Insights into the Design of Congestion Control Protocols for Multi-Hop Wireless Mesh Networks

The widespread deployment of multi-hop wireless mesh networks will depend on the performance seen by the user. Unfortunately, the most predominant transport protocol, TCP, performs poorly over such networks, even leading to starvation in some topologies. In this work, we characterize the root causes of starvation in 802.11 scheduled multi-hop wireless networks via simulations. We analyze the performance of three categories of transport protocols. (1) end-to-end protocols that require implicit feedback (TCP SACK), (2) Explicit feedback based protocols (XCP and VCP) and (3) Open-loop protocol (UDP). We ask and answer the following questions in relation to these protocols: (a) Why does starvation occur in different topologies? Is it intrinsic to TCP or, in general, to feedback-based protocols? or does it also occur in the case of open-loop transfers such as CBR over UDP? (a) What is the role of application behavior on transport layer performance in multi-hop wireless mesh networks? (b) Is sharing congestion in the wireless neighborhood essential for avoiding starvation? (c) For explicit feedback based transport protocols, such as XCP and VCP, what performance can be expected when their capacity estimate is inaccurate? Based on the insights derived from the above analysis, we design a rate-based protocol called VRate that uses the two ECN bits for conveying load feedback information. VRate achieves near optimal rates when configured with the correct capacity estimate

An Efficient Framework of Congestion Control for Next-Generation Networks

The success of the Internet can partly be attributed to the congestion control algorithm in the Transmission Control Protocol (TCP). However, with the tremendous increase in the diversity of networked systems and applications, TCP performance limitations are becoming increasingly problematic and the need for new transport protocol designs has become increasingly important.Prior research has focused on the design of either end-to-end protocols (e.g., CUBIC) that rely on implicit congestion signals such as loss and/or delay or network-based protocols (e.g., XCP) that use precise per-flow feedback from the network. While the former category of schemes haveperformance limitations, the latter are hard to deploy, can introduce high per-packet overhead, and open up new security challenges. This dissertation explores the middle ground between these designs and makes four contributions. First, we study the interplay between performance and feedback in congestion control protocols. We argue that congestion feedback in the form of aggregate load can provide the richness needed to meet the challenges of next-generation networks and applications. Second, we present the design, analysis, and evaluation of an efficient framework for congestion control called Binary Marking Congestion Control (BMCC). BMCC uses aggregate load feedback to achieve efficient and fair bandwidth allocations on high bandwidth-delaynetworks while minimizing packet loss rates and average queue length. BMCC reduces flow completiontimes by up to 4x over TCP and uses only the existing Explicit Congestion Notification bits.Next, we consider the incremental deployment of BMCC. We study the bandwidth sharing properties of BMCC and TCP over different partial deployment scenarios. We then present algorithms for ensuring safe co-existence of BMCC and TCP on the Internet. Finally, we consider the performance of BMCC over Wireless LANs. We show that the time-varying nature of the capacity of a WLAN can lead to significant performance issues for protocols that require capacity estimates for feedback computation. Using a simple model we characterize the capacity of a WLAN and propose the usage of the average service rate experienced by network layer packets as an estimate for capacity. Through extensive evaluation, we show that the resulting estimates provide good performance

Inside the Walled Garden: Deconstructing Facebook's Free Basics Program

Free Basics is a Facebook initiative to provide zero-rated web services in developing countries. The program has grown rapidly to 60+ countries in the past two years. But it has also seen strong opposition from Internet activists and has been banned in some countries like India. Facebook highlights the societal benefits of providing low-income populations with free Internet access, while detractors point to concerns about privacy and network neutrality. In this paper, we provide the first independent analysis of such claims regarding the Free Basics service, using both the perspective of a Free Basics service provider and of web clients visiting the service via cellular phones providing access to Free Basics in Pakistan and South Africa. Specifically, with control of both endpoints, we not only provide a more detailed view of how the Free Basics service is architected, but also can isolate the likely causes of network performance impairments. Our analysis reveals that Free Basics services experience 4 to 12 times worse network performance than their paid counterparts. We isolate the root causes using factors such as network path inflation and throttling policies by Facebook and telecom service providers. The Free Basics service and its restrictions are designed with assumptions about users' device capabilities (e.g., lack of JavaScript support). To evaluate such assumptions, we infer the types of mobile devices that generated 47K unique visitors to our Free Basics services between Sep 2016 and Jan 2017. We find that there are large numbers of requests from constrained WAP browsers, but also large fractions of high-capability mobile phones that send Free Basics requests. We discuss the implications of our observations, with the hope to aid more informed debates on such telecom policies

An Empirical Analysis of Facebook’s Free Basics Program

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Designing experiments using GENI cluster B

In this paper, we analyze Cluster B aggregates' technologies and design an experiment using them. Global Environment for Network Innovations (GENI) is a novel suite of infrastructure now being designed to support experimental research in network science and engineering. GENI is envisioned to support at-scale experimentation on shared, heterogeneous, highly instrumented infrastructure

On the design of load factor based congestion control protocols for next-generation networks

Load factor based congestion control schemes have shown to enhance network performance, in terms of utilization, packet loss and delay. In these schemes, using more accurate representation of network load levels is likely to lead to a more efficient way of communicating congestion information to hosts. Increasing the amount of congestion information, however, may end up adversely affecting the performance of the network. This paper focuses on this trade-off and addresses two important and challenging questions: (i) How many congestion levels should be represented by the feedback signal to provide near-optimal performance? and (ii) What window adjustment policies must be in place to ensure robustness in the face of congestion and achieve efficient and fair bandwidth allocations in high Bandwidth-Delay Product (BDP) networks, while keeping low queues and negligible packet drop rates? Based on theoretical analysis and simulations, our results show that 3-bit feedback is sufficient for achieving near-optimal rate convergence to an efficient bandwidth allocation. While the performance gap between 2-bit and 3-bit schemes is large, gains follow the law of diminishing returns when more than 3 bits are used. Further, we show that using multiple back-off factors enables the protocol to adjust its fairness convergence rate, rate variations and responsiveness to congestion based on the degree of congestion at the bottleneck. Based on these insights, we design Multi-Level feedback Congestion control Protocol (MLCP). In addition to being efficient, MLCP converges to a fair bandwidth allocation in the presence of diverse RTT flows while maintaining near-zero packet drop rate and low persistent queue length. A fluid model for the protocol reinforces the stability properties that we observe in our simulations and provides a good theoretical grounding for MLCP

Digital Literacy and Vulnerability to Misinformation: Evidence from Facebook Users in Pakistan

Lack of digital literacy can be a major barrier towards improving the informational well-being of Internet users. Using a field survey of 674 Facebook users in urban Pakistan, we find significant differences in individuals' ability to use common Facebook features. We find that digital literacy is lower among older, less educated, lower income and female users, which points to barriers faced by different demographic groups in improving their digital literacy. Moreover, lower digital literacy is associated with worse truth discernment, lower sharing of true news, emotional reactions to online content, but not more confirmation bias