Local Lightwave Network Research Articles

Probability distribution of the receiver busy time in a multicasting local lightwave network

Wavelength-division multiplexing (WDM) has the ability to utilize the enormous bandwidth offered by optical networks using today's electronics. A reservation-based multicasting protocol for local lightwave networks was examined in Borella and Mukherjee, 1995. If implemented properly, multicasting allows the use of scarce network resources more efficiently than unicasting. On the other hand, a multicasting protocol is usually more complex than a unicasting protocol. An analytical model of a multicasting protocol can enable its comparison with a simpler but less efficient unicasting protocol. We present an approximate analytical solution for the average packet delay in a local lightwave network, which employs the Multicast Scheduling Algorithm (Borella and Mukherjee, 1995) as its medium-access control (MAC) protocol. First, we develop an approximate analytical solution for the probability distribution of the receiver busy time. We demonstrate and explain some interesting and unobvious behavior of this distribution. Then, using the receiver busy time distribution, we calculate the maximum receiver throughput and the average packet delay. Results from the analytical solution match very well with those obtained from simulation.

Channel sharing in multi-hop WDM lightwave networks: realization and performance of multicast traffic

A local lightwave network can be constructed by employing two-way fibers to connect nodes in a passive-star physical topology, and the available optical bandwidth may be effectively accessed by the nodal transmitters and receivers at electronic rates using wavelength division multiplexing (WDM). The number of channels, /spl omega/, in a WDM network is limited by technology and is usually less than the number of nodes, N, in the network. We provide a general method using channel sharing to construct practical multi-hop networks under this limitation. Channel sharing may be achieved through time division multiplexing. The method is applied to a generalized shuffle-exchange-based multi-hop architecture, called GEMNET. Multicasting-the ability to transmit information from a single source node to multiple destination nodes-is becoming an important requirement in high-performance networks. Multicasting, if improperly implemented, can be bandwidth-abusive. Channel sharing is one approach toward efficient management of multicast traffic. We develop a general modeling procedure for the analysis of multicast (point-to-multipoint) traffic in shared-channel, multihop WDM networks. The analysis is comprehensive in that it considers all components of delay that packets in the network experience-namely, synchronization, queuing, transmission, and propagation. The results show that, in the presence of multicast traffic, WDM networks with /spl omega/<N channels may actually perform better than networks with /spl omega//spl ges/N channels.

Channel sharing in multi-hop WDM lightwave networks: do we need more channels?

A local lightwave network can be constructed by employing two-way fibers to connect nodes in a passive-star physical topology, and the available optical bandwidth may be accessed by the nodal transmitters and receivers at electronic rates using wavelength-division multiplexing (WDM). The number of WDM channels, w, in such a network is technology-limited and is less than the number of network nodes, N, especially if the network should support a scalable number of nodes. We describe a general and practical channel sharing method, which requires each node to be equipped with only one transmitter-receiver pair, and in which each WDM channel is shared in a time-division multiplexed fashion; optical fiber LANs are discussed in particular. We also develop a general model for analyzing such a shared-channel, multi-hop, WDM network. Our analysis yields a counterintuitive result: it is sometimes better to employ fewer channels than a larger number of channels. We explore bounds on the ranges of w which admit queueing stability-using too few or too many channels can lead to instability. We also obtain an estimate for the optimal number of channels that minimizes network-wide queueing delay.

Efficient scheduling of nonuniform packet traffic in a WDM/TDM local lightwave network with arbitrary transceiver tuning latencies

A passive-star-based, broadcast-and-select, local lightwave network which can support a limited number of wavelength-division multiplexed (WDM) channels, but serve a much larger number of nodes, is considered. Each node is equipped with one tunable transmitter and one fixed receiver, and each WDM channel is operated in a time-division multiplexed (TDM) fashion for carrying packet traffic. Bandwidth is allocated to the node pairs when traffic flow between them is nonuniform, while also accommodating transceiver tuning latency. Our approach exploits well-known results from scheduling theory to create efficient transmission schedules. Multiprocessor task scheduling heuristics that can be applied to load balancing in a multichannel network is also examined.

