Alexander D. Gelman

A store-and-forward architecture for video-on-demand service

A store-and-forward architecture is presented that can provide video-on-demand (VOD) as well as other database distribution services. It assumes a B-ISDN network to be in place. The four major elements in this architecture are the information warehouse (IWH), where video material is archived; the central office (CO) server, which contains a processor responsible for service management and a video buffer that interacts directly with network customers; and the customer premise equipment. A requested video program is provided in a real-time fashion from the CO server to the customer. At the information warehouse the video program is retrieved from the archival storage in blocks, and with transfer rates much faster than real-time. Subsequently, it is sent in a bursty mode to the CO servers via high speed trunks.<<ETX>>

Study of Beaconing in Multihop Wireless PAN with Distributed Control

Distributed media access control (MAC) architecture has many merits to make it a favorable candidate for high-data-rate wireless personal area networks (WPANs) with physical layer (PHY) based on ultrawideband (UWB) technology. This paper focuses on the WiMedia MAC, which is the first distributed MAC for WPANs, approved as a standard. In such a MAC, all devices transmit their beacons to provide timing reference and to broadcast control and reservation information, that is, to maintain device synchronization. We investigate problems related to beacon collisions, which occur when multiple devices join a piconet almost at the same time. To join a piconet or to resolve a collision, a device chooses a slot for its beacon randomly within some window. We show that an improper slot choice scheme leads to repeated collisions, increasing the time overhead to achieve device synchronization. It also leads devices into trouble in joining and collision resolution, even into deadlocks, when devices have no chance to escape repeated collisions. We develop an analytical model to evaluate the performance of various slot choice schemes for multihop WPANs. The model is employed to compare the efficiency of these choice schemes and to optimize their parameters to achieve the best performance.

Scalable blind search and broadcasting over Distributed Hash Tables

Typical blind search algorithms in P2P networks generate a significant amount of duplicate query messages in order to increase the success rate. We present a novel framework, named Recursive Partitioning Search (RPS), for blind search over structured peer-to-peer (P2P) networks, by which the query message duplication can be avoided. Two realizations of the framework for Chord and Pastry are presented. By simulation, we compare success rate, lookup delay and overlay network load of RPS with various well-known blind search algorithms, and illustrate RPS being a superior blind search algorithm running over DHTs. The algorithm guarantees that with high probability the lookup delay to visit every peer is of O(logN) hops, comparable to the delay of the exact-match search over the DHTs, which is proved for two example DHTs, Chord and Pastry in the paper. RPS is a simple and intuitive method for blind search over DHTs compared to other complex approaches like those building sophisticated index structures or requiring analysis of the words in the stored documents, yet a lot more efficient than known simple methods like Flooding and Random Walk. With RPS, every node in the overlay network is visited not more than once by design. These characteristics qualify the Recursive Partitioning Search over DHT as an efficient broadcasting algorithm. We investigate RPS scalability and propose a formula to choose an appropriate Time-to-Live (TTL) parameter value to maintain the balance between high success rate and reasonable network load. Active peer churn degrades the performance of RPS as a broadcasting mechanism proportionally to the churn rate. But the success rate of blind search using RPS may be affected negligibly if proper replications exist as in most P2P file sharing networks.

UP2P: a peer-to-peer overlay architecture for ubiquitous communications and networking

Approaches to building an intelligent consumer-friendly network have evolved over time from centralized switch-based to router- and server-based Internet architectures. We propose to drive this evolution further with a new highly scalable architecture that provides features to users derived from the computational and networking capabilities of very large populations of sophisticated terminals. This architecture relies on emerging peer-to-peer overlay technology. We describe a peer-to-peer overlay design that addresses requirements crucial for consumer applications, including overlay federation, peer heterogeneity, peer mobility, and service discovery. In addition, we introduce the concept of an overlay operator and describe the requirements for managed overlays. We have designed and implemented both a middleware and a peer-topeer platform that illustrates these concepts.

