Bhaskaran Raman

Design and evaluation of a new MAC protocol for long-distance 802.11 mesh networks

802.11 has been used well beyond its original intended use of WLANs. Of particular interest to us in this paper is its use in long-distance mesh networks being designed/used for low-cost rural connectivity. We describe in detail a new MAC protocol, called 2P, that is suited for such networks in terms of efficiency. A significant challenge here is the implementation of this protocol on top of off-the-shelf 802.11 hardware, to preserve the cost benefits. We show how this can be achieved, by exploiting the flexibilities available within Prism2-based chipsets. We then present the dependence of 2P on the network topology, and show that it is indeed possible to design in practice, network topologies compatible with 2P. We describe experimental as well as simulation-based evaluations of 2P, and show that 2P achieves significant performance improvement (as much as 20 times more throughput) over 802.11 CSMA/CA in long-distance mesh networks.

Long-distance 802.11b links: performance measurements and experience

The use of 802.11 long-distance links is a cost-effective means of providing wireless connectivity to rural areas. Although deployments in this setting are increasing, a systematic study of the performance of 802.11 in these settings is lacking. The contributions of this paper are two-fold: (a)we present a detailed performance study of a set of long-distance 802.11b links at various layers of the network stack, and (b)we document the various non-obvious experiences during our study.Our study includes eight long-distance links, ranging from 1km to 37km in length. Unlike prior studies of outdoor 802.11 links, we find that the error rate as a function of the received signal strength behaves close to theory. Time correlation of any packet errors is negligible across a range of time-scales. We have observed at least one of the link to be robust to rain and fog. But any interference on the long-distance links can be detrimental to performance. Apart from this however, such long-distance links can be planned to work well with predictable performance. During our measurements, we have observed a few hardware/driver quirks as well as system bottlenecks apart from the wireless link itself. We believe that our measurements and the documentation of our experience will help future network planning as well as protocol design for these networks.

ICEBERG: an Internet core network architecture for integrated communications

In the ICEBERG project at UC Berkeley, we are developing an Internet-based integration of telephony and data services spanning diverse access networks. Our primary goals are extensibility, scalability, robustness, and personalized communication. We leverage the Internets low cost of entry for service creation, provision, deployment, and integration. We present our solutions to signaling, easy service creation, resource reservation, admission control, billing, and security in the ICEBERG network architecture.

Turning 802.11 inside-out

The past decade has seen communication revolution in the form of cellular telephony as well as the Internet, but much of it has been restricted to the developed world and metro pockets in the developing world. While the use of cellular technologies can cut down on the time to deploy access networks, the cost economics make this non-viable in growing telecom economies. In the Digital Gangetic Plains (DGP) project, we are exploring the use of 802.11 as a long-distance access technology. 802.11 is currently cost-priced due to competitive mass production and hence is attractive for low cost and rapid deployment in rural areas.We have built an extensive testbed in a rural setting consisting of multi-hop directional 802.11 links, the testbed spanning up to 80km at its longest. To our knowledge such a long-distance, multi-hop testbed based on 802.11 is unique thus far. While 802.11 is attractive in terms of cost economics, it was inherently designed for indoor use. Our novel use of the technology for outdoor, long-distance access links presents several challenges. Our experience with the testbed has brought several research as well as operational issues to the fore. In this paper, we describe the novel technical challenges that lie ahead in using 802.11 to bridge the digital divide.

Brimon: a sensor network system for railway bridge monitoring

Railway systems are critical in many regions, and can consist of several tens of thousands of bridges, being used over several decades. It is critical to have a system to monitor the health of these bridges and report when and where maintenance operations are needed. This paper presents BriMon, a wireless sensor network based system for such monitoring. The design of BriMon is driven by two important factors: application requirements, and detailed measurement studies of several pieces of the architecture. In comparison with prior bridge monitoring systems and sensor network prototypes, our contributions are three-fold. First, we have designed a novel event detection mechanism that triggers data collection in response to an oncoming train. Next, BriMon employs a simple yet effective multi-channel data transfer mechanism to transfer the collected data onto a sink located on the moving train. Third, the BriMon architecture is designed with careful consideration of the interaction between the multiple requisite functionalities such as time synchronization, event detection, routing, and data transfer. Based on a prototype implementation, this paper also presents several measurement studies to show that our design choices are indeed quite effective.

Experiences in using WiFi for rural internet in India

Access to communication can play a pivotal role in the socio-economic development of rural regions in the third world. For affordability, the choice of technology to achieve this is a significant aspect. We have chosen IEEE 802.11 as a cost-effective technology to provide rural connectivity in the context of two projects in India: digital Gangetic plains (DGP) and Ashwini. This article presents our experiences with these two projects and discusses five important aspects in the use of WiFi for rural connectivity: network planning and deployment, network protocols, network management and operations, power savings, and applications and services

Universal Inbox: providing extensible personal mobility and service mobility in an integrated communication network

Communication technology has been seeing rapid growth, characterized by new access networks (e.g. cellular, pager, wireless-IP) and end-devices (e.g. PDAs, two-way pagers, multi-model access devices). There have been several efforts at integrating services across such heterogeneity. However, little work has been done on identifying an underlying architecture for such an integration. We identify the requirements for this in the context of an integrated network with heterogeneous end-points. The Universal Inbox provides (a) generic data type transformation, (b) customizable redirection of incoming communication based on user preference profiles, and (c) device name mapping and translation. We present an architecture mapping these functionalities to reusable infrastructure components realized as Internet services. The unique feature of the architecture is its extensibility-it allows not only the integration of existing end-points but also extension in terms of the end-devices and novel services it can handle. We have implemented the Universal Inbox components in a test-bed setting, supporting a variety of devices and services: GSM cellular phones, voice-over-IP end-points, voice-mail, e-mail, instant messaging service, etc. With our architecture, building personal mobility and service mobility features and extending them to new end-points has been easy in concept and in implementation. The performance analyses with the initial implementation show that even the heavy-weight components can be scaled to accommodate a large user base.

Channel Allocation in 802.11-Based Mesh Networks

IEEE 802.11 (WiFi) has been used beyond its original intended purpose of a tether-free LAN. In this paper, we are interested in the use of 802.11 in mesh networks. Specifically, we consider those which involve directional antennas and longdistance point-to-point links. In recent work, the 2P MAC protocol has been designed to suit such a network architecture. In this paper, we assume the use of the 2P MAC protocol in the links of the network, and consider the problem of link channel allocation. We first formulate the problem of minimizing the mismatch between link capacities desired by the network operator and that achieved under a channel allocation. We show that this problem is NP-hard. We then explore several heuristics for channel allocation and find a set of heuristics that achieve the optimal allocation in most scenarios.

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.

Wolverine: Traffic and road condition estimation using smartphone sensors

Monitoring road and traffic conditions in a city is a problem widely studied. Several methods have been proposed towards addressing this problem. Several proposed techniques require dedicated hardware such as GPS devices and accelerometers in vehicles [7][15][8] or cameras on roadside and near traffic signals [13]. All such methods are expensive in terms of monetary cost and human effort required. We propose Wolverine - a non-intrusive method that uses sensors present on smartphones. We extend a prior study [12] to improve the algorithm based on using accelerometer, GPS and magnetometer sensor readings for traffic and road conditions detection. We are specifically interested in identifying braking events - frequent braking indicates congested traffic conditions - and bumps on the roads to characterize the type of road. We evaluate the effectiveness of the proposed method based on experiments conducted on the roads in Mumbai, with promising results.