VC Integrity

VC integrity is used to monitor the operational status of an individual VC. VC integrity provides continuous ATM VC-layer connectivity verification by periodically sending F5 end-to-end loopback cells on individual PVCs to verify end-to-end connectivity. You can set the frequency with which loopback cells are transmitted for an individual VC.

If VC integrity is enabled, the peer ATM host must respond to the router’s loopback cells, or the circuit will be disabled. The ATM interface does not reenable the circuit until it receives loopback responses or until local VC integrity is disabled.

You can set the following VC integrity parameters for an individual VC with the oam retry command. For more information, see oam retry.

• The retry frequency with which loopback cells are transmitted when the router verifies the down status of the circuit; that is, when the peer ATM host does not respond to a loopback cell
• The retry frequency with which loopback cells are transmitted when the router verifies the up status of the circuit; that is, when the ATM host resumes responding to a loopback cell
• The number of successive loopback cell responses missed before the router determines that the circuit is down
• The number of successive loopback responses received before the router determines that the circuit is up

VC integrity is a best-effort mechanism that tries to adhere to the loopback cell transmission frequency and retry frequency values configured for each VC without consuming excessive processing time on the line module. When you configure VC integrity for a large number of circuits on the line module, delays in transmitting OAM loopback cells might occur so new subscribers can connect and to maintain existing subscriber connections.

To set up the ATM interface to transmit F5 end-to-end loopback cells over a VC, use the oam keyword and an optional frequency with the atm pvc command. To send F5 segment loopback cells, use the ATM ping mechanism, described in ATM Ping .

F5 loopback receive and transmit statistics are available with show atm vc atm .

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