When Voice over IP (VoIP) was introduced, wireless operators struggled with making
VoIP implementations support their wireless networks. The updating of the subscriber
data and other myriad functions defined in the wireless domain was not supported in
VoIP protocols, and SIP did not support multimedia communications such as messaging
very efficiently.
There were also many issues with interoperability experienced by the wireline operators
implementing VoIP, which had to be addressed prior to implementation in the
wireless domain. These were some of the drivers that led the 3GPP to define a new
implementation standard called the IMS. The IMS is really about implementing VoIP
in a wireless network, supporting the requirements of a wireless operator.
Figure 1.2 The Intelligent Network (wireless implementation)
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8 Chapter 1
Certainly IMS makes a great model for wireless, which is what it was originally designed
for as part of the evolution of wireless networks. However, as the IMS evolved
and further developed, wireline operators saw the value for use in their own networks,
and IMS quickly gained popularity for wireline. Figure 1.3 illustrates the migration
from 2G Wireless, to 2.5G, then 3G, on to the IMS and its role.
The evolution of wireless began with simple voice services using the IN and SS7 to
provide call control as well as service control.
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