They do not indicate the specific technology used to interconnect.
39 Telecommunications has evolved from analog to more efficient digital transmission, from being
primarily circuit-switched to being a mixture of circuit-switched and packetized; from using exclusively
copper to using some fiber, and so on.
24 Chapter 1
optimized to handle voice traffic (which almost always means telephony traffic??”traffic
originating and terminating on a telephone). Offering data solutions, therefore, meant
transporting bursty, packet-based traffic over a voice-based infrastructure using Time
Division Multiplexing (TDM) technologies (see chapter on TDM for an explanation of
TDM) such as the T-carrier (T-1, T-3, etc.) on copper and fiber, and SONET (Synchronous
Optical NETworking) rings over a fiber infrastructure. However, as traffic data (essentially
non voice; could be anything like email, file transfers, etc.) began to reach a critical
mass, alternative (and most often separate) packet-based network infrastructures
were developed to carry data traffic (i.e., offer data services).
Initial packet services used a technology called X.25 quite extensively.
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