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VoLTE: Voice over LTE

Everything about "real" telephony via 4G cellular networks

LTE cellular technology has been making turbo-fast internet possible for on the go for 9 years now. However, voice is still mainly handled via the old 3G or 2G. The so-called "Voice-over-IP over LTE ”, VoLTE for short, huge improvements for consumers and providers alike. Nevertheless, LTE is still mainly used for data transmission to this day. But the new technology is slowly gaining momentum. In the following special, you will find out why not all mobile phone calls have long been running over 4G, who offers VoLTE, what advantages the process has and much more.




1. What is VoLTE?

Most cell phone customers who use their smartphones still inevitably end up using "ancient" cell phone standards such as GSM or UMTS when making a phone call. These work purely wired and still transmit the language on physical or virtual channels. With VoLTE, on the other hand, voice transmission is handled completely digitally in the LTE network. In the form of data packets based on the IP protocol.

Definition:VoLTE is a standard officially adopted by the GSMA that implements voice services over LTE networks. And exclusively IP packet-oriented and based on the so-called IP Multimedia Subsystem, IMS for short. Defined in the PRD IR.92 [Info] protocol. Roaming for VoLTE, on the other hand, is defined in the PRD IR.88 guidelines.

This has considerable advantages, as we will show below. Unfortunately, for a long time, the implementation proved to be relatively difficult for the mobile phone providers. We will explain why this is so later in this special. First, let's take a closer look at the numerous pluses.

2. Advantages of VoLTE

Voice over LTE is revolutionizing mobile telephony just as positively as LTE has already achieved with mobile Internet. After all, you can surf on the go with 4G at 100, 150 or even 500 Mbit / s. VoLTE opens up a whole range of advantages - for the end customer and the cellular provider!



2.1 Advantages for the user:


  • 1) VoLTE offers higher voice quality
    Probably the most interesting aspect at first is the improved voice quality compared to 3G or OTT VOIP, such as Skype. VoLTE offers "HD telephony" as a standard, so that speech sounds even more natural and clear. Modern AMR-WB codecs [Adaptive Multirate Wideband] with 12.65 or 23.85 Kbit / s are used. In addition, the mobile network providers prioritize the data IP packets via QoS for the lowest possible latency and maximum reliability. And video telephony should finally become an experience with VoLTE.

  • 2) VoLTE reduces power consumption
    It's not just the ears that benefit from the new technology. Also the Smartphone battery lasts significantly longer. Compared to telephone calls via common VOIP services, the energy requirement drops by approx. 40 percent with otherwise the same quality![1] But energy consumption is also significantly reduced compared to 3G or 2G-based calls. However, this effect is largely dependent on the efficiency of the chipset installed in the device.

  • 3) Enormously accelerated connection establishment
    Anyone who is not used to telephoning with VoLTE will probably be the first to be amazed at the extremely fast call setup. So far, as is well known, you could easily refill a cup of coffee until the doorbell rang. With VoLTE, this process takes between 1 and 2 seconds! Choose, click, speak!


2.2 advantages for providers:
The process is not only beneficial for the consumer. The mobile phone providers are also well advised to use VoLTE. In the end, however, some of the optimization potential also reaches the end customer. For example in the form of relieved networks.

  • a) VoLTE offers better spectral efficiency
    That sounds a bit complicated at first, but in principle it only means: The provider requires less frequency bandwidth for Voice over LTE than for 2G or 3G calls. Theoretically, with a complete changeover to VoLTE and the same volume of calls, more capacity would be available for mobile data services. In figures, this means the following: A provider can handle twice as many calls with the same frequency base and identical costs as with 3G. Compared to the most modern GSM technology even by a factor of 6. Samsung goes even further: According to analyzes of the group, 15 times more users per mega-hertz could be processed with LTE than with GSM (EFR). Twice as much as compared to HSPA / 3G.[2]

    And even in comparison to OTT-Voip, VoLTE scores significantly with a lower volume of traffic. With approximately the same quality, a VoIP phone call generates a data volume of approx. 45-50 Kbit / s. In contrast, VoLTE stands at around 13-25 Kbit / s.

  • b) easy implementation of RCS
    With VoLTE, Vodafone & Co. have a comparatively simple, technological basis for the implementation of so-called "Rich Media Services" - that is, additional customer value-added services. For example for video telephony, instant messaging and so on.

  • c) Added value for customers
    The technology can also be viewed from the perspective of customer loyalty. The advantages that are inevitably perceived and honored by the user have already been mentioned above. At least if everything goes smoothly. Thanks to QoS and the best voice quality, the user then receives a simple, stable and reliable alternative to OTT-VOIP. The latter puts unnecessary strain on the networks anyway, since the volume consumption, as indicated under a), is significantly higher.

