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Towards energy-awareness in managing wireless LAN applications
Abstract
We have investigated the scope for enabling WLAN applications to manage the trade-off between performance and energy usage. We have conducted measurements of energy usage and performance in our 802.11n WLAN testbed, which operates in the 5 GHz ISM band. We have defined an effective energy usage envelope with respect to application-level packet transmission, and we demonstrate how performance as well as the effective energy usage envelope is effected by various configurations of IEEE 802.11n, including transmission power levels and channel width. Our findings show that the packet size and packet rate of the application flow have the greatest impact on application-level energy usage, compared to transmission power and channel width. As well as testing across a range of packet sizes and packet rates, we emulate a Skype flow, a YouTube flow and file transfers (HTTP over Internet and local server) to place our results in context. Based on our measurements we discuss approaches and potential improvements of management in effective energy usage for the tested applications.
Supplementary resource (1)
... We explore the possibilities of improving client-side energy efficiency by changing the configuration of applications or other client-side software components that are amenable to application developers and application programming interfaces (APIs). If we can observe energy efficiency gains through such application-level adaptations, then they could be applied to a large base of legacy applications to achieve improved energy efficiency, even in the absence of newer, energyefficient hardware [4]. If energy efficient hardware is present, any application-level adaptation can work in complement. ...
... Our own previous work in this area, using a similar methodology and testbed, established the use of the energy metric, E A (see Section III-C) and the notion of the energy envelope, which gives the upper and lower bounds of the energy usage during the transmission of a flow [6]. We have also investigated the possibility of application adaptation within the scope of this energy envelope [4] to trade of performance against energy usage. Also the comparative effectiveness of the generic 802.11 power save mode (PSM) versus the application adaptation approach has been explored [7]. ...
... We acknowledge that YouTube is not real-time, but for the sake of using a well-known video encoding, and to permit comparison 4 4K video will be interesting for the future! with our previous work [4], [6], [7], we use the YouTube flow construction. The relevant parameters are given in Table II. ...
We show that the Datagram Congestion Control Protocol (DCCP) provides ~10% - ~40% greater energy efficiency than the User Datagram Protocol (UDP) in a wireless LAN (WLAN) client. Our empirical evaluation uses a test bed comprised of consumer components and open source software to measure typical performance that can be expected by a user, rather than highly-tuned performance which most users will not be able to configure. We focus our measurements on a scenario using IEEE 802.11n at 5GHz as energy efficiency will be particularly important to mobile and wireless users. We consider overall performance as well as the energy efficiency of the protocol usage to give a rounded comparison of UDP and DCCP. Overall, we see there would be great benefit in many applications using DCCP instead of UDP.
... In our recent work [2], [3], we have found that traffic characteristics for individual GoAs, such as data rate and packet size, have a great effect on the exhibited performance in WLAN operation for the different 802.11 variants. We find that the upper and lower bounds of GoA-neutral performance envelopes can be evaluated, empirically, across a range of flow constructions by controlled combinations of packet size and offered load. ...
... We then compare these to a performance envelope, based on the operation of a single client, generated on an IEEE 802.11n/g testbed. While we have constrained ourselves to 802.11g and 802.11n for practical purposes (e.g. the network configuration of the University of Twente deployment), our methodology for generating the performance envelopes has been applied to other IEEE 802.11 variants in our previous work [2], [3]. The considered GoAs are: real-time audio, realtime video, streamed (non-real-time) audio, streamed video and bulk data transfers. ...
... We compared testbed results for a performance envelope, with analyses of NetFlow data from a campus network. We used the same testbed and harness as already described in [2], [3] for our WLAN performance measurements. We extracted traffic profiles from NetFlow traces comprising a base of ∼5000 users of 802.11n/g wireless networks operating at 2.4GHz at the University of Twente. ...
We demonstrate that in a future converged network scenario, it may be beneficial to allow selection of 802.11 variant based on application requirements. We analyse traces from the campus network from the University of Twente, comprising ∼5000 users. We have evaluated a performance envelope derived from testbed experiments for individual IEEE 802.11 variants and compare these with the traffic patterns from the campus network. From our comparison, we find that specific IEEE 802.11 variants (e.g. 802.11g or 802.11n) may be better suited to specific applications, such as video streaming, rather than using a single WLAN standard for all traffic.
