Metro-access Network Research Articles

Signaling Based Discard with Flags: Per-Flow Fairness in Ring Aggregation Networks

Ring aggregation networks are widely employed for metro access networks. A layer-2 ring with Ethernet Ring Protection is a popular topology for carrier services. Since frames are forwarded along ring nodes, a fairness scheme is required to achieve throughput fairness. Although per-node fairness algorithms have been developed for the Resilient Packet Ring, the per-node fairness is insufficient if there is bias in a flow distribution. To achieve per-flow fairness, N Rate N+1 Color Marking (NRN+1CM) was proposed. However, NRN+1CM can achieve fairness in case there are sufficient numbers of available bits on a frame header. It cannot be employed if the frame header cannot be overwritten. Therefore, the application range of NRN+1CM is limited. This paper proposes a Signaling based Discard with Flags (SDF) scheme for per-flow fairness. The objective of SDF is to eliminate the drawback of NRN+1CM. The key idea is to attach a flag to frames according to the input rate and to discard them selectively based on the flags and a dropping threshold. The flag is removed before the frame is transmitted to another node. The dropping threshold is cyclically updated by signaling between ring nodes and a master node. The SDF performance was confirmed by employing a theoretical analysis and computer simulations. The performance of SDF was comparable to that of NRN+1CM. It was verified that SDF can achieve per-flow throughput fairness without using a frame header in ring aggregation networks.

Amplification of advanced modulation formats with a semiconductor optical amplifier cascade.

The convergence of optical metro networks and access networks extends the area of network coverage, and therefore requires the use of optical amplifiers. For this purpose, semiconductor optical amplifiers (SOA) would be attractive, because they are broadband, can be centered between 1250 nm and 1600 nm, and because they are cheap in production and operation. We show that signals encoded with advanced modulation formats such as BPSK, QPSK, 8PSK, and 16QAM can be amplified by a cascade of at least four SOAs. This enables high-capacity paths with a capacity in the order of Tbit/s for converged metro-access networks.

Transmission Performance of Optical Add/Drop Multiplexers in Metro Optical Access Communication Networks

multimedia domains develop, metro access networks are desired to allow for flexible configuration changes as well as higher speed and capacity. An optical network configuration that combines optical add/drop multiplexers (OADMs) with wavelength division multiplexing (WDM) system began to be introduced in these networks for its suitability. This paper presents the performance analysis of the optical add/drop multiplexer (OADM) on the Q-factor, and eye opening of the eye diagram over wide range of varying parameters. The transmission Performance over fiber transmission system is considering impact of: add/drop channels, transmitted and received power, fiber length, and frequency spacing. Among the important results obtained is the fact that as the received power increases, the Q factor also increases; until a certain level the Q factor reaches the saturation and would be constant no matter how much the power is increased. Thus, any power added after this point is a wasted power. In addition, the performance characteristics of the OADMs, which are capable of dealing with one to several channels arbitrarily selected, were analyzed.

Demonstration of an SOA-assisted open metro-access infrastructure for heterogeneous services

An open converged metro-access network approach allows for sharing optical layer resources like fibers and optical spectrum among different services and operators. We demonstrated experimentally the feasibility of such a concept by the simultaneous operation of multiple services showing different modulation formats and multiplexing techniques. Flexible access nodes are implemented including semiconductor optical amplifiers to create a transparent and reconfigurable optical ring network. The impact of cascaded optical amplifiers on the signal quality is studied along the ring. In addition, the influence of high power rival signals in the same waveband and in the same fiber is analyzed.

Novel cobweb-topology WDM access network architecture featuring ultra-high reliability and easy scalability

A wavelength division multiplexing access network architecture with cobweb topology is proposed in this paper. It can be a candidate for metro access network with high reliability in the future. This architecture can provide two protection methods. The protection strategy which can maximize the protected traffic is elaborated in the context. Mathematical models of system performance such as network scale and link reliability are established and analyzed in this paper.

Reconfigurable digital coherent receiver for metro-access networks supporting mixed modulation formats and bit-rates

A single, reconfigurable, digital coherent receiver is proposed and experimentally demonstrated for converged wireless and optical fiber transport. The capacity of reconstructing the full transmitted optical field allows for the demodulation of mixed modulation formats and bit-rates. We performed experimental validation of different modulation formats, including VCSEL based OOK, baseband QPSK, RoF OFDM and wireless IR-UWB over a 78km deployed fiber link.

