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AQM: A Mechanism of Congestion Control in Networks

Saira Saeed, Bilal Shams, Abstract: Congestion in the network occurs when node or link carries so much data that its quality of service downgrade. Active queue management is the most well-known algorithm to control congestion in the network. This paper discussed some of the queue length based and load based algorithms in AQM, we also highlighted its pros and cons. Keyword: congestion, Active queue management 1. Introduction: Congestion can take place at sensors that receive more data than its maximum forwarding rate. These consequences in long delay in data delivery and wasting of resources due to lost or dropped packets. When congestion occurs in network the Quality of service will disturb which is an important feature in sending data from node to another. When buffer overflow the packet drops so it would increase the energy consumptions of a sensor as the packets need to be retransmitted. Higher packet drops will also reduce the throughput of the data. Some multimedia data such as voice and video are critical to time delay [1]. Thus, congestion needs to be controlled to ensure that the end-to-end delay is also minimized. 2. Active queue management (AQM) The role of Active Queue Management (AQM) in IP networks was to balance the work of end-system protocols such as the Transmission Control Protocol (TCP) in congestion control hence to enlarge network utilization, and limit packet loss and delay.[2] AQM is a scheme which shares bandwidth fairly and control congestion over the routers/internet. According to the congestion metric active queue management has classified in to queue length based, load based and queue length and load based. Fig.2. Classification of AQM scheme. [3] Congestion is observed by average queue length in queue based schemes, and the control aspires to stabilize the queue length. The downside of queue based scheme is that a backlog is inherently required. Load based schemes precisely predict the utilization of the link, and determine congestion and take actions based on the packet arrival rate. Rate-based schemes can grant Early feedback for congestion. The goals of the load based AQMs are to alleviate rate mismatch between enqueue and dequeue, and achieve low loss, low delay and high link utilization. The third AQM scheme is the combination of load based and queue length which measure congestion and get a tradeoff between queues stability and responsiveness. [3] In this paper we just discussed the queue length based and load based briefly. 3. AQMs Based On Queue Length Merit. 3.1. Random Early Detection (RED). The main objectives of RED is to minimize packet loss and queuing delay, avoid global synchronization of sources, maintain high link utilization, and remove biases against bursty flows. RED avoids congestion early and delivers congestion notification to the end source and allows them to reduce the transmission rate before overflow occurs. To reduce the delay of flows RED keeps the queue size full. RED maintains an exponentially weighted moving average (EWMA) of the queue length which is used to detect incipient congestion. When average queue length greater than min threshold, packets are randomly dropped or marked with explicitly congestion notification (ECN). [4][5] When average queue length greater max threshold all packets are dropped or marked. Fig.3. RED algorithm [3] 3.2. FRED (Fair random early detection) FRED is modified version of RED therefore it reduces the unfairness of RED. Inside the internet route FRED maintains state information for every flow. When different types of traffic shares one link, RED allows unfair bandwidth sharing because RED does not take the bandwidth utilization of the flow into account when dropping packets. The author proposes FRED as solution. The main objective of fair random flow is to provide different strategies of dropping to different kind of flows. Flows that take more bandwidth shall be isolated where as low speed and bursty flows should be protected and safe from dropping. [survey2]FRED maintains queue size of per flow and drops packets conditionally comparing per flow queue size with average per flow queue. Fig.4. FRED Algorithm [4] 3.3. CHOKE (Choose and Keep for responsive flows, Choose and Kill for unresponsive flows) In the CHOKE algorithm a packet is drawn randomly from FIFO buffer whenever a new packet arrived at congestion router. This packet is compared with newly arriving packet. Both packets are dropped if it belongs to the same flow, otherwise the new incoming packet is confessed into the buffer with a probability that depends on the level of congestion and the randomly chosen packet is kept intact. CHOKE is simplest and stateless algorithm which does not provide any special data structure. However when the number of flows is large compared to the buffer space than this algorithm performance is not well. [6] Fig.5. CHOKE algorithm 4. AQM on load based. 