A quantitative analysis and performance study of fast congestion notification (FN) mechanism

Congestion in computer network happens when the number of transmission requests exceeds the transmission capacity at a certain network point (called a bottle-neck resource) at a specific time. Congestion usually causes buffers overflow and packets loss. The purpose of congestion management is to maintain a balance between the transmission requests and the transmission capacity so that the bottle-neck resources operate on an optimal level, and the sources are offered service in a way that assures fairness. Fast Congestion Notification (FN) is one of the proactive queue management mechanisms that limits the queuing delay and achieves the maximum link utilization possible with minimum packet drops. In this paper we present a detailed performance comparison of the Linear FN algorithm to RED based on the results obtained through simulations. The paper shows how FN can be tuned for different window size (Ws) and periods of time constant (T) to achieve higher link utilization; reduce the queuing delay, and lower packet drop ratio

Fast Congestion Notification Mechanism for Next Generation Routers

The aim of this thesis is to present a new proactive congestion control mechanism, namely "Fast Congestion Notification (FN)" for TCP/IP ECN-capable routers. FN has been developed and implemented in Network Simulator 2 (ns-2). It uses the instan-taneous(current) queue length and the average packet arrival rate to make its control decisions. The new mechanism drops the arriving packets (if non-ECN) and marks packets (if ECN) at the head of the queue before the buffer overflows, to effectively control the current queue length (Qcur) below the required optimal queue length (Qopt) in order to reduce the queuing delay and avoid the buffer overflows; and to maintain the average packet arrival rate (R) about the outgoing transmission link capacity (U) in order to enable the congestion and queue length control. Currently, Random Early Detection (RED) mechanism is used in the Internet. RED uses the average queue length for making the control decisions. The use of average queue length makes RED reacts to congestion slowly. This results in large queue length variation and untimely congestion detection and notification which would cause performance degradation due to high queuing delays and high packet loss. The combination of the instantaneous (current) queue length and the average packet arrival rate used by FN showed superior performance to that of RED in term of fast congestion detection and notification. The limitation of the new mechanism is that it works only with responsive connections which play a big role in avoiding and controlling the congestion. Since this thesis considers the necessity for modern queue management mechanisms that can control the Internet traffic efficiently and improve the Internet performance, the major contribution of this thesis is to provide a new pro-active queue management mechanism that responds to congestion more quickly, delivers congestion notification timely, and controls queue length directly to congestion which results in minimizing queue length variation. All these would help improve the Internet performance

The Uniformization Process of the Fast Congestion Notification (FN)

Fast Congestion Notification (FN) is one of the proactive queue management mechanisms that practices congestion avoidance to help avoid the beginning of congestion by marking or dropping packets before the routers queue gets full; and exercises congestion control, when congestion avoidance fails, by increasing the rate of packet marking or dropping. Technically, FN avoids the queue overflows by controlling the instantaneous queue size below the optimal queue size, and control congestion by keeping the average arrival rate close to the outgoing link capacity. Upon arrival of each packet, FN uses the instantaneous queue size and the average arrival rate to calculate the packet marking or dropping probability. FN marks or drops packets at fairly regular intervals to avoid long intermarking intervals and clustered packet marks or drops. Too many marked or dropped packets close together can cause global synchronization, and also too long packet intermarking times between marked or dropped packets can cause large queue sizes and congestion. This paper shows how FN controls the queue size, avoids congestion, and reduces global synchronization by uniformizing marked or dropped packet intervals.Comment: 5 Pages IEEE format, International Journal of Computer Science and Information Security, IJCSIS 2009, ISSN 1947 5500,Impact Factor 0.423, http://sites.google.com/site/ijcsis

Mobile ad hoc networks under wormhole attack: A simulation study

Security has become the main concern to grant protected communication between mobile nodes in an unfriendly environment.Wireless Ad Hoc network might be unprotected against attacks by malicious nodes.This paper evaluates the impact of some adversary attack on mobile Ad Hoc Network (MANET) system which has been tested using QualNet simulator.Moreover, it investigates the active and passive attack on MANET.At the same time, it measures the performance of MANET with and without these attacks.The simulation is done on data link layer and network layer of mobile nodes in wireless Ad Hoc network.The results of this evaluation are very important to estimate the deployment of the MANET nodes for security. Furthermore, this study analyzes the performance of MANET and performs “what-if” analyses to optimize them

