Sonesh Surana

Internet indirection infrastructure

Attempts to generalize the Internets point-to-point communication abstraction to provide services like multicast, anycast, and mobility have faced challenging technical problems and deployment barriers. To ease the deployment of such services, this paper proposes a general, overlay-based Internet Indirection Infrastructure (i3) that offers a rendezvous-based communication abstraction. Instead of explicitly sending a packet to a destination, each packet is associated with an identifier; this identifier is then used by the receiver to obtain delivery of the packet. This level of indirection decouples the act of sending from the act of receiving, and allows i3 to efficiently support a wide variety of fundamental communication services. To demonstrate the feasibility of this approach, we have designed and built a prototype based on the Chord lookup protocol.

Load Balancing in Structured P2P Systems

Most P2P systems that provide a DHT abstraction distribute objects among “peer nodes” by choosing random identifiers for the objects. This could result in an O(log N) imbalance. Besides, P2P systems can be highly heterogeneous, i.e. they may consist of peers that range from old desktops behind modem lines to powerful servers connected to the Internet through high-bandwidth lines. In this paper, we address the problem of load balancing in such P2P systems. We explore the space of designing load-balancing algorithms that uses the notion of “virtual servers”. We present three schemes that differ primarily in the amount of information used to decide how to re-arrange load. Our simulation results show that even the simplest scheme is able to balance the load within 80% of the optimal value, while the most complex scheme is able to balance the load within 95% of the optimal value.

Packet Loss Characterization in WiFi-Based Long Distance Networks

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 802.11 MAC protocol. The channel induced losses that we study are external WiFi, non-WiFi and multipath 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 significant 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. The key lessons from this study were also used in the design of a TDMA based MAC protocol for high performance long distance multihop wireless networks [12].

Deploying a Rural Wireless Telemedicine System: Experiences in Sustainability

A primary concern for projects supported by aid programs is sustainability. Although there is a growing belief that information and communication technologies (ICT) can significantly impact development, in practice creating sustainable ICT projects is extremely difficult. A typical project consists of a pilot stage that aims to demonstrate the basic goals, followed by a deployment stage that aims for both scale and sustainability. A novel ICT project in rural India uses long-distance Wi-Fi networking to enable high-quality videoconferencing between eye hospitals and remote village clinics. The project highlights the importance of sustainability as a first-class goal for systems research.

An adaptive, high performance mac for long-distance multihop wireless networks

We consider the problem of efficientMAC design for long-distance WiFi-based mesh networks. In such networks it is common to find long propagation delays, the use of directional antennas, and the presence of inter-link interference. Prior work has shown that these characteristics make traditional CSMA-based MACs a poor choice for long-distance mesh networks and this finding has led to several recent research efforts exploring the use of TDMA-based approaches to media access. In this paper we first identify, and then address, several shortcomings of current TDMA-based proposals. First, because they use fixed-length transmission slots, current TDMA-based solutions do not adapt to dynamic variations in traffic load leading to inefficiencies in both throughput and delay. As we show in this paper, the throughput achieved by existing solutions falls far short of the optimal achievable network throughput. Finally, due to the scheduling constraints imposed by inter-link interference, current TDMA-based solutions only apply to bipartite network topologies. In this paper, we present JazzyMac, a simple, practical and efficient MAC protocol that addresses the above limitations. JazzyMac achieves efficiency by allowing variable-length link transmissions slots and then defining a distributed protocol by which nodes adapt the length of their transmission slots to changing traffic demands. JazzyMac is practical in that the adaptation at each node uses purely local information and that our protocol applies to arbitrary network topologies. Finally, the use of dynamic slot sizes allows JazzyMac to achieve better tradeoffs between throughput and delay. We evaluate JazzyMac using detailed simulation over a range of traffic patterns and realistic topologies. Our results show that JazzyMac improves throughput in all considered scenarios. This improvement is often substantial (e.g.,in 50% of our scenarios, throughput improves by over 40%) and is particularly pronounced for the common case of asymmetric traffic (e.g.,leading to almost 100% improvements). Furthermore, compared to current solutions, JazzyMac can achieve much better average delay for the same throughput.

Internet Indirection Infrastructure

This paper argues for an Internet Indirection Infrastructure that replaces the point-to-point communication abstraction of todays Internet with a rendezvous-based communication abstraction: instead of explicitly sending a packet to a destination, each packet is associated an identifier, which is then used by the receiver to get the packet. This level of indirection decouples the sender and the receiver behaviors, and allows us to efficiently support basic communication services such as multicast, anycast and mobility in the Internet. To demonstrate the feasibility of this approach, we are currently designing and building an overlay network solution based on the Chord lookup system.

Potential of CDMA450 for rural network connectivity

This article 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, from both 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

Hierarchical identity based cryptography for end-to-end security in DTNs

Delay Tolerant Networks (DTN) arise whenever traditional assumptions about todaypsilas Internet such as continuous end-to-end connectivity, low latencies and low error rates are not applicable. These challenges impose constraints on the choice and implementation of possible security mechanisms in DTNs. The key requirements for a security architecture in DTNs include ensuring the protection of DTN infrastructure from unauthorized use as well as application protection by providing confidentiality, integrity and authentication services for end-to-end communication. In this paper, we examine the issues in providing application protection in DTNs and look at various possible mechanisms. We then propose an architecture based on Hierarchical Identity Based Encryption (HIBE) that provides end-to-end security services along with the ability to have fine-grained revocation and access control while at the same time ensuring efficient key management and distribution. We believe that a HIBE based mechanism would be much more efficient in dealing with the unique constraints of DTNs compared to standard public key mechanisms (PKI).

Simplifying fault diagnosis in locally managed rural WiFi networks

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 en-abler for locally managed WiLD 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.

Optimal scheduling and power control for tdma based point to multipoint wireless networks

In TDMA-based point-to-multipoint rural wireless deployments, co-located base station radios and sector antennas are used to increase base station capacity. To achieve maximum capacity with limited availability of non-overlapping wireless channels, we need to operate as many radios as possible from different sectors on the same channel. However, operating co-located radios on the same channel can result in substantial interference especially with the current practice of operating all radios at maximum power. We investigate techniques that increase network throughput by eliminating this interference. To this end we formulate an LP optimization problem that maximizes throughput by computing optimal transmit schedules, optimal allocation of clients to base station radios, and optimal radio power levels. Our results suggest that there is a large gap between currently-used and optimal strategies, creating opportunities for simple, practical algorithms to address these issues. Our techniques are equally applicable to both WiFi based networks as well as other point-to-multipoint technologies such as WiMax.