Drop Probability Research Articles

LRED: A Robust and Responsive AQM Algorithm Using Packet Loss Ratio Measurement

Active queue management (AQM) is an effective means to enhance congestion control, and to achieve trade-off between link utilization and delay. The de facto standard, random early detection (RED), and many of its variants employ queue length as a congestion indicator to trigger packet dropping. Despite their simplicity, these approaches often suffer from unstable behaviors in a dynamic network. Adaptive parameter settings, though might solve the problem, remain difficult in such a complex system. Recent proposals based on analytical TCP control and AQM models suggest the use of both queue length and traffic input rate as congestion indicators, which effectively enhances stability. Their response time generally increases however, leading to frequent buffer overflow and emptiness. In this paper, we propose a novel AQM algorithm that achieves fast response time and yet good robustness. The algorithm, called Loss Ratio-based RED (LRED), measures the latest packet loss ratio, and uses it as a complement to queue length for adaptively adjusting the packet drop probability. We develop an analytical model for LRED, which demonstrates that LRED is responsive even if the number of TCP flows and their persisting times vary significantly. It also provides a general guideline for the parameter settings in LRED. The performance of LRED is further examined under various simulated network environments, and compared to existing AQM algorithms. Our simulation results show that, with comparable complexities, LRED achieves shorter response time and higher robustness. More importantly, it trades off the goodput with queue length better than existing algorithms, enabling flexible system configurations

Performance Analysis of the Contention Resolution Scheme in IEEE 802.16

At present, the mandatory contention resolution that shall be supported by IEEE 802.16 is based on truncated binary exponential backoff algorithm. In this paper, the differences of contention mechanism between IEEE 802.16 and IEEE 802.11 are analyzed. The calculations of performance metrics such as the utilization of transmission opportunity u, the delay of bandwidth request d and the drop probability of bandwidth request pd are presented. Based on simulation results, the effects of contention parameters such as the initial window W, the number of subscriber station n and the number of transmission opportunity Nto are discussed. Some policies to adjust the parameters are also provided. These policies are useful for BS to schedule its uplink bandwidth resource.

Dynamic non-collision packet reservation MAP for time division duplex-based wireless networks

The non-collision packet reservation multiple access (NC-PRMA) protocol was proposed by Wen and Wang to eliminate the unstable phenomenon in the PRMA protocol under heavy load conditions by allocating dedicated control mini-slots to mobile terminals (MTs). However, this does not utilise the channel resource efficiently. A dynamic non-collision PRMA (DNC-PRMA) protocol has been proposed to dynamically allocate control mini-slots to MTs such that the channel resource can be utilised efficiently. Using simulation, the proposed DNC-PRMA protocol is shown to yield significantly higher channel utilisation, lower packet dropping probability and lower channel access delay than a protocol that allocates a dedicated mini-slot to each MT.

Discrete-time performance analysis of a congestion control mechanism based on RED under multi-class bursty and correlated traffic

Internet traffic congestion control using queue thresholds is a well known and effective mechanism. This motivates the stochastic analysis of a discrete-time queueing systems for the performance evaluation of the active queue management (AQM) based congestion control mechanism called Random Early Detection (RED) with bursty and correlated traffic using a two-state Markov-Modulated Bernoulli arrival process (MMBP-2) as the traffic source. A two-dimensional discrete-time Markov chain is introduced to model the RED mechanism for two traffic classes where each dimension corresponds to a traffic class with its own parameters. This mechanism takes into account the reduction of incoming traffic arrival rate due to packets dropped probabilistically with the drop probability increasing linearly with system contents. The stochastic analysis of the queue considered could be of interest for the performance evaluation of the RED mechanism for the multi-class traffic with short range dependent (SRD) traffic characteristics. The performance metrics including mean system occupancy, mean packet delay, packet loss probability and system throughput are computed from the analytical model for a dropping policy which is a function of the thresholds and maximum drop probability. Typical numerical results are included to illustrate the credibility of the proposed mechanism in the context of external bursty and correlated traffic. These results clearly demonstrate how different threshold settings can provide different trade-offs between loss probability and delay to suit different service requirements. The effects on various performance measures of changes in the input parameters and of burstiness and correlations exhibited by the arrival process are also presented. The model would be applicable to high-speed networks which use slotted protocols.

