Preparing for sunset: the role of interworking in supporting roaming

On 06-07-2022
Reading time : 5 minutes

2G and 3G sunsets are underway, with many carriers worldwide shutting down 2G and 3G connectivity to make spectrum room for 4G and 5G. And while that will benefit users of high-bandwidth applications, there is a significant roaming issue to address. Could interworking solutions help?

2G and 3G networks are being decommissioned worldwide, and their spectrum reallocated to more in-demand 4G and 5G connectivity. It’s been coming for some time, with AT&T the first major operator to announce the shutting down of its 2G network back in early 2017, and as of today, most other operators around the world have plans to decommission their 3G networks by end 2025.

But while this is simply something that has to happen, end-users of these operators’ roaming partners that have not implemented VoLTE services can no longer enjoy roaming, either voice or mobile data. According to the GSMA, LTE has been launched by over 750 operators worldwide, and serves more than 90% of the global population, giving end-users the higher data speeds they demand. However, at the same time, there hasn’t been quite the same rate of adoption in VoLTE: just 30% of LTE operators have launched VoLTE services. Further, and perhaps more concerningly, only a few dozen operators offer VoLTE roaming.

What it means in mobile roaming reality

There are typically two types of device in use: voice-centric devices and data-centric devices. Voice-centric devices are always looking for networks that offer voice services, namely Circuit Switch and/or VoLTE networks. If a network cannot provide voice service, the device won’t register with it and will seek out a new network that offers voice service. And for context, all smartphones are voice-centric devices. Data-centric devices, however, such as smartwatches or tablets that aren’t typically used for voice, are just looking for networks that support mobile data connectivity, so no check for voice service is carried out during the registration process.


The result of this is that any roaming end-user who is a customer of an operator that hasn’t yet deployed an IP Multimedia Subsystem (IMS) core and VoLTE will not benefit from roaming, either voice or data, with roaming partners who have already undergone a full 2G/3G sunset. In practice, for operators who are decommissioning their 2G and 3G networks, this can mean a loss of roaming revenues as roamers will won’t be able to use their services anymore.

What could networks offer roamers?

The simplest way of managing this is for the visited network to keep its MME function active and switch off its 2G/3G radio. This means that roamers can get onto the network with limitations: they can only access data and SMS, but voice will not be available. It’s relatively easy to implement since it requires only the visited network to be involved in the equation. However, it does have the drawback of forcing roamers to turn to OTT services if they want to make voice calls, which goes against telcos’ typical strategies.

Interworking solutions: a viable way forward?

Deploying an IMS core in the network is an expensive, complex, and time-consuming exercise for operators. And even with one, launching VoLTE and - more significantly, VoLTE roaming - is far from straightforward. Introducing VoLTE roaming requires a huge amount of testing before being launched successfully. As mentioned, only around one-third of operators that have launched LTE services offer VoLTE too: and of those operators, just 7% offer VoLTE roaming with it.

 However, at the same time, operators who have made good progress towards 5G standalone deployment and plan to switch off their 2G/3G services risk losing significant roaming revenues.

To try and bridge this gap, some providers have launched interworking solutions. These are platforms that enable operators who are in the process of shutting down their legacy networks to keep serving inbound roamers with VoLTE- enabled devices from roaming partners who have not yet launched VoLTE on their networks. This is done by giving them continued use of circuit-switch fallback to connect to voice and mobile data services.

Interworking does offer a potential solution, but it comes with limitations. 

1.    4G roaming agreement in place: the visited network operator must have a 4G roaming agreement with the home operator. An interworking solution doesn’t remove that need which is a prerequisite.

2.    Not every device will be compatible: the home operator must provide roaming customers with devices that are VoLTE roaming-enabled. Furthermore, not every device is workable with interworking: for example, there are interworking offers today that only support iOS 15 or later on iPhones. So owners of older handsets can risk being excluded from roaming under interworking, which obviously impacts countries where most smartphones are low-cost models.

3.    Not a plug-and-play rollout: As with any new roaming agreement, the interworking partner’s IR21 roaming database must be loaded up to the home network. At the same time, an extensive testing period is necessary, in which both SIM cards and devices are tested – and the devices must be those that have been selected by the home network to provide VoLTE roaming in the visited network. All services need to be tested at this time, including voice, SMS, data and, if required to ensure consistency of billing across the solution, Customised Applications for Mobile network Enhanced Logic (CAMEL). 

Orange Wholesale International roaming experts have estimated that launching interworking successfully requires a minimum testing period of 30 days per roaming partner. 

Maintaining roaming revenues moving forward

Putting an IMS into the network is no small undertaking, and as things stand today, most operators have not gone down that road. So, the most advanced operators who are already going through 2G/3G sunsets run the risk of losing business from their less advanced roaming-in partners.

As mentioned, deploying an interworking solution means evaluating the number of likely users that will want to roam using interworking in a given marketplace, whether their devices are compatible, and an understanding that you don’t “just” roll out an interworking solution. It is an intricate exercise that takes time and effort. In terms of complexity, it is in the same neighbourhood as putting a completely new roaming agreement in place.

Ultimately, despite its limitations and some less than practical implementation challenges, an interworking solution can help visited operators maintain roaming-in revenues while moving forward with innovation and 5G standalone.

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