Cisco Cisco IOS Software Release 12.0(23)S
ATM OAM Traffic Reduction
Restrictions for ATM OAM Traffic Reduction
2
Cisco IOS Release: Multiple releases (see the Feature History table)
Restrictions for ATM OAM Traffic Reduction
•
This feature supports only permanent virtual circuits (PVCs) for F5 END_TO_END OAM loopback
cells. This feature is not applicable for F4 OAM cells, AIS/RDI cells, or F5 SEGMENT OAM
loopback cells.
cells. This feature is not applicable for F4 OAM cells, AIS/RDI cells, or F5 SEGMENT OAM
loopback cells.
•
This feature will break OAM loopback functionality when there is a unidirectional breakage and
when retry frequency is configured to be the same as the F5 OAM loopback frequency.
when retry frequency is configured to be the same as the F5 OAM loopback frequency.
Information About ATM OAM Traffic Reduction
To configure ATM OAM traffic reduction, you need to understand the following concepts:
•
OAM Traffic Flow
The OAM management portion of a PVC sends OAM loopback cells at periodic intervals. When OAM
management is enabled at both ends of the PVC, the cells are transmitted and looped back at both ends.
This transmission is redundant, because the OAM cells travel through the same physical circuit twice.
management is enabled at both ends of the PVC, the cells are transmitted and looped back at both ends.
This transmission is redundant, because the OAM cells travel through the same physical circuit twice.
, assume PVCs are configured between router R1 and router R2 , and that OAM management
is enabled on both ends of the PVC. Router R1, upon receiving OAM command cells from router R2,
can stop its own OAM command cell transmission and can manage the link on the basis of incoming
OAM command cells. Router R1 can reinitiate OAM command cell transmission upon discovering the
absence of command cells from router R2.
can stop its own OAM command cell transmission and can manage the link on the basis of incoming
OAM command cells. Router R1 can reinitiate OAM command cell transmission upon discovering the
absence of command cells from router R2.
Figure 1
ATM OAM Traffic Flow
When router R1 detects the first OAM command cell from router R2, time stamp T1 is noted. When the
next OAM command cell is detected, time stamp T2 is noted. The interval T1 minus T2 provides the
OAM the loopback frequency of router R2. The average value of this interval is taken by measuring it a
random number of times. (The interval needs to be taken a random number of times to avoid a race
condition that might happen when routers R1 and R2 implement this algorithm and the frequency is the
same.)
next OAM command cell is detected, time stamp T2 is noted. The interval T1 minus T2 provides the
OAM the loopback frequency of router R2. The average value of this interval is taken by measuring it a
random number of times. (The interval needs to be taken a random number of times to avoid a race
condition that might happen when routers R1 and R2 implement this algorithm and the frequency is the
same.)
At the end of the random time period, router R1 stops sending OAM command cells and starts the OAM
traffic monitoring timer. This timer in router R1 checks for a change in interval frequency in router R2.
If there is a change, the traffic monitoring timer is stopped and the VC goes into Retry mode and checks
whether the link is still up. In Retry mode, OAM command loopback cells are transmitted at an interval
of one per second for 3 seconds. If router R1 does not receive a response to the command cell, the link
is changed to the Down state.
traffic monitoring timer. This timer in router R1 checks for a change in interval frequency in router R2.
If there is a change, the traffic monitoring timer is stopped and the VC goes into Retry mode and checks
whether the link is still up. In Retry mode, OAM command loopback cells are transmitted at an interval
of one per second for 3 seconds. If router R1 does not receive a response to the command cell, the link
is changed to the Down state.
R1
R2
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