Srivatsan Balasubramanian

Light-trail testbed for IP-centric applications

The Internet transport infrastructure is evolving toward a model of high-speed routers interconnected by intelligent optical networks. In this article we review current optical networking architectures and describe a new concept proposed in A. Gumaste and I. Chlamtac [2003]: light-trails. We develop light-trails as a novel and amenable control and management solution to address IP-centric communication problems at the optical layer. We implement a testbed to demonstrate light-trail feasibility. We also present three medium access control protocols for light-trails and evaluate their performance. The goal of light-trails and our solution is to combine commercially available components with emerging network technologies to provide a transparent, reliable, and highly scalable communication network.

Network design for IP-centric light-trail networks

We explore network design principles for next-generation all-optical wide-area networks, employing light-trail technology. Light-trail is a light-wave circuit that allows multiple nodes to share the optical bandwidth through the inclusion of simple but flexible hardware overlaid with a lightweight control protocol. We develop light-trails as a novel and amenable control and management solution to address IP-centric communication problems at the optical layer. We propose optical switch architectures that allow seamless integration of lightpath and light-trail networks, and assess their costs and capabilities. We formulate the static light-trail RWA problem as an integer linear program. Since this programming problem is computationally intractable, we split it into two subproblems: (a) trail routing, for which we provide three heuristics, (b) wavelength assignment, for which we use the largest first heuristic available in literature. The objective of our design is to minimize the optical layer and electronic layer costs in terms of the number of wavelengths and communication equipment required. We illustrate our approach by comparing the performance of our trail design heuristics on some test networks.

Light-Trail Networks: Design and Survivability

The light-trail architecture provides a novel solution to address IP-centric issues at the optical layer. By incorporating drop and continue functionality, overlaid with a lightweight control protocol, light-trails enable efficient sharing of network resources, support subwavelength traffic and minimize costs. In this work, we investigate network design and survivability issues in such networks in the presence of multi-granularity subwavelength traffic subject to nonbifurcation constraints. We first establish the NP-hardness of the light-trail routing problem by reduction from a Hamiltonian path problem. We propose three heuristics for light-trail network design and study their performance with limited network resources. We observe the effect of tunable and fixed transceiver equipment on network throughput. We observe that our heuristics yield excellent wavelength utilization under moderate to high loads even in the presence of heavily fractional traffic. We propose two additional heuristics for shared and dedicated protection and conclude that with only a modest amount of spare capacity, full protection can be achieved for all single link failures

Traffic Grooming in Statistically Shared Optical Networks

We investigate the characteristics and performance of architectures that allow statistical sharing of wavelengths in the optical layer. The bandwidth of a light-wave circuit can be shared in the optical layer by multiple nodes that are along a linear path in a network through the inclusion of simple but flexible hardware overlaid with control software. We consider three types of architectures - lightpath (LP), light-trail (LT) and source based light-trail (SLT) networks. The three differ in their level of optical sharing, in their hardware and software requirements and in their performance. We study the interplay between statistical sharing at the optical layer and circuit switched sharing at the electronic layer. We develop a generic auxiliary graph model for traffic grooming in heterogeneous WDM mesh networks that can accommodate constraints related to transceivers, wavelengths, and groomers for architectures with different levels of statistical sharing and for both static and dynamic scenarios. We conclude based on our simulation results that sharing wavelength in the optical domain is beneficial and can lead to reduced blocking

On Traffic Grooming Choices for IP over WDM networks

Traffic grooming continues to be a rich area of research in the context of WDM optical networks. We provide an overview of the optical and electronic grooming techniques available with focus on IP as the client layer. We discuss the various architectural alternatives available: peer, overlay and augmented models. We first provide a survey on the research work in the area of traffic grooming in optical circuit switched networks. We then identify problems with electronic grooming in terms of high speed router design and bring out the merits of optical grooming. Next, we describe the shared wavelength optical network technology called light-trails and compare its performance with electronic grooming networks for both the peer and overlay models. Based on our simulations on random graphs of various diameters, we identify the threshold router speeds at which light-trails can compete with the electronic grooming solution for a given network scenario. We conclude that since the present router capacities are below the threshold speed or such routers are likely to remain expensive for some time, light-trails is an appealing candidate solution.

