Mobile Optical Free Space networks are an emerg- ing technology that will offer low-delay and high speed con- nectivity using air-borne and ground wireless laser terminals. The time-variable link capacity and dynamic topology make Quality of Service provisioning a difficult problem. We present an architecture for end-to-end statistical delay guarantees. We describe a delay model that uses the concept of virtual traffic to accommodate link capacity variations and transient outages. A mechanism for deploying dependable TCP services is imple- mented in this QoS-enabled network. The primary-backup TCP replication mechanism is supported by the routing infrastructure and allows transparent server replication. We illustrate perfor- mance improvements with simulation results.

Mobile optical free space networks are an emerging architecture that can provide high speed connectivity between a ground-based backbone network and mobile users in challenging environments. In such a network traffic could be relayed by airborne or ground routers using wireless optical links. The variable nature of the wireless optical channel complicates support for real-time distributed applications demanding bounds on communication delay. In this paper we present an architecture for provisioning end-to-end statistical delay guarantees in MOFS networks. We describe a delay model that uses a concept of virtual traffic to accommodate link capacity variation. The link delay estimation is integrated with a population-insensitive utilization based flow admission control technique and IP differentiated services. The models and architecture for QoS are presented and the system performance is analyzed

The paper presents an innovative hierarchical feedback adaptation method that efficiently controls the dynamic QoS behavior of real time distributed data flow applications, such as sensor based data streams or mission-critical command and control applications. We applied this method in the context of the Real Time Adaptive Resource Management system, a middleware integrated services, developed at the Honeywell Technology Center. We present the analytical model for Automatic Target Recognition pipeline application and the impact of hierarchical feedback adaptation on the application behavior and its QoS parameters.

The successful operation of mission critical systems requires a sophisticated control network which provides for the real-time delivery of data from a very large number of diverse sources such as sensors, audio/video surveillance, computational sources, etc., as well as remote monitoring and diagnosis sources. It is expected that many of the traffic sources will be in the form of periodic sources with real-time requirements. In this study, we propose fast scheduling algorithms for multiplexing periodic source flows with real-time delivery requirements. We assume a single switch environment with periodic source flows being supported over a constant bit rate (CBR) type circuit. We undertake a systematic study beginning from the simplest scenario where all traffic flows consist of data frames of the same size and with the same real-time delay requirement. In this case, we prove that the FCFS algorithm is optimal. We conclude with the most difficult case of examining CBR flows of variable bandwidth requirements and variable delay requirements. Algorithms and analysis are presented for all the cases. The simulation results show the substantial performance gains provided by the proposed algorithms.

Wavelength division multiplexing (WDM) has been widely used for studying the performance of optical networks, especially those employing optical passive star couplers. The current technology only allows the transceivers to be tunable in a small range, a fact ignored in previous studies. In this paper, we focus on the design of WDM optical passive star networks with tunable transmitters of limited tuning range and fixed wavelength receivers. The limited tuning range has effects on the maximum delay, the total number of wavelengths which can be used, and the topological embedding. Complete graphs, meshes and hypercubes are the three topologies studied in this paper. The relationship between the total number of wavelengths which can be utilized and the embedded topology is established. The bound for the maximum delay is analyzed. The optimal embedding algorithms are given for the systems embedded with one of the three topologies.

Wavelength Division Multiplexing (WDM) has been widely used for studying the performance of optical networks, especially those employing optical passive star couplers. Many models have been proposed for WDM on an optical passive star coupler, such as each station equipped with a single tunable transmitter and a single fixed wavelength receiver, and each station with multiple tunable transmitters and multiple tunable receivers. The current technology only allows the transceivers to be tunable in a small range, a fact ignored in previous studies. In this paper, we focus on the design of WDM optical passive star networks with tunable transmitters of limited tuning range and fixed wavelength receivers. The limited tuning range has effects on the maximum delay, the total number of wavelengths which can be used, and the topological embedding. Complete graphs, meshes, and hypercubes are the three topologies studied in this paper. The relationship between the total number of wavelengths which can be utilized and the embedded topology is established. The bound for the maximum delay is analyzed. The optimal embedding algorithms are given for the systems embedded with one of the three topologies.

Lightwave networks can be built by embedding virtual topologies over physical topologies. The optical passive star enables such embeddings easily. The Shuffle-net and the De-Bruijn graph are two popular virtual topologies proposed in the past for lightwave networks. Both however suffer from a lack of flexibility in scaling network sizes. We present a generalization of the De-Bruijn network which overcomes the limitation of the strict relationships between the network size parameters seen in the Shuffle-net and the De-Bruijn networks. A generalization for the Shuffle-net is also possible with this idea. We emphasize the support of time and wavelength division multiplexed media access protocols for such architectures and present several properties of the proposed network with respect to the same.

