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    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 1 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 1: 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 1 shows a graph of the dynamic rate when the video flow starts.

    Figure 1: Dynamic Rate When Video Flow Starts

    Dynamic Rate When Video Flow Starts

    Stopping Video Flow

    Table 2 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 2: 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 2 shows a graph of the dynamic rate when the video flow stops.

    Figure 2: Dynamic Rate When Video Flow Stops

    Dynamic Rate When Video Flow Stops

    Published: 2014-08-11