Ge Fan

GMPLS-based passive optical network

The significance of Generalized Multi-protocol Label Switching (GMPLS) has been proven by its significant adoption in ASON. In recent years GMPLS has become the most global solution to provide intelligent optical resource configuration through not only devices that perform packet switching, but also devices that perform switching in the time, wavelength, and space domain. This new technology can be used to support services for applications that requiring high QoS performances in any network which using the Internet Protocol (IP), including the Passive Optical Network (PON). In this paper, we will propose a new PON technology that uses GMPLS as layer2 protocol. The focus of this paper is mainly on the issues and key characters that will encounter in the combination of GMPLS technology and PON technology. Compared to other PON technologies, such as APON and EPON, GMPLS-based PON (GMPLS PON) can provide more powerful and efficient service in access network, and it can also provide better QoS support to the video and audio applications. The most significant is GMPLS PON can also provide common control and data and administrative planes between the backbone network and the access network, so it will be more convenient and efficient to operate and manage.

On design of physical and logical topologies with fault-tolerant ability in wavelength-routed optical networks

We consider the problem of designing a network consisting of optical cross connects (OXCs) to provide end-to-end lightpath services for label switched routers (LSRs). Unlike previous work, we take into account the fault-tolerant ability of both physical and logical topologies. In addition, we present a novel routing policy that combines the shortest-path principle and the minimal-congestion rule. At the same time, we employ different wavelength assignment strategies for working lightpaths and protection lightpaths. We adopt the tabu search algorithm to find out the near optimal solution. Then we explore the lower bounds for the number of OXCs. We present numerical results for up to 1000 LSRs and for a wide range of system parameters, such as the number of wavelengths supported by each fiber link and traffic. The results indicate that it is possible to build a large-scale optical network with rich connectivity in a cost-effective manner, requiring relatively few, but properly dimensioned, OXCs.

Design of physical and logical topologies with fault-tolerant ability in wavelength-routed optical network

In this paper we consider the problem of designing a network of optical cross-connects(OXCs) to provide end-to-end lightpath services to label switched routers (LSRs). Like some previous work, we select the number of OXCs as our objective. Compared with the previous studies, we take into account the fault-tolerant characteristic of logical topology. First of all, using a Prufer number randomly generated, we generate a tree. By adding some edges to the tree, we can obtain a physical topology which consists of a certain number of OXCs and fiber links connecting OXCs. It is notable that we for the first time limit the number of layers of the tree produced according to the method mentioned above. Then we design the logical topologies based on the physical topologies mentioned above. In principle, we will select the shortest path in addition to some consideration on the load balancing of links and the limitation owing to the SRLG. Notably, we implement the routing algorithm for the nodes in increasing order of the degree of the nodes. With regarding to the problem of the wavelength assignment, we adopt the heuristic algorithm of the graph coloring commonly used. It is clear our problem is computationally intractable especially when the scale of the network is large. We adopt the taboo search algorithm to find the near optimal solution to our objective. We present numerical results for up to 1000 LSRs and for a wide range of system parameters such as the number of wavelengths supported by each fiber link and traffic. The results indicate that it is possible to build large-scale optical networks with rich connectivity in a cost-effective manner, using relatively few but properly dimensioned OXCs.

Reconfiguration of virtual topology on wavelength-routed optical ring networks with dynamic traffic

In this paper we consider the problem of reconfiguration of virtual topology on wavelength-routed optical ring networks with dynamic changes in traffic. Unlike previous studies on this problem, we select the traffic needing rerouting and the most congested link load as our objectives. In addition, we consider the traffic with both rapid and slow changes. When the traffic changes slowly, we will select the routing strategy based on the shortest path, taking into account the cost caused by the reconfiguration and choose a heuristic similar to generalized least processing time (GLPT) as the wavelength assignment algorithm. Our consideration does make sense in that the strategies mentioned above enable the virtual topology to be updated to follow the change in traffic closely, while considering some certain cost of the reconfiguration. On the other hand, if the traffic changes dramatically, we choose the strategy of adding lightpaths or deleting lightpaths(LAD). It is clear that this strategy will result in a smaller change in the virtual topology. This implies the reconfiguration will lead to a lower cost. Numerical results show that our approach outperforms the previous ones and that we can set up a network with no change in our physical topology, which can sustain various patterns of traffic.

