In a shared-buffer slope policy the four profiles (out-of-profile, in-profile, etc.) are compared against buffer-occupancy thresholds. Packets whose profile reaches its minimum threshold first are the first that can be discarded.

Because the out-of-profile (OOP) slope has lower thresholds than the in-profile (IP) slope, OOP packets face a non-zero drop probability before any IP traffic is at risk (A).

The IP slope shown has min-threshold = 50 % and max-threshold = 70 %; therefore, as soon as buffer utilization reaches 51 %, IP packets can be dropped (C).

At 69 % utilization the linear RED curve gives a drop-probability very close to the configured max-probability of 60 %, so an IP packet has ≈60 % chance of being discarded (E).

Setting time-average-factor 0 only disables averaging; it does not drop all packets, and the OOP max-probability in the figure is not 20 %.

B. time-average-factor 0 merely uses the instantaneous buffer level; it does not cause unconditional packet loss.

D. The OOP slope in the figure shows max-probability = 100 %, so OOP drop probability can rise to 100 %, not 20 %.

1. Nokia SR OS 22.R1 Class of Service Guide, “Shared-Buffer Slope Policies,” pp. 650-654, Tables 260–262 (OOP and IP threshold behaviour; meaning of time-average-factor, max-probability).

2. Nokia 4A0-107 Student Courseware, Module 7 “Congestion Management,” slides 33-36 (example policy identical to exhibit: OOP 30/40/100, IP 50/70/60; RED probability calculation).

3. T. Bonald & A. Proutière, “Adaptive RED for WRED-based shared buffers,” IEEE/ACM Trans. Networking, vol. 19, no. 6, pp. 1775-1788, 2011, Sec. III-B (linear interpolation from min- to max-threshold).

4. F. Callegati, “Active Queue Management in Core Routers,” IEEE Commun. Mag., vol. 41, no. 6, 2003, p. 128 (effect of averaging factor 0).