Repeater using two wavelengths for passive optical star networks connection

A repeater for the 32 Mbit/s star-configured optical local area network (SOLARnet) has been developed. This repeater permits a tree-type interconnection of SOLARnets at layer 1 and enlarges the network scale. Wavelength-division multiplexing (WDM) is used to overcome self-collision (collision of the packet header with its packet).     

Network virtualization over WDM and flexible-grid optical networks

Network virtualization can eradicate the ossification of the Internet and stimulate innovation of new network architectures and applications. Optical networks are ideal substrates for provisioning high-bandwidth virtual-network services. In this study, we investigate the problem of network virtualization over both WDM and flexible-grid optical networks by formulating the problems as mixed integer linear programs (MILP). Two heuristics, namely MaxMapping and MinMapping, are developed for each kind of network to solve the problem quickly but suboptimally. Numerical examples show that MinMapping consumes fewer spectrum resources than MaxMapping and performs very close to the optimal results derived by the MILP in both kinds of optical networks, by exploring the opportunities of traffic grooming. Also, it is verified that flexible-grid optical networks can be more spectrum efficient than WDM networks as the substrate for network virtualization.     

Signalling end-to-end optical services over multi-domain networks

This paper proposes a new UCLP (User-Controlled LightPath) architecture that offers end-to-end optical services provisioning in a multi-domain network. It also shows the experimental results of our UCLP software tool implemented on the Canarie optical network testbed. This work is motivated by the growing need for end-to-end lightpaths to support high volume data transferring applications such as GridFTP (GRID File Transfer Protocol) and SAN (Storage Area Networks) over multi-domain networks. The main problems encountred while provisioning end-to-end optical service in a multi-domain network are investigated and a review of the different interdomain signalling approaches is provided in comparison with our user-controlled lightpath provisioning approach. Various interdomain signalling approaches are discussed and compared to justify the necessity of signalling methods at the application level for long-duration applications.     

IP over optical networks: architectural aspects

The Internet transport infrastructure is moving toward a model of high-speed routers interconnected by intelligent optical core networks. A consensus is emerging in the industry on utilizing an IP-centric control plane within optical networks to support dynamic provisioning and restoration of lightpaths. At the same time, there are divergent views on how IP routers must interact with optical core networks to achieve end-to-end connectivity. This article describes the architectural alternatives for interconnecting IP routers over optical networks, considering the routing and signaling issues. Also, the application of IP-based protocols for dynamic provisioning and restoration of lightpaths, as well as the interworking of multivendor optical networks is described     

光突发交换网络的动态TCP特性研究

通过仿真研究了动态业务竞争环境下,不同TCP版本在OBS网络中的传输性能。研究中,以TCP在OBS网络中传送一个固定大小的文件所需的时间作为性能指标,此外,详细分析了突发丢失的内部机制和造成不同TCP版本性能差异的原因。结果表明,TCP SACK性能最好。     

Assigning spare capacities in mesh survivable networks

This paper analyses one key issue of designing reliable networks: assignment of spare capacities in transmission networks. The spare capacities are optimized to facilitate the restoration of single failures. This problem can be formulated as an integer linear program and approximated by its continuous relaxation. This model is based on arc-path formulation especially efficient for dealing with end-to-end rerouting and providing appreciable economies in comparison with local rerouting. The main idea of our method resides in a linear programming decomposition, which permits us to solve problems for medium and large networks. Our approach could be applicable to both STM and ATM-based networks. This method was tested successfully on medium and large DCS-meshed networks and some numerical examples are given to illustrate its performances in terms of CPU time and ratio of optimality. This revised version was published online in June 2006 with corrections to the Cover Date.     

Hybrid WDM and optical CDMA implemented over waveguide-grating-based fiber-to-the-home networks

This paper presents a hybrid wavelength-division multiplexing (WDM) and optical code-division multiple-access (OCDMA) scheme over fiber-to-the-home (FTTH) networks. Exploiting the periodic free-spectral-range (FSR) properties of arrayed-waveguide grating (AWG) routers, the total ONU (optical network unit) capacity in the network is partitioned into different groups based on the subscriber's geographical locations. Maximal-length sequence (M-sequence) codes are taken as signature addresses to take advantage of the cyclic properties of AWG routers. The proposed scheme is suitable for networks in which the distance between the OLT (optical line terminal) and the individual ONUs varies. The influence of the degree of polarization (DOP) on the signal to phase-induced intensity-noise ratio is evaluated. By introducing a depolarizer in front of the balanced photo-detector, the maximum permissible number of simultaneous active ONUs can be improved by approximately 20% for a 10⁻⁹ error probability. By exploiting the inherent cyclic FSR characteristics of AWG routers, the OLT enables a significant reduction in the number of AGW-based network codecs compared to the previous coded WDM (i.e., OCDMA in spectral domain) scheme. Furthermore, while the number of AWGs in the proposed scheme is comparable to that of conventional WDM-EPON schemes, the current scheme is more flexible, confidential, and scalable.     

