For interfaces that carry IPv4 or MPLS traffic, you can configure JUNOS class-of-service (CoS) features to provide multiple classes of service for different applications. On the router, you can configure multiple output queues for transmitting packets, define which packets are placed into each output queue, schedule the transmission service level for each queue using a weighted round-robin algorithm, and manage congestion using a Random Early Detection (RED) algorithm.
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 routers in a CoS domain. You must consider all the routers 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 routers implement CoS in hardware rather than in software, you have the ability to experiment with and deploy CoS features without any adverse affects on packet forwarding and routing.