From TIER

Abstracts

Beyond Pilots: Keeping Rural Wireless Networks Alive

Sonesh Surana, Rabin Patra, Sergiu Nedevschi, Manuel Ramos, Lakshminarayanan Subramanian, Yahel Ben-David, Eric Brewer

To appear in ACM USENIX NSDI, 2008

Very few computer systems that have ever been deployed in rural areas in developing regions have been opera- tional and sustainable in the long term — most such systems have not gone beyond the pilot phase. This paper describes our experiences in deploying and maintaining two rural WiFi-based long-distance networks over the last three years: (a) the Aravind network interconnecting rural eye hospitals in South India which served so far over 30,000 patients, and currently serves about 2500 patients per month, and (b) the AirJaldi network in North India that provides Internet access and VoIP services to over 10,000 users in rural mountainous terrain.

In this paper, we elaborate upon the various systems challenges we had to overcome to make both these networks operationally sustainable. We explore system design issues around simplifying system management issues such as monitoring and administration, and also around improving sustainability in the context of rural challenges such as low-quality power, limited local expertise, lack of remote management opportunities (bad connectivity), and limited budgets. Based on initial successes, the pilot network at Aravind is now scaling from 5 centers to 50, with a target of 500,000 patients per year and the AirJaldi model is being now replicated in Rajasthan and Dehradun.

Reducing Network Energy Consumption via Rate-Adaptation and Sleeping

Sergiu Nedevschi, Lucian Popa, Gianluca Iannaccone, Sylvia Ratnasamy, David Wetherall

To appear in ACM USENIX NSDI, 2008

We present the design and evaluation of two forms of power management schemes that reduce the energy consumption of networks. The first is based on adapting the rate of network operation to the offered workload, reducing the energy consumed when actively processing packets. The second is based on putting network components to sleep during idle times, reducing energy consumed in the absence of packets. Using real-world network topologies and traffic workloads, we show that: (1) even simple schemes for sleeping or rate-adaptation can offer substantial savings without significantly degrading network performance and (2) both forms of solutions are valuable depending (primarily) on the power profile of network equipment and the utilization of the network itself.

Simplifying Fault Diagnosis in Locally Managed Rural WiFi Networks

Sonesh Surana, Rabin Patra, Eric Brewer

ACM SIGCOMM Workshop on Networked Systems for Developing Regions (NSDR), August 2007. PDF,

The last three years have seen a lot of work in making WiFi-enabled Long Distance (WiLD) networking a reality in rural areas. Generally these networks are managed by non-local users who cannot guarantee long term support beyond a pilot. For long term operational sustainability, it is essential that maintenance duties be transferred to local administrators. In this paper, we argue that the research agenda should expand into areas of simplified diagnosis solutions as an enabler for locally managedWiLD networks. Motivated by real faults we have seen in our own deployment at the Aravind Eye Hospital, we propose a framework to simplify diagnosis and show some initial results towards this direction.

WiLDNet: Design and Implementation of High Performance WiFi Based Long Distance Networks

Rabin Patra, Sergiu Nedevschi, Sonesh Surana, Anmol Sheth, Lakshminarayanan Subramanian, Eric Brewer

USENIX NSDI, April 2007. PDF, HTML.

WiFi-based Long Distance (WiLD) networks with links as long as 50–100 km have the potential to provide connectivity at substantially lower costs than traditional approaches. However, real-world deployments of such networks yield very poor end-to-end performance due to two reasons. First, the current 802.11 MAC protocol has fundamental shortcomings when used over long-distances. Second, WiLD networks can exhibit high and variable loss characteristics, thereby severely limiting end-to-end throughput. This paper describes the design, implementation and evaluation of WiLDNet, a system that overcomes these two problems and provides enhanced end-to-end performance in WiLD networks. To address the protocol shortcomings, WiLDNet makes several essential changes to the 802.11 MAC protocol, but continues to rely on standard WiFi network cards. To better handle losses and improve link utilization, WiLDNet uses an adaptive loss-recovery mechanism using FEC and bulk acknowledgements. Based on a real-world deployment, WiLDNet provides a 2–5 fold improvement in TCP/UDP throughput (along with significantly reduced loss-rates) in comparison to the best throughput achievable by conventional 802.11 MAC. WiLDNet can also be configured to adapt to a range of end-toend performance requirements (bandwidth, delay, loss, jitter)

Packet Loss Characterization in WiFi-based Long Distance Networks

Anmol Sheth, Sergiu Nedevschi, Rabin Patra, Sonesh Surana, Lakshminarayanan Subramanian, Eric Brewer

IEEE INFOCOM, 2007. PDF.

Despite the increasing number of WiFi-based Long Distance (WiLD) network deployments, there is a lack of understanding of how WiLD networks perform in practice. In this paper, we perform a systematic study to investigate the commonly cited sources of packet loss induced by the wireless channel and by the MAC protocol. The channel induced losses that we study are external WiFi, non-WiFi and mulipath interference. The protocol induced losses that we study are protocol timeouts and the breakdown of CSMA over WiLD links. Our results are based on measurements performed on two real-world WiLD deployments and a wireless channel emulator. The two deployments allow us to compare measurements across rural and urban settings. The channel emulator allows us to study each source of packet loss in isolation in a controlled environment. Based on our experiments we observe that the presence of external WiFi interference leads to signi�cant amount of packet loss in WiLD links. In addition to identifying the sources of packet loss, we analyze the loss variability across time. We also explore the solution space and propose a range of MAC and network layer adaptation algorithms to mitigate the channel and protocol induced losses.

Potential of CDMA450 for Rural Network Connectivity

Sergiu Nedevschi, Sonesh Surana, Bowei Du, Rabin Patra, Eric Brewer and Victor Stan.

IEEE Communications Magazine, Special Issue on New Directions In Networking Technologies In Emerging Economies, Jan 2007. PDF.

This paper evaluates CDMA450 as a potential solution for rural data and voice connectivity. We begin by analyzing the main strengths of CDMA450, but also some of the potential limitations for rural coverage, both from a technical and an economic standpoint. We argue that CDMA450 is a promising technology, competitive in both capacity-centric urban environments and in coverage-centric rural environments. Consequently, we discuss the opportunities of providing universal coverage by adopting a business model targeting both urban and rural deployments, and utilizing urban to rural cross-subsidization. We then explore the advantages of deploying CDMA450 using a fixed wireless (WLL) model. To this end, we explore the effective range of WLL CDMA450, and the impact of using directional antennas and receive antenna diversity in real-world commercial CDMA450 deployment in Romania. If used properly, these techniques can aid us in increasing cell radii and thus lead to substantial cost benefits.

Rethinking Wireless in the Developing World

Lakshminarayanan Subramanian, Sonesh Surana, Rabin Patra, Sergiu Nedevschi, Melissa Ho, Eric Brewer and Anmol Sheth.

Hot Topics in Networks (HotNets-V), November 2006. PDF.

Many rural regions in developing and developed countries with low user densities do not have good connectivity solutions. To date, networking research has largely focused on urban areas of the industrialized world with high user densities. In this paper, we make the case for research on new appropriate wireless technologies that can provide lowcost, rapidly deployable connectivity solutions for low userdensity regions. To this end, we compare and contrast the connectivity requirements that arise in the two domains and pinpoint the new research challenges that arise in low userdensity environments. We describe our research efforts in this space and also share our initial experiences in deploying low-cost Wifi-based Long Distance (WiLD) networks in India, Ghana and the San Francisco Bay area.