b. CAP-AKA' Authentication 6c. HSGW caches Subscriber Profile default APN, NAI etc. 7. Establish PDN Connection(s) 7. Interactions among HSGW, P-GW, PCRF and HSS/AAA 8. Establish Flows (TFT QoS) 8. Interactions between HSGW and PCRF this point, all HRPD context and IP context has been established. If changes are necessry in these contexts e.g., due to mobility events then steps 9-10 may be executed to perform context updates. 9. HRDP Session Maintenance 10. IP context maintenance 11. Gateway Control Request/Ack (QoS Policy Rules-S7a) Figure 11.9 E-UTRAN to eHRPD handover. Reproduced with permission from C 2009 3GPP2 [10] X1: The X1 interface carries HRPD signaling information between the MS/AT and the HRPD Signal Forwarding Function (SFF). X2: The X2 interface carries control information via a layer 3 tunnel between the WiMAX SFF and the MS/AT. X3: The X3 interface carries IP traffic between the PDSN and the LMA/HA. It uses PMIPv6 for IP traffic between the PDSN and the LMA. 11.8 Key Interoperability Challenges The integration of 3GPP, 3GPP2, and IEEE related accesses into a common architecture that can offer inter-operability among them is a daunting challenge. Such integration will require addressing all the challenges that will surface when such technologies are allowed to interoperate. The key interoperability challenges are related to procedural differences in security and authentication, mapping of QoS classes, minimizing handover latency, having a suitable backhaul that can provide required throughput and bandwidth and having devices that have similar attributes for different radio access networks that it allowed to acquire services. These challenges are briefly described in this section. E2E Network Architecture and Mobility Management WiMAX 802.16 Air Interface WiMAX MS/AT IP Network Air Interface HRPD RAN AN AAA A15, A16, A17, A19 HRPD ANPCF HRPD AN Figure 11.10 WiMAX-HRPD IOS architecture reference model (single transmitter MS/AT). Reproduced with permission from C 2009 3GPP2 [12] IP Services WiMAX ASN