Synchronous Optical Network Research Articles

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.

Major Players Battle over Layers: Layer-2 and Layer-3 Vendors Tussle over Metro Links

Buried amid industry hoopla about end-user gadgets and macroeconomic issues such as upcoming wireless spectrum auctions, an arcane but increasingly vexing niche of the Internet's architecture has become the subject of considerable debate. At stake is the promised land of carrier Ethernet traffic traversing the globe. In preparing for the next-generation network, however, carriers have had to combine their IP-based core resources with legacy synchronous optical network (SONET) and synchronous digital hierarchy (SDH) access technology in the transport layer. How the world's carriers will best combine and migrate those resources into a robust and warrantable packet-based network is the crux of the issue.

Multiple access interference cancellation in Manchester-coded synchronous optical PPM-CDMA network

A new interference cancellation technique for direct-detection optical code- division multiple-access (OCDMA) network employing pulse-position modulation (PPM) is proposed in this paper. The multiple access interference (MAI) estimation is achieved by pre-reserving one of optical spreading code sequences at the receiver based on the correlation property of padded modified prime codes (PMPC). The estimated interference is then cancelled out after photo-detection process. Additionally, the transmitted signal is Manchester-coded to further improve the system performance. Based on this proposed interference canceller in a shot-noise limited regime, we have obtained an expression for the upper bound of the bit-error probability (BEP) taking into account effects of both MAI and shot-noise. This BEP is compared with that of a PPM-OCDMA without cancellation. Finally, the receiver structure of the proposed optical network unit (ONU) is fairly simple to compare with the conventional cancellation schemes.

Economics of ethernet over SONET/SDH

Ethernet provides a simple, cost-effective solution for transporting enterprise data applications that is fast replacing traditional private line and frame relay services. However, carrier-class Ethernet architecture is still evolving and transport vendors need a flexible architecture that provides a hedge against the timing and extent of migration to Ethernet. Ethernet over Synchronous Optical Network (SONET) provides a viable architecture that allows service providers to start offering Ethernet service without overcommitting themselves, while protecting their embedded base. This paper presents an economic evaluation of Ethernet-over-SONET architecture based on a number of scenarios that serve as building blocks for service provider network transformation. We construct a business model that evaluates the various alternative strategies available to the service provider to address bandwidth demand growth and simultaneous migration from legacy to Ethernet services. © 2007 Alcatel-Lucent.

Analysis of a clock‐recovery technique for circuit emulation services over packet networks

AbstractOne important requirement of circuit emulation services (CES) over packet networks is clock synchronization and timing distribution among the nodes. CES depends on reliable and high‐quality timing for operations. In the time division multiplexing (TDM) world, whether plesiochronous digital hierarchy (PDH), synchronous digital hierarchy (SDH) or synchronous optical network (SONET) based, timing and synchronization is inherent in the design of the network. However, when timing critical services such PDH and SDH/SONET are carried over packet network (e.g. IP, Ethernet, etc.), the timing element is lost and has to be carried across the packet network by other means. A well‐known and widely implemented technique for clock recovery in CES is one that is based on packet inter‐arrival time (sometimes called time difference of arrival) averaging. The technique is very simple to implement but provides good performance only when packet losses and packet delay variation (PDV) are very low and well controlled. This technique has been extensively analysed through simulations but has not been fully characterized analytically with correlated traffic in the literature. In this paper, we provide a full analytical examination of this well‐known clock recovery technique. We analyse the effects of correlation of the delay variation in the traffic stream on the quality of the clock recovered by a receiver. We prove analytically that, for a general input process, high correlation of the delay variation produces a large variance of the recovered clock. Copyright © 2007 John Wiley & Sons, Ltd.

