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Schedulers Overview for ACX Series Routers

 

You use schedulers to define the properties of output queues. These properties include the amount of interface bandwidth assigned to the queue, the size of the memory buffer allocated for storing packets, the priority of the queue, and the random early detection (RED) drop profiles associated with the queue.

You associate the schedulers with forwarding classes by means of scheduler maps. You can then associate each scheduler map with an interface, thereby configuring the hardware queues, packet schedulers, and RED processes that operate according to this mapping.

In ACX Series routers, you can configure more than one strict-priority queue per port. The hardware services the queues in the descending order of queue numbers marked as strict priority. All the strict-priority queues are given preferential treatment by the scheduler as long as their shaping rates (or peak information rates) are not met. Unlike MX Series routers, the ACX Series routers configured with queues as strict-high at the [edit class-of-service schedulers scheduler-name priority strict-high] statement hierarchy, the service is based on queue number and not based on sharing the strict-high queues.

Unlike other ACX Series routers, ACX5048 and ACX5096 router supports CIR among strict-priority queues. There is no implicit queue number-based priority among the strict-priority queues. Unlike other ACX Series routers, ACX5048 and ACX5096 router supports configuring drop profiles for loss-priority low, medium-high, and high for non-TCP protocols as well.

Note

The options buffer-partition multicast percent <0-100> at the [edit class-of-service schedulers scheduler-name buffer-size] hierarchy level and multicast <0-100> at the [edit class-of-service schedulers scheduler-name shared-buffer-maximum] hierarchy level are supported only on ACX5048 and ACX5096 routers. For more information, see Shared and Dedicated Buffer Memory Pools on ACX Series Routers.

ACX5448 routers support port-based queueing, scheduling, and shaping. You can configure up to eight queues (virtual output queues) per physical interface (port). Scheduling properties can be applied at both physical as well as logical interface levels. The egress scheduler supports two priority levels (strict-high and low). Multiple strict-high priority queues and multiple low (default) priority queues can be configured.

By default a port on an ACX5448 router gets a dedicated buffer of 100 microseconds and shared buffer from DRAM. Delay buffer controls the latency of the queue during congestion and maximum number of packets that can be held in a queue. Default buffer size per port is 100 microseconds.

Note

In ACX Series routers, the transmit-rates statement cannot be configured on strict-priority queues because of hardware limitations.

On an ACX 4000 router, whenever the scheduling and shaping parameters of a port or any of its queues are changed, the entire scheduling configuration on the port is erased and the new configuration is applied. During this window, the traffic pattern does not adhere to user parameters. We recommend configuring scheduling for enabling live traffic.