Optical Packet Networks Research Articles

Add-drop Benes network for scalable optical packet networks

For the scalable optical packet transport networks, an innovative design of add-drop Benes network (ADBN) is presented where the cost and energy consumption can be considerably reduced by element savings in the architecture. In a WDM optical packet transport switching node, the ADBNs are interconnected to achieve buffer sharing among multiple ADBNs. A corresponding switch configuration algorithm and architecture rules for the single ADBN and shared ADBN are proposed to mitigate the limited connection capability of the proposed ADBN designs. Switch scalability is verified in consideration of a crosstalk noise performance and element counts.

Investigating the Performance of a Transient-Suppressed EDFA in Optical Packet and Burst-Switched Networks

We describe a series of system measurements investigating the performance of a burst-mode or transient-suppressed (TS)-EDFA, specifically designed to reduce the impact of gain transients in dynamic optical networks. We assess the performance of this TS-EDFA in a variety of network contexts. We compare the performance of the TS-EDFA with conventional amplifiers (C-EDFAs) and show its compatibility with supplementary gain control techniques. Finally, we measure gain-transient accumulation along long links using a recirculating transmission loop and show that, for packet-transmission, the number of hops is limited by accumulated transients for a C-EDFA, but limited by accumulated noise for the TS-EDFA.

An Overview of Optical Label Switching Technology

Optical label switching is a new technology of optical switching, which can overcome the electronic bottleneck of optical communication effectively, optical label switching (OLS) network as a specific implementation of future optical packet network has been paid more and more attention, its key technology is the generation and extraction of optical label. In this paper, subcarrier multiplexing label, OCDM optical code label and orthogonal modulation label are described and discussed. Their strength and weakness are analyzed.

Quality of Service Provisioning in Optical CDMA Packet Networks

An enhanced media access control (MAC) layer protocol that uses the signaling method benefits of the physical layer in order to provide different levels of quality to different users in optical code-division multiple-access (OCDMA) packet networks is presented. In the proposed network architecture the users are categorized into two classes of service, one having a higher quality level and the other having a lower quality level. Users of each class transmit at the same power level and different from the other classes’ users. Also, the MAC of each user estimates the amount of interference on the channel and adjusts the packet transmission’s time to improve network performance. Through simulation it is shown that the combination of appropriate power assignment to users and proper MAC algorithm parameters can provide various quality of service (QoS) metric levels on metrics such as normalized throughput and packet error rate. This is achieved by dividing the available resources of the OCDMA network between the users of each class. To make the QoS provider method more practical in data communication networks, we have studied the fairness issue by defining two parameters related to the normalized throughput of each class.

IP--: A Reduced Internet Protocol for Optical Packet Networking

IP− − is proposed as an Internet Protocol suitable for optical packet networking. As optical routers require much faster control than electric ones and lack of optical buffers other than those by fiber delay lines requires fixed time control, Internet Protocols must be at least as simple as IPv4 and much simpler than IPv6. IP− − also addresses issues of IP address space exhaustion and IP routing table explosion.

Optical Packet Network With Limited-Range Wavelength Conversion: A Novel Formalization of the Optimal Scheduling Problem

In this paper, we consider synchronous optical packet networks formed by switches equipped with a complete set of limited-range wavelength converters. On these networks, we dealt with scheduling algorithm that maximizes the switch throughput. So far, previous literature works have formalized this scheduling problem as the finding of a maximum bipartite matching (MBM) in a convex graph. The MBM formalization has collected various follow-ups, mainly focused on measuring switch-level performance. We revise the MBM formalization by measuring network-level performance. Surprisingly, we find out that when optical switches are cascaded, MBM formalization has two not negligible lacks: (1) a useless degradation of optical signal quality and (2) a tendency of shifting optical packets toward lower wavelengths, thus increasing the occurrence of wavelength contention. To solve these issues, we propose a novel formalization of the scheduling problem as the finding of a MBM with minimum edges weights (MW-MBM). We show that MW-MBM outperforms MBM in terms of both network throughput and optical SNR. Performance evaluation is carried out by means of NS2 simulator that we extend to toughly model optical components (e.g., semiconductor optical amplifier four-wave-mixing wavelength converter). The simulator is provided as open source.

Performance Analysis of a Spectrally Phase-Encoded Optical Code Division Multiple Access Packet Network

We analyze the performance of a spectrally phase-encoded optical code division multiple access slotted packet network based on a simple protocol. The steady-state throughput and average packet delay are derived as two measures to assess the performance of the network. First, only multiple access interference is considered and other sources of noise are neglected. In this context, comparing different systems with the fixed bit rate and chip duration leads us to conclude that increasing the code length improves the performance of networks with small average activity; but in highly active networks, decreasing the code length results in a significant improvement in the throughput and average packet delay. Next, Gaussian approximation is used in our performance analysis to consider both shot noise and thermal noise as well as multiple access interference. The packet success probability is derived as a function of transmitted power. It is shown that in a fixed bandwidth and with a fixed bit rate, increasing the code length can lead to better performance in high average powers. But, in the low-power regime, decreasing code length leads to better performance due to the lower level of activity.

