N:1 PVC Mapping to PWE with Nonunique VPIs

N:1 PVC Mapping to PWE with Nonunique VPIs

The N:1 PVC Mapping to PseudoWire Emulation (PWE) with Nonunique virtual path identifiers (VPIs) feature maps one or more ATM permanent virtual circuits (PVCs) to a single pseudowire (PW). There are two modes of AAL0 encapsulation, N:1 and 1:1 mapping. In N:1 mapping, multiple unrelated virtual path identifier/virtual channel identifier (VPI/VCI) are carried over a single Multiprotocol Label Switching (MPLS) PW. This is an efficient mapping method because less resources are used from the MPLS network. In 1:1 mapping, a single VPI/VCI is carried over a single MPLS PW. Benefits of this feature include the following:

  • Aggregate quality of service (QoS) can be applied to related PVCs.

  • Bandwidth is conserved with the reduction in the number of pseudowires that are used.

Restrictions for N:1 PVC Mapping to PWE with Nonunique VPIs

  • N:1 permanent virtual circuits (PVC) mapping configuration is supported only on multipoint subinterfaces; it is not supported on main interfaces or point-to-point subinterfaces.

  • N:1 PVC mapping mode is not supported on Access Circuit Redundancy subinterfaces.

  • Preconfigured PVCs cannot exist on the multipoint subinterface on which you want to configure N:1 PVC mapping.

  • An attachment circuit that has been bound to a pseudowire cannot be removed unless all Layer 2 virtual circuits (VCs) have been removed.

  • Layer 3 PVCs cannot be configured on N:1 subinterfaces.

  • Cell packing values configured under a VC class attached to the PVC, main interface, or subinterface will not be inherited by N:1 PVCs.

  • Operation, Administration, and Maintenance (OAM) functionality is not supported on N:1 Layer 2 PVCs. OAM cells coming from the customer edge (CE) network will be treated as normal data traffic and will traverse through the pseudowire.

  • Only ATM adaptation layer type 0 (AAL0) encapsulation is supported for N:1 PVCs.

  • The service policy configuration can be configured only at the subinterface level for N:1 PVCs.

  • ATM N:1 and PVP modes cannot be configured on different subinterfaces that belong to a physical interface.

  • You cannot change the ATM interface mode from point-to-point to multipoint or from multipoint to point-to-point.

  • If you change a layer 2 ATM interface to a layer 3 ATM interface, traffic will not flow.

Information About N:1 PVC Mapping to PWE with Nonunique VPIs

N:1 PVC Mapping to PWE with Nonunique VPIs Feature Description

To transport ATM cells over Multiprotocol Label Switching (MPLS), a VC is established between the provider edge (PE) routers on both ends of the MPLS backbone. With the N:1 permanent virtual circuit (PVC) Mapping to PseudoWire Emulation (PWE) with Nonunique VPIs feature, multiple PVCs irrespective of their Virtual Path Identifiers (VPIs), are transported over a single pseudowire configured on a subinterface. (“N:1” refers to the number of PVCs transported over one pseudowire). ATM cells are packed together in a single frame and sent over the single pseudowire. The ATM cell header information is packed together with the cell payload on a per-cell basis in the packets so that packets received at the egress end are unpacked and the ATM cells are mapped to the respective PVCs.

In N:1 PVC mapping mode, the device can pack cells only from a single PVC in an MPLS packet to transmit over a pseudowire; cells from multiple PVCs cannot be packed in a single MPLS packet and mapped to a single pseudowire for transmission. However, if a device receives an MPLS packet that is packed with cells from multiple PVCs, then those cells will be unpacked and sent to the respective PVCs.

How to Configure N:1 PVC Mapping to PWE with Nonunique VPIs

Configuring N:1 PVC Mapping to PWE with Nonunique VPIs

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    interface atm slot/subslot/port

    4.    atm mcpt-timers timer1 timer2 timer3

    5.    exit

    6.    configure terminal

    7.    interface atm slot/subslot/port.subslot multipoint

    8.    no ip address

    9.    atm enable-ilmi-trap

    10.    cell-packing maxcells mcpt-timer timer-number

    11.    xconnect peer-ipaddress vc-id encapsulation mpls

    12.    pvc vpi/vci l2transport

    13.    Repeat Step 12 for the number of PVCs that you want to configure.

    14.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example: 
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.

