VSC7440 datasheet(253/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

236

Figure 72 •

Fine Tuning Bandwidth of DTI Sequence

By combining the setting of INJ_CNT and the DELAY value of the last delay depicted, the bandwidth of

the DTI sequence can be controlled with high granularity, because the additional (blue) delay will only be

applied for every INJ_CNT injections of frame A.

The bandwidth adjustment mechanism shown may be insufficient for controlling the bandwidth of multi-

frame sequences (sequences with different frames), because the last delay will be applied for every

injection of the frame sequence.

3.25.3.3 Fine Tuning Bandwidth of Multiframe Sequence

For multiframe sequences, additional fine tuning of the bandwidth of the entire sequence can be

achieved by configuring the last delay in the sequence, also known as the “trailing delay”, to only be

applied for every Nth injection of the sequence. This is achieved using the

TRAILING_DELAY_SEQ_CNT parameter and is shown in the following illustration.

Figure 73 •

Fine Tuning Bandwidth of Multiframe DTI Sequence

3.25.3.4 Burst Size Test Using Single DTI

If a NEXT_PTR is set to point back to a previous entry in the sequence, then injection will continue

forever, that is, until the DTI is stopped. This is depicted in the following illustration. The configuration

shown can be used for leaky bucket burst size testing, where the first part of the sequence empties the

bucket, followed by a steady frame flow with the rate of the leaky bucket.

DTI

Frame A

INJ_CNT=4

Delay

DELAY=150

FIRST_PTR

150

Time

Frame A

Resulting frame sequence:

150

Frame A

...

NEXT_PTR=0

150

Frame A

150

Frame A

Delay

DELAY=3

Fine tune bandwidth

of DTI sequence.

DTI

TRAILING_DELAY_SEQ_CNT = 2

Frame A

Delay

DELAY=150

FIRST_PTR

Frame B

INJ_CNT=2

Delay

DELAY=100

Delay

DELAY=50

Delay

DELAY=1

150

100

100 + 50 = 150

Time

Frame A

Frame B

Resulting frame sequence:

...

Inserted after each

injection of Frame B.

Inserted after last injection of

Frame B.

NEXT_PTR=0

Inserted after every

second sequence injection.

150

100

100 + 50 = 150

Frame A

Frame B

Frame A

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