  • d) accelerates the evolution of LTE in general
    In the long term, providers could convert bands that are no longer required that were previously used for 3G or 2G to LTE. In the 4G data networks, additional bandwidth would be available without additional costs. Of course, this would first require a complete migration or only partial spectra are used.


3. VoLTE provider - who offers Voice over LTE?

Meanwhile have all German network providers VoLTE introduced. Vodafone started in March 2015 - shortly afterwards O2 Telefónica followed suit. Deutsche Telekom started in January 2016. The network service has also been available through most virtual providers (e.g. prepaid) since 2020 ...


Vodafone: At Cebit 2015 the time had finally come - for the first time, a German mobile operator introduced the voice network of the future in this country. Since March 16, 2015, Vodafone has been offering its customers the option of making calls in the in-house network using Voice over LTE. Fortunately, there are no extra costs for the not inconsiderable added value. All RED tariffs are compatible. Prepaid customers (Callya) were left out for a long time. But since mid-2020, the feature has finally also been available for prepaid offers.

O2 Telefonica: The mobile operator initiated the VoLTE launch on April 16, 2015. Since then, O2 users can theoretically also make calls via LTE. At least if your own smartphone has this function technically and has already received a corresponding firmware update from the provider. New end devices are added every week, and more are added piece by piece. By the way, O2 has been leaving since March 2018 all customers Participate in the advantages in your own network, also through third-party providers such as Blau or Aldi-Talk. In January 2019 we also asked O2 about the distribution and plans for VoLTE - for the O2 interview.

German Telekom: Otherwise known as an innovation leader, Telekom took its time this time. It wasn't until the beginning of 2016 that the provider announced the introduction of VoLTE. Since then, customers have been able to make free calls with a higher voice quality. The only requirement is a Magenta mobile phone tariff. But many prepaid customers are already benefiting (see point 6).

Conclusion: Since 2016, all three major mobile phone providers have been offering VoLTE in their own 4G network! By the beginning of 2022 at the latest, everyone should offer the technology, as all providers will have switched off 3G by then.

4. Compatible devices for VoLTE

Since 2016, however, more and more brand-free smartphones have been coming onto the market that are "ready" for VoLTE for all networks. Almost all current models since 2019 offer VoLTE support by default. Before that, although many smartphones were technically suitable for LTE telephony, they still had to be made "compatible" with firmware updates by the wireless service providers. Which models are already supported by your provider are revealed on their websites, albeit somewhat hidden. Here are the models by provider (as of Q3 / 2020).


Vodafone support list:

  • from Apple iPhone SE, 6s / 6s Plus and newer
  • BlackBerry Priv *, DTEK50 *, KEYone *, Motion *
  • Google Pixel 2 / Pixel 2 XL and newer
  • HTC 10 and U11 and newer
  • HUAWEI Blanc, GX8 *, HUAWEI Mate S *, HUAWEI Nova, HUAWEI P8 * / P8 Lite * / P8 Lite 2017, P9 / P9 Lite / P9 Plus, P10 / P10 Lite / P10 Plus, P20 (Lite / Pus) and newer
  • LG G4 *, LG G5, G5 SE *, LG G6, LG G7, LG K8 LTE *, Q6, X-Screen * and newer
  • Microsoft Lumia 550, 640 * / 640 XL *, 650, 950/950 XL
  • Nokia N3
  • Samsung Galaxy A3, A5, J3, J5 (2016 & 2017), Galaxy Note 7 / Note 8, S5 * / S5 Neo *, S6 * / S6 EDGE / S6 EDGE Plus, S7 / S7 EDGE, S8 / S8 +, S9 / S9 +, Galaxy XCover 4 and newer
  • Sony Xperia X * / X compact *, Xperia XA1 *, XZ * (Premium *), XZ1 * (Compact *), Z3 * (Z3 Compact *), Xperia Z5 * (Compact *) and newer
  • Vodafone Smart speed 6 *, ultra 6 * / ultra 6 VE *, Smart prime 6 *, Smart prime 7 *, Smart Platinum 7 *, Smart turbo 7 *, Smart N8 *


PS: The addition of an asterisk (*) means that the device must (te) be purchased from Vodafone.

Support list O2 Telefonica:
You can find an up-to-date support list from O2 directly from the provider here in the help forum.


Telekom support list:

from Apple iPhone 6 (Plus) and newer; from Samsung Galaxy S6 (Edge) and newer + Galaxy A3 / A5 / J3 / J5 from version 2017; e.g. from Huawei P8, P9 (Plus or Lite), Mate 10 Pro, P10 (Lite / Plus) or later; Microsoft 550, 650, 950, 950 X; Sony Xperia XZ or newer; Google Pixel 1 or newer.