A reliable wavelength division multiplexing metro-access network realizing crosstalk-free transmission between uplink and downlink

A novel wavelength division multiplexing metro-access network based on dual-fiber ring of remote nodes and star topology of optical network units is designed to realize the reliable network in case of either single or dual fiber failure. In the design, the survivability of the network is largely enhanced by three work modes. Simultaneously, this network structure can also avoid the crosstalk between uplink and downlink. The simulation results demonstrated with 2.5-Gb/s up/downstream signals show this approach could work very well.

VCSEL-based gigabit IR-UWB link for converged communication and sensing applications in optical metro-access networks

We report on experimental demonstration of an impulse radio ultrawideband (IR-UWB) based converged communication and sensing system. A 1550-nm VCSEL-generated IR-UWB signal is used for 2-Gbps wireless data distribution over 800-m and 50-km single mode fiber links which present short-range in-building and long-reach access network applications. The IR-UWB signal is also used to simultaneously measure the rotational speed of a blade spinning between 18 and 30Hz. To the best of our knowledge, this is the very first demonstration of a simultaneous gigabit UWB telecommunication and wireless UWB sensing application, paving the way forward for the development and deployment of converged UWB VCSEL-based technologies in access and in-building networks of the future.

Inter-Band Crosstalk Reduction Using Sinc Apodization of Super-Structured Fiber Bragg Gratings for Hybrid WDM/OCDM Add/Drop Filters

Here, we propose a newly developed hybrid system of wavelength-division multiplexing (WDM) and optical code-division multiplexing (OCDM) with phase-shifted coherent time-spreading for the future metro-access integrated network. In order to suppress the inter-band crosstalk from the WDM interfering channels, the sinc-apodizing technique is proposed for the super-structured fiber Bragg gratings (SSFBGs) as the add/drop filters. The suppression of crosstalk is demonstrated by two-channel WDM and OCDM experiments, compared with conventional SSFBGs with uniform index profile. The proposed method suppresses the crosstalk and shows the feasibility of the 160 (10 WDM 16 OCDM)-channel system.

RPR–EPON–WiMAX Hybrid Network: A Solution for Access and Metro Networks

The integration of Ethernet passive optical networks (EPONs) with wireless worldwide interoperability for microwave access (WiMAX) is an approved solution for an access network. A resilient packet ring (RPR) is a good candidate for a metro network. Hence RPR, EPON, and WiMAX integration is a viable solution for metro-access network bridging. The present paper examines such integration, including an architecture and a joint media access control (MAC) protocol, as a solution for both access and metro networks. The proposed architecture is reliable due to the dependability of the RPR standard and the protection mechanism employed in the EPON. Moreover, the architecture contains a high fault tolerance against node and connection failure. The suggested MAC protocol includes a multi-level dynamic bandwidth allocation algorithm, a distributed admission control, a scheduler, and a routing algorithm. This MAC protocol aims at maximizing the advantages of the proposed architecture by distributing its functionalities over different parts of the architecture and jointly executing the parts of the MAC protocol.

Reliable overlay topology design for the smart microgrid network

Integration of the advances in information and communication technologies to the power grid technologies is changing the architecture and operation of the traditional grid, leading the grid to gradually evolve into a smart grid. Generation in the smart grid will be different than it is in today's grid, mainly due to the high penetration level of distributed renewable power generators. The distributed generator (DG) is favorable for its low transmission losses and low emissions. On the other hand, control of a high number of DGs is challenging. Almost a decade ago, microgrids were proposed to tackle the challenge of handling the growing number of DGs and fault isolation. A microgrid is a medium voltage or low voltage electrical power system that contains DGs, storage units, controllable loads, small-scale combined heat and power units, and an energy management system. In this article, we revisit the microgrid concept in light of survivability approaches borrowed from high-speed networks. We provide an analogy between survivability in metroaccess networks and reliability of the overlay topology for the smart microgrid network (SMGN). We develop the idea of resource sharing among smart microgrids for the sake of increased reliability. In our case, reliability corresponds to supplying power to the loads using the energy generated in the SMGN, without importing power from the utility grid. We provide a reliable overlay topology design scheme that maximizes the usage of renewable energy in the SMGN.

