Telecommunication transmission systems continue to evolve towards higher data rates, increased wavelength numbers and density, longer transmission distances and more intelligence. Further development of dense wavelength division multiplexing (DWDM) and all-optical networking (AON) will require ever-tighter monitoring to assure an agreed quality of service (QoS), characterized by network availability and bit-error rate (BER). However, it becomes complex with traditional methods when applied in next generation networks. For the purpose of obtaining information quickly and accurately in future transmission systems, new monitoring schemes need to be developed and deployed. The paper provides a view of next generation monitoring requirements, business drivers as well as performance monitoring techniques, potentially applicable as next generation performance surveillance methods.
KEYWORDS: Transmitters, Fiber to the x, Signal attenuation, Video, Passive optical networks, Wavelength division multiplexing, Receivers, Analog electronics, Standards development, Asynchronous transfer mode
The simulation models for a typical PON layout
are developed and three major PON technologies are
considered. The models support the analysis of various
important characteristic parameters, namely: 1) link budget
for acceptable losses from splices, attenuation and splitters,
2) link performance characterization based on data (BER,
SNR) or video signal quality, and 3) linear and nonlinear
fiber effects such as dispersion, PMD, self- and crossmodulation,
Analysis outcomes may be used to optimize the performance
of the applied system design including fiber maximum
length and type, the need to change some of the optical
components (e.g. couplers, splitters, etc.) and digital
links bit rate (e.g. 1.2 Gb/s or 2.4 Gb/s) according to the
The simulation models developed enable us with these
detailed analyses of PON technologies without the need to
Reconfigurable Optical Add/Drop Multiplexers (ROADMs) are going to change the landscape for future metro optical networks. In this paper, we present the detailed design layouts for next generation metro optical network equipped with the most advanced 3rd generation ROADM modules. Mathematical equations have been developed to design complex network architecture based on traffic demand and the characteristics of network equipments. Our proposed design layout for next generation network alleviates some conventional design concepts that will ultimately reduce the capital- and operational-expenditure for the overall network.
As the telecom industry responds with technological innovations to requests for higher data rates, increased number of wavelengths at higher densities, longer transmission distances and more intelligence for next generation optical networks, new monitoring schemes based on monitoring and tracking of each wavelength need to be developed and deployed. An optical layer monitoring scheme, based on tracking key optical parameters per each wavelength, is considered to be one of enablers for the transformation of today's opaque networks to dynamic, agile future networks. Ever-tighter network monitoring and control will be required to fulfill customer Service Level Agreements (SLAs). A wavelength monitoring and tracking concept was developed as a three-step approach. It started with the identification of all critical parameters required to obtain sufficient information about each wavelength; followed by the deployment of a cost-efficient device to provide simultaneous, accurate measurements in real-time of all critical parameters; and finally, the formulation of a specification for wavelength monitoring and tracking devices for real-time, simultaneous measurements and processing the data. A prototype solution based on a commercially available integrated modular spectrometer within a testbed environment associated with the all-optical network (AON) demonstrator program was used to verify and validate the wavelength monitoring and tracking concept. The developed concept verified that it can manage tracking of 32 wavelengths within a wavelength division multiplexing network. The developed concept presented in this paper can be used inside the transparent domains of networks to detect, identify and locate signal degradations in real-time, even sometimes to recognize the cause of the failure. Aside from the reduction of operational expenses due to the elimination of the need for operators at every site and skilled field technicians to isolate and repair faults, the developed wavelength monitoring concept provides critical inputs for protection switching, line equalization and span monitoring. Additionally, it can unlock the capabilities of tunable technologies, ensuring network agility. Finally, further developments of the presented concept might enable building and controlling of complex network topologies while efficiently maintaining a high quality of service (QoS).
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 <i>hello</i> packets to the destination node exactly following the path for data traffic. The destination node generates an alarm once a certain number of consecutive <i>hello</i> 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 <i>hello</i> packets is negligible.
Communication transmission systems continue to evolve towards higher data rates, increased wavelength densities, longer transmission distances and more intelligence. Further development of dense wavelength division multiplexing (DWDM) and all-optical networks (AON) will demand ever-tighter monitoring to assure quality of service (QoS). Traditional monitoring methods prove to be insufficient. Higher degree of self-control, intelligence and optimization for functions within next generation networks require new monitoring schemes to be developed and deployed.
Both perspective and challenges of performance monitoring, its techniques, requirements and drivers are discussed. It is pointed out that optical layer monitoring is a key enabler for self-control of next generation networks. Aside from its real-time feedback and safeguarding of neighboring channels, optical performance monitoring ensures the ability to build and control complex network topologies while maintaining an efficiently high QoS.
Within an all-optical network testbed environment, key performance monitoring parameters are identified, assessed through real-time proof-of-concept, and proposed for network applications in safeguarding of neighboring channels in WDM systems.
Switching is one of the key functionalities in next generation optical networks. It might be performed by either an optical switch (optical-electrical-optical, or OEO) or a "purely" photonic switch (optical-optical-optical or OOO). Both switches are analyzed from two perspectives - as an individual network element, and as an integral part within the communication network. As an individual network element, the performance evaluation of the two switch types is based on the individual assessment of switch footprint and power dissipation, bandwidth utilization, scalability to high speed, transparency, interoperability, technology maturity and ability to manipulate data. Although both switch types have their own advantages as a network element, the full judgement of their role in next generation optical networks requires an overall network perspective. From that viewpoint, network functionalities such as grooming capabilities, scalability, traffic management, protection, line equalization and performance monitoring are those taken into account for comparative analyses to gain an understanding of the impacts of switch choice in the network.
As a result of the comparative performance assessment, the merits and benefits of both switch types in actual network applications are analyzed and outlined. Although the paper evaluates some criteria for switch choice in a network, it points out potential technologies or techniques critical to next generation architectural solutions and protocols as well as the challenges to bridge the gap towards implementing flexible, cost-effective and dynamically provisioned networks of the future. Finally, the paper responds to one critical question - What is the expected role of each switch type in next generation applications and services?
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.