In
routers and
switches
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
, active queue management (AQM) is the policy of dropping packets inside a buffer associated with a
network interface controller
A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network.
Ear ...
(NIC) before that buffer becomes full, often with the goal of reducing network congestion or improving end-to-end latency. This task is performed by the
network scheduler
A network scheduler, also called packet scheduler, queueing discipline (qdisc) or queueing algorithm, is an arbiter on a node in a packet switching communication network. It manages the sequence of network packets in the transmit and receive q ...
, which for this purpose uses various algorithms such as
random early detection
Random early detection (RED), also known as random early discard or random early drop is a queuing discipline for a network scheduler suited for congestion avoidance.
In the conventional tail drop algorithm, a router or other network component ...
(RED),
Explicit Congestion Notification
Explicit Congestion Notification (ECN) is an extension to the Internet Protocol and to the Transmission Control Protocol and is defined in RFC 3168 (2001). ECN allows end-to-end notification of network congestion without dropping packets. ECN is ...
(ECN), or controlled delay (
CoDel
CoDel (''Controlled Delay''; pronounced "coddle") is an active queue management (AQM) algorithm in network routing, developed by Van Jacobson and Kathleen Nichols and published as RFC8289. It is designed to overcome bufferbloat in networking har ...
). RFC 7567 recommends active queue management as a best practice.
Overview
An Internet router typically maintains a set of queues, one or more per interface, that hold packets scheduled to go out on that interface. Historically, such queues use a ''drop-tail'' discipline: a packet is put onto the queue if the queue is shorter than its maximum size (measured in packets or in bytes), and dropped otherwise.
Active queue disciplines drop or mark packets before the queue is full. Typically, they operate by maintaining one or more drop/mark probabilities, and occasionally dropping or marking packets according to the probabilities before the queue is full.
Benefits
Drop-tail queues have a tendency to penalise bursty flows, and to cause
global synchronisation between flows. By dropping packets probabilistically, AQM disciplines typically avoid both of these issues.
By providing endpoints with congestion indication before the queue is full, AQM disciplines are able to maintain a shorter queue length than drop-tail queues, which combats
bufferbloat
Bufferbloat is a cause of high latency and jitter in packet-switched networks caused by excess buffering of packets. Bufferbloat can also cause packet delay variation (also known as jitter), as well as reduce the overall network throughput. ...
and reduces
network latency
Network delay is a design and performance characteristic of a telecommunications network. It specifies the Latency (engineering), latency for a bit of data to travel across the network from one communication endpoint to another. It is typically ...
.
Drawbacks
Early AQM disciplines (notably
RED
Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondar ...
and SRED) require careful tuning of their parameters in order to provide good performance. These systems are not optimally behaved from a
control theory
Control theory is a field of mathematics that deals with the control of dynamical systems in engineered processes and machines. The objective is to develop a model or algorithm governing the application of system inputs to drive the system to a ...
perspective.
[C.V. Hollot, Vishal Misra, Don Towsley and Wei-Bo Gong]
Analysis and Design of Controllers for AQM Routers Supporting TCP Flows
/ref> Modern AQM disciplines (ARED, Blue
Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...
, PI, CoDel
CoDel (''Controlled Delay''; pronounced "coddle") is an active queue management (AQM) algorithm in network routing, developed by Van Jacobson and Kathleen Nichols and published as RFC8289. It is designed to overcome bufferbloat in networking har ...
, CAKE) are self-tuning, and can be run with their default parameters in most circumstances.
Network engineers have historically been trained to avoid packet loss, and have therefore sometimes been critical of AQM systems that drop packets: "Why should I drop perfectly good packets when I still have free buffer space?"
Simulation
An active queue management and denial-of-Service
In computing, a denial-of-service attack (DoS attack) is a cyber-attack in which the perpetrator seeks to make a machine or network resource unavailable to its intended users by temporarily or indefinitely disrupting services of a host conne ...
(AQM&DoS) simulation platform is established based on the NS-2 simulation code of the RRED Robust random early detection (RRED) is a queueing disclipine for a network scheduler. The existing random early detection (RED) algorithm and its variants are found vulnerable to emerging attacks, especially the Low-rate Denial-of-Service attacks ...
algorithm. The AQM&DoS simulation platform can simulate a variety of DoS attacks (Distributed DoS, Spoofing DoS, Low-rate DoS, etc.) and AQM algorithms (RED, RRED Robust random early detection (RRED) is a queueing disclipine for a network scheduler. The existing random early detection (RED) algorithm and its variants are found vulnerable to emerging attacks, especially the Low-rate Denial-of-Service attacks ...
, SFB, etc.). It automatically calculates and records the average throughput of normal TCP flows before and after DoS attacks to facilitate the analysis of the impact of DoS attacks on normal TCP flows and AQM algorithms.
Active queue management algorithms
* Blue and Stochastic Fair Blue (SFB)
* Common Applications Kept Enhanced (CAKE)
* Controlled Delay
Control may refer to:
Basic meanings Economics and business
* Control (management), an element of management
* Control, an element of management accounting
* Comptroller (or controller), a senior financial officer in an organization
* Controllin ...
(CoDel)
* FQ-CoDel
* Modified-REM (M-REM)
* PI controller
* Random early detection
Random early detection (RED), also known as random early discard or random early drop is a queuing discipline for a network scheduler suited for congestion avoidance.
In the conventional tail drop algorithm, a router or other network component ...
(RED)
* Random Exponential Marking
In common usage, randomness is the apparent or actual lack of pattern or predictability in events. A random sequence of events, symbols or steps often has no order and does not follow an intelligible pattern or combination. Individual ran ...
(REM)
* RED with Preferential Dropping
Red is the color at the long wavelength end of the visible spectrum of light, next to Orange (colour), orange and opposite Violet (color), violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the ...
(RED-PD) [Ratul Mahajan, Sally Floyd, and David Wetherall]
Controlling high-bandwidth flows at the congested router
ICNP 2001
* Robust random early detection Robust random early detection (RRED) is a queueing disclipine for a network scheduler. The existing random early detection (RED) algorithm and its variants are found vulnerable to emerging attacks, especially the Low-rate Denial-of-Service attacks ...
br>(RRED)
[Changwang Zhang, Jianping Yin, Zhiping Cai, and Weifeng Chen]
RRED: Robust RED Algorithm to Counter Low-rate Denial-of-Service Attacks
IEEE Communications Letters, vol. 14, pp. 489-491, 2010
Ref
/ref>
RSFB
a Resilient Stochastic Fair Blue algorithm against spoofing DDoS attacks [Changwang Zhang, Jianping Yin, and Zhiping Cai]
RSFB: a Resilient Stochastic Fair Blue algorithm against spoofing DDoS attacks
in International Symposium on Communication and Information Technology (ISCIT), 2009
Ref
/ref>
* Smart Queue Management
Smart or SMART may refer to:
Arts and entertainment
* ''Smart'' (Hey! Say! JUMP album), 2014
* Smart (Hotels.com), former mascot of Hotels.com
* ''Smart'' (Sleeper album), 1995 debut album by Sleeper
* ''SMart'', a children's television ser ...
(SQM) - combining AQM with QOS and other techniques
References
{{Reflist, 30em
Network performance
Network scheduling algorithms
Packets (information technology)