Showing papers presented at "International Conference on Transparent Optical Networks in 2005"

Channel modeling for terrestrial free space optical links

Abstract: With recent advances and interest in free space optics (FSO) for commercial deployments, a proper understanding of optical signal propagation in different atmospheric conditions has become essential, and thus arises the need to rationalize the effects of atmospheric channel on terrestrial FSO links. In this paper, we present the preliminary results of our effort to simulate the atmospheric free space terrestrial optical channel with precise mathematical models of the most deterrent attenuators. Attenuations due to fog, rain, snow and scintillation are considered. Thus, the channel model acquired is a first step towards developing a comprehensive model predicting the performance of a terrestrial FSO link operating under natural weather conditions.

Design, availability and reliability analysis on an experimental outdoor FSO/RF communication system

Abstract: This work highlights the characteristics of an experimental outdoor free space optical (FSO) communication system combined with a redundant radio frequency (RF) link that provides high availability and uninterrupted communication even in adverse weather conditions. The system provides wireless connection between the two of the five campuses of Ankara University. The rationale behind the selection of design parameters is given and the structure of the hybrid system is outlined. Results, regarding the link availability of the system, which has been operational for over 2 years, are presented.

Multi-format transmitters for coherent optical M-PSK and M-QAM transmission

Abstract: Coherent optical transmission returns into the focus of research. One significant advantage is the preservation of all the information of the optical field during detection, leading to enhanced possibilities for optical multi-level modulation. This paper investigates the generation of optical multi-level modulation signals. Several possible structures of optical M-PSK and M-QAM transmitters are shown and theoretically analyzed. Differences in the optical transmitter configuration and the electrical driving lead to different properties of the optical multi-level modulation signals. This is shown by deriving general expressions applicable to every M-PSK and M-QAM modulation format and exemplarily clarified for square-16-QAM modulation.

Reliability of FSO links in next generation optical networks

Abstract: Free space optical (FSO) links can be used to setup FSO communication networks or to supplement radio and optical fibre networks. Hence, it is the broadband wireless solution for closing the "last mile" connectivity gap throughout metropolitan networks. This paper gives an overview of free-space laser communications in principles and applications. Investigations in cooperation with COST 270 and SatNEx and improvements for the future systems will form the core of the publication.

P-cycles in multi-failure network survivability

Abstract: We introduce a new mechanism to provide multi-failure survivability based on p-cycles. This mechanism called MFS (multifailure survivability scheme) consists of two stages: off-line centralized calculation and on-line distributed selection. Simulation results show that MFS has high probability to survive multiple failures without adding any extra capacity.

Failure-independent path protection with p-cycles: efficient, fast and simple protection for transparent optical networks

Abstract: Failure independent path-protecting (FIPP) p-cycles are an extension of the basic p-cycle concept which retains the property of pre-cross-connection of protection paths while acheiving end-to-end failure-independent path protection switching against either span or node failures. An issue with the current method of shared-backup path protection (SBPP) in a transparent optical network is that spare channels for the backup path must be cross-connected on-the-fly upon failure. It takes extra time and signaling to make the required cross-connections but, more importantly, until all connections are made it is not actually known if the backup optical path has adequate transmission integrity. Thus, pre-failure certainty about optical path integrity is an important reason to have backup paths fully pre-connected before failure. FIPP p-cycles support the same failure-independent, end-node activated switching of SBPP but with fully pre-connected protection paths. FIPP p-cycles may therefore be especially attractive for transparent optical networks. FIPP p-cycle network designs also exhibit capacity efficiency that is characteristic of path-oriented schemes. We think it is the only scheme known with these very high efficiencies, failure independence, and the property of fully pre-cross-connected protection paths.

Capacity analysis in indoor wireless infrared communication using adaptive multiple subcarrier transmission

Abstract: In the research field of indoor wireless IR communications state-of-the-art systems achieve high data rates through angular or spatial diversity. An innovative concept for performance improvement in IR system, based on signal processing and adaptive modulation, is proposed. This technique, known from DSL, and currently under discussion for RF wireless, seems also attractive for IR indoor systems, but needs to be examined under the specific conditions of the wireless optical channel (new problem statement). As first evaluation step, we perform capacity analysis to assess potential data rates in the multi-path IR channel present in most rooms. We derive the optimal power control for IR channels subject to an optical power constraint. Results show that, depending on the channel state, system capacity dramatically varies which can be efficiently exploited only by an adaptive system.