... By experimenting with packet size and (packet) transmission rate we are able to evaluate the upper and lower bounds of performancea performance envelope -under 'good' and 'poor' RSSI conditions, within which real applications operate. This will show the scope over which management actions or adaptation policies will be effective, narrowing down the solution space as well as providing bounds on the potential benefits [8]. ...
... This paper is part of a body of work carried out in the context of performance-and energy-related topics. Hence, we use the same testbed, experimental harness and, partially, the approach as already described in [7], [8]. ...
... Our overall aim is to provide the foundations for the development of protocols and applications which are able to adapt themselves to a changing environment and, for instance, choose a more appropriate operational mode depending on the use case. This is not only true for performance but also for energy efficiency in WLAN for which we have investigated a number of scenarios and discuss dynamic intervention strategies in [7], [8]. This is, again, in support of our overall aim to make applications able to adapt them self in the presence of a changing operational environment. ...
Widespread use of wireless LAN (WLAN) may soon cause an over-crowding problem in use of the ISM spectrum. One way in which this manifests itself is the low Received Signal Strength Indication (RSSI) at the WLAN stations, impacting performance. Meanwhile, the IEEE 802.11 standard is being evolved and extended, for example with new coding schemes and the 802.11n standard, which makes use of 5GHz and 2.4GHz. We report on measurements of the upper and lower bounds of performance with good and poor RSSI in 802.11g and 802.11n. We find that in operation under poor (low) RSSI, performance is indeed impacted. In some cases the impact is such that there may be little benefit in using the newer 802.11n over the mature 802.11g.
... Motivated by the scenarios identified in 1) we assess in testbed experiments what power savings can be observed when using PSM for active devices. Recent work [7], [8] in this area shows that traffic flow characteristics, such as data rate and packet size of the offered load, have a significant impact on effective energy usage. We extend that work by considering the impact of PSM on energy efficiency and performance and showing the upper and lower bounds of this impact at the application level. ...
... We find no significant effect due to the use of PSM for active devices, but, as observed previously, energy efficiency is affected strongly by application-specific flow characteristics such as packet size and data rate and hence support and extend the findings reported in [7], [8] by considering a typical power save mechanism. ...
... Our experiments are based on work described in [7], [8]. However, for this study, we take new measurements using enhanced power-meters and adapting the WLAN NIC kernel module to monitor state changes of the WLAN NIC from active to inactivate to record sleep times. ...
802.11 WLAN is a popular choice for wireless access on a range of ICT devices. A growing concern is the increased energy usage of ICT, for reasons of cost and environmental protection. The Power Save Mode (PSM) in 802.11 deactivates the wireless network interface during periods of inactivity. However, applications increasingly use push models, and so devices may be active much of the time. We have investigated the effectiveness of PSM, and considered its impact on performance when a device is active. Rather than concentrate on the NIC, we have taken a system-wide approach, to gauge the impact of the PSM from an application perspective. We experimentally evaluated performance at the packet level and system-wide power usage under various offered loads, controlled by packet size and data rate, on our 802.11n testbed. We have measured the system- wide power consumption corresponding to the individual traffic profiles and have derived application-specific effective energy-usage. We have found that in our scenarios, no significant benefit can be gained from using PSM.
... In addition to that some of the presented approaches are often limited by the usage of a single metric. For instance, in [20,55] the authors show how the performance of a process can be measured, while the focus in [30,[50][51][52] is on evaluating the energy consumption. A summary of related work regarding security metrics has been provided by Yee in [62]. ...
Cyber-Physical Systems (CPS) are formed through interconnected components capable of computation, communication, sensing and changing the physical world. The development of these systems poses a significant challenge since they have to be designed in a way to ensure cyber-security without impacting their performance. This article presents the Security Cost Modelling Framework (SCMF) and shows supported by an experimental study how it can be used to measure, normalise and aggregate the overall performance of a CPS. Unlike previous studies, our approach uses different metrics to measure the overall performance of a CPS and provides a methodology for normalising the measurement results of different units to a common Cost Unit. Moreover, we show how the Security Costs can be extracted from the overall performance measurements which allows to quantify the overhead imposed by performing security-related tasks. Furthermore, we describe the architecture of our experimental testbed and demonstrate the applicability of SCMF in an experimental study. Our results show that measuring the overall performance and extracting the security costs using SCMF can serve as basis to redesign interactions to achieve the same overall goal at less costs.
