IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 18, NO. 4, FEBRUARY 15, 2006 607 Packet Labeling Technique Using Electronic Code-Division Multiple-Access for WDM Packet-Based Access Networks Nishaanthan Nadarajah, Student Member, IEEE, Elaine Wong, Member, IEEE, and Ampalavanapillai Nirmalathas, Senior Member, IEEE Abstract—We propose and experimentally demonstrate the fea- sibility of a packet labeling technique using electronic code-division multiple-access for a wavelength-division-multiplexing (WDM) packet-based access network, whereby each wavelength is as- signed a unique electronic code-based label on a radio-frequency subcarrier. Such a technique allows individual wavelength chan- nels to be electronically identified without requiring the use of a WDM demultiplexer. We experimentally demonstrate this tech- nique with two WDM channels each with 1.25-Gb/s payload data and 10-Mb/s header coded onto an electronic code at 160 Mb/s. The experimental results and theoretical analysis show that this technique has the potential to support large numbers of WDM channels. Index Terms—Electronic code-division multiple-access (E-CDMA), multiple-access interference, optical label switching, subcarrier multiplexing, wavelength-division-multiplexing (WDM) packet networks. I. INTRODUCTION W AVELENGTH-DIVISION-MULTIPLEXING (WDM) packet networks based on fast Ethernet are becoming an ideal candidate for the deployment of access networks [1]. Integrating Ethernet interfaces with optical label-switching mechanisms can lead to all-Ethernet packet-based architectures with low packet latency and transparent switching. In such WDM packet-based access networks, the nodes should be ca- pable of providing a label-switching mechanism for identifying packet transmissions within the WDM channels. There have been a few architectures and techniques targeted at providing such a capability. The HORNET architecture [2] uses a unique radio-frequency (RF) subcarrier, assigned to each wavelength to perform label switching. A dedicated wavelength is also used to carry the label of the packet in synchronized time frames to realize label switching across multiple WDM channels [3]. However, the use of RF subcarriers limits the performance due to dispersion, optical beat interference, and the scalability, as RF subcarrier label processing requires higher bandwidth optoelectronic components. The usage of a wavelength to carry the label requires frame alignment between the WDM channels at each node due to wavelength walkoffs. In this letter, we pro- pose a packet labeling technique using electronic code-division Manuscript received September 6, 2005; revised November 24, 2005. The authors are with the National ICT Australia, Victoria Research Labo- ratory, Department of Electrical and Electronic Engineering, The University of Melbourne, Victoria 3010, Australia (e-mail: nnad@ee.unimelb.edu.au; e.wong@ee.unimelb.edu.au; a.nirmalathas@ee.unimelb.edu.au). Digital Object Identifier 10.1109/LPT.2005.863996 Fig. 1. Node architecture of a packet ring network incorporating the E-CDMA packet labeling technique. multiple-access (E-CDMA) that is capable of being digitally implemented [4]. In this work, we consider a WDM packet ring network employing the E-CDMA packet labeling technique. Fig. 1 shows the architecture of a node in such a network which uses fixed wavelength receivers and tunable wavelength transmit- ters. However, node configuarations such as fixed wavelength transmitters and tunable wavelength receivers can also be implemented. Each wavelength in the network is assigned a unique electronic code ( ), allowing the wavelength to be identified anywhere in its path by its predefined electronic code. If a node decides to send a packet to another node, the header ( ) of the packet is multiplexed with the predefined code and the resulting direct sequence spread spectrum CDMA signal, which is defined as the E-CDMA label, is modulated onto an RF carrier frequency ( ). The baseband payload data of the packet is then multiplexed with the RF up-converted E-CDMA label such that both payload and label are transmitted simultaneously in the same timeslot such that the modulation depth is shared between these signals. As each wavelength uses a separate code, the RF carrier ( ) used by all nodes is common to all wavelengths. Therefore, the scalability of the network is not limited by the RF bandwidth. For a packet insertion at a node, a small percentage of optical power may be tapped off and all WDM channels are detected using a single photodetector (PD). The tapped power percentage relies on the modulation depth of the E-CDMA signal. The inset of Fig. 1 shows the expected RF spectrum of the detected signal containing the overlapped baseband payload data and multiple E-CDMA labels at from all WDM channels. The 1041-1135/$20.00 © 2006 IEEE