8. ATM QoS Traffic Descriptor Profiles
This chapter provides information to configure QoS traffic descriptor profiles using the command line interface.
Topics in this chapter include:
8.1. ATM Traffic Descriptor Profiles
This section provides a description of support for ATM QoS policy features. Each traffic descriptor defines the expected rates and characteristics of traffic.
8.1.1. ATM Traffic Management
The 7705 SAR supports the ATM Forum Traffic Management Specification Version 4.1.
This section contains the following topics related to the QoS features for ATM Permanent Virtual Connections (PVCs):
8.1.1.1. ATM Service Categories
The 7705 SAR supports the following service categories:
- CBR – Constant Bit Rate
- rt-VBR – Real-Time Variable Bit Rate
- nrt-VBR –Non-Real-Time Variable Bit Rate
- UBR/UBR+MIR – Unspecified Bit Rate with Minimum Cell Rate (UBR is a special case of UBR+MIR where MIR=0)
8.1.1.2. ATM Traffic Descriptors and QoS Parameters
Table 52 shows the ATM traffic descriptors supported on the 7705 SAR.
Table 52: ATM Traffic Descriptors
Service Category | Traffic Descriptors |
CBR | P0_1 |
PIR in kb/s (applies to CLP=0 and CLP=1 flows) | |
rt-VBR and nrt-VBR | P0_1 and S0_1 |
PIR in kb/s (applies to CLP=0 and CLP=1 flows) | |
SIR in kb/s (applies to CLP=0 and CLP=1 flows) | |
MBS in cells (applies to CLP=0 and CLP=1 flows) | |
P0_1 and S0 | |
PIR in kb/s (applies to CLP=0 and CLP=1 flows; non-conforming CLP=0 cells are discarded) | |
SIR in kb/s (applies to CLP=0 flow only) | |
MBS in cells (applies to CLP=0 flow only) | |
P0_1 and S0_Tag | |
PIR in kb/s (applies to CLP=0 and CLP=1 flows; non-conforming CLP=0 flows are tagged to CLP=1 flows) | |
UBR/UBR+MIR | P0_1 |
PIR in kb/s (applies to CLP=0 and CLP=1 flows) | |
MIR in kb/s (applies to CLP=0 and CLP=1 flows) |
8.1.1.3. ATM Policing
The policing option, when enabled, applies only to ingress traffic. Similarly, the shaping option, if enabled, applies only to egress traffic. For example, if a traffic descriptor has both policing and shaping enabled, the policing option is enforced for the ingress traffic, while the shaping option is enforced for the egress traffic. The following ATM service category conformance definitions are supported:
- P0_1 – CBR
- P0_1 and S0_1 – VBR.1
- P0_1 and S0 – VBR.2
- P0_1 and S0_Tag – VBR.3
P represents the peak rate, S represents the sustained rate, 0 or 1 represents the CLP value to which policing is applied if the cell is non-conforming, and Tag indicates that the CLP value has changed from 0 to 1. For example:
- P0_1 — means that policing is applied to non-conforming peak rate cells with CLP values of 0 or 1
- P0_1 and S0_Tag — means that policing is applied to non-conforming peak rate cells with CLP values of 0 or 1 and policing is applied to non-conforming sustained rate cells with a CLP value of 0 with the action to change the CLP value to 1
8.1.1.4. Shaping
ATM layer egress shaping is supported for CBR, rt-VBR, and nrt-VBR VCs. A CBR VC is shaped to a single leaky bucket with the parameter PIR from the traffic descriptor. An rt-VBR VC or an nrt-VBR VC is shaped to two leaky buckets with parameters PIR and SIR, BT from the traffic descriptor, where BT is the Burst Tolerance and is a function of the MBS parameters configured by the user. The traffic rates and shaping parameter that are configured in the sap-egress QoS policy are not used at ATM SAPs.
