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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

214

The congestion control information from the analyzer result involved in the congestion control is listed in

the following table.

The current consumption of resources in the congestion controller is updated when a reference is added

to one of the egress queues. The congestion controller tracks four different resources:

•

Ingress packet memory consumption. Each frame uses a number of 176-byte words.

•

Egress packet memory consumption. Each frame uses a number of 176-byte words.

•

Ingress frame reference consumption. Each frame uses one frame reference per frame copy.

•

Egress frame reference consumption. Each uses one frame reference per frame copy.

There are 5,952 memory words and 5,952 frame references in total.

The accounting is done based on QoS classes and port numbers. Each account has a threshold

specifying how many resources the account is permitted to consume. The accounts are as follows:

•

Consumption per port per QoS class. This is a reservation account.

•

Consumption per port. A frame does not consume resources from this account before the resources

belonging to the previous account are consumed. This is a reservation account.

•

Consumption per QoS class. A frame does not consume resources from this account before the

resources belonging to the previous two accounts are consumed. This is a sharing account.

•

Consumption in addition to the above. A frame does not consume from this account before the

resources belonging to the previous three accounts are consumed. This is a sharing account.

The congestion controller updates an accounting sheet with the listed accounts for each of the tracked

resources.

The following illustration shows reservation accounts for the packet memory accounting sheets when a

700-byte frame from port 0 forwarded to ports 1 and 5 with QoS class 2 is added. The frame size

requires the use of five words in the packet memory. The account for ingress port 0, QoS class 2 is

reserved three words. Before the frame is added, it is checked if the account was fully utilized. If the

account was not fully used, the frame is allowed into the queue system. After the frame is added, the

account is updated with the five words and therefore uses two more than was reserved. These are

consumed from the port account. The port account is reserved 0 words and the added two words

therefore also close the port account. This affects further frame reception.

In the egress side, there are no words reserved for the account per port, per QoS class. The port account

for port 1 is reserved 8 words and 0 for port 5.

Figure 55 •

Accounting Sheet Example

Table 143 •

Analyzer Congestion Results

Field

Function

Drop mode

This frame can be dropped even if port is setup for flow control. This function is mainly used by the

analyzer for stacking use where the ingress unit's source port determines how congestion should

be handled.

Drop precedence level. A value 0-3, telling how yellow the frame is.

QoS class

Frame’s ingress QoS class

Priority

Port

0 1

...

Packet memory, ingress user

Priority

Port

0 1

...

Packet memory, egress user

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