Fault Management; How The Atm Interface Handles Ais Cells; How The Atm Interface Handles Rdi Cells - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - LINK LAYER CONFIGURATION GUIDE 2010-10-13 Configuration Manual

Fault Management

Copyright © 2010, Juniper Networks, Inc.
ATM uses two types of fault management cells to convey defect information to the
endpoints of a VP/VC:
Alarm indication signal (AIS) cells, which are used to indicate a fault to the downstream
endpoint. AIS cells contain defect type and defect location fields, which optionally
convey information about the type of defect detected and the location of the defect.
Remote defect indication (RDI) cells, which are received from the remote endpoint of
the VP/VC and indicate an interruption in the cell transfer capability of the VP/VC.
Connecting points in the VP/VC that detect a fault send AIS cells in the downstream
direction to the endpoint of the VP/VC. Upon receipt of AIS cells, the downstream endpoint
generates RDI cells in the upstream direction to alert all connecting points and the remote
endpoint of an interruption in the cell transfer capability of the VP/VC.
If fault management detects a failure condition (because of arrival of AIS or RDI cells),
the router disables the corresponding VC until the fault condition is no longer detected.

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:
When an ATM interface receives a configurable number of F4 or F5 AIS cells, it enters
1.
the AIS state.
While in the AIS state, the ATM interface sends F4 or F5 RDI cells to the remote
2.
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.
RDI cell generation stops when one of the following conditions occurs:
3.
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" on page 91 shows that the circuit is
in AIS state.

How the ATM Interface Handles RDI Cells

RDI cells received from the remote endpoint of the VP/VC indicate an interruption in the
cell transfer capability of the VP/VC. For example, the remote endpoint of a VC receives
an F5 AIS cell, enters the AIS state, and transmits F5 RDI cells for the duration of the AIS
condition. On receipt of a configurable number of F4 or F5 RDI cells, the ATM interface
declares an RDI state but does not generate OAM fault management cells in response
Chapter 1: Configuring ATM
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