Gabriele Maria Galimberti

Distributed Optical Control Plane Architectures for Handling Transmission Impairments in Transparent Optical Networks

Transmission impairments in wavelength-division- multiplexing (WDM) transparent optical networks accumulate along an optical path and determine the feasibility of lightpaths; hence, the impairments need to be managed efficiently by the control plane. This paper presents impairment-aware distributed optical control plane (OCP) based on enhancements to resource reservation protocol-traffic engineering (RSVP-TE) signaling protocol (S-OCP). In particular, four architectural options [K-sequential (K-SEQ), K-parallel (K-PAR), hop-by-hop (HbH), and full flooding (FF)] within the S-OCP approach are defined and compared. Simulation results show that a combination of HbH routing and feasibility check can be considered as a good compromise both in terms of blocking probability and control plane overhead. The feasibility of a signaling-based approach for the control plane is further demonstrated by comparing simulation results with the results obtained from the implementation of the proposed architectural options in a commercial generalized multiprotocol label switching (GMPLS) protocol emulator. Furthermore, we argue that the real networks will rarely be homogeneous concerning transponder types, creating the need for a transponder selection policy at the end nodes. We introduce and compare two policies: best-first and worst-first. The results obtained from our experiments show that a worst-first policy for selecting transponders can save up to 50% enhanced transponders thereby reducing the overall cost.

Signalling-Based Architectures for Impairment-Aware Lightpath Set-Up in GMPLS Networks

This paper explores the solution space for extending the signaling protocol of a GMPLS control plane for an impairment-aware path setup in transparent optical networks. Four combinations of routing and optical feasibility checking architectures based on modifications of RSVP-TE are proposed and studied. Simulation results show that a combination of hop- by-hop routing and feasibility check can be considered as a good compromise both in term of blocking probability and limited impact on the control plane. The slightly higher lightpath set-up time compared to other architectures can be tolerated especially considering the impact on the RSVP protocol current behavior as well as its independence from parameters strictly related to the network properties and topology.

Novel signalling based approach for handling linear and non-linear impairments in transparent optical networks

In GMPLS-based transparent optical networks, the switching and routing functionalities are performed in optical domain. However in these networks, physical layer impairments (PLIs) incurred by non-ideal transmission media accumulate along an optical path, and the overall effect determines the feasibility of lightpaths. Introducing transparency in optical layer reduces the possibility of GMPLS protocols interaction with optical layer at intermediate nodes along the path. Hence there is an urgent need to develop techniques that provide PLI information to GMPLS protocols and algorithms that efficiently utilize this information to realize dynamically reconfigurable GMPLS/WDM networks. We propose an optical control plane (OCP) architecture based on extensions to RSVP-TE, which is capable of handling both linear impairments (LIs) and non-linear impairments (NLIs). We propose a method to deal with the possible disruption of existing lightpaths because of excessive crosstalk introduced due to new lightpath setup. The simulation results suggest that OCP architectures to handle NLIs are important to avoid potential lightpath disruption.

Handling race conditions among bidirectional LSP requests via WA-method-TLV in GMPLS WDM networks

This paper defines three types of race conditions that may occur while attempting to reserve optical circuits in GMPLS WDM networks. It then investigates the effect on network blocking by race condition type and explains how to use an already existing TLV in the IETF RSVP signaling to inform the destination node of a potential race condition occurrence. An informed destination can then choose the appropriate wavelength assignment algorithm to best handle such situation.

Impairment and regenerator aware lightpath setup using distributed reachability graphs

GMPLS-based transparent optical networks suffer from accumulation of physical layer impairments (PLIs) along the optical path and inefficient wavelength utilization due to wavelength continuity constraint. To increase the optical reach, resource utilization, and average call acceptance ratio, network operators resort to translucent optical networks in which a limited number of regenerators are placed at a selected set of nodes. In this scenario development of an optical control plane which is aware of PLIs, location and number of regenerators, is of paramount importance for on-demand lightpath provisioning. In this paper, we propose a novel three phase approach—reachability graph construction, route computation on reachability graph, and signaling—impairment and regenerator aware routing and wavelength assignment (IRA-RWA). We also propose corresponding GMPLS protocol extensions. The simulation results suggest that our proposed approach together with LSP stitching signaling mechanism can be deployed in realworld translucent optical networks.

Distributed optical control plane for dynamic lightpath establishment in translucent optical networks based on reachability graph

In transparent optical networks, physical layer impairments (PLIs) incurred by non-ideal optical transmission media accumulate along an optical path, and the overall effect determines the optical feasibility of the lightpaths. In addition, transparent optical networks suffer from inefficient wavelength utilization, as a connection request may be rejected because of non-availability of a common wavelength on all the links along the chosen route. To increase optical reach, resource utilization, and average call acceptance ratio (and hence revenues), network operators are resort to translucent optical networks. In these networks a limited number of regenerators are placed at a selected set of nodes. In this scenario development of an optical control plane which is aware of PLIs, location and number of regenerators, is of paramount importance for on-demand lightpath provisioning. In this paper, we propose a novel approach of constructing a reachability graph of the physical network considering PLIs and regenerators. If there is no transparent path in the physical network, we route the connections with multiple transparent segments on the reachability graph. We propose efficient mechanisms and corresponding GMPLS protocol extensions for impairment and regenerator aware routing and wavelength assignment (IRA-RWA) in translucent optical networks. The simulation results suggest that our proposed approach together with LSP stitching signaling mechanism is feasible to implement and close to deployment.

Towards deployment of signalling based approaches for impairment aware lightpath setup in transparent WDM optical networks

We implement extensions to intrinsic functionality of standard RSVP-TE on a commercially available GMPLS protocol stack to setup optically feasible lightpaths and study the performance and deployment feasibility in real-world transparent WDM optical networks.

Toward deployment of signalling-based approach for linear and non-linear impairment-aware lightpath setup in transparent optical networks

We propose signalling based approaches for handling linear and non-linear impairments and implement RSVP-TE extensions and related mechanisms on a commercially available GMPLS stack. The emulation results demonstrate that the proposed solutions are feasible and close to deployment.

Demonstration of an SDN orchestrator for both flow provisioning and fault handling in an Ethernet-over-WDM Network

PROnet is a two-layer Research and Education Network (REN) deployed at and around the UT Dallas campus. PROnet makes use of a Software Defined Networking (SDN) orchestrator, described in this paper. The PROnet Orchestrator provides two critical functions in an Ethernet-over-Wavelength Division Multiplexing (WDM) network. The two functions are: 1) on-demand flow provisioning at the Ethernet layer and 2) coordinated fault handling at both the Ethernet and WDM layer. With the first function, the orchestrator automatically provisions optical circuits to efficiently satisfy the Ethernet flow fault-tolerant requirement. With the second function, the orchestrator coordinates response procedures at both layers in order to quickly re-route disrupted flows and ensure that the network is prepared to handle a potential second outage.

Optical layer-driven network restoration and redesign for improved fast reroute reliability

Fast Reroute (FRR) is a local restoration mechanism available in Multi-Protocol Label Switching (MPLS). With FRR, data traffic over a failing MPLS-link is swiftly rerouted through a pre-provisioned restoration tunnel. The FRR solution works well so long as the restoration tunnel is not adversely affected by other concurrent failures. Additional protection against this drawback is offered by the lower (optical) layer, which provides restoration lightpaths to replace the failing MPLS-link(s). The optical layer can also provide a second remedy, which consists of redesigning a portion of the MPLS-topology on-the-fly. This paper investigates the reliability improvement that these two optical layer-driven techniques can yield.