Photonic crystal ring resonator based add-drop filter using hexagonal rods for CWDM systems

In this paper, theoretical analysis of two-dimensional photonic crystal ring resonator (2D PCRR) based add-drop filter (ADF) is presented for coarse wavelength division multiplexing (CWDM) system to drop a channel at 1511 nm using hexagonal rods that are positioned in the square lattice. The 2D finite difference time domain (2D FDTD) method and plane wave expansion (PWE) method are used for obtaining the filter response and band structure of the filter respectively. Close to 100% dropping and coupling efficiencies at 1511 nm and 16 nm of bandwidth are observed through simulation. This is very well meeting the requirement of ITU-T G. 694.2 standard, which is specified for metro access and short haul optical networks. The overall size of the proposed filter is 11.4 μm ×11.4 μm. It can also be used in integrated optics.

Time-, wavelength-, and code-domain optical reflection monitoring for next-generation access-metro networks

Distributed optical reflectors are proposed to implement essential fault management operations such as fault detection, localization, and notification, in next generation all-optical access-metro networks in the optical layer. Fixed time-slots, wavelengths, or optical codes are assigned to selected key network locations along the path of a monitoring signal where corresponding mirrors are placed. The reflection received at a transmitting node enables online all-optical monitoring of the selected locations. After detailing the network architecture, we explore fundamental system design issues such as real-time fault localization algorithms, fault notification delay upperbounds, and delay line calculation algorithms for synchronous operation. Our simulation results showcase standard and long-reach passive optical networks, and demonstrate that our algorithms achieve fault notification at light speed using off-the-shelf components.

QoS Provisioning Techniques for Future Fiber-Wireless (FiWi) Access Networks

A plethora of enabling optical and wireless access-metro network technologies have been emerging that can be used to build future-proof bimodal fiber-wireless (FiWi) networks. Hybrid FiWi networks aim at providing wired and wireless quad-play services over the same infrastructure simultaneously and hold great promise to mitigate the digital divide and change the way we live and work by replacing commuting with teleworking. After overviewing enabling optical and wireless network technologies and their QoS provisioning techniques, we elaborate on enabling radio-over-fiber (RoF) and radio-and-fiber (R&F) technologies. We describe and investigate new QoS provisioning techniques for future FiWi networks, ranging from traffic class mapping, scheduling, and resource management to advanced aggregation techniques, congestion control, and layer-2 path selection algorithms.

Optical homodyne receiver utilizing image rejection in FSK/ASK re-modulation WDM-PON

Optical frequency shift keying (FSK) homodyne detection utilizing image rejection in FSK/amplitude shift keying (ASK) re-modulation wavelength-division-multiplexed passive optical network (WDM-PON) is proposed and demonstrated. Image rejection is adopted to achieve better performance. We show the result in back-to-back and 40-km distance respectively and apparent improvement is obtained in the latter situation by using image rejection. Several factors which affect the image rejection receiver are analyzed in order to find out the optimum parameters. Result shows that the presented scheme is suitable for super long reach access network, especially for future metro access network.

Ultrasmall 100 GHz 40-Channel VMUX/DEMUX Based on Single-Chip 2.5%-$\Delta$ PLC

The extension of optical add/drop multiplexing (OADM) systems to metro-core and metro-access networks has led to the need for economical and compact OADM devices. In this paper, we demonstrate a 1-in. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 100 GHz spacing 40-channel (ch) single-chip variable attenuator multiplexer/demultiplexer based on a monolithic 2.5%-Delta silica planar lightwave circuit (PLC) and stacked photodiode arrays. We also investigate the particular issues raised by monolithic integration with such high Delta waveguides. One is the loss increase caused by high index contrast of the waveguides. Performance fluctuation and thermal interference between the integrated circuits are also inherent issues. By utilizing effective solutions, we have successfully overcome such problems and confirmed that a 2.5%-Delta silica PLC is effective for use in monolithic integration.

