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1.
使用EHN-HP机制提高移动切换中TCP性能 总被引:1,自引:0,他引:1
移动通讯技术的发展促使传统有线互联网向无线移动网络延伸.TCP协议是现在互联网上使用最为广泛的端到端可靠传输协议,但TCP协议是在有线链路基础上设计的,直接在无线移动网络上使用TCP协议会造成TCP性能的下降.本文详细分析了移动切换对TCP协议造成的影响,比较并分析现有的几种解决方案,针对切换对TCP造成的影响提出了EHN-HP机制.EHN-HP机制在现有的TCP协议上进行改进,增加了切换处理机制(Handoff Process),通过网络模拟器的模拟结果表明,EHN-HP机制有效的改善了TCP协议在切换过程中的性能. 相似文献
2.
无线链路控制协议(RLC)是WCDMA无线接入层(RAN)的重要组成,在无线通信系统中,它可以用来弥补无线信道对TCP性能的影响。本文对RLC三种模式数据传输过程进行了分析,提出了具体的实现方案,同时对缓冲区提出了一种较好的设计方法。这些对WCDMA无线接入层协议栈的开发有一定的指导意义。 相似文献
3.
在3G(第3代移动通信系统)中,为了给不同类型的业务提供不同级别的端到端QoS,网络资源必须进行合理分配。QoS和资源分配是密不可分的,而无线资源分配显得尤为重要。文中提出了UMTS的QoS结构,分3部分对空中接口部分的QoS(即无线资源分配策略问题)进行了讨论:首先提出了一种RRA算法,接着讨论了W-CDMA和TD-CDMA系统的无线资源分配问题,最后讨论了下行链路及上行链路的呼叫允许控制(CAC)。 相似文献
4.
网络切换对TCP吞吐量和公平性的影响分析 总被引:2,自引:1,他引:1
无线移动网络的发展日新月异.TCP协议是目前互联网上使用的最为广泛的端到端可靠传输协议,但其应用在无线网络上的时候,TCP性能下降明显.文中详细分析了TCP移动网络的切换对TCP造成影响的几个重要方面.最后通过在NS2上进行实验揭示了对多个TCP流公平性的影响,即切换后RTT越小的TCP流的吞吐量增长的越快,同时静态链路会夺取无线链路的链路资源. 相似文献
5.
本论文在分析无线传感器网络不同于普通有线网络的特征后,提出了一种适用于无线传感器网络的TCP 拥塞控制机制DW-TCP,此机制将TCP拥塞窗口分为拥塞丢包窗口和误码丢包窗口,在链路误码率较高时通过降低发送速率提高数据发送的可靠性,节约无线节点的能源消耗和系统不必要的开销,该机制不但考虑到拥塞丢包对数据发送速率的影响,而且考虑到无线链路中的误码丢包对数据发送速率的影响. 相似文献
6.
针对无线环境下TCP(传输控制协议)调用拥塞控制算法致使性能下降的问题,提出一种基于ECN(显式拥塞通知)跨层机制的无线TCP改进方法。算法在ECN机制上判断网络是否拥塞以及丢包发生时具体丢包类型。并在此基础上针对网络具体状况采取不同的拥塞窗口控制机制,更精确的网络信息有效提高了数据发送的可靠性。仿真结果表明该算法可提... 相似文献
7.
无线网络中TCP友好流媒体传输改进机制 总被引:1,自引:0,他引:1
为保持无线网络中多媒体业务对TCP的友好性,提出了一种适用于无线网络的动态自适应的流媒体传输速率调节机制。该机制通过在接收端区分网络拥塞丢包和链路错误随机丢包,准确判断网络的拥塞状况结合接收端缓存区占用程度,自适应实施多级速率调节,实现了TCP流友好性和流媒体服务质量(QoS)的折中。由于准确区分出无线链路误码丢包和动态调整流媒体QoS要求,该机制能维持较高的网络利用率。仿真实验结果显示在连接数为2和32,链路误码率从0到0.1变化时TCP,TFRC和吞吐量幅度下降幅度较大,WTFCC幅度下降相对较慢,最大相差达2M;在网络负载重时,尽管链路误码率较低,WTFCC区分链路错误与拥塞丢包,因此,端到端丢包率高于TCP和TFRC,但整体传输吞吐量也高于两者。归一化吞吐量显示WTFCC对TCP流友好。 相似文献
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《Selected Areas in Communications, IEEE Journal on》2009,27(2):182-190
In this paper, we study the determination of downlink (DL) and uplink (UL) channel split ratio for Time Division Duplex (TDD)-based IEEE 802.16 (WiMAX) wireless networks. In a TDD system, uplink and downlink transmissions share the same frequency at different time intervals. The TDD framing in WiMAX is adaptive in the sense that the downlink to uplink bandwidth ratio may vary with time. In this work, we focus on TCP based traffic and explore the impact of improper bandwidth allocation to DL and UL channels on the performance of TCP. We then propose an Adaptive Split Ratio (ASR) scheme which adjusts the bandwidth ratio of DL to UL adaptively according to the current traffic profile, wireless interference, and transport layer parameters, so as to maximize the aggregate throughput of TCP based traffic. Our scheme can also cooperate with the Base Station (BS) scheduler to throttle the TCP source when acknowledgements (ACKs) are transmitted infrequently. The performance of the proposed ASR scheme is validated via ns-2 simulations. The results show that our scheme outperforms static allocation (such as the default value specified in the WiMAX standard and other possible settings in existing access networks) in terms of higher aggregate throughput and better adaptivity to network dynamics. 相似文献
12.
