Cisco CX-AIP-TM Installation And Configuration Manual page 37

Configuring Virtual Circuits
A VC is a point-to-point connection between remote hosts and routers. A VC is established for each
ATM end node with which the router communicates. The characteristics of the VC are established
when the VC is created and include the following:
•
Quality of service (QOS)
•
AAL mode (AAL3/4 or AAL5)
•
Encapsulation type (LLC/SNAP, MUX, NLPID, and QSAAL)
•
Peak and average transmission rates
Each VC supports the following router functions:
•
Multiprotocol (AppleTalk, CLNS, DECnet, IP, IPX, VINES, XNS, and so forth)
•
Fast switching of IP, IPX, VINES, CLNS, and AppleTalk packets
•
Autonomous switching of IP packets
•
Pseudobroadcast support for multicast packets
By default, fast switching is enabled on all AIP interfaces. These switching features can be turned
off with interface configuration commands. Autonomous switching must be explicitly enabled per
interface.
Configuring Permanent Virtual Circuits
All permanent virtual circuits (PVCs) configured into the router remain active until the circuit is
removed from the configuration. The PVCs also require a permanent connection to the ATM switch.
All virtual circuit characteristics apply to PVCs. When a PVC is configured, all the configuration
options are passed on to the AIP. These PVCs are writable into the nonvolatile RAM (NVRAM) as
part of the configuration and are used when the Cisco IOS image is reloaded.
Some ATM switches have point-to-multipoint PVCs that do the equivalent of broadcasting. If a
point-to-multipoint PVC exists, then that PVC can be used as the sole broadcast PVC for all
multicast requests.
To configure a PVC, you must perform the following tasks:
•
Create a PVC
•
Map a protocol address to a PVC
Using PVC Configuration Commands
When you create a PVC, you create a virtual circuit descriptor (VCD) and attach it to the VPI and
VCI. A VCD is an AIP-specific mechanism that identifies to the AIP which VPI/VCI to use for a
particular packet. The AIP requires this feature to manage the packets for transmission. The number
chosen for the VCD is independent of the VPI/VCI used.
When you create a PVC, you also specify the AAL and encapsulation. A rate queue is used that
matches the peak and average rate selections, which are specified in kilobits per second. Omitting a
peak and average value causes the PVC to be connected to the highest bandwidth rate queue
available. In that case, the peak and average values are equal.
Asynchronous Transfer Mode Interface Processor (AIP) Installation and Configuration
Configuring the AIP
37