Cisco Systems 8600 Series manual PVCs and SVCs, ATM and Frame Relay SVCs and SPVCs

ATM and Frame Relay SVCs and SPVCs

The ESP provides the BPX switch with the ATM or Frame Relay signaling function. It interprets industry-standard signaling messages from ATM or Frame Relay CPE to provide the call setup and tear down for switched virtual circuits across the ATM network. In addition to SVC signaling, the ESP also performs PNNI routing, collects statistics, and processes alarms and billing records for SVC connections through the BPX switch.

Figure 8-1 Wide Area Network with BPX Switch and ESP

ATM

CPE

Frame

Relay

CPE

SVC

PVC

SVC

PVC

WAN		WAN
Service		Service
Node		Node
Cisco WAN switching network
	with PNNI routing
WAN		WAN
Service		Service
Node		Node

SVC

PVC

SVC

PVC

ATM

CPE

Frame

Relay

CPE

S6357

PVCs and SVCs

Both permanent virtual circuits and switched virtual circuits are defined by ATM and Frame Relay standards groups.

PVCs

After being added to a network, permanent virtual circuits (PVCs) remain relatively static. The PVC only allocates a physical circuit and consumes bandwidth when there is data to send. However, the permanent virtual circuit remains in place, always available for use, and is similar to a dedicated private line in this respect.

SPVCs

Soft permanent virtual circuits (SPVCs) are PVCs which are routed using the Private Network-Network Interface (PNNI) routing protocol. The “permanent” qualifier indicates that the virtual connection is established administratively, through an operator’s command, rather than on demand by signaling. A soft PVC is one where the establishment within the network is done by the ESP signaling (in this case, PNNI signaling), just as it is done for Frame Relay and ATM switched virtual circuits.

In the PNNI network, SPVC connections are established using the best available route. During a network failure, SPVC connections could be rerouted and the newly selected path many not be the optimal route. The ESP’s SPVC feature provides for auto-grooming of SPVCs. Auto-grooming is a background management process that evaluates SPVC connections; if a better path for the connection is found, the SPVC will be released and rerouted to the optimized path.

8-2Cisco BPX 8600 Series Reference