In one of the frame relay specifications, an algorithm for monitoring queue lengths is suggested; this is shown in Figure $20\mathrm{.}15.$ A cycle begins when the outgoing circuit goes from idle $($queue empty$)$ to busy $($nonzero queue size, including the current frame$).$ If a threshold value is exceeded, then the circuit is in a state of incipient congestion, and the congestion avoidance bits should be set on some or all logical connections that use that circuit. Describe the algorithm in words and explain its advantages.