They are discussed in Chapter 1.
124 Chapter 4
The transport technologies that Service Providers overwhelmingly employed were
mostly optimized for the delivery of voice services over the different physical media.
Subsequently, as data services began to emerge, these services were still largely
delivered over this voice-efficient infrastructure; the billions of dollars invested in these
voice-optimized networks made it unrealistic to discard and replace them with data-optimized
networks. As this infrastructure equipment depreciates2 and competition intensifies,
however, Service Providers are beginning to transition to next-generation packetized
networks; a fair number of Service Providers have already begun this transition,
but it will be a long while before this is complete. The pace is slow due to the amount of
investment needed, fear of cannibalization of existing TDM services3, and the changes
required to the existing support infrastructure (methods and procedures and personnel
skill sets, for instance). Furthermore, legacy solutions such as SONET are also evolving
to be more accommodating to Ethernet services and consequently extending their appeal
and longevity.
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