... In addition to that some of the presented approaches are limited by the usage of a single metric. For instance, in [13,14] the authors show how the performance of a process can be measured, while the focus in [15,16,17,18] is on evaluating the energy consumption. Other related work use methods and frameworks to evaluate how secure e.g. a system is [19,20,21,22,23]. ...
In times of Industry 4.0 and cyber-physical systems (CPS) providing security is one of the biggest challenges. A cyber attack launched at a CPS poses a huge threat, since a security incident may affect both the cyber and the physical world. Since CPS are very flexible systems, which are capable of adapting to environmental changes, it is important to keep an overview of the resulting costs of providing security. However, research regarding CPS currently focuses more on engineering secure systems and does not satisfactorily provide approaches for evaluating the resulting costs. This paper presents an interaction-based model for evaluating security costs in a CPS. Furthermore, the paper demonstrates in a use case driven study, how this approach could be used to model the resulting costs for guaranteeing security.
... Baliga et al. [18] estimate that the energy consumption of data transmitted over the Internet is 2 -4 µJ/b at higher access rates (<100Mbps), to 75 µJ/b at lower access rates. Similarly, in our previous work [19], we investigated how various wireless access networking technologies (802.11) can consume a varying amount of energy at the client, varying between 0.5 -1.1 µJ/bit for large packet sizes to 2.3 -10 µJ/b for smaller packet sizes. ...
... We have observed that at different picture sizes, different codecs may provide the best trade-off between energy use and picture quality. Based on this, an energy-aware application could dynamically adapt its picture-size and/or video codec with the aim of conserving energy while maintaining the best possible quality [27,28]. (A similar analysis is possible for the encoding results.) ...
Allowing digital video users to make choices of picture size and codec would significantly reduce energy usage, electricity costs and the carbon footprint of Internet users. Our empirical investigation shows a difference of up to a factor of 3 in energy usage for video decoding using different codecs at the same picture size and bitrate, on a desktop client system. With video traffic already responsible for the largest and fastest growing proportion of traffic on the Internet, a significant amount of energy, money and carbon output is due to video. We present a simple methodology and metrics that can be used to give an intuitive, quantitative and comparable assessment of the energy usage of video decoding. Providing energy usage information to users would empower them to make sensible choices. We demonstrate how small energy savings for individual client systems could give significant energy savings when considered at a global scale.
... Our own previous work in this area, established the use of the energy metric, E A (see Section III-C) and the notion of the energy envelope, which gives the upper and lower bounds of the energy usage during the transmission of a flow [2]. We have also investigated the possibility of application adaptation within the scope of this energy envelope [3] to trade of performance against energy usage. Also, we have found that the generic 802.11 power save mode (PSM) has little effect during system usage [8]. ...
In mature wireless LAN (WLAN) deployments, we show that introducing 802.11ac could have little benefit compared to existing 802.11n deployments. Using a testbed with common characteristics for a WLAN deployment, we compare throughput for 802.11ac and 802.11n (in both 5GHz and 2.4GHz bands). We find that 802.11ac has lower throughput than for 802.11n for our testbed configuration. We also provide an evaluation of energy usage for 802.11ac and 802.11n.
... These models then also result in optimization of the grid-powered access points instead of focusing on the more critical battery operated devices. Further works rely on measurements of entire chip sets or network interface cards [6,13,21,34] that do not provide insight into the energy consumption of the PHY layer itself. ...
Energy in today's short-range wireless communication is mostly spent on the
analog- and digital hardware rather than on radiated power. Hence, purely
information-theoretic considerations fail to achieve the lowest energy per
information bit and the optimization process must carefully consider the
overall transceiver. In this paper, we propose to perform cross-layer
optimization, based on an energy-aware rate adaptation scheme combined with a
physical layer that is able to properly adjust its processing effort to the
data rate and the channel conditions to minimize the energy consumption per
information bit. This energy proportional behavior is enabled by extending the
classical system modes with additional configuration parameters at the various
layers. Fine grained models of the power consumption of the hardware are
developed to provide awareness of the physical layer capabilities to the medium
access control layer. The joint application of the proposed energy-aware rate
adaptation and modifications to the physical layer of an IEEE 802.11n system,
improves energy-efficiency (averaged over many noise and channel realizations)
in all considered scenarios by up to 44%.
