Lower Average Delay Research Articles

Pi: A practical incentive protocol for delay tolerant networks

Delay Tolerant Networks (DTNs) are a class of networks characterized by lack of guaranteed connectivity, typically low frequency of encounters between DTN nodes and long propagation delays within the network. As a result, the message propagation process in DTNs follows a store-carryand- forward manner, and the in-transit bundle messages can be opportunistically routed towards the destinations through intermittent connections under the hypothesis that each individual DTN node is willing to help with forwarding. Unfortunately, there may exist some selfish nodes, especially in a cooperative network like DTN, and the presence of selfish DTN nodes could cause catastrophic damage to any well designed opportunistic routing scheme and jeopardize the whole network. In this paper, to address the selfishness problem in DTNs, we propose a practical incentive protocol, called Pi, such that when a source node sends a bundle message, it also attaches some incentive on the bundle, which is not only attractive but also fair to all participating DTN nodes. With the fair incentive, the selfish DTN nodes could be stimulated to help with forwarding bundles to achieve better packet delivery performance. In addition, the proposed Pi protocol can also thwart various attacks, which could be launched by selfish DTN nodes, such as free ride attack, layer removing and adding attacks. Extensive simulation results demonstrate the effectiveness of the proposed Pi protocol in terms of high delivery ratio and lower average delay.

Energy efficient and QoS based routing protocol for wireless sensor networks

The increasing demand for real-time applications in Wireless Sensor Networks (WSNs) has made the Quality of Service (QoS) based communication protocols an interesting and hot research topic. Satisfying Quality of Service (QoS) requirements (e.g. bandwidth and delay constraints) for the different QoS based applications of WSNs raises significant challenges. More precisely, the networking protocols need to cope up with energy constraints, while providing precise QoS guarantee. Therefore, enabling QoS applications in sensor networks requires energy and QoS awareness in different layers of the protocol stack. In many of these applications (such as multimedia applications, or real-time and mission critical applications), the network traffic is mixed of delay sensitive and delay tolerant traffic. Hence, QoS routing becomes an important issue. In this paper, we propose an Energy Efficient and QoS aware multipath routing protocol (abbreviated shortly as EQSR) that maximizes the network lifetime through balancing energy consumption across multiple nodes, uses the concept of service differentiation to allow delay sensitive traffic to reach the sink node within an acceptable delay, reduces the end to end delay through spreading out the traffic across multiple paths, and increases the throughput through introducing data redundancy. EQSR uses the residual energy, node available buffer size, and Signal-to-Noise Ratio (SNR) to predict the best next hop through the paths construction phase. Based on the concept of service differentiation, EQSR protocol employs a queuing model to handle both real-time and non-real-time traffic. By means of simulations, we evaluate and compare the performance of our routing protocol with the MCMP (Multi-Constraint Multi-Path) routing protocol. Simulation results have shown that our protocol achieves lower average delay, more energy savings, and higher packet delivery ratio than the MCMP protocol.

Packet Scheduling and Fairness for Multiuser MIMO Systems

This paper investigates the network resource allocation in multiuser downlink wireless systems where the base station and the mobile stations are equipped with multiple antennas to provide fair and efficient transmission services to the mobile users. We focus on packet scheduling, given that it has a significant impact on the overall performance of a multiple-input-multiple-output (MIMO) system. Most previous schedulers designed at the packet level do not take into account the traffic characteristics (different packet lengths and the arrival process parameters); consequently, they fall short of simultaneously providing fairness and a low average packet transmission delay. We are making use of a flexible packet transmission algorithm at the medium access control (MAC) layer to develop and propose a novel scheduler, which is referred to as MIMO packet-based proportional fairness (MP-PF). The new scheduler is designed with the goal of providing high performance in terms of a low average packet transmission delay and time and service fairness among the users based on the concept of proportional fairness. The scheduler also conserves work and takes into consideration the packet length, the user queue length, the user transmission rate (related to its channel quality), and the service guarantees for heterogeneous users. The well-known ideal service fair scheduler called max-min can also significantly be improved using our framework by taking into consideration the traffic characteristics. We also provide an analysis for the fairness of the new scheduler in terms of time and service allocation, which is the key contribution of this paper. Simulations that consider the traffic characteristics and the mobility of users show the relatively low average packet transmission delay and demonstrate the time and service fairness capabilities of MP-PF, compared with other well-known MIMO schedulers.

