Upper Limit on the capacity of Subscriber Access Networks T.M.Prasanna * a , Rajiv Srivastava a , Yatindra Nath Singh a Department of Electrical Engineering, Indian Institute of Technology, Kanpur, Uttar Pradesh, India 208016 ABSTRACT WDM is an answer to increasing bandwidth requirement, as it carves up the huge bandwidth of single mode fiber into channels whose bandwidths are compatible with peak electronic processing speeds. The paper deals with the unidirectional aspect of the Dual Bus Architecture for Subscriber Access Network with passive optical splitting being employed at the Optical Network Unit (ONU). The aim is to give an upper bound on the number of WDM channels that can be transmitted, and the number of subscribers that can be accommodated (by maximizing the number of power splits) for broadcast applications. Three cases discussed in this paper are (i) Analog broadcast channels along with unicast transmission (which are also called switched services). (ii) Digital broadcast channels with switched services. (iii) The hybrid of both analog and digital broadcast channels with switched services. Keywords: Access Network, Modulation Schemes, EDFA and WDM. 1. INTRODUCTION Increased demand for bandwidth arises from a proliferation of applications such as voice, video and data traffic as well as by the bootstrapping effect of increased consumption resulting from lower rates. The term ‘Broadband Services’ is coined for the hybrid transfer of data, voice and video services. Technologies like video on demand, teleconferencing and virtual reality that requires enormous bandwidth can be now realized. This dream is envisaged by optical communication along with Wavelength Division Multiplexing (WDM) technology. The deployment of networks [1] for sharing gave birth to operators providing the full service encompassing the triple play- voice, video and data. With services being classified as broadcast or switched, with the former one meaning the distribution of the same information to all subscribers as in CATV and the latter one as subscriber specific data being transmitted in the last leg like in internet and telephone services; paved the way for the classification of networks. The final links between the service provider’s facility to the home or business is called the Access Network [2]. The architecture, which has been considered, is shown in figure 1. 2. SALIENT FEATURES OF THE ARCHITECTURE In this architecture, different wavelengths can be transmitted simultaneously and each wavelength contain many channels mounted on it, like, one wavelength may be containing broadcast data and the rest may contain unicast transmission data and all these channels are subcarrier multiplexed. On the Bus, EDFAs are employed to maximize the number of branching out of it using a 3-dB coupler. This coupler is wavelength flattened, which allows WDM in the network. This is a very cost effective approach, as more and more subscribers can be adhered to without incurring too much of loss. tmprasanna@gmail.com; Phone +91 9886471891 Figure1 Schematic of the architecture for access network Central Office EDFA Coupler ONU PID No. PP-FIO-54