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CoS Overview

For interfaces that carry IPv4, IPv6, or MPLS traffic, you can configure JUNOS class-of-service (CoS) features to provide multiple classes of service for different applications. On the routing platform, you can configure multiple forwarding classes for transmitting packets, define which packets are placed into each output queue, schedule the transmission service level for each queue, and manage congestion using a Random Early Detection (RED) algorithm.

NOTE: JUNOS CoS features are not supported on ATM interfaces. ATM has traffic-shaping capabilities that would override CoS, because ATM traffic shaping is performed at the ATM layer and CoS is performed at the IP layer. For more information about ATM traffic shaping, see Defining the ATM Traffic-Shaping Profile and Configuring ATM2 IQ VC Tunnel CoS Components.

The JUNOS CoS features provide a set of mechanisms that you can use to provide differentiated services when best-effort traffic delivery is insufficient. In designing CoS applications, you must give careful consideration to your service needs, and you must thoroughly plan and design your CoS configuration to ensure consistency across all routing platforms in a CoS domain. You must also consider all the routing platforms and other networking equipment in the CoS domain to ensure interoperability among all equipment.

The Internet community has little experience with CoS and quality of service (QoS). However, because Juniper Networks routing platforms implement CoS in hardware rather than in software, you can experiment with and deploy CoS features without adversely affecting packet forwarding and routing performance.

The standards are defined in the following RFCs:

This chapter discusses the following topics:

For information about CoS components that you apply to the ATM2 intelligent queuing (IQ) interface specifically, see Configuring ATM2 IQ VC Tunnel CoS Components.

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