| In recent years, communication techniques have been gaining the significant progress, while the emerging services such as cloud computing, mobile Internet and big data applications are flourishing. The prosperity of both communication techniques and emerging services encourages the advance of backbone transport networks towards larger capacity and higher data rate. However, as the bridge between local subscriber networks and backbone transport networks, access networks advances in a comparatively slow pace and it is becoming the bottleneck of last mile on the information highway. The optical access network such as Passive Optical Network (PON) gains advantages in providing large bandwidth capacity. However, it requires huge cost for network deployment and fails to support the ubiquitous access with more flexibility. The wireless access network such as WiMax and WiFi gains popularity due to its cost-efficiency and it can facilitate users with the functionality of mobile roaming. However, due to the limited spectrum resource, wireless access network discourages users from the large bandwidth capacity. Both the expansion of various services and the surge of innovative techniques promote the evolution of next generation broadband access networks. In view of the complementary features of wireless and optical access techniques, the converged Fiber-Wireless (FiWi) access network has been proposed academically and attracted many attentions.Survivability refers to the ability of network in maintaining service continuity in case of the unexpected failure. The frequent occurrence of nature disasters worldwide imposes severe challenges on the planning of survivable network and disaster-resilient communication infrastructures. The network component failure not only leads to the huge economical loss but also restricts the efficiency of disaster rescue. How to enhance the network disaster-resilience and guarantee the service continuity has become one of the focuses in the academic and industrial communities. As one of the promising broadband access technologies, Fiber-Wireless (FiWi) access network integrates the technological merits of larger bandwidth capacity and better reliability from optical access network with that of lower deployment cost and better flexibility from wireless access network. More importantly, the ability of traffic switching inherent in FiWi access network provides the research opportunity for the design of next generation survivable access networks. Therefore, the research of protection mechanism in survivable FiWi access network takes theoretical and realistic significance for the development of next-generation disaster-resilient communication infrastructures.This dissertation focuses on the research of protection mechanisms in survivable FiWi access network. Combining with the typical features of FiWi access network such as the topological complexity, variety of failures and heterogeneity of network resource, we are engaged in studying the protection mechanisms against intra-segment failure, single segment failure, multiple segments failures and the protection mechanism with connection availability, respectively. The main issues in most related works can be generalized as follows:1) the optimization scope in the protection against intra-segment failure is limited; 2) the network resource in the protection against single segment failure is underutilized; 3) the principles and approaches in the protection against multiple segments failures need to be explored; and 4) the protection with connection availability remains less touched. Motivated by these issues, the works of this dissertation are located at the frontier of next generation survivable broadband access networks. Following the trends of fiber-wireless convergence, author first analyzes the technical challenges and penetrates the essence of problems, then proposes a series of novel solution principles and implementation approaches, aiming to provide the necessary theoretical guidelines and technological references for the development of survivable FiWi access network in future.(1) Protection mechanism against intra-segment failureThe wireless rerouting approach is employed in some of the related works for the protection against single distribution-fiber link failure or Optical Network Unit (ONU) failure. This approach does not need the deployment of additional fiber links for traffic recovery and thus gains the remarkable advantages in cost-efficiency. Particularly, the wireless rerouting approach is applicable to the scenarios of lower traffic demand which is not sensitive to the traffic recovery delay. However, the previous works focus major attentions on the design of survivable routing and remain less touched on the planning of survivable FiWi access network. Network planning is the premise and foundation to support the highly efficient operation and maintenance of FiWi access network. Particularly, it is of great significance for FiWi access network in survivability guarantee. Therefore, author proposes a protection mechanism called WRBR (Wireless Rerouting with Backup Radios) against single distribution-fiber link failure. With the objective of minimizing network deployment cost, author puts more importance on the joint optimization of wireless routers placement and backup radios configuration. The constraints are introduced on the length of backup wireless path, backup ONU capacity and backup radio capacity. Compared to the traditional fiber duplication approach, the WRBR mechanism can significantly reduce the network deployment cost.In the scenario of large-scale traffic transferring, the wireless rerouting approach usually suffers from the heavy bandwidth pressure, and it may not satisfy the bandwidth requirement and the constraint of recovery time. In comparison, the backup fiber approach can provide the abundant bandwidth resource and fast protection switching, thus it is a preferable solution for the survivability issue of FiWi access network with large-scale traffic. Therefore, author is motivated to investigate the approach of backup fiber against single distribution-fiber link failure, and analyze theoretically the tradeoff between deployment cost of backup fibers and traffic recovery time. A protection mechanism called CNT (Continuous Neighbor Transferring) is further proposed. In the CNT mechanism, each single-hop backup ONU can reserve more bandwidth capacity to carry the traffic from the failed ONUs by transferring the traffic continuously between the neighboring ONUs. Thus, the bandwidth capacity of single-hop ONU is utilized more efficiently, which contributes to the saving of backup fibers.To tolerate the simultaneous failures of multiple distribution-fiber links, which is a more severe failure scenario, author proposes a protection mechanism with backup fibers against single Shared-Risk-Link-Group (SRLG) failure. A reliability estimation model is structured mathematically based on SRLG configuration. The optimal solution for joint backup capacity allocation and backup fibers deployment is obtained by Integer Linear Programming (ILP). The heuristics are also proposed to obtain the near-optimal solution for large-scale network.