-company agreement on these is the huge amount of acronyms involved. I look at the two diagrams there and see about half a dozen words I recognise plus a couple of the acronyms that I can understand or guess.

    Or is it just me with my poor little dumb-phone that only allows me to do odd things like talk to people?

    1. Bassey

      Re: You have to wonder...

      "Or is it just me with my poor little dumb-phone that only allows me to do odd things like talk to people?"

      Erm, yes. This is a Technology forum on a technology website.


  9. Anonymous Coward
    Anonymous Coward

    It took me ages to find the Volte-face joke. I knew it had to be in there....

  10. Jeff 11

    VoIP technologies will suffer exactly the same problems on LTE that they have had on 3G and fixed line broadband since they were conceived, because guaranteed voice quality *absolutely depends* on having a dedicated, uncontended IP connection or a quality of service on a contended line that prioritises voice traffic.

    Contrary to what Skype et al say, there's no software innovation which can reliably work around this fact; it's completely up to the operator to provide either of these and that's why today's status quo on voice will remain for the foreseeable future.

    1. Yet Another Anonymous coward Silver badge

      >dedicated, uncontended IP connection

      How exactly do you get a dedicated IP connection ?

      Other than running your own bit of Cat-5 between every phone and an exchange, and having a woman with a beehive perm and horn rimmed glasses plugging and unplugging network jack to connect calls - you are going to be switching packets somewhere

  11. Alan Brown Silver badge

    acceptable voice quality

    I don't get that on my existing EE connection. Why would slight deterioration make any difference?

  12. Christian Berger

    Meanwhile in the real world

    Users are simply digging VPN tunnels through LTE since LTE data, as most mobile forms of data connections, is horribly messed with by the operators. (For example by adding the telephone number to the HTTP headers)

    Those users will then simply use VoIP if they should choose to use voice.

  13. Anonymous Coward
    Anonymous Coward

    Shirley we can do away with all the GGSN/SGSN/HLR/VLR network boxes

    and just use terminal to terminal protocols (even considering beyond IP)? There's enough terminals (handsets) around nowadays to propagate a fair communications mesh network without the restrictions of operators/delays in even thinking about horsetrading bands/sharing of BTS. - in my EU country there are currently more 2G/3G handsets than people and that's before the shiny 4G terminal rollout really starts. IIRC already at 3G debut it would have been cheaper and faster to just write an App and hop data/voice from phone to phone. mesh should please the oh noes 'tower near my school' worriers as well as I reckon my phone would only need 5 milliwatts to hop data to the next phone - rather than blast a battery sapping 2 watts to find the distant tower, which hence wouldn't be needed and would make the DailyMail readers happier. Mesh network = kindle battery life from your comms device?

    Oh I forgot, the 4G frequencies need to be sold-off to pay for the 50%->45% tax break/100k houses delete as appropriate, so we're politically/financially prevented from discussing this?

    1. Christian Berger

      There's little money in that

      Not to mention the carriers loosing an important market.

  14. Stevie Silver badge


    That diagram reminded me of that Rex Harrison film where he is trying to use an old disc-cutting dictaphone and keeps referring to "the simplified diagram" - which is a fanfold circuit diagram of fiendish complexity.

  15. Anonymous Coward
    Anonymous Coward


    Just bill for data then they don't need to care what you're up to, voice or pron doesn't matter.

  16. Henry Wertz 1 Gold badge

    4G LTE in reality

    "Circuit switching is a lot less efficient than packet switching, that's why it's not the best for data and ultimately why it's not best for voice either. When some technical person hands their boss a piece of paper in the future indicating that they can support 10-20% more users by going entirely to packet switched VoLTE they'll see savings and do it."

    CDMA and UMTS already effectively do this. I mean, you have a voice "circuit" but really it's not a dedicated timeslot or frequency, it's all virtual; the actual capacity of the cell site is interference-limited, not circuit limited (there is a limit on # of circuits but it's unreachable unless you intentionally load the site down with dead-silent phone calls). There is a symbol to indicate a whole frame is silence, and with variable bitrate voice background noise will not be transmitted full quality while your voice will. Forget 10-20%, they actually increase capacity by over 40% this way! VoLTE should still save since LTE is more efficient in terms of bits/mhz however.

