Lakshminarayanan Subramanian

Characterizing the Internet hierarchy from multiple vantage points

The delivery of IP traffic through the Internet depends on the complex interactions between thousands of autonomous systems (AS) that exchange routing information using the border gateway protocol (BGP). This paper investigates the topological structure of the Internet in terms of customer-provider and peer-peer relationships between autonomous systems, as manifested in BGP routing policies. We describe a technique for inferring AS relationships by exploiting partial views of the AS graph available from different vantage points. Next we apply the technique to a collection of ten BGP routing tables to infer the relationships between neighboring autonomous systems. Based on these results, we analyze the hierarchical structure of the Internet and propose a five-level classification of AS. Our characterization differs from previous studies by focusing on the commercial relationships between autonomous systems rather than simply the connectivity between the nodes.

An investigation of geographic mapping techniques for internet hosts

In this paper, we ask whether it is possible to build an IP address to geographic location mapping service for Internet hosts. Such a service would enable a large and interesting class of location-aware applications. This is a challenging problem because an IP address does not inherently contain an indication of location.We present and evaluate three distinct techniques, collectively referred to as IP2Geo, for determining the geographic location of Internet hosts. The first technique, Geo Track, infers location based on the DNS names of the target host or other nearby network nodes. The second technique, GeoPing, uses network delay measurements from geographically distributed locations to deduce the coordinates of the target host. The third technique, GeoCluster, combines partial (and possibly inaccurate) host-to-location mapping information and BGP prefix information to infer the location of the target host. Using extensive and varied data sets, we evaluate the performance of these techniques and identify fundamental challenges in deducing geographic location from the IP address of an Internet host.

An architecture for building self-configurable systems

Developing wireless sensor networks can enable information gathering, information processing and reliable monitoring of a variety of environments for both civil and military applications. It is however necessary to agree upon a basic architecture for building sensor network applications. This paper presents a general classification of sensor network applications based on their network configurations and discusses some of their architectural requirements. We propose a generic architecture for a specific subclass of sensor applications which we define as self-configurable systems where a large number of sensors coordinate amongst themselves to achieve a large sensing task. Throughout this paper we assume a certain subset of the sensors to be immobile. This paper lists the general architectural and infra-structural components necessary for building this class of sensor applications. Given the various architectural components, we present an algorithm that self-organizes the sensors into a network in a transparent manner. Some of the basic goals of our algorithm include minimizing power utilization, localizing operations and tolerating node and link failures.

Optimal Sybil-resilient node admission control

Most existing large-scale networked systems on the Internet such as peer-to-peer systems are vulnerable to Sybil attacks where a single adversary can introduce many bogus identities. One promising defense of Sybil attacks is to perform social-network based admission control to bound the number of Sybil identities admitted. SybilLimit [22], the best known Sybil admission control mechanism, can restrict the number of Sybil identities admitted per attack edge to O(log n) with high probability assuming O(n/ log n) attack edges. In this paper, we propose Gatekeeper, a decentralized Sybil-resilient admission control protocol that significantly improves over SybilLimit. Gatekeeper is optimal for the case of O(1) attack edges and admits only O(1) Sybil identities (with high probability) in a random expander social networks (real-world social networks exhibit expander properties). In the face of O(k) attack edges (for any k ∈ O(n/ log n)), Gatekeeper admits O(log k) Sybils per attack edge. This result provides a graceful continuum across the spectrum of attack edges. We demonstrate the effectiveness of Gatekeeper experimentally on real-world social networks and synthetic topologies.

Practical, distributed channel assignment and routing in dual-radio mesh networks

Realizing the full potential of a multi-radio mesh network involves two main challenges: how to assign channels to radios at each node to minimize interference and how to choose high throughput routing paths in the face of lossy links, variable channel conditions and external load. This paper presents ROMA, a practical, distributed channel assignment and routing protocol that achieves good multi-hop path performance between every node and one or more designated gateway nodes in a dual-radio network. ROMA assigns non-overlapping channels to links along each gateway path to eliminate intra-path interference. ROMA reduces inter-path interference by assigning different channels to paths destined for different gateways whenever possible. Evaluations on a 24-node dual-radio testbed show that ROMA achieves high throughput in a variety of scenarios.

OverQoS: offering Internet QoS using overlays

This paper proposes OverQoS, an architecture for providing Internet QoS using overlay networks. OverQoS empowers third-party providers to offer enhanced network services to their customers using the notion of a controlled loss virtual link (CLVL). The CLVL abstraction bounds the loss-rate experienced by the overlay traffic; OverQoS uses it to provide differential rate allocations, statistical bandwidth and loss assurances, and enables explicit-rate congestion control algorithms.

The SAHARA Model for Service Composition across Multiple Providers

Services are capabilities that enable applications and are of crucial importance to pervasive computing in next-generation networks. Service Composition is the construction of complex services from primitive ones; thus enabling rapid and flexible creation of new services. The presence of multiple independent service providers poses new and significant challenges. Managing trust across providers and verifying the performance of the components in composition become essential issues. Adapting the composed service to network and user dynamics by choosing service providers and instances is yet another challenge. In SAHARA, we are developing a comprehensive architecture for the creation, placement, and management of services for composition across independent providers. In this paper, we present a layered reference model for composition based on a classification of different kinds of composition. We then discuss the different overarching mechanisms necessary for the successful deployment of such an architecture through a variety of case-studies involving composition.

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].

Economic analysis of networking technologies for rural developing regions

Providing network connectivity to rural regions in the developing world is an economically challenging problem especially given the low income levels and low population densities in such regions. Many existing connectivity technologies incur a high deployment cost that limits their affordability. Leveraging several emerging wireless technologies, this paper presents the case for economically viable networks in rural developing regions. We use the Akshaya Network located in Kerala, India as a specific case study. and show that a wireless network using WiFi for the backhaul, CDMA450 for the access network, and shared PCs for end user devices has the lowest deployment cost. However, if we include the expected spectrum licensing cost for CDMA450, a network with lease exempt spectrum using WiFi for the backhaul and WiMax for access is the most economically attractive option. Even with license exemption, regulatory costs comprise nearly half the total cost in the WiFi/WiMax case suggesting the possibility of significant improvement in network economics with more favorable regulatory policies. Finally, we also demonstrate the business case for a WiFi/CDMA450 network with nearly fully subsidized cellular handsets as end user devices.

QoS provisioning using a clearing house architecture

We have designed a clearing house (CH) architecture that facilitates resource reservations over multiple network domains, and performs local admission control. Two key ideas employed in this design to make the CH scalable to a large user base are hierarchy and aggregation. In our model, we assume the network is composed of various basic routing domains which can be aggregated to form logical domains. This introduces a hierarchical tree of logical domains and a distributed CH architecture is associated with each logical domain to maintain the intra-domain aggregate reservations. The parent CH in the logical tree maintains the inter-domain reservation requests. Call setup time is reduced by performing advanced reservations based on statistical estimates of the call traffic across various links. We explore, with simulations, the efficiency of the CH-architecture in terms of resource utilization, call rejections and reservation setup time.