Cyber-Physical Systems (CPS) are formed through interconnected components capable of computation, communication, sensing and changing the physical world. The development of these systems poses a significant challenge since they have to be designed in a way to ensure cyber-security without impacting their performance. This article presents the Security Cost Modelling Framework (SCMF) and shows supported by an experimental study how it can be used to measure, normalise and aggregate the overall performance of a CPS. Unlike previous studies, our approach uses different metrics to measure the overall performance of a CPS and provides a methodology for normalising the measurement results of different units to a common Cost Unit. Moreover, we show how the Security Costs can be extracted from the overall performance measurements which allows to quantify the overhead imposed by performing security-related tasks. Furthermore, we describe the architecture of our experimental testbed and demonstrate the applicability of SCMF in an experimental study. Our results show that measuring the overall performance and extracting the security costs using SCMF can serve as basis to redesign interactions to achieve the same overall goal at less costs.
In times of Industry 4.0 and cyber-physical systems (CPS) providing security is one of the biggest challenges. A cyber attack launched at a CPS poses a huge threat, since a security incident may affect both the cyber and the physical world. Since CPS are very flexible systems, which are capable of adapting to environmental changes, it is important to keep an overview of the resulting costs of providing security. However, research regarding CPS currently focuses more on engineering secure systems and does not satisfactorily provide approaches for evaluating the resulting costs. This paper presents an interaction-based model for evaluating security costs in a CPS. Furthermore, the paper demonstrates in a use case driven study, how this approach could be used to model the resulting costs for guaranteeing security.
Mobile communication - anytime, anywhere access to data and communication services - has been continuously increasing since the operation of the first wireless communication link by Guglielmo Marconi. The demand for higher data rates, despite the limited bandwidth, led to the development of multiple-input multiple-output (MIMO) communication which is often combined with orthogonal frequency division multiplexing (OFDM). Together, these two techniques achieve a high bandwidth efficiency. Unfortunately, techniques such as MIMO-OFDM significantly increase the signal processing complexity of transceivers. While fast improvements in the integrated circuit (IC) technology enabled to implement more signal processing complexity per chip, large efforts had and have to be done for novel algorithms as well as for efficient very large scaled integration (VLSI) architectures in order to meet today's and tomorrow's requirements for mobile wireless communication systems. In this thesis, we will present architectures and VLSI implementations of complete physical (PHY) layer application specific integrated circuits (ASICs) under the constraints imposed by an industrial wireless communication standard. Contrary to many other publications, we do not elaborate individual components of a MIMO-OFDM communication system stand-alone, but in the context of the complete PHY layer ASIC. We will investigate the performance of several MIMO detectors and the corresponding preprocessing circuits, being integrated into the entire PHY layer ASIC, in terms of achievable error-rate, power consumption, and area requirement. Finally, we will assemble the results from the proposed PHY layer implementations in order to enhance the energy efficiency of a transceiver. To this end, we propose a cross-layer optimization of PHY layer and medium access control (MAC) layer.
We report what we believe to be the first measure- ments of the power consumption of an 802.11n NIC across a broad set of operating states (channel width, transmit power, rates, antennas, MIMO streams, sleep, and active modes). We find the popular practice of rac- ing to sleep (by sending data at the highest possible rate) to be a useful heuristic to save energy, but that it does not always hold. We contribute three other useful heuristics: wide channels are an energy-efficient way to increase rates; multiple RF chains are more energy-efficient only when the channel is good enough to support the high- est MIMO rates; and single antenna operation is always most energy-efficient for short packets.
User Generated Content has become very popular since the birth of web services such as YouTube allowing the distribution of such user-produced media content in an easy manner. YouTube-like services are different from existing traditional VoD services because the service provider has only limited control over the creation of new content. We analyze how the content distribution in YouTube is realized and then conduct a measurement study of YouTube traffic in a large university campus network. The analysis of the traffic shows that: (1) No strong correlation is observed between global and local popularity; (2) neither time scale nor user population has an impact on the local popularity distribution; (3) video clips of local interest have a high local popularity. Using our measurement data to drive trace-driven simulations, we also demonstrate the implications of alternative distribution infrastructures on the performance of a YouTube-like VoD service. The results of these simulations show that client-based local caching, P2P-based distribution, and proxy caching can reduce network traffic significantly and allow faster access to video clips.