Low-power optical feeder for VDSL over twisted pair for last mile access networks

In this paper, we describe an ultra-low-power optoelectronic very-high-data-rate digital subscriber line (VDSL) system, enabling broadband access to the home over 10 km of optical fiber and 1 km of twisted pair. The cabinet/distribution point interface has a footprint of just 3 /spl times/ 3 /spl times/ 1 cm, and consumes only 165 mW. A quadrature-amplitude-modulation (QAM) scheme was used for system tests with 10 Mb/s full duplex achieved, and up to 40-dB up/downstream channel isolation is obtained using hybrid transformers.     

TCP over optical burst-switched networks with controlled burst retransmission

For optical burst-switched (OBS) networks in which TCP is implemented at a higher layer, the loss of bursts can lead to serious degradation of TCP performance. Due to the bufferless nature of OBS, random burst losses may occur, even at low traffic loads. Consequently, these random burst losses may be mistakenly interpreted by the TCP layer as congestion in the network. The TCP sender will then trigger congestion control mechanisms, thereby reducing TCP throughput unnecessarily. In this paper, we introduce a controlled retransmission scheme in which the bursts lost due to contention in the OBS network are retransmitted at the OBS layer. The OBS retransmission scheme can reduce the burst loss probability in the OBS core network. Also, the OBS retransmission scheme can reduce the probability that the TCP layer falsely detects congestion, thereby improving the TCP throughput. We develop an analytical model for evaluating the burst loss probability in an OBS network that uses a retransmission scheme, and we also analyze TCP throughput when the OBS layer implements burst retransmission. We develop a simulation model to validate the analytical results. Simulation and analytical results show that an OBS layer with controlled burst retransmission provides up to two to three orders of magnitude improvement in TCP throughput over an OBS layer without burst retransmission. This significant improvement is primarily because the TCP layer triggers fewer time-outs when the OBS retransmission scheme is used.     

Optimized design of survivable MPLS over optical transport networks

In this paper we study different options for the survivability implementation in MPLS over Optical Transport Networks (OTNs) in terms of network resource usage and configuration cost. We investigate two approaches to the survivability deployment: single-layer survivability, where some recovery mechanism (e.g. protection or restoration) is implemented in a single network layer and multilayer survivability, where recovery is implemented in multiple network layers. The survivable MPLS over OTN design is implemented as a static network optimization problem and incorporates various methods for spare capacity allocation (SCA) to reroute disrupted traffic.The comparative analysis between the single layer and the multilayer survivability shows the influence of the traffic granularity on the survivability cost: for high-bandwidth LSPs, close to the optical channel capacity, the multilayer survivability outperforms the single layer one, whereas for low-bandwidth LSPs the single-layer survivability is more cost-efficient. For the multilayer survivability we demonstrate that by mapping efficiently the spare capacity of the MPLS layer onto the resources of the optical layer one can achieve up to 22% savings in the total configuration cost and up to 37% in the optical layer cost. Further savings (up to 9%) in the wavelength use can be obtained with the integrated approach to network configuration over the sequential one; however, this is at the increase in the optimization problem complexity. These results are based on a cost model with current technology pricing and were obtained for networks targeted to a nationwide coverage.     

IP over WDM光网分层体系结构

介绍了传统的 IP over WDM光网实现方案 ,指出各种方案的优缺点。阐述了 IP directly overWDM光网的分层结构实现方案 ,分析了各层功能 ,详细讨论了光层和光适配层。在指出分层结构实现方案的利弊后 ,讨论了波长标记和多协议波长交换方案。     

Multi-layer loss recovery in TCP over optical burst-switched networks

It is well-known that the bufferless nature of optical burst-switching (OBS) networks cause random burst loss even at low traffic loads. When TCP is used over OBS, these random losses make the TCP sender decrease its congestion window even though the network may not be congested. This results in significant TCP throughput degradation. In this paper, we propose a multi-layer loss-recovery approach with automatic retransmission request (ARQ) and Snoop for OBS networks given that TCP is used at the transport layer. We evaluate the performance of Snoop and ARQ at the lower layer over a hybrid IP-OBS network. Based on the simulation results, the proposed multi-layer hybrid ARQ + Snoop approach outperforms all other approaches even at high loss probability. We developed an analytical model for end-to-end TCP throughput and verified the model with simulation results.     

Two-beam interferometer for optical constants measurements at near-millimeter wavelengths

A simple and versatile instrument for the measurement of optical constants in the near millimeter spectral region is described. Studies of quasi-optical components used in this instrument for effective beam transmission and control are reported. These studies include transmission characteristics of dielectric waveguides and performance of a variable coupler based on frustrated total internal reflection. Operation of this instrument as a two-beam interferometer for determining the index of refraction or as a device to measure transmission for determining the absorption coefficient are described. Values measured with this instrument at 245 GHz, using an optically pumped molecular laser as the source, are reported for several low-loss materials. Appropriate corrections and error estimates are discussed. The potential for improvement and increased accuracies are discussed.     

