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Handover mechanisms in next generation heterogeneous wireless ...

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PROXY BASED AUTHENTICATION LOCALISATION SCHEME FOR HANDOVER<br />

Figure 6.2 Classification of fast authentication approaches<br />

The IAPP protocol [96] def<strong>in</strong>es a standard method to transfer context <strong>in</strong>formation<br />

between two 802.11 APs when an <strong>in</strong>tra-doma<strong>in</strong> handover takes place. It relies on secure<br />

communications between two APs at layer 2, which have to be under the control of the<br />

same Extended Service Set (ESS) [96]. To support handover between different ESSs,<br />

Bargh et al. proposed <strong>in</strong> [98] that IAPP messages can be encapsulated us<strong>in</strong>g the CTP<br />

protocol [97]. The IAPP-CTP comb<strong>in</strong>ed approach [98] requires secure communications<br />

between Access Routers (AR) at L3. Sethom et al. proposed a distributed architecture<br />

with a Location Server (LS) for key derivation [70]. The proposed architecture supports<br />

pre-authentication to be performed through the serv<strong>in</strong>g AR after a mobile user has<br />

determ<strong>in</strong>ed its <strong>next</strong> po<strong>in</strong>t of attachment. In all these solutions, handover authentication<br />

is usually triggered <strong>in</strong> a reactive manner as shown <strong>in</strong> Figure 6.2, which means context<br />

transfer for fast authentication is made after <strong>in</strong>itiat<strong>in</strong>g a handover.<br />

The <strong>in</strong>direct pre-authentication can be performed <strong>in</strong> a proactive manner as shown <strong>in</strong><br />

Figure 6.2. In the proactive authentication approach, fast authentication is achieved by<br />

pre-distribut<strong>in</strong>g the key<strong>in</strong>g materials to the target network prior to conduct<strong>in</strong>g a<br />

handover to it. In [69], Mishra et al. def<strong>in</strong>ed a new data structure – Neighbour Graph,<br />

which can dynamically identify and ma<strong>in</strong>ta<strong>in</strong> the mobility topology of a network. The<br />

home AAA server learns the association pattern of a mobile user by observ<strong>in</strong>g its<br />

neighbour graph, and thus determ<strong>in</strong>es the candidate set of APs. Before the mobile user<br />

moves to <strong>next</strong> AP, the home AAA server generates Pairwise Master Keys (PMK), and<br />

pre-distributes the keys to the candidate APs. When any one of the candidate APs<br />

receives an authentication request for handover from the mobile user, the identity<br />

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