Sunil Samtani

Recent Advances and Research Problems in Data Warehousing

In the recent years, the database community has witnessed the emergence of a new technology, namely data warehousing. A data warehouse is a global repository that stores pre-processed queries on data which resides in multiple, possibly heterogeneous, operational or legacy sources. The information stored in the data warehouse can be easily and efficiently accessed for making effective decisions. The On-Line Analytical Processing (OLAP) tools access data from the data warehouse for complex data analysis, such as multidimensional data analysis, and decision support activities. Current research has lead to new developments in all aspects of data warehousing, however, there are still a number of problems that need to be solved for making data warehousing effective. In this paper, we discuss recent developments in data warehouse modelling, view maintenance, and parallel query processing. A number of technical issues for exploratory research are presented and possible solutions are discussed.

A novel approach to OSPF-area design for large wireless ad-hoc networks

To build ad-hoc networks with hundreds or even thousands of nodes, the network must be split into relatively independent layer 3 clusters. There are currently no general approaches or methodologies for the creation of domains that take into account the following important engineering constraints: balanced domains, minimal inter-domain traffic, robust network design. Moreover, there is also no contribution that specifically addresses the problem of area formation for OSPF-based ad hoc networks. By assuming that the creation of layer 3 clusters is done after layer 2 topology management has set local radio parameters, we have re-formulated the problem at hand in a graph theoretic framework and found a strong connection between the problem of area design and a classical problem in graph theory, the graph partitioning (GP) problem. The limitation of GP algorithms (GPAs) is that they are OSPF-agnostic and, therefore, are not capable of solving the problem of robust backbone network (Area 0) design. We here propose a two-step approach for OSPF area design: the first step consists of an efficient GPA that will create areas (including a rough Area 0 design), and the second step consists of ad-hoc heuristics that are able to ameliorate the Area 0 design as well as factoring in OSPF specific metrics.

On the adaptation of commercial smartphones to tactical environments

Commercial smartphones are being actively looked at as solving the communication needs of the future warfighter. Several ongoing efforts are driving the research and development of custom hardware, architectures, middleware and software to bring smartphones into the tactical realm. In this work2, we first present a deployment architecture and use cases for commercial smartphones to be used in a heterogeneous environment that includes expeditionary cellular, ad-hoc wireless and indigenous cellular networks as well as smartphone connecting to traditional military radios over other native interfaces. We then introduce the Heterogeneous Tactical Gateway (HTG), an appliqué based platform that attaches to the expeditionary cellular system in a tactical vehicle and offers a fully configurable set of capabilities such as, tunneling, multicast, NAT(Network Address Translation), mobility and security management. The HTG is an IP-based solution completely independent of underlying radio access technology (e.g., EV-DO, HSPA, LTE and WiMAX) and vendor specific hardware box. HTG functional components can be incorporated when standards interfaces emerge that attempt to collate tactical and commercial requirements for communications and security. We also discuss some experiments and results that have been performed in the S&TCD lab at CERDEC, Ft Monmouth, NJ.

A resource friendly approach for estimating available bandwidth in secure mobile wireless IP networks

Estimation of available bandwidth for an end-to-end network path allows traffic sources to judiciously regulate the volume of application traffic injected into the network. For example, knowing that the available bandwidth is small could be applied at a source for proactive congestion control by preempting low priority traffic. To address bandwidth estimation in future battlefield networks, a study was launched under the ARMY CERDEC multi-functional on-the-move secure adaptive integrated communications (MOSAIC) program. In this paper, novel techniques developed under the MOSAIC program for estimating end-to-end available bandwidth are presented that do not require active probing and are immune to clock offset. The path parameters that are estimated include end-to-end queuing, transmission and deterministic delays, in addition to available bandwidth, narrow link capacity, and path utilization. Furthermore, the proposed techniques are suitable for encrypted wireless networks with strict rules forbidding interactions across a cryptographic boundary between network routers and traffic sources (e.g., red-black networks). Results of simulations that assess the performance of the available bandwidth estimation techniques are reported herein

Self maintenance of multiple views in data warehousing

Materialized views (<italic>MV</italic>) at the data warehouse (<italic>DW</italic>) can be kept up to date in response to changes in data sources without accessing data sources for additional information. This process is usually refered to as “self maintenance of views”. A number of algorithms have been proposed for self maintenance of views, which use <italic>auxiliary views (AV)</italic> to keep some additional information in <italic>DW</italic>. In this paper we propose an algorithm for self maintainability of multiple <italic>MVs</italic> using the above approach. Our algorithm generates a simple maintenance query to incrementally maintain an <italic>MV</italic> along with its <italic>AV</italic> at <italic>DW</italic>. The algorithm maintains these views by minimizing the number and the size of the <italic>AVs</italic>. Our approach provides better insight into view maintenance issues by exploiting the dependencies and constraints that might exist in the data sources and multiple <italic>MVs</italic> at <italic>DW</italic>.

