Agent based automated trust negotiation model

To enhance the practicability of the trust negotiation system, an agent based automated trust negotiation model （ABAM） is proposed. The ABAM introduces an agent to keep the negotiation process with no human intervention. Meanwhile, the ABAM specifies the format of a meta access control policy, and adopts credentials with flexible format to meet the requirements of access control policies instead of disclosing the whole contents of a certificate. Furthermore, the ABAM uses asymmetric functions with a high security intensity to encrypt the transmitting message, which can prevent information from being attacked. Finally, the ABAM presents a new negotiation protocol to guide the negotiation process. A use case is studied to illuminate that the ABAM is sound and reasonable. Compared with the existing work, the intelligence, privacy and negotiation efficiency are improved in the ABAM.

Dynamic Polling MAC Scheme Considering Emergency Access in WSNs Based on Priorities

In Wireless Sensor Networks(WSNs),polling can obviously improve the throughput and decrease average access delay by allocating bandwidth efficiently and reasonably.In this paper,a Dynamic Polling Media Access Control (DPMAC) scheme designed according to WSNs' features is proposed.DPMAC is a priority based access control protocol with the characteristics that its polling table is dynamically refreshed depending on whether the sensor node is active and that the bandwidth is dynamically allocated according to the traffic types.The access priorities are determined by the emergency levels of events and the scheduler proposed in our MAC is preemptive based on the deadline of the events.Simulation results show that DPMAC can efficiently utilize bandwidth and decrease average access delay and response time for emergency events with different access priorities in WSNs.

Energy efficient mechanism using flexible medium access control protocol for hybrid wireless sensor networks

Energy efficiency is a primary consideration in a wireless sensor network (WSN). This is also a major parameter when designing a medium access control (MAC) protocol for WSNs. Hierarchical clustering structure is regarded suitable for WSNs due to its good performance in energy conservation. In this work, an adequately flexible mechanism for clustering WSNs is designed, in which some creative or promotional metrics are utilized, such as cluster head selection algorithm, cluster optional reconstruction, interested data transmission, multiple path routing protocol. All these strategies were cooperated to maximize energy saving of whole system. An appropriate MAC protocol for this mechanism is proposed, by flexibly switching the status of diverse sensor nodes in different strategies. The simulation results show that the proposed MAC protocol is suitable for clustering WSNs and performs well in aspects of energy efficiency, flexibility and scalability.

Performance Analysis of Medium Access Control Protocol for IEEE 802.11g-over-Fiber Networks

This paper investigates the Medium Access Control(MAC)protocol performance in the IEEE 802.11g-over-fiber network for different payloads and fiber lengths using Direct Sequence Spread Spectrum-Orthogonal Frequency Division Multiplexing(DSSSOFDM)and Extended Rate PhysicalsOrthogonal Frequency Division Multiplexing(ERP-OFDM)physical layers using basic access mode,Request to Send/Clear to Send(RTS/CTS)and CTS-to-self mechanisms.The results show that IEEE 802.11g-over-fiber network employing the ERP-OFDM physical layer is much more efficient than that employing the DSSS-OFDM physical layer,with regards to both throughput and delay.For a given maximum throughput/minimum delay,the tradeoff among the access mechanism,the fiber length,and the payload size must be considered.Our quantified results give a selection basis for the operators to quickly select suitable IEEE 802.11g physical layers and the different access mechanisms,and accurately predict the data throughput and delay given the specific parameters.

A Performance Comparison of Two Real Time WLAN MAC Protocols

By modifying the IEEE 802.11 wireless local area network(WLAN) medium access protocol(MAC),a contention based and a polling based protocol are proposed to deal with the case every station possesses two classes of frame in real time applications.Both protocols can ensure the real time frame only need to wait a determinable bounded time.These two protocols are introduced briefly and a performance comparison between them is made.Simulation results show that each protocol has advantage over the others in certain network condition.

