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In order to better understand the diversity of the call routing and circuit
switching processes, each is presented as a distinct element in this section. In
practice, you will likely find that the two are so inter-related as to be one. In
many systems, however, there is a difference.
Switching in the PBX system is the mapping of a channel on one interface to
another channel on another interface. For example, this may involve linking a
DS-0 to a DS-1 (T-1), or an FXS port to a T-1 trunk on another PBX.The logic
that decides which path to be taken is part of the call processing function. Once
established, however, the switching of these TDM packets is transparent to the
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10 Chapter 1 • Old World Technologies
processor until the call is torn down.This is a significant difference between IP
networking and voice traffic, as a routing process typically takes place for each
packet—in voice, the call setup only requires processing before the call begins.
It is significant to note that, as with data networking switches, the technology
can be blocking or nonblocking and this, coupled with other factors, can greatly
impact total capacity. For example, Siemens’ blocking architecture can switch up
to 5,760 ports, while the nonblocking Intecom can switch up to 60,000 ports.