In this paper, we empirically demonstrate the growing importance of reliability by measuring its effect on user behavior. We present an approach for broadband reliability characterization using data collected by many emerging national initiatives to study broadband and apply it to the data gathered by the Federal Communications Commission's Measuring Broadband America project. Motivated by our findings, we present the design, implementation, and evaluation of a practical approach for improving the reliability of broadband Internet access with multihoming.
Baltr = u @cite_48 presented a study of the reliability of four mobile broadband providers in Norway using the Nornet Edge dedicated infrastructure. This work illustrates the value of end-to-end measurements to identify failures and performance events not always captured by the operators' monitoring systems. Broadband reliability has received little attention until recently. @cite_67 discuss some of the challenges of characterizing reliability and their economic and policy implications and identify three different ways in which the reliability'' of broadband services can be measured: (1) the reliability of the service itself; (2) the reliability of network services offered by the ISP (e.g., DNS); and (3) the consistency of the service's performance. We focus on characterizing reliability in terms of the former two categories and leave the latter as future work.
@cite_48 @cite_67
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Mobile broadband networks play an increasingly important role in society, and there is a strong need for independent assessments of their robustness and performance. A promising source of such information is active end-to-end measurements. It is, however, a challenging task to go from individual measurements to an assessment of network reliability, which is a complex notion encompassing many stability and performance related metrics. This paper presents a framework for measuring the user-experienced reliability in mobile broadband networks. We argue that reliability must be assessed at several levels, from the availability of the network connection to the stability of application performance. Based on the proposed framework, we conduct a large-scale measurement study of reliability in 5 mobile broadband networks. The study builds on active measurements from hundreds of measurement nodes over a period of 10 months. The results show that the reliability of mobile broadband networks is lower than one could hope: more than 20 of connections from stationary nodes are unavailable more than 10 minutes per day. There is, however, a significant potential for improving robustness if a device can connect simultaneously to several networks. We find that in most cases, our devices can achieve 99.999 ("five nines") connection availability by combining two operators. We further show how both radio conditions and network configuration play important roles in determining reliability, and how external measurements can reveal weaknesses and incidents that are not always captured by the operators' existing monitoring tools. With broadband availability now approaching universal service in the United States, the focus on broadband metrics is shifting toward the assessment of broadband performance. The initial focus has been on the measurement and reporting of the speeds achieved by broadband services. As we develop more comprehensive and, hopefully, more meaningful frameworks for characterizing, measuring, and evaluating broadband performance, one obvious measure of merit will be reliability. In a survey, consumers identified concerns about reliability as second only to speed in importance. Moreover, as our collective reliance on broadband as critical socio-economic infrastructure increases, and as a growing range of services move into the Internet, it is reasonable to expect that demand for reliable broadband service will increase. At the same time, the growth of streaming and interactive rich multimedia, the convergence of fixed and mobile services, and the evolution of the Internet services industry pose new challenges for developing appropriate reliability metrics. While the measurement of broadband availability or speeds and the appropriate interpretation of measurement data are not simple tasks, evaluating reliability is inherently much more complex and difficult. We present the first study of broadband services in their broader context, evaluating the impact of service characteristics (such as capacity, latency and loss), their broadband pricing and user demand. We explore these relationships, beyond correlation, with the application of natural experiments. Most efforts on broadband service characterization have so far focused on performance and availability, yet we lack a clear understanding of how such services are being utilized and how their use is impacted by the particulars of the market. By analyzing over 23-months of data collected from 53,000 end hosts and residential gateways in 160 countries, along with a global survey of retail broadband plans, we empirically study the relationship between broadband service characteristics, pricing and demand. We show a strong correlation between capacity and demand, even though subscribers rarely fully utilize their links, but note a law of diminishing returns with relatively smaller increases in demand at higher capacities. Despite the fourfold increase in global IP traffic, we find that user demand on the network over a three year period remained constant for a given bandwidth capacity. We exploit natural experiments to examine the causality