Mobility: a double-edged sword for HSPA networks

This paper presents an empirical study on the performance of mobile High Speed Packet Access (HSPA, a 3.5G cellular standard) networks in Hong Kong via extensive field tests. Our study, from the viewpoint of end users, covers virtually all possible mobile scenarios in urban areas, including subways, trains, off-shore ferries and city buses. We have confirmed that mobility has largely negative impacts on the performance of HSPA networks, as fast-changing wireless environment causes serious service deterioration or even interruption. Meanwhile our field experiment results have shown unexpected new findings and thereby exposed new features of the mobile HSPA networks, which contradict commonly held views. We surprisingly find out that mobility can improve fairness of bandwidth sharing among users and traffic flows. Also the triggering and final results of handoffs in mobile HSPA networks are unpredictable and often inappropriate, thus calling for fast reacting fallover mechanisms. We have conducted in-depth research to furnish detailed analysis and explanations to what we have observed. We conclude that mobility is a double-edged sword for HSPA networks. To the best of our knowledge, this is the first public report on a large scale empirical study on the performance of commercial mobile HSPA networks

The Glasgow raspberry pi cloud: a scale model for cloud computing infrastructures

Data Centers (DC) used to support Cloud services often consist of tens of thousands of networked machines under a single roof. The significant capital outlay required to replicate such infrastructures constitutes a major obstacle to practical implementation and evaluation of research in this domain. Currently, most research into Cloud computing relies on either limited software simulation, or the use of a testbed environments with a handful of machines. The recent introduction of the Raspberry Pi, a low-cost, low-power single-board computer, has made the construction of a miniature Cloud DCs more affordable. In this paper, we present the Glasgow Raspberry Pi Cloud (PiCloud), a scale model of a DC composed of clusters of Raspberry Pi devices. The PiCloud emulates every layer of a Cloud stack, ranging from resource virtualisation to network behaviour, providing a full-featured Cloud Computing research and educational environment

DragonNet: a robust mobile internet services system for long distance trains

Wide range wireless networks often suffer from annoying service deterioration due to ever-changing wireless environments. This is especially the case with passengers on long-distance trains (LDT, such as intercity, interprovincial, and international commuter trains) connecting to the Internet. To improve the service quality of wide-area wireless networks, we present the DragonNet system and protocol with practical implementations. The DragonNet system is a chained gateway that consists of a group of interlinked DragonNet routers running the DragonNet protocol for node failure amortization across the long stretching router chain. The protocol makes use of the spatial diversity of wireless signals when not all spots on a surface see the same level of radio frequency radiation. In the case of an LDT of around 500 meters, it is highly possible that some of the DragonNet routers in the gateway chain still see sound signal quality when the LDT is partially blocked from the wireless Internet. The DragonNet protocol fully utilizes this feature to amortize single-point router failure over the whole router chain by intelligently rerouting traffic on failed ones to sound ones. We have implemented the DragonNet system and tested it in real railways over a period of three months. Our results have pinpointed two fundamental contributions of the DragonNet protocol. First, DragonNet significantly reduces the average temporary communication blackout (i.e., no Internet connection) to 1.5 seconds compared with 6 seconds without the DragonNet protocol. Second, DragonNet nearly doubles the aggregate system throughput compared with gateway without running the DragonNet protocol

Improving data centre network utilisation using near-optimal traffic engineering

Equal Cost Multiple Path (ECMP) forwarding is the most prevalent multipath routing used in Data Centre (DC) networks today. However, it fails to exploit increased path diversity that can be provided by traffic engineering techniques through the assignment of non-uniform link weights to optimise network resource usage. To this extent, constructing a routing algorithm that provides path diversity over non-uniform link weights (i.e., unequal cost links), simplicity in path discovery and optimality in minimising Maximum Link Utilisation (MLU) is non-trivial. In this paper, we have implemented and evaluated the Penalizing Exponential Flow-spliTing (PEFT) algorithm in a cloud DC environment based on two dominant topologies, canonical and fattree. In addition, we have proposed a new cloud DC topology which, with only a marginal modification of the current canonical tree DC architecture, can further reduce MLU and increase overall network capacity utilisation through PEFT routing

Baatdaat: measurement-based flow scheduling for cloud data centers

Software-Defined Networking (SDN) allows for efficient network-wide Traffic Engineering through the logical centralization of the control plane over individual switches that perform packet forwarding independently. Such abstraction is particularly suitable for Data Center (DC) networks that need to react to fluctuating traffic dynamics over short timescales. In this paper, we propose a low-cost, SDN-based system that exposes the temporal network-wide utilization through direct measurement, rather than estimation. We then present the Baatdaat1 flow scheduling algorithm which uses spare DC network capacity to mitigate the performance degradation of heavily utilized links. Results show that Baatdaat achieves close to optimal Traffic Engineering by reducing network-wide maximum link utilization by up to 18% over ECMP, while at the same time improving flow completion time by as much as 41% - 95% for different types of flows

