Active queue management in DOCSIS 3.1 networks

An important new feature in the DOCSIS 3.1 specification is active queue management (AQM). AQM provides a solution to the problem of providing good application layer quality of experience when multiple applications share a network connection. The need for AQM arises due to the presence of packet buffering in network elements and the mechanics of the TCP congestion avoidance algorithm. Based on simulated performance and implementation considerations, a variant of the Proportional Integral Controller Enhanced (PIE) algorithm, called DOCSIS-PIE, is now included in DOCSIS 3.1 and has recently been added to the DOCSIS 3.0 specification as well. Implementation of DOCSIS-PIE is mandatory for implementation in DOCSIS 3.1 cable modems, and recommended for implementation in DOCSIS 3.0 cable modems. In addition to the mandatory/ recommended algorithm, DOCSIS 3.1 and 3.0 cable modem vendors are free to support additional AQM algorithms of their choosing. For managing downstream traffic, the DOCSIS 3.1 specification mandates that the CMTS support an AQM technology, but does not require a specific algorithm. This article discusses the underlying problem that is addressed by AQM, the selection of DOCSIS-PIE as the algorithm of choice for DOCSIS 3.1 cable modems, and the expected performance of the algorithm in simulated network conditions.