Efficient protection schemes for hybrid WDM/TDM passive optical networks

Hybrid WDM/TDM Passive Optical Network (PON) is a promising candidate for next-generation optical access (NGOA) solutions as it is able to offer a high splitting ratio and consequently achieves a relatively low cost and power consumption on a per-user basis compared with other NGOA architectures. On the other hand, the end users require a certain level of connection availability while the operators need to reduce the failure impact (i.e. to avoid a huge number of end users being affected by any single failure). Therefore, by evaluating the connection availability and failure impact robustness we identify the most efficient parts to provide resilience in a hybrid WDM/TDM PON from an operator and an end-user perspective. Then, we select the appropriate protection schemes to construct some novel reliable architectures and analyze their reliability performance in urban and rural scenarios. In this way, this paper provides a comprehensive insight into the most relevant protection mechanisms for hybrid WDM/TDM PONs

Protection strategies for next generation passive optical networks -2

Next Generation Passive Optical Networks-2 (NGPON2) are being considered to upgrade the current PON technology to meet the ever increasing bandwidth requirements of the end users while optimizing the network operators' investment. Reliability performance of NG-PON2 is very important due to the extended reach and, consequently, large number of served customers per PON segment. On the other hand, the use of more complex and hence more failure prone components than in the current PON systems may degrade reliability performance of the network. Thus designing reliable NG-PON2 architectures is of a paramount importance. Moreover, for appropriately evaluating network reliability performance, new models are required. For example, the commonly used reliability parameter, i.e., connection availability, defined as the percentage of time for which a connection remains operable, doesn't reflect the network wide reliability performance. The network operators are often more concerned about a single failure affecting a large number of customers than many uncorrelated failures disconnecting fewer customers while leading to the same average failure time. With this view, we introduce a new parameter for reliability performance evaluation, referred to as the failure impact. In this paper, we propose several reliable architectures for two important NGPON2 candidates: wavelength division multiplexed (WDM) PON and time and wavelength division multiplexed (TWDM) PON. Furthermore, we evaluate protection coverage, availability, failure impact and cost of the proposed schemes in order to identify the most efficient protection architecture

Trade-off between end-to-end reliable and cost-effective TDMA/WDM passive optical networks

Hybrid TDMA/VVDM (TWDM) Passive Optical Network (PON) is a promising candidate for Next-Generation PON (NG-PON) solutions. We propose end-to end reliable architectures for business users and a cost-effective network for residential users. We evaluate the proposed reliable architectures in terms of protection coverage, connection availability, impact of failure (i.e. to avoid a huge number of end users being affected by any single failure) and cost in different populated scenarios

Toward reliable hybrid WDM/TDM passive optical networks

Individual users and enterprises are increasingly relying on the access to internet services and cannot accept long interruption time as easily as before. Moreover, the main characteristics of next generation optical access (NGOA) networks, such as long reach and a large number of users per feeder line, turn the network reliability to an important design parameter to offer uninterrupted service delivery. In this regard, protection mechanisms become one of the crucial aspects that need to be considered in the design process of access networks. On the other hand, it should be noted that not all users can afford to pay a high extra cost for protection; hence, it is important to provide resilience in a cost-efficient way. A PON combining WDM and TDM technologies, referred to as hybrid WDM/TDM PON or HPON, is one of the most promising candidates for NGOA networks due to its ability to serve a large number of subscribers and offer high capacity per user. For these reasons, in this article, we propose HPON architecture offering different degrees of resilience depending on the user profiles (i.e., partial and full protection for residential and business access, respectively). Also, the investment cost of providing resilience for the proposed schemes is investigated considering various protection upgrade road maps. Our results confirm that protecting the shared part of network with a large number of users is required in order to keep the failure impact at an acceptable level, with less than 5 percent increase of investment cost compared to the unprotected case. Meanwhile, the proposed end-to-end protection for business users considerably reduces the risk of service interruption for this type of demanding user without a need to duplicate the deployment cost of an unprotected connection. Furthermore, a sensitivity analysis is performed to investigate the impact of changes in business user percentage and protection upgrade time on the deployment cost. The results may be used as advice on cost-efficient deployment of reliable fiber access networks

