Scheduling and Shaping on SONET/SDH OC48/STM16 IQE PICs

The SONET/SDH OC48/STM16 IQE PIC supports the following scheduling and the shaping behavior:

Per unit scheduling via data-link connection identifier (DLCI) at egress, where each DLCI gets a dedicated set of queues and a scheduler.

Note:
Because the SONET/SDH OC48/STM16 IQE PIC is not an oversubscribed PIC, there is no ingress queuing. therefore, the ingress scheduling or shaping is not supported in SONET/SDH OC48/STM16 IQE PIC.
When a per unit scheduling is configured , the shaping can be configured at the logical and the physical interface levels.
In both guaranteed and excess regions, the traffic on queues at the same priority is scheduled in weighted-round-robin (WRR) discipline and there is no shaping at queue-level.

On SONET/SDH OC48/STM16 IQE interfaces, you can configure a CIR (guaranteed rate) and a PIR (shaping rate) per data-link connection identifier (DLCI). The configured rates are gathered into a traffic control profile. If you configure a traffic control profile with a CIR (guaranteed rate) only, the PIR (shaping rate) is set to the physical interface (port) rate.

The computation of CIR and PIR on logical interfaces is shown in Table 1. X and Y are values configured from the command-line interface.

Table 1: Computation of CIR and PIR on the Logical Interfaces
Port Mode	Junos OS CLI Configuration		SONET/SDH OC48/STM16 IQE PIC
Port Mode	Configured CIR	Configured PIR	Computed CIR	Computed PIR
Default (no CIR or PIR configured on logical interface)	Not configured	Not configured	Port speed	Port speed
Both CIR and PIR are configured on logical interface	X	Y	X	Y
CIR Mode (CIR is configured on at least one logical interface)	X	Not configured	X	Port speed
	Not configured	Y	50 Kbps	Y
	Not configured	Not configured	50 Kbps	Port speed
PIR Mode (PIR is configured on at least one logical interface)	Not configured	Y	Y	Y
	Not configured	Not configured	Remaining (port speed minus sum of PIRs of other logical interfaces) bandwidth is equally divided.	Port speed

The SONET/SDH OC48/STM16 IQE PIC supports rate limit on all queues. The computation of rate limit is shown in Table 2.

Table 2: Computation of Rate for the Rate Limit Configured on the Queue with Transmit Rate Percentage
Scenario	Configured CIR Value for the Logical Interface or DLCI	Configured PIR Value for the Logical Interface or DLCI	SONET/SDH OC48/STM16 IQE PIC
1	No	No	Port value
2	Yes	No	CIR value
3	No	Yes	PIR value
4	Yes	Yes	CIR value

Note:

When the queue transmission rates are oversubscribed, the rate-limit option configured on any of the queues uses the configured rate limit values, although the transmission rates are oversubscribed.

Transmit Rate Adding Up to More than 100 Percent

The SONET/SDH OC48/STM16 IQE PIC supports the maximum bandwidth optimization by overconfiguring the bandwidth up to 300 percent.

When the sum of transmission rates for all queues exceeds 100 percent, the interface is in an oversubscribed state. At the time of oversubscription, the queues are split into three priority groups. :

Strict-High
High, Medium-High, and Medium-Low
Low

This computation is done after the internal mapping of the excess priority or the excess rate.

The sum of transmission rates for all queues in each of the priority groups is less than or equal to 100 percent, thereby allowing the SONET/SDH OC48/STM16 IQE PICs to support the maximum bandwidth optimization by overconfiguring the available bandwidth up to 300 percent.

Note:

The remainder option is not supported on an oversubscribed SONET/SDH OC48/STM16 IQE PIC. When the sum of transmission rates for all queues exceeds 100 percent, and if one or more queues are configured with the remainder option, a syslog error message is generated and the configuration is ignored.
When the sum of transmission rates of all queues in any of the priority groups exceeds 100 percent, the commit fails and an error message is displayed.

Scheduling and Shaping on SONET/SDH OC48/STM16 IQE PICs

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