S8HR – Faster Path to VoLTE Roaming, but not Without Challenges

With 46 operators having commercially launched VoLTE-HD voice services in 29 countries and more than 117 operators investing in VoLTE*, VoLTE roaming has become a major focus of mobile operators’ attention. Many are involved in discussions about Local Breakout (LBO) and S8 Home Routed (S8HR) roaming models that are ongoing within the GSMA and 3GPP standards and specifications communities.

S8HR, which uses the LTE S8 interface for transporting VoLTE traffic between the visited and home network as data traffic, has recently gained momentum. The main reason is that S8HR implementation is simpler to implement than LBO, resulting in faster time to market for global VoLTE roaming deployment. Unlike LBO, S8HR does not require IMS in the visited LTE network and therefore IMS interoperability testing is not required between the home network and each visited network. This significantly simplifies implementation. Although the GSMA continues to identify LBO as the default roaming model, many mobile operators eager to bring VoLTE roaming to market quickly are considering adopting S8HR first.

While S8HR does simplify VoLTE roaming implementation, it also presents many challenges resulting from several technical gaps that have been identified by the GSMA. For example, not all services normally provided by the visited network can continue to be provided with S8HR. As previously mentioned, the visited network in S8HR does not use IMS, therefore, the visited network is not service aware. As a result, it cannot support Lawful Interception and non-authenticated user emergency calling for visiting end users. In many countries Lawful Interception and emergency calling for visiting end users are required by local regulators.

Another challenge is end user experience in situations of 4G handover to legacy 2G/3G, enabled by SRVCC/eSRVCC. Because all visiting end user calls in S8HR go back to the home network for routing, the SRVCC/eSRVCC signaling to initiate the handover also goes back to the home network. This can result in significant handover delay and “dead air” time for the end user.

The technical gaps of S8HR, identified by the GSMA, are detailed in the GSMA’s S8 Home Routed VoLTE Roaming Technical Report, dated April 2015. These gaps, plus other technical and commercial gaps, are summarized in the tables at the end of this article.

As part of our standard VoLTE roaming offerings, iBasis supports both the S8HR and LBO roaming models. In addition to standard VoLTE offerings, iBasis has enhanced solutions that address challenges in both roaming and interworking. The GSMA is working on solutions to overcome the S8HR challenges they have identified. However, this effort could take a year or more. iBasis offers solutions today that allow mobile operators to address the challenges sooner rather than later. At iBasis, we understand the importance of time to market. Therefore, our goal is to provide solutions that enable mobile operators to quickly and confidently deploy S8HR and assist them on their path to global VoLTE roaming.



* Global mobile Supplier Association (GSA), January 25, 2016

** Not identified by GSMA in S8 Home Routed VoLTE Roaming Technical Report.

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