SWIFT: a testbed with optically switched data paths for computing applications

Abstract: This paper reports the implementation of SWIFT, designed to enable testing of novel network architecture for optical interconnects, optical devices, and real world applications. We describe the design and implementation of the testbed using semisynchronous timing and multiple wavelength striping.

OTDM light trail networks

Abstract: Due to the limitation of the electrical port speed, current Ethernet switches can only run at most 10 Gb/s. In order to realize 100 Gb/s Ethernet switching, the OTDM technology can be exploited. OTDM lightpath network has the ability for 100 Gb/s Ethernet switching, however, more modulators need to be equipped in the transmitters, and only connections from the source node to its downstream nodes in a super lightpath can be realized. In this paper, the concept of OTDM light trail networks is proposed. Based on the light trail principle, which allows intermediate nodes to access the light trail, by using OTDM technology, the 100 Gb/s line speed can be realized without increasing the port speed or the number of modulators in the transmitters. One node structure for the OTDM light trail network is proposed and four methods for time slots assignment are classified. It is proved by numerical simulation that OTDM light trail networks can successfully increase the capacity of normal light trail networks. Compared with OTDM lightpath networks, cost can be saved and better performance can be obtained in OTDM light trail networks.

Multi-domain issues of resilience

Abstract: This paper gives an overview and classification of issues related to resilience in a multi-layer multi-domain network environment. Then the work focuses on the Internet inter-AS context, where the introduction of G/MPLS capabilities for traffic engineering may enhance the way traffic is exchanged today. This paper shows that, in this context, network resilience based on fast re-routing can be achieved, complementing existing inter-domain link protection strategies, by using alternative disjoint multi-domain backup paths through other domains. Furthermore, the paper proposes a specific method to apply MPLS label stacking to make such backup paths scalable to larger clusters of inter-protected domains by means of MPLS transit. This transit can be used as a temporary solution before BGP routes are stable. Finally, the latest standardisation activity on the provision of such multiple path information for BGP is also reviewed.

Performance comparison of OCS and OBS switching paradigms

Abstract: Optical burst switching (OBS) is a new optical switching paradigm where traffic can be switched and groomed at a lower level compared to optical switched circuit (OCS). While OCS is useful in carrying highly aggregated long-lived streams that require absolute quality of service (QoS) guarantees, OBS has a role in efficiently carrying bursty best-effort traffic. In this paper, we investigate further the comparative goodput and bandwidth efficiency of OBS and OCS using, on one hand, an adaptive deflection OBS routing that aims at minimizing the burst loss rate and, on the other hand, a routing and wavelength OCS strategy using the best possible routing paths for minimizing the blocking rate.

Impact of deflection routing on TCP performance in optical burst switching networks

Abstract: This work analyzes the behaviour of TCP connections in optical burst switching networks with deflection routing. A simplified model of an OBS network was implemented and a number of TCP based file transfer connections in the OBS network were simulated. Different TCP versions (Tahoe, Reno) in conjunction with different deflection ratios and burst loss probabilities were investigated and compared. The results show that deflection routing leads to a degradation of TCP performance, which is however much lower as in the case where the deflected bursts are dropped instead. The simulations were performed using the simulation program OPNET modeler.

Cost comparison of IP/WDM vs. IP/OTN for European backbone networks

Abstract: As the demand for Internet-based services grows rapidly, carrier IP networks are becoming more of a crucial social infrastructure. Network operators must target to offer higher speeds, larger capacities and higher reliability while trying to reduce cost of operation, flexible introduction of new services and easy adaptation of legacy low-speed traffic to high-speed networks. In this work we compare two proposed architectures from a cost point of view. These two emerging solutions are IP/WDM and IP/OTN. The former consists of core routers connected directly over point-to-point WDM links, whereas the latter connects the core routers through a reconfigurable optical backbone (OTN) consisting of electro-optical cross-connects (OXCs) interconnected in a mesh WDM network. The main result of our analysis is the quantitative cost difference between IP/OTN and IP/WDM for the coming years and the use of 2.5 Gbps vs. 10 Gbps interfaces. Indeed, IP/OTN leads to significant decrease in network cost through reduction of expensive transit IP router ports and by exploiting more scalable and cheap OXC ports.

Impact of burst length differentiation on QoS performance in OBS networks

Abstract: In this paper we address the problem of quality of service (QoS) provisioning in OBS networks focusing in efficiently support of two different classes of service, namely high priority (HP)-to transport loss/delay sensitive traffic like real-time voice; and best effort (BE)-for regular data traffic. First, we provide a brief overview of the state of the art on the addressed problem focusing on the main drawbacks of presented both offset time differentiation and burst pre-emption (BP) schemes. Then we describe a burst length differentiation (BLD) technique that aims to improve the performance when applied together with other QoS techniques. The performance results show that BLD bring profits in particular when combining with BP scheme.

