Handover mechanisms in next generation heterogeneous wireless ...

TRUST ASSISTED HANDOVER ALGORITHM FOR RELIABLE HANDOVER
t � � � � � ( h �1)
�t
� t
(Equation 5.8)
NR
n
TAH
AAA
In the roaming AAA architecture, HAAA and FAAA are actually similar entities with
common AAA functions and implementations, but play different roles for a particular
mobile user. They exchange their roles for different roaming users. For this reason, the
same AAA signalling delays between a FAAA and an AAA proxy, and between an
AAA proxy and a HAAA can be expected in the AAA broker network [8]. Equation 5.8
can thus be simplified:
t � � � h �t
� t
(Equation 5.9)
NR
n
TAH
AAA
Based on the above analysis and Equation 5.9, handover delay incurred in each
handover attempt is derived as follows:
D
j
� t
� t
MD
MD
� t
NS
� t
� � � t
AC
AC
� t
NR,
j
� � � h
n,
j
� t
TAH
� t
- 97 -
AAA
(j =1, 2 …)
where j means the jth handover attempt. Thus, for Case A (lack of trust association)
described in Figure 5.2, the trust relationship verification by the HAAA can be done
locally at the visited network by the FAAA. The incurred delay for all the related
operations is represented as t auth . The handover delay function for the “no trust
association” scenario is given below:
m
D � tMD
��
( tAC
� � � tauth)
(j =1, 2 …m) (Equation 5.10)
j
For Case B (authentication failure) shown in Figure 5.2, the following handover delay
function applies:
m
D � tMD
� � ��
( tAC
� � � hn,
j �tTAH
� tAAA)
j
Because the handover decision computing time � is rather small compared to the total
signalling delay, it is omitted in this analysis.