Overview
694 Quality of Service Guide
Policing
The policing option, when enabled, applies only for ingress traffic. Similarly, the shaping
option, if enabled, applies only for egress traffic. For example, if a traffic descriptor has both
options, policing and shaping enabled, the policing option is enforced for the ingress traffic,
while the shaping option is enforced for the egress traffic. The policing option is valid for all
service categories. The following ATM service category conformance definitions are
supported:
• P0_1 - CBR, UBR
• P0_1andS0_1 – VBR.1
• P0_1andS0 – VBR.2
• P0_1andS0_Tag – VBR.3
Shaping
• Ingress shaping — ATM layer ingress shaping is not supported. Packet level shaping
is supported as per the service ingress QoS policy applied to the ATM SAP.
• Egress 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 parameter PIR. A rt-
VBR VC or a nrt-VBR VC is shaped to two leaky buckets with parameters PIR and
{SIR, BT}, where BT is the Burst Tolerance and is a function of the MBS parameters
configured by the user in the traffic descriptor.
In the egress direction, packet level shaping is supported as per the service egress
QoS policy applied to the ATM SAP.
ATM Queuing and Scheduling
The router provides a per-VC queuing architecture in the ATM-capable MDAs. In the egress
direction towards the ATM port, the scheduling priority at the ATM layer is as follows:
• CBR VCs are scheduled with strict priority over all other service categories
• rt-VBR VCs 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.
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