The packet-switched domain can be wireline focused or wireless focused, so this section is
broken into two parts to discuss both Voice over IP (VoIP) and wireless implementations.
VoIP Domain
We have talked quite a bit about the VoIP domain already in the sense that calls from
the circuit-switched domain must then be routed through the VoIP domain to packetize
the voice, and to convert the signaling from SS7 to SIP. This being the case, we have
already identified several of the functions within this domain, but we will cover them
again here from a different perspective.
Moving from Legacy to Convergence 49
The VoIP domain consists of entities that provide the functions commonly found
in a telephone switch, with one major difference: the functions are distributed. When
the concept of VoIP first began, the idea was to separate the function within a switch
and provide these functions in a more economical fashion. As shown in Figure 2.4, the
switch can be broken into three major functions:
?– Switching fabric (or matrix in legacy terms)
?– Signaling
?– Applications
The switching fabric is the cheapest part of the switch. This is where circuits are
connected to other circuits within the switch, for connecting of a call. Think of the
telephone operators of days far gone and how they used their answering positions to
connect calls with other parties.
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