On Minimizing Delay with Probabilistic Splitting of Traffic Flow in Heterogeneous Wireless Networks

In the paper,we propose a framework to investigate how to effectively perform traffic flow splitting in heterogeneous wireless networks from a queue point.The average packet delay in heterogeneous wireless networks is derived in a probabilistic manner.The basic idea can be understood via treating the integrated heterogeneous wireless networks as different coupled and parallel queuing systems.The integrated network performance can approach that of one queue with maximal the multiplexing gain.For the purpose of illustrating the effectively of our proposed model,the Cellular/WLAN interworking is exploited.To minimize the average delay,a heuristic search algorithm is used to get the optimal probability of splitting traffic flow.Further,a Markov process is applied to evaluate the performance of the proposed scheme and compare with that of selecting the best network to access in terms of packet mean delay and blocking probability.Numerical results illustrate our proposed framework is effective and the flow splitting transmission can obtain more performance gain in heterogeneous wireless networks.     

UNITED STABILIZING SCHEME FOR EDGE DELAY IN OPTICAL BURST SWITCHED NETWORKS

A novel scheme, namely united stabilizing scheme for edge delay, is introduced in optical burst switched networks. In the scheme, the limits of burst length and assembly time are both set according to certain qualifications. For executing the scheme, the conception for unit input bit rate is introduced to improve universality, and the assembly algorithm with a buffer safety space under the self-similar traffic model at each ingress edge router is proposed. Then, the components of burst and packet delay are concluded, and the equations that limits of burst length and assembly time should satisfy to stabilize the burst edge delay under different buffer offered loads are educed. The simulation results show that united stabilizing scheme stabilizes both burst and packet edge delay to a great extent when buffer offered load changes from 0.1 to 1, and the edge delay of burst and packet are near the limit values under larger offered load, respectively.     

Using Chain of Mobile Access Gateway to Reduce Delay for PMIPv6 Protocol Applied in WLAN

Wireless LAN controller (WLC) is used to manage and control Access points (APs) in Wireless local area network (WLAN).Proxy mobile IPv6 (PMIPv6) protocol supports network-layer mobility in WLC based WLAN.However,it introduces extra delay in delivering packets from the APs to the WLC.We use Mobile access gateway (MAG) chain to reduce packet delay.The handoff delay and packet delivery delay under the proposed scheme are derived,based on which we formulate the delay minimization problem whose solution leads to the optimal MAG chain length.Numerical analysis results indicate that the proposed scheme outperforms the existing scheme in terms of delay in the case when the delay between Local mobility anchor (LMA) and WLC is relatively greater than the delay between two neighboring WLCs.The proposed scheme is able to reduce packet loss resulting from the traditional handoff procedure introduced in the PMIPv6 protocol and that due to delay limitation.     

A new composite assembly mechanism for supporting QoS in OBS networks

To provide the differential quality of service（QoS）for different classes of packets and reduce the packet loss probabil ity（PLP）,a novel priority-based composite assembly scheme for optical burst switching（OBS）networks is proposed The low and high packet classes are aggregated into a single burst simultaneously,and the highest-priority packets ar placed in the middle,while the low-priority packets are at the tail and head of the burst.The priority is lowered gradu ally from the middle to the ends.Simulation results demonstrate that the proposed assembly strategy not only guaran tees the integrity of the high-priority bursts,but also significantly reduces the average end-to-end delay of the burst and the PLP of network.So it can adapt to the flexible network with QoS requirement.     

NEW METHOD TO RECOVER INTERNET PACKET LOSSES USING（2，1，m）SYSTEMATIC CONVOLUTIONAL CODES

A new method to recover packet losses using (2,1,m)convolutional codes is proposed.The erasure correcting decoding algorithm and the decoding determinant theorem is presented.It is also proved that the codes with optimal distance profile have also optimal delay characteristic.Simulation results show that the proposed method can recover the packet losses more efficiently than RS codes over different decoding delay conditions and thus suits for different packet network delay conditions.     

NEW METHOD TO RECOVER INTERNET PACKET LOSSES USING(2,1,m)SYSTEMATIC CONVOLUTIONAL CODES

A new method to recover packet losses using (2,1,m)convolutional codes is proposed.The crasure correcting decoding algorithm and the decoding determinant theorem is presented.Itis also proved that the codes with optimal distance profile have also optimal delay characteristic.Simulation results show that the proposed method can recover the packet losses more efficientlythan RS codes over different decoding delay conditions and thus suits for different packet networkdelay conditions.     

