Active Queue Management and Packet Scheduling (aqm)

Last modified: 2017-10-16

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Internet routers, lower-layer switches, end-host operating systems, device drivers, and many types of additional middleboxes include memory buffers in which they implement queues to hold packets that require processing or otherwise need to wait for forwarding to the next hop.

The queues are intended to absorb bursts of traffic that may naturally occur, and avoid unneccessary losses. However, queues also cause latency and jitter in the eventual arrival times of packets. This can create issues and complications for interactive applications.

Extremely large unmanaged buffers have been noticed in some software and equipment. When these buffers start to fill, interactive applications and other traffic can be severely impacted or completely broken, due to high and potentially oscillating delays.

The Active Queue Management and Packet Scheduling working group (AQM) works on algorithms for managing queues in order to:

(1) minimize the length of standing queues, helping to reduce delay for interactive applications

(2) help flow sources control their sending rates without unnecessary losses, e.g., through Explicit Congestion Notification (ECN)

(3) consider the merits of various techniques to protect flows from negative impacts of other more aggressive or misbehaving flows

(4) help avoid global synchronization of flows sharing a bottleneck

The AQM working group will produce documents that cover the design, use, configuration, and monitoring of algorithms for managing queues in Internet devices and software. The scope includes both how to best configure existing equipment and software, as well as recommendations on designing new equipment and software.

The AQM working group will also publish algorithm specifications that are found to be broadly applicable and beneficial. Evaluating these algorithms shall be done in coordination with the Internet Congestion Control Research Group (ICCRG), and related IETF Working Groups, such as the RTP Media Congestion Avoidance Techniques Working Group (RMCAT), in order to select and assess the relevant criteria, scenarios, and metrics.

The working group will also explore the merits of whether to isolate flows, and mechanisms for performing this function. Note that isolation and potentially policing of flows implies some policy beyond what is required to simply minimize queues. This topic requires significant attention in the working group.

AQM algorithms do not have to be implemented universally in order to be effective. Specifications will aid in producing proper implementations that avoid potential ambiguities and corner cases. "Interoperability" of algorithms and implementations of them is not the reason for creating these specifications; correctness is the primary motivation.

The working group will not make changes to existing IETF protocols, but the working group may use Explicit Congestion Notification (ECN), Diffserv, and other mechanisms maintained by the TSVWG working group. Since the implementation of these mechanisms is likely to be entwined with AQM algorithms, there is expected to be close coordination between the TSVWG and AQM groups.

Many AQM algorithms have been proposed in academic literature, but a smaller number are widely implemented and deployed. The goal of the working group is to produce recommendations that will actually be used, and algorithms that will actually be implemented, deployed in equipment, and enabled. Towards these ends, the group actively encourages participation from operators and implementers. Furthermore, the group will jointly work with the Routing and Internet Area in order to involve vendors of networking equipment in the development of the AQM mechanisms.

Wider research and evaluation of AQM mechanisms shall be coordinated with the IRTF/ICCRG, and significant participation in this WG from the academic and research community is highly desirable, when it is directly relevant to implementation and deployment.

Combined Queue Management / Packet Scheduling algorithms are in-scope, provided their benefits have been evaluated against the established requirements for an AQM algorithm. It is expected that some classes of algorithms will focus on software implementations, while others on existing or new hardware deployments, and algorithms may be specific to distinct scenarios.


Dec 2015 Submit first algorithm specification to IESG for publication as Proposed Standard
Done Submit AQM algorithm evaluation guidelines to IESG for publication as Informational
Done Submit AQM recommendations to IESG for publication, obsoleting RFC 2309


Request for Comments


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