between these factors. The reported findings represent an important step towards understanding how user behavior, and the market features that shape it, affect broadband networks and the Internet at large. A large and rapidly growing proportion of users connect to the Internet via residential broadband networks such as Digital Subscriber Lines (DSL) and cable. Residential networks are often the bottleneck in the last mile of today's Internet. Their characteristics critically affect Internet applications, including voice-over-IP, online games, and peer-to-peer content sharing delivery systems. However, to date, few studies have investigated commercial broadband deployments, and rigorous measurement data that characterize these networks at scale are lacking. In this paper, we present the first large-scale measurement study of major cable and DSL providers in North America and Europe. We describe and evaluate the measurement tools we developed for this purpose. Our study characterizes several properties of broadband networks, including link capacities, packet round-trip times and jitter, packet loss rates, queue lengths, and queue drop policies. Our analysis reveals important ways in which residential networks differ from how the Internet is conventionally thought to operate. We also discuss the implications of our findings for many emerging protocols and systems, including delay-based congestion control (e.g., PCP) and network coordinate systems (e.g., Vivaldi). Recent progress in active measurement techniques has made it possible to estimate end-to-end path available bandwidth. However, how to efficiently obtain available bandwidth information for the N2 paths in a large N-node system remains an open problem. While researchers have developed coordinate-based models that allow any node to quickly and accurately estimate latency in a scalable fashion, no such models exist for available bandwidth. In this paper we introduce BRoute--a scalable available bandwidth estimation system that is based on a route sharing model. The characteristics of BRoute are that its overhead is linear with the number of end nodes in the system, and that it requires only limited cooperation among end nodes. BRoute leverages the fact that most Internet bottlenecks are on path edges, and that edges are shared by many different paths. It uses AS-level source and sink trees to characterize and infer path-edge sharing in a scalable fashion. In this paper, we describe the BRoute architecture and evaluate the performance of its components. Initial experiments show that BRoute can infer path edges with an accuracy of over 80 . In a small case study on Planetlab, 80 of the available bandwidth estimates obtained from BRoute are accurate within 50 . The performance of Internet services is intrinsically tied to propagation delays between end points (i.e., network latency). Standard active probe-based or passive host-based methods for measuring end-to-end latency are difficult to deploy at scale and typically offer limited precision and accuracy. In this paper, we investigate a novel but non-obvious source of latency measurement---logs from network time protocol (NTP) servers. Using NTP-derived data for studying latency is compelling due to NTP's pervasive use in the Internet and its inherent focus on accurate end-to-end delay estimation. We consider the efficacy of an NTP-based approach for studying propagation delays by analyzing logs collected from 10 NTP servers distributed across the United States. These logs include over 73M latency measurements to 7.4M worldwide clients (as indicated by unique IP addresses) collected over the period of one day. Our initial analysis of the general characteristics of propagation delays derived from the log data reveals that delay measurements from NTP must be carefully filtered in order to extract accurate results. We develop a filtering process that removes measurements that are likely to be inaccurate. After applying our filter to NTP measurements, we report on the scope and reach for US-based clients and the characteristics of the end-to-end latency for those clients. Fiber optic cables are the workhorses of today's Internet services. Operators spend millions of dollars to purchase, lease and maintain their optical backbone, making the efficiency of fiber essential to their business. In this work, we make a case for adapting the capacity of optical links based on their signal-to-noise ratio (SNR). We show two immediate benefits of this by analyzing the SNR of over 2000 links in an optical backbone over a period of 2.5 years. First, the capacity of 80 of IP links can be augmented by 75 or more, leading to an overall capacity gain of 145 Tbps in a large optical backbone in North America. Second, at least 25 of link failures are caused by SNR degradation, not complete loss-of-light, highlighting the opportunity to replace link failures by link flaps wherein the capacity is adjusted according to the new SNR. Given these benefits, we identify the disconnect between current optical and networking infrastructure which hinders the deployment of dynamic capacity links in wide area networks (WANs). To bridge this gap, we propose a graph abstraction that enables existing traffic engineering algorithms to benefit from dynamic link capacities. We evaluate the feasibility of dynamic link capacities using a small testbed and simulate the throughput gains from deploying our approach. Evaluating and characterizing Internet Service Providers (ISPs) is critical to subscribers shopping for alternative ISPs, companies providing reliable Internet services, and governments