According to Juniper Mist documentation, the Throughput Service Level Expectation (SLE) is the primary metric used to represent the ability of wired users to pass traffic across the network without impedance. This SLE provides a comprehensive oversight of network performance by identifying issues that degrade the user experience, such as storm control events, interface anomalies, and specifically uplink congestion.
Within the Throughput SLE, the Congestion classifier (also referred to as Congestion Uplink) is specifically designed to monitor for buffer saturation and packet drops (TxDrops). When traffic arriving at an interface exceeds its processing or forwarding capacity, packets are queued in a buffer; if this buffer becomes full, the switch begins dropping packets. Juniper Mist utilizes a specific formula considering the ratios of TxDrops to TxPackets, Transmitted bps to Link Speed, and Received Speed to Link Speed to determine if a "Bad User Minute" has occurred due to congestion.
A critical feature of Wired Assurance is the automatic identification of uplink interfaces. Mist identifies these high-capacity ports by analyzing switch telemetry for characteristics such as having a switch or router as an LLDP neighbor, being designated as a Spanning Tree Protocol (STP) root port, or exhibiting significantly higher packet counts compared to access ports. When congestion is detected on an interface identified as an uplink, the system recognizes that this bottleneck impacts every user on that switch. By correlating these drops with the Throughput SLE, network administrators can proactively identify when a site requires more bandwidth or a different fabric architecture to handle current traffic demands, rather than simply monitoring if the link is physically "up" or "down".