In order to enforce the Service Level Agreement, ATM layer ingress policing is supported at ingress, so no shaping is needed. At ingress, after optional policing is applied, packet level queue-based soft-policing is supported per the service ingress QoS policy applied to the ATM SAP.
 | Note: Shaping to the specified traffic descriptor in the ATM traffic descriptor profile is always enabled for CBR and rt-VBR VCs. |
8.1.1.5. ATM Queuing and Scheduling
The 7705 SAR provides a per-VC queuing architecture on the 16-port T1/E1 ASAP Adapter card, 32-port T1/E1 ASAP Adapter card, and 2-port OC3/STM1 Channelized Adapter card with atm/ima encapsulation. The 7705 SAR provides a per-VC queuing architecture on the 4-port OC3/STM1 Clear Channel Adapter card and 4-port DS3/E3 Adapter card with atm encapsulation. In the egress direction toward the ATM port, the scheduling priority at the ATM layer is as follows.
- CBR VCs are always shaped and are scheduled with strict priority over all other service categories.
- rt-VBR VCs are always shaped and are scheduled next with strict priority over nrt-VBR and UBR VCs.
- nrt-VBR shaped VCs are scheduled next with strict priority over nrt-VBR unshaped VCs and UBR VCs.
- nrt-VBR unshaped VCs and UBR VCs are scheduled as a common class. Scheduling among these VCs is done using a Weighted Round Robin (WRR) scheduler, where the weight of each VC is determined by the configured SIR for nrt-VBR and by the MIR for UBR VCs. The scheduling is work-conserving, so each VC has access to excess bandwidth in proportion to its SIR/MIR. Under congestion, the performance of each VC degrades proportionally to the weight of the VC.
8.1.1.6. Congestion Avoidance
Congestion and potential discards are performed on a per-forwarding class basis in the SAP queues in the CSM.
8.2. Basic Configuration
This section contains the following topics related to creating and applying ATM QoS policies:
A basic ATM QoS traffic descriptor profile must conform to the following rules.
- Each policy must have a unique policy ID.
- Default values can be modified but parameters cannot be deleted.
8.2.1. Creating an ATM Traffic Descriptor Profile QoS Policy
Configuring and applying QoS policies and profiles other than the default policy is optional. To create an ATM QoS traffic descriptor profile, perform the following:
- assign a policy ID (policy number) — the system does not dynamically assign an ID
- include a description — provides a brief overview of policy features
- configure traffic attributes of the ATM traffic profile
- determine whether egress shaping should occur
Use the following CLI syntax to configure an atm-td-profile policy.
The following output displays an example of the command syntax.
The following output displays the profile configuration for ATM TD profile 3:
8.2.2. Applying ATM Traffic Descriptor Profile Policies
ATM QoS traffic descriptor profiles are applied to ATM VLL (Apipe) SAPs. ATM QoS traffic descriptor profiles can also be applied on egress to ATM VCC SAPs that are members of a SAP aggregation group. You cannot apply ATM QoS traffic descriptor profiles on ingress to a SAP in a SAP aggregation group; the profile is set to the default (1).
8.2.2.1. ATM VLL (Apipe) SAPs
Use the following CLI syntax to apply ATM QoS traffic descriptor profile policies to Apipe SAPs on ingress and egress.
8.2.3. Default ATM Traffic Descriptor Profile Policy Values
The default ATM QoS traffic descriptor profile is 1. The default profile cannot be edited or deleted.
Table 53 below shows the ATM TD profile defaults.
Table 53: ATM-TD-Profile Defaults
Field | Default |
atm-td-profile traffic-desc-profile-id | 1 |
description | Default Traffic Descriptor |
descriptor-type | Based on service category: CBR: P0_1 UBR: P0_1 UBR+MIR: P0_1 rt-VBR or nrt-VBR: P0_1 and S0 _ 1 |
policing | No policing |
service-category | UBR |
traffic | No traffic |
shaping | No shaping |
The following output displays the default configuration:
8.3. Service Management Tasks
This section describes the following ATM Traffic Descriptor Profile service management tasks:
8.3.1. Removing an ATM Traffic Descriptor Profile from the QoS Configuration
The default ATM traffic descriptor profile cannot be deleted.
To delete an ATM QoS traffic descriptor profile, enter the following command:
8.3.2. Copying and Overwriting an ATM Traffic Descriptor Profile
You can copy an existing profile, rename it with a new profile ID value, or overwrite an existing profile ID. The overwrite option must be specified or an error occurs if the destination profile ID exists.
8.3.3. Editing QoS Policies
You can change existing policies and entries in the CLI. The changes are applied immediately to all services where this policy is applied. To prevent configuration errors, copy the policy to a work area, make the edits, and then write over the original policy.