Port-Based Rate Limiting, Policing, and Shaping

Table 1. Port-Based Rate Limiting, Policing, and Shaping product support

Feature

Product

Release introduced

Egress port shaper

5320 Series

Fabric Engine 8.6

5420 Series

VOSS 8.4

5520 Series

VOSS 8.2.5

5720 Series

Fabric Engine 8.7

7520 Series

Fabric Engine 8.10

7720 Series

Fabric Engine 8.10

VSP 4900 Series

VOSS 8.1

VSP 7400 Series

VOSS 8.0

Ingress policer and port rate limiter

5320 Series

Fabric Engine 8.6

5420 Series

VOSS 8.5

5520 Series

VOSS 8.5

5720 Series

Fabric Engine 8.7

7520 Series

Fabric Engine 8.10

7720 Series

Fabric Engine 8.10

VSP 4900 Series

VOSS 8.5

VSP 7400 Series

VOSS 8.5

QoS ingress port-based rate limiter

5320 Series

Not Supported

5420 Series

Not Supported

5520 Series

Not Supported

5720 Series

Not Supported

7520 Series

Not Supported

7720 Series

Not Supported

VSP 4900 Series

VOSS 8.1

VSP 7400 Series

Not Supported

The switch QoS implementation supports egress port-based shaping for bandwidth management and traffic control. Egress port-based shaping is the process by which the system delays and transmits packets to produce an even and predictable flow rate.

Each port has eight unicast and multicast queues, Class of Service (CoS) 0 to CoS 7. Traffic shaping exists on the egress CoS 6 and CoS 7, but you cannot change the configuration. CoS 6 and CoS 7 are strict priority queues, with traffic shaping for CoS 6 at 50 percent and CoS 7 to five percent of line rate.

Each feature is important to deliver DiffServ within a QoS network domain.

The switch supports an ingress flow-based policer for ACLs. For information, see Ingress Policer and Port Rate Limiter.

Token Buckets

Tokens are a key concept in traffic control. A port-based rate limiter, policer, shaper, or an ingress flow-based policer calculates the number of packets that passed, and at what data rate. Each packet corresponds to a token, and the port-based rate limiter, policer, shaper, or an ingress flow-based policer transmits or passes the packet if the token is available. For more information, see Token flow.

The token container is like a bucket. In this view, the bucket represents both the number of tokens that a port-rate limiter, policer, or shaper can use instantaneously (the depth of the bucket) and the rate at which the tokens replenish (how fast the bucket refills).

Each policer has two token buckets: one for the peak rate and the other for the service rate. The following figure shows the flow of tokens.

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Token flow