Network

China and South-East Asian countries are in progress of 3G mobile commercialisation; and some countries have been commencing the deployment of WiMAX. Apparently some mobile operators have shown their interests in WiMAX technology and license. A possible reason is that the operators are trying to avoid more competitive powers generated by these converging technologies. Another reason is that the operators perceive WiMAX technology as an important complement for their 3G/UMTS services. While saving UMTS bandwidth, WiMAX could provide better data access to non-moving mobile customers.

However, when both UMTS and WiMAX technologies are managed by one entity or one affiliated group, a scheme is required to make them complementary. The network would be a complete dual-technology network, with single user identity system, with continuous service for customers who sometimes need to exchange the network, without too many redundancies in system.Assuming that the 3GPP standard implemented for UMTS network has adopted Release 5 (with IMS), an interworking scheme could be arranged on service layer on both network. Traffic negotiation would still utilise SIP as recommended in IMS. User management with AAA would be performed on UMTS infrastructure. The scheme is illustrated below.

The orange lines indicate media flow, and the blue lines for signalling. HSS (home subscriber server) stores user information, including the authorisation and profiles. AAA performs authentication, authorisation, and accounting (charging) functions. A group of CSCFs (call session control functions) on IMS structure manage session information. Signalling between IMS and WiMAX are carried out through I-CSCF (I for interrogator) to CSN of WiMAX. On WiMAX structure, CSN manages the issues of QoS, and the ASN arranges access strategies.

A certain mapping is required between QoS of 3GPP and WiMAX. UMTS has defined four QoS classes: conversational, streaming, interactive, and background. WiMAX has also defined QoS in four classes: UGS (unsolicited grant service), rt-PS (realtime polling service), nrt-PS (non-realtime polling service), and BE (best effort). What left to do is arrange the class mapping for each service and application targeted. Resources for QoS could be provided with pre-configuration, or with client-triggered reservation.

There are indeed many issues to be considered. AAA between two networks is one of them, including for roaming users, which should be considered both as business and security issues. Hand-over issues are also interesting to discuss separately.