Performance Analysis of WLAN Medium Access Control Protocols in Simulcast Radio-Over-Fiber-Based Distributed Antenna Systems

The performance of three wireless local-area network(WLAN) media access control(MAC) protocols is investigated and compared in the context of simulcast radioover-fiber-based distributed antenna systems(RoF-DASs) where multiple remote antenna units(RAUs) are connected to one access point(AP) with different-length fiber links.The three WLAN MAC protocols under investigation are distributed coordination function(DCF) in basic access mode,DCF in request/clear to send(RTS/CTS) exchange mode,and point coordination function(PCF).In the analysis,the inter-RAU hidden nodes problems and fiber-length difference effect are both taken into account.Results show that adaptive PCF mechanism has better throughput performances than the other two DCF modes,especially when the inserted fiber length is short.

Non-saturation Throughput of S-ALOHA Using the Time-Scale Decomposition Technique

S-ALOHA （Slotted ALOHA） random access protocol is a widely used protocol mainly for the transmission of short packets in wireless networks. Most papers consider either an infinite population model where the impact of the backoff protocol cannot be adequately evaluated or a finite population model where the number of nodes is fixed. In this letter, a combination of both models is proposed using the time-scale decomposition technique. This methodology allows to study the system under more realistic conditions where the dynamics of users enter and leaving the system are reflected on the performance of the system as well as the impact of the backoff protocol. Also, it allows studying the system in non-saturation conditions. The proposed methodology divides the analysis in two parts： packet-level and connection-level. This analysis renders suitable results when the time scale of the packet level and connection level statistics is different. On the other hand, when these scales are similar, the proposed methodology is no longer suited.

Distributed multichannel medium access control protocol without common control channel for single-hop cognitive radio networks

A novel distributed cognitive radio multichannel medium access protocol without common control channel was proposed.The protocol divided a transmission interval into two parts for exchanging control information and data,respectively.In addition to evaluating system saturation throughput of the proposed protocol,a three-dimensional multi channel Markov chain model to describe the sate of the cognitive users (CUs) in dynamic spectrum access was presented.The proposed analysis was applied to the packet transmission schemes employed by the basic,RTS/CTS access mechanism adopted in the normal IEEE 802.11.Analyzing the advantage of the two methods,a hybrid access mechanism was proposed to improve the system throughput.The simulation results show that the experiment results are close to the value computed by the model (less than 5%),and the proposed protocol significantly improves the performance of the system throughput by borrowing the licensed spectrum.By analyzing the dependence of throughput on system parameters,hybrid mechanism dynamically selecting access mechanism can maintain high throughput.

河北藁城市计生服务回访为计生干部带上“紧箍咒”

＂您好,我是藁城市计划生育服务回访中心02号回访员,请问是杜晓飞先生吗？您是在8月1日在南孟镇计生办办理第一个子女生育登记吗？……＂近日,刚刚办理完一胎生育证的藁城市南孟镇杜家庄村村民杜晓飞接到回访电话,请他对计生服务进行评价,这让他又惊又喜,＂没想到现在咱老百姓也能给计生服务打分了。＂杜晓飞高兴地说。

习近平:千方百计为群众排忧解难 不断开创信访工作新局面

【新华社北京7月19日电】中共中央总书记、国家主席、中央军委主席习近平近日对信访工作作出重要指示,向全国信访系统广大干部职工致以诚挚的问候,向受到表彰的先进集体和先进工作者表示热烈的祝贺。

左宗棠不畏人谤

左宗棠是近代史上'事功'特著的名将,其才高、政明、功显又兼生性'刚峻',也给左宗棠招来了麻烦——'忌者日众、谤议四起'。对于他人谤议,左宗棠并非懵然不知,亦非无动于衷。难能可贵的是,他能深持自己对待谤议的独到见解,从而不为毁谤所误。

In-home Power Line Communication Media Access Control Protocol Based on Collision Resolution

Most existing media access control(MAC) protocols in power line communication(PLC) networks just discard the colliding data packets when collision occurs.The collision deteriorates throughput and delay performance of system under high traffic conditions.This article presents a novel media access scheme with fast collision resolution for in-home power line networks.It works by first recognizing the colliding stations through detecting the inserted unique ID sequence ahead of data packets,then the source nodes retransmitting their packets immediately after the collision slot.The proposed protocol maintains the benefits of ALOHA systems.It needs no scheduling overhead and is suitable for bursty sources,such as multimedia data packets.Computer simulations have demonstrated that this approach can achieve high throughput due to its ability of resolving collisions.