surveying the coverage of broadband services to its citizens. Ideally, ISP characterization should be done at scale, continuously, and from end users. While there has been significant progress toward this end, current approaches exhibit apparently unavoidable tradeoffs between coverage, continuous monitoring and capturing user-perceived performance. In this paper, we argue that network-intensive applications running on end systems avoid these tradeoffs, thereby offering an ideal platform for ISP characterization. Based on data collected from 500,000 peer-to-peer BitTorrent users across 3,150 networks, together with the reported results from the U.K. Ofcom SamKnows studies, we show the feasibility of this approach to characterize the service that subscribers can expect from a particular ISP. We discuss remaining research challenges and design requirements for a solution that enables efficient and accurate ISP characterization at an Internet scale. Reliability is critical to a variety of network applications. Unfortunately, due to lack of QoS support across ISP boundaries, it is difficult to achieve even two 9s (99 ) reliability in toadyism Internet. In this paper, we propose SmartTunnel, an end-to-end approach to achieving reliability. A SmartTunnel is a logical point-to-point tunnel between two end points that spans multiple physical network paths. It achieves reliability by strategically allocating traffic onto multiple paths and performing FEC coding. Such an end-to-end approach requires no explicit QoS support from intermediate ISPs, and is therefore easy to deploy in today's Internet. To fully realize the potential of SmartTunnel, we analytically derive near-optimal traffic allocation schemes that minimize loss rates. We extensively evaluate our approach using trace-driven simulations, ns-2 simulations, and experiments on PlanetLab. Our results clearly demonstrate that SmartTunnel is effective in achieving high reliability. Reliability and availability have always been important characteristics of systems but become even more critical and complex issues on networks. Due to the high complexity of accurate calculation methods, simulation methods for network reliability and availability evaluation have been a popular area of research, and received significant attention. In this paper the network topology model, the failure driven simulation method and the reliability and availability statistical algorithms are put forward, and then the network reliability and availability simulation flow based on the Monte Carlo method was designed. This simulation method can be used to calculate the reliability and availability of a network whose nodes and links may be failure. Two repair policies, immediate repair and delay repair, are provided to choose. Finally, the backbone of CERNET (China Education and Research Network) is taken as an example and the simulation results are analyzed. We consider the problem of resource allocation in downlink OFDMA systems for multi service and unknown environment. Due to users' mobility and intercell interference, the base station cannot predict neither the Signal to Noise Ratio (SNR) of each user in future time slots nor their probability distribution functions. In addition, the traffic is bursty in general with unknown arrival. The probability distribution functions of the SNR, channel state and traffic arrival density are then unknown. Achieving a multi service Quality of Service (QoS) while optimizing the performance of the system (e.g. total throughput) is a hard and interesting task since it depends on the unknown future traffic and SNR values. In this paper we solve this problem by modeling the multiuser queuing system as a discrete time linear dynamic system. We develop a robust H∞ controller to regulate the queues of different users. The queues and Packet Drop Rates (PDR) are controlled by proposing a minimum data rate according to the demanded service type of each user. The data rate vector proposed by the controller is then fed as a constraint to an instantaneous resource allocation framework. This instantaneous problem is formulated as a convex optimization problem for instantaneous subcarrier and power allocation decisions. Simulation results show small delays and better fairness among users. Research on performance, robustness, and evolution of the global Internet is fundamentally handicapped without accurate and thorough knowledge of the nature and structure of the contractual relationships between Autonomous Systems (ASs). In this work we introduce novel heuristics for inferring AS relationships. Our heuristics improve upon previous works in several technical aspects, which we outline in detail and demonstrate with several examples. Seeking to increase the value and reliability of our inference results, we then focus on validation of inferred AS relationships. We perform a survey with ASs' network administrators to collect information on the actual connectivity and policies of the surveyed ASs. Based on the survey results, we find that our new AS relationship inference techniques achieve high levels of accuracy: we correctly infer 96.5 customer to provider (c2p), 82.8 peer to peer (p2p), and 90.3 sibling to sibling (s2s) relationships. We then cross-compare the reported AS connectivity with the AS connectivity data contained in BGP tables. We find that BGP tables miss up to 86.2 of the true adjacencies of the surveyed ASs. The majority of the missing links are of the p2p type, which highlights the limitations of present measuring techniques to capture links of this type. Finally, to make our results easily accessible