Enabling Roaming in Heterogeneous Multi-Operator Wireless Networks

In a future, existing wireless access technologies such as WiFi (Wireless Fidelity), WiMAX (Worldwide Interoperability for Microwave Access) and UMTS (Universal Mobile Telecommunication System) will coexist on daily basis. Nevertheless, this daily coexistence does not imply that they will be able to fully interoperate. We considered that in a future, the roaming landscape will be characterized by different access networks managed by different entities, such as cellular network operators, ISPs (Internet Service Providers), and independent organizations or individuals. Thus, our research work focuses on a specific roaming scenario which is formed by heterogeneous wireless access networks managed by different operators. Our main objective is to provide a seamless (for the mobile user) roaming architecture to enable network interoperability under a heterogeneous multi-operator wireless environment, all this without major changes in current wireless architectures. The SIP-based roaming architecture aims at the creation of a suitable environment for the support of seamless service mobility in heterogeneous multioperator wireless networks, this without major changes in current wireless network architectures. To achieve this, we rely on an element called the Roaming Broker. The goal of this entity is to establishmutual trust between the cellular and the Unlicensed Wireless Networks. As trust can be built by different means, for our research we consider that mutual trust between the cellular network and the Roaming Broker is endorsed by contractual agreements. On the other hand, trust between the Roaming Broker and the independent wireless networks is endorsed by SLA (Service Level Agreements) and efficient access control mechanisms. Furthermore, we assume that roaming between heterogeneous wireless networks, follows economic rather than technical reasons. Consequently, heterogeneous roaming must be allowed only if the Visiting Networks respects the accorded Service Level Agreements. The SIP-based RoamingArchitecture enables roaming in heterogeneousmultioperator wireless environments. In this architecture, the HN is always the roaming decision maker as it is determines, based on the mobile user’s and VN’s credentials, whether or not the mobile user can roam in to the VNs. That is mobile user authentication and authorization are always performed by the HN and from the HN. Furthermore, as VNs are not allowed to communicate directly with the HN, all these roaming signaling messages must pass through the RB. Thus, as confirmed by the simulation results, this process clearly contributes with an increment in the overall delay of the network registration and session initiation process. In this regard, we aim at reducing the roaming signaling exchange caused by the authentication and authorizationmechanisms in the network registration and session initiation process while providing robust network security. To achieve this, we rely on the use of Public Key Infrastructure and Privilege Management Infrastructure) techniques deployed on top of our architecture. Moreover, for authorization, we propose the use of PMI and XML Attribute Certificates to define the rights and roles of the key elements of our architecture. The results obtained through computer simulation indicated that the use of this approach reduces significantly the network registration and session initiation delay, hence outperforming the traditional Roaming-SIP method. We also confirmed that the wireless delay introduced by the VN increases considerably when increasing the traffic congestion level in the Visiting Networks. Thus, from the simulations results we can state that by reducing the signaling message exchange, and maintaining acceptable congestion levels in the wireless network, hence reducing the wireless transmission delay, we can improved the overall delay in both network registration and session initiaition process.