Rongping Lin

Design of WDM Networks With Multicast Traffic Grooming

With the growing popularity of multicast applications and the recognition of the potential of achievable efficiency gain of traffic grooming, we face the challenge of optimizing the design of WDM networks with multicast traffic grooming. As higher layer electronic ports become the dominant factor of the WDM network cost, it is critical to reduce their number when grooming multicast traffic into high bandwidth light-trees. This paper provides an optimal cost design of WDM networks with multicast traffic grooming. In particular, a light-tree based Integer Linear Programming (ILP) formulation is proposed to minimize the network cost associated with the number of higher layer electronic ports and the number of wavelengths used. Since solving the ILP formulation is time consuming for large networks, we propose a heuristic algorithm, called sub-light-tree saturated grooming (SLTSG), to achieve scalability. This algorithm tries to construct sub-light-trees which can be fully utilized. Simulations are conducted on several networks to compare the design cost and the required number of electronic ports and wavelengths. The results demonstrate significant benefits of using a light-tree based design over a design that only uses lightpaths.

A New Network Availability Algorithm for WDM Optical Networks

As the need of network users for high-availability increase, how to evaluate the network availability justly becomes an on edge problem. Under the dynamic connections, a new network availability algorithm (NAA), which considers the high network performance, for WDM optical networks is proposed. It is practically to the users and operators of the network. Simulation results show that NAA not only is correct but also is efficient

Multicast traffic grooming in tap-and-continue WDM mesh networks

Multicast applications are expected to be major drivers of Internet traffic growth. As most multicast connections require much lower bandwidth than the capacity offered by a wavelength, multicast traffic grooming is needed to efficiently use network resources. Recent research on multicast grooming has focused on light-trees because of their natural advantage for multicast traffic. However, using light-trees may lead to some serious negative side effects because of light splitting. In this paper, we investigate the multicast traffic grooming problem in tap-and-continue (TaC) networks, where a node can tap a small amount of incoming optical power for the local station while forwarding the remainder to an output. We first propose a simple and efficient node architecture with the TaC mechanism. We use this in an integer linear programming (ILP) formulation with the objective of minimizing the network cost in terms of the number of higher layer electronic ports and the number of wavelengths used. Since the ILP is not scalable, two heuristic algorithms, multicast trail grooming (MTG) and multiple destination trail-based grooming (MDTG), are proposed. Using the ILP, we show that having more costly nodes with multicast capability does not improve the performance significantly. The solutions obtained by MTG and MDTG are close to the ILP optimal solution. MTG and MDTG are shown to work efficiently for typical network topologies such as NSFNET, with MTG showing better performance than MDTG.

Light-tree configuration for multicast traffic grooming in WDM mesh networks

Recent advances in wavelength-division multiplexing (WDM) technology will provide bandwidth intensive multicast applications with large transmit capacities. This article provides two new grooming schemes that lead to efficient resource utilization in WDM networks. They are called Light-Tree Division-Destination Branch Node-based Grooming scheme (LTD-DBNG) and Light-Tree Division-Adjacent Node Component-based Grooming scheme (LTD-ANCG). These schemes are based on the idea of dividing a light-tree into smaller sub-light-trees. They improve the efficiency of resource utilization and also lower the optical-electronic-optical conversion overhead. We use computer simulations to evaluate the performance of these schemes. Our simulations demonstrate that compared with existing algorithms, these schemes significantly reduce the request blocking probability (BP) but can be implemented with very reasonable electronic processing, with LTD-ANCG performing better than LTD-DBNG but with greater complexity. We also evaluate the BP of these schemes considering variations in the add/drop ratio and demonstrate that a proper choice of this ratio will provide target BP with low network costs.

Dynamic Sub-Light-Tree Based Traffic Grooming for Multicast in WDM Networks

This paper proposes a multicast traffic grooming scheme for efficient resource utilization in wavelength- division multiplexing (WDM) mesh networks. This Light-Tree Division -Adjacent Node Component based Grooming scheme (LTD-ANCG) is based on the idea of dividing a light-tree into smaller sub-light-trees. It improves the efficiency of resource utilization and lowers the optical- electronic-optical (OEO) conversion overhead. We use computer simulations to evaluate the performance of the scheme. Our simulations demonstrate that compared with existing algorithms, the new scheme significantly reduces the request blocking probability but can be implemented with very reasonable electronic processing.

Errata to “Multicast Routing and Distance-Adaptive Spectrum Allocation in Elastic Optical Networks With Shared Protection”

