Long-reach passive optical networks.
详细信息
文摘
With the advances in optical technology, the span of a broadband access network using Passive Optical Network PON) technology can be increased from todays standard of 20 km to 100 km or higher. Such an extended-reach PON is known as Long-Reach PON LR-PON). This technology can enable broadband access for a large number of customers in the access/metro area, while decreasing capital and operational expenditures for the network operator. Therefore, it is very desirable to comprehensively investigate this technology for future broadband access. This dissertation is dedicated to the research of architecture, management, and reliability of LR-PON. This dissertation first reviews the evolutionary path of access networks and shows the drivers from technology and business perspectives for high bandwidth and low cost. A variety of research challenges in this field is reviewed, from optical components in the physical layer to the control and management issues in the upper layers. We discuss the requisites for optical sources, optical amplifiers, and optical receivers in optical access networks with high transmission rate 10 Gbps) and large power attenuation due to large split, transmission over 100 km and beyond, and propagation). We analyze the key topological structures to guarantee physical protection e.g., tree-and-branch, ring-and-spur). Then, some relevant demonstrations of Long-Reach optical access networks developed worldwide by different research institutes are presented. A major challenge in LR-PON is that the propagation delay for data as well as control signals) between the telecom central office CO) and the end user is increased by a very significant amount. Now, traditional PON algorithms for scheduling the upstream transmission, such as dynamic bandwidth allocation DBA) algorithms, may not be sufficient； actually, they may lead to degraded performance because of the long delay of the CO-to-Users "control loop". This challenge motivates us to propose and study a multi-thread polling algorithm to effectively and fairly distribute the upstream bandwidth dynamically. This algorithm exploits the benefits of having multiple polling processes running simultaneously and enabling users to send bandwidth requests before receiving acknowledgement from the CO. We compare the proposed algorithm with traditional DBA, and show its advantage on average packet delay. With the increased bandwidth requests from the expanding base of users, LR-PON should utilize the network resource e.g., wavelengths, lasers, etc.) more effectively. We propose a new and efficient protocol to achieve better utilization of tunable lasers, as well as wavelength resources across different user groups in LR-PON. In order to accommodate downstream bursty traffic and provide Quality of Service QoS) in the user-specified Service-Level Agreements SLA), the protocol integrates our proposed SLA-aware bandwidth allocation scheme based on flow scheduling. We show the protocols advantage to support incremental upgrade of bandwidth with increasing user bandwidth requests, and to provide a user with a SLA which guarantees a number of streaming flows with average bandwidth and maximum delay guarantee e.g., 5 ms), as well as data flows with average bandwidth specifications. Since LR-PON serves a lot more users, a network failure may lead to a huge amount of data loss and negative user experience. Thus, to understand the importance of LR-PON survivability, we propose hardware-accelerated protection schemes for the LR-PON, incorporating the "ring-and-spur" structure to achieve fast protection-switching time, and automatic failure location at the Optical Line Terminal OLT), which is located at the head end of the optical access network. We design the protection schemes for multiple network environments, e.g., unidirectional transmission vs. bidirectional transmission, and 1＋1 protection vs. 1:1 protection. The numerical examples demonstrate that protection paths can be established within a few tens of ms after a failure occurs. This dissertation makes important contributions by studying novel architectures, protocols, and algorithms of LR-PON that will help to improve the next-generation telecom access networks.