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Excess Rate and Excess Priority Configuration Examples

To configure the excess rate for nonqueuing Packet Forwarding Engines, include the excess-rate statement at the [edit class-of-service schedulers scheduler-name] hierarchy level.

To configure the excess priority for nonqueuing Packet Forwarding Engines, include the excess-priority statement at the [edit class-of-service schedulers scheduler-name] hierarchy level.

The relationship between the configured guaranteed rate, excess rate, guaranteed priority, excess priority, and offered load is not always obvious. The following tables show the expected throughput of a Gigabit Ethernet port with various bandwidth-sharing parameters configured on the queues.

The default behavior of a nonqueuing Gigabit Ethernet interface with multiple priority levels is shown in Table 1. All queues in the table get their guaranteed rate. The excess bandwidth is first offered to the excess high-priority queues. Because these use all available bandwidth, these is no remaining excess bandwidth for the low-priority queues.

Table 1: Current Behavior with Multiple Priority Levels

Queue	Guaranteed (Transmit) Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	high	high	600 Mbps	200 + 366.67 = 566.67 Mbps
Q1	10%	high	high	500 Mbps	100 + 183.33 = 283.33 Mbps
Q2	10%	low	low	500 Mbps	100 + 0 = 100 Mbps
Q3	5%	low	low	500 Mbps	50 + 0 = 50 Mbps

The default behavior of a nonqueuing Gigabit Ethernet interface with the same priority levels is shown in Table 2. All queues in the table get their guaranteed rate. Because all queues have the same excess priority, they share the excess bandwidth and each queue gets excess bandwidth in proportion to the transmit rate.

Table 2: Current Behavior with Same Priority Levels

Queue	Guaranteed (Transmit) Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	high	high	500 Mbps	200 + 244.44 = 444.44 Mbps
Q1	10%	high	high	500 Mbps	100 + 122.22 = 222.22 Mbps
Q2	10%	high	high	500 Mbps	100 + 122.22 = 222.22 Mbps
Q3	5%	high	high	500 Mbps	50 + 61.11= 111.11 Mbps

The default behavior of a nonqueuing Gigabit Ethernet interface with the at least one strict-high priority level is shown in Table 3. First the high priority and strict-high are serviced in a weighted round-robin fashion. The high priority queue gets its guaranteed bandwidth and the strict-high queue gets what remains. The high excess priority queue gets all the excess bandwidth.

Table 3: Current Behavior with Strict-High Priority

Queue	Guaranteed (Transmit) Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	strict-high	X	500 Mbps	500 Mbps
Q1	10%	high	high	500 Mbps	100 + 250 = 350 Mbps
Q2	10%	low	low	500 Mbps	100 + 0 = 100 Mbps
Q3	5%	low	low	500 Mbps	50 + 0= 50 Mbps

The default behavior of a nonqueuing Gigabit Ethernet interface with the at least one strict-high priority level and a higher offered load on Q0 is shown in Table 4. First the high priority and strict-high are serviced in a weighted round-robin fashion. The high priority queue gets its guaranteed bandwidth and the strict-high queue gets what remains. There is no excess bandwidth.

Table 4: Strict-High Priority with Higher Load

Queue	Guaranteed (Transmit) Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	strict-high	X	1 Gbps	900 Mbps
Q1	10%	high	high	500 Mbps	100 + 0 = 100 Mbps
Q2	10%	low	low	500 Mbps	0 + 0 = 0 Mbps
Q3	5%	low	low	500 Mbps	0 + 0= 0 Mbps

Now consider the behavior of the queues with configured excess rates and excess priorities.

The behavior with multiple priority levels is shown in Table 5. All queues get the guaranteed rate. The excess bandwidth is first offered to the excess high priority queues and these consume all the bandwidth. There is no remaining excess bandwidth for low priority queues.

Table 5: Sharing with Multiple Priority Levels

Queue	Guaranteed (Transmit) Rate	Excess Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	10%	high	high	500 Mbps	200 + 275 = 475 Mbps
Q1	10%	20%	high	low	500 Mbps	100 + 0 = 100 Mbps
Q2	10%	10%	low	high	500 Mbps	100 + 275 = 275 Mbps
Q3	5%	20%	low	low	500 Mbps	50 + 0= 50 Mbps

The behavior with the same (high) priority levels is shown in Table 6. All queues get the guaranteed rate. Because all queues have the same excess priority, they share the excess bandwidth in proportion to their transmit rate.