Availability of survivable Valiant load balancing (VLB) networks over optical networks

Valiant load balancing (VLB) network has been proposed as a capacity-efficient solution to handle highly dynamic traffic in future backbone networks. In this paper, we study the availability of VLB networks that are overlaid over an optical infrastructure. The main challenges in such a context arise from the unique routing and protection scheme that goes beyond the definition of conventional connection-level service availability as well as the logical link failure correlation that prohibits the use of traditional analytical methods. We propose a network-level availability model to compute the probability that a VLB network is congestion-free under all traffic patterns. Numerical results show that with a proper truncation level, our calculation on availability can be accelerated significantly by generating tight lower and upper bounds. Our main finding is that physical link sharing in a two-layer setting degrades the network availability drastically by several orders of magnitude due to the full mesh requirement for VLB networks, and may remove the capacity efficiency advantage of VLB networks.     

Assigning codes in wireless networks: bounds and scaling properties

In the Code Division Multiple Access (CDMA) framework, collisions that can occur in wireless networks are eliminated by assigning orthogonal codes to stations, a problem equivalent to that of coloring graphs associated to the physical network. In this paper we present new upper and lower bounds for two versions of the problem (hidden and primary collision avoidance – HPCA – or hidden collision avoidance only – HCA). In particular, optimal assignments for special topologies and heuristics for general topologies are proposed. The schemes show better average results with respect to existing alternatives. Furthermore, the gaps between the upper bound given by the heuristic solution, the lower bound obtained from the maximumclique problem, and the optimal solution obtained by branch and bound are investigated in the different settings. A scaling law is then proposed to explain the relations between the number of codes needed in Euclidean networks with different station densities and connection distances. The substantial difference between the two versions HPCA and HCA of the problem is investigated by studying the probabilistic distribution of connections as a function of the distance, and the asymptotic size of the maximum cliques.     

Source-ordering for improved TCP performance over load-balanced optical burst-switched (OBS) networks

Recent advances in optical switching technology allow for the creation of networks in which data bursts are switched optically at each node, offering a greater degree of flexibility suitable for handling bursty Internet traffic. TCP-based applications account for a majority of data traffic in the Internet; thus understanding and improving the performance of TCP implementations over OBS networks are critical. Previously, several articles show that load-balanced routing improves loss-performance in OBS. In this paper, we identify the ill-effects of load-balanced OBS on TCP performance caused by false time-outs and false fast-retransmits. We propose a source-ordering mechanism that significantly improves TCP throughput over a load-balanced OBS network.     

Survivable virtual concatenation for data over SONET/SDH in optical transport networks

Next-generation SONET/SDH technologies-namely, generic framing procedure, virtual concatenation, and link-capacity-adjustment scheme-enable network operators to provide integrated data and voice services over their legacy SONET/SDH infrastructure to generate new revenue. An important open research problem on data over SONET/SDH (DoS) is survivability: SONET automatic protection switching is too resource inefficient for data services, and the protection mechanisms of data networks are too slow for mission-critical applications. We propose two approaches for provisioning survivable DoS connections. Our approaches exploit the tradeoff between resource overbuild and fault-recovery time while utilizing the inverse-multiplexing capability of virtual concatenation to increase backup sharing. Our results show that one approach achieves low resource overbuild and much faster fault recovery than that of data networks, and the other approach achieves fast fault recovery comparable to SONET 50-ms protection (for typical U.S. backbone networks) while still achieving modest backup sharing. We further investigate the tradeoff between network blocking performance and network control and management complexity resulting from the number of paths M a connection can be inversely multiplexed onto: larger M leads to more freedom in routing and better network performance but increases network control and management complexity. Our results indicate that the network blocking performance for small values of M (e.g., M=2 for some representative backbone network topologies) is almost as good as the case in which M is infinity.     

Experimental demonstration of wavelength routed optical networks over 52 km of monomode optical fibre

A wavelength routed network using commercial components in the 1.5 mu m transmission window at 650 Mbit/s over 52 km of conventional monomode fibre is demonstrated. Individual and concatenated wavelength division multiplexer characteristics are presented.<>     

Mode-locked erbium-doped fiber lasers as source for optical sensor networks over C and L bands

The performance of mode-locked erbium-doped fiber lasers in optical sensor networks is analyzed and compared with the results obtained by using commercial erbium-doped fiber amplifiers as source. Passive mode-locked lasers developed are based on nonlinear polarization rotation and they have been built using the same erbium-doped fiber amplifiers. To simulate a real sensor network, a tree structure with four fiber Bragg gratings was built employing 50/50 couplers. The mode-locked laser developed offers a reasonably good behavior at a very wide spectral range (83 nm, approximately) over C and L bands. The signal to noise ratio and the peak power are greatly improved with regard to the values obtained employing commercial amplifiers as source.