An Improved ARED Algorithm for Congestion Control of Network Transmission

In order to achieve high throughput and low average delay in computer network, it is necessary to stabilize the queue length and avoid oscillation or chaos phenomenon. In this paper, based on Adaptive Random Early Detection (ARED), an improved algorithm is proposed, which dynamically changes the range of maximum drop probabilitypmaxaccording to different network scenarios and adjustspmaxto limit average queue sizeqavein a steady range. Moreover, exponential averaging weightwis adjusted based on linear stability condition to stabilizeqave. A number of simulations show that the improved ARED algorithm can effectively stabilize the queue length and perform better than other algorithms in terms of stability and chaos control.

Low-distance path-based multicast routing algorithm for network-on-chips

In this study, a low-distance path-based multicast routing algorithm for network-on-chips (NoCs) and multiprocessor systems-on-chip is proposed. The algorithm, which is based on the mesh topology, makes use of network partitioning, optimised destination ordering and the odd–even turn model adaptive routing technique for both the multicast and unicast messages. Additionally, the algorithm invokes non-congested paths in routing the messages to prevent creating highly congested areas. This is achieved by considering the congestion condition of the input ports. The efficiency of the proposed multicast routing algorithm is evaluated by comparing its performance with those of previously proposed algorithms under both multicast and mixed (mixture of unicast and multicast) traffic models. The results show that the proposed technique has lower average delays and lower average and peak power consumptions compared to those of the other path-based multicasting algorithm for different message injection rates. The technique has a hardware overhead of less than 8%.

Throughput-Optimal Scheduling with Low Average Delay for Cellular Broadcast Systems

While a number of scheduling policies achieve the maximum throughput region, the average delay minimization problem for cellular broadcast systems still awaits its complete solution. To this end, we introduce a scheduling policy which decomposes the cross-layer delay optimization problem into two subproblems: allocation of physical resources and user priority management. The first subproblem is translated into a weighted sum rate maximization problem that can be efficiently solved for different channel models. The solution of the second subproblem determines the weight factors in the maximization problem expressing the priorities of users. For the latter subproblem we present a so-called idle state prediction algorithm minimizing our relevant delay measure. Analytical and simulative tools are used to show that the introduced scheduling policy provides both optimal throughput and low delay performance.

An Adaptive Interpiconet Scheduling Algorithm Based on HOLD Mode in Bluetooth Scatternets

To efficiently relay packets between associated piconets in an arbitrary-sized scatternet, an adaptive interpiconet scheduling algorithm is a requisite in a bridge. In this paper, we proposed a new interpiconet scheduling algorithm based on the HOLD mode - a power-saving mode of Bluetooth - to reduce the average interpiconet packet delay while increasing the utilization of a bridge. Generally speaking, interpiconet packet delay mainly results from the phenomenon that a bridge stays in one piconet without any interpiconet transmission activity in progress while other associated piconets are waiting for the bridge to deal with interpiconet packets. Thus, our proposed scheme estimates the time duration for which the bridge should stay in each piconet according to the traffic pattern so that the bridge can avoid being idle as possible. In particular, neither Bluetooth specification modifications nor any extra devices are needed to integrate our proposed interpiconet scheduling algorithm. Finally, the simulation results show the superiority of our proposed scheme, including low average delay, high throughput, and remarkable scalability.

FP-MAC: A distributed MAC algorithm for 802.15.4-like wireless sensor networks

In this paper we focus on the problems of high latency and low throughput arising from the periodic operation of MAC protocols for wireless sensor networks. In order to meet both design criteria we propose an energy-efficient, low delay, fast-periodic MAC algorithm, namely FP-MAC, that is exclusively designed for 802.15.4-like networks utilizing in full the standard’s physical layer. Our proposal relies on the short periodic communication operation of the nodes comprising the WSN. This is achieved by decreasing the actions that a node needs to perform at the start of every communication period and by incorporating a variable radio-on operation. Moreover, the algorithm introduces differences in nodes’ scheduling to further reduce delay. Local synchronization and the crucial task of determining the proper timing for transmission and reception of data is achieved through the periodic broadcast of special synchronization frames at the beginning of each on-period. FP-MAC is evaluated and compared to S-MAC and T-MAC through extensive simulations, showing a significant improvement in terms of low energy consumption and average MAC delay.

