Aysegul Gencata

Virtual-topology adaptation for WDM mesh networks under dynamic traffic

We present a new approach to the virtual-topology reconfiguration problem for a wavelength-division-multiplexing-based optical wide-area mesh network under dynamic traffic demand. By utilizing the measured Internet backbone traffic characteristics, we propose an adaptation mechanism to follow the changes in traffic without a priori knowledge of the future traffic pattern. Our work differs from most previous studies on this subject which redesign the virtual topology according to an expected (or known) traffic pattern, and then modify the connectivity to reach the target topology. The key idea of our approach is to adapt the underlying optical connectivity by measuring the actual traffic load on lightpaths continuously (periodically based on a measurement period) and reacting promptly to the load imbalances caused by fluctuations on the traffic, by either adding or deleting one or more lightpath at a time. When a load imbalance is encountered, it is corrected either by tearing down a lightpath that is lightly loaded or by setting up a new lightpath when congestion occurs. We introduce high and low watermark parameters on lightpath loads to detect any over- or underutilized lightpath, and to trigger an adaptation step. We formulate an optimization problem which determines whether or not to add or delete lightpaths at the end of a measurement period, one lightpath at a time, as well as which lightpath to add or delete. This optimization problem turns out to be a mixed-integer linear program. Simulation experiments employing the adaptation algorithm on realistic network scenarios reveal interesting effects of the various system parameters (high and low watermarks, length of the measurement period, etc.). Specifically, we find that this method adapts very well to the changes in the offered traffic.

CATZ: Time-Zone-Aware Bandwidth Allocation in Layer 1 VPNs

The layer 1 virtual private network framework has emerged from the need to enable the dynamic coexistence of multiple circuit-switched client networks over a common physical network infrastructure. Such a VPN could be set up for an enterprise with offices across a wide geographical area (e.g., around the world or by a global ISP). Additionally, emerging IP over optical WDM technologies let IP traffic be carried directly over the optical WDM layer. Thus, different VPNs can share a common optical WDM core, and may demand different amounts of bandwidth at different time periods. This type of operation would require dynamic and reconfigurable allocation of bandwidth. This article evaluates the state of the art in layer 1 VPNs in the context of globally deployable optical networks and cost-efficient dynamic bandwidth usage. While exploiting the dynamism of IP traffic in a global network in which the nodes are located in different time zones, we study different bandwidth allocation methods for setting up a worldwide layer 1 VPN. We propose and investigate the characteristics of a cost-efficient bandwidth provisioning and reconfiguration algorithm, called capacity allocation using time zones (CATZ)

Virtual-topology adaptation with minimal lightpath change for dynamic traffic in WDM mesh networks

In a wavelength-routed network, a lightpath is set up by configuring the optical switches along its route to establish a virtual connection between two edge devices, e.g., IP routers. The set of lightpaths constitutes a virtual topology that carries the packet traffic on the corresponding IP-over WDM network. Our study should be of use to ISPs and enterprises running their own IP-over WDM networks.

Prudent creditization polling (PCP): a novel adaptive polling service for an EPON

In this paper a novel adaptive bandwidth allocation scheme called Prudent Creditization Polling (PCP) is proposed and adapted with the reservation protocol IPACT. PCP attempts to reduce the average queue length at the ONUs and the average packet delay throughout the network. At each polling period, PCP attempts to creditize the request of the ONUs that suffer from high RTT, high average delay per packet, and high buffer growth. We implemented PCP with a fuzzy functional approach and a linear regression approach. We simulated PCP and several service disciplines in IPACT and compared their performance in terms of average packet delay and queue length. We show that PCP improves the performance of IPACT significantly in terms of the performance metrics aforementioned.