SCTP multistreaming: preferential treatment among streams

FCS networks are presented with a new transport layer mechanism that, for transmitting multimedia, is markedly superior to transmission over UDP or TCP. SCTPs multistrearning provides an aggregation mechanism for transferring different objects belonging to the same logical application session; however, sharing the congestion state among the streams precludes efficient stream prioritization. We design an SCTP mechanism to provide the application with the service of being able to mark data such that different parts of a transfer (different streams) could be requested to receive preferential treatment from the network. The data flow within an association is divided into separate subassociation flows (SF), each SF having its own set of congestion control parameters. We implemented this design using an SCTP stack from Siemens. A number of experiments show that the streams marked with higher priority achieve much better throughput. We plan to investigate a layered congestion avoidance technique that uses state information from individual subflows to allow: dynamic addition of subflows without slow start; load balancing between paths and subflows; and using network state information to provide intelligent feedback to the application.

Ad hoc mobility protocol suite for the MOSAIC ATD

An ad hoc mobility protocol suite (AMPS) aimed at providing rapidly deployable, secure, robust IP-based communications among tactical mobile ad hoc nodes is presented in this paper. AMPS is an integrated networking solution for the MOSAIC ATD in that it provides the following capabilities: autoconfiguration, mobility management, unicast and multicast routing, reliable transport, quality of service, security and network visualization tools. This paper describes the architecture and implementation of AMPS for the MOSAIC ATD. Both laboratory and field experiments to measure AMPS functionality and performance were conducted in 2002 and 2003. This paper reports on the results of those experiments and their impact on future AMPS design and operation.

Bandwidth broker architecture for VoIP QoS

We present a scalable architecture for assuring Quality of Service to VoIP applications in an Internet Service Providers network. This architecture is based on the Differentiated Services and Bandwidth Broker models, and can also be used by other resource-sensitive applications. In this paper, we elaborate on a number of significant issues involved in the design, implementation, deployment and use of the Bandwidth Broker. The Call Agent architecture is used as the VoIP application. We describe the Bandwidth Broker prototype that is used to validate our approach. Our findings suggest that it is feasible to use the Bandwidth Broker architecture for assuring QoS, and a trade-off exists between the granularity of resource requests and call-setup delay.

A Study on the Call Admission and Preemption Control Algorithms for Secure Wireless Ad Hoc Networks Using IPSec Tunneling

In this paper the network architecture under consideration is secure networking, in which an IPSec tunneling encryption device is located at the boundary between the insecure LAN and the secure WAN. This architecture has been used in many DoD tactical networks to satisfy the COMSEC requirements. This makes providing end-to-end QoS support in this type of network very challenging. To address this, a study was launched under the ARMY CERDEC multi-functional on-the-move secure adaptive integrated communications (MOSAIC) program. The salient feature of our solution is that call admission control and preemption control decision is based on the real-time measurements on the traffic loading. We simulated the QoS architecture using OPNET to evaluate the performance characteristics. We studied the performance over five different priority classes for six different applications. The performance metrics under consideration include average delay per priority class for UDP applications, throughput and file transfer completion time for TCP applications, and per class preemption/blocking probability. Our study showed that this integrated solution exhibited superb end-to-end QoS performance over a wide range of traffic loadings

Performance study of reliable server pooling

The reliable server pooling allows redundant information sources to be viewed as a single transport endpoint, and therefore is able to provide persistent connections and balanced traffic. The IETF RSerPool Working Group has proposed an architecture to implement the reliable server pooling. We conducted a number of simulation experiments with the current definitions of the RSerPool protocols to quantify their performance in both wired and wireless environments. The simulation results show that the RSerPool works well in fixed and relatively reliable environments, but its performance worsens rapidly as the networks become more unreliable or mobile. The issues we identified in wireless mobile ad-hoc networks include network partitioning, high signaling overhead, and excessive aggressiveness in handling failures. These problems are partly due to the heavy reliance of the RSerPool architecture on the reliability of the underlying network,, which is unlikely to be guaranteed in a wireless mobile ad-hoc environment.