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Enhanced Queuing DPC Hardware Properties

MX-series routers with Enhanced Queuing DPCs have Packet Forwarding Engines that can support up to 515 MB of frame memory, and packets are stored in 512–byte frames. Table 53 compares the major properties of the Intelligent Queuing 2 (IQ2) PIC and the Packet Forwarding Engine within the Enhanced Queuing DPC.

Table 53: IQ2 PIC and Enhanced Queuing DPC Compared

Feature	IQ2 PIC	PFE Within Enhanced Queuing DPC
Number of usable queues	8,000	16,000
Number of shaped logical interfaces	1,000 with 8 queues each.	2,000 with 8 queues each, or 4,000 with 4 queues each.
Number of hardware priorities	2	4
Priority propagation	No	Yes
Dynamic mapping	No: schedulers/port are fixed.	Yes: schedulers/port are not fixed.
Drop statistics	Per queues	Per queue per color (PLP high, low)

In addition, the Enhanced Queuing DPC features support for hierarchical weighted random early detection (WRED) and enhanced queuing on aggregated Ethernet interfaces with link protection as well.

The Enhanced Queuing DPC supports the following hierarchical scheduler characteristics:

Shaping at the physical interface level
Shaping and scheduling at the service VLAN interface set level
Shaping and scheduling at the customer VLAN logical interface level
Scheduling at the queue level

The Enhanced Queuing DPC supports the following features for scalability:

16,000 queues per PFE
4 Packet Forwarding Engines per DPC
- 4000 schedulers at logical interface level (Level 3) with 4 queues each
- 2000 schedulers at logical interface level (Level 3) with 8 queues each
255 schedulers at the interface set level (Level 2) per 1-port PFE on a 10-Gigabit Ethernet DPC
15 schedulers at the interface set level (Level 2) per 10-port PFE on a 1-Gigabit Ethernet DPC
About 400 milliseconds of buffer delay (this varies by packet size and if large buffers are enabled)
4 levels of priority (strict-high, high, medium, and low)

Note: Use of the exact option for a transmit-rate (transmit-rate rate exact) is not supported on the Enhanced Queuing DPCs on MX-series routers.

The way that the Enhanced Queuing DPC maps a queue to a scheduler depends on whether 8 queues or 4 queues are configured. By default, a scheduler at level 3 has 4 queues. Level 3 scheduler X controls queue X*4 to X*4+3, so that scheduler 100 (for example) controls queues 400 to 403. However, when 8 queues per scheduler are enabled, the odd numbered schedulers are disabled, allowing twice the number of queues per subscriber as before. With 8 queues, level 3 scheduler X controls queue X*4 to X*4+7, so that scheduler 100 (for example) now controls queues 400 to 407.

You configure the max-queues-per-interface statement to set the number of queues at 4 or 8 at the FPC level of the hierarchy. Changing this statement will result in a restart of the DPC. For more information about the max-queues-per-interface statement, see the JUNOS Software Network Interfaces Configuration Guide.

The Enhanced Queuing DPC maps level 3 (customer VLAN) schedulers in groups to level 2 (service VLAN) schedulers. Sixteen contiguous level 3 schedulers are mapped to level 2 when 4 queues are enabled, and 8 contiguous level 3 schedulers are mapped to level 2 when 8 queues are enabled. All of the schedulers in the group should use the same queue priority mapping. For example, if the queue priorities of one scheduler are high, medium, low, and low, then all members of this group should have the same queue priority.

Mapping of a group at level 3 to level 2 can be done at any time. However, a group at level 3 can only be unmapped from a level 2 scheduler only if all the schedulers in the group are free. Once unmapped, a level 3 group can be remapped to any level 2 scheduler. There is no restriction on the number of level 3 groups that can be mapped to a particular level 2 scheduler. There can be 256 level 3 groups, but fragmentation of the scheduler space can reduce the number of schedulers available. In other words, there are scheduler allocation patterns that might fail even though there are free schedulers.

In contrast to level-3-to-level-2 mapping, the Enhanced Queuing DPC maps level 2 (service VLAN) schedulers in a fixed mode to level 1 (physical interface) schedulers. On 40-port Gigabit Ethernet DPCs, there are 16 level 1 schedulers, and 10 of these are used for the physical interfaces. There are 256 level 2 schedulers, or 16 per level 1 scheduler. A level 1 scheduler uses level schedulers X*16 through X*16+15. So level 1 scheduler 0 uses level 2 schedulers 0 through 15, level 1 scheduler 1 uses level 2 schedulers 16 through 31, and so on. On 4-port 10-Gigabit Ethernet PICs, there is one level 1 scheduler for the physical interface, and 256 level 2 schedulers are mapped to the single level 1 scheduler.

The maximum number of level 3 (customer VLAN) schedulers that can be used is 4076 (4 queues) or 2028 (8 queues) for the 10-port Gigabit Ethernet Packet Forwarding Engine and 4094 (4 queues) or 2046 (8 queues) for the 10-Gigabit Ethernet Packet Forwarding Engine.

Enhanced Queuing is supported on aggregated Ethernet (AE) interfaces with two links in link protection mode. However, only one link in the AE bundle can be active at a time. Traffic is shaped independently on the two links, but the member’s links do not need to reside in the same Packet Forwarding Engine or the same DPC. Finally, shared schedulers are not supported on the Enhanced Queuing DPC (use hierarchical schedulers to group logical interfaces).

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