Table 6: Sharing with the Same Priority Levels

Queue	Guaranteed (Transmit) Rate	Excess Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	10%	high	high	500 Mbps	200 + 91.67 = 291.67 Mbps
Q1	10%	20%	high	high	500 Mbps	100 + 183.33 = 283.33 Mbps
Q2	10%	10%	high	high	500 Mbps	100 + 91.67 = 191.67 Mbps
Q3	5%	20%	high	high	500 Mbps	50 + 183.33 = 233.33 Mbps

The behavior with at least one strict-high priority level is shown in Table 7. The high priority and strict-high queues are serviced in a weighted round-robin fashion. The high priority queue gets its guaranteed rate and the strict-high queue gets the rest. The excess high-priority queue get all the excess bandwidth.

Table 7: Sharing with at Least One Strict-High Priority

Queue	Guaranteed (Transmit) Rate	Excess Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	X	strict-high	X	500 Mbps	500 Mbps
Q1	10%	20%	high	low	500 Mbps	100 + 0 = 100 Mbps
Q2	10%	10%	low	high	500 Mbps	100 + 250 = 350 Mbps
Q3	5%	20%	low	low	500 Mbps	50 + 0 = 50 Mbps

The behavior with at least one strict-high priority level and a higher offered load is shown in Table 8. The high priority and strict-high queues are serviced in a weighted round-robin fashion. The high priority queue gets its guaranteed rate and the strict-high queue gets the rest. There is no excess bandwidth.

Table 8: Sharing with at Least One Strict-High Priority and Higher Load

Queue	Guaranteed (Transmit) Rate	Excess Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	X	strict-high	X	900 Mbps	900 Mbps
Q1	10%	20%	high	low	500 Mbps	100 + 0 = 100 Mbps
Q2	10%	10%	low	high	500 Mbps	0 + 0 = 0 Mbps
Q3	5%	20%	low	low	500 Mbps	0 + 0 = 0 Mbps

The behavior with at least one strict-high priority level and a rate limit is shown in Table 9. Queue 0 and Queue 2 are rate limited, so the maximum bandwidth they are offered is the transmit bandwidth and they will not be offered any excess bandwidth. All other queues are offered the guaranteed bandwidth and the excess is shared by the non-rate-limited queues.

Table 9: Sharing with at Least One Strict-High Priority and Rate Limit

Queue	Guaranteed (Transmit) Rate	Rate Limit	Excess Rate	Guaranteed Priority	Excess Priority	Offered Load	Expected Throughput
Q0	20%	Yes	X	strict-high	X	500 Mbps	200 + 0 = 200 Mbps
Q1	10%	No	20%	high	low	500 Mbps	100 + 275 = 375 Mbps
Q2	10%	Yes	10%	low	high	500 Mbps	100 + 0 = 100 Mbps
Q3	5%	No	20%	low	low	500 Mbps	50 + 275 = 325 Mbps

Configuring the Schedulers

The following example configures schedulers, forwarding classes, and a scheduler map for an interface with excess rates and excess priorities.

[edit class-of-service schedulers]

scheduler-1 {transmit-rate percent 20;priority high;excess-rate percent 10;excess-priority low;}

scheduler-2 {transmit-rate percent 10;priority strict-high;}

scheduler-3 {transmit-rate percent 10;priority medium-high;excess-rate percent 20;excess-priority high;}

scheduler-4 {transmit-rate percent 5;priority medium-high;excess-rate percent 30;excess-priority low;}

Configuring the Forwarding Classes

[edit class-of-service]

forwarding-classes {class cp_000 queue-num 0;class cp_001 queue-num 1;class cp_010 queue-num 2;class cp_011 queue-num 3;class cp_100 queue-num 4;class cp_101 queue-num 5;class cp_110 queue-num 6;class cp_111 queue-num 7;}

Configuring the Scheduler Map

[edit class-of-service scheduler-maps]

scheduler-map-1 {forwarding-class cp_000 scheduler scheduler-1;forwarding-class cp_001 scheduler scheduler-2;forwarding-class cp_010 scheduler scheduler-3;forwarding-class cp_011 scheduler scheduler-4;}

Applying the Scheduler Map to the Interface

[edit interfaces]

ge-1/1/0 {scheduler-map scheduler-map-1;unit 0 {family inet {address 192.168.1.2/32;}}}

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Supported Platforms

Excess Rate and Excess Priority Configuration Examples

Published: 2013-08-28

Supported Platforms

Published: 2013-08-28