Hybrid Multicast Mode in All-Optical Networks

Although serial multicast mode (SMM) can increase the multicast success ratio (MSR) more than parallel multicast mode (PMM), it suffers from the signal impairment and the extra delay caused by the optical loop. In this letter, a novel hybrid multicast mode (HMM), which combines PMM and SMM, is proposed to mitigate those issues. Moreover, an HMM-based two-level-buffered all-optical multicast module is also proposed to further mitigate the signal impairment in this letter. Finally, with the simulations, a conclusion can be drawn that HMM can get higher MSR and lower average delay than both PMM and SMM.

Modified user-dependent perfect-scheduling multiple access protocol for WLAN

Based on effective contention access and perfect scheduling transmission, an enhanced multiple access protocol UPMA++ protocol is proposed. It allocates the resource dynamically according to the actual traffic requirement and does not require the synchronisation in the whole network. This protocol adjusts the length of contention access period and polling period effectively to resolve the conflicts between active stations and transmission stations. By analysis, the optimal contention access period length for the given polling period length is found, and the performance evaluations show that UPMA++ protocol has a high throughput, low average message delay and small average message dropping probability.

Degree-sequenced matching algorithms for input-queued switches

This paper presents a class of algorithms for scheduling packets in input-queued switches. As opposed to previously known algorithms that focus only on achieving high throughput, these algorithms seek to achieve low average delay without compromising the throughput achieved. Packet scheduling in input-queued switches based on the virtual-output-queued architecture is a bipartite graph matching problem wherein ports are represented by vertices and the traffic flows by the edges. The set of matched edges determine the packets that are to be transferred from the input ports to the output ports. Current matching algorithms implicitly prioritize high-degree vertices, i.e., ports with a large number of flows, causing longer delays at ports with a smaller number of flows. Motivated by this observation, we present three matching algorithms based on explicitly prioritizing low-degree vertices and the edges through them. Using both real gateway traffic traces as well as synthetically generated traffic, we present simulation results showing that this class of algorithms achieves a low average delay as compared to other scheduling algorithms of equivalent complexity while still achieving similar throughput. We also show that these algorithms determine the maximum size matching in almost all cases.

An energy‐efficient multipath routing protocol for wireless sensor networks

AbstractThe energy consumption is a key design criterion for the routing protocols in wireless sensor networks. Some of the conventional single path routing schemes may not be optimal to maximize the network lifetime and connectivity. In this paper, we propose a distributed, scalable and localized multipath search protocol to discover multiple node‐disjoint paths between the sink and source nodes. We also propose a load balancing algorithm to distribute the traffic over the multiple paths discovered. We compare our proposed scheme with the directed diffusion, directed transmission, N‐to‐1 multipath routing, and the energy‐aware routing protocols. Simulation results show that our proposed scheme has a higher node energy efficiency, lower average delay and control overhead than those protocols. Copyright © 2006 John Wiley & Sons, Ltd.

Mantle wedge anisotropy in the Hikurangi subduction zone, central North Island, New Zealand

The anisotropic characteristics of the Hikurangi subduction zone in central North Island, New Zealand are studied using shear‐wave splitting measurements from 55 local earthquakes recorded on a 200 km profile of 19 stations. The eastern fore‐arc shows trench‐parallel fast directions and a low average delay time of 0.2 s. The source of anisotropy is confined to the upper 60 km and is likely to be deformation induced within the overriding Australian plate. Central western North Island shows N‐S trending fast anisotropy which may signify the presence of a viscous blanket of mantle material being entrained by the absolute motion of the Australian plate. Between these regions a dramatic switch to extension‐parallel fast directions and delay times of 0.35 s are seen across the back‐arc in the Taupo Volcanic Zone (TVZ). These results suggest asthenospheric flow beneath the overriding plate with the olivine a‐axes oriented in the extension direction down to a maximum depth of 100 km.

Preemptive Short Packets Priority Scheduling for Asynchronous Optical Packet Switching

The average queue delay of optical packet increases when the packets block in the virtual output queue header in the asynchronous optical packet switching. We analyze the character of variable length Internet packet and propose the preemptive short packets priority (PSPP) algorithm for reducing the total packet queue time in the queue. In the PSPP algorithm, the short packet can preempt the transmission time of the long packet and can be served first. The analysis and the simulation showed the PSPP algorithm can make the average queue time of the short packet decrease to zero almost and can decrease the total packet average queue time largely when the traffic load was middle and low. The PSPP could guarantee the low average queue delay for the real -time TCP traffic.

