Challenges in interoperability and roaming between LTE - Legacy core for mobility management, routing, real time charging

One of the significant criteria for the acceptability and reach of the LTE worldwide will be based on its ability to seamlessly interoperate in the 2G/3G networks. Interoperability in this case, implies that subscribers from one or the other network should be able to seamlessly roam for voice, SMS and data. This will entail in actuating mobility and location management across the two network domains, render all categories of data and services, and to ensure the Real Time Charging. The mode of operation for voice, SMS and Data is philosophically different in LTE. So it is not only a question of bridging two core network protocols for LTE and legacy. The main challenge is also to synchronise the two different operation models, adopted by LTE and Legacy. In LTE, we have Home routing and Local breakout. The voice and SMS interworking principle implemented by LTE is chalk and cheese compared to 2G/3G. The charging and billing processes have disparities. This paper attempts to address the key challenges and identify the solutions for actuating Interoperability across the LTE and the traditional (2G/3G) Networks during roaming.