Is your service provider ready for LTE roaming?

The issue of long term evolution (LTE) 4G roaming is back in the news as the new Apple iPhone 5 supports LTE and the Apple legions will join the global evolution to 4G, all-IP networks—well, sort of. The iPhone voice is still TDM, unless it’s FaceTime and then it is over the top (OTT) voice over IP (VoIP) and video.

Many stories have focused on the LTE spectrum bands, looking at what service providers will be able to support to the iPhone 5 on their network. Bands also affects where the iPhone or any LTE phone can roam. Spectrum bands are one issue that service providers need to consider, but are there are also network concerns as well—namely enable a signaling network that facilitates data and voice roaming. Last week I wrote about how IPX and roaming hubs have been preparing to enable global LTE roaming. Today I want to expand on the challenges that I briefly touched on in that post.

All aspects of roaming—attachment to the visited network and use of data or voice services—generate Diameter signaling. This IP signaling protocol, like its relative, SIP, has challenges as Internet Protocol itself lacks the security, congestion management, and quality controls of the predecessor TDM networks, and SS7.

For roaming, there are two basic Diameter interfaces: 1) S6a for authentication between the visited MME and the home HSS database and 2) S9 which carries charging and quality of service (QoS) profiles between the visited and home policy servers. This is a considerably shorter list than the Diameter interfaces used in LTE in general, but they still face the same set of challenges, including:

• Connection management – connecting the numerous network elements in visited and home networks directly is not feasible due to the number of elements that would need route provisioning. Managing hundreds of elements across hundreds of partners is an operational nightmare.
   
• Security – direct connection and network topology exposure also creates security threats including malicious attacks and result in network downtime. Confidentiality of Diameter signaling passed between operators is also a concern for some.
   
• Overload – the servers involved in processing authentication, QoS or charging are not equipped to deal with spikes in volume; this can impact availability of services should those elements be taken out of service.
   
• Multi-vendor interoperability – while Diameter is a standard, there are numerous interpretations of that standard as IMS and LTE has evolved and as more vendors enter the market. There are also differences in networks, such as transport protocol, IP versions or address spaces, that can cause incompatibility and transaction failures. Service providers do not have control over the vendor selections in the networks to which they connect, so multi-vendor environments present interoperability problems that add extra time or costs to an initial deployment and ongoing operations. The lack of interoperability hinders flexibility, service reach, and time to market.
   
• Lack of visibility – with signaling generated and received across multiple nodes in a network, the ability to collect and correlate all messages across the number of elements and vendors is formidable; the information from these messages is critical for network planning, troubleshooting and settlement between mobile operators as well as roaming hubs.

And so the GSMA has defined a network element that alleviates these challenges: the Diameter Edge Agent (DEA). These application-specific Diameter signaling controllers, manage and secure the border between visited and home service providers. They also enable wholesale IPX carriers and roaming hubs to enable multilateral LTE roaming services. In my next post, I’ll explore the key functions that make a DEA essential to LTE roaming.

I’ve dwelt on Diameter here as it underpins all services when roaming. However, when voice over LTE (VoLTE) is added to the service mix, it raises a related set of concerns in regards to SIP. Those are ones more familiar given the VoIP evolution of the last 10­-15 years and are well-guarded against with session border controllers.

But bringing the focus back to what spurred this post, the reality is that the broader industry isn’t ready yet for LTE roaming; with your iPhone 5, Samsung, HTC or other LTE phone, you’ll likely be roaming on GSM for voice and 3G for data for the near term. However, the ecosystem is gearing up. The roaming hubs are investing in the relevant Diameter signaling infrastructure to offering trials and services ahead of the demand. Likewise, mobile service providers in the midst of building out their LTE footprint, Evolved Packet Core and IMS networks are also looking at their needs at that roaming edge.

Read the next blog post in this series: Diameter Edge Agent Essentials for LTE Roaming

Kevin Mitchell leads service provider product and solution marketing at Acme Packet, focusing on IMS service delivery, next generation signaling core and interconnect and roaming. He directs marketing strategy, and sales support for Acme Packet's solutions encompassing VoLTE, RCS, SIP trunking, fixed mobile convergence, VoIP services, SIP interconnect and LTE roaming.