Fast congestion notification mechanism for ECN-capable routers

While computer networks go towards dealing with varied traffic types with different service requirements, there is a necessity for modern network control mechanisms that can control the network traffic to meet the users' service requirements. Optimizing the network utilization by improving the network performance can help to accommodate more users and thus increase operators' profits. Controlling the congestion at the gateway leads to better performance ofthe network.Sending congestion signal sooner can be of great benefit to the TCP connection. In this paper, we propose Fast Congestion Notification (FN) mechanism which is a new method for managing the gateway queues and fast sending of congestion signal to the sender. We tested our mechanism on Explicit Congestion Notification (ECN) packets which have higher priority; we achieved good results in terms offaster congestion signal propagation and better network utilization. Our analysis and simulations results show that the use of FN over TCP connections sharing one bottleneck can improve the throughput, having less loss, less delay time, and better network utilization

The drop activation function of the fast congestion notification (FN) mechanism

Fast Congestion Notification (FN) one of the proactive queue management mechanisms that practices congestion avoidance to help avoid the beginning of congestion by marking/dropping packets before the router’s queue gets full; and exercises congestion control, when congestion avoidance fails, by increasing the rate of packet marking/dropping. Upon arrival of each packet, FN uses the instantaneous queue size and the average arrival rate to calculate the packet marking/dropping probability.This paper presents the Drop/Mark Activation Function, which is an internal (built in) function of FN marking/dropping probably function, and shows the conditions under which the FN will trigger a probabilistic packet marking/dropping. This paper shows that the FN’s drop activation function is given by L(Ri, Qcur) =(Ri −μ).T−(Qopt −Qcur)which compares the predicted and required/allowed changes in the queue level, over a time period, to decide whether to attempt or not to attempt packet dropping. L(Ri, Qcur) = 0 defines the set of the drop activation threshold , the set of (average rate, current queue size), (Ri, Qcur), points for which the required/allowed and predicted decrease/increase in the queue level exactly equal each other and that identify the boundary between the drop region (L(Ri, Qcur) > 0), the sets of points at which the packet dropping is attempted, and the no-drop region (L(Ri, Qcur) < 0), the set of points at which the packet dropping is not attempted

The FN quadratic marking/dropping probability function

The gateway queuing performance depends on the marking/dropping probability function chosen. This function plays an important role in managing the gateway buffer. It maps the current congestion level to marking/dropping probability that is applied to each arriving packet. Active queue management mechanisms drop arriving packets probabilistically before the gateway buffer gets full. Fast Congestion Notification (FN) mechanism is a proactive queue management mechanism that marks/drops packets before a buffer overflow happens to avoid congestion. FN avoids the queue overflows by controlling the instantaneous queue size below the optimal queue size, and control congestion by keeping the average arrival rate close to the outgoing link capacity.Upon arrival of each packet, FN uses the instantaneous queue size and the average arrival rate to calculate the packet marking/dropping probability. This paper presents the derivation of the FN quadratic marking/dropping probability function based on the assumption that the average packet arrival rate changes during the control time constant period with the constant acceleration

Effects of Steel Fibers Geometry on the Mechanical Properties of SIFCON Concrete

This research aims to shed light on the effect of steel fiber shape, length, diameter, and aspect ratio on the mechanical properties of slurry infiltration fiber reinforced concrete (SIFCON). This study comprised of casting and testing three groups of SIFCON specimens with 6% fiber volume fraction. The first group was reinforced with micro steel fiber, other reinforced by hook end steel fibers, while the last group of specimens reinforced by mixing two shape of steel fiber as hybrid fiber (3% micro steel fiber +3% hook end steel fiber). Silica fume was used as a partial replacement (10%) by weight of cement. 3.7% super plasticizer was used to make the slurry liquid enough to penetrate through the fiber network, while the w/c ratio kept constant at 0.33. It was found from the results achieved that the compressive strength, static modulus of elasticity, splitting tensile strength and toughness are extremely affected by the geometry of fibers because the network of fibers formed and their density depends on the size and shape of fibers. Where the values of micro steel fibers are far outweighing the values of hooked end fibers. It was also deduced from empiricism results that combining long and short fibers gives excellent results

A demonstration of the FN packet marking probability

The effectiveness of queue management mechanisms relies on how good their control decisions will help in satisfying their goals regarding congestion avoidance and control.These decisions are implemented and compelled during the design of the packet mark probability and the mark activation functions. The design of Fast Congestion Notification (FN) drop/mark probability function enables the two control decisions, packet admissions and congestion control directing, to be made along with each other. This permits sending congestion avoidance notification as early as required even if the queue is almost empty, and preventing congestion notification even if the queue is almost full but the arrival rate is controllable. This leads to good buffer utilization and proper congestion detection. This paper demonstrates the drop/mark probability functions that the fast FN policy would exercise for different values of optimal queue size, and also for a specific optimal queue size value