Performance Investigation of IEEE 802.11e EDCA Under Non-Saturation Condition Based on the M/G/1/K Model

The IEEE 802.11e network provides different with QoS （Quality of service） guarantee for different traffic streams. The Enhanced distributed channel access （EDCA） in IEEE 802.11e MAC protocol is proposed to support prioritized QoS on the basis of the Distributed coordination function （DCF） in IEEE 802.11. We first build a new Markov chain model for the EDCA. The model takes into account both the idle state that represents that there are no packets to be transmitted and differentiation based on different AIFS-value （Arbitration inter-frame space） for different traffic. We can use the signal transfer function of the generalized Z-transform domain state transition diagram to derive a probability distribution of the MAC layer service time and analyze the performance of EDCA from a non-saturated channel to a saturated medium by using M/G/1/K queuing model. The proposed model is calculated numerically and validated against simulation results, we observed a good match between the analytical model and simulation. Simulation and theoretical results show that despite providing prloritized QoS, the EDCA still can not support strict QoS for real-time application. On the other hand, it is inevitable that there is unfairness of channel access to prloritized traffic due to EDCA.     

A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.     

PERFORMANCE ANALYSIS OF AN INPUT-BUFFERED ATM SWITCHING FABRIC WITH INDEPENDENT WINDOW-ACCESS SCHEME

In this paper, an Independent Window-Access(IWA) scheme is proposed, and the performance of an input-buffered ATM switching fabric with the IWA scheme is analysed by means of a probability generating function approach, the closed formulas of the average cell delay and the maximum throughput are given, and results show that the IWA scheme makes the switching fabric have better performances than traditional window-access scheme. The computer simulation results are in good agreement with these analytical results.     

PERFORMANCE COMPARISON OF CELL－BASED AND PACKET－BASED SWITCHING SCHEMES FOR SHARED MEMORY SWITCHES

Shared Memory (SM) switches are widely used for its high throughput,low delay and efficient use of memory.This paper compares the performance of two prominent switching schemes of SM packet switches:Cell-Based Switching (CBS) and Packet-Based Switching (PBS).Theoretical analysis is carried out to draw qualitative conclusion on the memory requirement,throughput and packet delay of the two schemes.Furthermore,simulations are carried out to get quantitative results of the performance comparison under various system load,traffic patterns,and memory sizes.Simulation results show that PBS has the advantage of shorter time delay while CBS has lower memory requirement and outperforms in throughput when the memory size is limited.The comparison can be used for tradeoff between performance and complexity in switch design.     

A novel self‐adaptive transmission scheme over an IEEE 802.11 WLAN for supporting multi‐service

The IEEE 802.11 wireless local area network (WLAN) media access control (MAC) specification is a hybrid protocol of random access and polling when both distributed coordination function (DCF) and point coordination function (PCF) are used. Data traffic is transmitted with the DCF, while voice transmission is carried out with the PCF. Based on the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self‐adaptive transmission scheme to support multi‐service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self‐adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, voice traffic is sensitive to delay jitter, and the self‐adaptive scheme can effectively decrease it. Finally, it is worth noting that the adaptive scheme is easy to be realized, whereas no change in the MAC protocol is needed. Copyright © 2006 John Wiley & Sons, Ltd.     

IEEE 802.11 WLAN支持语音与数据业务的自适应传输方案研究

IEEE 802.11标准中的MAC协议当采用DCF和PCF时是一种随机竞争接入与轮询相结合的协议。该文通过仿真在分析研究此MAC协议对语音、数据业务综合传输性能的基础上,提出了一种支持语音与数据业务的自适应传输方案。仿真结果表明,在满足语音业务最大允许时延的前提下,自适应传输方案通过动态、合理地调整协议参数,可以提高数据业务的传输性能,从而增加网络容量。特别地,本方案不需要改动协议本身,易于实现。     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance Analysis of IEEE 802.11 DCF in Imperfect Channels

IEEE 802.11 is the most important standard for wireless local area networks (WLANs). In IEEE 802.11, the fundamental medium access control (MAC) scheme is the distributed coordination function (DCF). To understand the performance of WLANs, it is important to analyze IEEE 802.11 DCF. Recently, several analytical models have been proposed to evaluate the performance of DCF under different incoming traffic conditions. However, to the best of the authors' knowledge, there is no accurate model that takes into account both the incoming traffic loads and the effect of imperfect wireless channels, in which unsuccessful packet delivery may occur due to bit transmission errors. In this paper, the authors address this issue and provide an analytical model to evaluate the performance of DCF in imperfect wireless channels. The authors consider the impact of different factors together, including the binary exponential backoff mechanism in DCF, various incoming traffic loads, distribution of incoming packet size, queueing system at the MAC layer, and the imperfect wireless channels, which has never been done before. Extensive simulation and analysis results show that the proposed analytical model can accurately predict the delay and throughput performance of IEEE 802.11 DCF under different channel and traffic conditions.     