Time and wavelength division multiplexing (TWDM) has been shown to be one of the most promising ways to exploit the enormous bandwidth of single mode optical fiber. Lightwave networks employing TWDM are commonly based on optical passive star couplers. To overcome some existing technology constraints, a general hardware configuration that each station uses multiple fixed transmitters and fixed receivers is proposed. The maximal concurrency that can be possibly achieved by the TWDM single-hop lightwave networks with such general configuration is studied.

This paper introduces the concept of time slot synchronization in time-wave division multiplexed (TWDM) multihop lightwave networks. It is shown that the time slot assignments of the intermediate nodes in a multihop path have significant effect on the end-to-end message delay. This is different from traditional notions in routing, where the hop count and congestion control are the primary concerns. Assuming a TWDM embedding of a given logical topology already exists, we formulate the optimal routing problem for arbitrary propagation delays. We propose a graph unfolding technique which converts this problem into the shortest path routing problem for weighted graphs with well known solutions. We show a method to estimate the buffering cost at the intermediate nodes (in multihop routing) to accommodate high-bandwidth traffic (e.g., video). Next, we address the question: given a logical topology what should the TWDM embedding be so that the routing delays are optimized P This leads us to an iterative approach for TWDM embedding. Given an initial embedding an optimal route is estimated for each pair of nodes. A weighted average of these optimal route distances is used as a metric to evaluate the TWDM embedding. Using a heuristic the TWDM embedding is modified and the process iterated to improve along this metric. Preliminary performance results illustrating the improvement in routing delay are provided. For example, for a 4-cube network on average delay minimization of 10% to 20% is observed.

ATM has been widely accepted as the key enabling technology for emerging multimedia applications. We at the Honeywell Technology Center are investigating the application of this technology to real-time control systems. The Mercuri wide area ATM testbed is a collaborative research effort in this direction. In this paper we describe our experiences from a series of performance evaluation experiments on the Mercuri testbed. Besides measuring application level throughput and round-trip delay, we investigated the support for real-time provisions like priority and deadline guarantees, which are especially important for control applications. We also measured delay and jitter for remote video transfer under no-load and loaded conditions. The major conclusion of our experiments is that the end systems remain a major bottleneck for high speed communications. We point out possible causes of performance degradation in this paper and outline some issues that need to be resolved for ATM to become a viable alternative for real-time multimedia based control applications.

This paper describes the distributed system, network and software architecture, the application development environment, the performance, and the early lessons learned on the ATM LAN testbed Mercuri established at the Honeywell Technology Center, to develop distributed multimedia technologies for real-time control applications. We have developed a client-server-based software architecture on Sun Sparcstation-2s connected by a Fore Systems' ASX-100 ATM switch, with video processing handled by Parallax's X Video cards. The architecture enables network-transparent applications and provides simple primitives for multimedia capture, display, transmission, storage, and retrieval. A real-time multimedia-in-the-loop control application was developed as the vehicle for testing the capabilities and performance of the network. Our test measurements focus on the end-user-level performance metrics such as message throughput and round-trip delay as well as video-frame jitter under no-load and load conditions. Our results show that the maximum burst throughput that can be supported at the user level is 48 Mb/s using AAL 5, while round-trip delays for 4-kbyte messages are about 3 ms. Our experience reveals a number of performance bottlenecks and open issues in using commercial ATM switches for practical applications. Our conclusions are outlined.>

There is growing interest in using switched network technology such as asynchronous transfer mode (ATM) to support both continuous bit rate multimedia data and variable bit rate burst traffic for distributed computing. Most previous work and studies have focused only on the real-time support imposed by the isochronous requirements of the video or audio sources. This paper reports the results of our early study on how ATM can support real-time and prioritized traffic. We describe some basic approaches in handling real-time quality of service parameters within the context of ATM, and observe from simulation experiments that simple priority-based scheduling approaches at the virtual circuit level provides improvement in the deadline guarantee for all real-time traffic, especially the burst traffic. We believe that additional techniques such as deadline-based scheduling will be necessary to provide better real-time support.>

The idea of providing reverse channels with minimal hardware costs in Shuffle-nets to reduce the network diameter improve mean delay, and provide other advantages is discussed. The reverse channel idea can be applied to any multistage network with wrapped around connections. The advantages of reverse channels are demonstrated by providing a simple reverse connection between adjacent stages of the Shuffle-net. It is shown how a time- and wavelength-division-multiplexed media access protocol for the Shuffle-net can be easily adapted for the reverse channel augmented Shuffle-net (RC-Shuffle-net). The performance of the RC-Shuffle-net and its advantages over the Shuffle-net are shown.>