There are several IEEE 802.11 variants to interconnect several wireless devices. Usually, a variant is chosen based on their bandwidth and their coverage area. However, sometimes, there are special cases where the best technology is not the newest one. E.g., in the case where devices are going to transmit at a maximum of 1 Mbps, any choice is acceptable. In this paper, we are going to compare IEEE 802.11a/b/g/n in indoor environments in order to know which technology is better. This comparison will be taken in terms of RSSI, coverage area, and measuring the interferences between channels. This study will help the researchers to choose the best technology depending of their deploying case and we will see that the best technologies for in indoors are IEEE 802.11b and IEEE 802.11n.
In this paper, we shed light on the cross-layer interactions between the PHY, link and routing layers in networks with MIMO links operating in the diversity mode. Many previous studies assume an overly simplistic PHY layer model that does not sufficiently capture these interactions. We show that the use of simplistic models can in fact lead to misleading conclusions with regards to the higher layer performance with MIMO diversity. Towards understanding the impact of various PHY layer features on MIMO diversity, we begin with a simple but widely-used model and progressively incorporate these features to create new models. We examine the goodness of these models by comparing the simulated performance results with each, with measurements on an indoor 802.11 n testbed. Our work reveals several interesting cross-layer dependencies that affect the gains due to MIMO diversity. In particular, we observe that relative to SISO links: (a) PHY layer gains due to MIMO diversity do not always carry over to the higher layers, (b) the use of other PHY layer features such as FEC codes significantly influence the gains due to MIMO diversity, and (c) the choice of the routing metric can impact the gains possible with MIMO.
The success of Skype has inspired a generation of peer-to-peer-based solutions for satisfactory real-time multimedia services over the Internet. However, fundamental questions, such as whether VoIP services like Skype are good enough in terms of user satisfaction,have not been formally addressed. One of the major challenges lies in the lack of an easily accessible and objective index to quantify the degree of user satisfaction.In this work, we propose a model, geared to Skype, but generalizable to other VoIP services, to quantify VoIP user satisfaction based on a rigorous analysis of the call duration from actual Skype traces. The User Satisfaction Index (USI) derived from the model is unique in that 1) it is composed by objective source-and network-level metrics, such as the bit rate, bit rate jitter, and round-trip time, 2) unlike speech quality measures based on voice signals, such as the PESQ model standardized by ITU-T, the metrics are easily accessible and computable for real-time adaptation, and 3) the model development only requires network measurements, i.e., no user surveys or voice signals are necessary. Our model is validated by an independent set of metrics that quantifies the degree of user interaction from the actual traces.
Skype is a very popular VoIP software which has recently attracted the attention of the research community and network operators. Following a closed source and proprietary design, Skype protocols and algorithms are unknown. Moreover, strong encryption mechanisms are adopted by Skype, making it very difficult to even glimpse its presence from a traffic aggregate. In this paper, we propose a framework based on two complementary techniques to reveal Skypetraffic in real time. The first approach, based on Pearson'sChi-Square test and agnostic to VoIP-related trafficcharacteristics, is used to detect Skype's fingerprint from the packet framing structure, exploiting the randomness introduced at the bit level by the encryption process. Conversely, the second approach is based on a stochastic characterization of Skype traffic in terms of packet arrival rate and packet length, which are used as features of a decision process based on Naive Bayesian Classifiers.In order to assess the effectiveness of the above techniques, we develop an off-line cross-checking heuristic based on deep-packet inspection and flow correlation, which is interesting per se. This heuristic allows us to quantify the amount of false negatives and false positives gathered by means of the two proposed approaches: results obtained from measurements in different networks show that the technique is very effective in identifying Skype traffic. While both Bayesian classifier and packet inspection techniques are commonly used, the idea of leveraging on randomness to reveal traffic is novel. We adopt this to identify Skype traffic, but the same methodology can be applied to other classification problems as well.
