共查询到20条相似文献,搜索用时 15 毫秒
1.
Neng-Chung Wang Jong-Shin Chen Yung-Fa Huang Chi-Lun Chiou 《Wireless Personal Communications》2008,47(3):399-415
In this paper, we propose a scheme that dynamically adjusts the slow start threshold (ssthresh) of TCP. The ssthresh estimation is used to set an appropriate ssthresh. A good ssthresh would improve the transmission performance of TCP. For the congestion avoidance state, we present a mechanism that probes
the available bandwidth. We adjust the congestion window size (cwnd) appropriately by observing the round trip time (RTT) and reset the ssthresh after quick retransmission or timeout using the ssthresh estimation. Then the TCP sender can enhance its performance by using the ssthresh estimation and the observed RTT. Our scheme defines what is considered an efficient transmission rate. It achieves better
utilization than other TCP versions. Simulation results show that our scheme effectively improves TCP performance. For example,
when the average bottleneck bandwidth is close to 30% of the whole network bandwidth, our scheme improves TCP performance
by at least 10%.
相似文献
Chi-Lun ChiouEmail: |
2.
This paper addresses when and how to adjust bandwidth allocation on uplink and downlink in a multi-service mobile wireless network under dynamic traffic load conditions. Our design objective is to improve system bandwidth utilization while satisfying call level QoS requirements of various call classes. We first develop a new threshold-based multi-service admission control scheme (DMS-AC) as the study base for bandwidth re-allocation. When the traffic load brought by some specific classes under dynamic traffic conditions in a system exceeds the control range of DMS-AC, the QoS of some call classes may not be guaranteed. In such a situation, bandwidth re-allocation process is activated and the admission control scheme will try to meet the QoS requirements under the adjusted bandwidth allocation. We explore the relationship between admission thresholds and bandwidth allocation by identifying certain constraints for verifying the feasibility of the adjusted bandwidth allocation. We conduct extensive simulation experiments to validate the effectiveness of the proposed bandwidth re-allocation scheme. Numerical results show that when traffic pattern with certain bandwidth asymmetry between uplink and downlink changes, the system can re-allocate the bandwidth on uplink and downlink adaptively and at the same time improve the system performance significantly. 相似文献
3.
TCP Westwood: End-to-End Congestion Control for Wired/Wireless Networks 总被引:11,自引:0,他引:11
Casetti Claudio Gerla Mario Mascolo Saverio Sanadidi M.Y. Wang Ren 《Wireless Networks》2002,8(5):467-479
TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links. In fact, TCPW performance is not very sensitive to random errors, while TCP Reno is equally sensitive to random loss and congestion loss and cannot discriminate between them. Hence, the tendency of TCP Reno to overreact to errors. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP extensions is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, TCPW fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP sender side the bandwidth used by the connection via monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno which blindly halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the overhead of a specialized link layer protocol. 相似文献
4.
基于已有的带宽管理机制,采用加权公平对竞争的流分配带宽,不仅可以对流实现准入控制,以保证每条流的最低信道时间需求,同时也能动态地调节流所分配的信道时间。另外,我们的方案,也适用于多跳的情况,通过例子说明,在考虑到用户需求的同时,也提高了网络的吞吐量。 相似文献
5.
This paper proposes an improved version of time-division duplex (TDD) mode called slot-splitting TDD (SS-TDD), which increases the average achievable capacity of a TDD cellular network by splitting a slot. The improvement results from partial relaxation of the restriction in the former versions of TDD, which requires an integer number of downlink slots. The proposed method can be implemented with no significant increase in computational complexity. In addition, with a few minor modifications, the proposed SS-TDD can be applied to two out of three burst types in UTRA TDD with a single-switching-point configuration. In a multi-cell environment with mixed traffic, our analysis shows that the proposed SS-TDD increases the average cell capacity (in Mbps) by up to 18.5-10.0%, and the Erlang capacity by up to 20.5-44.3%, for targeted SIRs in the range of 5-7dB. 相似文献
6.