PS: Unfortunately, Telekom does not offer an official list. Therefore, most of the models have been incorporated through research. It can also be more. It is best to ask support.

5. How do I know if I already have VoLTE (activated)?

In principle, it is extremely easy to see whether you are already telephoning via VoLTE or not. First, if not active, establish the mobile data connection. Now (assuming the right tariff) the LTE or 4G or 5G symbol should appear in the status bar of the smartphone. The following image shows the VoLTE symbol at the top right when a 5G data connection is in place at the same time. If a phone call is activated, the connection must not jump back to 3G or 2G ...



Conclusion: Will the 4G or 5G symbol appear during a phone call Not Replaced by 3G or 2G or UMTS or H +, VoLTE is active. Otherwise the phone will switch to one of the previous standards.

Sometimes Voice over LTE has to be activated separately in the end device. On Android devices you will find the setting under "Settings" -> "Cellular networks". If the end device is compatible or has received the firmware update from the provider, you will find the item "VoLTE calls" ("Use 4G LTE data for HD calls") or something similar.



6. Prepaid and virtual operators are (still) left out

More and more prepaid customers are also benefiting from VoLTE. The subsidiary brand congstar was activated for service at the beginning of 2020. The same applies to Klarmobil. Since then, other providers have joined the telecommunications network Konkret ja! Mobil, Kaufland Mobil, Edeka Smart and Norma Connect.

Vodafone also blocked VoLTE for its prepaid users for a long time. Since mid-2020, Callya customers have finally been able to make calls with 4G.

O2 led the way early on as a positive example. O2 all users In the O2 network, the possibility for crystal-clear telephony via VoLTE, i.e. also via third-party brands such as Blau, Smartmobil, Aldi and so on. So also for all prepaid tariffs in the O2 network!

VoLTE should arrive everywhere by 2022 at the latest. Because the network operators want to get rid of the outdated 3G by then (sometimes even sooner). In order to avoid a fallback to 2G during calls, Voice over LTE would have to be available to all customers by this date!

7. Alternative Wifi Calling

Another technology for cellular telephony has been gaining ground since 2017 - WiFi calling, also known as WiFi calling or WiFi telephony. If the provider and smartphone support the service, the customer can also make calls without conventional cell phone reception, provided that only a WiFi hotspot is accessible on site. For example on campsites abroad or in your own cellar. You can find more on the subject here in our large WiFi calling guide.

8. Technology problems: Every beginning (was) difficult

In terms of network technology, mobile telephony is a rather complicated matter. In addition to the purely physical transmission of information via the air interface, participants from different networks, for example, must also be brought together smoothly. And this across all cellular standards and technologies and possibly even from countries far away. The reason why the introduction of VoLTE took so long is due to the difficult interaction between 4G and older predecessor standards. For years, engineers around the world only worked on one central problem: the trouble-free and Seamless transfer of calls made via LTE to previous networks - the so-called handover

What was the problem? We remember: With Voice over LTE, voice is transmitted purely IP-based in the form of data packets. However, if a mobile phone user leaves the range of his LTE cell with his cell phone into an area without 4G coverage, he must immediately switch to the next best standard such as 3G. One also speaks of a fallback to a legacy network. But here language is technically transmitted completely differently. This changeover in the provider's core network must be so quick and problem-free that the end customer should not even notice it. The first breakthroughs for this problem solution came in 2013.



The procedure for a smooth handover from LTE to 3G (or lower) is SRVCC or eSRVCC. The abbreviation means "enhanced single radio voice call continuity". Without the technology, every call conducted via VoLTE would abruptly end as soon as one of the two participants no longer has LTE reception.

9. The long way to LTE telephony

The development of handling calls via LTE devices can be roughly divided into three technical evolutionary steps. Phase 1 shows the period before the introduction of VoLTE. The LTE networks were used here exclusively for data transfer, which has serious consequences. Because during all incoming and outgoing calls, the end device has to switch to outdated 2G / 3G voice and Switch data services. Much to the chagrin of the users, who pay a considerable amount of money for the fast LTE. The conversion from 4G to previous standards for calls is called "Circuit-Switched Fall Back" - CSFB for short. This service practically guarantees the parallel use of LTE for mobile internet and telephony until VoLTE is operational.

In Phase 2 VoLTE is implemented as a standard in cellular networks. Since March 2015 we have been practically in the transition from phase 1 to phase 2. Together with SRVCC (see above), the customer is guaranteed ideal availability and quality of service. The simultaneous use of Internet applications and telephone calls is no longer a problem. On the contrary: even video telephony and other services (RCS) are standard. Roaming in foreign networks, on the other hand, is usually still handled via CSFB.