Dynamic Wavelength Allocation in IP/WDM Metro Access Networks

Increasing demand for bandwidth and proliferation of packet based traffic represent a challenge for today's metro networks, which have been traditionally designed to carry circuit- switched connections. The problem is further complicated by the constraints of cost efficiency and traffic adaptability, imposed by the limited customer base in the metro area. Recently, several architectures have been proposed for future metro access networks. Nearly all of these solutions support dynamic reconfigurability, however reconfiguration policies have not been fully explored yet. In this paper, reconfiguration policies for IP/WDM metro access networks with switching delays are considered, where dynamic reconfiguration corresponds to dynamic allocation of wavelengths to access nodes. Exact formulation of the dynamic wavelength allocation (DWA) problem is developed as a Markov Decision Process (MDP) and a new cost function is proposed to attain both throughput efficiency and fairness. For larger problems, a heuristic approach based on first passage probabilities is developed and shown to yield nearly optimum performance through simulations.

An All-Optical Access–Metro Interface for Hybrid WDM/TDM PON Based on OBS

A new all-optical access-metro network interface based on optical burst switching (OBS) is proposed. A hybrid wavelength-division multiplexing/time-division multiplexing (WDM/TDM) access architecture with reflective optical network units (ONUs), an arrayed-waveguide-grating outside plant, and a tunable laser stack at the optical line terminal (OLT) is presented as a solution for the passive optical network. By means of OBS and a dynamic bandwidth allocation (DBA) protocol, which polls the ONUs, the available access bandwidth is managed. All the network intelligence and costly equipment is located at the OLT, where the DBA module is centrally implemented, providing quality of service (QoS). To scale this access network, an optical cross connect (OXC) is then used to attain a large number of ONUs by the same OLT. The hybrid WDM/TDM structure is also extended toward the metropolitan area network (MAN) by introducing the concept of OBS multiplexer (OBS-M). The network element OBS-M bridges the MAN and access networks by offering all-optical cross connection, wavelength conversion, and data signaling. The proposed innovative OBS-M node yields a full optical data network, interfacing access and metro with a geographically distributed access control. The resulting novel access-metro architectures are nonblocking and, with an improved signaling, provide QoS, scalability, and very low latency. Finally, numerical analysis and simulations demonstrate the traffic performance of the proposed access scheme and all-optical access-metro interface and architectures

Application of WDM holographic devices in access and metro networks

In this paper, a design of a generic multipurpose device is described. It can operate, in its basic structure, as a tunable wavelength filter, wavelength multiplexer or λ router; by using a more complex structure, the device works as an optical add drop multiplexer (OADM) or/and optical switch (OS). It can be used in both coarse and dense wavelength division multiplexing technology (CWDM/DWDM) according to the network application. Performance parameters of the device, like switching time, losses, crosstalk or polarization insensitivity are analyzed and compared with other switching technologies. Some applications of the holographic WDM multifunction device in METRO networks are described, such as the utilization of OADMs in optical path protection/reconfiguration between nodes (1 + 1 configuration) and the use of optical switches to interconnect nodes of the METRO–access network with the METRO-Core or long haul networks in a reconfigurable topology. Other applications in Access networks are possible, like the use of the OADMs in optical path protection between the optical line termination (OLT) at the central office (CO) and the remote node (RN) in a fiber to the office passive-optical network (FTTO-PON) or, in some specific cases, the utilization as tuneable holographic filters in a FTTO application, at the Business ONT (BONT), to select the assigned optical wavelength according to the services provided to the customer.

Next generation PON

Passive optical networks (PON) for fiber to the home/cabinet (FTTH/C) have become popular recently due the unstoppable bandwidth demand. Data rates downstream of up to 2.5 Gbps and upstream of up to 1.2 Gbps with splitting factors reaching 64 are in the focus of worldwide product developments. An attractive solution for next generation PON with splitting factors of more than 512, 10 Gbps downstream and 2.5 Gbps upstream data signals is outlined in this paper. The increased splitting factor compensates for the higher components costs due to the higher data rates. By adding optical amplifiers and wavelength division multiplexing (WDM) distances over 100 km and ring structures with more than three nodes are possible leading to a promising and cost-effective next generation "super"-PON thus making MAN (metro access networks) obsolete.