Maher A. Al-Sanabani Subramaniam K. Shamala Mohamed Othman Zuriati A. Zukarnain 《Wireless Personal Communications》2008,46(2):143-163
Next generation of wireless cellular networks aim at supporting a diverse range of multimedia services to Mobile Terminal
(MT) with guaranteed Quality of Service (QoS). The challenge is to maintain the playing continuity of multimedia streams during
handoff. In this paper, a bandwidth reservation scheme based on mobility prediction is proposed, to enable high accurate prediction
of next crossing cell (target cell) which a MT is going to, in order to avoid too early or over reservation resulting in a
waste of resources. The amount of bandwidth to be reserved is dynamically adjusted according to (a) the current position (location)
and the extrapolated direction of MT and; (b) the sector and zones of the cell. A Call Admission Control scheme (CAC) is also
considered to further guarantee the QoS of real time traffic. The performance of the system is evaluated through discrete
event simulation of the wireless cellular environment. Simulation results show that the proposed scheme as compared to several
existing schemes is able to reduce the Handoff Call Dropping Probability (HCDP) of real time traffic and the number of terminated
ongoing calls of non-real time traffic. In addition, it is efficient to reduce the number of cancelled reservation and subsequently
increase the system bandwidth utilization.
相似文献
Maher A. Al-SanabaniEmail: |
7.
8.
Wireless bandwidth is a scarce resource in a cellular mobile network. As such, it is important to effectively allocate bandwidth to each cell such that the overall system performance is optimized. Channel allocation strategies have been extensively studied for voice communications in cellular networks. However, for data dissemination applications, studies on bandwidth allocation have thus far been limited to a single-cell environment. This paper investigates the problem of bandwidth allocation for data dissemination in a multi-cell environment, which, to the best of our knowledge, has not been investigated before. The performance objective is to minimize the overall expected access latency given the workload for each cell in a data dissemination system. Two heuristic techniques, called compact allocation and cluster-step allocation, are proposed to effectively allocate bandwidth for a cellular network. Simulation experiments are conducted to evaluate the performance of the proposed bandwidth allocation schemes. Experimental results show that the proposed schemes substantially outperform the uniform allocation and proportional allocation schemes. 相似文献
9.
针对有线网络设计的传输控制协议(TCP),在应用到无线环境中时存在许多不兼容问题,必须对TCP进行修改.目前人们提出了几种对TCP协议在无线网络环境下的改进方案,但是这些改进方案同IP安全协议(IPsec)存在一定的中突.文章分析了IPsec与TCP的改进方案之间的冲突问题,给出了4种解决方案:用传输层安全协议/安全套接层协议(TLS/SSL)代替IPsec、扩展封装安全载荷(ESP)协议、对TCP路径分段和修改IPsec的端到端保护模式,并分析了各方案的优缺点. 相似文献
10.
Roland Zander Johan M. Karlsson 《International Journal of Wireless Information Networks》2005,12(3):187-201
In the third generation cellular networks and beyond, a wide variety of different services are/will be provided by the operators. Out of QoS reasons, it is preferable to assign higher priority to certain connection types. These include calls carrying delay-sensitive services and already ongoing calls. In this paper, a prioritization method combining bandwidth borrowing and reservation, called BBR, will be presented. BBR monitors the rate-adaptiveness of the ongoing calls in a cell. Simultaneously, advanced movement predictions are applied to estimate the arrival rate to each cell. If it is determined that the use of bandwidth borrowing (temporarily reducing the data rate of other connections in the same cell) is not sufficient to support the high priority calls that are expected to arrive, a portion of the assigned bandwidth to the cell is exclusively reserved for these calls to prevent call dropping. The scheme enables the operator to increase the average user satisfaction in the network. This is achieved by defining appropriate penalty functions for the events of blocking, dropping and bandwidth reduction of a call. 相似文献
11.
