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High Performance Two Port 10/100 Managed Ethernet Switch with 32-Bit Non-PCI CPU Interface

Datasheet

SMSC LAN9312

Revision 1.2 (04-08-08)

DATASHEET

6.4.6

Ingress Flow Metering and Coloring

The LAN9312 supports hardware ingress rate limiting by metering packet streams and marking packets

as either Green, Yellow, or Red according to three traffic parameters: Committed Information Rate

(CIR), Committed Burst Size (CBS), and Excess Burst Size (EBS). A packet is marked Green if it does

not exceed the CBS, Yellow if it exceeds to CBS but not the EBS, or Red otherwise.

Ingress flow metering and coloring is enabled via the Ingress Rate Enable bit in the Switch Engine

Ingress Rate Configuration Register (SWE_INGRSS_RATE_CFG). Once enabled, each incoming

packet is classified into a stream. Streams are defined as per port (3 streams), per priority (8 streams),

or per port & priority (24 streams) as selected via the Rate Mode bits in the Switch Engine Ingress

Rate Configuration Register (SWE_INGRSS_RATE_CFG). Each stream can have a different CIR

setting. All streams share common CBS and EBS settings. CIR, CBS, and EBS are programmed via

the Switch Engine Ingress Rate Command Register (SWE_INGRSS_RATE_CMD) and Switch Engine

Ingress Rate Write Data Register (SWE_INGRSS_RATE_WR_DATA).

Each stream is metered according to RFC 2697. At the rate set by the CIR, two token buckets are

credited per stream. First, the Committed Burst bucket is incremented up to the maximum set by the

CBS. Once the Committed Burst bucket is full, the Excess Burst bucket is incremented up to the

maximum set by the EBS. The CIR rate is specified in time per byte. The value programmed is in

approximately 20 nS per byte increments. Typical values are listed in Table 6.3. When a port is

receiving at 10Mbps, any setting faster than 39 has the effect of not limiting the rate.

11 - Listening

Received packets on the port are

discarded.

Transmissions to the port are blocked.

Learning on the port is disabled.

The MAC Address Table should be programmed

with entries that the host CPU needs to receive

(e.g. the BPDU address). The static and override

bits should be set.

The host CPU may send packets to the port in this

state.

10 - Learning

Received packets on the port are

discarded.

Transmissions to the port are blocked.

Learning on the port is enabled.

The MAC Address Table should be programmed

with entries that the host CPU needs to receive

(e.g. the BPDU address). The static and override

bits should be set.

The host CPU may send packets to the port in this

state.

00 - Forwarding

Received packets on the port are

forwarded normally.

Transmissions to the port are sent

normally.

Learning on the port is enabled.

The MAC Address Table should be programmed

with entries that the host CPU needs to receive

(e.g. the BPDU address). The static and override

bits should be set.

The host CPU may send packets to the port in this

state.

Table 6.2 Spanning Tree States (continued)

Port State

Hardware Action

Software Action

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