MultiS-Net: A high-capacity, packet-switched, multichannel, single-hop architecture and protocol for a local lightwave network

A variety of multichannel single-hop network architectures and protocols have recently been proposed to exploit the vast capacity of fiber-optics which can well exceed the maximum electronic speed limit. Our MultiS-Net proposal is a new multichannel, single-hop architecture and protocol for a local network which provides packet-switched services to a large number of users connected to a multichannel broadcast medium. A separate channel, called control channel, is established to coordinate data packet transmissions on the other channels (called data channels). To allow low network interfacing costs, each node.in MultiS-Net is only equipped with a single tunable transmitter and a single tunable receiver, both of which are responsible for data channel access as well as control channel access. Without a separate transmitter and a separate receiver dedicated to the control channel, a node cannot have global knowledge of the network status all the time. Hence, global reservation is infeasible here, and all previously proposed schemes with the same low-cost network interface as in MultiS-Net fail to achieve a system throughput as high as those achieved by global-reservation schemes. MultiS-Net successfully incorporates a simple medium access mechanism, which can also achieve high system throughput. In addition, MultiS-Net can accommodate a variable number of nodes as well as time-varying load; typically, however, the number of nodes may be much larger than the number of available data channels. We analyze the performance of MultiS-Net by first constructing a multidimensional Markov chain. Then, the equilibrium point analysis (EPA) technique is adopted to obtain the average data packet delay and system throughput, which are verified by simulation. Numerical results from both the analytical model and simulations are presented, and the impact of various parameters on the system performance is discussed. Nearly-full utilization of total data channel bandwidth can be achieved under proper configurations of system parameters.

Limits of Multicasting in a Packet-Switched WDM Single-Hop Local Lightwave Network

Wavelength division multiplexing (WDM) is a technique used to divide the tremendous optical bandwidth of a fiber into many non-interfering channels. A WDM single-hop local lightwave network can be designed by using two-way fibers to connect every node to a passive star coupler, and equipping the nodes with tunable transmitters and/or receivers. The passive star broadcasts data transmitted on each wavelength channel to all nodes in the system. This type of network, known as broadcast and select, is naturally suited to multicasting; every node in the network has the opportunity to receive any particular packet. In this study, we show how multicasting in a broadcast and select environment can dramatically increase the throughput of the network. Using a Markov model and a simulation, we show that multicasting significantly improves the limiting performance of both small and large networks, especially when each node is equipped with multiple receivers.

Scheduling variable-length messages in a single-hop multichannel local lightwave network

The design of a medium access control scheme for a single-hop, wavelength-division-multiplexing-(WDM) multichannel local lightwave network poses two major difficulties: relatively large transmitter/receiver tuning overhead and large ratio of propagation delay to packet transmission time. Most schemes proposed so far have ignored the tuning overhead, and they can only schedule fixed-length packet transmissions. To overcome these two difficulties, the authors propose several scheduling algorithms which can reduce the negative impact of tuning overhead and schedule variable-length messages. A separate channel (control channel) is employed for transmission of control packets, and a distributed scheduling algorithm is invoked at each node every time it receives a control packet. By allowing the length of messages to be variable, a long message can be scheduled with a single control packet transmission, instead of fragmenting it into many fixed-length packets, thereby significantly reducing the overhead of control packet transmissions and improving the overall system performance. Three novel scheduling algorithms are proposed, varying in the amount of global information and processing time they need. Two approximate analytical models are formulated to study the effect of tuning time and the effect of having a limited number of data channels. Extensive simulations are conducted. Average message delays are compared for all of the algorithms. >

An efficient transmission scheduling algorithm for a wavelength-reusable local lightwave network

