GMPLS-controlled Optical Networks Research Articles

PCE: What is It, How Does It Work and What are Its Limitations?

In GMPLS-controlled optical networks, the utilization of source-based path computation has some limitations, especially in large networks with stringent constraints (e.g., optical impairments) or in multilayer and multidomain networks, which leads to suboptimal routing solutions. The path computation eElement (PCE) can mitigate some weaknesses of GMPLS-controlled optical networks. The main idea behind the PCE is to decouple the path computation function from the GMPLS controllers into a dedicated entity with an open and well-defined interface and protocol. A (stateless) PCE is capable of computing a network path or route based on a network graph (i.e., the traffic engineering database-TED) and applying computational constraints. First, we present an overview of the PCE architecture and its communication protocol (PCEP). Then, we present in detail the considered source-routing shortcomings in GMPLS-controlled networks, namely, impairment-aware path computation, multidomain path computation and multilayer path computation, as well as the different PCE-based solutions that have been proposed to overcome each one of these problems. However, PCE-based computation also presents some limitations that lead to an increase in the path computation blocking or to suboptimal path computations. The stateful PCE overcomes the limitations of the stateless PCE, such as the outdated TED, the lack of global LSP state (i.e., set of computed paths and reserved resources in use in the network), and the lack of control of path reservations. A passive stateful PCE allows optimal path computation and increased path computation success, considering both the network state (TED) and the Label Switched Paths (LSP) state (LSP Database-LSPDB). Additionally, an active stateful PCE can modify existing LSPs (i.e., connections), and optionally, setup and/or release existing LSPs. Finally, the formal decoupling of the path computation allows more flexibility in the deployment of PCEs in other control paradigms outside their original scope (MPLS/GMPLS). In this sense, we provide an overview of three PCE deployment models in the software defined network (SDN) control architecture.

Deployment and Validation of GMPLS-Controlled Multi-layer Integrated Routing over the ASON/GMPLS CARISMA Test-bed

The efficient accommodation of subwavelength client flows on optical channels is a current challenge for the optimization of resources in GMPLS-controlled optical networks. While the capacity of the optical channels usually exceeds 10 Gbps, connection requests show finer granularity. This paper concentrates on the design and implementation of the ASON/GMPLS CARISMA test-bed a GMPLS-controlled grooming-capable transport network. Through the paper, the operation of a GMPLS-controlled multi-layer network architecture is introduced, reviewing those implementation issues that come into light. Then, an experimental evaluation is conducted on two alternative network scenarios with different number of nodes and nodal degree. From the results, GMPLScontrolled grooming makes a good trade-off between network blocking probability and E/O port usage when compared to all-optical and opaque solutions, leading to enhanced network performance while reducing network capital expenditures (CAPEX) .

Application-Driven Control of Network Resources in Multiservice Optical Networks

Network architectures whose resources are open to control by user applications require the design of a service platform that performs resource virtualization and service abstraction. While a few commercial architectures for packet networks already exist, service platforms for connection-oriented networks (e.g., optical) are currently under investigation. After introducing the service concept in the optical network scenario, the paper proposes and experimentally validates a service platform for application-driven resource management in a GMPLS-controlled optical network. Specifically, upon a service request issued by an application, the proposed service platform performs admission control and enforces proper traffic policies to ensure the quality of service (QoS) required by the application data flow. This enables QoS control on a per-application basis while preserving scalability and timing of application signaling. The experimental results show that service setup is realized in a time of the order of a few seconds. Scalability remarks show that this order of magnitude can also be guaranteed for networks of larger size.

SONET-Framed Optical Packet Networking in the Context of Generalized Multiprotocol Label Switching

This article discusses the evolution of Synchronous Optical Network (SONET) towards support for shared packet media, particularly in light of new developments in the control plane, such as Generalized Multiprotocol Label Switching (GMPLS) and the (UNI) specification. Whereas the current SONET network is largely static and circuitcentered, and typically supports DS-1 and DS-3-level granularities, the emerging packet-centric, GMPLS-controlled optical network will be significantly more dynamic, and characterized by concatenated or virtually concatenated payloads such as STS-3c/12c/48c/192c, and, possibly, STS-1-24v (i.e., 'STS-24c'). In this environment, it will be shown that the differences between such packet-centric SONET networks and 'IP over Optical' network architectures begin to disappear.

Recovery from control plane failures in GMPLS‐controlled optical networks

AbstractThe health status of the control plane and the data plane of a GMPLS‐controlled optical network is independent in the physically separated control network implementation. In most control plane designs, besides the topology information, the entities of the routing protocol only record the number of available wavelengths on each link. However, the status of each wavelength is maintained by the entities of the signalling protocol. Without recovery ability of the signalling protocol CR‐LDP, a failure in the control plane will result in the permanent loss of the status information of wavelengths. A mechanism to recover the status information of the wavelengths is proposed. A downstream node maintains a label information database (LID) about assignable (free) labels in each incoming link. A copy of LID is redundantly stored in the upstream node as a label information mirror (LIM). A systematic procedure is proposed to synchronize the contents of a LIM and the corresponding LID. The initialization of a new LDP session with the enhanced recovery mechanism will guarantee the revival of the status information of wavelengths. It can recover multiple control channel failures, but it only applies to single node failure among any pair of adjacent nodes. © Crown copyright 2002. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.