Browsing by Author "Injong Rhee, Committee Chair"

Now showing 1 - 4 of 4

Cache Aided Video Coding.
(2010-12-09) Gokare Somashekhar, Kumar; Injong Rhee, Committee Chair; Rudra Dutta, Committee Member; Khaled Abdel Harfoush, Committee Member
Performance Analysis of Data Aggregation Schemes for Wireless Sensor Networks
(2006-06-29) Park, Sangjoon; Injong Rhee, Committee Chair
Wireless sensor networks are suitable for applications in which sensors detect moving targets in the area of interest. In such applications, one of the key challenges is how to design efficient data aggregation protocols which reduce redundant packet transmissions in the sensor network. Towards this goal, centralized, tree-based, static-cluster, and dynamic-cluster aggregation schemes have been proposed. However, each scheme has its share of benefits and corresponding costs, and it is difficult to say with certainty whether a particular scheme is always better than others. In this paper, our goal is to compare all of the above mentioned aggregation schemes with comprehensive theoretical analysis, simulation and real experiments and attempt to give clear scenarios where a particular scheme may be more beneficial compared to others. Along the way, we also propose two cluster-based aggregation algorithms, which are simple enough to be implemented on resource-constrained sensor networks. As a first step towards this goal, we model the sensor network environment under certain simplifying assumptions and then derive closed form expressions for the total number of packet transmissions incurred by each aggregation scheme. Next, we complement the assumptions made for the analysis by performing extensive simulations under different environmental conditions, such as channel capacity (1Mbps, 250Kbbps) and MAC (B-MAC, IEEE 802.11) protocol. Finally, we test the aggregation schemes on a real sensor network testbed comprising of 31 Mica2 sensors. Various metrics, such as total number of packet transmissions, aggregation ratio, average energy consumption, network lifetime, average end-to-end delay, and packet delivery ratio, are used to evaluate the performance of aggregation schemes. The results show that the performance of data aggregation is highly dependant on setup overhead, node density, sensing range, and the distance from sources to the sink. When the sources are close to the sink and the sensing range is short, tree-based aggregation, with long aggregation delay, achieves better performance in all metrics, except end-to-end delays. However, as the distance from sources to the sink and the sensing range increase, dynamic-cluster aggregation shows the best performance over other schemes, because a large number of generated packets are reduced by the local data aggregation.
A Scalable Architecture for SIP using Content Addressable Networks
(2005-06-07) Balasubramanian, Ramrajprabu; Jaewoo Kang, Committee Member; Khaled Harfoush, Committee Member; Injong Rhee, Committee Chair
Session initiation protocol (SIP) provides call establishment functions for VoIP including location resolution, authentication, signaling compression, and billing. These functions, when combined with the text-based nature of the protocol, are highly CPU-intensive under a peak load. Practical limitation on the available CPU power of a single SIP server mandates that the SIP infrastructure supporting these functions be distributed over multiple servers. Existing approaches to this problem using multiple nodes for SIP processing with a shared location database or a replicated location database to distribute the load are unfortunately not scalable or fault-tolerant, incurring high maintenance and update overheads or introducing a single point of failure. This thesis presents a proof-of-concept design and analysis of a scalable, robust architecture for SIP infrastructures using a content addressable network (CAN) model, called CASIP (CAN-based SIP). The combination of CAN and SIP is highly complementary. The performance study of CASIP using an implementation using a real SIP stack and NS-2 simulations shows that the proposed system distributes the SIP processing (both location update and lookup) load of the network over multiple nodes very effectively without incurring much routing and maintenance overhead; with use of simple cache schemes, CASIP can linearly add the number of servers in proportion to the increase in the subscriber base. The study also indicates that CASIP keeps the reconfiguration overhead minimal. Furthermore, the CASIP architecture exhibits high availability: a CASIP network of 50 nodes recovers from a server crash within 5 minutes, during which only 2% of call setup requests are dropped. These features enable cost-effective, incremental deployment of SIP servers in response to the user population growth
Swarm Over Swarm.
(2010-12-09) Selvanayagam, Alphonse Hansel; Injong Rhee, Committee Chair; Khaled Abdel Harfoush, Committee Member; Rudra Dutta, Committee Member