Phase 3 however, is still a relatively fictitious scenario for the future. The keyword is convergence. All transmission methods (UMTS, WiFi, etc.) should be able to interlock and work without any problems, regardless of the standard or provider [3].

We have summarized some of the most important key events in recent years below. These show how the technology has developed to this day.

  • Oct. 2012: the first VoLTE networks for end customers are launched in the USA and South Korea [more]
  • Feb. 2013: O2 technicians succeed in seamless handover in laboratory to UMTS [more]
  • May 2013: We talk to O2 about the plans for the VoLTE start [more]
  • Sep 2013: LTE-Anbieter.info tests VoLTE at the IFA [more]
  • Jan. 2014: O2 shows handover to UMTS for the first time in its own network under practical conditions [more]
  • Feb. 2014: Swisscom also wants to introduce VoLTE in 2014 [more]
  • Jun. 2014: Austrian A1 tests VoLTE [more]
  • Jul. 2014: O2 reports VoLTE is already "ready" in many cities [more]
  • Sep 2014: iPhone6 ​​comes with VoLTE support [more]
  • Sep 2014: VoLTE only used by 11 providers worldwide [more]
  • Sep 2014: Eplus and ZTE prepare for launch [more]
  • Oct. 2014: O2 network is ready for Voice or LTE [more]
  • Nov. 2014: VoLTE has been booming in the USA since the iPhone 6 [more]
  • Dec. 2014: Telekom Austria also successfully tests VoLTE [more]
  • Jan. 2015: 80 countries are working on the introduction [more]
  • March 2015: Vodafone lunches VoLTE in the entire network [more]
  • April 2015: O2 also starts the age of 4G telephony [more]
  • Jan. 2016: With Telekom, the last German provider goes to the start [more]
  • Aug2016: GAS certifies enormous growth at VoLTE worldwide [more]
  • Jan. 2017: O2 finally unlocks Multicard customers [more]
  • Feb. 2018: O2 wants to activate VoLTE for everyone in 2018 [more]
  • Feb. 2020: congstar and klarmobile now also with VoLTE [more]
  • June 2020: Vodafone releases VoLTE for prepaid [more]

10. Frequently asked questions on the topic (FAQ)

Does voice over LTE cost extra?

No, the providers offer the service at no extra cost to all customers who have an LTE-compatible tariff and suitable smartphones.

Does calling via VoLTE consume my internet flat rate data?

No, it is a pure network service. No volume is taken into account.

Does Voice over LTE also work with LTE home tariffs?
No, the telephony is implemented here via VOIP. This is of course relatively similar, but within the network these are two completely different services. Telecom customers still benefit if the basic connection is based on All-IP. The high-quality and similar HD voice is then used for conversations with VoLTE call participants on the other line.

Glossary: ​​What does ...

OTT VoiP: free transmission of voice content via the data network of the mobile phone provider

GSMA: This is an association of interests of several hundred mobile phone providers and network equipment providers worldwide. Development of cross-network standards for mobile communications.

IP Multimedia Subsystem (IMS): This is a purely IP-based system in the telecommunications network that handles mobile services from different networks in a standardized manner. The main task is the interface between “Pre-4G” networks such as GSM and IP-based networks, including the provision of VoLTE. See also here at Wiki.

RCS: Rich Communications Services: These are additional value-added services for mobile communications customers for communication, based on IMS. For example, video telephony on the smartphone, simultaneous sharing of data while you are on the phone and improved instant messaging / chat functions. But it is also possible to transmit your own position to selected contacts.

QoS: Quality of Service: Here a communication service is to be assigned a special relevance. Put simply, IP data packets are given a kind of preference during transmission. Like an express letter that is delivered much faster than a "normal" letter.




Something that takes a long time...

An introduction in Germany was actually planned earlier. At the end of 2013, O2 is quite confident that it will soon be able to introduce Voice over LTE. As early as May of the same year, plans were based on a start before 2014. They were probably a little too optimistic. After all: In Berlin and Munich, for example, O2 had already activated VoLTE in mid-2014, but could not yet be used by end customers and was only accessible to network engineers.

The delay was not due to the fact that the changeover was too slow. The providers want to be absolutely certain that the technology works reliably and tested the use of VoLTE intensively. One very essential main reason, however, was far more trivial: It Until 2015, there was simply still a lack of sufficient end deviceswhich are compatible. It took until 2016 for Telekom to follow suit. So a full 5 years after the introduction of LTE as a data standard in Germany.




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careful research. However, we do not guarantee correctness and completeness! © LTE-Anbieter.info

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