Peer-to-peer streaming for networked consumer electronics [Peer-to-Peer Multimedia Streaming]

Applications such as multimedia communications and entertainment make media streaming a key feature for peer-to-peer (P2P) technology embedded in networked consumer electronics. In this article, we discuss some key issues that are relevant to enabling peer-to-peer streaming in networked consumer electronics and address possible technical solutions to the issues of interoperability, NAT/firewall traversal, and codec inflexibility. We also address how to improve overall system performance by introducing a notion of node coordinates into the discovery of services on a P2P network and confirm the effectiveness of our approach using simulation. We conclude with a discussion of our prototype CE-oriented P2P streaming system.

Scalable Blind Search and Broadcasting in Peer-to-Peer Networks

Typical blind search algorithms in P2P networks generate a significant amount of duplicate query messages to increase the success rate. We present a framework, named recursive partitioning search (RPS), for blind search over structured peer-to-peer (P2P) networks, by which the query message duplication can be avoided. Two realizations of the framework for Chord and Pastry are presented. With simulation model, we compare success rate, lookup delay and overlay network load of RPS and various well-known blind search algorithms, and show RPS is the superior blind search algorithm running over a DHT. The algorithm guarantees that with high probability the lookup delay to visit every peer is of O(log N) hops, comparable to the delay of the exact match search over the DHTs. With RPS, every node in the overlay network is visited not more than once by design. These characteristics qualify the recursive partitioning search over DHT as an efficient broadcasting algorithm. We investigate RPS scalability and propose the way to choose an appropriate time-to-live (TTL) parameter value to maintain the balance between high success rate and reasonable network load

Frame synchronization in UWB using multiple sync words to eliminate line frequencies

Ultra wide-band (UWB) is now under consideration as an alternative physical layer technology for wireless PAN. UWB radio uses base-band pulses of very short duration, thereby spreading the energy of radio signal very thinly over gigahertz. The power spectral density (PSD) of UWB signals consists of a continuous component and discrete component. Generally speaking, the discrete component presents greater interference to narrow-band communication systems than the continuous component. Frame synchronization is commonly used in multiple access systems, including wireless PAN systems. The sync word will generate strong PSD. In this paper, we devise a more efficient and better performance mechanism to suppress the discrete component of the PSD of UWB signals by randomizing the pattern of UWB signals. The mechanism can also be applied to payload data to smooth the PSD of USB signals.

Beaconing in distributed controlwireless PAN: problems and solutions

In this paper, we investigate beaconing problems in Wireless Personal Area Networks (WPANs) with distributed control, which is being developed by Multi-Band OFDM Alliance. The problems are related to collision that is caused by multiple access to a piconet; and the collision resolution that is used in the MBOA MAC, i.e. random slot allocation for devices’ beacons. The collision problem and the current resolution may cause deadlock and prevent other devices from joining a piconet. We propose new solutions to resolve the collision without causing potential deadlock. We develop an analytical model to evaluate performance of the new schemes. The model can also be employed to determine parameters to achieve optimized performance.

Networked multimedia: issues and perspectives

In this opinion article, we see digital multimedia communications of the future dependent on business vision, evolving networking and consumer electronics technologies, and public policies regarding intellectual property and investment in communications infrastructure. As always, it is easy to predict a rich networked multimedia future, but difficult to say when or exactly how. These will be determined by social and business understandings on the divisive issues, by still uncertain consumer tastes and willingness to pay, and by resolving some technical obstacles. This brief article gives our personal perspectives on the current status of networked multimedia, the most promising multimedia applications, and the social and technical bottlenecks.

On the power spectral density of UWB signals in IEEE 802.15.3a

Ultra wide-band (UWB) radio uses base-band pulses of very short duration, thereby spreading the energy of radio signal very thinly over gigahertz. Power spectral density (PSD) of UWB signals consists of continuous and discrete components. Since the discrete component contributes more to PSD than continuous component, it presents greater interference to other narrow-band wireless systems. UWB was approved by the FCC for commercial deployment in 2002. In order to ensure negligible mutual interference, the FCC has specified emission limits for UWB applications. UWB is now under consideration as an alternative physical layer technology for wireless PAN in IEEE 802.15.3a. However, little study has been reported on PSD issues in IEEE 802.15.3a. This paper presents analysis on PSD of UWB signals in IEEE 802.15.3a systems, and on what frame reversion can achieve in reducing the PSD.