Narendra K. Singhal

Provisioning of survivable multicast sessions against single link failures in optical WDM mesh networks

In this paper, we investigate approaches and algorithms for establishing a multicast session in a mesh network while protecting the session against any single link failure, e.g., a fiber cut in an optical network. First, we study these approaches and algorithms to protect a single multicast tree in a mesh network and then extend it to dynamically provision survivable multicast connections (where connections come and go) in an optical wavelength-division multiplexing (WDM) network. We propose two new and efficient approaches for protecting a multicast session: 1) segment protection in which we protect each segment in the primary tree separately (rather than the entire tree) and allow these backup segments to share edges with the other existing primary and backup segments and 2) the path-pair protection in which we find a path-pair (disjoint primary and backup paths) to each destination and allow a new path pair to share edges with already-found path pairs. Unlike previous schemes, such as finding link-disjoint trees and arc-disjoint trees, our new schemes 1) guarantee a solution where previous schemes fail and 2) find an efficient solution requiring less network resources. We study these approaches and algorithms systematically, starting with the existing approaches such as fully link-disjoint and arc-disjoint trees and then presenting our new and efficient proposed approaches, such as segment-disjoint and path-disjoint schemes for protecting multicast connections. Our most efficient algorithm, based on the path-pair protection scheme, called optimal path-pair-based shared disjoint paths (OPP-SDP) algorithm, finds a solution if such a solution exists and outperforms all the other schemes in terms of network cost. We also show that OPP-SDP performs close to the optimal solution obtained by solving a mathematical formulation of the problem expressed as an integer linear program. Building upon the study on protecting a single tree, we perform simulations, employing the above protection schemes, to study dynamic provisioning of survivable multicast sessions (where sessions come and go) in a WDM mesh network. Our simulations show that the most efficient scheme, OPP-SDP, has minimum blocking probability.

Fair queueing with service envelopes (FQSE): a cousin-fair hierarchical scheduler for subscriber access networks

In this paper, we propose and investigate the characteristics of a fair queueing with service envelopes (FQSE) algorithm-a hierarchical fair-share scheduling algorithm for access networks based on a remote scheduling system such as Ethernet passive optical networks (EPON) or cable TV network. FQSE is designed to overcome the limiting factors of a typical remote scheduling system such as large control-plane delay, limited control-plane bandwidth, and significant queue switch-over overhead. The algorithm is based on a concept of service envelope-a function representing the fair allocation of resources based on a global network condition called satisfiability parameter (SP). We define properties of cousin-fairness and sibling-fairness and show the FQSE to be cousin-fair. FQSE is unique in that it is the only hierarchical algorithm that is simultaneously cousin-fair. Furthermore, we show the necessary techniques to adapt FQSE to variable-sized packet-based networks. We analyze FQSE performance in EPON serving 1024 independent queues and demonstrate FQSEs ability to provide guaranteed bandwidth to each queue and to share the excess bandwidth fairly.

Subpath protection for scalability and fast recovery in optical WDM mesh networks

This paper investigates survivable lightpath provisioning and fast protection switching for generic mesh-based optical networks employing wavelength-division multiplexing (WDM). We propose subpath protection, which is a generalization of shared-path protection. The main ideas of subpath protection are: 1) to partition a large optical network into smaller domains and 2) to apply shared-path protection to the optical network such that an intradomain lightpath does not use resources of other domains and the primary/backup paths of an interdomain lightpath exit a domain (and enter another domain) through a common domain-border node. We mathematically formulate the routing and wavelength-assignment (RWA) problem under subpath protection for a given set of lightpath requests, prove that the problem is NP-complete, and develop a heuristic to find efficient solutions. Comparisons between subpath protection and shared-path protection on a nationwide network with dozens of wavelengths per fiber show that, for a modest sacrifice in resource utilization, subpath protection achieves improved survivability, much higher scalability, and significantly reduced fault-recovery time.

Cross-sharing vs. self-sharing trees for protecting multicast sessions in mesh networks

In this study, we investigate a cost-effective approach for protecting several multicast sessions from any link failure in an optical network. The approach, referred to as cross-sharing, provides an optimal sharing of backup resources among several multicast sessions. Our cross-sharing approach employs the link-vector model, modified for multicast sessions, and provides significant cost savings (48% for a small six-node network and 39% for a large nationwide network) of backup resources relative to arc-disjoint and self-sharing approaches, especially for a large number of sessions.

Architectures and algorithm for multicasting in WDM optical mesh networks using opaque and transparent optical cross-connects

As the WDM technology grows, multicast applications will become widely popular. In the study, we present two kinds of switch architectures to support multicasting. We present preliminary results obtained for efficient routing and wavelength assignment (RWA) of multicast sessions.

Dynamic provisioning of survivable multicast sessions in optical WDM mesh networks

We investigate dynamic provisioning of multicast sessions while protecting them against any single fiber cut in optical WDM mesh networks. Our proposed segment-protection and path-pair-protection schemes exhibit very good performance relative to other schemes.

Shared protection for multicast sessions in mesh networks

We investigate optimal sharing among backups of several multicast sessions in an optical mesh network. Our cross-sharing approach provides significant cost-savings of backup resources relative to arc-disjoint and self-sharing approaches, especially for a large number of sessions.

Protecting a multicast session against single link failures in a mesh network

In this report, we investigate approaches and algorithms for establishing a multicast session in a mesh network while protecting the session against any single link failure, e.g., a fiber cut in an optical network. We propose two new and efficient approaches for protecting a multicast session: 1) segment protection in which we protect each segment in the primary tree separately (rather than the entire tree) and allow these backup segments to share arcs with the other existing primary and backup segments; and 2) path-pair protection in which we protect a path between each source-destination pair by finding a disjoint backup path. Unlike previous schemes such as finding link-disjoint trees and arc-disjoint trees, our new schemes 1) guarantee a solution where previous schemes fail and 2) find efficient solution requiring less network resources. Our algorithm, based on the path-pair protection scheme, called optimal path-pair-based shared disjoint paths (OPP-SDP) algorithm, finds a solution if such a solution exists and outperforms all the other schemes in terms of network cost. We also show that OPP-SDP performs close to the optimal solution obtained by solving a mathematical formulation of the problem expressed as an integer linear program (ILP).

A time-path scheduling problem (TPSP) for aggregating large data files from distributed databases using an optical burst-switched network

The problem of aggregating large data files from distributed databases and address the corresponding challenges involved from a network architecture perspective is considered. We model this problem as one of identifying a time-path schedule (TPS) in a graph representation of the network. We prove that the TPS problem (TPSP) is NP-complete. We then propose a mixed integer linear programming (MILP)-based approach and three heuristics longest-file-first (LFF), disjoint-paths (DP), and most-distant-file-first (MDFF) - to solve TPSP.

Minimum-cost topology adaptation for an ISP's mesh network

We propose a topology adaptation model for Internet service providers for minimizing their total dollar-cost for network operations. We observe significant cost-savings of 21% on a nationwide network employing realistic traffic models and bandwidth cost.