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Mobility architecture in a future IP network

Fast hand-over prototype: A significant result of the project was the implementation of fast handover in the mobility and integrated prototypes towards seamless mobility. Using just MIPv6, there is quite some delay when the access point (access router) is changed, in the range of up to 10 seconds. This could be significantly reduced using Fast Handover, which uses the make-before-break approach compared to break-before-make of plain MIPv6.

Before fast handover was implemented, Fast Handover was compared to using just Mobile IPv6, and it could be shown that it we could expect significant improvements. The following ns-2 simulations done in the project demonstrates the gains we get via Fast Handover regarding latency.

Further simulations showed that data loss could also almost be eliminated using Fast Handover. These simulation results led to Moby Dick using this technology for seamless handovers.

The prototype confirmed our expectations regarding seamlessness. In addition, it turned out that Fast Handover could nicely be integrated with AAA and QoS to carry context data (user identity, QoS) from the old Access Router to the new Access Router, thus supporting context transfer. Though not yet officially taken up, such results have been discussed at IETF in the Seamoby group, and it such combinations will hopefully be taken up in future.

The results here have resulted in a major step of our understanding: We may use Fast Handover to achieve the kind of functions in a pure IP-based environments regarding AAA and QoS that we so far only had in traditional circuit-switched networks.

Driver and Wireless-LAN-cards: They are not optimised for fast hand-over. Future wireless networks will need to use the wireless LAN (802.11b) infrastructure mode to provide the kind of services that Moby Dick has prototyped. However, the available wireless LAN cards do not allow fast discovery (in infrastructure mode) of new access points while connected. In addition, the layer-2 latency was too high. For these reasons, the ad-hoc mode was chosen for the purposes of the project. The WLAN Linux driver was modified and enhanced to simulate the infrastructure mode. This solution allows the mobile terminal to receive and send data via the access point and, in the meanwhile, to process beacons advertised by other access points. The decision for handovers is based on the signal strength of the received router advertisement. It was the common understanding in the project, that the ad hoc mode is a temporary solution, and that future solutions would use the infrastructure mode provided the issues mentioned above, such as layer-2 latency, as solved by the WLAN card manufacturers. It is expected that upcoming solutions, such as offered by Moby Dick, will motivate WLAN vendors to tackle these problems, which may not be relevant for the current uses of the cards. The solution could lie both in generally improving the functionality and performance of the cards, or by providing specialised WLAN cards for such purposes.

MTNM: The MTNM is a prototype of what could be implemented in future multimode terminals (phones or PDAs). It handles user preferences and interactions as well as control access technologies, including handover management. It is also used to synchronise other functionalities on the terminal.

The user interface part, the NCP, provides a set of information elements and interactions that should be implemented in a "ready to market" device. It becomes possible for the user to register on the network and to define preferences in terms of Access Technology to use and handover management strategy. It also provides feedback on the networking conditions (signal levels for instance) and on the ability to trigger a handover manually if the user wants to choose the network to use.

The MTNM itself is a prototype of the kind of middleware that could be embedded in a commercial terminal. It controls the network drivers for each access technology, implements a handover algorithm to take decisions on when to perform the handover (based on access technology conditions, but also on user preferences, and Quality of Service feedbacks). It interacts with all other entities on the mobile terminal (AAA registration software, paging software, in the case of Moby Dick) to synchronise all of them.
More information on the Moby Dick project can be found at:

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