Skip to content

VoLTE roaming. Things That Make You Love And Hate.

VoLTE roaming is the latest version of voice roaming for mobile network customers.

One of the most important factors determining the success of digital mobile telephony development is international roaming.

The client uses his own phone anywhere in the world to communicate with others.

Such a simple and important function appeared with the advent of GSM (2G) and UMTS (3G) telephony, so it would seem that it should also be implemented in 4G (LTE) and 5G networks.

Is it so?

The first 4G networks appeared in 2011, so a decade ago.

So, you will be surprised that almost no operator in the world has yet introduced VoLTE roaming for 4G networks.

Why did this happen? What are the risks for operators and customers? I will explain it to you in the article. In my opinion, the threats are huge, because operators can lose huge amounts of money due to the growing popularity of OTT (Over The Top) providers, such as WhatsApp or Messenger.

What is VoLTE?

In their architecture, GSM and UMTS networks have separate devices for handling voice calls and separate devices for data transmission.

The most important change in the architecture of 4G and 5G networks is getting rid of devices dedicated to voice calls. All services, including voice and video, are offered only through the network transmission of data, Website.

In the case of the 4G network, the voice calls and international roaming services were to be provided by VoLTE technology (Voice over LTE – Voice calls over LTE).

They were supposed to be, but until recently they were not.

It is worth understanding why this happened. This issue will explain why VoLTE roaming is practically non-existent today.

At the beginning of the implementation of the LTE network, there were no terminals supporting VoLTE. Logic would indicate that along with 4G networks, operators should naturally switch all voice calls to VoLTE, but after all, millions of customers used 2G and 3G phones.

Operators couldn’t just stop offering 2G and 3G voice connections to their customers, and they haven’t built a full 4G coverage yet.

The solution was a special feature called CSFB – CS Fall Back.

CS Fall-back

You have probably noticed that when you use your phone to browse the Internet, when someone calls you, your phone switches to the 3G network. This is what the CSFB function does. The phone switches to a dedicated network for 3G voice calls.

The introduction of CSFB allowed operators to focus on building a 4G network to support high-speed Internet. 

Consequently, they postponed the implementation of the VoLTE function for the future.

It was a dropout strategy, as you will see later on is a risky strategy.

In my opinion, CSFB became the main reason for the very late implementation of VoLTE.

Let’s start with getting to know the advantages of VoLTE.

Advantages of VoLTE and VoLTE Roaming

  • VoLTE offers an instant connection setup. Compared to 2G and 3G, connections are made in seconds,
  • Works with data services. You can chat and browse the Internet at the same time. For 2G networks, either voice or data works.
  • Today, the coverage of 4G networks is generally better and greater than that of 2G and 3G networks. Operators use more bands to build 4G networks.
  • It has the function of transferring the voice connection between LTE and Wifi, i.e. it works with VoWifi.
  • It allows you to call any number in the world based on MSISDN number. WhatsApp and Messenger only to people registered in these applications.
  • It offers good and even very good quality of voice calls. WB-AMR quality voice coders were introduced first, followed by even better EVS voice coders called VoLTE HD. The result is crystal clear sound quality.

However, no solution is free from disadvantages.

Disadvantages of VoLTE and VoLTE Roaming

  • VoLTE roaming is based on call charges. In terms of fees, this service does not differ from voice roaming on 2G and 3G. You can feel the differences when we compare the fees for VoWifi services or with the prices of OTT services. The latter offers free calls regardless of the place of calling.
  • In practice, poor quality of voice calls. Incredible isn’t it? Due to the poor quality of international interconnect connections, the above-mentioned super quality of WB-AMR and EVS codecs is not enough. That sounds pretty dry and needs some explanation. I will develop this topic further.
  • The customer has to buy a telephone that supports VoLTE functions, preferably from his operator.
  • 4G terminals must-have software prepared by the home operator. It is not easy to ensure VoLTE operation on an “off-market” terminal.

