There are three basic architectures for DSL, each of which makes use of a different layer of the communications stack for carrying the voice-over DSL connection. Figure 16.7 illustrates these three basic architectures:
Voice-over IP (VoIP) in which voice is encapsulated within IP data packets. In this case voice is transmitted at Layers 3 and 4 of the communications stack.
Voice-over ATM in which the voice is encapsulated within ATM cells. In this case the voice traffic is transmitted at layer 2 of the communication stack.
Channelized voice over DSL (CVoDSL), where the digitized voice is carried directly on the PHY of the DSL link.
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