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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

216

One important property of this mode is that higher QoS classes can block lower QoS classes. A

congested flow with a high QoS class uses all of the shared resources up to its threshold setting and

frame with lower QoS classes are thus affected (lower burst capacity).

The following table shows the configuration settings for strict priority sharing mode.

3.24.4.2 Per Priority Sharing

This mode sets aside some memory for each QoS class and can in addition have an amount of memory

reserved for green traffic only. This mode operates on ingress resources, in order to utilize that frames

with multiple destinations are only stored once.

Figure 58 •

Per Priority Sharing

The following table shows the configuration settings for per priority sharing mode.

Table 144 •

Strict Priority Sharing Configuration Settings

Configuration

Setting

Reservation thresholds

These can be set to any desired value. The amount set aside for each account should

be subtracted from the overall resource size, before the sharing thresholds are set up.

Ingress QoS class thresholds

Levels at which each QoS class should start to reject further enqueuing. Frames with

multiple destinations are only accounted once because they are physically only

stored once.

Ingress color thresholds

Set to their maximum value to disable. The color is not considered in this mode.

WRED group memberships

Disable all.

Egress sharing thresholds

Set all to 0, because only use ingress sharing control is . Egress would account for

multiple copies, which is not intended.

QoS reservation

(QRES::RES_QOS_MODE)

Disable for all. No shared resources are set aside per QoS class.

Table 145 •

Per Priority Sharing Configuration Settings

Configuration

Setting

Reservation thresholds

These can be set to any desired value, except for ingress per port reservation. The

algorithm requires these to be zeroed.

Ingress QoS class thresholds

Set to amount of shared memory which should be set aside for each QoS class. The

sum of all these should not exceed the amount of memory left after all the

reservations has been subtracted.

Ingress color thresholds

Subtracting all reservations including QoS class shared areas may end up in some

unused memory. Set the color thresholds to various levels to guarantee more space

the greener.

WRED group memberships

Disable all.

Egress sharing thresholds

Set all to 0, as we only use ingress sharing control. Egress would account for

multiple copies, which is not intended.

d Res

ource

DP=3 limit

DP=2 limit

DP=1 limit

DP=0 limit

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