Handover mechanisms in next generation heterogeneous wireless ...

MULTI-INTERFACE MOBILE MODEL FOR MEDIA INDEPENDENT HANDOVER
upper layers. The HMM Commands to lower layers are used to instruct the switching of
network interfaces. In contrast, the HMM Commands to upper layers indicate the
actions that can be taken at upper layers when the predefined events, e.g. loss of radio
connection, take place at lower layers. The notifications via the HMM can thus enable
cross-layer trigger, which resolves handover delay problem of the MIAU.
7.4 Implementation Issues
According to the proposed generic multi-interface model, a dual-interface mobile
terminal has been implemented in Network Simulation 2 (ns-2) [120]. The
implementation is intended to find out the implementation issues in real systems. In the
dual-interface implementation, a mobile terminal is supposed to be equipped with two
IEEE 802.11 WLAN cards. And a Handover Manager (HOMgr) resides on the mobile
terminal to execute the HMM functions. The architecture of the mobile terminal is
shown in Figure 7.3. ns 2.29 [120] is used as the platform for development. The
following modifications have been made to ns 2.29 for the implementation of the
proposed mobile architecture:
� Support for multiple wireless channels on a mobile terminal;
� Probe embedded in lower layer objects for handover metrics’ gathering;
� Customisation of NO Ad-Hoc Routing Agent (NOAH) [121] for routing
capability in the dual-interface mobile terminal;
� Proactive triggering mechanism added to the mobile IP implementation of ns
2.29;
In ns 2.29, only single network interface is originally supported for a mobile terminal
[122]. For this reason, a number of new components and functions that enable the
controlling and management of multiple interfaces have been developed.
� Handover Manager (HOMgr) with handover decision and policy engine;
� New functions for accommodating additional network interface on a mobile
terminal and interface switching;
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