VoLTE roaming - from “could do” to “must have”


In our last blog, we looked at the emergence of Voice over LTE; understanding how it has evolved over the last decade to replace circuit switched voice and ending with a look at where the market stands today. Now, we’ll turn our attention more specifically to VoLTE roaming.

It’s worth beginning with a summary of the key points so far (though if you haven’t done so already, we’d suggest reading the full text of our last blog here. Those points are that the introduction of VoLTE around 2012 brought in a new voice service optimised for LTE networks to replace legacy, circuit-switched voice but that take up was initially slow mainly because VoLTE was more complicated to deploy and there was a lack of device clients. The latter is no longer the case and, today, VoLTE is commonplace – The GSA reports that there are now more than 230 live VoLTE networks (LTE Device Ecosystem, August update: GSA, 2022).

In contrast, however, VoLTE roaming remains largely neglected. By and large, CSFB (circuit switched fall back) is still the preferred (and easier to deploy) approach for voice roaming. The trouble is that strategy is now fast becoming unsustainable. With 3G network shutdowns moving at an increased pace around the globe CSFB is coming off the table so tackling VoLTE roaming is unavoidable.

Finally, we ended the last blog by noting that three new parameters to support VoLTE roaming had been defined by the GSMA, with three alternative reference architectures. Two were based on an approach that involves calls being broken out locally:

  • LBO Home Routing (LBO-HR)
  • LBO Visitor Routing (LBO-VR)

The third reference architecture – comfortably the most embedded to date and likely the one that will continue to dominate going forward is an interface between the Serving Gateway (SGW) and the Packet Data Network (PDN) Gateway (PGW) known as S8 Home Routing (S8HR). It’s S8HR on which we’ll thus be focusing from here on.

VoLTE roaming: why the rush?

With the above understanding of the landscape now clear, why (notwithstanding the inevitable 3G network sunset) should operators be embracing VoLTE roaming as a matter of priority? Aside from the standard advantages conferred by VoLTE vs legacy voice (the former delivering better voice quality, faster call set-up, etc.), two immediately stand out:

  • First, S8HR assures an identical user experience when roaming as the experience when the subscriber is on the home network
  • Second, because interworking with the VPMN (Visited Public Mobile Network) is unnecessary in VoLTE roaming, voicemail is more reliable and call forwarding is activated as it would be when the subscriber is at home.

In short, the VoLTE roaming experience can be described as “seamless”.

Advantages accrued

This seamlessness of both coverage and user experience is important, but for operators there are other benefits that accrue from VoLTE roaming. For instance, for new operators (several whom have already or are now launching with 4G only), enabling VoLTE roaming immediately opens their networks to inbound roamers and with many operators now decommissioning their 3G networks, this is likely to have a significant positive impact on building and profiting from partnerships.

Beyond that, advantages of VoLTE roaming across the board also include:

  • Operational efficiencies as fewer network elements are involved for S8 Home Routed VoLTE traffic
  • Roaming agreements for VoLTE are far more straightforward than for legacy voice
  • Bill shock mechanisms not impacted by the switch to VoLTE roaming
  • Reduced complexity in development, deployment, and settlement results in a faster “time to market” solution
  • Familiarity, as the VoLTE roaming architecture model largely mirrors existing roaming for legacy network and LTE data networks

The strategic imperative

The extensive list of advantages should mean implementing VoLTE roaming becomes not only desirable but a strategic imperative. Becoming the destination of choice for inbound roamers yields significant commercial advantages for those who are ready and a major point of differentiation from other operators who are not. With 3G networks in decline, fast movers have an opportunity to capture key ground. There’s also the corollary; the slower you are to launch, the slower to launch you’ll be as testing queues will expand as more and more operators, ultimately out of sheer necessity, eventually make the leap. It’s the early birds who, as we’ve seen, will expand their new roaming partner relationships and establish strong positions in the market.

And then there’s IoT, the ultimate next generation network driver many of whose opportunities even now remain emergent. Already, numerous IoT solutions have voice requirements (eCalling in Automobiles is one example) and the future is likely to hold many more. VoLTE is already being chosen as the solution to future proof many of these deployments which means a lack of VoLTE roaming will result in devices not being able to access an operator’s network when innovative services arrive.

The reality is that, today, VoLTE roaming provides operators with the best global footprint including protection from being impacted by the shrinking availability of circuit switched networks while at the same time giving the enabled operator first-mover advantage, if it moves quickly, in securing its own commercial future.


In short, it’s time to get moving. We know beyond all doubt that the shift from circuit switched legacy networks is on. GSMA Intelligence noted that, while LTE roaming is common, fewer than 50 VoLTE deployments include full VoLTE roaming. That means that more than 180 operators could move to VoLTE roaming in the near future, while hundreds more can anticipate doing so when they have launched VoLTE domestically. So, we can expect a flurry of activity in the coming months and years.

As we’ve seen (above), these operators are missing out on a range of benefits. Don’t expect this status quo to remain in place for long. It won’t. And part of the reason is that VoLTE roaming will have to become widely embedded before legacy CS networks can be decommissioned. The time to act is now.
About Utel

Having defined the landscape and understood the theory, in our next blog, we’ll look more closely at the practice; VoLTE in action and what early deployments can teach us. Utel helps telcos to gain greater control of how their networks are performing, improve service assurance, and benefit from an enhanced ability to deliver the best possible experience to their customers.

Would you like to explore this topic in more depth with our team? Book a meeting with Tommy Lindhagen using the calendar below and we’ll be happy to show you how we can help!