ASSOCIATION FOR COMPUTING MACHINERY
Abstract
The complexity and enormous costs of installing new long-haul fiber-optic infrastructure has led to a significant amount of infrastructure sharing in previously installed conduits. In this paper, we study the characteristics and implications of infrastructure sharing by analyzing the long-haul fiber-optic network in the US.
We start by using fiber maps provided by tier-1 ISPs and major cable providers to construct a map of the long-haul US fiber-optic infrastructure. We also rely on previously underutilized data sources in the form of public records from federal, state, and municipal agencies to improve the fidelity of our map. We quantify the resulting map’s1 connectivity characteristics and confirm a clear correspondence between long-haul fiber-optic, roadway, and railway infrastructures. Next, we examine the prevalence of high-risk links by mapping end-to-end paths resulting from large-scale traceroute campaigns onto our fiber-optic infrastructure map. We show how both risk and latency (i.e., propagation delay) can be reduced by deploying new links along previously unused transportation corridors and rights-of-way. In particular, focusing on a subset of high-risk links is sufficient to improve the overall robustness of the network to failures. Finally, we discuss the implications of our findings on issues related to performance, net neutrality, and policy decision-making.
Introduction
The desire to tackle the many challenges posed by novel designs, technologies and applications such as data centers, cloud services, software-defined networking (SDN), network functions virtualization (NFV), mobile communication and the Internet-of-Things (IoT) has fueled many of the recent research efforts in networking. The excitement surrounding the future envisioned by such new architectural designs, services, and applications is understandable, both from a research and industry perspective. At the same time, it is either taken for granted or implicitly assumed that the physical infrastructure of tomorrow’s Internet will have the capacity, performance, and resilience required to develop and support ever more bandwidth-hungry, delay-intolerant, or QoS-sensitive services and applications. In fact, despite some 20 years of research efforts that have focused on understanding aspects of the Internet’s infrastructure such as its router-level topology or the graph structure resulting from its inter-connected Autonomous Systems (AS), very little is known about today’s physical Internet where individual components such as cell towers, routers or switches, and fiber-optic cables are concrete entities with well-defined geographic locations (see, e.g., [2, 36, 83]). This general lack of a basic understanding of the physical Internet is exemplified by the much-ridiculed metaphor used in 2006 by the late U.S. Senator Ted Stevens (R-Alaska) who referred to the Internet as “a series of tubes” [65].
The focus of this paper is the physical Internet. In particular, we are concerned with the physical aspects of the wired Internet, ignoring entirely the wireless access portion of the Internet as well as satellite or any other form of wireless communication. Moreover, we are exclusively interested in the long-haul fiber-optic portion of the wired Internet in the US. The detailed metro-level fiber maps (with corresponding colocation and data center facilities) and international undersea cable maps (with corresponding landing stations) are only accounted for to the extent necessary. In contrast to short-haul fiber routes that are specifically built for short distance use and purpose (e.g., to add or drop off network services in many different places within metro-sized areas), long-haul fiber routes (including ultra long-haul routes) typically run between major city pairs and allow for minimal use of repeaters.
With the US long-haul fiber-optic network being the main focal point of our work, the first contribution of this paper consists of constructing a reproducible map of this basic component of the physical Internet infrastructure. To that end, we rely on publicly available fiber maps provided by many of the tier-1 ISPs and major cable providers. While some of these maps include the precise geographic locations of all the long-haul routes deployed or used by the corresponding networks, other maps lack such detailed information. For the latter, we make extensive use of previously neglected or under-utilized data sources in the form of public records from federal, state, or municipal agencies or documentation generated by commercial entities (e.g., commercial fiber map providers [34], utility rights-of-way (ROW) information, environmental impact statements, fiber sharing arrangements by the different states’ DOTs). When combined, the information available in these records is often sufficient to reverse-engineer the geography of the actual long-haul fiber routes of those networks that have decided against publishing their fiber maps. We study the resulting map’s diverse connectivity characteristics and quantify the ways in which the observed long-haul fiber-optic connectivity is consistent with existing transportation (e.g., roadway and railway) infrastructure. We note that our work can be repeated by anyone for every other region of the world assuming similar source materials.
A striking characteristic of the constructed US long-haul fiber-optic network is a significant amount of observed infrastructure sharing. A qualitative assessment of the risk inherent in this observed sharing of the US long-haul fiberoptic infrastructure forms the second contribution of this paper. Such infrastructure sharing is the result of a common practice among many of the existing service providers to deploy their fiber in jointly-used and previously installed conduits and is dictated by simple economics—substantial cost savings as compared to deploying fiber in newly constructed conduits. By considering different metrics for measuring the risks associated with infrastructure sharing, we examine the presence of high-risk links in the existing long-haul infrastructure, both from a connectivity and usage perspective. In the process, we follow prior work [99] and use the popularity of a route on the Internet as an informative proxy for the volume of traffic that route carries. End-to-end paths derived from large-scale trace-route campaigns are overlaid on the actual long-haul fiber-optic routes traversed by the corresponding trace-route probes. The resulting first-of-its-kind map enables the identification of those components of the long-haul fiber-optic infrastructure which experience high levels of infrastructure sharing as well as high volumes of traffic.
The third and final contribution of our work is a detailed analysis of how to improve the existing long-haul fiber-optic infrastructure in the US so as to increase its resilience to failures of individual links or entire shared conduits, or to achieve better performance in terms of reduced documents such as utility right-of-way information; (3) we add links from publicly available ISP fiber maps (both tier- 1 and major providers) which have geographic information about link endpoints, but which do not have explicit information about geographic pathways of fiber links; and (4) we again employ a variety of public records to infer the geographic locations of this latter set of links added to the map. Below, we describe this process in detail, providing examples to illustrate how we employ different information sources.
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