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 Action Purpose
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

Related Topic

Document Title

Cisco IOS commands

Master Command List

ATM commands

Asynchronous Transfer Mode Command Reference

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