How the ATM Interface Handles AIS Cells

Nodes that detect a failure send AIS cells to the downstream endpoint. Because the ATM interface is an endpoint and there is no downstream neighbor to an ATM endpoint, the ATM interface never generates AIS cells. The ATM interface responds to the receipt of AIS cells as follows:

1. When an ATM interface receives a configurable number of F4 or F5 AIS cells, it enters the AIS state.
2. While in the AIS state, the ATM interface sends F4 or F5 RDI cells to the remote endpoint. It sends the RDI cells at the rate of one cell per second for as long as the AIS condition exists.

   For all RDI cells sent, the defect type and defect location fields contain the values from the received AIS cells.

3. RDI cell generation stops when one of the following conditions occurs:
   • The interface receives an F4 or F5 loopback cell or an F4 or F5 CC cell.
   • The interface does not receive an AIS cell for a configurable time period.
   • The OAM VC status field of show atm vc atm shows that the circuit is in AIS state.

Copyright © 2008, Juniper Networks, Inc. All rights reserved. Trademark Notice.