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FAQ: Class of Service (CoS) for Juniper Routing Devices

The Juniper Networks Junos operating system (Junos OS) class of service (CoS) enables you to divide traffic into classes and offer various levels of throughput and packet loss when congestion occurs. Class of service (CoS) is the assignment of traffic flows to different service levels. Service providers can use router-based CoS features to define service levels that provide different delay, jitter (delay variation), and packet loss characteristics to particular applications served by specific traffic flows

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Where can I learn about hierarchical class of service?

Question Where can I learn about hierarchical class of service? Answer Hierarchical class of service (HCoS) is the ability to provide CoS functionality as a more granular level (for example, per subscriber rather than per port) by applying traffic schedulers and shapers to a hierarchy of scheduler nodes . Each level of the scheduler hierarchy can be used to treat traffic based on different criteria such as per application, user, VLAN, and physical port. This allows you to support the requirements of different services / applications, and users on the same physical device and infrastructure. For more information, please refer to our Hierarchical Class of Service Feature Guide: US/junos15.1/information-products/pathway-pages/cos/config-guide-hierarchical-cos.html #HCoS #hierarchical #COS #FAQ #ClassofService #QOS #qualityofservice

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What is the default scheduler policy for Junos CoS on routing devices?

By default, the best effort forwarding class (queue 0) receives 95 percent of the total port bandwidth and buffer space for the output link, and the network control forwarding class (queue 3) receives 5 percent

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What are the default Juniper CoS forwarding classes?

Each packet is associated with one of the following default forwarding classes: Expedited forwarding (EF)—Provides a low-loss, low-latency, low-jitter and assured bandwidth end-to-end service. Assured forwarding (AF)—Provides a group of values you can define and includes four subclasses: AF1, AF2, AF3, and AF4, each with three drop probabilities: low, medium and high. Best effort (BE)—Provides no service profile. For the best effort forwarding class, loss priority is typically not carried in a class-of-service (CoS) value and random early detection (RED) drop profiles are more aggressive

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How do I get started with CoS or QoS?

Answer Please see the following resources: QOS-Enabled Networks – Tools and Foundations by Miguel Barreiros and Peter Lundqvist: Day One Guides Day One: Deploying Basic QoS: Day One: Junos QoS for IOS Engineers: Day One: Advanced Junos CoS Troubleshooting Cookbook: Feature Guides CoS Feature Guide for Routing Devices Traffic Management Feature Guide(s) for QFX Devices Class of Service Feature Guide for EX Devices Class of Service Feature Guide for Security Devices NCEs Learning Byte series on Class of Service Basics: activity info.aspx?

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How many forwarding classes does Junos CoS support?

You map incoming traffic to a forwarding class, define the class-of-service (CoS) properties for the forwarding class through a scheduler, and assign the forwarding class to an output queue

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What is the difference between CoS and QoS?

Answer There are many possible definitions of Quality of Service (QoS), but for the purposes contrasting QoS to Junos Class of Service (CoS), QoS is the manipulation of aggregates of traffic such that each is forwarded in a fashion that is consistent with the required behaviors of the applications generating that traffic. From an individual user’s point of view, QoS is experienced on the end-to-end flow of traffic. However, it is implemented as a set of behaviors at each hop – this is an important distinction that is absolutely fundamental to QoS

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How does Juniper use shapers to help manage congestion?

Answer Shaping is the application of a limit to the rate at which traffic can be transmitted...Therefore, shaping can be less aggressive than policing and can have fewer of the negative side effects