| Summary: | <p> Broadband networks are one of the most economically significant and fastest growing sectors of the Internet. Recent studies have shown that providing broadband Internet access is instrumental for social and economic development. Several governments, as well as the UN, have gone so far as to label broadband access a basic human right, similar to education and water. Motivated by the increased importance of broadband access, recent efforts are shedding light on the availability of broadband services. However, these works tend to focus on measuring service capacity. As a result, we still lack an understanding of how factors such as a link's capacity, quality, dependability, or cost affect user behavior and network demand.</p><p> We believe that realizing the full benefits of broadband access requires an understanding of how these services are being used by subscribers. The thesis of this work is that broadband service characterization must take a user-centric perspective, understanding how different aspects of the service impact its users' experiences, and thus should be done in a broader context. It should include an analysis of factors such as link quality, service dependability, and market factors (e.g. monthly income and cost of broadband access) and an understanding of how each affects user behavior.</p><p> To achieve this, we need to look beyond controlled experiments and regression analysis, two techniques commonly used in the field of networking. Controlled experiments, where subjects in the study are assigned randomly to "treated" and "untreated" groups for comparisons, are not feasible for studying the effect of complex treatments such as market and economic factors at scale. On the other hand, regression analysis is insufficient for causal inference. A key contribution of this work is the application of natural experiments and related experiment designs, techniques common in fields such as epidemiology and the social sciences, in the context of broadband services.</p><p> In this dissertation, we study broadband services in this broader context. We present the results of our empirical study on the relationship between service characteristics (capacity, latency, loss rates, and reliability), price, time and user demand. We find a strong correlation between capacity and user demand, but note a law of diminishing returns with lower increases in relative demand as service capacity increases. We also find that subscribing to unreliable broadband services tends to result in users generating less network traffic, even during periods of normal operation. These findings suggest that service dependability is becoming more important to subscribers as service capacities increase globally.</p><p> We include a characterization of broadband services in terms of bandwidth, latency, and loss. For bandwidth, we find that a number of providers struggle to consistently meet their advertised throughput rates and identify multiple instances where service throughput is correlated with the time of day. We also show that access latencies can vary widely by region, even within the same provider. In terms of service reliability, we find that broadband service providers in the US are able to provide at most two nines (99%) of availability. </p><p> Motivated by our findings on both the importance and current state of service reliability, we present an approach to improving service reliability using broadband multihoming and describe our prototype implementation. Our evaluation shows that in many cases, users could add up to two nines to service availability (from 99% to 99.99%) by multihoming with a neighbor's connection. Due to the fact that an individual subscriber may experience a wide range of performance, we then explore the possibility of adopting broadband service level agreements (SLAs). We argue that the use of broadband SLAs could help service providers to better differentiate their retail services from competitors and better inform both customers and policymakers of the broadband services offered in their communities. Using four years of data collected from residential gateways, we show that many ISPs could offer meaningful service level agreements immediately at little to no cost.</p>
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