Although single-hop star networks based on wave-length division multiplexing (WDM) are attractive owing to their all-optical communication features, the throughput of such lightwave networks is limited due to the small number of available wavelengths. In this paper, a wavelength-reusable local lightwave network that consists of two interconnected WDM star networks is proposed. Based on this architecture, the lower bounds for the problems of minimizing the switching duration and the number of switching modes are derived. A transmission scheduling algorithm for this architecture to efficiently reuse the wavelengths is also proposed. The analytical result shows that the proposed scheduling algorithm always produces solutions close to the lower bounds. Simulation results show that given the same number of users and available wavelengths, the solutions (in terms of the average switching duration and the average number of switching matrices) obtained by the proposed scheduling algorithm on the interconnected WDM networks are better than the optimal solution on a single-star WDM network. In most cases, the performance improvement achieves 20 to 45%. >

Free-space optical mesh-connected bus networks using wavelength-division multiple access

A novel optical free-space mesh-connected bus interconnect network architecture is proposed. A mesh-connected bus [IEEE Trans. Comput. C-30, 264-273 (1981)] is known to have the capability of interconnecting, with a three-stage switching, N nodes with a power distribution loss proportional to √N and is therefore advantageous for networking a large number, say over 1000, of communicating ports. Based on conventional space-invariant optical components in a compact and efficient geometry, the proposed optical mesh-connected bus system concept can be used to build either free-space optical interconnect links for parallel processing applications or central switching systems for local or global lightwave communication networks. The proposed architecture lends itself to networking under both the wavelength-division multiple access and other multiple-access environments. In this paper, based on the wavelength-division multiple-access environment, various optical system implementation and performance issues are discused and parameters are analyzed. It was found that by use of a reasonably compact three-dimensional free-space volume, more than 100,000 dispersion-limited communication nodes at a uniform channel spacing of 0.75 nm can be linked with a moderate power distribution loss of 28 dB. Some preliminary optical wavelength-division multiple-access mesh-connected bus experiments based on a 27 × 27 panchromatic optical source array were performed to confirm the operational principle of the proposed concept.

The receiver collision avoidance (RCA) protocol for a single-hop WDM lightwave network

We propose a multiple access protocol for a single-hop wavelength division multiplexing (WDM)-based multichannel local lightwave network. The protocol can support a large number of high-speed bursty traffic nodes interconnected via a passive optical star coupler. Each node is equipped with only one transmitter and one receiver, both of which are tunable over all the channels. A single control channel is established to arbitrate access to the other channels, called data channels. Access to the control channel is provided via a variation of slotted ALOHA so that the system is scalable. Unlike other protocols proposed in [11], [18], [23], our protocol contains a simple mechanism which can dynamically detect and avoid receiver collisions (hence it is called the receiver collision avoidance (RCA) protocol)

WDM-based local lightwave networks. II. Multihop systems

For pt.I see ibid., vol.6, no.3, p.12-27, 1992. A survey of wavelength-division-multiplexing (WDM)-based local lightwave networks is presented. The general characteristics of multihop systems are discussed, and various multihop approaches are reviewed. The construction of optimal structures based on minimizing the maximum link flow and optimizations based on minimization of the mean network packet delay are also reviewed. Regular topologies that have been studied as candidates for multihop lightwave networks, including the perfect shuffle, the de Bruijn graph, the toroid, and the hypercube, are discussed. Near-optimal node placement algorithms and shared-channel multihop systems are also discussed. >

WDM-based local lightwave networks. I. Single-hop systems

An overview of emerging all-optical networks is given. The characteristics and alternative architectures for single-hop systems are discussed. The characteristics of lightwave technology that facilitate the design of wavelength-division-multiplexing (WDM) networks are reviewed, and it is explained how WDM local networks can be built based on the single-hop and multihop approaches. Various categories of single-hop systems are discussed: experimental systems, systems based on no pretransmission coordination, and systems based on pretransmission coordination, which also require a separate control channel. A simple classification for single-hop systems is provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>