Handover mechanisms in next generation heterogeneous wireless ...

MULTI-INTERFACE MOBILE MODEL FOR MEDIA INDEPENDENT HANDOVER
With the MIAU, data traffic can not be recovered until the switching of network
interfaces has been completed in a handover. In this section, a multi-interface mobile
terminal model based on the MIAU is presented. The proposed model can retain the
MIAU’s support for ordinary upper layer protocols, and enable fast handover, which is
not achieved in the traditional MIAU solutions.
With the MIAU, the proposed multi-interface model can maximise its compatibility
with upper layer protocols such as Mobile IP and TCP. Meanwhile, the support on the
latest IEEE 802.21 framework [118] provides extensibility. MIH functional services are
utilised for internal communications among the system modules at a mobile terminal. In
the proposed model, IEEE 802.21 is utilised in such a way that a mobile terminal can
cooperate with both non-MIH networks infrastructure and MIH enabled networks in
future. To tackle handover delay problem of the MIAU, the cross-layer design is
introduced into the model to shorten the gap between adjacent layers.
The proposed generic multi-interface architecture is shown in Figure 7.2. An
intermediate component, named as Handover Management Module (HMM) is proposed
between upper layers and lower layers. Acting as a logical layer to isolate the
heterogeneities of physical network media from applications, the HMM is responsible
for handover related processing. The HMM is composed of four subsystem modules:
Policy Manager (PM), Handover Decision Trigger (HDT), Network Selector (NS) and
POA Candidate Cache (PCC). Four subsystem modules work together to gathers
versatile information from heterogeneous network interfaces and make handover
decision. The internal communications can be based on the MIH services or any userdefined
services.
The HDT is included in the HMM to receive the cross-layer trigger commands from the
NS, and prompt the corresponding processing at Mobile IP [21]. In this thesis, crosslayer
trigger is referred to as the process of informing Mobile IP of changes to link
status at lower layers. Handover policies are managed by the PM, and executed by the
NS, in which various handover decision algorithms can be implemented. The
communications between the HMM and lower layers are relayed by the PCC. The PCC
helps to mitigate the heterogeneity of lower layer network stack, and ensure that lower
layer metric information conforms to the common rules for processing at the HMM.
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