Feyza Keceli Inanc Inan Ender Ayanoglu 《Wireless Communications and Mobile Computing》2015,15(9):1376-1390
When the stations in an IEEE 802.11 infrastructure basic service set employ Transmission Control Protocol (TCP), this exacerbates per‐flow unfair access problem. We propose a novel analytical model to approximately calculate the maximum per‐flow TCP congestion window limit that prevents packet losses at the access point buffer and therefore provides fair TCP access both in the downlink and uplink. The proposed analysis is unique in considering the effects of varying number of uplink and downlink TCP flows, differing round trip times among TCP connections and the use of delayed TCP acknowledgment (ACK) mechanism. Motivated by the findings of this theoretical analysis and simulations, we design a link layer access control block to be employed only at the access point in order to resolve the unfair access problem. The proposed link layer access control block uses congestion control and ACK filtering approach by prioritizing the access of TCP data packets of downlink flows over TCP ACK packets of uplink flows. Via simulations, we show that the proposed algorithm can provide both short‐term and long‐term fair accesses while improving channel utilization and access delay. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
13.
A Cross-layer Dual Queue Approach for Improving TCP Fairness in Infrastructure WLANs 总被引:1,自引:1,他引:0
Juho Ha Eun-Chan Park Kyung-Joon Park Chong-Ho Choi 《Wireless Personal Communications》2009,51(3):499-516
Fairness is one of the most important performance measures in IEEE 802.11 Wireless Local Area Networks (WLANs), where channel
is accessed through competition. In this paper, we focus on the fairness problem between TCP uplink and downlink flows in
infrastructure WLANs from the cross-layer perspective. First, we show that there exists a notable discrepancy between throughput
of uplink flow and that of downlink flow, and discuss its root cause from the standpoint of different responses to TCP data
packet drop and TCP ACK packet drop at the access point (AP) buffer. In order to mitigate this unfairness, we propose a dual
queue scheme, which works in a cross-layer manner. It employs two separate queues at the AP, one for the data packets of downlink
TCP flows and another for the ACK packets of uplink TCP flows, and selects these queues with appropriate probabilities so
that TCP per-flow fairness is improved. Moreover, we analyze the behavior of the dual queue scheme and derive throughputs
of uplink and downlink flows. Based on this analysis, we obtain the optimal queue selection probabilities for fairness. Extensive
simulation results confirm that the proposed scheme is effective and useful in resolving the TCP unfairness problem without
deteriorating overall utilization. 相似文献
14.
In this paper, we propose a bidirectional bandwidth-allocation mechanism to improve TCP performance in the IEEE 802.16 broadband wireless access networks. By coupling
the bandwidth allocation for uplink and downlink connections, the proposed mechanism increases the throughput of the downlink
TCP flow and it enhances the efficiency of uplink bandwidth allocation for the TCP acknowledgment (ACK). According to the
IEEE 802.16 standard, when serving a downlink TCP flow, the transmission of the uplink ACK, which is performed over a separate
unidirectional connection, incurs additional bandwidth-request/allocation delay. Thus, it increases the round trip time of
the downlink TCP flow and results in the decrease of throughput accordingly. First, we derive an analytical model to investigate
the effect of the uplink bandwidth-request/allocation delay on the downlink TCP throughput. Second, we propose a simple, yet
effective, bidirectional bandwidth-allocation scheme that combines proactive bandwidth allocation with piggyback bandwidth request. The proposed scheme reduces unnecessary bandwidth-request delay and the relevant signaling overhead due to proactive allocation;
meanwhile, it maintains high efficiency of uplink bandwidth usage by using piggyback request. Moreover, our proposed scheme
is quite simple and practical; it can be simply implemented in the base station without requiring any modification in the
subscriber stations or resorting to any cross-layer signaling mechanisms. The simulation results ascertain that the proposed
approach significantly increases the downlink TCP throughput and the uplink bandwidth efficiency. 相似文献
15.
Byongkwon Moon Jeonghoon Mo 《Communications Letters, IEEE》2008,12(4):256-258
In WiMAX networks, a bandwidth request-grant process is required for uplink operation. However, the process is not optimized for TCP, since the uplink ACK stream is disrupted due to the following: (a) The process consists of several stages which in turn introduce big transmission delay; and (b) it requires additional uplink bandwidth which is significant compared to the ACK packet size. In this paper, the authors propose a new ACK transmission scheme, where ACK packets are combined with a bandwidth request (BR) header. Through simulation, it is demonstrated that the proposed scheme reduces the overheads of TCP-ACK transmissions effectively. 相似文献
16.
