Sudipta Sengupta

Capacity performance of dynamic provisioning in optical networks

This paper describes an architecture and analyzes the performance of dynamic provisioning of lightpaths in an optical network. In dynamic provisioning, a lightpath is set up in real-time without rearranging the working and protection routes of existing lightpaths, and without the knowledge of future lightpath provisioning events. This paper develops a general model of the physical topology of the optical network, and outlines routing approaches for dynamic provisioning of lightpaths. It analyzes via simulations the performance of dynamically provisioned unprotected, 1+1 protected and mesh-restored lightpaths. The analysis of the efficiency of network utilization of dynamic provisioning focuses on the spare capacity needed for protection, and in particular focuses on the impact of sharing of wavelength channels for mesh-restored lightpaths. The main conclusion from the performance studies is that significant capacity gains are achieved with sharing of wavelength-channels for mesh-restored lightpaths with dynamic provisioning even for sparse topologies, and even at moderate loads.

Capacity efficient distributed routing of mesh-restored lightpaths in optical networks

A mesh-restored lightpath in an optical network has a primary route and a diversely routed backup route. The wavelength channels on the primary route of a mesh-restored lightpath are dedicated for that lightpath whereas the wavelength channels on the backup route are shared among different mesh-restored lightpaths. Wavelength channels are shared in a way that ensures restoration of all lightpaths affected by any single link failure. In the centralized scenario, complete knowledge of the network state allows determination of the sharability of a backup channel during path computation. This information is not available in the distributed scenario. Use of 1+1 routing algorithms for mesh-restored lightpaths leads to inefficient capacity sharing. We propose distributed routing techniques to decrease the capacity efficiency gap between centralized routing and 1+1 routing of mesh-restored lightpaths. The algorithm uses information about the number of available and (shared) backup channels in a link, which can be disseminated through traffic engineering extensions to OSPF. A sharing database at each OXC maintains information about the lightpaths whose primary or backup paths traverse that OXC. The approach involves distributed determination of the sharability of a link on the backup path during path signaling using the sharing database at each OXC on the backup path. This, combined with a retry scheme facilitated by crankback routing extensions to CR-LDP/RSVP-TE to reduce lightpath blocking, leads to capacity efficient distributed routing of mesh-restored lightpaths.

Maximum Throughput Routing of Traffic in the Hose Model

A computer-implemented method of computing throughput of a data-routing scheme for a network of nodes interconnected by links and having at least one ingress point and at least one egress point. The method includes: deriving a polynomial-size linear program from a combination of a first linear program and a second linear program and solving the polynomial-size linear program. The first linear program has infinite constraints and minimizes maximum-link utilization of a link in a path between the ingress point and the egress point. The second linear program determines whether any constraint of the first linear program is violated.

Algorithms and Approximation Schemes for Minimum Lateness/Tardiness Scheduling with Rejection

We consider the problem of minimum lateness/tardiness scheduling with rejection for which the objective function is the sum of the maximum lateness/tardiness of the scheduled jobs and the total rejection penalty (sum of rejection costs) of the rejected jobs. If rejection is not considered, the problems are solvable in polynomial time using the Earliest Due Date (EDD) rule. We show that adding the option of rejection makes the problems \(\mathcal{NP}\)-complete. We give pseudo-polynomial time algorithms, based on dynamic programming, for these problems. We also develop a fully polynomial time approximation scheme (FPTAS) for minimum tardiness scheduling with rejection using a geometric rounding technique on the total rejection penalty.

Analysis of enhanced OSPF for routing lightpaths in optical mesh networks

We discuss enhancements to the OSPF (open shortest path first) protocol for routing and topology discovery in optical mesh networks. OSPFs opaque LSA (link state advertisement) mechanism is used to extend OSPF to disseminate optical resource related information through optical LSAs. Standard link-state database flooding mechanisms are used for distribution of optical LSAs. Each optical LSA carries optical resource information pertaining to a single optical link bundle between two adjacent OXCs (optical cross connects), allowing for fine granularity changes in topology to be incorporated in path computation algorithms. OSPF packets are carried over a single IP control channel between adjacent OXCs. We analyze the performance of OSPF with optical extensions. Specifically, we compute control channel bandwidth used due to LSA updates. We also estimate the amount of memory required to store the LSA database. Finally, we study CPU usage for computing primary and backup lightpaths. Our analysis shows that the control channel bandwidth usage, memory requirement, and CPU usage are small enough to not be limiting factors for designing optical networks with single OSPF areas consisting of a large number (more than 500) of OXCs.

Comparison of centralized and distributed provisioning of lightpaths in optical networks

This paper compares centralized and distributed online provisioning approaches in optical networks. In the centralized approach, complete network state is available for path computation. In the distributed approach, summarized information is available for path computation.

Two-phase routing, scheduling and power control for wireless mesh networks with variable traffic

We consider the problem of joint routing, scheduling and transmission power assignment in multi-hop wireless mesh networks with unknown traffic. We assume the traffic is unknown, but the traffic matrix, which specifies the traffic load between every source-destination pair in the network, always lies inside a polytope defined by hose model constraints. The objective is to minimize the maximum of the total transmission power in the network over all traffic matrices in a given polytope. We propose efficient algorithms that compute a two-phase routing, schedule and power assignment, and prove the solution to be 3-approximation with respect to an optimal two-phase routing, scheduling and power assignment. We show via extensive simulations that the proposed algorithm has good performance at its worst operating traffic compared to an algorithm optimized for that traffic.