and practically useful for the community, we open an AS relationship repository where we archive, on a weekly basis, and make publicly available the complete Internet AS-level topology annotated with AS relationship information for every pair of AS neighbors. In analyzing the point-to-point wireless channel, insights about two qualitatively different operating regimes-bandwidth and power-limited-have proven indispensable in the design of good communication schemes. In this paper, we propose a new scaling law formulation for wireless networks that allows us to develop a theory that is analogous to the point-to-point case. We identify fundamental operating regimes of wireless networks and derive architectural guidelines for the design of optimal schemes. Our analysis shows that in a given wireless network with arbitrary size, area, power, bandwidth, etc., there are three parameters of importance: the short-distance signal-to-noise ratio (SNR), the long-distance SNR, and the power path loss exponent of the environment. Depending on these parameters, we identify four qualitatively different regimes. One of these regimes is especially interesting since it is fundamentally a consequence of the heterogeneous nature of links in a network and does not occur in the point-to-point case; the network capacity is both power and bandwidth limited. This regime has thus far remained hidden due to the limitations of the existing formulation. Existing schemes, either multihop transmission or hierarchical cooperation, fail to achieve capacity in this regime; we propose a new hybrid scheme that achieves capacity. This paper address issues about cooperation among and competition between mobile network operators. The starting point is to examine why and how operators share infrastructure for mobile communication services, so called network sharing. The paper analyzes drivers, benefits and obstacles of network cooperation. We also analyze how roles and responsibilities are distributed for the network related functions while concurrently operators compete for customers and have separate functionality for service provisioning, marketing, customer relation management, charging and billing. Next, we analyze how network sharing as such and strategies for network sharing have changed in Sweden from the year 2000 when the 3G licenses were awarded and up to the year 2010. Moreover, network sharing in Sweden is compared with India where the market situation is different, as the number of operators is four times more and the cooperation is organized in another way, with separate tower companies, which provides base stations sites where operators are tenants. Finally, we compare the network sharing cases with how mobile operators organize cooperation for mobile payments services. From our empirical data we can identify four different types of co-opetition among mobile operators. 1. A co-operative spirit with focus on working practices and or principles that will facilitate the common use of resources or solutions. 2. Infrastructure cooperation through a third party, e.g. a tower company or a SMS aggregator with the main objective to reduce costs or to provide a common solution. The operators have agreements with a third party but not with each other. 3. Infrastructure cooperation through a joint venture that is responsible for network deployment and operation. The driver is to achieve cost-savings. The operators have their own service provisioning, billing, customer relations management and compete for end-users. 4. Service and infrastructure cooperation through a joint venture that is fully responsible for providing the end-user service, in our case mobile payments. The main driver is to offer a payment solution common for all operators in order to complement or compete with solutions provided by banks or payment service providers. Despite its growing use in critical infrastructure services, the performance of IP(v4) Anycast and its interaction with IP routing practices is not well understood. In this paper, we present the results of a detailed measurement study of IP Anycast. Our study uses a two-pronged approach. First, using a variant of known latency estimation techniques, we measure the performance of current commercially operational IP Anycast deployments from a large number (>20,000) of vantage points. Second, we deploy our own small-scale anycast service that allows us to perform controlled tests under different deployment and failure scenarios. To the best of our knowledge, our study represents the first large-scale evaluation of existing anycast services and the first evaluation of the behavior of IP Anycast under failure.We find that: (1) IP Anycast, if deployed in an ad-hoc manner, does not offer good latency-based proximity, (2) IP Anycast, if deployed in an ad-hoc manner, does not provide fast failover to clients, (3) IP Anycast typically offers good affinity to all clients with the exception of those that explicitly load balance traffic across multiple providers, (4) IP Anycast, by itself, is not effective in balancing client load across multiple sites. We thus propose and evaluate practical means by which anycast deployments can achieve good proximity, fast failover and control over the distribution of client load. Overall, our results suggest that an IP Anycast service, if deployed carefully, can offer good proximity, load balance, and failover behavior. Abstract--- This paper studies the carrier-to-interference ratio (CIR) and carrier-to-interference-plus-noise ratio (CINR) performance at the mobile station (MS) within a multi-tier network composed of M tiers of wireless