All-optical packet synchronizer for slotted core/metropolitan networks

In the framework of synchronous optical packet networks, a cost-effective all-optical synchronizer is an important building block to effectively switch the packets through an optical router. In striking difference to its time-division multiplexing-based electronic counterparts requiring bit level synchronization, an optical router can operate effectively with a much coarser synchronization at packet level. Such a synchronizer is proposed, which can compensate for the time variations between packets transported over several wavelengths. The requested synchronization is achieved with a resolution that is a fraction of the packet duration, which is a process that is adequate to compensate for the delays due to thermal variations between the transport fibers. Because this WDM synchronizer is constructed using slowly reconfigurable and mainly passive components, it is potentially a cost-effective solution. The principle of operation of this synchronizer is described in the context of synchronous slotted optical networks; the functionality of the various building blocks is analyzed, and practical implementation issues of various subsystems for a 80 Gbit/s synchronizer are discussed. Finally, an experimental validation of the proposed synchronizer is made demonstrating the viability of the method.

WONDER: A resilient WDM packet network for metro applications

This paper presents the architecture of a Wavelength Division Multiplexing (WDM) optical packet network, called WONDER, that was designed and prototyped in the PhotonLab at Politecnico di Torino, Italy. The design and implementation of the WONDER network aim to assess the effectiveness of optical technologies with respect to electronic ones, trying to identify an optimal mix of the two technologies. The architecture shows interesting resilience properties that enable the design of fast fault-recovery schemes. In this paper, we present the physical topology and node structure of the prototype, and discuss the implementation and performance of a fault-recovery algorithm.

On Constraints for Path Computation in Multi-Layer Switched Networks

This paper considers optical transport and packet networks and discusses the constraints and solutions in computation of traffic engineering paths. We categorize the constraints into prunable or non-prunable classes. The former involves a simple metric which can be applied for filtering to determine the path. The latter requires a methodic consideration of more complicated network element attributes. An example of this type of constraints is path loss in which the metric can be evaluated only on a path basis, as opposed to simply applying the metric to the link. Another form of non-prunable constraint requires adaptation and common vector operation. Examples are the switching type adaptation and wavelength continuity, respectively. We provide possible solutions to cases with different classes of constraints and address the problem of path computation in support of traffic engineering in multi-layer networks where a set of constrains are concurrently present. The solutions include the application of channel graph and common vector to support switching type adaptation and label continuity, respectively.

Performance analysis of an optical CDMA MAC protocol with variable-size sliding window

A media access control protocol for optical code-division multiple-access packet networks with variable length data traffic is proposed. This protocol exhibits a sliding window with variable size. A model for interference-level fluctuation and an accurate analysis for channel usage are presented. Both multiple-access interference (MAI) and photodetector's shot noise are considered. Both chip-level and correlation receivers are adopted. The system performance is evaluated using a traditional average system throughput and average delay. Finally, in order to enhance the overall performance, error control codes (ECCs) are applied. The results indicate that the performance can be enhanced to reach its peak using the ECC with an optimum number of correctable errors. Furthermore, chip-level receivers are shown to give much higher performance than that of correlation receivers. Also, it has been shown that MAI is the main source of signal degradation

Automatic laser shutdown implications for all optical data networks

Generalized multiprotocol label switching (GMPLS), optical packet, and burst-switched networks in which the synchronous digital hierarchy/synchronous optical network (SDH/SONET) layer is removed may be rendered nonfunctional because the current standard for triggering Automatic Power Reduction (APR) cannot distinguish between a fiber that has been de-energized and a fiber failure. If this standard is applied, without modification, the likelihood of unnecessary amplifier shutdown in optical networks is significant. These shutdown events may impact large regions of the network and render optical links inoperable. To avoid unnecessary amplifier shutdown, amendments to the current operation of APR are suggested.

Performance comparison between S-ALOHA and R3T protocols for multirate OFFH-CDMA systems in optical packet networks

We discuss two newly proposed multiple-access control (MAC) protocols for multirate optical code-division multiple access (OCDMA) networks. The first protocol is slotted ALOHA/optical fast-frequency-hopping code-division multiple access (S-ALOHA/OFFH-CDMA), and the second is round-robin receiver-transmitter/optical fast-frequency-hopping code-division multiple access (R3/OFFH-CDMA). Our main subject is to exploit the potential of the optical fast-frequency-hopping CDMA using a fiber Bragg grating when jointly used with two different MAC protocols in a link layer as an effective way of integrating multirate traffic. The system throughput and the average packet delay are compared for both systems. It is shown that S-ALOHA is better than R3T when the user's activity and the offered load are high, whereas R3T is better for smaller values. Both protocols can be competitive in terms of the system throughput, with the advantage going to the R3T protocol at a moderate offered load. However, the R3T protocol suffers a higher delay mainly because of the presence of additional modes. Finally, the overlapped OCDMA system always outperforms the variable processing gain (VPG) OCDMA system regardless of the protocol used.

