Solution 2 Does not waste system
capacity.
Incurs additional delay due to sequential paging.
Solution 3 The MS is not required
to monitor both systems
simultaneously for
incoming calls.
Does not have a fall back mechanism when paging over
one system fails.
Requires repeated registration when switching between
two domains.
17.3.13 Voice Call Continuity
With the small coverage area supported by WLANs, continuity of QoS applications
becomes fundamental to deployments. Voice as a service will be one of the first services
supported over WLAN as the operators will desire to offload user to the WLAN system,
allowing for 2G/3G systems to support an increased customer base with existing
deployments. This section describes the Voice Call Continuity (VCC) feature. The VCC
feature consists of two parts: 1) domain registration itself and 2) transfer of the active call
from WLAN to 2G/3G and 2G/3G to WLAN domains. As part of the active call transfers,
the current standard only supports HO between the IMS/WLAN packet-switched domain
and the 2G/3G circuit-switched domains.
The call transfer between two IMS packet-switched domains is still being studied in
the standards bodies.
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