Remote amplification in high-density passive optical networks

Abstract: In this work, we aim to highly increase the splitting ratio of FTTH access passive optical networks (PON), by means of remote optical amplification. A remote optical coupler accommodating a remotely-pumped EDFA is proposed, and it is designed for burst mode operation in access networks, increasing the splitting ratio in a factor of /spl times/ 128, in combination with local EDFA.

Efficiency of information update strategies for automatically switched multi-domain optical networks

Abstract: The routing and wavelength assignment algorithm is a complex task in today's dynamically switched networks As the number of network nodes and links increases, advertising link states requires more control messages, larger databases and more processing capacity while searching for an available path Information aggregation in multi-domain networks helps us to reduce the number of advertised links Furthermore, there are numerous information update strategies that also result in less link state control messages However, these enhancements are done on the account of information inaccuracy, which leads to higher blocking ratio and longer setup delays In our article we present a physical device abstraction layer for the control plane where interior optical switches having different multiplexing capabilities and exterior autonomous domains are treated in a unified way Next we show and analyse solutions for how to apply information update strategies on multilayer networks and how to extend these strategies to fit into multi-domain environment

Sensitivity of quantum dot semiconductor lasers to optical feedback

Abstract: Summary form only given. We measure the line-width enhancement factor of quantum dot semiconductor lasers and analyse its impact on the sensitivity to optical feedback. In particular, we show that the line-width enhancement factor can be relatively large due to both inhomogeneous broadening but also due to the plasma effects from non-resonant carriers. However, the devices have a low sensitivity to optical feedback mainly due to the strong damping of the relaxation oscillations that can be associated with gain saturation.

Techno-economic comparison of optical access networks

Abstract: A techno-economic comparison of five different optical access network (OAN) architectures is presented. We consider several novel techniques that we have presented and demonstrated in previous works, offering more efficient fiber use than point-to-point (P2P) networks as well as power splitting passive optical networks (PS-PON). A total cost and cost-per-bandwidth value for the each architecture is calculated in order to have a fair comparison between them. Both CWDM and DWDM combined with bidirectional reflective optical network units (ONU) have been demonstrated to decrease the CAPEX of the network.

Ultrafast header processing in all-optical packet switched-network

Abstract: Header processing in all-optical domain in ultrafast photonics network is challenging issue. In this paper, we present modelling and simulation of all-optical header processing based on pulse position modulation (PPM) format for 100 Gbit/s packet-switched network composed up to 256 nodes. Both the header address codeword (8-bit) and the routing table are converted into PPM format, where the later offers reduced entries compared with the existing routing table. Simulation results show that matching of 256 8-bit header address with routing table entries can be performed effectively and as fast as possible using all optical AND gates.

Evolution of the user controlled lightpath provisioning system

Abstract: New network management tools such as user controlled lightpath provisioning, UCLP, have appeared to allow institutions and research centres manage their own dark fiber and wavelength networks. Early versions of UCLP have been released and its functionality has been demonstrated; but two main drawbacks have been identified: only one switch model is supported and there is no topology discovery/routing schema. The work presented in this paper overcomes these limitations.

Hybrid WDM/TDM PON based on bidirectional reflective ONUs offering differentiated QoS via OBS

Abstract: An AWG access architecture based on reflective ONUs and a laser stack at the OLT is presented. By means of optical bursts switching, the network is capable of offering QoS and dynamic bandwidth allocation. All the network intelligence is located at the OLT, simplifying the end user equipment and reducing overall costs. The ONUs are dynamically polled by the OLT, which runs a centralized OBS protocol. Numerical analysis and network simulations have been carried out to demonstrate the performance of the proposed access scheme.

Routing techniques in optical packet-switched networks

Abstract: In the last few years research on optical packet-switching has mainly concentrated on issues at the single node level. This paper intends to discuss about the problems arising when the focus is moved towards a network-wide scope. In particular, an overview of routing techniques that may be adopted in an optical packet-switched backbone is presented, showing the effects of adaptive multi-path routing strategies on the network performance. Furthermore, performance differentiation based on different routing and contention resolution strategies is proposed and analyzed in a simple QoS-aware scenario. Then, the application of adaptive routing strategies to network recovery in case of single link failure is also discussed.

