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A novel technique to enhance throughput and fairness over wireless mesh networks
This extended abstract was submitted to and published in the ReSCon '12 Book of Abstracts. The fifth SED Research Student Conference (ReSCon2012) was hosted over three days, 18-20 June 2012, in the Hamilton Centre at Brunel University
TCP-Aware Backpressure Routing and Scheduling
In this work, we explore the performance of backpressure routing and
scheduling for TCP flows over wireless networks. TCP and backpressure are not
compatible due to a mismatch between the congestion control mechanism of TCP
and the queue size based routing and scheduling of the backpressure framework.
We propose a TCP-aware backpressure routing and scheduling that takes into
account the behavior of TCP flows. TCP-aware backpressure (i) provides
throughput optimality guarantees in the Lyapunov optimization framework, (ii)
gracefully combines TCP and backpressure without making any changes to the TCP
protocol, (iii) improves the throughput of TCP flows significantly, and (iv)
provides fairness across competing TCP flows
Class-Based Weighted Window for TCP Fairness in WLANs
The explosive growth of the Internet has extended to the wireless domain. The number of Internet users and mobile devices with wireless Internet access is continuously increasing. However, the network resource is essentially limited, and fair service is a key issue in bandwidth allocation. In this research, the focus is on the issue of fairness among wireless stations having different number and direction of flows for different required bandwidth to ensure that fair channel is fairly shared between wireless stations in the same class of bandwidth. It is shown that the current WLANs allocate bandwidth unfairly. It is also identified that the cause of this problem of unfairness is the TCP cumulative ACK mechanism combined with the packet dropping mechanism of AP queue and the irregular space for each wireless station in AP queue. The proposed method allocate converged bandwidth by introducing a Class-Based Weighted Window method which adjusts the TCP window size based on the current conditions of the network and according to the networkâs requirements. This method works in wireless stations without requiring any modification in MAC. It can guarantee fair service in terms of throughput among wireless users whether they require the same or different bandwidth.Wireless LAN, TCP, Fairness
Performance of TCP/UDP under Ad Hoc IEEE802.11
TCP is the De facto standard for connection oriented transport layer
protocol, while UDP is the De facto standard for transport layer protocol,
which is used with real time traffic for audio and video. Although there have
been many attempts to measure and analyze the performance of the TCP protocol
in wireless networks, very few research was done on the UDP or the interaction
between TCP and UDP traffic over the wireless link. In this paper, we tudy the
performance of TCP and UDP over IEEE802.11 ad hoc network. We used two
topologies, a string and a mesh topology. Our work indicates that IEEE802.11 as
a ad-hoc network is not very suitable for bulk transfer using TCP. It also
indicates that it is much better for real-time audio. Although one has to be
careful here since real-time audio does require much less bandwidth than the
wireless link bandwidth. Careful and detailed studies are needed to further
clarify that issue.Comment: 9 pages, 5 figures, ICT 2003 (10th International Conference on
Telecommunication
CapEst: A Measurement-based Approach to Estimating Link Capacity in Wireless Networks
Estimating link capacity in a wireless network is a complex task because the
available capacity at a link is a function of not only the current arrival rate
at that link, but also of the arrival rate at links which interfere with that
link as well as of the nature of interference between these links. Models which
accurately characterize this dependence are either too computationally complex
to be useful or lack accuracy. Further, they have a high implementation
overhead and make restrictive assumptions, which makes them inapplicable to
real networks.
In this paper, we propose CapEst, a general, simple yet accurate,
measurement-based approach to estimating link capacity in a wireless network.
To be computationally light, CapEst allows inaccuracy in estimation; however,
using measurements, it can correct this inaccuracy in an iterative fashion and
converge to the correct estimate. Our evaluation shows that CapEst always
converged to within 5% of the correct value in less than 18 iterations. CapEst
is model-independent, hence, is applicable to any MAC/PHY layer and works with
auto-rate adaptation. Moreover, it has a low implementation overhead, can be
used with any application which requires an estimate of residual capacity on a
wireless link and can be implemented completely at the network layer without
any support from the underlying chipset
Insights into the Design of Congestion Control Protocols for Multi-Hop Wireless Mesh Networks
The widespread deployment of multi-hop wireless mesh networks will depend on the performance seen by the user. Unfortunately, the most predominant transport protocol, TCP, performs poorly over such networks, even leading to starvation in some topologies. In this work, we characterize the root causes of starvation in 802.11 scheduled multi-hop wireless networks via simulations. We analyze the performance of three categories of transport protocols. (1) end-to-end protocols that require implicit feedback (TCP SACK), (2) Explicit feedback based protocols (XCP and VCP) and (3) Open-loop protocol (UDP). We ask and answer the following questions in relation to these protocols: (a) Why does starvation occur in different topologies? Is it intrinsic to TCP or, in general, to feedback-based protocols? or does it also occur in the case of open-loop transfers such as CBR over UDP? (a) What is the role of application behavior on transport layer performance in multi-hop wireless mesh networks? (b) Is sharing congestion in the wireless neighborhood essential for avoiding starvation? (c) For explicit feedback based transport protocols, such as XCP and VCP, what performance can be expected when their capacity estimate is inaccurate? Based on the insights derived from the above analysis, we design a rate-based protocol called VRate that uses the two ECN bits for conveying load feedback information. VRate achieves near optimal rates when configured with the correct capacity estimate
Channel Allocation in An Overlaid Mesh Network
In spite of recent advancement of Wireless Mesh Technology, a lot of research challenges remained to be solved to extract the full capacity of this modern technology. As 802.11a/b/g standards make available the use of multi radio multi channel in a wireless node, a lot of research activities are going on to efficiently allocate the channel of a Mesh Network to boost its overall performances. In this research, the prospect of dividing the total network area into two non-overlapping channels of a given Mesh Network is investigated and analyzed numerically. It is found that the throughput is doubled as well as the fairness improves considerably if we deploy two channels instead of single channel backbone. An extensive simulation study has been carried out to find the optimum coverage area between two channels. The study shows that at a particular point of allocation, the network gives the optimum response.fi=OpinnÀytetyö kokotekstinÀ PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=LÀrdomsprov tillgÀngligt som fulltext i PDF-format
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