On utility-fair bandwidth adaptation for multi-class traffic QoS provisioning in wireless networks

The ability to adjust the allocated bandwidth of ongoing calls to cope with wireless network resource fluctuations is becoming increasingly important. In this paper, we describe a utility-based bandwidth adaptation scheme for multi-class traffic quality-of-service (QoS) provisioning in wireless networks. With the proposed scheme, each call is assigned a utility function according to its adaptive characteristics. Depending on the network load the allocated bandwidth of ongoing calls are upgraded or degraded dynamically such that each call receives fair utility. The quantization of utility function by dividing the utility range into a fixed number of equal intervals is a key feature of our proposed utility-fair algorithm. Appropriate call admission control and bandwidth reservation policies are also integrated into the proposed scheme to provide QoS guarantees to the new and handoff calls. Extensive simulation experiments have been conducted to evaluate the performance of the proposed scheme compared with two other existing ones. Results show that our bandwidth adaptation scheme is effective in achieving utility fairness while keeping the call blocking and handoff dropping probabilities substantially low.

Mobility Influences on the Capacity of Wireless Cellular Networks

Capacity has always been a major concern in wireless networks. This letter studies the impact of mobility on the overall system capacity in wireless cellular networks. In this letter, we present a simple system model which we developed to capture the inherent relationships among system capacity, new call blocking probability, handoff dropping probability, call terminating probability, and bandwidth utilization rate. We investigate the complex relationship between mobility and capacity-related parameters. Through simulation, we demonstrate that mobility has a significant impact on capacity and is reversely proportional to the bandwidth reserved for handoff traffic.

Can high-speed networks survive with DropTail queues management?

It has been observed that TCP connections that go through multiple congested links (MCL) have a smaller transmission rate than the other connections. Such TCP behavior is a result of two components (i) the cumulative packet losses that a flow experiences at each router along its path; (ii) the longer round trip times (RTTs) suffered by such flows due to non-negligible queueing delays at congested routers. This double ''bias'' against connections with MCLs has been shown to approximate the so-called minimum potential delay fairness principle in the current Internet. Despite the recent proliferation of new congestion control proposals for TCP in high-speed networks, it is still unclear what kind of fairness principle could be achieved with such newly proposed congestion control protocols in high-speed networks with large-delays. Studies already show that some high-speed TCP variants may cause surprisingly severe RTT unfairness in high-speed networks with DropTail routers. This paper studies the problem of unfairness in high-speed networks with some well-known high-speed TCP variants in presence of multiple congested links and highlights the severity of such unfairness when DropTail queue management is adopted. Through a simple synchronized loss model analysis, we show how synchronized losses with DropTail in high-speed networks could lead to severe RTT unfairness and drop probability (DP) unfairness; while random marking AQM schemes, which break the packet loss synchrony mitigate such unfairness dramatically by ensuring that the packet loss probability of a flow is the sum of the loss probabilities on the congested routers it crosses. Extensive simulations are carried out and the results support our findings.

Design and Analysis of a Multiscale Active Queue Management Scheme

Since Internet is dominated by TCP-based applications, active queue management (AQM) is considered as an effective way for congestion control. However, most AQM schemes suffer obvious performance degradation with dynamic traffic. Extensive measurements found that Internet traffic is extremely bursty and possibly self-similar. We propose in this paper a new AQM scheme called multiscale controller (MSC) based on the understanding of traffic burstiness in multiple time, scale. Different from most of other AQM schemes, MSC combines rate-based and queue-based control in two time scales. While the rate-based dropping on burst level (large time scales) determines the packet drop aggressiveness and is responsible for low and stable queuing delay, good robustness and responsiveness, the queue-based modulation of the packet drop probability on packet level (small time scales) will bring low loss and high throughput. Stability analysis is performed based on a fluid-flow model of the TCP/MSC congestion control system and simulation results show that MSC outperforms many of the current AQM schemes.

Performance Analysis of Call Admission Control in WCDMA Systems with Mobility based Interference Margin Reservation

This study presents performance of call admission control and resource reservation schemes based on the mobility of the users in WCDMA cellular systems. In order to guarantee the handoff dropping probability, the mobility of the user is predicted based on a realistic mobility model. The mobility prediction scheme used in this study is used to estimate the set of candidate cells into which the mobile may move in the near future and calculates the likeliness value for each candidate cell. It also estimates the time slot at which the mobile may enter into the candidate cells based on the distance between the current location of the mobile and the candidate cell center distance. Based on the mobility prediction, resource is reserved in terms of Interference Guard margin (IGM) to guarantee some target handoff dropping probability. The admission threshold is adaptively controlled to achieve a better balance between guaranteeing handoff-dropping probability and maximizing resource utilization. Simulation results show that the call admission control scheme with mobility based resource reservation scheme outperforms well when compared with the fixed reservation scheme.

