Configuring VP Shaping on the PA-A3 ATM Port Adapter [ATM Traffic Management]

Document ID: 10534

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
PVP Restrictions
Configure
      Configuration
Verify
Troubleshoot
Related Information

Introduction

This document provides a sample configuration for VP shaping on the PA-A3 ATM port adapter.

The PA-A3 supports multiplexing of one or more permanent virtual circuits (PVCs) over a virtual path (VP) that is shaped at a constant bandwidth. In order to use this feature, configure a permanent virtual path (PVP) with a specific virtual path identifier (VPI). A transmitted cell of a PVC that is created subsequently with the same VPI is multiplexed onto the traffic shaping scheduler for the PVP; the traffic parameters of individual PVCs are ignored.

This feature is useful when you want to define a maximum amount of traffic toward certain destinations that a single VPI can represent. For example, when the ATM network connects a digital subscriber line (DSL) aggregation router to multiple digital subscriber line access multiplexers (DSLAMs), the ATM routing, provisioning and Quality of Service (QoS) can be simplified by using a single PVP to each DSLAM.

The only ATM QoS service category that can be configured for the VP is unspecified bit rate (UBR), and the peak cell rate (PCR) is the single parameter to be specified when you create the VP. Several data PVCs can share the same VP. VP shaping regulates the output rate at the VP level rather than on each VC. The PCR of each VC with the same VPI is bound by the PCR configured on the PVP. When the PVP becomes congested, the PVCs created under it share bandwidth roughly proportional to their individual traffic.

The peak-rate argument is the maximum rate (in kbps) at which the PVP is allowed to transmit data. Valid values are in the range of 84 kbps to line rate. The default peak rate is the line rate.

When you create a PVP, the router also creates two PVCs for end-to-end and segment loopback operation, administration and maintenance (OAM) cells. OAM cells at the VP level use the same VPI value as the user cells of the PVP, and use predefined or well-known VCI values. These VPI values are three for segment OAM F4 flow and four for end-to-end OAM F4 flow. The router will not generate cells on these VCs but will respond to loopback cells received from the connected device. In addition, the router will not bring down a VC under VPs when alarm indication signal (AIS) cells are detected on the VP level. These problems are reported in Cisco bug ID CSCdu66968. Bug ID CSCdu66968 is a feature request to add PA-A3 OAM cell generation on PVPs. If you are a registered user and logged in, you can view the details of the bugs in the Bug Toolkit (registered customers only) .

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these software versions:

Cisco IOS® Software Release 12.0(4)T
Cisco IOS Software Release 12.0(5)S
Cisco IOS Software Release 12.0(7)XE

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

PVP Restrictions

These restrictions apply to PVPs on the PA-A3:

You can configure up to 256 PVPs on a single ATM interface.
A PVP supports VCs in the UBR service class only. Thus, the cell scheduler assigns the same priority to all VCs within the PVP, and services each VC on a best-effort basis.

Note: From Cisco IOS Software Releases 12.0(7)T and 12.0(7)XE1 onwards, Cisco Bug ID CSCdm22263 (registered customers only) removed the available bit rate (ABR), unspecified bit rate plus (UBR+), and variable bit rate non-real time (VBR-nrt) configuration commands from VC configuration mode when the PVC uses the same VPI number as the PVP.

