A CSMA/CD compatible MAC for real-time transmissions based on varying collision intervals

This paper suggests a CSMA/CD compatible MAC protocol for real-time transmissions in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted.     

Enhanced MAC protocol to support multimedia traffic in cognitive wireless mesh networks

With the advanced physical layer techniques such as multiple-input and multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM), transmission real-time 2D/3D contents and applications becomes more and more necessary in wireless networks for the amazing growing in demand of customers. However, the low efficiency of medium access control (MAC) protocol degrades the performance of real-time traffic greatly in multihop, wireless and mobile environment. Focusing on supporting real-time multimedia traffic in cognitive wireless mesh networks (WMNs), an enhanced MAC protocol is proposed. And the contribution of this paper is twofold: (1) An efficient carrier sense multiple access with collision avoidance (CSMA/CA) compatible time division multiple access (TDMA)-like MAC protocol called T-MAC is proposed, which aims to improve the system performance by allocating more channel access time in centralized manner and decreasing overhead. (2) An optimal adaptive scheduling scheme is proposed to support real-time multimedia applications and guarantee QoS for different priority traffic, which aims to find the optimized schedule among all possible sequences of concurrent transmissions by minimizing the occupied resources. Detailed simulation results and comparison with IEEE 802.11e MAC scheme show that the proposed T-MAC can effectively improve quality of service (QoS) for multimedia traffic in terms of throughput, end-to-end delay and packet loss rate, which also manifests that T-MAC is an efficient multimedia applications transmission scheme for mobile terminals and MAPs in cognitive WMNs.     

分布式控制系统内部强实时通信研究

研究了基于OSI／ISO七层参考模型的Mac子层的通信协议的效率，计算并通过实验证明了应用于分布式控制系统时以太网Mac子层的最大潜力，在对基于连接的协议和基于无连接的协议进行实时性测试后，大量实验数据论证了对于采用IP协议族的分布式控制系统来讲，必须在传输层采用基于无连接的UDP协议，最后通过电力系统故障实验证明在分布式控制系统中采用以上方案可以达到实时性的要求。     

Channel time allocation scheme based on feedback information in IEEE 802.11e wireless LANs

The IEEE 802.11e standard defines a set of quality of service (QoS) enhancements for wireless local area network (WLAN) applications such as voice and streaming multimedia traffic. In the standard, a new medium access control (MAC) protocol is called the hybrid coordinator function (HCF), and also a channel access scheme to transmit multimedia traffic is called the HCF controlled channel access (HCCA). In the IEEE 802.11e WLANs, to satisfy the stringent real-time constraints of multimedia services it is very important to provide an efficient method of allocating network resources. In this regard, we propose a feedback-assisted dynamic channel time allocation scheme considering the application layer information in order to achieve better performance of multimedia traffic over IEEE 802.11e HCCA under the constrained QoS requirements. Performance of the proposed scheme is investigated by simulation. Our results show that under typical channel error conditions, the proposed scheme is very effective regardless of the variation of station numbers and service intervals. Also, it yields high performances while guaranteeing the delay bound.     

A cross-layer elastic CAC and holistic opportunistic scheduling for QoS support in WiMAX

QoS provisioning is an important issue in the deployment of broadband wireless access networks with real-time and non-real-time traffic integration. An opportunistic MAC (OMAC) combines cross-layer design features with opportunistic scheduling scheme to achieve high system utilization while providing QoS support to various applications. A single scheduling algorithm cannot guarantee all the QoS requirements of traffics without the support of a suitable CAC and vice versa. In this paper, we propose a cross-layer MAC scheduling framework and a corresponding opportunistic scheduling algorithm in tandem with the CAC algorithm to support QoS in WiMAX point-to-multipoint (PMP) networks. Extensive experimental simulations have been carried out to evaluate the performance of our proposal. The simulation results show that our proposed solution can improve the performance of WiMAX networks in terms of packet delay, packet loss rate and throughput. The proposed CAC scheme can guarantee the admitted connections to meet their QoS requirements.     

