
Configuring ATM and MPLS Services
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117374-C Rev 00
Permanent and Switched Virtual Connections
Virtual channels and virtual paths allow you to establish virtual channel links
(VCLs). You can create VCLs as either permanent virtual circuits (PVCs) or
switched virtual circuits (SVCs). After you establish a PVC, you can transfer
information over it at any time. SVCs activate, through signaling and network
switching, only when there is information ready for transmission.
ATM Layers
The B-ISDN protocol reference model, on which ATM is based, consists of four
layers (Figure 1-4
). Each layer communicates only with the layer directly above it
and the layer directly below it.
Figure 1-4. B-ISDN ATM Protocol Reference Model
Higher protocol layer
ATM
adaptation
layer
(AAL)
Convergence sublayer (CS)
Segmentation and reassembly sublayer (SAR)
ATM layer
Transmission convergence sublayer
Physical medium dependent sublayer (PMD)
Physical
layer
(PHY)
ATM0003A
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