Impact of the Mean Nodal Degree on Optical Networks Claunir Pavan a,b , Rui M. Morais b , Abel R. Correia a and Armando N. Pinto a,b a Dept. of Electronic, Telecom. and Informatics, University of Aveiro, Aveiro, Portugal; b Institute of Telecommunications, Aveiro, Portugal. ABSTRACT We present the cost impact of establishing new links in mesh optical networks. The analysis is based on an analytical study for quickly calculate the transmission and bandwidth management systems costs. Results show that each network has a mean nodal degree that minimizes the total cost. Keywords: Optical networks, Capital expenditure. 1. INTRODUCTION Telecommunications network operators desire a flexible and cost-efficient network to carry a traffic load. Network designers must define an appropriate network which provisioned resources match the demand with minimal capital expenditure (CAPEX). 1 This task imply to decide the location and number of links and network nodes. While insufficient resources leads to loss of revenue, over-provisioning leads to some waste of capital investment. The set of elements that constitutes an optical network can be grouped into two distinct categories, 2–4 transmission and bandwidth management. The first category relates with equipments such as optical line terminals, transponders and optical amplifiers. The second one relates with equipments placed in the nodes, such as electrical cross connects, optical cross connects and ports (both electrical and optical). Network cost is an important factor in the dimensioning problem. In a Korotky’s 2 work, he presents a model for calculating the value of network key variables without necessity of in-advanced knowledge of the network topology. Recently we have also published a work 5 on the dimensioning of optical networks with incomplete information. The aims of the present study consist in evaluating the impact of the number of links on network costs and to gain a deeper insight into the network dimensioning issue. To accomplish this, in this paper we focused on five elements: optical line terminals, optical transponders, optical amplifiers, optical and electrical bandwidth management. The quantities of these elements provide enough information to account for transmission costs (C T RAN S ) and bandwidth management costs (C BWM ). Furthermore, allow us to analyze the impact of each element over the total cost (C T ) in function of the mean nodal degree. The optical fiber cable is part of the transmission system. Since there exist a vast amount of already installed dark fibers, the operators can only light up the required fibers and equip them with transponders, amplifiers and regenerators. Thus, we assume fiber cost as an operational cost, and it is not considered in the CAPEX. The next sections of this paper are organized in the following way: in section II is presented the network architecture considered. In section III the cost model is drawn. Experiments and results are stated in section IV and the main conclusions of this work are presented in section V. 2. NETWORK ARCHITECTURE We consider that the optical networks comprise a set of N opaque nodes and L links. Opaque technology refers to the switching with optical-to-electronic conversion. 6, 7 Each multi-layer node comprises a non-blocking optical cross-connect (OXC) with a set of optical ports and a non-blocking electrical cross-connect (EXC) with a set of electrical ports (Figure 1). The first with switching capabilities for wavelength channels and the second one with switching capabilities for smaller granularities. 8 OXCs and EXCs are connected by a number of short reach transponders (not present in Figure 1). We ignore the cost of short reach transponders since it has an insignificant weight over the total CAPEX. C.P.: pavan@av.it.pt, R.M.M.: rmorais@av.it.pt, A.R.C.: a12129@ua.pt, A.N.P.: anp@ua.pt Photonics North 2008, Réal Vallée, Michel Piché, Peter Mascher, Pavel Cheben, Daniel Côté, Sophie LaRochelle, Henry P. Schriemer, Jacques Albert, Tsuneyuki Ozaki, Eds., Proc. of SPIE Vol. 7099, 709910, (2008) · 0277-786X/08/$18 · doi: 10.1117/12.804698 Proc. of SPIE Vol. 7099 709910-1 2008 SPIE Digital Library -- Subscriber Archive Copy