OpenFlow-Controlled Elastic Optical Networks with Direct- Detection Optical OFDM (DDO-OFDM) Transmission

We design and deploy an extended OpenFlow-based control plane for elastic optical networks with DDO-OFDM transmission, detailing the network architecture, the two-phase routing and spectrum assignment algorithm, OpenFlow protocol extensions and the experimental validation. Introduction An elastic optical network (EON), which is able to dynamically and adaptively allocate the necessary optical spectrum according to the traffic demand, the selected modulation format and path conditions (e.g., physical length or optical impairments), has been proposed to efficiently utilize network spectrum resources. For intelligent end-to-end path provisioning and dynamic route computation (known as routing and spectrum assignment (RSA)), a control plane is a key enabling technique. To date, two different control plane solutions have been proposed and experimentally demonstrated for an EON. The first one is based on the distributed GMPLS architecture and its associated protocols . The second solution is based on extending OpenFlow, which uses a centralized controller (e.g. NOX) to perform both RSA computation and path provisioning. Compared with GMPLS, the OpenFlow provides satisfactory flexibility for the operators to control a network given its open interfaces, the open nature of its source code, and the fact that GMPLS is usually deployed in closed boxes . The first extended OpenFlow-based control plane for an EON has been reported in, focusing on the protocol extensions and overall feasibility validation. Further studies have investigated the control of flexible transmitters, integration with PCE, interoperability with optical performance monitors, and field trial demonstration. Despite massive progress, it should be noted that all the previous works only considered single-carrier transmission schemes , or coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission. It is well known that the optical OFDM system can be mainly categorized as coherent and incoherent (direct-detected) systems. Compared with the CO-OFDM systems, the direct-detection optical OFDM (DDO-OFDM) exhibits much simpler hardware and software realizations, potentially offering a low-cost solution for EON. But to the best of our knowledge, the OpenFlowcontrolled EON by using DDO-OFDM transmission has not been addressed yet. This paper experimentally presents an OpenFlow-controlled EON with DDO-OFDM transmission, assessing its overall feasibility and quantitatively evaluating its performance. Fig. 1:(a) Network architecture; (b) Transmitter (Tx); and (c) Receiver (Rx) of DDO-OFDM Network architecture The network architecture for an OpenFlowcontrolled EON with DDO-OFDM transmission is shown in Fig.1(a). The EON is configured with bandwidth-variable wavelength cross-connects (BV-WXCs), which are implemented by using BV wavelength selective switches (BV-WSS). DDO-OFDM transmitters (Tx) and receivers (Rx), which are supported by advanced digital signal processing, are connected to ingress and egress BV-WXCs respectively, as shown in Fig.1(b) and Fig.1(c) respectively. At the Tx, the random binary bits are firstly mapped to the predefined QAM symbols (e.g. 4, 16, or 64QAM), We.1.E.4.pdf