networks, with each tier modeled as the homogeneous n-dimensional (n-D, n=1,2, and 3) shotgun cellular system, where the base station (BS) distribution is given by the homogeneous Poisson point process in n-D. The CIR and CINR at the MS in a single tier network are thoroughly analyzed to simplify the analysis of the multi-tier network. For the multi-tier network with given system parameters, the following are the main results of this paper: (1) semi-analytical expressions for the tail probabilities of CIR and CINR; (2) a closed form expression for the tail probability of CIR in the range [1,infinity); (3) a closed form expression for the tail probability of an approximation to CINR in the entire range [0,infinity); (4) a lookup table based approach for obtaining the tail probability of CINR, and (5) the study of the effect of shadow fading and BSs with ideal sectorized antennas on the CIR and CINR. Based on these results, it is shown that, in a practical cellular system, the installation of additional wireless networks (microcells, picocells and femtocells) with low power BSs over the already existing macrocell network will always improve the CINR performance at the MS. Communications networks used for transmitting and receiving voice or digital data involve copper wire, fiber optics, radio, satellite, and microwave links. In general, these networks are large, diffuse, and complex. Even using modern high-speed computers, exact computations of the network reliability for use as a figure of merit in an interactive network design procedure can take an inordinate amount of time. This paper discusses various exact techniques whose complexity results in run-times short enough for practical network design. We model the network by an undirected probabilistic graph whose vertices represent the nodes and whose edges represent the links. A special feature of our model is that it allows nodes to be imperfect and associates a reliability measure with each node, assumed to succeed or fail independently. Therefore, the network reliability measure is based upon the reliability measures of the individual links and nodes. > As the Internet evolves into a ubiquitous communication infrastructure and provides various services including telephony, it will be expected to meet the quality standards achieved in the public switched telephone network. Our objective in this paper is to assess to what extent today's Internet meets this expectation. Our assessment is based on delay and loss measurements taken over wide-area backbone networks and uses subjective voice quality measures capturing the various impairments incurred. First, we compile the results of various studies into a single model for assessing the voice-over-IP (VoIP) quality. Then, we identify different types of typical Internet paths and study their VoIP performance. For each type of path, we identify those characteristics that affect the VoIP perceived quality. Such characteristics include the network loss and the delay variability that should be appropriately handled by the playout scheduling at the receiver. Our findings indicate that although voice services can be adequately provided by some ISPs, a significant number of Internet backbone paths lead to poor performance. In recent years the research community has developed many techniques to estimate the end-to-end available bandwidth of an Internet path. This important metric can be potentially exploited to optimize the performance of several distributed systems and, even, to improve the effectiveness of the congestion control mechanism of TCP. Thus, it has been suggested that some existing estimation techniques could be used for this purpose. However, existing tools were not designed for large-scale deployments and were mostly validated in controlled settings, considering only one measurement running at a time. In this paper, we argue that current tools, while offering good estimates when used alone, might not work in large-scale systems where several estimations severely interfere with each other. We analyze the properties of the measurement paradigms employed today and discuss their functioning, study their overhead and analyze their interference. Our testbed results show that current techniques are insufficient as they are. Finally, we will discuss and propose some principles that should be taken into account for including available bandwidth measurements in large-scale distributed systems. In cellular network models, the base stations are usually assumed to form a lattice or a Poisson point process (PPP). In reality, however, they are deployed neither fully regularly nor completely randomly. Accordingly, in this paper, we consider the very general class of motion-invariant models and analyze the behavior of the outage probability (the probability that the signal-to-interference-plus-noise-ratio (SINR) is smaller than a threshold) as the threshold goes to zero. We show that, remarkably, the slope of the outage probability (in dB) as a function of the threshold (also in dB) is the same for essentially all motion-invariant point processes. The slope merely depends on the fading statistics. Using this result, we introduce the notion of the asymptotic deployment gain (ADG), which characterizes the horizontal gap between the success probabilities of the PPP and another point process in the high-reliability regime (where the success probability is near 1). To demonstrate the usefulness of the ADG for the characterization of the SINR distribution, we investigate the outage probabilities and the ADGs for different point processes and fading statistics by simulations.