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CoS on Enhanced IQ2 PICs Overview

Some PICs, such as the Gigabit Ethernet Intelligent Queuing 2 (IQ2) and Ethernet Enhanced IQ2 (IQ2E) PICs, have eight egress queues enabled by default on platforms that support eight queues.

The IQ2E PICs preserve all of the features of the IQ2 PICs, such as the default support for eight egress queues on platforms that support eight queues.

The IQ2E PICs add features such as the ability to perform hierarchical scheduling. You can mix IQ2 and IQ2E PICs on the same router.

The IQ2E PICs offer:

  • Three levels of hierarchical CoS

  • More granularity than a high priority queue

  • 16,000 queues

  • 2,000 schedulers with 8 queues

  • 4,000 schedulers with 4 queues

The IQ2E PICs also offer automatic scheduler allocation across ports, so there is no need to reset the PIC when this changes. Random early detection (RED) keeps statistics on a per-drop-profile basis, improving the ability to perform network capacity planning.

When you include the per-unit-scheduler statement at the [edit interfaces interface-name] hierarchy level, each logical interface (unit) gets a dedicated scheduler (one scheduler is reserved for overflow). You can include the per-session-scheduler statement at the [edit interfaces interface-name unit logical-unit-number] hierarchy level to shape Layer 2 Tunneling Protocol (L2TP) sessions. The behavior of these two-port scheduler modes is the same as in IQ2 PICs. However, IQ2E PICs use hierarchical schedulers and not shared schedulers; IQ2E PICs do not support the shared-scheduler statement at the [edit interfaces interface-name] hierarchy level.

For more information about configuring hierarchical schedulers, including examples, see Configuring Hierarchical Schedulers for CoS.

You can shape traffic at the physical interface (port), logical interface (unit), or interface set (set of units) levels. Shaping is not supported at the queue level. However, you can include the transmit-rate statement with the rate-limit option at the [edit class-of-service schedulers scheduler-name] hierarchy level to police the traffic passing through a queue (but only in the egress direction). See Configuring Rate Limits to Protect Lower Queues on IQ2 and Enhanced IQ2 PICs.

At the physical interface (port) level, you can configure only a shaping rate (PIR). At the logical interface (unit) and interface set levels, you can configure both a shaping rate and a guaranteed rate (CIR). Note that the guaranteed rates at any level must be consistent with the parent level’s capacity. In other words, the sum of the guaranteed rates on the logical interface (units) should be less than the guaranteed rate on the interface set, and the sum of the guaranteed rates on the logical interface (units) and interface sets should be less than the guaranteed rate on the physical interface (port).

You can control the rate of traffic that passes through the interface by configuring a policer overhead. When you configure a policer overhead, the configured policer overhead value is added to the length of the final Ethernet frame. This calculated length of the frame is used to determine the policer or the rate limit action. It does this because the policer overhead needs to be applied to policers just like shaping overhead is accounted for by shapers. The policer overhead is to be configured on the interface so that it is accounted for in the total packet length when policing traffic. See Configuring a Policer Overhead

The weighed RED (WRED) decision on the IQ2E PICs is done at the queue level. Once the accept or drop decision is made and the packet is queued, it is never dropped. Four drop profiles are associated with each queue: low, low-medium, medium-high, and high. WRED statistics are available for each loss priority (this feature is not supported on the IQ2 PICs). Also in contrast to the IQ2 PICs, the IQ2E PICs support WRED scaling profiles, allowing a single drop profile to be reused with a wide range of values. This practice increases the effective number of WRED drop profiles.

The IQ2E PICs provide four levels of strict priorities: strict-high, high, medium-high (medium-low) and low. In contrast to the IQ2 PICs, which support only one strict-high queue, the IQ2E PICs do not restrict the number of queues with a given priority. There is priority propagation among three levels: the logical interface, the logical interface set, and the physical port. These features are the same as those supported by Enhanced Queuing Dense Port Concentrators (DPCs) for Juniper Network MX Series 5G Universal Routing Platforms. For more information about configuring these features, see Enhanced Queuing DPC CoS Properties.

The IQ2E PIC’s queues are serviced with modified deficit round-robin (MDRR), as with the Enhanced Queuing DPCs. Excess bandwidth (bandwidth available after all guaranteed rates have been satisfied) can be shared equally or in proportion to the guaranteed rates. For more information about excess bandwidth sharing, see Configuring Excess Bandwidth Sharing.