JUNOSe 9.1.x Quality of Service Configuration Guide > Configuring Variables in the Simple Shared Shaping Algorithm > Sample Process for Controlling the Simple Shared Shaper Algorithm

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 10 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 10: 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 25 shows a graph of the dynamic rate when the video flow starts.

Figure 25: Dynamic Rate When Video Flow Starts

Stopping Video Flow

Table 11 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 11: 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 26 shows a graph of the dynamic rate when the video flow stops.

Figure 26: Dynamic Rate When Video Flow Stops

Related Topics

• Simple Shared Shaping Algorithm Overview
• Variables of the Simple Shared Shaper Algorithm
• Configuring Simple Shared Shaper Algorithm Variables