Juniper JUNOSE 11.1.X - LINK LAYER CONFIGURATION 4-7-2010, Руководство по настройке

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which optionally convey information about the type of defect detected and the
location of the defect.
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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:
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:
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The interface receives an F4 or F5 loopback cell or an F4 or F5 CC cell.
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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 94 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 to the condition. The ATM interface leaves the RDI
condition when no RDI cells have been received for a configurable time period.
The OAM VC status field of “show atm vc atm” on page 94 shows whether the circuit
is in RDI state.
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Operations, Administration, and Management of ATM Interfaces
JUNOSe 11.1.x Link Layer Configuration Guide