Cost optimization method for multiple attack localization and identification in all-optical networks

Abstract: In emerging all-optical networks, efficient monitoring and estimation of signal quality along a lightpath are of highest interest because of their importance in diagnosing and assessing the overall health of the network. This is because transmission in these networks is limited by a number of effects such as optical crosstalk and amplified spontaneous emission. In particular, crosstalk is additive and can be exploited to perform service disruption attacks upon the whole network. Since these attacks can spread rapidly through the network, causing additional awkward failures and triggering multiple undesirable alarms, they must be detected and identified at any point in the network where they may occur. Due to transparency, this requires particularly the availability of expert diagnostic techniques to measure and control the smallest granular component, the wavelength channel. However, to monitor all wavelengths at several detection points in a node is likely to be a very expensive solution. In this paper we show that monitoring information for any established lightpath on the output side of each optical cross-connect node, is sufficient to correlate additional monitoring information that can be very useful for localizing multiple attacks and identifying their natures in all-optical networks.

Novel glass compositions and fabrication technologies for photonic integrated circuits

Abstract: Heavy metal fluoride, chalcogenide, and fluoro-tellurite glasses proffer photonic integrated circuit functionality over a wide wavelength range, and combine high optical non-linearity with the ability to incorporate active dopants. The ability to access a range of glass compositions offers great flexibility in both design and processing. In this paper, we present fabrication methodologies for producing such novel glass-based waveguide components.

Quality of service differentiation in optical packet/burst switching: a performance and reliability perspective

Abstract: This article addresses the broad definition of quality of service (QoS) in optical packet/burst switched (OPS/OBS) networks. First we identify the QoS concept, we then provide an overview of existing service differentiation techniques available for OPS/OBS. We include both performance and dependability, and discuss how OBS/OPS networks can be implemented taking both parameters into consideration. Specific reliability issues in OPS/OBS networks are identified, and the function of performance differentiation techniques is evaluated in light of reliability and differentiation of reliability.

Measurement-based alternative routing strategies in optical burst-switched networks

Abstract: Optical burst switching (OBS) is a very promising technology for the next generation of optical Internet. In OBS networks, contention caused by multiple bursts competing simultaneously for a given wavelength on a fiber link, significantly increases the burst dropping probability and hence deteriorates the overall network performance. That is the reason why finding solutions in order to minimize burst dropping due to resource contention is one of the critical design issue in OBS. This paper proposes and analyzes three new deflection routing strategies that resolve contention with significantly better performance compared to the previous ones that have been previously proposed. One of the drawbacks of the deflection routing mechanisms presented in the literature is their lack of flexibility for computing the alternative paths based on some clear design constraints. The proposed deflection strategies are based on different alternative path computing methods with a burst dropping anticipated feature: (i) Least loaded node (LLN), (ii) LLN/U-turn and (iii) LLN/U-turn with load balancing. Simulation was conducted on the Pan-European COST 266 optical network to analyze the proposed strategies.

Numerical optimisation of side pump-light couplings in power lasers based on double-clad optical fibres

Abstract: The coupling of fibre power laser pump light through special couplers is described. The results of the numerical optimisation of the couplers' parameters are reported and compared with experimental results.

Optimal monitor placement scheme for single fault detection in optical network

Abstract: This paper presents monitor placement scheme for single node fault detection in optical network. A single fault at a node may generally produce single/many alarms; as a result it becomes very difficult to detect the exact origin of failure. Our two-phased scheme minimizes the placement of the number of monitors to detect the origin of fault in polynomial time. We demonstrate the performance of our scheme on 14-node NSFnet.

/spl lambda/-path fragmentation and de-fragmentation through dynamic grooming

Abstract: In multi-layer networks, where more than one layer is dynamic, i.e., connections are set up using not only the upper, e.g., IP layer but the underlying wavelength layer as well leads often to suboptimal performance. In this paper we discuss the lightpath fragmentation and de-fragmentation problem, where the lightpath system cannot follow the traffic changes fast enough. We show what it depends on, when is it critical and how much does it deteriorate the performance of the network.

Analysis of a bandwidth allocation protocol for Ethernet passive optical networks (EPONs)

Abstract: This article deals with the problem of bandwidth allocation in the upstream channel for Ethernet passive optical networks (EPONs). EPONs are an emerging access network technology that provides a low-cost solution for deploying optical access lines between a carrier's central office and a customer site. In particular, in this paper we evaluate a simple modification of the bandwidth allocation algorithm called multi point control protocol (MPCP). Simulations results, obtained using OPNET/spl trade/ modeler, show that the modified algorithm outperform the original one in terms of maximum available bandwidth and packet wait time in upstream direction.