QoS and energy efficiency in network wide broadcasting: A MAC layer perspective

In this paper we investigate the role of medium access control on the performance of network-wide real-time data broadcasting through flooding using three MAC protocols (IEEE 802.11, CPS, and MH-TRACE) in terms of QoS (packet delivery ratio, packet delay, and delay jitter) and energy dissipation. We conduct extensive simulations to evaluate the performance of network-wide broadcasting through flooding in the node density, traffic load, and network size/topology parameter space. The results of our study show that different MAC protocols produce better performance than the others in different parts of the parameter space. Thus, in designing network layer broadcast architectures, the characteristics of the medium access control layer should be given the utmost importance to ensure the satisfactory performance of the system.     

工业以太网实时调度技术的设计与实现

鉴于以太网在工业现场设备控制层的应用前景,有意将以太网引入武器装备的底层控制环境.但它必须满足确定性实时调度的要求.基于以太网的TCP/IP通信机制和IEEE1588时钟同步协议,在数据链路层之上引入实时调度机制以消除现有的CSMA/CD机制在时间行为上的不确定性.相关的分析和测试表明,新设计的通信调度机制能够使得网络...     

车载自组织网络协作MAC协议研究

车载自组织网络(Vehicular Ad Hoc Network,VANET)的关键技术之一就是 设计一个高效的媒体接入控制(Medium Access Control,MAC)协议。MAC协议因对网络的吞吐量、时延和丢包率等具有重大影响而成为研究热点。针对车载自组织网络对MAC协议的特殊性要求,提出了一种基于协作方案的TDMA MAC协议,即C-TDMA MAC。该协议中,当源节点到目的节点间直接传输失败时,其邻近辅助节点利用未被预留的时隙协作重传其先前侦听到的数据包到目的节点,而不影响其它数据包的正常传输。数值分析和仿真结果表明,所提出的协议提高了数据包成功传输的概率。     

一种跨平台的实时TCP/IP协议栈设计

为提高异构系统下网络通信的实时性,提出一种跨平台的实时TCP/IP协议栈(RTTCP/IP)实现方法。运用操作系统适配技术屏蔽底层数据处理的差异性,增强协议栈的可移植性和可扩展性;通过简化TCP/IP协议栈的结构,减少协议栈对系统资源的占用;采用内存映射技术,将内核空间地址映射到用户空间,避免用户与内核间的数据拷贝操作;引入基于时分多址的介质访问机制和数据包优先级策略,防止网络传输冲突,解决数据包优先级倒置问题。测试结果表明,RTTCP/IP实现方法能够减少系统开销和通信延迟,提高系统实时性和稳定性。     

Medium-access control protocols for WDM-based optical access networks with passive-star clusters interconnected by a backbone ring

This paper investigates the performance of medium access control (MAC) protocols in a wavelength-division multiplexing (WDM) based optical access network consisting of a backbone ring interconnecting several passive-star-based clusters of optical networking units (ONUs) at customer premises. Each cluster is connected to the backbone through an access node (AN). A scheduler located in each AN, executes two MAC protocols, one for the intracluster traffic and the other for the intercluster traffic. In order to maintain the quality of service, the scheduler in the AN employs, priority-based queuing for the intercluster traffic on pre-assigned wavelengths. For controlling the intracluster traffic, the scheduler employs pre-transmission coordination with ranging and look-ahead functionalities in the MAC protocol. The performance of MAC protocol for intracluster traffic is evaluated through event-driven simulation, while for intercluster traffic the MAC performance is evaluated through analytical modeling of the queuing system employing two dynamic bandwidth management schemes. Performance of the intracluster MAC protocol is shown to be improved by novel use of subcarrier multiplexing on the wavelength used for the control packet transmission. A comparative study of the two intercluster schemes in terms of end-to-end delay is carried out, to understand the effect of priority queuing on the real-time and non-real-time service packets.     

基于FC-AE-ASM的IP业务传输方法的设计实现

随着FC-AE网络在高可靠性网络中的应用越来越广泛,在FC-AE网络上传输IP业务不仅拓宽了FC-AE网络的应用范围,而且能够实现FC-AE网络与以太网网络的融合.提出了基于FC-AE-ASM协议的IP业务传输方案,在支持FC-AE-ASM协议的HBA卡物理设备上,构建了一个虚拟网卡内核模块.本方案扩展了TCP/IP协议栈,在网络接入层下扩展了一个FC接口层,实现了FC-AE-ASM帧对以太网帧的封装和解封装.同时,利用FC网络底层流控机制,实现了IP业务在FC-AE网络上的高可靠性传输.通过实验组网测试可知,本方案在延时、带宽、抖动、丢包率等方面相对于商用千兆网卡都有较多的优势,在航空航天等应用场景具有重要的应用价值.     

