Ralf Huelsermann

Cost modeling and evaluation of capital expenditures in optical multilayer networks

Optical multilayer networks offer a high degree of freedom in network design, adapting to actual network requirements (demand types, topologies, etc.) and achieving cost-efficient realizations. Capital expenditures are one of the key differentiators for the evaluation of multilayer networks. A realistic cost model for Internet protocol/multiprotocol label switching (IP/MPLS), carrier-grade Ethernet, synchronous digital hierarchy/optical transport network (SDH/OTN), and WDM equipment from which overall capital expenditures can consistently be derived is contributed and discussed. A comprehensive collection of detailed cost values for different equipment types is presented. Furthermore, the cost model is applied to two case studies, one IP/MPLS-over-WDM study and one WDM study with two topologies, showing substitution effects of network elements to achieve overall capital expenditure minimization.

General availability model for multilayer transport networks

This paper reports the initiative taken within the IST-project NOBEL to define a general availability model and collect general availability numbers for several network equipment types, independent from vendor specific product information. The model includes optical layer equipment as well as IP and SDH equipment, described using a triplet-representation for each of the availability measures with optimistic, nominal and conservative values. The availability model has been applied to different typical transport network scenarios. Several case studies were performed to compare the end-to-end connection availability and the required network capacity for different resilience mechanisms.

Evaluation of novel resilience schemes in dynamic optical transport networks

Today, Wavelength Division Multiplexing (WDM) transmission systems are deployed extensively in transport networks. They are used mainly for static point-to-point connections. With the availability of fast reconfigurable Optical Cross Connects (OXC) and the introduction of a control plane in the Optical Transport Network (OTN), optical channel based logical networks can be built for dynamic WDM networks. Resilience in current transport networks is mainly based on static SONET/SDH dedicated and shared protection. Distributed control planes allow new, flexible protection mechanisms (e.g. GMPLS reroute and fast reroute). To evaluate future distributed control concepts and new resilience schemes in transport networks, we have implemented a dynamic OTN simulation model. Several case studies have been performed using different protection and restoration methods. Different failure scenarios (single or multiple link failures) were used. The paper evaluates the case studies in terms of scalability, recovery time criteria, capacity use (efficiency) and availability. It is shown that the new and flexible resilience schemes are a promising alternative to traditional statically preplanned protection in transport networks. Furthermore, they provide increased network availability in multiple failure cases.

Quantitative evaluation of architectures for multilayer transport networks

This paper evaluates different architectures for multilayer IP transport networks. The evaluation is based on an exemplary network dimensioning of a reference IP backbone network topology, connecting 63 points of presence (PoPs) in Germany. The network dimensioning results are used for a techno-economic analysis of the different network architectures, taking into account hypothetical but realistic cost models.

Optical networks at cross roads

The paper addresses the migration path and trade-offs involved in the evolution towards intelligent optical networks that allow scalable and flexible transport of a range of client formats and services. Disruptive all-optical switching and ultra-long reach WDM transmission technologies enable all-optical networks without opto-electronic conversion along paths that can span thousands of kilometers. Optical transport networks coupled with advances in distributed routing and signaling mechanisms are enabling the deployment of Automatically Switched Optical Networks (ASON). The paper discusses in detail the network architecture, optical switching capability, and network management and control architecture involved in the migration from existing and widely deployed WDM optical point-to-point systems to ASONs. The paper reports the findings of the Global Seamless Network (GSN) demonstrator at Deutsche Telekom, in which the concepts of intelligent optical transport networks are being demonstrated and evaluated. Further, a special emphasis is devoted to the question of managing survivability in ASONs. Simulation results comparing different approaches are presented, which illustrate the trade-off between dimensioning and performance of resilience mechanisms. The multi-layer integration between optical and higher layers is addressed from both a control plane and survivability perspective. Scenarios with different clients of the optical layer such as SDH and IP/MPLS are analyzed.