In the
meantime, existing networks will have to interface to the IMS as part of a transitional
strategy.
This is not uncommon in this industry. Many new technologies have been implemented
through transitional strategies (the IN and SS7 is a good example of this). In
fact we can draw many similarities and lessons learned from the early implementations
of the IN.
The concept of an Intelligent Network (IN) using SS7 for call control started in 1964,
continued to evolve as a standard throughout the 1970s, and was finally implemented
in the U.S. in the 1980s. Europe adopted SS7 for connecting switches to one another
for simple call control, but using a mesh network configuration without signal transfer
points (STPs). The U.S. did the opposite, implementing SS7 with STPs for the support
of 8xx service.
This was a long road from the inception of the technology to the actual implementation.
But this is not the only example. ATM development began in 1969 but did not
really begin taking off until the 1990s. This represents about a 20-year cycle, from
beginning, to maturing the standards, to actual implementation.
Even newer technologies and architectures such as Voice over IP (VoIP) will require
interworking with IMS, as these two architectures are not 100 percent interoperable
with one another. Gateway functions are required to ensure this interoperability, which
is the focus of the next section.
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