4.1. BLUE: A New Class of Active Queue Management Algorithms. RED queue length gives very little information about the number of competing connections in a shared link. BLUE overcome the drawbacks of RED by using packet loss and link idle events for protecting TCP flows against non-responsive flows. [1] BLUE, basically is a different active queue management algorithm which uses packet loss and link utilization history to manage congestion. BLUE keep up a single probability, which it uses to mark or drop packets when they are queued. If the queue is frequently dropping packets due to buffer overflow, BLUE increments the marking probability, therefore increasing the rate at which it sends back congestion notification. On the other hand, if the queue becomes empty or if the link is idle, BLUE decreases its marking probability. The main purpose of using BLUE is that congestion control can be performed with a least amount of buffer size. Other algorithms like RED need a large buffer size to attain the same goal. [7] Fig.6. BLUE Algorithm. 4.2. SFED: Selective Fair Early Detection Selective fair early detection is an easy to implement rate control based AQM discipline which can be joined with any scheduling discipline. It maintains a token bucket for every flow or comprehensive flows. The token filling rates are in proportion to the allowable bandwidths. The tokens are removed from the corresponding bucket whenever a packet is enqueued. The decision to enqueue or drop a packet of any flow depends on the occupancy of its bucket at that time. A sending rate higher than the permitted bandwidth results in low bucket occupancy and so a larger drop probability thus indicating the onset of congestion at the gateway. This ensures the adaptive flow to attain a steady state and prevents it from getting penalized severely. However non-adaptive flows will continue to send at the same rate and thus will suffer more losses. The rate at which the tokens are removed from bucket of a flow is equal to the rate of incoming packets of that flow, but the rate of addition of tokens in a bucket depends on its permitted share of bandwidth and not on the rate at which packets of that particular flow are dequeued. In this way token bucket controls the bandwidth consumed by a flow.[8]. 4.3. FABA: Fair adaptive bandwidth allocation: FABA is the extension of SFED and can be coupled with any simplest scheduling discipline like FCFS first in first served). FABA has many objectives like It allocates fair bandwidth amongst flows. It can avoid congestion by early detection and notification, It has low implementation complexity. Easy extension to provide differentiated services. FABA deals with both adaptive and non-adaptive traffic while providing incentive for flows to incorporate end-to end congestion control. It uses a rate control based mechanism to achieve fairness amongst flows at a router. [9] As in random early detection (RED), congestion is detected early and notified to the source. Table.1. Strength and Weakness of AQM Algorisms. Algorithm Strength Weakness RED provide both congestion recovery and congestion avoidance avoid global synchronization and biases against bursty traffic maintain an upper bound of average queue size work with TCP and non-TCP transport-layer protocol Cannot protect TCP flows from unresponsive flows. Cannot prevent buffer overflows when there are many flows. Cannot guarantee fairness because it assumes that all flows send data at the same rate. FRED FRED is very robust in identifying different kind of traffic, and protecting adaptive flows. Penalizing non-adaptive flows by imposing a maximum number of buffered packets, and better their share to average per-flow buffer usage. protecting fragile flows by deterministically accepting flows from low bandwidth connections; Providing fair sharing for large numbers of flows by using “two-packet-buffer” when buffer is used up. The “basic” FRED algorithm does not do very well when alarge numberof (TCP) flows share a bottle neck link. If there is alarge numberof (TCP) flows, the queue in the router may benear its capacity When the queue isnearly full, a short burst of packet arrival will cause aqueue overflow. When a queue overflowhappens, theFREDalgorithm degenerate intodrop tail. CHOKE CHOKE both identifies and penalizes unresponsive flows. It seeks to achieve max-min fairness without any state information. It does not handle unresponsive flows in case of few packets. CHOKE algorithm is not likely to perform well when the number of flows is large compared to the buffer space. BLUE Congestion control can be performed with a minimal amount of buffer size. BLUE uses a hashing function to discover the non-responsive flows. This depends on the assumption that non-responsive flows would not be very large in number. this is true but there could be cases when this assumption does not hold true SFED It maintains the token bucket for every flow. Token bucket keep record of the corresponding flows. It had any scheduling discipline FABA Very high link utilization and high Throughput. It have low loss rate. It is a scalable algorithm. Very high complexity, computation. 6. Conclusion: In this paper we have state the term AQM and its algorithms. We have highlighted some of queue length based and queue based algorithm with its strength and weakness. References: [1] husna zainol abidin , yuslinda wati mohamad yusof,saiful izwan suliman,” network using fairness bandwidth allocation. “october 2008. [2] richelle adams, “active queue management: a survey”, ieee communications surveys

