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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 buffers as many packets as it can, and simply drops the ones it cannot buffer. If buffers are constantly full, the network is congested. Tail drop distributes buffer space unfairly among traffic flows. Tail drop can also lead to TCP global synchronization as all TCP connections "hold back" simultaneously, and then step forward simultaneously. Networks become under-utilized and flooded—alternately, in waves. RED addresses these issues by pre-emptively dropping packets before the buffer becomes completely full. It uses predictive models to decide which packets to drop. It was invented in the early 1990s by Sally Floyd and Van Jacobson. Operation RED monitors the average queue size and drops (or marks when used in conjunction with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Random Early Detection Algorithm En
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 random events are, by definition, unpredictable, but if the probability distribution is known, the frequency of different outcomes over repeated events (or "trials") is predictable.Strictly speaking, the frequency of an outcome will converge almost surely to a predictable value as the number of trials becomes arbitrarily large. Non-convergence or convergence to a different value is possible, but has probability zero. For example, when throwing two dice, the outcome of any particular roll is unpredictable, but a sum of 7 will tend to occur twice as often as 4. In this view, randomness is not haphazardness; it is a measure of uncertainty of an outcome. Randomness applies to concepts of chance, probability, and information entropy. The fields of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 an optional feature that may be used between two ECN-enabled endpoints when the underlying network infrastructure also supports it. Conventionally, TCP/IP networks signal congestion by dropping packets. When ECN is successfully negotiated, an ECN-aware router may set a mark in the IP header instead of dropping a packet in order to signal impending congestion. The receiver of the packet echoes the congestion indication to the sender, which reduces its transmission rate as if it detected a dropped packet. Rather than responding properly or ignoring the bits, some outdated or faulty network equipment has historically dropped or mangled packets that have ECN bits set. , measurements suggested that the fraction of web servers on the public I ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Performance
Network performance refers to measures of service quality of a network as seen by the customer. There are many different ways to measure the performance of a network, as each network is different in nature and design. Performance can also be modeled and simulated instead of measured; one example of this is using state transition diagrams to model queuing performance or to use a Network Simulator. Performance measures The following measures are often considered important: * Bandwidth commonly measured in bits/second is the maximum rate that information can be transferred * Throughput is the actual rate that information is transferred * Latency the delay between the sender and the receiver decoding it, this is mainly a function of the signals travel time, and processing time at any nodes the information traverses * Jitter variation in packet delay at the receiver of the information * Error rate the number of corrupted bits expressed as a percentage or fraction of the total sent Ba ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Active Queue Management
In routers and switches, active queue management (AQM) is the policy of dropping packets inside a buffer associated with a network interface controller (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, which for this purpose uses various algorithms such as random early detection (RED), Explicit Congestion Notification (ECN), or controlled delay (CoDel). 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 maintain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blue (queue Management Algorithm)
Blue is a scheduling discipline for the network scheduler developed by graduate student Wu-chang Feng for Professor Kang G. Shin at the University of Michigan and others at the Thomas J. Watson Research Center of IBM in 1999. Functioning Like random early detection (RED), Blue operates by randomly dropping or marking packet with explicit congestion notification mark before the transmit buffer of the network interface controller overflows. Unlike RED, however, it requires little or no tuning to be performed by the network administrator. A Blue queue maintains a drop/mark probability ''p'', and drops/marks packets with probability ''p'' as they enter the queue. Whenever the queue overflows, ''p'' is increased by a small constant ''pi'', and whenever the queue is empty, ''p'' is decreased by a constant ''pd < pi''. If the mix of traffic on the interface does not change, ''p'' will slowly converge to a value that keeps the queue within its bounds with full link u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Differentiated Services Code Point
Differentiated services or DiffServ is a computer networking architecture that specifies a mechanism for classifying and managing network traffic and providing quality of service (QoS) on modern IP networks. DiffServ can, for example, be used to provide low-latency to critical network traffic such as voice or streaming media while providing best-effort service to non-critical services such as web traffic or file transfers. DiffServ uses a 6-bit differentiated services code point (DSCP) in the 8-bit differentiated services field (DS field) in the IP header for packet classification purposes. The DS field replaces the outdated IPv4 TOS field. Background Modern data networks carry many different types of services, including voice, video, streaming music, web pages and email. Many of the proposed QoS mechanisms that allowed these services to co-exist were both complex and failed to scale to meet the demands of the public Internet. In December 1998, the IETF published - ''Defini ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weighted Random Early Detection
Weighted random early detection (WRED) is a queueing discipline for a network scheduler suited for congestion avoidance. It is an extension to random early detection (RED) where a single queue may have several different sets of queue thresholds. Each threshold set is associated to a particular traffic class. For example, a queue may have lower thresholds for lower priority packet. A queue buildup will cause the lower priority packets to be dropped, hence protecting the higher priority packets in the same queue. In this way quality of service prioritization is made possible for important packets from a pool of packets using the same buffer. It is more likely that standard traffic will be dropped instead of higher prioritized traffic. Restrictions On Cisco switches WRED is restricted to * TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks accordin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quality Of Service
Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitatively measure quality of service, several related aspects of the network service are often considered, such as packet loss, bit rate, throughput, transmission delay, availability, jitter, etc. In the field of computer networking and other packet-switched telecommunication networks, quality of service refers to traffic prioritization and resource reservation control mechanisms rather than the achieved service quality. Quality of service is the ability to provide different priorities to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow. Quality of service is particularly important for the transport of traffic with special requirements. In particular, developers have introduced ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Probability
Probability is the branch of mathematics concerning numerical descriptions of how likely an Event (probability theory), event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speaking, 0 indicates impossibility of the event and 1 indicates certainty."Kendall's Advanced Theory of Statistics, Volume 1: Distribution Theory", Alan Stuart and Keith Ord, 6th Ed, (2009), .William Feller, ''An Introduction to Probability Theory and Its Applications'', (Vol 1), 3rd Ed, (1968), Wiley, . The higher the probability of an event, the more likely it is that the event will occur. A simple example is the tossing of a fair (unbiased) coin. Since the coin is fair, the two outcomes ("heads" and "tails") are both equally probable; the probability of "heads" equals the probability of "tails"; and since no other outcomes are possible, the probability of either "heads" or "tails" is 1/2 (which could also be written ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Van Jacobson
Van Jacobson (born 1950) is an American computer scientist, renowned for his work on TCP/IP network performance and scaling.2001 SIGCOMM Award for Lifetime Achievement to Van Jacobson "for contributions to protocol architecture and congestion control." He is one of the primary contributors to the TCP/IP protocol stack—the technological foundation of today’s Internet. Since 2013, Jacobson is an at the University of California, Los Angeles (UCLA) working on [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Active Queue Management
In routers and switches, active queue management (AQM) is the policy of dropping packets inside a buffer associated with a network interface controller (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, which for this purpose uses various algorithms such as random early detection (RED), Explicit Congestion Notification (ECN), or controlled delay (CoDel). 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 maintain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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