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CoS Support on the SRX5000 Module Port Concentrator Overview

The SRX5000 Module Port Concentrator (SRX5K-MPC) for the SRX5600 and SRX5800 uses the Trio chipset-based queuing model, which supports class of service (CoS) characteristics that are optimized compared to CoS characteristics supported by the standard queuing model. These CoS features enable SRX5600 and SRX5800 devices to achieve end-to-end quality of service and protect the network using various security functions.

CoS features on the SRX5600 and SRX5800 devices provide differentiated services to traffic in addition to the best-effort packet processing. The main CoS features include classification, CoS field rewriting, queuing, scheduling, and traffic shaping.

When a network experiences congestion and delay, you can use the CoS features to classify packets; assign them with different levels of packet loss priority, delay, and throughput; and mark their CoS-related fields defined in Layer 2 and Layer 3 headers.

The MPC supports the following CoS features:

  • BA classifier based on IEEE 802.1p for packet classification (Layer 2 headers) for priority bits of ingress packets

  • Rewrite rule based on IEEE 802.1p for priority bits of egress packets


    You can configure up to 32 IEEE 802.1p rewriters on each SRX5K-MPC on the SRX5600 and SRX5800 devices.

  • Eight priority queues per port with configurable schedulers at the egress physical interface

By default, the MPC supports eight queues. You can use the following CLI statement to change that setting to four queues:

set chassis fpc fpc-number pic pic-number max-queues-per-interface 4

Changing to four-queue mode limits that number of configurable queues to four on the MPC. This does not have any effect on the performance.

The CoS features on the MPC have the following limitations:

  • On the MPC, the per-unit-scheduler or the hierarchical-scheduler is not supported. For egress scheduling and queuing, only the default mode is supported.

  • When an SPU is too busy to process every ingress packet from the MPC, some high-priority packets, such as voice packets, might be delayed or dropped by the SRX5600 or SRX5800.


The total number of classifiers supported on a Services Processing Unit (SPU) is 79. Three classifiers are installed on the SPU as default classifiers in the Layer 3 mode, independent of any CoS configuration, which leaves 76 classifiers that can be configured using the CoS CLI commands. The default classifiers number might vary in future releases or in different modes. You can verify the number of default classifiers installed on the SPU to determine how many classifiers can be configured using the CoS CLI commands.