How VoLTE Roaming works, and why doesn’t it really work …

Voice calls VoLTE, based only on the service transmission of data. Voice calls, just like other applications, require the choice of the standard of the IT development environment and the method of communication between servers.

The debate about which solution to use under 3GPP standards took many years for operators. They couldn’t decide what kind of servers to use to create 4G platforms.

When it was finally decided to choose the standard IMS (IP Multimedia Subsystem) solution (early 2008-2010), it was no longer the most modern technology. This choice was the result of a compromise between suppliers and operators.

Years later, I rate this decision as one of the two basic mistakes of the cellular operator environment.

The choice of IMS and the very complex 3GPP standards have led to the emergence of much more agile competition in this field. 

For example, Facebook, using modern, quick-to-implement based on open interfaces (OPEN API) solutions on the Java environment on servers and smartphone applications, effectively threatened the voice services of operators.

As if that were not enough, the technical standard for international roaming was not thought out from the very beginning.

In total, two versions of the standard were created to ultimately simplify the solution.

The effective change of the technical implementation method took several years for the operating environment.

VoLTE Roaming technical solutions

Interconnection of operators between IMS systems (3GPP Rel. 11)

According to the original assumption of 3GPP standards, the connection between the two foreign operators was to take place at the level of IMS platforms.

IMS platforms were supposed to communicate with each other and control the customer’s voice connection abroad.

The idea was interesting, but as I mentioned before, unrealistic.

Operators did not have to implement IMS platforms because they had an alternative in the form of voice calls over 2G and 3G via CSFB.

Until today, some operators have not implemented VoLTE.

Even though the standard was ultra-modern, it was absolutely not adapted to the reality.

There was no way out, 3GPP had to look for an alternative.

Solutions were found based on the idea implemented by OTT service providers.

Connecting operators using the S8HR standard (S8 Home Routed)

So, what has changed? The need to implement the IMS platform was eliminated at both operators.

The requirement for interoperability between IMS platforms, which simply do not exist in many cases, has been minimized.

Now, only an operator who wants to offer VoLTE roaming to his customers must have an IMS platform.

The operator, in the visited country, only needs to enable the communication via the data network on the S8 interface to the IMS platform.

The S8 interface is used to ensure data roaming between operators. For VoLTE roaming, a dedicated APN-IMS is used.

What is the lesson from this story?

Creating complex 3GPP standards only provided room for development for OTT Internet Service Providers.

Can operators easily implement VoLTE roaming thanks to the new S8HR standard? Let’s look at the statistics.

Services VoLTE roaming the world

What percentage of operators in the world have implemented VoLTE roaming ?

Statistics on VOLTE and VOLTE roaming are not looking the best (GSA October 2020):

  • 750 operators in 200 markets have implemented LTE
  • VoLTE voice call services have been implemented by approximately 230 operators in 100 world markets
  • VoLTE HD, or VoLTE in HD quality (EVS Codec), has been implemented by approximately 104 operators
  • only about 40 operators have implemented VoLTE roaming. All based on the S8HR standard.

Participation of VoLTE roaming on LTE market:

VOLTE roaming
VOLTE roaming

Isn’t that a drama? Only 5% of operators were prepared to support voice roaming in 4G networks.

Unfortunately, the situation is much more complicated. There are more obstacles.

Problems with VoLTE roaming implementation and testing

In the case of testing 2G or 3G voice roaming services, the operator had a very simple procedure.

The operators exchanged SIM cards and connected their networks through transmission lines dedicated to voice calls.

After that, they tested each other’s SIM card services and made sure everything was working. This process was a simple task and even apprentices could do it.

In the case of VoLTE roaming, there were many more settings on the side of both operators’ networks.

Before starting the test procedure, operators exchange 30 questions from different network areas and must ensure that they are technically met.

Remember that VoLTE no longer uses a dedicated network for voice calls, so you need to establish a connection via the Internet and additional I-SBC devices (Interconnect Session Border Controller).