Hamed Mohsenian Rad A. Wong V.W.S. 《Wireless Communications, IEEE Transactions on》2008,7(9):3436-3445
In a wireless mesh network (WMN) with a number of stationary wireless routers, the aggregate capacity can be increased when each router is equipped with multiple network interface cards (NICs) and each NIC is assigned to a distinct orthogonal frequency channel. In this paper, given the logical topology of the network, we mathematically formulate a crosslayer fair bandwidth sharing problem as a non-linear mixedinteger network utility maximization problem. An optimal joint design, based on exact binary linearization techniques, is proposed which leads to a global maximum. A near-optimal joint design, based on approximate dual decomposition techniques, is also proposed which is practical for deployment. Performance is assessed through several numerical examples in terms of network utility, aggregate network throughput, and fairness index. Results show that our proposed designs can lead to multi-channelWMNs which are more efficient and fair compared to their singlechannel counterparts. The performance gain on both efficiency and fairness increase as the number of available NICs per router or the number of available frequency channels increases. 相似文献
12.
13.
We propose using the TCP decoupling approach to improve a TCP connection's goodput over wireless networks. The performance improvement can be analytically shown to be proportional to
, where MTU is the maximum transmission unit of participating wireless links and HP_Sz is the size of a packet containing only a TCP/IP header. For example, on a WaveLAN [32] wireless network, where MTU is 1500 bytes and HP_Sz is 40 bytes, the achieved goodput improvement is about 350%. We present experimental results demonstrating that TCP decoupling outperforms TCP reno and TCP SACK. These results confirm the analysis of
performance improvement. 相似文献
14.
15.
Wireless Personal Communications - Nowadays, users of wireless cellular networks are ever increasing, but wireless link bandwidth is limited. Due to heavy traffic in this network and frequent... 相似文献
16.
In this paper a new TCP variant, named TCP-Binary Increase, Adaptive Decrease is presented. The suggested congestion control algorithm is a joint approach of Westwood and an enhanced version of BIC, for improving TCP performance in broadband wireless access networks. BIAD has been evaluated with respect to other TCP variants such as Reno, Westwood, BIC, CUBIC, HSTCP and STCP with the use of network simulator 2. The results indicate that the proposed solution achieves high network utilization levels in a wide range of network settings, including wireless channel errors, link asymmetry and congestion. We also evaluated TCP-BIAD when multiple flows share a bottlenecked access link and we show that it demonstrates the fairness features required for network deployment. 相似文献
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18.
Bandwidth Adaptation Algorithms for Adaptive Multimedia Services in Mobile Cellular Networks 总被引:3,自引:0,他引:3
The fluctuation of available link bandwidth in mobilecellular networks motivates the study of adaptive multimediaservices, where the bandwidth of an ongoing multimedia call can bedynamically adjusted. We analyze the diverse objectives of theadaptive multimedia framework and propose two bandwidth adaptationalgorithms (BAAs) that can satisfy these objectives. The firstalgorithm, BAA-RA, takes into consideration revenue and``anti-adaptation' where anti-adaptation means that a user feelsuncomfortable whenever the bandwidth of the user's call ischanged. This algorithm achieves near-optimal total revenue withmuch less complexity compared to an optimal BAA. The secondalgorithm, BAA-RF, considers revenue and fairness, and aims at themaximum revenue generation while satisfying the fairnessconstraint defined herein. Comprehensive simulation experimentsshow that the difference of the total revenue of BAA-RA and thatof an optimal BAA is negligible. Also, numerical results revealthat there is a conflicting relationship between anti-adaptationand fairness. 相似文献
19.
Reliable data transfer is one of the most difficult tasks to be accomplished in multihop wireless networks. Traditional transport protocols like TCP face severe performance degradation over multihop networks given the noisy nature of wireless media as well as unstable connectivity conditions in place. The success of TCP in wired networks motivates its extension to wireless networks. A crucial challenge faced by TCP over these networks is how to operate smoothly with the 802.11 wireless MAC protocol which also implements a retransmission mechanism at link level in addition to short RTS/CTS control frames for avoiding collisions. These features render TCP acknowledgments (ACK) transmission quite costly. Data and ACK packets cause similar medium access overheads despite the much smaller size of the ACKs. In this paper, we further evaluate our dynamic adaptive strategy for reducing ACK-induced overhead and consequent collisions. Our approach resembles the sender side's congestion control. The receiver is self-adaptive by delaying more ACKs under nonconstrained channels and less otherwise. This improves not only throughput but also power consumption. Simulation evaluations exhibit significant improvement in several scenarios 相似文献