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QoS in Junos Multi-Access User Plane

Quality of service (QoS) is a set of Junos OS performance features. You (the network administrator) can use these features to improve network performance by differentiating traffic into classes and then applying different behaviors to different types of traffic. These features also enable you to guarantee a certain level of network performance.

Usually, routers forward traffic using best-effort service without any control on throughput, packet loss, jitter, or delay. The QoS features provide differentiated services depending on the type of traffic. This feature improves performance in cases where the best-effort delivery is insufficient, such as in transmission of real-time audio and video.

Junos Multi-Access User Plane provides the following QoS features:

  • GBR forwarding queues—Ensure that traffic on these queues has a minimum bit rate or guaranteed bit rate (GBR). We support eight preconfigured forwarding queues on the virtual routing and forwarding (VRF) loopback interface of the anchor Packet Forwarding Engine. Of the eight queues, four are guaranteed bit rate queues with three priorities each (high, medium, and low), and four are excess or best-effort queues with two priorities each (high and low).


    The user plane sends all downlink traffic over the VRF interface using these eight forwarding queues. In the case of an intermediate UPF, which uses the VRF interface for both uplink and downlink traffic, the uplink traffic uses the best-effort queues. Otherwise, the uplink traffic does not use the VRF interface.

  • Forwarding queue mapping—Uses the DiffServ code point (DSCP) value that the control plane provides in the Transport Level Marking to map the bearer or flow to the appropriate forwarding queue. For 4G, the user plane determines the DSCP value based on the QoS Class Identifier (QCI) and, optionally, the Admission Retention and Pre-emption Policy level. For 5G, the user plane determines the DSCP value based on the 5G QoS Identifier (5QI), the priority level, and, optionally, the Admission Retention and Pre-emption Policy level.

  • Bandwidth reservation—Supports reserving a fraction of the bandwidth for queues with express traffic and guaranteed bit rate traffic in the downlink direction. The express queue handles high-priority, highly policed traffic that has a higher priority than guaranteed bit rate traffic. For example, the express queue handles IP Multimedia subsystem (IMS) signals, which have a higher priority than guaranteed bit rate traffic. Three queues—gbr-high, gbr-medium, and gbr-low—handle the guaranteed bit rate traffic.

  • Call admission control—Tracks the total guaranteed bit rate bandwidth in the downlink direction across all bearers and flows assigned to each anchor Packet Forwarding Engine. This feature ensures that bearers and flows do not oversubscribe the reserved guaranteed bit rate bandwidth.

    The user plane admits a new session with guaranteed bit rate flow only if the least utilized anchor Packet Forwarding Engine can accommodate the requested guaranteed bit rate bandwidth. If an existing session is modified such that the new total guaranteed bandwidth exceeds the reserved bandwidth, the user plane accepts the modification and logs an oversubscription error message.

    The user plane always admits non-guaranteed bit rate flows as they are not offered any guaranteed bandwidth.

  • Policing—Enables you to limit traffic in the uplink and downlink directions to a specified bandwidth. Guaranteed bit rate flows support policers for both guaranteed bit rate and maximum bit rate. Express flows and best-effort flows support only maximum bit rate policers.

    The user plane always transmits green packets (conforming to the guaranteed bit rate). Yellow packets exceed the guaranteed bit rate but conform to the maximum bit rate. The user plane drops these packets immediately for express queues, and drops them based on the overall load for guaranteed bit rate and best-effort queues. The user plane always drops red packets (exceeding the maximum bit rate).