ATM Hierarchical Shaping ATM VC into VP Shaping

ATM Hierarchical Shaping ATM VC into VP Shaping

Traffic shaping is a quality of service (QoS) mechanism that is used to manage the network traffic by shaping the traffic to a specified rate. Traffic shaping enables the network administrator to:

  • Control access to the available bandwidth.
  • Ensure that the traffic conforms to the policies.
  • Regulate the flow of traffic to avoid congestion that can occur when the transmitted traffic exceeds the access speed of its remote target interface.

Traffic shaping uses queues to constrain data bursts, limit peak data rate, and smooth jitters so that traffic will fit within the promised envelope. Traffic shaping limits the throughput by buffering excess traffic instead of dropping packets.

ATM VP/VC hierarchical shaping provides two levels of traffic shaping--per-VC and per-VP--to control or modify the flow of traffic on an interface. The shaping function also ensures that the traffic from one VC does not adversely impact another VC, thus preventing the loss of data. The traffic is shaped first at the VC level and then at the VP level.

Restrictions for ATM Hierarchical Shaping

All virtual channels (VCs) within a given virtual path (VP) must belong to the same ATM service category.

Information About ATM Hierarchical Shaping

ATM Hierarchical Shaping

If a service (or an application) wants to use an ATM network to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performance requirements of that traffic. The ATM service categories provide a method to relate traffic characteristics and QoS requirements to network behavior. Hierarchical shaping requires that all VCs belonging to a given VP have the same ATM service category. This hierarchy ensures that packets are shaped first at the VC level and then at the VP level. At the interface level, the priority is based on the ATM service category. The service category is determined by the first PVC that is configured under a VP. The priority is in the following order:

  1. Constant Bit Rate (CBR)
  2. Unspecified Bit Rate (UBR)
  3. Unspecified Bit Rate + (UBR+)
  4. Variable Bit Rate Non Real-Time (VBR-nRT)
  5. Real-time Variable Bit Rate (VBR-RT)

If no service category is specified at the VC level, the default is unshaped UBR. The ATM Hierarchical Shaping feature is supported for the all the above ATM traffic service categories.

For VBR-nRT traffic the output sustainable cell rate (SCR) value that is configured will be taken into account for VC shaping. For UBR traffic, the output peak cell rate (PCR) value that is configured will be taken into account for VC shaping.

The ATM Hierarchical Shaping feature supports over-subscription. Over-subscription occurs when the sum of the configured rate of UBR and VBR PVCs exceeds the line rate.

How to Configure ATM Hierarchical Shaping

Configuring ATM Hierarchical Shaping

Perform this task to configure ATM hierarchical shaping.

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface atm interface-number [. subinterface-number {multipoint | point-to-point}]

    4.    pvc vpi / vci

    5.    exit

    6.    ubr output-pcr

    7.    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 {multipoint | point-to-point}]


    Example: 
    Router(config)# interface atm 0/3/2.1 point-to-point
     

    Configure an ATM interface and enters subinterface configuration mode.

     
    Step 4 pvc vpi / vci


    Example: 
    Router(config-subif)# pvc 2/200
     

    Creates or assigns a name to an ATM PVC and enters ATM virtual circuit configuration mode.

     
    Step 5 exit


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

    Exits ATM virtual circuit configuration mode and returns to subinterface configuration mode.

     
    Step 6 ubr output-pcr


    Example: 
    Router(config-if-atm-vc)# ubr 4000
     

    Configures UBR QoS and specifies the output PCR for an ATM PVC, PVC range, switched virtual circuit (SVC), VC class, or VC bundle member.

     
    Step 7 exit


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

    Exits ATM virtual circuit configuration mode and returns to subinterface configuration mode.

     

    Configuration Examples for ATM Hierarchical Shaping

    Example Configuring ATM Hierarchical Shaping

    The following example shows how to configure ATM hierarchical shaping: 

    enable
 configure terminal
  interface atm 0/3/2.1 multipoint
   atm pvp 2
   pvc 2/200
    exit
   range range1 pvc 2/100 2/102
    ubr 4000
    exit
   atm pvp 3
   pvc 3/100
    vbr-nrt 1000 1000
    
    end

    Additional References

    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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    Standard

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    RFC

    Title

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