Mobilitätsunterstützung mit programmierbaren Netzen

Besides conventional cellular mobile radio networks like, e.g., GSM, with voice communication being the main application, other technologies primarily used for local Internet access – especially Wireless LAN – are gaining momentum. However, while mobility is an inherent feature of cellular radio networks, it is not well supported by the various wireless extensions of local area networks yet. For IP-based communications, the IETF has created Mobile IP, a standard supporting both aspects of mobility, roaming and handovers. However, besides pure datagram delivery, mobile subscribers need advanced network services which should be provided in a flexible way in order to enable efficient communication. In a roaming scenario, there are two major challenges. On the one hand, subscribers are not being offered the identical set of services everywhere. Thus, some services may not be available after performing a handover to a foreign access network. On the other hand, the subscriber may only use those functions for enhancing the handover performance, which are being provided by both of the operators, the previous as well as the new one. Both of these challenges may be solved by employing the technology of Programmable Networks, whose core aim lies in enabling the subscriber to establish services within the network by himself. In mobile environments, these dynamically loaded services may provide, e. g., particular functions adapted for optimized datagram delivery or functions for mobility support specifically matching the subscribers’ characteristics. In this thesis, a novel architecture for transparent mobile programmable network services is described, that addresses especially the aspects of continously providing such services to mobile subscribers. The essential functions targeting the latter (mobility detection, control and routing) are separated from the general service management as self-contained processes in order to allow for utmost flexibility regarding their extensibility or exchangeability, respectively, as well as their lieu of execution. Together, these three mobility-related functions control all aspects of the underlying services’ mobility as well as – in close cooperation with Mobile IP, if applicable – the delivery of datagrams to the mobile subscriber, differentiated by the applications’ data flows. An additional degree of freedom for controlling the subscribers’ mobility, especially in case of handovers, arises from the flexibility introduced. Following a handover, a network service may either be transferred to the new point of attachment. Alternatively, a transient tunneling of the respective data flows may be initiated. The mobility control selects the most appropriate of these methods by estimating the expectancy of the accumulated effort associated with each of the two. The respective algorithm proposed herein is evaluated using an abstracted analytical examination of the subscribers’ handover behavior. For that purpose, the modeling used hitherto for cellular mobile radio networks is extended to encompass the effect of handover hysteresis that appears inevitably with Wireless LANs channel selection strategy. The core aspects of an exemplary transparent mobile programmable network service have been evaluated successfully in a prototype implementation, proving the viability of the approach at the same time. The results are complemented by means of simulation.