Self-adaptation can be achieved by autonomic management of facets of a system's constituent components. This paper reports on a generic autonomic management framework and on its application to a key-based routing protocol as used in the peer-to-peer overlay Chord. The framework implements generic components of the autonomic management cycle. In the work reported here it was used to build a manager which autonomically controls the maintenance scheduling of the peer-set in individual Chord nodes, governed by some high-level policies. This manager improved routing performance and resource consumption in comparison to statically configured Chord nodes in a deployed network which was exposed to various membership churn and workload patterns.
In this paper, we propose an adaptive technique exploiting transmission mode switching between multiple input multiple output (MIMO) and single input multiple output (SIMO) with antenna selection to conserve mobile terminals' energy. We focus on saving uplink RF transmission energy in cellular systems supporting dynamic best effort (file transfer) traffic loads. The key idea is to judiciously slow down file transfer rates when a base station is underutilized. Due to the DC power components associated with the multiplicity of transmission chains, MIMO may have higher power consumption than SIMO. Thus, considering a desired user perceived target throughput as well as energy-efficiency, we propose an algorithm for mode switching (MIMO/SIMO) and rate selection. Extensive flow-level simulations under dynamic loads and Rayleigh fading channels confirm that the proposed technique can save more than 50 % of the mobile terminals' transmission energy and enable an effective tradeoff between performance and energy conservation.
We derive formulas for the energy J(n) that a station's radio consumes when it transmits 1 MB of data in an IEEE 802.11 network with n stations. Calculations show that J(ra) grows approximately linearly with n, for n ges 4. The useful energy consumed in successful transmission and reception of data is constant; the remaining energy is wasted. When n = 15, the waste amounts to 80 percent of total energy, and this proportion grows with n. More than 60 percent of the waste is due to overhearing - reception of packets intended for another station. Overhearing can be eliminated by using information in RTS/CTS packets.
Skype is a very popular VoIP software which has recently attracted the attention of the research community and network operators. Following a closed source and proprietary design, Skype protocols and algorithms are unknown. Moreover, strong encryption mechanisms are adopted by Skype, making it very difficult to even glimpse its presence from a traffic aggregate. In this paper, we propose a framework based on two complementary techniques to reveal Skypetraffic in real time. The first approach, based on Pearson'sChi-Square test and agnostic to VoIP-related trafficcharacteristics, is used to detect Skype's fingerprint from the packet framing structure, exploiting the randomness introduced at the bit level by the encryption process. Conversely, the second approach is based on a stochastic characterization of Skype traffic in terms of packet arrival rate and packet length, which are used as features of a decision process based on Naive Bayesian Classifiers.In order to assess the effectiveness of the above techniques, we develop an off-line cross-checking heuristic based on deep-packet inspection and flow correlation, which is interesting per se. This heuristic allows us to quantify the amount of false negatives and false positives gathered by means of the two proposed approaches: results obtained from measurements in different networks show that the technique is very effective in identifying Skype traffic. While both Bayesian classifier and packet inspection techniques are commonly used, the idea of leveraging on randomness to reveal traffic is novel. We adopt this to identify Skype traffic, but the same methodology can be applied to other classification problems as well.
The importance of wireless communications, involving electronic devices, has been growing. Performance is a crucial issue, leading to more reliable and efficient communications. Security is equally important. Laboratory measurements are made about several performance aspects of Wi-Fi (IEEE 802.11 b, g) WEP and WPA point-to-point links. A contribution is given to performance evaluation of this technology, using available wireless routers from Linksys (WRT54GL). Detailed results are presented and discussed, namely at OSI levels 4 and 7, from TCP, UDP and FTP experiments: TCP throughput, jitter, percentage datagram loss and FTP transfer rate. Comparisons are made to corresponding results obtained for, mainly, open links. Conclusions are drawn about the comparative performance of the links.
For the battery-powered wireless stations, power saving is one of the significant issues in IEEE 802.11 wireless local area network (WLAN). Recently, Lei and Nilsson investigated power save mode in IEEE 802.11 infrastructure network by an M/G/1 with bulk service where they obtained mean packet delay and bound of the average Percentage of time a station stays in the doze state (PTD). In this paper, the further investigation of power save mode is done; simple derivation of the mean and the variance of packet delay and the exact value of PTD are obtained. Numerical results show that our analytic results for PTD match quite well with simulation results by Lei and Nilsson. Using our performance analysis, we can find the maximal listen interval which maximizes the average PTD of a station while satisfying the required quality of service (QoS) on the mean and the variance of packet delay.
