Jim Machi, Dialogic

Jim Machi, vice president of product management for Dialogic

By Jim Machi, vice president of product management for Dialogic, where he is responsible for driving the overall roadmap and product strategy.

In my last blog, I discussed Wi-Fi roaming and the WRIX. The WRIX, an IPX-like exchange for Wi-Fi roaming, is broken into three levels that cover the various interactions needed between operators to support roaming.

First is the WRIX-i, or interconnect, which specifies the interface between the visited network provider (VNP) and the home service provider (HSP). WRIX-i requires use of RADIUS authentication, authorization and accounting (AAA) procedures and some specific attributes associated with access and accounting services. The WRIX-d is for data clearing and wholesale accounting. Lastly, the WRIX-I is for financial clearing and wholesale billing.

The WRIX specifications provide a high degree of interoperability between Wi-Fi operators, but real-world implementation has some obstacles. For example, it may still require RADIUS-to-RADIUS mediation and the need for interworking functionality with other signaling protocols to correct incompatibilities between operator networks. This is because one implementation of RADIUS may not exactly match another implementation of RADIUS. Plus, in order to accommodate roaming over a diverse set of user devices and network implementations, Wi-Fi and 3rd Generation Partnership Project (3GPP) network architectures will need to provide interworking between different protocols used for AAA, as well as mediate between variations of the same protocol.

To break down the process, a customer with a Wi-Fi device would need to authenticate back to the HSP network. Authentication messages would then be sent over the Wd or SWd interface between the 3GPP network’s AAA proxy and the Wi-Fi operator’s AAA server. For operators on a pre-Release 8 version of 3GPP specifications, it would be the Wd interface, which uses RADIUS; for operators using 3GPP Release 8 or higher, it would use the specifications for the SWd interface, which requires Diameter. There would also need to be interworking with the WRIX-i interface of the Wi-Fi operator so both scenarios can function properly.

On the other hand, if a customer in a 3GPP network wanted to roam and use services from a Wi-Fi operator, the subscriber’s device would use SIM-based authentication methods that would need to proxy through the Wi-Fi operator’s network. Authentication messages would go through the AAA proxy of the VSP over the WRIX-i interface and would require interworking with the Wd or SWd interface of the 3GPP operator.

Interworking is also required, in many cases, in the 3GPP operator’s mobile core. In pre-Release 8 3GPP networks, SS7/MAP is used for connecting the Home AAA server to the home location register (HLR) to authenticate the user. A RADIUS-to-MAP gateway function is needed to interwork the RADIUS-based Home AAA server with the SS7-based HLR. In the case of 4G networks or Release 8 or later 3GPP networks, there would be a home subscriber server (HSS) that would connect to the AAA proxy/server in place of the HLR. The HSS uses Diameter as the enabling protocol, and thus would require an interworking function that would convert the RADIUS to Diameter signaling.

Still not satisfied? In my next blog, I will discuss the need for signaling interworking.Want to keep up with my industry musings? Follow me on Twitter at @JMachiDialogic.

Comments on: "Wi-Fi Offload/Roaming Part 2: Wi-Fi, 3G/4G Roaming and Interworking Architectures" (1)

  1. […] my last blog I discussed the architectures needed to roam between WiFi and 3G/4G networks. In order to enable interoperability between the different architectures, a mediation and […]

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