??? Step 10: If the CSCF did not receive the page response within a timeout period for the
page sent over the IMS/WWAN domain, it pages the MS over the CS domain.
??? Step 11: A potential optimization that the MS can perform to avoid the delays incurred
due to sequential paging under transition scenarios is to detect that the MS is going out
WLAN Interworking with 2G/3G systems 396
of WLAN coverage and perform IMS deregistration to stop receiving it services over
WLAN.
??? Step 12: The MS sends a IMS de-registration while still under weakened WLAN
coverage. The MS when it loses the WLAN coverage prior to de-registration, can use
the IMS/WWAN domain to de-register its IMS/WLAN domain if both WLAN and
WWAN IMS belong to the same IMS core network.
??? Step 13: The CSCF forwards the de-registration message to the VCC AS.
??? Step 14: The MS is subsequently paged only over IMS/WWAN or the CS domains.
??? Step 15: The MS can use the Special SMS to indicate to the network that it wishes to
receive all its services over CS domain only. This should be rare since when the MS
has CS coverage it should also have IMS/WWAN coverage.
At the end of the procedure the MS is paged over the appropriate domain based on it
current registration status.
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