Venugopalan Ramasubramanian

The design and implementation of a next generation name service for the internet

Name services are critical for mapping logical resource names to physical resources in large-scale distributed systems. The Domain Name System (DNS) used on the Internet, however, is slow, vulnerable to denial of service attacks, and does not support fast updates. These problems stem fundamentally from the structure of the legacy DNS.This paper describes the design and implementation of the Cooperative Domain Name System (CoDoNS), a novel name service, which provides high lookup performance through proactive caching, resilience to denial of service attacks through automatic load-balancing, and fast propagation of updates. CoDoNS derives its scalability, decentralization, self-organization, and failure resilience from peer-to-peer overlays, while it achieves high performance using the Beehive replication framework. Cryptographic delegation, instead of host-based physical delegation, limits potential malfeasance by namespace operators and creates a competitive market for namespace management. Backwards compatibility with existing protocols and wire formats enables CoDoNS to serve as a backup for legacy DNS, as well as a complete replacement. Performance measurements from a real-life deployment of the system in PlanetLab shows that CoDoNS provides fast lookups, automatically reconfigures around faults without manual involvement and thwarts distributed denial of service attacks by promptly redistributing load across nodes.

SHARP: a hybrid adaptive routing protocol for mobile ad hoc networks

A central challenge in ad hoc networks is the design of routing protocols that can adapt their behavior to frequent and rapid changes in the network. The performance of proactive and reactive routing protocols varies with network characteristics, and one protocol may outperform the other in different network conditions. The optimal routing strategy depends on the underlying network topology, rate of change, and traffic pattern, and varies dynamically. This paper introduces the Sharp Hybrid Adaptive Routing Protocol (SHARP), which automatically finds the balance point between proactive and reactive routing by adjusting the degree to which route information is propagated proactively versus the degree to which it needs to be discovered reactively. SHARP enables each node to use a different application-specific performance metric to control the adaptation of the routing layer. This paper describes application-specific protocols built on top of SHARP for minimizing packet overhead, bounding loss rate, and controlling jitter. Simulation studies show that the resulting protocols outperform the purely proactive and purely reactive protocols across a wide range of network characteristics.

Anonymous Gossip: improving multicast reliability in mobile ad-hoc networks

In recent years, a number of applications of ad-hoc networks have been proposed. Many of them are based on the availability of a robust and reliable multicast protocol. We address the issue of reliability and propose a scalable method to improve packet delivery of multicast routing protocols and decrease the variation in the number of packets received by different nodes. The proposed protocol works in two phases. In the first phase, any suitable protocol is used to multicast a message to the group, while in the second concurrent phase, the gossip protocol tries to recover lost messages. Our proposed gossip protocol is called Anonymous Gossip (AG) since nodes need not know the other group members for gossip to be successful. This is extremely desirable for mobile nodes, that have limited resources, and where the knowledge of group membership is difficult to obtain. As a first step, anonymous gossip is implemented over MAODV without much overhead and its performance is studied. Simulations show that the packet delivery of MAODV is significantly improved and the variation in number of packets delivered is decreased.

Client behavior and feed characteristics of RSS, a publish-subscribe system for web micronews

While publish-subscribe systems have attracted much research interest since the last decade, few established benchmarks have emerged, and there has been little characterization of how publish-subscribe systems are used in practice. This paper examines RSS, a newly emerging, widely used publish-subscribe system for Web micronews. Based on a trace study spanning 45 days at a medium-size academic department and periodic polling of approximately 100,000 RSS feeds, we extract characteristics of RSS content and usage. We find that RSS workload resembles the Web in content size and popularity; feeds are typically small (less than 10KB), albeit with a heavy tail, and feed popularity follows a power law distribution. The update rate of RSS feeds is widely distributed; 55% of RSS feeds are updated hourly, while 25% show no updates for several days. And, only small portions of RSS content typically change during an update; 64% of updates involve less than three lines of the RSS content. Overall, this paper presents an analysis of RSS, the first widely deployed publish-subscribe system, and provides insights for the design of next generation publish-subscribe systems.

Providing a bidirectional abstraction for unidirectional ad hoc networks

Several routing protocols for mobile ad hoc networks work efficiently only in bidirectional networks. Unidirectional links may exist in a real network due to variations in transmission power of different nodes, noise or other signal propagation phenomena, and heterogeneity in the transmission hardware of nodes in the network. We introduce a sub-layer called sub routing layer, SRL, between the network and the MAC layer to provide a bidirectional abstraction of the unidirectional network to the routing protocols. We present a scalable and efficient way to provide this abstraction by finding and maintaining multi-hop reverse routes to each unidirectional link. We simulate SRL and a modified version of AODV (ad hoc on demand distance vector) that uses SRL to route packets in a unidirectional network. We observed that with SRL, the packet delivery of AODV in unidirectional networks increases substantially. Further our simulations indicate that reverse routes are often only a few hops long and hence the overhead of using SRL is very low.

Perils of transitive trust in the domain name system

The Domain Name System, DNS, is based on nameserver delegations, which introduce complex and subtle dependencies between names and nameservers. In this paper, we present results from a large scale survey of DNS, and show that these dependencies lead to a highly insecure naming system. We report specifically on three aspects of DNS security: the properties of the DNS trusted computing base, the extent and impact of existing vulnerabilities in the DNS infrastructure, and the ease with which attacks against DNS can be launched. The survey shows that a typical name depends on 46 servers on average, whose compromise can lead to domain hijacks, while names belonging to some countries depend on a few hundred servers. An attacker exploiting well-documented vulnerabilities in DNS nameservers can hijack more than 30% of the names appearing in the Yahoo and DMOZ.org directories. And certain nameservers, especially in educational institutions, control as much as 10% of the namespace.

Statistical analysis of connectivity in unidirectional ad hoc networks

A unidirectional link exists in an ad-hoc network when a node B is within the transmission range of another node A while node A cannot directly hear node B. However, a reverse route from B to A might exist, by going through multiple nodes. Unidirectional links may exist in an ad hoc network due to variation in transmission power of different nodes, noise or other signal propagation phenomena, and heterogeneity in transmission hardware of nodes in the network In this paper, we statistically analyze the connectivity of ad hoc networks in the presence of unidirectional links. We generate several random topologies employing two models and study the connectivity of the sub-graphs formed by including unidirectional links of different reverse-route lengths. We observe from this analysis that the connectivity has a heavy-tail distribution and that using only bidirectional links could cause partitions in the network. This analysis also shows that the inclusion of unidirectional links with short reverse-routes (2-3 hops) is often sufficient to restore good connectivity in unidirectional networks.

CobWeb: a proactive analysis-driven approach to content distribution

CobWeb is an open-access content distribution network (CDN) that provides low latency lookups, resilience to flash crowds, and optimal utilization of network resources. Unlike traditional Web caches and CDNs, which rely on ad hoc heuristics for replica placement and cache management, CobWeb achieves superior performance through a unique analysis driven approach. CobWeb derives the optimal replica placement strategy by posing the fundamental performance-overhead tradeoff as a resource constraint problem. Analytically modeling the costs and performance benefits of replicas enables CobWeb to convert the systems problem to an optimization problem. The optimization problem can then be solved to provide, for instance, minimal lookup latency while achieving a targeted bandwidth cost, or to achieve a targeted lookup performance while minimizing bandwidth consumption. CobWeb is currently deployed on Planet-Lab and is available for open access through an intuitive easy-to-use interface.