Mobility: a double-edged sword for HSPA networks: a large-scale test on Hong Kong mobile HSPA networks

This paper presents an empirical study on the performance of mobile High Speed Packet Access (a 3.5G cellular standard usually abbreviated as HSPA) networks in Hong Kong via extensive field tests. Our study, from the viewpoint of end users, covers virtually all possible mobile scenarios in urban areas, including subways, trains, off-shore ferries, and city buses. We have confirmed that mobility has largely negative impacts on the performance of HSPA networks, as fast-changing wireless environment causes serious service deterioration or even interruption. Meanwhile, our field experiment results have shown unexpected new findings and thereby exposed new features of the mobile HSPA networks, which contradict commonly held views. We surprisingly find out that mobility can improve fairness of bandwidth sharing among users and traffic flows. Also, the triggering and final results of handoffs in mobile HSPA networks are unpredictable and often inappropriate, thus calling for fast reacting fallover mechanisms. Moreover, we find that throughput performance does not monotonically decrease with increased mobility level. We have conducted in-depth research to furnish detailed analysis and explanations to what we have observed. We conclude that mobility is a double-edged sword for HSPA networks. To the best of our knowledge, this is the first public report on a large-scale empirical study on the performance of commercial mobile HSPA networks

Implementing scalable, network-aware virtual machine migration for cloud data centers

Virtualization has been key to the success of Cloud Computing through the on-demand allocation of shared hardware resources to Virtual Machines (VM)s. However, the network-agnostic placement of VMs over the underlying network topology can itself be a factor of performance degradation by causing congestion at the core layers of the infrastructure where bandwidth is heavily oversubscribed. In this paper, we design and implement S-CORE, a scalable live VM migration scheme to dynamically reallocate VMs to servers while minimizing the overall communication footprint of active traffic flows. We evaluate SCORE over diverse aggregate load and coordination policies. Our results show that it can achieve up to a 87% communication cost reduction with a limited number of migration rounds, and can be easily accommodated within commodity hardware and hypervisor architectures. The associated memory, CPU, and network overhead are also minimum under typical Cloud Data Center workloads

WeFiLab: a web-based WiFi laboratory platform for wireless networking education

Remote access to physical laboratories for education has been received significant attention from both researchers and educators as it provides access at reduced cost in sharing manner of real devices and gives students practical training. With the rapid growing of wireless technologies, it has been become an essential of learning to have the hand-on experience on wireless networking for the proliferated number of students in engineering. Some of current implementations for wireless networking are either using simulations, which lose the reality, or too complicated for undergraduate students to control experiments. In this paper, we present a practical online laboratory platform, Web-based WiFi Laboratory (WeFiLab). WeFiLab mainly focuses on providing students hand-on experience of doing experiments on real devices through webpage anytime anywhere. It uses the structure of two-level operations, which facilities increasing the scale of wireless devices and allows WeFiLab to be extended to more complicated operations. The schedule schemes of WeFiLab let more students share and make efficient use of wireless devices. A prototype of WeFiLab has been implemented and used successfully as complements for an undergraduate course for two years in a university. Totally 315 computer science students attended the evaluation

Longer is better: exploiting path diversity in data center networks

Data Center (DC) networks exhibit much more centralized characteristics than the legacy Internet, yet they are operated by similar distributed routing and control algorithms that fail to exploit topological redundancy to deliver better and more sustainable performance. Multipath protocols, for example, use node-local and heuristic information to only exploit path diversity between shortest paths. In this paper, we use a measurementbased approach to schedule flows over both shortest and nonshortest paths based on temporal network-wide utilization. We present the Baatdaat1 flow scheduling algorithm which uses spare DC network capacity to mitigate the performance degradation of heavily utilized links. Results show that Baatdaat achieves close to optimal Traffic Engineering by reducing network-wide maximum link utilization by up to 18% over Equal-Cost MultiPath (ECMP) routing, while at the same time improving flow completion time by 41% - 95%

User-level data center tomography

Measurement and inference in data centers presents a set of opportunities and challenges distinct from the Internet domain. Existing toolsets may be perturbed or be mislead by issues related to virtualization. Yet, while equally confronted by scale, data centers are relatively homogenous and symmetric. We believe these may be attributes to be exploited. However, data is required to better evaluate our hypotheses. Therefore, we present our efforts to gather data using a single framework from which we can launch tests of our choosing. Our observations reinforce recent claims, but indicate changes in the network. They also reveal additional obfuscations stemming from virtualization