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. II. Multihop systems

We explore design principles for next-generation optical wide-area networks, employing wavelength-division multiplexing (WDM) and targeted to nationwide coverage. This optical network exploits wavelength multiplexers and optical switches in routing nodes, so that an arbitrary virtual topology may be embedded on a given physical fiber network. The virtual topology, which is used as a packet-switched network and which consists of a set of all-optical "lightpaths", is set up to exploit the relative strengths of both optics and electronics-viz. packets of information are carried by the virtual topology "as far as possible" in the optical domain, but packet forwarding from lightpath to lightpath is performed via electronic switching, whenever required. We formulate the virtual topology design problem as an optimization problem with one of two possible objective functions: (1) for a given traffic matrix, minimize the network-wide average packet delay (corresponding to a solution for present traffic demands), or (2) maximize the scale factor by which the traffic matrix can be scaled up (to provide the maximum capacity upgrade for future traffic demands). Since simpler versions of this problem have been shown to be NP-hard, we resort to heuristic approaches. Specifically, we employ an iterative approach which combines "simulated annealing" (to search for a good virtual topology) and "flow deviation" (to optimally route the traffic-and possibly bifurcate its components-on the virtual topology). We do not consider the number of available wavelengths to be a constraint, i.e., we ignore the routing of lightpaths and wavelength assignment for these lightpaths. We illustrate our approaches by employing experimental traffic statistics collected from NSFNET.

Some principles for designing a wide-area WDM optical network

A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

WDM optical network with passive pass-through at each node

Explores design principles for next generation optical wide-area networks, employing wavelength-division multiplexing (WDM), and targeted to nationwide coverage. This almost-all-optical network will exploit wavelength multiplexers and optical switches in routing nodes, so that arbitrary virtual topologies may be imbedded on a given physical network. The virtual topology, which is packet switched and which consists of a set of all-optical lightpaths, is set up to exploit the relative strengths of both optics and electronics viz. packets of information are carried by the virtual topology "as far as possible" in the optical domain, but packet forwarding from lightpath to lightpath is performed via electronic switching, whenever required. Algorithms are developed so that the WDM-based network architecture will (a) provide a high aggregate system capacity due to spatial reuse of wavelengths, and (b) support a large and scalable number of users, given a limited number of wavelengths. The authors illustrate their approaches by employing experimental traffic statistics collected from NSFNET. >

Some principles for designing a wide-area optical network

A designer of reliable multi level secure (MLS) networks must consider covert channels and denial of service attacks in addition to traditional network performance measures such as throughput, fairness, and reliability. We show how to extend the NRL data Pump to a certain MLS network architecture in order to balance the requirements of congestion control, fairness, good performance, and reliability against those of minimal threats from covert channels and denial of service attacks. We back up our claims with simulation results.

A network pump

GEMNET is a generalization of shuffle-exchange networks and it can represent a family of network structures (including ShuffleNet and de Bruijn graph) for an arbitrary number of nodes. GEMNET employs a regular interconnection graph with highly desirable properties such as small nodal degree, simple routing, small diameter, and growth capability (viz. scalability). GEMNET can serve as a logical (virtual), packet-switched, multihop topology which can be employed for constructing the next generation of lightwave networks using wavelength-division multiplexing (WDM). Various properties of GEMNET are studied. >

GEMNET: a generalized, shuffle-exchange-based, regular, scalable, modular, multihop, WDM lightwave network

This study deals with the distributed queue dual bus (DQDB) (IEEE 802.6) network, and makes two independent contributions. First, the unfairness problem of DQDB is addressed, and several alternative solutions that can improve the network's fairness are proposed. They include (1) the proportional assignment scheme (PR); (2) the (multiple-request) FCFS (first come first served)-message-queue-based DQDB scheme (MD); and (3) a combination of MD and PR, denoted by MP. Implementation methods that require simple hardware in addition to the regular DQDB interface are outlined. The schemes are compared through simulation, and insights into their characteristics are gained. The performance of these schemes is also compared with that of regular DQDB and bandwidth balancing DQDB. The second contribution is the development of an analytical model of the DQDB network. By employing some constrained assumptions for analytical tractability, a Markov chain model for (an earlier version of) the entire DQDB network is formulated. The model is verified via simulation. >

Alternative strategies for improving the fairness in an analytical model of DQDB networks

Several important modifications to the distributed queue dual bus (DQDB) (IEEE 802.6) protocol for metropolitan area networks (MANs) are proposed. These modifications are aimed at improving not only the throughout and delay performance of the network but also its fairness performance. The first proposal exploits the continuation-of-message (COM) information in a DQDB segment in order to minimize the mean overhead for multi-segment messages. Then, a scheme for combining the COM information along with the spatial reuse of slots is proposed, thereby achieving even higher throughput and lower delay. Simulation models are used to study the performance gains achievable by using the COM and the slot reuse approaches. Although slot reuse has been proposed before to improve the DQDB protocol's performance, DQDB's unfairness problem becomes more pronounced when slots are reused. This paper also proposes several schemes to achieve different fairness criteria in a DQDB network employing slot reuse, namely: (a) an individual station's throughput proportional to the number of stations downstream from itself, (b) equal throughput at all stations, and (c) an individual station's throughput proportional to its own offered load. Analytical results corresponding to these schemes are developed, and they are verified via simulation. The proposed schemes can be implemented with just one additional counter and one register (on top of the regular DQDB hardware) at each station.

Incorporating continuation-of-message information, slot reuse, and fairness in DQDB networks

The unique capabilities of lightwave technology are exploited in order to construct optimized regular multihop networks when the traffic flow among the network nodes is asymmetric. The specific problem addressed is as follows: given that the network nodes must be connected in a regular interconnection pattern and that the node positions in the regular network can be adjusted by properly tuning their (optical) transceivers, what is the best node placement in a given regular topology? In particular, the ShuffleNet-based regular topology is examined. ShuffleNet has the property of producing large connected graphs with small degree and diameter. In order words, it can interconnect a large number of nodes with a small number of transceivers per node such that information from a source can reach its destination in a small number of hops. Since finding the optimal node placement is a computationally hard problem, efficient heuristic algorithms are formulated to design optimized ShuffleNet structures for a given traffic matrix. >

Algorithms for optimized node arrangements in ShuffleNet based multihop lightwave networks

The goal of the study described is to exploit the capabilities of emerging lightwave technology and the fact that the IEEE 802.6 MAN is a linear network, to construct near optimal linear multihop lightwave networks. Heuristic algorithms are proposed for constructing photonic implementations of near optimal distributed queue dual bus (DQDB) structures. Two sets of heuristic optimization algorithms are formulated. The first set is concerned with minimizing the maximum flow in any link in the network, while the second set of heuristics is aimed at minimizing the network-wide mean packet delay. Important properties of these algorithms are analyzed and their performance is demonstrated with several representative numerical examples. >

Subrata Banerjee

Papers

GEMNET: a generalized, shuffle-exchange-based, regular, scalable, modular, multihop, WDM lightwave network

Alternative strategies for improving the fairness in an analytical model of DQDB networks

Incorporating continuation-of-message information, slot reuse, and fairness in DQDB networks

Algorithms for optimized node arrangements in ShuffleNet based multihop lightwave networks

Heuristic algorithms for constructing near-optimal structures of linear multihop lightwave networks