A smart exponential‐threshold‐linear backoff mechanism for IEEE 802.11 WLANs

Based on the standardized IEEE 802.11 Distributed Coordination Function (DCF) protocol, this paper proposes a new backoff mechanism, called Smart Exponential‐Threshold‐Linear (SETL) Backoff Mechanism, to enhance the system performance of contention‐based wireless networks. In the IEEE 802.11 DCF scheme, the smaller contention window (CW) will increase the collision probability, but the larger CW will delay the transmission. Hence, in the proposed SETL scheme, a threshold is set to determine the behavior of CW after each transmission. When the CW is smaller than the threshold, the CW of a competing station is exponentially adjusted to lower collision probability. Conversely, if the CW is larger than the threshold, the CW size is tuned linearly to prevent large transmission delay. Through extensive simulations, the results show that the proposed SETL scheme provides a better system throughput and lower collision rate in both light and heavy network loads than the related backoff algorithm schemes, including Binary Exponential Backoff (BEB), Exponential Increase Exponential Decrease (EIED) and Linear Increase Linear Decrease (LILD). Copyright © 2011 John Wiley & Sons, Ltd.     

Model-based admission control for IEEE 802.11e enhanced distributed channel access

IEEE 802.11e enhanced distributed channel access (EDCA) is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this paper, a model-based admission control (MBAC) scheme that performs real-timely at medium access control (MAC) layer is proposed for the decision of accepting or rejecting requests for adding traffic streams to an IEEE 802.11e EDCA wireless local area network (WLAN). The admission control strategy is implemented in access point (AP), which employs collision probability and access delay measures from active flows to estimate throughput and packet delay of each traffic class by the proposed unsaturation analytical model. Simulation results prove accuracy of the proposed analytical model and effectiveness of MBAC scheme.     

An adaptive p-persistent MAC scheme for multimedia WLAN

The letter proposes an adaptive p-persistent-based (APP) medium access control (MAC) scheme for the IEEE 802.11e distributed WLAN supporting multimedia services. The APP MAC scheme adaptively gives differentiated permission probabilities to transmission stations which are in different access category and with various waiting delay. Simulation results show that the APP MAC scheme can improve the performance of multimedia WLAN, such as small voice packet dropping probability, low delay variation, and high system throughput, compared to conventional MAC algorithms     

Adaptive Priority Sliding Admission Control and Scheduling Scheme for DCF and EDCA WLANs

In this paper an Adaptive Priority Sliding Admission Control and Scheduling (APSAS) scheme is proposed to provide QoS over the existing IEEE802.11 WLANs which operate on Distributed Coordination Function (DCF) and Enhanced Distributed Channel Access (EDCA) mechanisms. The roles of this scheme are generally two folds: (1) To control the number of delay-sensitive real time flows that can be admitted into the WLAN Basic Service Set network and (2) To adjust the priority of selected real time flows in order to accommodate more real time flows without violating the QoS requirement. Extensive simulation studies show that APSAS improves the total throughput, flow throughput ratio, packets end-to-end delay, and jitter of the real time applications when compared with conventional best effort and scheduling-enhanced DCF/EDCA. APSAS also offers near to unity average throughput ratio, lower mean VoIP end-to-end packet delay (<130 ms) and lower mean video packet jitter (<130 ms) over DCF and EDCA.     

Improving throughput through dynamically tuning contention window size in dense wireless network

With the boom of wireless devices, the number of wireless users under wireless local area networks (WLANs) has increased dramatically. However, the standard backoff mechanism in IEEE 802.11 adopts fixed initial contention window (CW) size without considering changes of network load, which leads to a high collision probability and low channel utilization in bursty arrivals. In this paper, a novel CW dynamic adjustment scheme is proposed to achieve high throughput performance in dense user environment. In the proposed scheme, the initial CW size is dynamically adjusted to optimum according to the measured packet collision probability. Simulation results show that the proposed scheme can significantly improve the throughput performance.     

Packet telephony support for the IEEE 802.11 wireless LAN

Packet telephony is one of the most promising applications in the Internet. In this paper, we propose a modified MAC protocol supporting voice traffic over the IEEE 802.11 WLAN. The proposed scheme adapts the power-saved mode of the IEEE 802.11 specifications in such a way that it approaches the TDM access mode carrying voice traffic, and is compatible with the IEEE 802.11 standard. Simulation results show that the proposed scheme does not degrade the performance of the IEEE 802.11 WLAN using the DCF and also provides good voice quality