VSC7511 datasheet(139/324 Pages) MICROSEMI

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Functional Descriptions

VMDS-10488 VSC7511 Datasheet Revision 4.2

124

When a frame is enqueued into the shared queue system, the frame consumes first from the queue’s

reserved frame reference area, then from the port’s reserved frame reference area. When all the frame’s

reserved frame reference areas are full, it consumes from the shared frame reference area.

3.11.3

Resource Depletion Condition

A frame copy is made from an ingress port to an egress port when both a memory check and a frame

reference check succeed. The memory check succeeds when at least one of the following conditions is

met.

•

Ingress memory is available: BUF_Q_RSRV_I or BUF_P_RSRV_I are not exceeded.

•

Egress memory is available: BUF_Q_RSRV_E or BUF_P_RSRV_E are not exceeded.

•

Shared memory is available: None of BUF_PRIO_SHR_E, BUF_COL_SHR_E, BUF_PRIO_SHR_I,

or BUF_COL_SHR_I are exceeded.

The frame reference check succeeds when at least one of the following conditions is met.

•

Ingress frame references are available: REF_Q_RSRV_I or REF_P_RSRV_I are not exceeded.

•

Egress frame references are available: REF_Q_RSRV_E or REF_P_RSRV_E are not exceeded.

•

Shared frame references are available: None of REF_PRIO_SHR_E, REF_COL_SHR_E,

REF_PRIO_SHR_I, or REF_COL_SHR_I are exceeded.

3.11.4

Configuration Example

This section provides an example of how the watermarks can be configured for a QoS-aware switch with

no color handling and the effects of the settings.

Table 98 •

Watermark Configuration Example

Watermark

Value

Comment

BUF_Q_RSRV_I

500 bytes

Guarantees that a port is capable of receiving at least one

frame in all QoS classes.

Note It is not necessary to assign a full MTU, because the

watermarks are checked before the frame is added to the

memory consumption.

BUF_P_RSRV_I

No additional guarantees for the ingress port.

BUF_Q_RSRV_E

200 bytes

Guarantees that all QoS classes are capable of sending a

non-congested stream of traffic through the switch.

BUF_P_RSRV_E

10 kilobytes

Guarantees that all egress ports have 10 kilobytes of

buffer, independently of other traffic in the switch. This is

the most demanding reservation in this setup, reserving

110 kilobytes of the total 224 kilobytes.

BUF_COL_SHR_E

BUF_COL_SHR_I

Maximum

Effectively disables frame coloring as watermark is never

reached.

BUF_PRIO_SHR_E

BUF_PRIO_SHR_I

42 kilobytes to

63 kilobytes

The different QoS classes are cut-off with 3 kilobytes

distance (42, 45, 48, 51, 54, 57, 60, and 63 kilobytes). This

gives frames with higher QoS classes a larger part of the

shared buffer area. Effectively, this means that the burst

capacity is 52 kilobytes for frames belonging to QoS

class 0 and up to 73 kilobytes for frame belonging to QoS

class 7.

REF_Q_RSRV_E

REF_Q_RSRV_I

For both ingress and egress, this guarantees that four

frames can be pending from and to each port.

REF_P_RSRV_E

REF_P_RSRV_I

For both ingress and egress, this guarantees that an extra

20 frames can be pending, shared between all QoS

classes within the port.

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