Recently the wavelength division multiplexing (WDM) networks are becoming prevalent for telecommunication networks. However, even a very short disruption of service caused by network faults may lead to high data loss in such networks due to the high date rates, increased wavelength numbers and density. Therefore, the network survivability is critical and has been intensively studied, where fault detection and localization is the vital part but has received disproportional attentions. In this paper we describe and analyze an end-to-end lightpath fault detection scheme in data plane with the fault notification in control plane. The endeavor is focused on reducing the fault detection time. In this protocol, the source node of each lightpath keeps sending hello packets to the destination node exactly following the path for data traffic. The destination node generates an alarm once a certain number of consecutive hello packets are missed within a given time period. Then the network management unit collects all alarms and locates the faulty source based on the network topology, as well as sends fault notification messages via control plane to either the source node or all upstream nodes along the lightpath. The performance evaluation shows such a protocol can achieve fast fault detection, and at the same time, the overhead brought to the user data by hello packets is negligible.
Recently pilot tones have been widely deployed as a path supervisory method for optical crossconnects (OXCs). In this work we present a wavelength-routing fault detection scheme for concatenated OXCs in an all-optical network (AON) testbed, in which pilot tones are added to wavelength channels as channel identifiers (CIDs) at input ports. OXC routing errors then can be detected by comparing the CIDs at output ports with the stored routing information.
The AON testbed is based on commercially available photonic switches, which support dynamic wavelength switching. At each input port of an OXC, a unique frequency tone is added. We compare the performance of two sets of candidacy pilot frequencies, 101 kHz ~ 117 kHz and 1.01 MHz ~ 1.17 MHz (with 2 kHz and 20 kHz separation respectively). The modulation index is set to 10%. On the output side of each OXC, a modulator is inserted after each output port. We detect the tone after the modulator and feed the amplified, filtered, and inverted signal back to the modulator, for removing the tone.
The pilot tones added to all OXCs construct the concatenated wavelength-routing fault detection scheme. This work numerically evaluates the effects of concatenated pilot tones and different pilot frequencies on the overall system performance, e.g., bit error rate or Q-factor. The simulation results show that the proposed scheme is feasible and the degradation of system performance due to pilot tones is negligible.
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