Monitoring of passive optical networks utilising an optical coding technique

Passive Optical Networks (PONs) have become the most popular fibre based access networks over the last decade. They are widely deployed for use in Fibre-to-the-Premises (FTTP) scenarios. PON is a point-to-multipoint connection (P2MP) between an optical line terminal (OLT) located at the central office (CO) and multiple optical network units (ONU) at the customer premises. The next generation of PONs (NG-PON) are likely to deploy a ring-and-spur long reach PON (LR-PON). NG-PON aims to accommodate more ONUs, extend the network coverage out to 100 km, minimize complexity and improve operational outcomes. An all fibre access network, operating over extended distances, presents a reliability risk, thereby increasing the need for a reliable and cost-effective monitoring system to enhance protection and reduce restoration time. Among existing monitoring techniques, attention is focused on approaches that use optical code division multiplexing (OCDM), also known as optical coding (OC). The OC is applied to a signal that is sent from the network management system (NMS) to the ONUs. The monitoring signal is transmitted onto a fibre and split into a number of sub-signals that are equal in number to the ONUs. Each one of the ONUs receives a sub-signal, encodes it, and then reflects it back to the NMS. The NMS has the capability to identify faulty ONUs by examining the code received from the ONUs. A review of the literature has shown that the use of OCs does improve system performance, especially in the timely detection of faults. Many of the studies, found in the literature, focus on how to implement optical spreading codes that are used in OCDM Access (OCDMA) systems and currently the optical orthogonal code (OOC) is the dominant code implemented for time-domain coding. Although the OOC code performs well, its construction is relatively complex. The available code-words (cardinality) that are offered by OOC are proportional to the code length. Implementing OOC in a high capacity PON requires a long code length causes an inevitable degradation of system performance. Therefore, an improved optical coding technique for PONs should provide code-words that conform to PON split ratios. The main objective of the research was to develop an optical spreading code, based on a prime code family for OCDMA systems, that has the capability to accommodate different PON split ratios and with characteristics that improve transmission system performance when compared to existing prime code families. The novel code presented in this thesis is identified as the extended grouped new modified prime code (EG-nMPC). The number of code-words generated by the proposed codes are substantially higher than those generated by the existing code families and more compatible to the different PON splitting ratios. In addition, with a low code weight, both power consumption and hardware complexity decreases. The code performance was evaluated using mathematical models for two transmission formats - pulse position modulation (PPM) and on-off keying (OOK) modulation. The performance of EG-nMPC was compared to other prime codes, and the results show that the proposed code improves the performance of OCDMA in terms of bit-error rate (BER). As PON is a point-to-multipoint connection oriented access network, downstream traffic is encrypted and broadcast to all ONUs, while the unencrypted upstream traffic from each ONU terminal occurs in a burst mode. The OLT carries out a ranging process to determine transmission delays between ONUs, to prevent collisions between the burst mode traffic from each of the ONUs. In this research, the burst mode traffic ranging process has been replicated in the monitoring system, with this replication providing a fixed equalization delay time for the monitoring transmissions. To investigate the ring-and-spur LR-PON reliability several protection architectures were evaluated, in term of cost and availability, to determine the optimal protection architecture. In this thesis, the reliability parameter Failure Impact Robustness (FIR), has been used to calculate the failure impact of the different components in ring-and-spur LR-PON, hence selecting the optimal protection scheme. A PON-based optical communication system model was developed and the proposed EG-nMPC code was incorporated. Fibre split ratios of 32, 64 and 128, were considered in this study. The simulation results show that the EG-nMPC code improves the performance, efficiency and accuracy of the PON transmission monitoring system. To conclude, this research aims to enhance the PON performance by a fast detection of the fault and quick restoration. This research has contributed to knowledge by identifying a new and novel spreading code that is compatible with the different PON splitting ratios for OC monitoring techniques. By using the ranging process, a fixed equalization delay time has been assigned to each ONU to manage the upstream burst traffic. The spreading code has been implemented in a real-time simulation to show the status of each fibre link. The implementation was carried out based on 1-D tree topology system. However, the proposed EG-nMPC can be exploited to enable network monitoring that is based on hybrid 1D/2D coding. This coding is complementary with the structure of LR-PON as explained in section ‎8.2.3. In addition, with the use of the FIR parameter for the different components in the ring-and-spur architecture, an optimal protection scheme for both OLT and the ring (feeder fibre), has been nominated. This protection scheme ensures that protection, availability and cost are at their optimal values