In such a scenario, an apprentice is not enough to perform the tests. You have to involve experts in the process. This complicates, irritates and lengthens the procedure.

As if that was not enough, another huge problem appeared, which is the complicated technical settings on the phone.

VoLTE and settings in smartphones – IMS settings

The list of manufacturers of devices supporting 4G / VoLTE already includes about 2,983 devices (October 2020). 82% are terminals, smartphones. About 85 5G devices supporting this function have already appeared.

The VoLTE service based on the IMS platform is a technically very complex service. In the parameter settings in the phone, dedicated to each operator, there are over 100 parameters to be established and set.

The problem is so big that the GSMA organization has created a central database (NSX) through which operators and terminal providers can exchange current settings. Currently, 200 manufacturers are registered in it. 

GSMA is currently counting on the participation of operators.

Therefore, if we add the question of settings in hundreds of different types of phones to the complicated setting procedure on the operator’s network side, we have a recipe for a big mess.

I do not need to add anything to stimulate your imagination and compassion for the employees of cellular operators.

This is a real technological hell and a consequence of overly complex 3GPP standards.

Life does not like a vacuum and customers do not like solutions to their needs. So who has benefited from this tetris?

Who will benefit from the bad situation with VoLTE roaming?

Where there is a market for services, there is always competition. It is no different with the market of mobile operators.

OTT service providers have been following the mobile operators’ heels for many years. You know them from WhatsApp, Messenger, Viber and many, many more.

These providers have a powerful tool on offer. Liked, free and well-rated voice services:

  • No charges for making calls to other platform members. Hm, WhatsApp and Messenger have a base of around 2 billion people 😉
  • Excellent quality of voice calls. This is due to the use of very good voice codecs and control over data transmission between your servers. Both of these parameters are crucial for the quality of connections.
  • Ease of making changes to the smartphone application. It does not require mastering complex telecommunications standards. All you need is the creativity of programmers and knowledge of the preferences of customers, which OTT knows very well.

There are a few other advantages that can be added, but these even crush the operators. The technological and process advantage is considerable.

The disadvantages, however, include the inability to make calls to the 112 emergency numbers and the lack of legal wiretapping for secret services.

Why should OTT providers take care of this, since these obligations do not legally apply to them and they are carried out by mobile operators all the time? 

2G and 3G networks are enough to make calls on 112.

And I have already mentioned that the operators have created additional barriers for themselves? No? So, read about the next surprises.

Terrible quality of calls abroad and in foreign roaming. Do you know it from experience?

I am convinced that each of you felt it the hard way.

You are buying a modern telephone. The seller assures you that the voice calls will be clear. You will hear your interlocutor as if he were standing next to you. You buy a phone.

When you leave the salon, you are enthusiastically calling someone you know abroad and suddenly be dismayed.

You can hardly hear anything; you cannot understand the interlocutor. Just drama.

In such a situation, operators lose their image, because customers associate such a situation with poor network coverage.

Do you know why this is happening? The main culprit in the case of voice calls between foreign operators is the way in which interconnect services are provided.

This problem is best explained by a simple drawing.

interconnect for international roaming
interconnect for international roaming

Principle of operation of interconnect

Operator A, let’s say in Poland, signs a connection agreement with operator B in the US. Than, Operator A tries to buy the best connection possible, but at the lowest possible rate. Operator B.

After all, they care about the quality of their own clients’ services and low client fees.

The problem is that there is a network of Interconnect providers between the two operators. A network that Operator A and Operator B do not know. They only sign a contract with the first provider connected directly to their network.

The source of the Interconnect provider’s income is the margin on wholesale sales of voice minutes. The interconnect supplier is looking for partners with whom it can exchange wholesale traffic at the lowest possible price.

This is the crux of the matter. You can get a lower price for international lines only for lower quality. Dot.

