Miguel Razo

Finding a simple path with multiple must-include nodes

This paper presents an algorithm to find a simple path in the given network with multiple must-include nodes in the path. The problem of finding a path with must-include node(s) can be easily found in some special cases. However, in general, including multiple nodes in the simple path has been shown to be NP-Complete. This problem may arise in network areas such as forcing the route to go through particular nodes, which have wavelength converter (optical), have monitoring provision (telecom), have gateway functions (in OSPF) or are base stations (in MANET). In this paper, a heuristic algorithm is described that follows divide and conquer approach, by dividing the problem in two subproblems. It is shown that the algorithm does not grow exponentially in this application and initial re-ordering of the given sequence of must-include nodes can improve the result. The experimental results demonstrate that the algorithm successfully computes near optimal path in reasonable time.

Network-wide signal power control strategies in WDM networks

Software Defined Networking (SDN) is enabling wavelength-division multiplexed (WDM) networks to be programmable down to individual components. While taking into account typical gain and noise figure profiles of erbium-doped fiber amplifier (EDFA) components, the authors consider a number of signal power control strategies and compare their performance in terms of achievable lightpath optical signal-to-noise ratio (OSNR). These strategies are applied network-wide to concurrently control the gain of each individual amplifier and the signal power equalization at each reconfigurable optical add/drop multiplexer (ROADM). Simulation results show that the lightpath OSNR is affected by three factors: the EDFA gain control strategy, power equalization strategy and wavelength assignment algorithm. A trade-off between lightpath average OSNR and OSNR variance across the WDM channels is also noted.

Handling race conditions among bidirectional LSP requests via WA-method-TLV in GMPLS WDM networks

This paper defines three types of race conditions that may occur while attempting to reserve optical circuits in GMPLS WDM networks. It then investigates the effect on network blocking by race condition type and explains how to use an already existing TLV in the IETF RSVP signaling to inform the destination node of a potential race condition occurrence. An informed destination can then choose the appropriate wavelength assignment algorithm to best handle such situation.

Cooperative Data Center Selection for Optimal Service Performance: An ILP Formulation

Cross layer optimization is well-known to offer certain cost and performance advantages when designing and operating data networks [1]. It is reasonable to anticipate similar advantages when applying such optimizations across the network layer and the application layer too. In this paper, the authors define one optimization problem whereby the service-to-hosting data center mapping is performed taking into account the available resources in both the data center (CPU cycles) and network (bandwidth) subsystems. The objective function of the optimization problem accounts for the amount of both CPU cycles and bandwidth, which are assigned to each requested service, with the assumption that the users Quality of Experience (QoE) strictly depends only on these two factors. The problem is formulated using ILP and its numerical results are discussed to gain insights into the potential QoE gains that might result from using this cross layer (cooperative) resource assignment technique.

Routing and wavelength assignment computed jointly for a given set of multicast trees reduces the total wavelength conversion

A significant drawback when establishing multicast optical trees (light-tree) using lambda channels in wavelength division multiplexing (WDM) network is the potentially large amount of wavelength converters (WCs), which are required when the wavelength continuity constraint cannot be satisfied across each light-tree. Prior works address this challenge by solving the routing and wavelength assignment (RWA) problem for each individual light-tree sequentially, to locally minimize the number of WCs required by each light-tree. In this paper, the authors intend to solve the RWA problem for a group of light-trees with the objective of globally minimizing the number of WCs that are required to support the entire group of multicast requests. The rationale for using the proposed RWA solution is that a joint solution of the RWA problem across the whole set of requested multicast trees may significantly reduce the number of WCs overall.

Blocking probability and fairness in two-rate Elastic Optical Networks

Routing and Spectrum Allocation (RSA) algorithms are used to compute both routing and spectrum allocation of connection demands in Elastic Optical Networks (EONs). A number of RSA algorithms have been proposed. Their performance is usually measured in terms of overall blocking probability. In this paper the authors pursue an additional performance indicator that is introduced to quantify the level of fairness (or unfairness) experienced by two types of demands, each type requiring a distinct spectrum bandwidth size. A new RSA algorithm is also proposed to jointly control blocking and fairness by partitioning the spectrum into dedicated and shared bands. Simulation results are used to estimate the trade-off between the blocking probability experienced by all demands and the level of fairness as it is achieved by a total of six RSA algorithms.

Multicast tree computation in networks with multicast incapable nodes

Multicast transmission offers a bandwidth efficient solution for delivering media content to multiple destinations over the Internet. However, in many existing networks, some (if not all) nodes do not support multicast, i.e., they cannot create multiple outgoing flows with one incoming data flow. In this paper, the authors propose an algorithm for multicast tree computation in networks with multicast incapable nodes. Paths that originate at the source and traversing all destinations are computed first; if such paths cannot be found, destinations are partitioned into subsets and traverse paths are computed over each subset, which is executed recursively until feasible trees can be built based on traverse paths found or no further partition is possible. Two procedures for traverse path computation are presented and their respective advantages are discussed, in terms of both complexity and solution optimality. The algorithm is also shown to be very effective in finding multicast trees even if only a few multicast capable nodes exist in the network.

The PlaNet-PTN Module: a Single Layer Design Tool for Packet Transport Network

PlaNet is a multilayer network planning tool developed at the University of Texas at Dallas. This paper illustrates some of the features of PlaNet-PTN, one of the modules available in the PlaNet tool. PlaNet-PTN can be used to design and plan a single layer packet transport network (PTN). Quality of protection, routing constraints, minimization of the network equipment cost, and user’s desired run time of the tool are just some examples of the features available in PlaNet. As shown in the paper, the PlaNet-PTN planning module is able to provide, among others, optimization of Label Switched Path (LSP) routes, link capacity placement, node and link equipment configuration.

Effects of signal power control strategies and wavelength assignment algorithms on circuit OSNR in WDM networks

Software-defined networking is enabling wavelength-division multiplexed (WDM) networks to be programmable down to individual components. While taking into account typical gain and noise figure profiles of erbium-doped fiber amplifier (EDFA) components, the authors consider a number of signal power control strategies and compare their performance in terms of achievable lightpath optical signal-to-noise ratio (OSNR). These strategies are applied network-wide to concurrently control the gain of each individual amplifier and the signal power equalization at each reconfigurable optical add/drop multiplexer. Simulation and (in part) experimental results show that the lightpath OSNR is affected by three factors: the EDFA gain control strategy, power equalization strategy and wavelength assignment (WA) algorithm. A trade-off between lightpath average OSNR and OSNR variance across the WDM channels is also noted. Experimental work is conducted using a five-node meshed WDM network testbed proving both feasibility and effectiveness of a coordinated use of signal power control strategies and WA algorithms.

Digital subcarrier optical networks (DSONs)

This paper describes an energy efficient and data rate flexible network transport solution to achieve sub-wavelength circuit provisioning between edge node pairs. Sub-wavelength circuits are obtained by concatenating spectrally efficient digital subcarrier channels along the network path, with each subcarrier frequency carrying only a fraction of the wavelength bandwidth. By reserving one or more such subcarrier frequencies along a path connecting two edge nodes, a dedicated end-to-end sub-wavelength circuit is provisioned. At intermediate nodes, incoming frequencies are switched to outgoing frequencies via a specially designed frequency selective switch or cross-connect, described in a companion paper [7]. The power consumption required to switch subcarrier frequencies across the network is estimated to be a fraction of the power dissipated by currently available transport solutions, e.g., optical transport network (OTN) and multiprotocol label switching transport profile (MPLS-TP).