《Networking, IEEE/ACM Transactions on》2006,14(4):753-766
In this paper, we focus on the performance of TCP enhancements for a hybrid terrestrial–satellite network. While a large body of literature exists regarding modeling TCP performance for the wired Internet, and recently over a single-hop wireless link, the literature is very sparse on TCP analysis over a hybrid wired–wireless (multi-hop) path. We seek to make a contribution to this problem (where the wireless segment is a satellite uplink) by deriving analytical estimates of TCP throughput for two widely deployed approaches: TCP splitting and E2E (End-to-End) TCP with link layer support as a function of key parameters such as terrestrial/satellite propagation delay, segment loss rate and buffer size. Our analysis is supported by simulations; throughput comparisons indicate superiority of TCP splitting over E2E scheme in most cases. However, in situations where end-to-end delay is dominated by terrestrial portion and buffering is very limited at intermediate node, E2E achieves higher throughput than TCP splitting. 相似文献
17.
Design of an enhanced access point to optimize TCP performance in Wi-Fi hotspot networks 总被引:1,自引:0,他引:1
In the last years, the number of Wi-Fi hotspots at public venues has undergone a substantial growth, promoting the WLAN technologies
as the ubiquitous solution to provide high-speed wireless connectivity in public areas. However, the adoption of a random
access CSMA-based paradigm for the 802.11 MAC protocol makes difficult to ensure high throughput and a fair allocation of
radio resources in 802.11-based WLANs. In this paper we evaluate extensively via simulations the interaction between the flow
control mechanisms implemented at the TCP layer and the contention avoidance techniques used at the 802.11 MAC layer. We conducted
our study considering initially M wireless stations performing downloads from the Internet. From our results, we observed that the TCP downlink throughput
is not limited by the collision events, but by the inability of the MAC protocol to assign a higher chance of accessing the
channel to the base station. We propose a simple and easy to implement modification of the base station’s behavior with the
purpose of increasing the TCP throughput reducing useless MAC protocol overheads. With our scheme, the base station is allowed
to transmit periodically bursts of data frames towards the mobile hosts. We design a resource allocation protocol aimed at
maximizing the success probability of the uplink transmissions by dynamically adapting the burst length to the collision probability
estimated by the base station. By its design, our scheme is also beneficial to achieve a fairer allocation of the channel
bandwidth among the downlink and uplink flows, and among TCP and UDP flows. Simulation results confirm both the improvement
in the TCP downlink throughput and the reduction of system unfairness. 相似文献
18.
Seungwoon Kim Ikjun Yeom 《Communications Letters, IEEE》2007,11(2):146-148
In IEEE 802.16 networks, a bandwidth request-grant mechanism is used to accommodate various QoS requirements of heterogeneous traffic. However, it may not be effective for TCP flows since (a) there is no strict QoS requirement in TCP traffic; and (b) it is difficult to estimate the amount of required bandwidth due to dynamic changes of the sending rate. In this letter, we propose a new uplink scheduling scheme for best-effort TCP traffic in IEEE 802.16 networks. The proposed scheme does not need any bandwidth request process for allocation. Instead, it estimates the amount of bandwidth required for a flow based on its current sending rate. Through simulation, we show that the proposed scheme is effective to allocate bandwidth for TCP flows 相似文献
19.
This paper presents a novel way to improve Transmission Control Protocol (TCP) performance of the users at the edge areas of the macro cells in Long Term Evolution Advanced (LTE-A) systems. Previous works on improving wireless TCP performance are reviewed and current considerations on TCP in LTE-A are explained. However, those solutions are neither too complex nor limited to some presuppositions which are too restricting for the deployment of LTE-A networks. In this paper a substituted TCP acknowledgement transmission scheme based on Automatic Repeat reQuest (ARQ) information in layer 2 is proposed. The simulation result shows that the proposed method can reduce the delay and improve the throughput of the edging users of the cell, as well as reducing radio resources in LTE-A macro cells. 相似文献
20.
A buffer management algorithm for improving up/down transmission congestion protocol fairness in IEEE 802.11 wireless local area networks 下载免费PDF全文
Jiawei Huang Jianxin Wang Jin Ye 《International Journal of Communication Systems》2014,27(10):2228-2240
The fair allocation of the resources is an important issue in wireless local area network (WLAN) because all wireless nodes compete for the same wireless radio channel. When uplink and downlink transmission congestion protocol (TCP) flows coexist in WLAN, the network service is biased toward the uplink TCP flows, and the downlink TCP flows tend to starve. In this article, we investigate the special up/down TCP unfairness problem and point out that the direct cause is the uplink acknowledgement (ACK) packets occupy most buffer space of access point. We thus propose a buffer management algorithm to ensure the fairness among uplink and downlink TCP flows. In order to limit the greedy behavior of ACK packets, the proposed algorithm adjusts the maximum size of buffer allocated for the ACK packets. Analysis and simulation results show that the proposed solution not only provides the fairness but also achieves 10–20% lower queue delay and higher network goodput than the other solutions. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献