We consider an elastic all-optical network, where each node is multicast-capable and does not support spectrum conversion. In such a network, for a given set of static multicast demands, we consider distance-adaptive spectrum resource allocation, and aim to optimize multicast routing, modulation, and spectrum assignment with shared protection in a way that minimizes the required spectrum resources for accommodating all multicast sessions. In our design, we provision each multicast demand by a light-tree where spectrum resources are allocated in all links included in the tree. We protect each light-tree from any single link failure in both directions by having a backup path that is link-disjoint to the path from the source to each destination on the primary tree. We reserve spectrum resources in the links that are not in the primary tree but in the backup paths between all source-destination pairs. The reserved spectrum resources can be shared to protect multiple light-trees as long as they do not fail simultaneously. For such a problem, we provide a mixed integer linear programming formulation. We also develop a scalable heuristic algorithm with an attribute that enables it to improve the quality of the results at the cost of longer running times. Numerical results for small problems show that the heuristic algorithm performs close to the optimum. In addition, we use a Markov chain simulation of the network to evaluate the performance of our proposed algorithm in terms of blocking probability in a dynamic environment, which demonstrates a significant improvement over straightforward approaches.We consider an elastic all-optical network, where each node is multicast-capable and does not support spectrum conversion. In such a network, for a given set of static multicast demands, we consider distance-adaptive spectrum resource allocation, and aim to optimize multicast routing, modulation, and spectrum assignment with shared protection in a way that minimizes the required spectrum resources for accommodating all multicast sessions. In our design, we provision each multicast demand by a light-tree where spectrum resources are allocated in all links included in the tree. We protect each light-tree from any single link failure in both directions by having a backup path that is link-disjoint to the path from the source to each destination on the primary tree. We reserve spectrum resources in the links that are not in the primary tree but in the backup paths between all source-destination pairs. The reserved spectrum resources can be shared to protect multiple light-trees as long as they do not fail simultaneously. For such a problem, we provide a mixed integer linear programming formulation. We also develop a scalable heuristic algorithm with an attribute that enables it to improve the quality of the results at the cost of longer running times. Numerical results for small problems show that the heuristic algorithm performs close to the optimum. In addition, we use a Markov chain simulation of the network to evaluate the performance of our proposed algorithm in terms of blocking probability in a dynamic environment, which demonstrates a significant improvement over straightforward approaches.

Leaking Strategy for Multicast Traffic Grooming in WDM Mesh Networks

The ever-increasing popularity and traffic volume of multicast applications motivates the need for development of methodologies for traffic management and network design that especially cater for multicast traffic. Addressing the disparity between the bandwidth offered by a wavelength and the bandwidth required by a single connection is a key challenge in the efficient usage of any wavelength-division multiplexing (WDM) network. This problem is also relevant to WDM networks that support multicast traffic and can be mitigated by multicast traffic grooming. This paper considers multicast traffic grooming with a leaking strategy where a light-tree may deliver the traffic of a multicast connection to nodes that are not in the destination set of the connection. This leaking strategy improves the sharing of light-trees and add/drop ports, leading to lower blocking ratios. Two multicast traffic grooming algorithms with leaking strategy, namely, multicast traffic leaky grooming (MTLG), and multicast traffic hybrid grooming (MTHG) are proposed. MTLG grooms traffic to light-trees if the traffic leaked is less than a given threshold value. MTHG first grooms traffic to light-trees without leaking; if some destinations remain, it then grooms traffic to light-trees with leaking. MTHG is an improvement over MTLG as it can attain higher light-tree sharing with less traffic leaked. Simulations show that the two proposed algorithms perform better than other algorithms at low add/drop port ratios with MTHG showing better performance.

Local Fast Reroute With Flow Aggregation in Software Defined Networks

In this letter, we propose a local fast reroute (LFR) algorithm with flow aggregation in software defined networks (SDN). In LFR, if a link failure is detected, all traffic flows affected by the failure are aggregated to be a new “big” flow. Then, a local reroute path is dynamically deployed by the SDN controller for the aggregated flow. LFR reduces the number of flow operations between the SDN controller and switches. Numerical results show that the LFR enables fast recovery while minimizing the total number of flow entries in SDN.

AHTM: Achieving efficient flow table utilization in Software Defined Networks

In Software Defined Networks (SDN), more packet fields are included to design fine-grained policies. These policies are stored as entries in switch Flow Table. However, fine-grained policies cause the scalability issue as a single flow entry needs larger storage space and a significant number of flow entries need to be stored, but the Flow Table is limited due to the constraints of Ternary Content Addressable Memory (TCAM). To address this issue, we propose Adaptive Hard Timeout Method (AHTM) to improve the Flow Table utilization by optimizing the timeouts of flow entries, thus the Flow Table is reused efficiently. AHTM models the Flow Table as a queueing system and derives closed-form formulas for analysis and optimization. We also implement AHTM as a light-weighted SDN application and it offers interfaces to other applications. The simulation results show that AHTM can achieve the balance between blocking probability and extra workload to SDN controller.

TimeoutX: An Adaptive Flow Table Management Method in Software Defined Networks

In Software Defined Networks (SDN), applications on the controller could enforce fine-grained control on flows by policies employing more packet fields. These policies are converted to flow entries and stored in switch Flow Table. To store these entries, Flow Table requires large storage space because an entry consisted of more packet fields needs more storage space and the number of entries also increases significantly due to fine-granularity definition of flows. However, Flow Table has limited storage space owing to the constraints of Ternary Content Addressable Memory (TCAM). As a result, the switch Flow Table in SDN faces scalability issue. We address this issue by means of adaptive Flow Table management, namely we manage how long the entries occupy the storage space by setting adaptive timeouts to them. Through this means, the storage space could be reused efficiently and more flows could be supported with the same Flow Table (without updating hardware devices). Our proposed method TimeoutX, for the first time, combines traffic characteristics, flow types and Flow Table utilization ratio to decide the timeout of each entry and it outperforms current timeout setting strategies in both metrics of table miss number and blocked packet number, which indicates TimeoutX could make the best of Flow Table and support more flows.