Note: CSCeg39747 (registered customers only) was committed in Cisco IOS Software Release 12.0(31)S, which removes the category of service commands from the VP. Without VCs, VP shaping is only supported with the UBR service category.
All VCs share the same peak cell rate (PCR) as the PVP. Hierarchical VP shaping, in which the member VCs use different PCRs or ATM service classes, is not supported.
Per-VC QoS features like modular QoS CLI (MQC), class-based weighted fair queueing (CBWFQ), or low latency queueing (LLQ) are not supported at the PVP level. Queueing per VC is still done. The segmentation and reassembly schedules the VCs within a VP in a round-robin like method. Since the VCs within the PVP can be UBR only, a service policy that assigns a minimum bandwidth guarantee is not supported. A service policy that applies Class-Based Weighted Fair Queueing will be rejected with the following error message:
```
d11-5-7206-16(config-if)#pvc 5/10
d11-5-7206-(config-if-atm-vc)#service-policy output test
d11-5-7206-16#
*Mar 5 23:00:50.477: I/f ATM5/0 VC 5/10 class gold requested bandwidth 500 
  (kbps) Available only 0 (kbps)
```
PVP status management is not supported; that is, the PVP status is always active and PVP F4 flow AIS and RDI cells that are received are ignored (CSCdu66968).
VP shaping in PA-A3 could cause Usage Parameter Control (UPC) violations for cell delay variation tolerance (CDVT) when there are multiple VCs in the VP that have cells to transmit at the same time. This issue, documented in CSCdy03586, explains that since VP shaping on PA-A3 is done with software, and if there are multiple VCs in the VP, there could be UPC (CDVT) violations depending on the traffic load of the VCs. While the CSCdy03586 is about multicast traffic, the problem is generic. Multicast traffic means that all VCs get loaded at the same time, which is a worst-case scenario for the issue. The workaround is to reduce the number of VCs.

Configure

In this section, you are presented with the information to configure the features described in this document.

Note: Use the Command Lookup Tool (registered customers only) to find more information on the commands used in this document.

Configuration

Complete these configuration steps:

Under the main interface, create a PVP and optionally specify the peak rate.
Under the main or subinterface, create a PVC with a VPI that matches the VPI specified in Step 1.
Exit configuration mode and issue the show atm vp command to confirm your configuration.

Example PVP Configuration on a PA-A3

interface ATM4/0/0
 no ip address
 atm pvp 10 50000
! 
interface ATM4/0/0.5 multipoint
 ip address 5.5.5.1 255.255.255.0
 pvc 10/100 
  protocol ip 5.5.5.2
!
interface ATM4/0/0.10 point-to-point
 ip address 10.10.10.1 255.255.255.0
 pvc 10/110

Note these key points about the configuration:

When a PVC uses the same VPI number as the PVP, it cannot be configured for an ATM service class other than UBR. Note that the ubr+, abr, and vbr-nrt commands no longer appear at the command line interface (CLI).

7500-1.5(config-subif)#pvc 10/100 
7500-1.5(config-if-atm-vc)#? 
ATM virtual circuit configuration commands: 
 atm               atm pvc commands
 broadcast         Pseudo-broadcast
 class-vc          Configure default vc-class name
 default           Set a command to its defaults
 dialer            set dialer pool this pvc belongs to
 encapsulation     Select ATM Encapsulation for VC
 exit-vc           Exit from ATM VC configuration mode
 ilmi              Configure ILMI management
 inarp             Change the inverse arp timer on the PVC
 no                Negate a command or set its defaults
 oam               Configure oam parameters
 oam-pvc           Send oam cells on this pvc
 protocol          Map an upper layer protocol to this connection.
 service-policy    Attach a policy-map to a VC
 transmit-priority set the transmit priority for this VC
 tx-ring-limit     Configure PA level transmit ring limit
 ubr               Enter Unspecified Peak Cell Rate (pcr) in Kbps.

Warning: If the shaping value is changed under a PVP in the main ATM interface, all VPI/VCIs under that main interface and/or the subinterfaces associated with it will bounce. Therefore, be careful when trying this in a production environment.