A MAC protocol for reliable communication in low power body area networks

Wireless Body Area Networks (BAN) are supposed to operate in very low transmit power regime in order to keep the Specific Absorption Rate (SAR) low. Low power transmissions are known to be very error prone. However, high reliability of communications is needed for several healthcare applications. It has been observed that the fluctuations of the Received Signal Strength (RSS) at the nodes of a BAN on a moving person show certain regularities and that the magnitude of these fluctuations are significant (5 – 20 dB). In this paper, we present BANMAC, a medium access control (MAC) protocol based on cross-layer design approach where medium access decisions are tightly integrated with physical layer conditions. BANMAC monitors and predicts the channel fluctuations and schedules transmissions opportunistically when the RSS is likely to be higher. We report the design and implementation details of BANMAC integrated with the IEEE 802.15.4 protocol stack. We present experimental data which show that the packet loss rate (PLR) of BANMAC is significantly lower as compared to that of the IEEE 802.15.4 MAC. For comparable PLR, the energy consumption of BANMAC is also significantly lower than that of the IEEE 802.15.4 MAC.     

无线局域网中一种自适应RTS门限调整算法

媒体访问控制是无线局域网的重要部分,决定了具有受限通信带宽的无线信道的共享效率.IEEE 802.11系列标准基于现有以太网技术,具有良好的操作性和兼容性,已发展成为WLAN的主要标准.IEEE 802.11 DCF中有两种接入方式:基本方式和RTS/CTS方式.RTS/CTS方式是IEEE 802.11无线网络的可选握手过程,用于减小碰撞的可能性.决定使用RTS/CTS握手方式的RTS门限值是研究的重要参数,不同的取值对数据传送会产生不同的性能特点.文章通过分析IEEE 802.11 DCF分组发送成功和碰撞的持续时间,获得了RTS和基本方式下分组传输时间开销与分组长度的关系.给出了以最小化分组传输时间代价为优化目标的最优RTS门限的计算公式.通过对当前信道分组发送的冲突概率的预测实现了最优RTS门限的计算;给出了一个具体的RTS门限自适应调整算法,使终端能自动调整其RTS门限以达到或接近最优值.仿真表明RTS门限自适应调整算法明显减小了分组传送时收发器发送单位比特数据的时间开销.     

Design issues of uplink media access control (MAC) protocols for multimedia traffic over DS-CDMA systems

We propose an efficient uplink media access control (MAC) protocol for a variable spreading gain interference-limited wideband CDMA system. It can, with high spectral efficiency, support both real-time traffic like speech and video and also nonreal-time data traffic based on packet transmission. The schemes for power allocation, joint scheduling, and transmission rate adaptation for nonreal time data traffic are designed as integrated parts of the MAC, working together to improve the system performance in terms of capacity and delay. With these associated resource management mechanisms, the performances of the MAC protocol with two different channel-allocation methods for real-time traffic are numerically compared. One is demanding channel allocation, and the other is reserve channel allocation, in which a certain bandwidth is reserved for concurrent real-time traffic.     

A performance study of uplink scheduling algorithms in point-to-multipoint WiMAX networks

The IEEE 802.16 standard defines the specifications for medium access control (MAC) and physical (PHY) layers of WiMAX networks. A critical part of the MAC layer specification is packet scheduling, which resolves contention for bandwidth and determines the transmission order of users. Evaluating the performance packet scheduling algorithms is of utmost importance towards realizing large-scale WiMAX deployment. In this paper, we conduct a comprehensive performance study of scheduling algorithms in point-to-multipoint mode of OFDM-based WiMAX networks. We first make a classification of WiMAX scheduling algorithms, then simulate a representative number of algorithms in each class taking into account that vital characteristics of the IEEE 802.16 MAC layer and OFDM physical layer. We evaluate the algorithms with respect to their abilities to support multiple classes of service, providing quality of service (QoS) guarantees, fairness amongst service classes and bandwidth utilization. To the best of our knowledge, no such comprehensive performance study has been reported in the literature. Simulation results indicate that none of the current algorithms is capable of effectively supporting all WiMAX classes of service. We demonstrate that an efficient, fair and robust scheduler for WiMAX is still an open research area. We conclude our study by making recommendations that can be used by WiMax protocol designers.     

