Improving the Upstream Channel Efficiency of Passive Optical Networks via Frame Aggregation and Compression João M. L. Santos †,¥,a , Pedro R. M. Inácio †,§,b , João V. P. Gomes †,§,c , Artur Arsénio †, ξ , João J. O. Pires ¥ , Mário M. Freire § , Paulo P. Monteiro †, £ † Nokia Siemens Networks Portugal S.A., Rua Irmãos Siemens, 2720-093 Amadora, Portugal ¥ Instituto de Telecomunicações, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal ξ Departamento de Engenharia Informática, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal § IT-Grupo de Redes e Multimédia, Departamento de Informática, Universidade da Beira Interior, Rua Marquês de Ávila e Bolama, 6201-001 Covilhã, Portugal £ Instituto de Telecomunicações, Universidade de Aveiro, 3810-193 Aveiro, Portugal e-mail (corresponding authors): a joao.santos@nsn.com, b pedro.inacio@nsn.com, c jgomes@penhas.di.ubi.pt Abstract 1 — The transmission medium connecting the Optical Line Terminal (OLT) to Passive Splitter Combiners (PSCs), in Passive Optical Networks (PONs) is shared by all Optical Network Units (ONUs). Therefore, each ONU has to store the data coming from the users, prior to sending it upstream, according to a time division multiple access policy. In this paper, the authors propose using the waiting periods in each ONU to aggregate and compress the Ethernet frames into composite data structures. It is shown that the method described here can significantly improve the efficiency of the upstream channel. I. INTRODUCTION The increasing end-user traffic demand is driving operators and service providers to boost the bandwidth capacity of the underlying access network infrastructure. The solution envisioned to mitigate the physical limitations in currently deployed copper and coaxial-based access networks is to extend the optical fiber communication closer to the customer premises. Following this strategy, Passive Optical Networks (PONs) are seen as the most promising technology to cost-effectively explore the fiber potential and deliver high-bandwidth volumes. This work proposes an innovative encapsulation mechanism for PON systems considering the following: 1) Typical PON infrastructures assume a tree-shaped configuration shared by a group of Optical Network Terminals (ONUs). To avoid unwanted signal collision and data losses, each ONU requests an upstream slot for transmission to the central office, known as Optical Line Terminal (OLT). The data is thus stored in the ONU for an undetermined (yet limited) amount of time, before the latter receives the transmission authorization. The authors would like to acknowledge financial support from Fundação para a Ciência e Tecnologia (grant contracts SFRH/BDE/15643/2006, SFRH/BDE/15592/2006 and SFRH/BDE/15652/2007) and from Nokia Siemens Networks Portugal S.A. Part of this work is matter of the international patent application entitled “Upstream Efficiency Improvement Method for Passive Optical Networks”. 2) Due to the Ethernet equipment ubiquity in the Local Area Network (LAN), the majority of the upstream traffic is framed using the Ethernet protocol. Since only a fraction of the overall PON bandwidth is assigned to each ONU, the number of users it supports is limited. It is thus expected that a greater share of the traffic sent upwards will contain similar (or even identical) Ethernet frame header information, such as destination and source Medium Access Control (MAC) addresses, Logical Link Identifiers (LLDIs), etc. In order to increase the upstream channel efficiency without affecting the system performance, a frame aggregation and compression mechanism, herein called Composite Frame Format (CFF), is proposed. This method explores the ONU waiting time mentioned in 1) and the Ethernet frame header redundancy referred in 2) to provide considerable bandwidth savings, resulting in higher bit rates per user, or enabling the support of additional ONUs (customers), with the same number of devices, and at the cost of a minor computational effort. This paper is structured as follows. Section II introduces the Composite Frame Format, describes the frame construction / deconstruction and compression procedures. Section III presents important and relevant results, obtained via computer simulation, and section IV concludes the manuscript. II. COMPOSITE FRAMING IN PONS A. EPON and GPON Standard Frame Formats The PON market is currently dominated by two technologies: Ethernet PON (EPON) and Gigabit PON (GPON). In face of the broad adoption of Ethernet in the customer premises, EPON was intentionally designed to support native Ethernet frames over the optical interface [1]. As depicted in Fig. 1(b), only the LLID information, used to identify the source / destination ONU, is added by the EPON to the standard Ethernet frame. However, the Ethernet framing protocol is known to suffer from high overhead, which can consume up to 9% of the total amount of information transmitted in the EPON [2]. To reduce the