Efficient scheduling algorithm for hybrid WDM/TDM optical passive optical networks

In this paper a novel hybrid WDM/TDM optical access network architecture and its media access control (MAC) alogrithm is proposed. Extensive simulations are conducted and the results show that the algorithm can provide determinate delay bound for each flow, possesses throughput fairness and decreases the packet delay of low priority flow.

Design of physical topologies in survivable WDM optical networks

In the physical topology design, the number of OXCs and/or links is takes as the objective. In this paper, we take aim at minimizing the maximal optical port number of each OXC, given the number of OXCs and the traffic. We present a traffic-oriented heuristic algorithm to generate an initial topology. This presented algorithm outperforms the previous algorithm, since our presented algorithm takes into account the traffic pattern. Furthermore, we present a routing strategy that is a balance between the shortest-path routing and the least-congestion routing. The tabu algorithm is adopted to attain the optimal solution. We choose the path-based sharing protection scheme to provide 100% recovery guarantee. Numerical results demonstrate the effectiveness of our algorithm and strategy.

A fast failures locating scheme for multilayer restoration in ASON

How to assemble different restoration scheme in multi-layer networks effectively is a sticking point to survivability of ASON. Among kinds of multi-layer restoration problems, failures locating is the primary one to be solved. Therefore, fast failures locating scheme is proposed in this paper. The main idea of this restoration scheme is that optical layer communicated with control layer dynamically and the restoration process of optical layer and control layer is mutually exclusive. When a new link is established in control layer, the optical layer’s nodes whose related links is used by this new link will recode the two neighbor nodes of this new link. This information is updated online. Thus, when optical layer find failure, the related nodes can transfer the failure message to the corresponding nodes on control layer immediately. Time parameter was set to start different restoration in different layer of networks. Thus, responsibility of optical layer and control layer is clear. Confusion that may be caused by multi-layer restoration was settled.

Linearization calculation of bit-error rates in optical transmission systems

We present novel linearization methods for both of single pulse system and single-channel chirped return-to-zero (CRZ) system with the linearization assumption. Both of them show that the Gaussian fit is a good approximation over about two orders of magnitude, but deviate strongly at low probability densities. Linearization allows us to efficiently and accurately compute eye diagrams and bit error rates (BERs) without the use of Monte-Carlo simulations and allows us to greatly increase the accuracy at small BERs at a fraction of the computational cost. We compare these results to the standard Monte-Carlo simulation technique and find that they are agreed very well.

Virtual nodes scheme for survivable optical mesh networks

The progress of the mesh networks technology makes optical networks more complex. An adverse result is the increased network vulnerability. It’s difficult for current methods of centralized restoration to deal with the problem mentioned above. A novel survival scheme, virtual nodes scheme, is proposed in this paper. The character of network topology is considered as an important factor in this scheme. The major idea of this scheme is dividing network into some subnets, which are named as virtual nodes, and different survival approaches are adopted within each virtual node and among virtual nodes. Each virtual node not only can dispose the interior failures independently, but also can settle faults collaborating with other virtual nodes. Compared with current survival schemes, which regard each node or link as a manageable object, virtual nodes scheme take each virtual node as a manageable object. Virtual nodes scheme can find failures and restore rapidly. In addition, utilization of capacity is optimized within each virtual node. Therefore, total capacity of network is distributed efficiently. Realization of virtual nodes scheme is explained in this paper. Through theoretical analysis and computer simulation, the performance of this new scheme is demonstrated.

EPON upstream traffic modeling with β-cascades process

The conservative cascades process with multipliers generated by symmetric β distribution is introduced as an EPON upstream traffic model, which can catch the amplitude burst and temporal burst behaviors of real traffic simultaneously. The traffic matching and synthesizing methods are illustrated through an example.