    "Is it just me thinking that yet-another-technology will be destroyed by commercial interests, deliberate incompatibilities, differing pricing structures and lack of co-operation?"

    Frankly, I think the plan is to just keep billing voice and data just as now. Unfortunately, here in the states... MetroPCS has publicly stated they are intending LTE to lower their costs, which they plan to pass to the customer. Verizon? AT&T? US Cellular? They have increased data pricing significantly as they roll LTE. USCC for instance went from $30 for 5GB to $30 for 2GB.. ouch!

    As for delays or whatever.. I have an LTE phone now. From what I've read, Verizon DOES run IMS over LTE, using CSFB to CDMA-1X for voice calls. What can I say? I don't have a 2-4 second delay; I just dialed my voicemail and it took approximately 1 second. Maybe CDMA kicks on faster than UMTS?

    As for 4G<->whatever handoffs.. I guess the plan for voice is CSFB. You should realize, though, the chances are good that for the few moments the handoff takes it should be possible to run the 4G and (3G or 2G) *simultaneously*, known as a soft handoff in CDMA/UMTS world. I think this is one reason VZW is not running VoLTE, this type of handoff would require digging into both networks and without this type of handoff it'd be dropped call city.

    As for data, my 4G drops back to 3G seamlessly, the 3G will kick up to 4G seamlessly due to some rig Verizon calls eHRPD (I think extended High Rate Packet Data?) general. I have had this not work though, instead the 4G will fade, there'll be a huge 15 or 20 second time period with no data, then the 3G will kick in. Kicking into 1X (in roaming areas -- Verizon effectively has at least 3G over their whole network...) takes about 15 or 20 seconds too.

    That said these are NOT a significant problem -- we listened to slacker on a road trip (about ~1100 miles each way), I had 4G about 1/3rd of the way and on average had to reset slacker maybe every 300 miles.

  17. Anonymous Coward
    Anonymous Coward

    However they end up doing it in the US, they'll choose multiple ways

    Which will be incompatible with each other. There is, after all, not only VoLTE but also VoLGA (Voice over LTE Generic Access) Verizon will choose one, AT&T the other.

    It'll be further complicated by having some phones only able to support one method or another, so some people will see problems that others don't see - even others with the same phone if it has a different software rev or even possibly a different point rev on the chips inside.

    It'll be a colossal mess still five years from now. But hey, we're the US, we don't believe in regulating the carriers. Clearly having the country covered by GSM and CDMA networks utterly incompatible with each other is a good thing. Not for consumers, obviously, but for the carriers that don't have to worry about letting their customers roam over their competitors' networks!

  18. hazydave

    Works today, no delay

    In the US on Verizon, the only voice protocol on CDMA2000 is 2G. So there's no switching... on fact, many devices have separate 2G/3G and 4G radios. A 2G voice connection disables a 3G data connection just as it always has on CDMA, while the 2G and 4G run in parallel, unaffected by one anothet. OK, if you have a new iPhone, you drop 4G for voice.

    LTE itself is not all that power hungry. It can be worse than 3G per minute, but never per byte. It can also be better than 3G, due to the superior radio bands here in the states

    Verizon at least is already laying some of the groundwork for an all IP network. Recently, their preferred plans have made voice and texts unlimited, but jacked the price of data way up. That would make it very easy for them to simply drop voice/MMS as separate things and make it all just data.

  19. Anonymous Coward

    Good whitepaper on VOLTE

    I did wonder what would happen with emergency service calls but it's handled;


    Most operators provide overlapping circuit-switched access network coverage for emergency calls.

    For operators without such coverage, the VoLTE profile includes an emergency VoIP over LTE solution

    based on 3GPP Release 9 to ensure compliance with international regulatory requirements.

    In all honesty, based on the 3G experience so far, where it spends most of the time on Edge or GPRS whilst travelling about - it is likely that it'll fall back quite frequently. The white paper above explains how that would occur.

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