Priority and delay aware packet management framework for real-time video transport over 802.11e WLANs

The rigid delay constraint is one of the most challenging issues in real-time video delivery over wireless networks. The expired video packets will become useless for the decoding and display even if they are received correctly at the receiver. Because the significance of each video packet is different, the schedulers have to take into account not only the urgency of the packet but also its importance in the real-time video applications. However, the existing QoS-based IEEE 802.11e MAC protocol leaves the urgency and the importance of video packets out of consideration. This paper proposes a Priority and Delay Aware Packet Management Framework (PDA-PMF) to improve the transmission quality of real-time video streaming over IEEE 802.11e WLANs. In the MAC layer, this framework estimates the delay of each video packet. Subsequently, video packets are sent or dropped according to both the significance of the video packets and the estimation value of the delay. Simulation results show that the proposed scheme can not only reduce the packet losses, but also protect the more important video packets, so as to improve the received video quality effectively.     

抗时延敏感性跨层自适应资源分配方案*

为了对抗多用户OFDM系统中用户实时业务对时延的敏感性,提出一种利用Hopfield神经网络(HNN)算法的跨层自适应资源分配方案。该方案设置用户调度优先级时同时考虑物理层的信道状态信息,及媒体接入层的用户队列状态信息和等待时间等;采用HNN算法,最大化系统容量的同时降低了平均时延和丢包率。仿真结果表明,相比于传统资源分配方案,该方案可以有效保障用户的服务质量,并提高了系统的整体性能。     

802.11 DCF中的自适应RTS门限调整算法*

通过分析IEEE 802．11 DCF的分组发送过程,获得了RTS和基本方式下分组传输的时间开销。给出了以最小化传输时间开销代价为优化目标的最优RTS门限的计算公式。通过对当前信道分组发送的成功概率P,的预测,实现了最优RTS门限的计算,并给出了一个具体的自适应RTS门限调整算法,使终端能自动调整其RTS门限以达到或接近最优值。仿真表明自适应RTS门限调整算法有效减小了MAC分组传送的时间开销,提高了信道的传输效率。     

Employing transport layer multi-railing in cluster networks

Building clusters from commodity off-the-shelf parts is a well-established technique for building inexpensive medium- to large-size computing clusters. Many commodity mid-range motherboards come with multiple Gigabit Ethernet interfaces, and the low cost per port for Gigabit Ethernet makes switches inexpensive as well. Our objective in this work is to take advantage of multiple inexpensive Gigabit network cards and Ethernet switches to enhance the communication and reliability performance of a cluster. Unlike previous approaches that take advantage of multiple network connections for multi-railing, we consider CMT (Concurrent Multipath Transfer) that extends SCTP (Stream Control Transmission Protocol), a transport protocol developed by the IETF, to make use of the multiple paths that exist between two hosts. In this work, we explore the applicability of CMT in the transport layer of the network stack to high-performance computing environments. We develop SCTP-based MPI (Message Passing Interface) middleware for MPICH2 and Open MPI, and evaluate the reliability and communication performance of the system. Using Open MPI with support for message striping over multiple paths at the middleware level, we compare the differences in supporting multi-railing in the middleware versus at the transport layer.     

基于马尔可夫链的IEEE802.15.4网络防丢包信道访问机制研究

为了降低802.15.4MAC层数据帧丢包率,在分析丢包率的原因基础上,提出了一种基于Markov链的信道竞争机制模型。通过对网络发送、退避和信道检测状态的稳态概率进行数学推导,研究了信道碰撞和数据帧的丢包率分析式;最后研究了参数数据包到达速率、节点数量、误码率、后退指数、后退等待次数对碰撞概率和丢包率的影响。实验结果表明,与节点无休眠态的802.15.4网络相比,节点丢包率平均降低了23.7%,模型较好地描述了提出的MAC层信道访问机制,合理的网络参数设置能够优化数据帧丢包率,研究结果对无线传感网的应用提供可靠传输优化参考。