Performance improvement of active queue management with per-flow scheduling

Active queue management (AQM) has two main objectives. One is to achieve high throughput and low average queueing delay simultaneously. The other is to achieve fair bandwidth allocation among competing flows. Although many algorithms have been proposed and investigated in an effort to fulfil the goal of AQM, there are few studies on AQM with per-flow scheduling. This is because longest queue drop (LQD), which is commonly used as a queue management discipline with per-flow scheduling, has good performance in terms of throughput and fairness. However, LQD suffers from long queueing delays. In addition, it cannot support explicit congestion notification (ECN). Accordingly, for AQM with per-flow scheduling, the following requirements can be specified: it achieves simultaneously lower average queueing delays than LQD and the same throughput as LQD, it achieves the same degree of fairness as LQD and it achieves lower packet loss ratios than LQD when flows are ECN-capable. A new AQM is proposed that fulfils these requirements. In the mechanism, packets are dropped probabilistically before the buffer is full. The probability is maintained for each active flow. The probability of the flow with the longest queue length is increased when the network is congested. Simulations confirm that the mechanism achieves the requirements set for AQM with per-flow scheduling.

Quality-of-service and quality-of-protection issues in preplanned recovery schemes using redundant trees

We study quality-of-service (QoS) and quality-of-protection (QoP) issues in redundant tree based preplanned recovery schemes for a single-link failure in two-edge connected graphs and for a single-node failure in two-connected graphs. We present schemes (to be called G-MFBG schemes) that generalize the schemes (to be called MFBG schemes) developed by Me/spl acute/dard et al. (1997) to construct a pair of redundant trees, called red and blue trees, which guarantees fast recovery from any single-link/node failure, as long as the failed node is not the root node. Using the G-MFBG schemes, we study QoS issues relating to red/blue trees. We present effective heuristics for computing a pair of redundant trees with low average delay or small total cost. We develop an optimal algorithm for computing a pair of red/blue trees with maximum bandwidth. Furthermore, a pair of red/blue trees guarantees fast recovery from simultaneous multiple failures if it satisfies certain properties. This leads us to define the concept of QoP of a pair of red/blue trees. We present an effective heuristic to construct a pair of red/blue trees with high QoP. The paper concludes with a discussion of computational results that demonstrate the effectiveness of the different algorithms presented.

A predictive demand assignment multiple access protocol for Internet access over broadband satellite networks

AbstractMedium access control (MAC) protocol is responsible for wireless resource management, which is crucial to satellite communication. To enhance the performance of broadband satellite networks, the application characteristics should be considered in the design of the MAC protocol. With the rapid expansion of Internet applications and the attractiveness of high speed Internet access via broadband satellite networks, it becomes an attractive objective to take into account the self‐similar nature of Internet traffic in MAC protocol designs. This paper presents a novel predictive demand assignment multiple access (PRDAMA) protocol for packet communications over broadband satellite networks. PRDAMA allocates free bandwidth resources by estimating the positive varying trend of the Internet traffic to facilitate prediction of the bandwidth requirements of the earth stations. Simulation results demonstrate that PRDAMA achieves a lower average delay and delay jitter compared with other DAMA protocols under highly bursty traffic due to its accurate traffic trend prediction. With less bursty traffic, PRDAMA still performs better than the other DAMA protocols under a heavy traffic load. Copyright © 2003 John Wiley & Sons, Ltd.

Packet-scheduling algorithm based on priority of separate buffers for unicast and multicast services

A new integrated packet-scheduling algorithm that handles both unicast and multicast traffic concurrently by using two logically divided buffers in each input port is proposed. Computer simulations show that the proposed scheme gives not only low average output packet delay, but also low output packet delay variance for packets with different fan-outs.

Load balanced Birkhoff-von Neumann switches with resequencing

Load balanced Birkhoff-von Neumann switches with resequencing

Multidestination communication over tunable-receiver single-hop WDM networks

We address the issue of providing efficient mechanisms for multidestination communication over one class of lightwave wavelength division multiplexing (WDM) architectures, namely, single-hop networks with tunability provided only at the receiving side. We distinguish a number of multicast traffic types, we present a number of alternative broadcast/multicast time-division multiple-access (TDMA) schedules for each type, and we develop heuristics to obtain schedules that result in low average packet delay. One of our major contributions is the development of a suite of adaptive multicast protocols which are simple to implement, and have good performance under changing multicast traffic conditions.