A Predictive Bandwidth Reservation Scheme Using Mobile Positioning and Road Topology Information

In cellular networks, an important practical issue is how to limit the handoff dropping probability efficiently. One possible approach is to perform dynamic bandwidth reservation based on mobility predictions. With the rapid advances in mobile positioning technology, and the widespread availability of digital road maps previously designed for navigational devices, we propose a predictive bandwidth reservation scheme built upon these timely opportunities. In contrast to the common practice of utilizing only incoming handoff predictions at each cell to compute the reservations, our scheme is more efficient as it innovatively utilizes both incoming and outgoing handoff predictions; it can meet the same target handoff dropping probability by blocking fewer new calls. The individual base stations are responsible for the computations, which are shown to be simple enough to be performed in real-time. We evaluate the scheme via simulation, along with five other schemes for comparison. Simulation results show that those schemes that rely on positioning information are significantly more efficient than those that do not. Our scheme's additional use of the road topology information further improves upon this advantage, bringing the efficiency closer to the bound set by a benchmark scheme that assumes perfect knowledge about future handoffs

Radio resource management for a mobile network with TD-CDMA

In the paper, we proposed a resource allocation method employing maximal compatible cliques to make use of channel bandwidth as efficiently as possible in a TD-CDMA system. Furthermore, the strength of beacon signals was also measured to decide whether or not to reserve resources for hand-off users, in order to reduce their dropping probabilities. Finally, we conducted several experiments to validate that our method could make use of the finite resources efficiently, thereby revealing better blocking probabilities and dropping probabilities than other methods.

Joint call and packet QoS in cellular packet networks

This paper proposes a novel call admission control scheme capable of providing a combination of call and packet level quality of service requirements in cellular packet networks. Specifically, we propose a distributed call admission control scheme called PFG, which maximizes the wireless channel utilization subject to a predetermined bound on the call dropping and packet loss probabilities for variable-bit-rate traffic in a packet-switched wireless cellular network. We show that in wireless packet networks, the undesired event of dropping an ongoing call can be completely eliminated without sacrificing the bandwidth utilization. Extensive simulation results confirm that our scheme satisfies the hard constraint on call dropping and packet loss probabilities while maintaining a high bandwidth utilization.

Adaptive path selection in OBS networks

In this paper, the authors investigate the concept of adaptive path selection in optical burst-switched networks and its potential to reducing the overall burst drop probability. Specifically, the authors assume that each source maintains a (short) list of alternate paths to each destination and uses information regarding the recent congestion status of the network links to rank the paths; it then transmits bursts along the least congested path. The authors present a suite of path selection strategies, each utilizing a different type of information regarding the link congestion status, and evaluate them using simulation. The results demonstrate that, in general, adaptive path selection outperforms shortest path routing, and, depending on the path strategy involved, the network topology, and the traffic pattern, this improvement can be significant. A new framework for the development of hybrid (or meta) path selection strategies, which make routing decisions based on a weighted combination of the decisions taken by several independent path selection strategies, has been presented. This paper presents two instances of such hybrid strategies, i.e., 1) one that assigns static weights and 2) one that dynamically adjusts the weights based on feedback from the network; it has been shown that these strategies can further improve the overall burst drop probability in the network.

Measurement-Based Predictive Admission Control for Mobile QoS in DiffServ Networks

The crucial issue for mobile Internet services is to provide the guaranteed mobile QoS for multicalls. In mobile networks, we should not only guarantee handoff dropping probability but also maximize resource utilization. In this paper, we propose a QoS admission control mechanism for macro Mobile QoS based on a dynamic resource reservation. We introduce the requirements for macro Mobile QoS as mobility features and predict required resources in each routing paths thorough the combined analysis of average movement pattern and pre-defined handoff dropping probability. Our simulation results show that the proposed scheme can guarantee the pre-defined handoff dropping probability and maintain lower call blocking probability and higher resource utilization than other schemes. The propose scheme gives a practical solution for mobile networks providing mobile Internet services.

