PD BTS HRPD Air Interface Figure 11.8 E-UTRAN-eHRPD interworking architecture (roaming). Reproduced with permission from C 2009 3GPP2 [10] the UE and then it makes a handover decision. The UE later acquires the eHRPD radio and finally E-UTRAN releases its resource. The details of eHRPD to E-UTRAN handoffs can be found in [8, 10]. 11.7 WiMAX and EV-DO Interworking The WiMAX-HRPD interworking for a single transmitter terminal is based on the Layer 3 (L3) approach (IP level traffic). In this approach, the MS/AT establishes an IP connection with the target network using the source network as a bearer to carry native signaling messages of the target network encapsulated in an IP packet tunneled between the MS/AT and the target network. For example, in a handoff from WiMAX to HRPD, the MS/AT establishes an IP connection with the HRPD network over the WiMAX access networks via the HRPD SFF (Signal Forwarding Function). The HRPD SFF provides a connection between the MS/AT (HRPD mode) and the HRPD AN/PCF. The HRPD SFF is the termination point of secured tunnel between MS/AT and the HRPD SFF. The WiMAX-HRPD interworking architecture is shown in Figure 11.10. A common IP core is used for the WiMAX-HRPD interworking. The PCRF, Local Mobility An- chor/Home Agent (LMA/HA), and AAA support both the WiMAX system and the HRPD system. Figures 11.11 and 11.12 show the high level interworking architecture mechanisms from WiMAX to HRPD and vice versa respectively [13]. The interfaces in these architectures are as follows: Ty: The Ty interface carries policy, charging, and control information between the PDSN and the PCRF. Next Generation Mobile Communications Ecosystem Roaming eANePCF 3GPP2 vPCRF hPCRF Proxy 1. Attached to E-UTRAN(UE has acquired IPv4 address or IPv6 prefix) 2. Decision to pre- register with 3. HRPD Session Establishment 4. Device PPP LCP Negotiation Authentication (A12) selects EAP for authentication. 5. PPP Establishment and Main A10 Connection Setup 6a. PPP CAP-AKA' Authentication 6b. PPP CAP-AKA' Authentication 6