The CLI accepts a PCR that is different from the PCR for the PVP, but this value is ignored. In the following example, a UBR PVC is configured with a PCR of 25000. The value is still 50 Mbps, as shown when the show atm pvc {vpi/vci} command is issued. Bug ID CSCdu03938 removes the ability to specify the UBR service category, which is the only one implicitly supported.

interface ATM4/0/0.5 multipoint

 ip address 5.5.5.1 255.255.255.0
 pvc 10/100
  ubr 25000
7500-1.5#show atm pvc 10/100
 ATM4/0/0.5: VCD: 10, VPI: 10, VCI: 100
 UBR, PeakRate: 50000
 AAL5-LLC/SNAP, etype:0x0, Flags: 0x20, VCmode: 0x0
 OAM frequency: 0 second(s), OAM retry frequency: 1 second(s), 
 OAM retry frequency: 1 second(s)
 OAM up retry count: 3, OAM down retry count: 5
 OAM Loopback status: OAM Disabled
 OAM VC state: Not Managed
 ILMI VC state: Not Managed
 InARP frequency: 15 minutes(s)
 Transmit priority 4
 [snip]

Verify

Use this section to confirm that your configuration works properly.

The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.

show atm vp—Displays the configuration of the PVP.
show atm vp {vpi#} —Displays packet counts for each PVC and for the PVP overall.
show atm vc—Displays the encapsulation and shaping parameters of the PVCs in the PVP.
show atm vc {vcd#} —Displays packet counts and other statistics per VC.

7500-1.5#show atm vp 
  Data CES Peak CES 
  Interface VPI VCs VCs    Kbps Kbps Status 
  ATM4/0/0   10 2    0     50000 0    ACTIVE

7500-1.5#show atm vp 10 
  ATM4/0/0 VPI: 10, PeakRate: 50000, CesRate: 0, DataVCs: 2,
 CesVCs: 0, Status: ACTIVE 
 VCD VCI Type InPkts    OutPkts AAL/Encap Status 
  8  3   PVC    0 0    F4 OAM ACTIVE 
  9  4   PVC    0 0    F4 OAM ACTIVE 
  10 100 PVC    0 0    AAL5-SNAP ACTIVE 
  11 110 PVC    0 0    AAL5-SNAP ACTIVE 
TotalInPkts: 0, TotalOutPkts: 0, TotalInFast: 0, TotalOutFast: 0,
 TotalBroadcasts: 0 
  TotalInPktDrops: 0, TotalOutPktDrops: 0

7500-1.5#show atm vc 
  VCD /    Peak   Avg/Min Burst 
 Interface Name   VPI  VCI Type    Encaps SC Kbps Kbps Cells Sts 
  4/0/0 8    10 3  PVC  F4-OAM    UBR 50000    UP 
  4/0/0 9    10 4  PVC  F4-OAM    UBR 50000    UP 
  4/0/0.5    10 10 100  PVC SNAP  UBR 50000    UP    
  4/0/0.10   11 10 110  PVC SNAP  UBR 50000    UP

500-1.5#show atm vc 10
  ATM4/0/0.5: VCD: 10, VPI: 10, VCI: 100
  UBR, PeakRate: 50000 
  AAL5-LLC/SNAP, etype:0x0, Flags: 0x20, VCmode: 0x0 
  OAM frequency: 0 second(s) 
  InARP frequency: 15 minutes(s) 
  Transmit priority 4 
  InPkts: 0, OutPkts: 0, InBytes: 0, OutBytes: 0 
  InPRoc: 0, OutPRoc: 0, Broadcasts: 0 
  InFast: 0, OutFast: 0, InAS: 0, OutAS: 0 
  InPktDrops: 0, OutPktDrops: 0 
  CrcErrors: 0, SarTimeOuts: 0, OverSizedSDUs: 0, LengthViolation: 0,
  CPIErrors: 0 
  Out CLP=1 Pkts: 0 
  OAM cells received: 0 
  OAM cells sent: 0 
  Status: UP

Troubleshoot

There is currently no specific troubleshooting information available for this configuration.

Related Information

Configuring VP Shaping on the 4xOC3ATM Line Card for the GSR
Configuring ATM
Tools and Utilities - Cisco Systems (registered customers only)
ATM Technical Support
Technical Support & Documentation - Cisco Systems

Updated: Jun 05, 2005

Document ID: 10534

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