A New Fair Call Admission Control for Integrated Voice and Data Traffic in Wireless Mobile Networks

It is essential to guarantee a handoff dropping probability below a predetermined threshold for wireless mobile networks. Previous studies have proposed admission control policies for integrated voice/data traffic in wireless mobile networks. However, since QoS has been considered only in terms of CDP (Call Dropping Probability), the result has been a serious CBP (Call Blocking Probability) unfairness problem between voice and data traffic. In this paper, we suggest a new admission control policy that treats integrated voice and data traffic fairly while maintaining the CDP constraint. For underprivileged data traffic, which requires more bandwidth units than voice traffic, the packet is placed in a queue when there are no available resources in the base station, instead of being immediately rejected. Furthermore, we have adapted the biased coin method concept to adjust unfairness in terms of CBP. We analyzed the system model of a cell using both a two-dimensional continuous-time Markov chain and the Gauss-Seidel method. Numerical results demonstrate that our CAC (Call Admission Control) scheme successfully achieves CBP fairness for voice and data traffic.

Determination of Optimal Cell Capacity for Initial Cell Planning in Wireless Cellular Networks

In wireless cellular networks, previous researches on admission control policies and resource allocation algorithm considered the QoS (Quality of Service) in terms of CDP (Call Dropping Probability) and CBP (Call Blocking Probability). However, since the QoS was considered only within a predetermined cell capacity, the results indicated a serious overload problem of systems not guaranteeing both CDP and CBP constraints, especially in the hotspot cell. That is why a close interrelationship between CDP, CBP and cell capacity exists. Thus, it is indispensable to consider optimal cell capacity guaranteeing multiple QoS (CDP and CBP) at the time of initial cell planning for networks deployment. In this paper, we will suggest a distributed determination scheme of optimal cell capacity guaranteeing both CDP and CBP from a long-term perspective for initial cell planning. The cell-provisioning scheme is performed by using both the two-dimensional continuous-time Markov chain and an iterative method called the Gauss-Seidel method. Finally, numerical and simulation results will demonstrate that our scheme successfully determines an optimal cell capacity guaranteeing both CDP and CBP constraints for initial cell planning.

An adaptive algorithm for active queue management

This paper proposes an adaptive proportional integral (API) algorithm for active queue management. API uses mean packet loss ratio and mean queue length as control error to adaptively adjust packet drop probability in order to expedite congestion control. The extensive simulations validate that API achieves faster control response and improved performance in terms of goodput, average queue length, and packet loss ratio.

Approximate fair bandwidth sharing in high-speed multimedia networks

Existing fair-queuing algorithms use complicated flow management mechanisms, thus making them expensive to deploy in current high-bandwidth networks. In this paper we propose a scalable SCORE (stateless core) approach to provide fair bandwidth sharing for a traffic environment composed of TCP and UDP flows. At an edge router, the arrival rates of each flow are estimated, each packet then being labelled with this estimate. The outgoing link's fair share at a router is estimated based on UDP traffic. Probabilistic dropping is used to regulate those flows that send more than the fair share. At a core router, all the functions performed by an edge router are repeated, excluding the flow rate estimation. The simulation results show that the degree of fairness achieved by the proposed solution is comparable to that of other algorithms, but with a lower implementation cost.

On the role and controllability of persistent clients in traffic aggregates

Flash crowd events (FCEs) present a real threat to the stability of routers and end-servers. Such events are characterized by a large and sustained spike in client arrival rates, usually to the point of service failure. Traditional rate-based drop policies, such as Random Early Drop (RED), become ineffective in such situations since clients tend to be persistent, in the sense that they make multiple retransmission attempts before aborting their connection. As it is built into TCP's congestion control, this persistence is very widespread, making it a major stumbling block to providing responsive aggregate traffic controls. This paper focuses on analyzing and modeling the effects of client persistence on the controllability of aggregate traffic. Based on this model, we propose a new drop strategy called persistent dropping to regulate the arrival of SYN packets and achieves three important goals: 1) it allows routers and end-servers to quickly converge to their control targets without sacrificing fairness; 2) it minimizes the portion of client delay that is attributed to the applied controls; and 3) it is both easily implementable and computationally tractable. Using a real implementation of this controller in the Linux kernel, we demonstrate its efficacy, up to 60 % delay reduction for drop probabilities less than 0.5.

Variable IP packets buffer management schemes for optical packet switching

Effective buffering of optical packets is essential to the efficient working of optical packet switches. In this paper three new schemes, which involve sorting and finding the least occupied buffer, are proposed. Their performance is compared with the common round-robin scheme. The results show that all these new schemes are able to enhance the optical packet switch performance significantly in terms of packet drop/loss probability. In addition, the results show that not all the newly arrived packets need to be sorted in order to obtain the minimum packet drop probability. As computation/processing time is significant in optical packet switching, partial sorting of the newly arrived packets with tolerable packet drop probability appears to be a viable proposition. Conversely, a complete sort of newly arrived packets wastes packet processing time unnecessarily while significantly increasing the packet drop probability.