Dynamic Survivable Network Design for Path Level Traffic Grooming in WDM Optical Networks

Recent research has focused on designing new architectures and protocols for pure optical grooming without resorting to fast optical switching. This is achieved in three steps: (1) the circuit is configured in the form of a path or a tree (2) optical devices like couplers/splitters are used to allow a wavelength to aggregate traffic from multiple transmitters and/or receivers through one of the following means - point to point, point to multi-point, multi-point to point and multipoint to multi-point (3) an arbitration mechanism is provided to avoid contention among end users of the circuit. In this paper, we focus on design of mesh networks that aggregate traffic at the path level. We develop a shared, mixed protection algorithms for guaranteed survival from single link failures in the context of dynamic traffic for mesh networks. Based on our simulations on random graphs, we conclude that light-trails, that enable multi-point to multi-point aggregation, performs multiple orders of magnitude better than lightpaths that allow point to point aggregation.

On path-level traffic grooming strategies in WDM metro optical networks

This article provides an overview of some of the optical grooming (aggregation) techniques that have been developed recently with IP as the client layer. We identify four kinds of aggregation strategies: point to point (P2P), point to multipoint (P2MP), multipoint to point (MP2P), and multipoint to multipoint (MP2MP). Using an auxiliary graph-based model, we evaluate the performance of these four strategies for singlehop and multihop scenarios that aggregate at the path level. In the case of partial mesh networks with dynamic traffic, we observe the following: MP2MP outperforms other architectures by multiple orders of magnitude in single-hop scenarios; P2P performs best in multihop transceiver-constrained scenarios; and P2MP performs the best in multihop wavelength-constrained scenarios.

A Comparative Study of Path Level Traffic Grooming Strategies for WDM Optical Networks with Dynamic Traffic - Invited Paper

Traffic grooming continues to be a rich area of research in WDM optical networks. In this paper, we identify four kinds of path level traffic aggregation/grooming strategies - point to point (P2P), point to multi-point (P2MP), multi-point to point (MP2P), and multi-point to multi-point (MP2MP). We develop an auxiliary graph based approach as a generic network dimensioning solution for these architectures. Using our model, we compare the performance of various architectures employing path level aggregation in both single hop and multi-hop scenarios. For the studied scenarios, we observe the following - (1) MP2MP outperforms other architectures by multiple orders of magnitude in single hop networks, (2) P2P performs the best in multi-hop transceiver constrained scenarios, and (3) P2MP performs the best in multi-hop wavelength constrained scenarios.

Design algorithms for path-level grooming of traffic in WDM metro optical networks

Recent research in new architecture design for wavelength-routed networks is focused on grooming (aggregation) of traffic at the optical layer. Typically, this is achieved in three steps: (1) configure the circuit in the form of a path or a tree; (2) use optical devices such as couplers or splitters to allow multiple users to share a circuit through point to point (P2P), point to multipoint (P2MP), multipoint to point (MP2P), or multipoint to multipoint (MP2MP); and (3) provide an arbitration mechanism to avoid contention among end users. We compare the performance of architectures that aggregate traffic at the path level. Based on extensive simulations, we conclude that, for the studied topology and traffic, (1) MP2MP outperforms other architectures by multiple orders of magnitude in single-hop scenarios, (2) P2P performs the best in multihop transceiver-constrained scenarios, and (3) P2MP performs the best in multihop wavelength-constrained scenarios.

Sparsely hubbed light-trail grooming networks

Recently, a new architecture called light-trails has been proposed that provides a novel control and management solution to address IP-centric issues at the optical layer. By inclusion of simple hardware that performs drop and continue functionality, overlaid with a light-weight control protocol, light-trails enable efficient sharing of network resources, improve bandwidth utilization and minimize network costs. Due to power budget constraints in such networks, it may not always be possible to have end to end communication in pure optical domain and requests may be required to traverse multiple intermediate transit points called hub nodes before reaching the final destination. The hub nodes need to be equipped with special hardware for switching and grooming connections. We investigate the problem of designing networks where such hubs are sparsely located. We show through our simulation results that by carefully designing heuristics for hub node placement and trail routing, it is possible to achieve high throughput with minimal number of hub nodes.