Handover mechanisms in next generation heterogeneous wireless ...

HANDOVER MANAGEMENT
proposed architecture incorporates a WLAN network by routing the AAA signalling
to/from a 3G AAA proxy residing in the associated visited 3G PLMN. A WLAN AAA
proxy with the WLAN acts as the “connector” between WLAN and 3G PLMN. 3GPP
endorses the loose coupling idea in its specification TS 23.234 for interworking [7].
Chen et al. presented a practical loose coupling architecture for the integration of GPRS
and WLAN systems, which has been put into commercial operation [20]. By placing a
logical gateway on the conjunctional point of GPRS and WLAN, the proposed
architecture can keep mobility management functions in GPRS and WLAN as they are.
The research on the integration architecture [4, 5, 20] argues that the loose coupling will
be deployed earlier than the tight coupling due to the architecture complexity in the tight
coupling.
The peer network architecture allows control signalling for interworking to pass through
the public Internet instead of using a dedicated link via a PDG at UMTS network. The
WLAN can be operated by a different operator and function independently by
incorporating its own AAA services. The WLAN ESSs terminate on a gateway at the
WLAN as in the aforementioned architectures. The gateway handles a mobile user’s
roaming to other peer networks. For example, a UMTS subscriber switches to a peered
WLAN network as illustrated in Figure 2.3. The mobility of a mobile user within
individual network infrastructure is handled by its local mobility protocols. In the peer
network architecture, mobility protocols like Mobile IP [21] plays a key role in
supporting a mobile user’s mobility across heterogeneous wireless networks. This is
because an access-technology-independent mobility protocol would decouple the
integrated heterogeneous networks in their functionalities, and thus allow each network
to function on their own. An AAA server residing in the WLAN manages its own
subscribers and communicates with other AAA servers in peer networks for roaming
related operations. Rather than having a WLAN appear as an attached routing area to
the UMTS, the peer network architecture maximises the autonomy of each type of
network. Shi et al. described an IEEE 802.11 and cellular network integrated
architecture from the perspective of roaming and authentication in [22]. The AAA
structure introduced in [22] was proposed to make IEEE 802.11 architecture and
signalling processes work with cellular networks. Reference [8] described an IP-based
interconnection solution that works on a global IP infrastructure like the Internet.
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