Programmable select multiwavelength gigahertz Raman soliton pulse generation

The generation of programmable multiwavelength pulses based on the self-frequency shift of a Raman soliton is demonstrated. The approach produces tunable multiwavelength picosecond pulses. Only select multiwavelength signals with a tuning range of approximately 50 nm are generated with a repetition rate of 9.95 GHz at each wavelength channel. A bit error rate (BER) of better than 1 x 10(-9) was successfully obtained for all the measured multiwavelength Raman soliton pulses. Furthermore, it was found that the signal has an excellent relative intensity noise (RIN) of better than -135.5 dBc/Hz. The BER and RIN measurements show that the frequency-shifted Raman soliton pulses are promising for use in measurement systems, optical gating, signal processing, and wavelength routing optical packet networks with the ability to provide 1:1 communication and 1:N multicasting.

RingO: An Experimental WDM Optical Packet Network for Metro Applications

This paper presents Ring Optical Network (RingO), a wavelength-division-multiplexing (WDM), ring-based, optical packet network suitable for a high-capacity metro environment. We present three alternative architectural designs and elaborate on the effectiveness of optic with respect to electronic technologies, trying to identify an optimal mix. We present the design and prototyping of a simple but efficient access control protocol, based upon the equivalence of the proposed network architecture with input-buffering packet switches. We discuss the problem of node allocation to WDM channels, which can be viewed as a particular optical network design problem. We, finally, briefly illustrate the fault protection properties of the RingO architecture. The main contribution of this paper is the identification and experimental validation of an innovative optical network architecture, which is feasible and cost effective with technologies available today, and can be a valid alternative to more consolidated solutions in metro applications.

Intensity-modulated labeling and all-optical label swapping on angle-modulated optical packets

We proposed and investigated superimposing intensity-modulated labels onto high-speed angle-modulated payloads in optical label-switching packet networks. This can largely simplify the all-optical label swapping, including label extraction, processing, removal, and new label insertion. The transmission performances of 1.244-Gb/s on-off keying labels on 9.953-Gb/s optical frequency-shift keying and differential phase-shift keying payloads were investigated; and the all-optical label swapping was successfully demonstrated with low penalty.

Cutting-Edge Technologies on Broadband and Scalable Photonic-Network?Packet switched networks based on all-optical label processing?

Ultra-high speed all-optical label processing methods are proposed and experimentally demonstrated. These methods dramatically increase the label processing capability. Optical packet switch (OPS) systems and networks based on OPS nodes are expressed as an application of optical processing technologies. First, the 40 Gbit/s/port OPS prototype with all-optical label processor, optical switch, optical buffer, and electronic scheduler is described. The feasibility of OPS networks is verified by experimental demonstrations.

Performance analysis of homowavelength crosstalk in optical packet networks

AbstractIn this paper, homowavelength crosstalk in optical packet networks is evaluated with the following aspects taken into consideration: device crosstalk coefficient, signal extinction ratio, traffic load, node size, and cascadability. Our results are very useful for the design of optical packet networks. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 36: 474–479, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10794

SONET-Framed Optical Packet Networking in the Context of Generalized Multiprotocol Label Switching

This article discusses the evolution of Synchronous Optical Network (SONET) towards support for shared packet media, particularly in light of new developments in the control plane, such as Generalized Multiprotocol Label Switching (GMPLS) and the (UNI) specification. Whereas the current SONET network is largely static and circuitcentered, and typically supports DS-1 and DS-3-level granularities, the emerging packet-centric, GMPLS-controlled optical network will be significantly more dynamic, and characterized by concatenated or virtually concatenated payloads such as STS-3c/12c/48c/192c, and, possibly, STS-1-24v (i.e., 'STS-24c'). In this environment, it will be shown that the differences between such packet-centric SONET networks and 'IP over Optical' network architectures begin to disappear.

Performance analysis of baseband carrier-sense circuit in optical CSMA networks

In future shared medium optical packet networks, collision-free transmission may be achieved by detecting the presence or absence of optical packets on specific channels. Using a baseband carrier-sense circuit (BCSC), the direct detection of baseband optical signals can be employed to provide the carrier-sense capability required to avoid collisions in optical carrier-sense multiple access (CSMA) networks. In this work, we present a new theoretical model to analyze the performance of a BCSC in the presence of additive post-detection electrical noise. We validate the model using experiments and simulations. Our model provides a useful approach to BCSC design in future optical CSMA packet-switched networks.