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The ATM OAM Traffic Reduction feature is a mechanism for reducing overhead when loopback cells are being used for fault detection in bidirectional virtual circuits (VCs) over ATM.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
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The Operations and Maintenance (OAM) loopback cells described in this document are defined in International Telecommunication Union (ITU) specification I.610 SERIES I: INTEGRATED SERVICES DIGITAL NETWORK,Maintenance principles , and understanding this specification is requisite to understanding the ATM OAM Traffic Reduction feature.
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.
In the figure below, 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.
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.)
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.
Note |
If ATM OAM traffic reduction is enabled on routers R1 and R2, then because of the random nature of the traffic reduction algorithm, either router can initiate OAM command cells and the other router will have to listen to the incoming OAM command cells. If this feature is enabled on only one router (R1, for example), then the frequency of that router must be greater than or equal to the interval frequency set in the other router (R2) in order for router R1 to stop sending OAM command cells. The ATM OAM Traffic Reduction feature is enabled by the oam-pvc command. When the optimum keyword is enabled, and when a change in the interval frequency of router R2 is detected, the VC initiates an OAM command cell from router R1 and does not go into the Retry mode immediately. If no response is obtained, the VC goes into the Retry mode and follows the OAM Retry procedure. |
To configure ATM OAM traffic reduction on an ATM interface, use the following commands .
To configure ATM OAM traffic reduction on a VC class, use the following commands.
To verify that the ATM OAM Traffic Reduction feature is working, perform the following steps.
The following example enables ATM OAM traffic reduction on an ATM interface:
interface ATM1/1/1.100 point-to-point ip address 60.1.2.1 255.255.255.0 no atm enable-ilmi-trap pvc 11/111 oam-pvc manage auto-detect optimum encapsulation aal5snap
The following example enables ATM OAM traffic reduction using a VC class:
vc-class atm oam-tests oam-pvc manage auto-detect optimum interface ATM1/1/2.100 point-to-point ip address 60.1.3.1 255.255.255.0 class-int oam-tests no atm enable-ilmi-trap pvc 12/222 encapsulation aal5snap
In the following examples, the output is displayed for each command in the task.
The following is sample output from the show atm oam auto-detect command:
Router# show atm oam auto-detect atm 1/1/2.100
ATM OAM Auto Detect statistics on ATM1/1/2
Auto Detection statistics:
ATM OAM AUTO DETECT INIT : 1
ATM OAM SENDING MONITORING : 0
ATM OAM MONITORING : 0
OAM Loopback statistics:
DownRetry : 0
UpRetry : 0
Verified : 1
Not Verified : 0
Verified and Not Monitoring: 1
Router#
The following is sample output from the show atm pvc command with ATM OAM traffic reduction enabled:
Router# show atm pvc 12/222
ATM1/1/2.100: VCD: 1, VPI: 12, VCI: 222
UBR, PeakRate: 149760 (353208 cps)
AAL5-LLC/SNAP, etype:0x0, Flags: 0x1840, VCmode: 0x0, Encapsize: 12
OAM frequency: 10 second(s), OAM retry frequency: 1 second(s)
OAM up retry count: 3, OAM down retry count: 5
OAM Loopback status: OAM Received
Last cell looped No
Loop detect state 0, Last cell looped 0, OAM Retries 0, Loop Retries 0
OAM VC Status: Verified
OAM Auto Detect state: ATM OAM AUTO DETECT INIT
OAM PEER frequency: 0 second(s)
Related Topic |
Document Title |
---|---|
ATM Commands |
Cisco IOS Asynchronous Transfer Mode Command Reference |
Standards |
Title |
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ITU-I Specification |
I.610 SERIES I: INTEGRATED SERVICES DIGITAL NETWORK, Maintenance principles |
MIBs |
MIBs Link |
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None |
To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
Description |
Link |
---|---|
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The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1 | Feature Information for ATM OAM Traffic Reduction |
Feature Name |
Releases |
Feature Information |
---|---|---|
ATM OAM Traffic Reduction |
Cisco IOS XE Release 2.3 |
The ATM OAM Traffic Reduction feature is a mechanism for reducing overhead when loopback cells are being used for fault detection in bidirectional virtual circuits (VCs) over ATM.. The following commands were introduced or modified: oam-pvc show atm oam auto-detect show atm pvc |
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