On the Transient Behavior of CHOKe

TL;DR

This paper investigates the transient behavior of CHOKe, an active queue management scheme, revealing how its protection of TCP flows can vary during sudden changes in UDP traffic rates, with derived expressions explaining its dynamic properties.

Contribution

It provides the first explicit analysis of CHOKe's transient regime, deriving formulas that describe flow throughput during rate changes, enhancing understanding of its dynamic behavior.

Findings

Derived explicit expressions for flow throughput in transient regimes.

Revealed that CHOKe's protection can weaken during sudden UDP rate drops.

Explained the behavior of CHOKe during flow rate transitions.

Abstract

CHOKe is a simple and stateless active queue management (AQM) scheme. Apart from low operational overhead, a highly attractive property of CHOKe is that it can protect responsive TCP flows from unresponsive UDP flows. Particularly, previous works have proven that CHOKe is able to bound both bandwidth share and buffer share of (a possible aggregate) UDP traffic (flow) on a link. However, these studies consider, and pertain only to, a steady state where the queue reaches equilibrium in the presence of many (long-lived) TCP flows and an unresponsive UDP flow of fixed arrival rate. If the steady state conditions are perturbed, particularly when UDP traffic rate changes over time, it is unclear whether the protection property of CHOKe still holds. Indeed, it can be examined, for example, that when UDP rate suddenly becomes 0 (i.e., flow stops), the unresponsive flow may assume close to full utilization in sub-RTT scales, potentially starving out the TCP flows. To explain this apparent discrepancy, this paper investigates CHOKe queue properties in a transient regime, which is the time period of transition between two steady states of the queue, initiated when the rate of the unresponsive flow changes. Explicit expressions that characterize flow throughputs in transient regimes are derived. These results provide additional understanding of CHOKe, and give some explanation on its intriguing behavior in the transient regime.