ATM OAM Traffic Reduction

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.

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Prerequisites for ATM OAM Traffic Reduction

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.

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.

  • This feature breaks 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.

Information About ATM OAM Traffic Reduction

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.

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.

How to Configure ATM OAM Traffic Reduction

Configuring ATM OAM Traffic Reduction on an ATM Interface

To configure ATM OAM traffic reduction on an ATM interface, use the following commands .

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface atm interface-number . subinterface-number

    4.    pvc vpi / vci

    5.    oam-pvc [frequency | manage [frequency [auto-detect [optimum] | keep-vc-up [seg aisrdi failure] | loop-detection]]]

    6.    exit


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Router> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.

     
    Step 2 configure terminal


    Example:
    Router# configure terminal
     

    Enters global configuration mode.

     
    Step 3 interface atm interface-number . subinterface-number


    Example:
    Router(config)# interface atm 1/1/1.100
     

    Configures an ATM interface type and enters interface configuration mode.

     
    Step 4 pvc vpi / vci


    Example:
    Router(config-if)# pvc 0/100
     

    Assigns a name to an ATM PVC and enters ATM VC configuration mode.

     
    Step 5 oam-pvc [frequency | manage [frequency [auto-detect [optimum] | keep-vc-up [seg aisrdi failure] | loop-detection]]]


    Example:
    Router(config-if-atm-vc)# oam-pvc manage auto-detect optimum
     

    Enables end-to-end F5 OAM loopback cell generation and OAM management for an ATM PVC or VC class, including the ATM OAM Traffic Reduction feature.

    • auto-detect --Initiates auto-detection of peer OAM command cells.

    • optimum --Configures an optimum mode so that when the traffic monitoring timer expires, the PVC sends an OAM command cell at the locally configured frequency instead of going into Retry mode immediately. If there is no response, the PVC goes into Retry mode.

     
    Step 6 exit


    Example:
    Router(config-if-atm-vc)# exit
     

    Exits the configuration mode.

    • Enter the exit command for each command mode to exit.

     

    Configuring ATM OAM Traffic Reduction on a VC Class

    To configure ATM OAM traffic reduction on a VC class, use the following commands.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    vc-class atm vc-class-name

      4.    oam-pvc [frequency | manage [frequency [auto-detect [optimum] | loop-detection]]]

      5.    exit

      6.    interface atm interface-number . subinterface-number

      7.    class-int vc-class-name

      8.    pvc vpi / vci

      9.    exit


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Router> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2 configure terminal


      Example:
      Router# configure terminal
       

      Enters global configuration mode.

       
      Step 3 vc-class atm vc-class-name


      Example:
      Router(config)# vc-class atm word
       

      Creates a VC class to an ATM VC bundle member.

       
      Step 4 oam-pvc [frequency | manage [frequency [auto-detect [optimum] | loop-detection]]]


      Example:
      Router(config-vc-class)# oam-pvc manage auto-detect optimum
       

      Enables end-to-end F5 OAM loopback cell generation and OAM management for an ATM PVC or VC class, including the ATM OAM Traffic Reduction feature.

      • auto-detect --Initiates autodetection of peer OAM command cells.

      • optimum --Configures an optimum mode so that when the traffic monitoring timer expires, the PVC sends an OAM command cell at the locally configured frequency instead of going into Retry mode. If there is no response, the PVC goes into Retry mode.

       
      Step 5 exit


      Example:
      Router(config-vc-class)# exit
       

      Exits the vc-class mode.

       
      Step 6 interface atm interface-number . subinterface-number


      Example:
      Router(config)# interface atm 1/1/2.100
       

      Configures an ATM interface and enters interface configuration mode.

       
      Step 7 class-int vc-class-name


      Example:
      Router(config-if)# class-int test
       

      Assigns a VC class to an ATM main interface.

       
      Step 8 pvc vpi / vci


      Example:
      Router(config-if)# pvc 0/100
       

      Creates an ATM PVC and attaches it to the designated network virtual path identifier (VPI) and virtual channel interface (VCI).

      In this case, more than one PVC is created.

       
      Step 9 exit


      Example:
      Router(config-if)# exit
Router(config)# exit
       

      Ends the configuration mode.

      • Enter the exit command for each command mode to exit.

       

      Verifying ATM OAM Traffic Reduction

      To verify that the ATM OAM Traffic Reduction feature is working, perform the following steps.

      SUMMARY STEPS

        1.    enable

        2.    show atm oam auto-detect [atm interface-number . subinterface-number]

        3.    show atm pvc [interface atm type number[vpi / vci | vci | word] vpi / vci | vci | word]


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Router> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.

         
        Step 2 show atm oam auto-detect [atm interface-number . subinterface-number]


        Example:
        Router# show atm oam auto-detect atm 1/1/2.100
         

        (Optional) Displays the state of the OAM cells when the ATM OAM traffic reduction is enabled.

        • The show atm oam auto-detect command reports the number of VCs in autodetection mode and in OAM loopback mode.

         
        Step 3 show atm pvc [interface atm type number[vpi / vci | vci | word] vpi / vci | vci | word]


        Example:
        Router# show atm pvc
         

        (Optional) Displays ATM PVCs and traffic reduction information.

        The show atm pvc command reports the OAM autodetect state, the OAM peer frequency, and the time the last OAM command cell was received.

         

        Configuration Examples for ATM OAM Traffic Reduction

        ATM OAM Traffic Reduction on an ATM Interface Example

        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

        ATM OAM Traffic Reduction on a VC Class Example

        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

        Verify ATM OAM Traffic Reduction Example

        In the following examples, the output is displayed for each command in the task.

        Sample Output for the show atm oam auto-detect Command

        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#

        Sample Output for the show atm pvc Command

        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)

        Additional References for ATM OAM Traffic Reduction

        Related Documents

        Related Topic

        Document Title

        Cisco IOS commands

        Cisco IOS Master Commands List, All Releases

        ATM commands

        Cisco IOS Asynchronous Transfer Mode Command Reference

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        MIB

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        http:/​/​www.cisco.com/​go/​mibs

        RFCs

        RFC

        Title

        None

        --

        Technical Assistance

        Description

        Link

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        http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

        Feature Information for ATM OAM Traffic Reduction

        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 2.3S

        Cisco IOS XE Release 3.14S

        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.

        In Cisco IOS Release XE 3.14S, support for the ATM OAM Traffic Reduction feature was added on the 4451-X Integrated Services Router.

        The following commands were introduced or modified: oam-pvc show atm oam auto-detect show atm pvc