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DYNAMIC NEIGHBOUR TRUST INFORMATION RETRIEVAL FOR GLOBAL ROAMING<br />

Figure 4.1 illustrates a multi-operator environment, <strong>in</strong> which multiple <strong>heterogeneous</strong><br />

networks belong<strong>in</strong>g to different network operators are <strong>in</strong>terconnected through an AAA<br />

broker network. The AAA broker network is responsible for <strong>in</strong>termediat<strong>in</strong>g<br />

Authentication, Authorisation and Account<strong>in</strong>g (AAA) messages [53]. Current research<br />

has mostly focused on quick establishment of implicit TR so as to reduce handover<br />

delay us<strong>in</strong>g a variety of fast authentication <strong>mechanisms</strong> [69-71]. All these solutions are<br />

based on the assumption that an explicit TR between a mobile’s home network and its<br />

selected network already exists, and does not need verification dur<strong>in</strong>g a handover. This<br />

assumption is reasonable only when a small number of network operators are available<br />

for network selection, and their trust relationships <strong>in</strong>formation can be easily made<br />

available to a mobile user. The mobile user can hold a network identifier list to assist it<br />

with network selection, as def<strong>in</strong>ed by 3GPP’s specification on system <strong>in</strong>terwork<strong>in</strong>g [72].<br />

However, such a solution lacks the scalability of support<strong>in</strong>g a large number of operators,<br />

and the flexibility of react<strong>in</strong>g to changes to network trust relationships. The current<br />

multi-operator support is largely provided as an add-on rather than an <strong>in</strong>tegral part of<br />

roam<strong>in</strong>g solution to be effective. As a result, a mobile user’s unawareness of the second<br />

explicit TR may lead to unnecessary handover attempts and affect handover<br />

performance <strong>in</strong> a multi-operator environment [73]. A mobile user requires additional<br />

network trust <strong>in</strong>formation <strong>in</strong> a handover to support global roam<strong>in</strong>g.<br />

In this chapter, a dynamic trust <strong>in</strong>formation retrieval scheme is proposed that overcomes<br />

the above mentioned problem. The proposed scheme called Dynamic Neighbour Trust<br />

Information Retrieval can provide a mobile user with ample network trust <strong>in</strong>formation<br />

about surround<strong>in</strong>g Po<strong>in</strong>ts of Attachment (POA).<br />

4.2 Network Trust Correlation<br />

The basic idea beh<strong>in</strong>d the proposed scheme is as follows. The network trust relation<br />

between two networks can be validated when a mobile subscriber of a network<br />

successfully handover to another network. In a handover, the AAA server on the<br />

mobile’s home network communicates with both the old POA (oPOA) and the new<br />

POA (nPOA) for AAA related services. The home AAA server can thus be used as an<br />

<strong>in</strong>termediate for exchang<strong>in</strong>g <strong>in</strong>formation. Tak<strong>in</strong>g advantage of the home AAA server,<br />

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