With the rapid development of information technology, wireless network technology becomes more and more widespread, transmission efficiency of wireless network has been a research focus. This paper firstly has discussed the principles of aggregation of the use of packet technology in the feasibility of the use of WLAN, and specific circumstances of the packages fusion method by NS2 simulation achieved under the aggregation of data packets so as to enhance the transmission efficiency of WLAN. Finally, it’s calculate the fusion of data packets with de-aggregation of data packets in the WLAN transmission efficiency.
We present an experimental evaluation of energy usage and performance in a wireless LAN cell based on a test bed using the 5 GHz ISM band for 802.11a and 802.11n. We have taken an application-level approach, by varying the packet size and transmission rate at the protocol level and evaluating energy usage across a range of application transmission rates using both large and small packet sizes. We have observed that both the application's transmission rate and the packet size have an impact on energy efficiency for transmission in our test bed. We also included in our experiments evaluation of the energy efficiency of emulations of YouTube and Skype flows, and a comparison with Ethernet transmissions.
The importance of wireless communications, involving electronic devices, has been growing. Performance is a very relevant issue, leading to more reliable and efficient communications. Laboratory measurements are made about several performance aspects of Wi-Fi (IEEE 802.11 a, g) WEP point-to-point links. A contribution is given to performance evaluation of this technology, using available access points from Enterasys Networks (RBTR2). Detailed results are presented and discussed, namely at OSI layers 4 and 7, from TCP, UDP and FTP experiments: TCP throughput, jitter, percentage datagram loss and FTP transfer rate. Comparisons are made to corresponding results obtained for open links.
We present a network model that allows processing of QoS (quality of service) information about media flows to enable applications to make adaptation decisions. Our model is based around a multi-dimensional spatial representation that allows QoS information describing the flow constructions and QoS parameters – flow-states – to interact with a representation of the network QoS. The model produces reports about the compatibility between the flow-states and the network QoS, indicating which flow-states the network can currently support. The simple nature of the reports allows the application to make decisions, dynamically, on which flow-state it should use. The model is relatively lightweight and scaleable. We demonstrate the use of the model by simulation of a dynamically adaptive audio tool. Our work is ongoing.
In recent years, IEEE 802.11 wireless local area networks (WLANs) have been widely deployed, and more and more mobile devices have built-in WLAN interfaces. However, WLAN employs the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol, which consumes a significant portion of the energy resources of a mobile device. Hence, minimizing the energy consumption of the WLAN interface in mobile devices has recently attracted considerable interest in both academia and industry. This article provides a survey and an experimental study of the energy consumption issues and energy-efficient technologies of the MAC protocol in IEEE 802.11 WLAN.
This paper presents a traffic characterization study of the popular video sharing service, YouTube. Over a three month period we observed almost 25 million transactions between users on an edge network and YouTube, including more than 600,000 video downloads. We also monitored the globally popular videos over this period of time. In the paper we examine usage patterns, file properties, popularity and referencing characteristics, and transfer behaviors of YouTube, and compare them to traditional Web and media streaming workload characteristics. We conclude the paper with a discussion of the implications of the observed characteristics. For example, we find that as with the traditional Web, caching could improve the end user experience, reduce network bandwidth consumption, and reduce the load on YouTube's core server infrastructure. Unlike traditional Web caching, Web 2.0 provides additional meta-data that should be exploited to improve the effectiveness of strategies like caching.
U-APSD is the power save procedure defined in IEEE802.11e to improve the QoS performance of multimedia applications. U-APSD is specially suited for bi-directional traffic streams. But in some scenario without synchronized uplink and downlink traffic, defects in U-APSD procedure will result in some problems. In order to address this issue, this paper develops a low power implementation scheme of U-APSD by exploiting the downlink traffic rate estimation algorithm, and using clock gating technique as circuit-level approach to save dynamic power. Our experiments show that the scheme brings significant reduction in power consumption of NIC with little impact to the performance.