(2) Protection mechanism against single segment failureAs mentioned above, the protection approach of wireless rerouting gains the advantage of cost-efficiency in tolerating the single segment failure. However, in the scenario of segment failure caused by feeder fiber cut, it is not feasible to transfer traffic between different segments by wireless rerouting. On one hand, different segments may be so far away from each other that no available wireless paths exist between them. On the other hand, it will spend a plenty of recovery time to transfer the traffic of the whole segment by using the bandwidth-limited wireless channel. Motivated by these considerations, author proposes a protection mechanism that is implemented by first selecting backup ONU in each segment and then deploying backup fibers between different segments. The strategy of remote backup ONU is proposed to improve the utilization of backup fibers. According to this strategy, the failed segment is allowed to transfer its traffic into not only the one-hop neighbor segments, but also the remote segments that are more than one hop far away. Therefore, the deployment cost of backup fibers is reduced significantly by improving the utilization of backup fibers.According to the approach mentioned above, the delay-sensitive service usually suffers from the loss of traffic recovery efficiency due to the long-distance and multi-hop transmission of optical path. In order to limit the loss of traffic recovery efficiency, author proposes a protection mechanism with backup optical ring. According to the proposed mechanism, all segments are divided into multiple clusters and the backup optical ring is established by deploying backup fibers in each cluster, such that each pair of segments in the same cluster have two backup optical paths with the reverse direction. When any segment fails, the failed segment can transfer its traffic into the normal backup segments along the two backup optical paths simultaneously, thus the recovery delay caused by traffic transferring can be reduced efficiently.(3) Protection mechanism against multiple segments failuresIn the multi-segment FiWi access network, different segments may have the feeder fibers in the same cable or tunnel in order to mitigate the construction difficulty or the geographical limitation. However, this also leads to the potential risk that different segments fail simultaneously. Particularly, in the scenario of large-scale disaster or concurrent failures, the simultaneous failures of different segments may bring about the worse results such as huge data loss or massive traffic interruption. Therefore, the multi-segment failure should not be ignored in the survivable planning. However, the protection against the simultaneous failures of multiple segments remains less touched in previous works. Because the protection against multi-segment failure usually requests the guarantees of stronger survivability and larger bandwidth capacity, the traditional protection approaches against intra-segment failure or single segment failure cannot be directly applied to tolerate the multi-segment failure. Furthermore, massive traffic transfer and connections recovery inevitably increase the overhead of network management.Due to the considerations above, author first proposes the cluster-based protection mechanism. In case of the simultaneous failures of any X segments, the overhead for traffic recovery is held down by dividing the segments in the network into several clusters. ILP is employed to formulate mathematically the joint optimization problem of backup ONUs selection, segments clustering and backup fibers deployment. The objective is to minimize the deployment cost of backup fibers, while satisfying the typical constraints such as maximum number of segments per cluster, full protection of traffic, maximum length of backup optical path. The optimal solution for small-scale network scenario is obtained by solving the ILP. The heuristic algorithms are also proposed to support the application of our protection mechanism in large-scale network and it is demonstrated to be near-optimal.Considering the dependency of SRLG failures between different segments, author also proposes the failure-dependency based protection to tolerate the SRLG failure. The emphasis of the proposed protection mechanism is to solve the joint optimization problem of backup capacity allocation and backup fibers deployment. ILP is employed to mathematically formulate this optimization problem under the constraint of failure dependency. Author also proposes the heuristic algorithms for purpose of the large-scale network application where the segments are densely distributed and heavily loaded. In the proposed heuristic algorithms, the greedy strategy is employed in the network resource allocation. Each unit of backup capacity and backup fiber is expected to protect the traffic demand as much as possible. The proposed heuristic algorithm is demonstrated to be efficient in producing the near-optimal solution.(4) Protection mechanism with connection availabilityThe existing works of survivable FiWi access network focus attentions on the issues of routing algorithms and network planning, etc, while the quantitative estimation of survivability remains to be a topic less touched. As a result, these protection mechanisms are usually implemented without the reference of precise survivability and provide only the qualitative survivability guarantee in a broad sense. As a result, the resource allocation is usually implemented roughly, thus the resource utilization and network scalability is weakened.The preliminary goal of FiWi access network is to support the ubiquitous broadband access of diverse user-ends. Various services usually have the different connection availability requirements in case of network component failure. How to differentiate the service types from the viewpoint of survivability level and then allocate the resource on demand is one of the key issues to enhance the capability of network in service provisioning. Therefore, the quantitative estimation of survivability has become one of the urgent needs for the advance of FiWi access network, which dominates the efficiency of resource allocation with much realistic significance.Motivated by the considerations above, author proposes the effective connection availability models for wireless rerouting protection and backup fiber protection respectively, which are two typical approaches for survivable FiWi access network. The effect of fiber link failure and resource contention on connection availability is considered sufficiently. A protection mechanism based on wireless rerouting is first proposed by introducing the connection availability requirement into the joint allocation of ONU capacity and radio capacity. Under the constraint of connection availability, our objective is to minimize the consumption of backup resource by optimizing the joint allocation of ONU capacity and radio capacity. Then, another protection mechanism based on backup fibers is proposed by considering the connection availability requirement into the deployment of backup fibers. The focus of this proposed protection mechanism is to establish the backup optical path by allocating backup capacity and deploying backup fibers. Thus, the joint optimization problem of backup capacity allocation and backup fibers deployment remains to be solved, while the connection availability requirement should be satisfied.FiWi access network still exists as a theoretical concept so far, and its protocol stack and technological hierarchy have not yet been completed. Most of the professional network simulation softwares such as OPNET and QualNet do not provide the necessary modules for FiWi access network. Thus, VC++6.0 is employed to establish and customize the simulation platform to evaluate and analyze the performance of the proposed mechanisms. The simulation is implemented on the PC with Intel Core i5 2.30 GHz CPU,2GB RAM, and Windows 7 operation system. Simulation results show that the proposed protection mechanisms in this dissertation gain significant advantages in reducing network deployment cost, improving resource utilization and saving bandwidth capacity.
|
PDF Full Text Request