Ori Gerstel

Benefits of limited wavelength conversion in WDM ring networks

A number of recent papers have studied the impact of wavelength conversion in wavelength-division multiplexing (WDM) networks. Relatively few works have studied the effect of providing limited wavelength conversion capability in these networks. This paper surveys our recent results on this topic. Consider a ring network of N nodes. We assume bidirectional links and lightpaths, which are typically realized using pairs of counter-propagating connections. For each lightpath we are given a route in the network and must assign a wavelength on each link along its route. Our results apply to the situation where no blocking whatsoever is allowed; in other words, all lightpath requests must be supported.

Hotlink Enhancement Algorithms for Web Directories

Consider a web site containing a collection of web pages with data. Each page is associated with a weight representing the frequency that page is accessed by users. In the tree hierarchy representation, ac- cessing each page requires the user to travel along the path leading to it from the root. By enhancing the index tree with additional edges (hotlinks) one may reduce the access cost of the system. That is, the hotlinks reduce the expected number of steps needed to reach a leaf page from the tree root, assuming that the user knows which hotlinks to take. The hotlink enhancement problem involves finding a set of hotlinks minimizing this cost. The paper proposes a hotlinks structure allowing a user with limited a-priori knowledge to determine which hotlink to use at every given point. Then, a polynomial algorithm is presented for solving the hotlink enhancement problem for such hotlinks on trees of logarithmic depth. The solution is first presented for binary trees and then extended to arbitrary degree trees. It is also shown how to gener- alize the solution to situations where more than one hotlink per node is allowed. The case in which the distribution on the leaves is unknown is discussed as well, and is given an algorithm guaranteeing (an optimal) logarithmic upper bound on the expected number of steps down the tree.

Cost Effective Architectures for Core Transport Networks

We describe recent approaches that are considered by carriers for building future core packet networks, combining DWDM, TDM and routing technologies. We compare the capital and operational cost of these approaches using real-world networks and pricing models.

Multiwavelength Ring Architectures and Protection Schemes

This paper describes different types of wavelength-division-multiplexed (WDM) ring architectures and the protection mechanisms that can be used to restore traffic in the event of failures. It points out why optical layer protection schemes are needed, and compares these architectures and protection mechanisms to those used in SONET.

Design and demonstration of a reconfigurable metro-regional WDM 32 /spl times/ 10 Gb/s system scaling beyond 500 kin of G.652 fiber

We demonstrate a industrial-strength 32 /spl times/ 10 Gb/s WDM system with multiple reconfigurable optical-add/drop nodes that enables metro regional networks to cost-effectively scale to < 500 km with span and installation/maintenance flexibility.

Dynamic wavelength conversion in optical networks

We propose algorithms for allocation of wavelengths to connections (lightpaths) in WDM networks, that is, optical wavelength division multiplexed networks. We investigate mainly ring and tree networks. The worst-case situation is considered since we investigate the case were no blocking is allowed. Also, there are no assumptions on the traffic arrival and holding times. The traffic is characterized only by its load L, which is the maximum number of lightpaths that can be present on any link assuming no blocklng. For a static scenario, and with networks without wavelength conversion, and prove that the known algorithm which requires 2L– 1 wavelengths is optimal. For a dynamic scenario we show first that shortest path routing produces a routing which

Sliceable Bandwidth Variable Transponders

Elastic Optical Networking (EON) supports Bandwidth Variable Transponders (BVTs) that can tune their bit-rate and bandwidth dynamically with a trade-off between reach and capacity. However, when BVTs need to transmit at low bit-rates, part of their capacity is wasted. This issue can be solved by adding elastic multi-flow performance according to the Sliceable Bandwidth Variable Transponder (S-BVT) approach. S-BVTs enable transmitting from one point to multiple destinations, changing the traffic rate to each destination and the number of destinations on demand. This chapter presents architectures to support the S-BVT and its techno-economic impact from a Capital Expenditures (CAPEX) and Operational Expenditures (OPEX) point of view.