In bridging the digital divide, two important criteria are cost-effectiveness, and power optimization. While 802.11 is cost-effective and is being used in several installations in the developing world, typical system configurations are not really power efficient. In this paper, we propose a novel "Wake-on-WLAN" mechanism for coarse-grained, on-demand power on/off of the networking equipment at a remote site. The novelty also lies in our implementation of a prototype system using low-power 802.15.4-based sensor motes. We describe the prototype, as well as its evaluation on field in a WiFi testbed. Preliminary estimates indicate that the proposed mechanism can save significant power in typical rural networking settings.
Many rural and remote communities around the world see them- selves on the wrong side of the digital divide. In particular, there is evidence to suggest that there is a growing digital divide between urban and rural areas in terms of broadband Internet access with people living in rural areas having fewer choices and pay higher prices for slower speeds. This is true even in developed countries. Motivated by the above observations, there has been an increasing interest in deploying and researching low cost rural wireless net- works with active community participation. This paper presents an overview of our efforts in this direction in deploying a rural WiFi- based long distance mesh network testbed in the Scottish Highlands and Islands. We highlight the unique aspects of our testbed that differentiate it from other existing rural wireless testbeds. We also outline some of the research issues that are currently being investi- gated in this project.
To support mobility, mobile devices are powered by batteries with limited energy. Thus, the good design of energy efficiency becomes one of the most important issues in wireless networks. A well-designed energy-efficient MAC protocols can be realized with both minimum energy consumption as well as maximum data throughput and can be easily implemented in products with de facto standards. Based on IEEE 802.11 infrastructure WLANs, we propose an energy-efficient MAC protocol which employs a novel approach to schedule those to-be-transmitted frames for saving energy by reducing the total waiting time and the collisions of the frames. Fault tolerance issues are also considered in the proposed protocol because frames are transmitted in fading interference wireless environment. Through analyses and simulations, we demonstrate that our protocol presents a better performance than IEEE 802.11 and other protocols not only in energy efficiency but also in aggregate throughput and frame transmission delay.
Static PSM (power-saving mode) schemes employed in the current IEEE 802.11 implementations could not provide any delay-performance guarantee because of their fixed wakeup intervals. In this paper, we propose a smart PSM (SPSM) scheme, which directs a wireless station to sleep/wake up according to an "optimal" sequence, such that the desired delay performance is guaranteed with minimum energy consumption. Instead of constructing the sequence directly, SPSM takes a unique two-step approach. First, it translates an arbitrary user-desired delay performance into a generic penalty function. Second, it provides a generic algorithm that takes the penalty function as the input and produces the optimal station action sequence automatically. This way, the potentially-complicated energy-consumption-minimization problem subject to delay-performance constraints is simplified and solved systematically. Our simulation results show that, with a two-stair penalty function, SPSM achieves delay performance similar to the BSD (bounded slowdown) protocol under various scenarios, but always with less energy consumption, thanks to its capability to adapt to changes in the response-time distribution. Moreover, because of SPSM's two-step design feature, it is more flexible than BSD in the sense of being able to meet arbitrary user-desired delay requirement, e.g., providing soft delay-bound guarantees with power penalty functions.
A good design of MAC protocols should realize both minimum energy consumption as well as maximum data throughput. IEEE 802.11 power management scheme for an ad hoc network is based on the carrier sense multiple access with collision avoidance (CSMA/CA) procedure to transmit/receive data frames. CSMA/CA may waste the scarce energy and bandwidth due to frame collisions and lengthen the frame delay due to waiting backoff time. In addition, the IEEE 802.11 power management scheme does not specify how to tune the ATIM (announcement traffic indication message) window size in a beacon interval. However, the ATIM window size affects the power consumption and throughput of a network considerably. The fixed ATIM window size cannot always accommodate the various traffic conditions. To conquer these problems and to improve the performance of networks, we propose a novel energy efficient MAC protocol for IEEE 802.11 networks by scheduling transmission after the ATIM window and adjusting the ATIM window dynamically to adapt to the traffic status. Simulation results show that our protocol attains a better energy efficiency and throughput than existing protocols.
The Wi-Fi Alliance's new WMM (Wi-Fi Multimedia) Power Save certification framework addresses the need for expanded battery life in Wi-Fi cell phones and other mobile devices. WMM Power Save is an extension of the Wi-Fi Multimedia program, which improves user experience with multimedia and latency-sensitive content.