The hard laws of the market. Higher wages, lower costs, and quality and the customer suffer.

And who wins on it? OTT application providers who use 100% only Internet connections between their servers and do not use voice Interconnect services.

A sad and painful fact for operators and customers. And it will unfortunately remain so for many years to come. I’m sorry to write this.

This is not the end of bad news. The operators plan to exclude 2G and 3G networks in the future.

The radio band needed for 4G and 5G networks makes it necessary to switch off 3G and 2G networks

Mobile operators are fighting to provide the fastest broadband Internet throughout the country.

The greater the number of Internet users and the faster the operator wants to offer the Internet, the more radio bandwidth it needs. This is where the laws of physics work.

A few years ago, network owners began to transform the bands dedicated to 3G networks (2100 MHz band) and 2G (800 MHz and 900 MHz bands) to the needs of 4G networks.

See how they present their plans:

2019 4%
2024 4%
2025 7%
No plans57%49%
Shutdown of individual networks – operator predictions – survey (Source: Wholesale Roaming 2020. ROCCO Research)

As you can see, in the next 5 years, half of the 2G / 3G networks may cease to exist.

At first glance, one might say, the matter is not. In practice, however, it is.

As an example, I can give the case of Poland’s closest neighbor, the Czech operator, which announced the shutdown of 3G networks in 2021. 

So how to provide voice roaming services in such a country? So, is only a 2G network with poor quality left?

Or maybe this means that in 5 years, foreign roaming voice services will be offered only through OTT applications? This will tell the time, but exactly where is the risk for mobile operators I mentioned at the beginning.

So, in whose hands is the future of voice roaming?

As you can see, almost to the naked eye, the innovation leader in the world of mobile technologies are no longer operators, but providers of OTT services and applications.

A dozen years ago, there were only mobile and cable operators. Today there are also OTT service providers. A new competition has arisen, and it is a much more modern competition.

Operators are drowning, literally drowning in a sea of ​​problems resulting from overly complex standards that they created for themselves many years ago.

The operators, however, do not give up and are increasing their efforts to build the VoLTE roaming base, despite so many difficulties.

In 3-4 years, most operators should have finished products in their package.

These are the operators’ plans to implement VoLTE Roaming:

YearVoLTE roaming launch planned
(Source: Wholesale Roaming 2020. ROCCO Research)

This statistic looks bad, and in my opinion not very realistic.

Soon 5G networks will appear, and as part of the new generation, voice calls will be supported by a new standard called VoNR (Voice over New Radio). The new complication isn’t it?

Is the situation that dramatic? Yes, but only for operators, not for customers.

The 2G and 3G networks are not going to disappear immediately, so there are customer alternatives.

However, where there will be no 2G and 3G networks, you can make use of voice connections via Wifi – VoWifi. But, this requires the coverage of any Wifi, and it is known that there is no Wifi everywhere.

I am afraid that the situation will not improve for operators, even if they implement a full VoLTE Roaming network.

Until then, customers can largely switch to free OTT calls, and this would mean the loss of a large part of the market for foreign and roaming calls by operators.

The customer will be satisfied, and the operator will not be completely satisfied.

Hope is dying last, so I hope that:

First of all, I hope I have explained to you the difficult situation with VoLTE services and roaming.

I hope even more that operators will understand what a big mistake they made in failing to implement VoLTE services early. There is a chance to fix it, let alone prevent similar errors when implementing VoNR.

My last hope is that lessons will be learned from the creation of the VoLTE roaming “standard monster”. Perhaps the complicated 3GPP standards for 5G and 6G technologies will be simplified.

And I wish you the best quality voice calls and the lowest fees possible.

We see you and hear you in the next post.

If you have any ideas about what to write about next time, please share your ideas and needs in the comments or in an email to me.

Take care.

1 thought on “VoLTE roaming. Things That Make You Love And Hate.”

  1. Pingback: Does your mobile phone support 5G? •

Comments are closed.