Dongmei Wang

Control plane design for reliable optical networks

The application of an IP-based control plane to optical networks has opened up new opportunities and challenges for network designers. Although much work has been done on standardization of protocols for IP networks, the applicability of these protocols to controlling optical networks and the overall reliability of optical networks needs further investigation. This article provides a detailed discussion of a number of subtle protocol design and implementation issues that were not addressed in early standardization efforts or published papers.

Efficient distributed restoration path selection for shared mesh restoration

In MPLS/GMPLS networks, a range of restoration schemes will be required to support different tradeoffs between service interruption time and network resource utilization. In light of these tradeoffs, path-based end-to-end shared mesh restoration provides a very attractive solution. However, efficient use of bandwidth for shared mesh restoration strongly relies on the procedure for selecting restoration paths. In this paper, we propose an efficient restoration path selection algorithm for restorable connections over shared bandwidth in a fully distributed MPLS/GMPLS architecture. We also describe how to extend MPLS/GMPLS signaling protocols to collect the necessary information efficiently. To evaluate the algorithms performance, we compare it via simulation with two other well-known algorithms on a typical intercity backbone network. The key figure of merit for restoration bandwidth efficiency is restoration overbuild, i.e., the extra bandwidth required to meet the network restoration objective as a percentage of the bandwidth of the network with no restoration. Our simulation results show that our algorithm uses significantly less restoration overbuild (63%-68%) compared with the other two algorithms (83%-90%).

Experiments in fast restoration using GMPLS in optical/electronic mesh networks

We present experimental results demonstrating that generalised multi-protocol label switching (GMPLS) with resource reservation protocol (RSVP) can be applied to optical/electrical mesh networks to yield ultra-fast provisioning and restoration times competitive with SONET rings, confirming results previously predicted by simulation.

Fast rerouting for IP multicast in managed IPTV networks

Recent deployment of IP based multimedia distribution, especially broadcast TV distribution has increased the importance of simple and fast restoration during IP network failures for service providers. In this paper, we propose and evaluate a simple but efficient method for fast rerouting of IP multicast traffic during link failures in managed IPTV networks. More specifically, we devise an algorithm for tuning IP link weights so that the multicast routing path and the unicast routing path between any two routers are failure disjoint, allowing us to use unicast IP encapsulation for undelivered multicast packets during link failures. We demonstrate that, our method can be realized with minor modification to the current multicast routing protocol (PIM-SM). We run our prototype implementation in Emulab which shows our method yields to good performance.

An efficient algorithm for OSPF subnet aggregation

Multiple addresses within an OSPF area can be aggregated and advertised together to other areas. This process is known as address aggregation and is used to reduce router computational overheads and memory requirements and to reduce the network bandwidth consumed by OSPF messages. The downside of address aggregation is that it leads to information loss and consequently sub-optimal (non-shortest path) routing of data packets. The resulting difference (path selection error) between the length of the actual forwarding path and the shortest path varies between different sources and destinations. This paper proves that the path selection error from any source to any destination can be bounded using only parameters describing the destination area. Based on this, the paper presents an efficient algorithm that generates the minimum number of aggregates subject to a maximum allowed path selection error. A major operational benefit of our algorithm is that network administrators can select aggregates for an area based solely on the topology of the area without worrying about remaining areas of the OSPF network. The other benefit is that the algorithm enables trade-offs between the number of aggregates and the bound on the path selection error. The paper also evaluates the algorithms performance on random topologies. Our results show that in some cases, the algorithm is capable of reducing the number of aggregates by as much as 50% with only a relatively small introduction of maximum path selection error.

Improving restoration success in mesh optical networks [Invited]

In shared mesh restoration, a distributed signaling protocol is used to reroute connections from failed service paths to restoration paths upon failure events. However, even when the network contains sufficient capacity, the restoration paths could be blocked for two different reasons: (1) with distributed restoration-path selection schemes, multiple restoration paths may compete for the capacity of the same logical links, even when other logical links have sufficient capacity; (2) multiple restoration-path setup attempts may compete for the same channels within the logical link (the glare problem), even when sufficient capacity is available within the logical link. We propose a hybrid distributed-centralized restoration mechanism for restoration-path selection and a channel-selection scheme that eliminates almost all glares. As shown from simulation in a typical intercity backbone network, our proposed hybrid mechanism improves the first restoration attempt success ratio by 40% compared with a pure distributed restoration approach. In addition, the proposed restoration-path selection algorithm saves up to 50% of restoration capacity compared with the disjoint shortest-path algorithm and 15% compared with a previously published greedy algorithm.

Demonstration of ultra-fast IP restoration using reconfigurable transport networks

We integrate IP, data-link and transport capabilities for ultra-fast IP interface and link provisioning, and demonstrate two IP restoration schemes that use re-configurable transport networks: 1:N router interface protection and dynamic establishment of a new link upon failure.