
Configuring ATM Services
1-8
Figure 1-6. ATM Transmission Components
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). Once you establish a PVC, you can transfer
information over it at any time. Switched virtual circuits only activate, through
signaling and network switching, when there is information ready for
transmission.
ATM DXI versus ATM
You can access an ATM network using either a synchronous link module running
ATM data exchange interface (DXI) or an ATM link module. However, each
method provides access in a different way.
A synchronous link module works in conjunction with a Fast Routing Engine
(FRE
®
or FRE-2) to form an intelligent link interface (ILI) pair. This ILI pair uses
ATM DXI as a wide area network (WAN) protocol.
ATM DXI allows you to configure an interface on a synchronous interface to
access an ATM network through an ATM DSU/CSU. In other words, the router
transfers variable-length ATM DXI packets to the DSU/CSU. The DSU/CSU then
converts these packets into uniform 53-byte cells for transmission over the ATM
network.
VP
VP
VP
VC
VC
VC
Transmission Path
VP = Virtual Path
VC = Virtual Channel
VC
VC
VC
VP
VP
VP
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