     
    Step 2 configure terminal


    Example: 
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 interface atm slot/subslot/port


    Example: 
    Device(config)# interface atm 9/1/1
     

    Enables the ATM interface and enters interface configuration mode.

     
    Step 4 atm mcpt-timers timer1 timer2 timer3


    Example: 
    Device(config-if)# atm mcpt-timers 100 200 300
     

    Sets the Maximum Cell Packing Timeout (MCPT) values in microseconds.

    • The MCPT timer sets the time for which the device waits for the raw cells (AAL0 encapsulation) to be packed into a single packet for punting to the pseudowire.

     
    Step 5 exit


    Example: 
    Device(config-if)# exit
     

    Exits interface configuration mode.

     
    Step 6 configure terminal


    Example: 
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 7 interface atm slot/subslot/port.subslot multipoint


    Example: 
    Device(config)# interface atm 9/1/1.1 multipoint
     

    Enters subinterface configuration mode and creates a multipoint subinterface on the given port on the specified ATM Shared Port Adapter (SPA).

     
    Step 8 no ip address


    Example: 
    Device(config-subif)# no ip address
     

    Removes the interface IP address.

     
    Step 9 atm enable-ilmi-trap


    Example: 
    Device(config-subif)# atm enable-ilmi-trap
     

    Generates an Integrated Local Management Interface (ILMI) atmfVccChange trap when an ATM interface or subinterface is enabled or shut down.

     
    Step 10 cell-packing maxcells mcpt-timer timer-number


    Example: 
    Device(config-subif)# cell-packing 20 mcpt-timer 2
     

    Enables ATM over MPLS to pack multiple ATM cells into each MPLS packet within the MCPT timing.

     
    Step 11 xconnect peer-ipaddress vc-id encapsulation mpls


    Example: 
    Device(config-subif)# xconnect 10.1.1.1 100 encapsulation mpls
     

    (Optional) Enables the attachment circuit and specifies the IP address of the peer, a VC ID, and the data encapsulation method.

     
    Step 12 pvc vpi/vci l2transport


    Example: 
    Device(config-subif)# pvc 10/100 l2transport
     

    Assigns a VPI and virtual channel identifier (VCI).

     
    Step 13 Repeat Step 12 for the number of PVCs that you want to configure.  

    —

     
    Step 14 end


    Example: 
    Device(config-subif)# end
     

    Exits subinterface configuration mode and returns to privileged EXEC mode.

     

    Configuration Examples for N:1 PVC Mapping to PWE with Nonunique VPIs

    Example: Configuring N:1 PVC Mapping to PWE with Nonunique VPIs

    The following example shows how to configure the N:1 ATM permanent virtual circuit (PVC) mapping to pseudowires with non unique virtual path identifiers ( VPIs): 

    Device> enable
Device# configure terminal
Device(config)# interface atm 0/1/0
Device(config-if)# atm mcpt-timers 500 5000 50000
Device(config-if)# exit
Device# configure terminal
Device(config)# interface atm 0/1/0.1 multipoint
Device(config-subif)# no ip address
Device(config-subif)# atm enable-ilmi-trap
Device(config-subif)# cell packing 20 mcpt-timer 2
Device(config-subif)# xconnect 10.1.1.1 100 encapsulation mpls
Device(config-subif)# pvc 10/100 l2transport
Device(config-subif)# pvc 11/122 l2transport
Device(config-subif)# pvc 19/231 l2transport
Device(config-subif)# end

    Verifying the N:1 PVC Mapping to PWE with Nonunique VPIs Configuration

    To verify the N:1 PVC Mapping to PWE with Nonunique VPIs Configuration, use the show mpls l2transport vc command in user EXEC or privileged EXEC mode.

    Router# show mpls l2transport vc

Local intf      Local circuit              Dest address    VC ID    Status
------------    ------------------------   --------------  -------  --------
AT0/1/1.1         ATM CELL ATM0/1/1.1         2.2.2.2       100      UP 

interface ATM0/0/0.1/1/1/1
atm mcpt-timers 20 30 40

interface ATM0/0/0.1/1/1/1.1 multipoint
no ip address
no atm enable-ilmi-trap
cell-packing 2 mcpt-timer 1
xconnect 2.2.2.2 100 encapsulation mpls
pvc 10/100 l2transport
pvc 20/200 l2transport
pvc 30/300 l2transport

    Additional References

    Related Documents

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    Document Title

    Cisco IOS commands

    Master Command List

    ATM commands

    Asynchronous Transfer Mode Command Reference

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