Sample Process for Controlling the Simple Shared Shaper Algorithm

The simple shared shaper in this example contains two constituents, best-effort and video. The shared-shaping rate is 15 Mbps, and the video rate is 4 Mbps.

The example contains two parts: when the video flow is turned on, and then turned off.

Note: The rates in this example are approximate and for illustrative purposes only. Your configuration might yield different results based on network variables.

Starting Video Flow

Table 9 lists the dynamic rate when the video flow is turned on for the five classes of simple shared shaper variables. Results vary because the amount of video measured in the first rising period is random, in the range 0–4 Mbps non-inclusive.

Table 9: Rising Edge Sample When Video Flow Starts

 

Period of Dynamic Rate, in Kbps

Control

1

2

3

4

5

6

7

8

9

10

Most liberal

15000

13080

11000

11000

11000

11000

11000

11000

11000

11000

Liberal

15000

9542

8880

10470

10867

10972

10979

10994

10998

10994

Moderate

15000

6510

5606

8303

9651

10329

10628

10814

10967

10953

Conservative

15000

6022

1604

3953

5714

7038

7978

8733

9300

9735

Most conservative

In this example, a liberal maximum VOQL value is ineffective because the 15 Mbps shared-shaping rate is much higher than the 4 Mbps video rate. The video rate divided by the shared shaping rate is 26.6 percent, so any value higher than this has no effect.

Note: The rates in this example represent approximate egress-queue enqueue rates on an Ethernet line module; therefore, there is no ATM SAR or downstream devices are not used. More liberal configurations can be inappropriate when there might be queuing between the scheduler and the destination. VLAN queuing is used, and saturation rates are offered.

The most liberal case heavily reduces VOQL and changes of rate, leading to a shared shaper that quickly converges. The conservative configuration overreacts to VOQL and the change of rate, and converges very slowly.

Figure 26 shows a graph of the dynamic rate when the video flow starts.

Figure 26: Dynamic Rate When Video Flow Starts

Dynamic Rate When Video Flow Starts

Stopping Video Flow

Table 10 lists the dynamic rate as the video flow stops for the five classes of simple shared shaper controls. Results might vary because the amount of video measured in the first falling period is random, in the range 0–4 Mbps non-inclusive.

Table 10: Data When Video Flow Stops

 

Period of Dynamic Rate, in Kbps

Control

1

2

3

4

5

6

7

8

9

10

Most liberal

11000

12132

15000

15000

15000

15000

15000

15000

15000

15000

Liberal

11000

11584

14146

14786

14946

14986

14996

14999

14999

15000

Moderate

11000

11728

13364

14182

14591

14795

14897

14948

14974

14987

Conservative

10955

11278

12208

12906

13429

13822

14116

14337

14503

14701

Most conservative

Figure 27 shows a graph of the dynamic rate when the video flow stops.

Figure 27: Dynamic Rate When Video Flow Stops

Dynamic Rate When Video Flow Stops

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