Longevity in marriage

Longevity in marriage. Paper details 1 topic you are interested in and ensure it can be written about in 1 of the following genres: Professional email advocating for a change at work How-to essay describing a process at home or work Civic action letter to an official or authority Persuasive essay on a debatable issue Personal brand story based on your journaling and the Personal Branding Guide (Note: Refer to the Model Brand Story for a personal brand story example.) a reflection addressing the following questions in at least 1 sentence each: What genre did you choose for your written piece? How does your writing demonstrate this genre? All writing has a purpose that is unique to the situation. What did you hope to accomplish with your written piece? What research did you do for this assignment? Cite and format references for your written piece according to APA guidelines. Do this to the best of your ability or use a citation generator if you need help. Longevity in marriage

Columbia University Fuguis Transformation in To Live Novel Essay

essay helper free Columbia University Fuguis Transformation in To Live Novel Essay.

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Open-Book Essay on To Live 
In the novel To Live, the protagonist Fugui changes from a privileged, selfish individual into someone who is grateful for the simple gift of life and values the lives of others. What are four specific events/experiences which lead Fugui to his profound appreciation of life? Why are these events transformative? 
In conclusion, how does Fugui as an old man embody the Taoist principle of Wu Wei (the action of inaction), an enlightened state of mind in which one’s actions effortlessly flow in accordance with the natural order of the world. What is Fugui’s essential purpose for living by the story’s end?
Columbia University Fuguis Transformation in To Live Novel Essay

American Intercontinential University Early Childhood Education Discussion

American Intercontinential University Early Childhood Education Discussion.

Watch this short video clip about children voting for their playground materials (Links to an external site.). Would Dewey consider this an educational experience? Why or why not? One quick place to look for criteria is page 26 in the Mooney text. You can use ideas from anywhere in the chapter and or presentations to support your idea.You must also post a response to a classmate or to yourself. In your response give an example of something that the teacher could do differently from what you saw in the video that would either make it educational, or improve its educational value even more from Dewey’s perspective.…Remember this is a discussion so it only needs to be 2-3 paragraphs long.
American Intercontinential University Early Childhood Education Discussion

Cultural Stereotypes of Native Americans in Cartoons and Movies Discussion

Cultural Stereotypes of Native Americans in Cartoons and Movies Discussion.

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Please choose one of the following options to write your argumentative essay1. How are cultural stereotypes of Native Americans in cartoons and movies harmful?2. The football team The Washington Redskins have been facing pressure from certain groups to change their name because it is disrespectful to Native Americans and promotes cultural stereotypes. Do you think sports teams that have names related to Native American culture should be forced to change their names? Why or why not?You will be using the 5 paragraph essay and MLA format for this assignment.I. IntroductionII. Body paragraph 1III. Body paragraph 2IV. Body paragraph 3V. ConclusionMake sure to include at least two sources (books, magazines, newspapers, websites, etc.) in your essay. Please include a “works cited” page for your sources.Requirements : 3 full pages essay. Separated work cited page that does not count as one of the 3 essay pages.The assignment will be due by the end of this week EST, New York time.
Cultural Stereotypes of Native Americans in Cartoons and Movies Discussion

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