Non-Compressed Video Signal Optical Transmission Equipment and Its Applications for Studio to Transmitter Link (STL)

This paper describes the newly developed video signal transmission equipment for Synchronous Optical Network (SONET) and the Synchronous Residual Time Stamp (SRTS) method for video signals. It explains why a low jitter signal transmission is possible by optimizing the SRTS parameters and reducing high frequency jitters by PLL circuit. Moreover, the broadcasting Transport Stream (TS) signal transmission methods for Studio to Transmitter Link (STL) are reviewed and the proposed reference clock transmission method is discussed. The TS signal transmission experiments are carried out using two route trunks between Sapporo and Asahikawa, for evaluating the characteristics of the reference clock, the modulator output signal, and the quality of the received video. The low jitter and error-free video signals transmission is realized in these trunks

Comparison on the Sensitivity of Fiber-Optic SONET OC-48 PIN-TIAs Measured by Using Synchronous Modulation Intermixing Technique and Bit Error Rate Tester

A novel synchronous modulation and intermixing (SMIM) technique is presented to measure the sensitivity and evaluate the bit error rate (BER) of p-i-n photodiode receivers with transimpedance amplifiers (PIN-TIAs) without using any BER tester (BERT). When using the SMIM technique, the premier receiving measurement performance from the data rates of the synchronous optical network OC-3 to OC-48 was demonstrated. For general TO-46 packaged PIN-TIAs, a minimum intermixed voltage of 12.5 mV obtained by the SMIM method is equivalent to a sensitivity of -31 dBm at a requested BER of <10-10 determined by BERT. The relationship between the monitoring voltage and the BER of the optical pattern received by the PIN-TIA and limited amplifier is estimated. The error of the measured voltage is 0.28 mV, which corresponds to the error sensitivity of 0.09 dB. This would show the accuracy of the simplified and low-cost SMIM technique for in situ diagnostics on a mass-production line

Traffic shaping at the edge node in synchronous optical packet-switched networks

Long-range dependence, short-range dependence and marginal distribution are three key statistical features for incoming traffic, which have a serious impact on network performance. This paper respectively, studies their characteristics during traffic shaping at the edge node in synchronous optical packet-switched networks and highlights the functions of the First-Come-First- Service (FCFS) schedule queue for various offered loads and assembly parameters, including normalized timeout and normalized threshold. Simulation results demonstrate that under light-medium load the FCFS schedule queue works as a low pass filter, i.e., the statistical features before and after the FCFS schedule queue is nearly the same and each of the statistical features approximately follows the same trend. Heavy load drives the FCFS schedule queue into an overload or saturation state and the three statistical features all exhibit different behavior. By adjusting the assembly parameters, the deficiency can be modified.

Traffic shaping at the edge node in synchronous optical packet-switched networks

We propose and demonstrate simple architectures with self-protection capability for the wavelength-division-multiplexed passive optical network (WDM PON). By utilizing two different wavelength bands for the neighboring WDM PONs, the proposed networks can recover the disrupted signals through the fiber links of the neighboring WDM PON. The protection time was measured to be less than 9 ms, and the power penalty caused by the protection process was negligible.

Comparison of transport network technologies for IPTV distribution

The delivery of video services is generally considered a critical and perhaps the most difficult problem for telecommunications service providers to solve to achieve the “triple-play” of video, data, and voice. Transport of a mix of video, high-speed data, and voice — which is vital to maintain a competitive position against cable multiple systems operators (MSOs) — requires new solutions. Gigabit Ethernet interfaces can offer better network economics when combined with reliable synchronous optical network (SONET), wavelength division multiplexing (WDM), and/or fiber transport infrastructure. Here, we compare these transport technologies and present case study results. The case study includes broadcast as well as unicast traffic; SONET drop and continue or Ethernet multicast; a core network to connect super and regional headends/central offices, and an access network to connect regional headends/central offices to serving area locations. In this paper, we demonstrate that next-generation SONET can provide a balanced approach considering network economics and reliability.

Beyond rapid provisioning: Driving value-added services on control plane foundations

Optical control planes came to the forefront during the Internet boom of the late 1990s as the network operations solution of choice for emerging mesh architectures. However, in spite of the numerous advantages, their deployments in service provider networks have been below expectations. While the telecom downturn of the last few years is often blamed, we also posit that control planes lost some of their luster because the applications they were primarily marketed for — rapid provisioning for bandwidth-on-demand services and mesh restoration — failed to get the requisite traction in the marketplace. In this paper, we propose that the changed landscape notwithstanding, optical control planes still fulfill a critical role in the service provider network. We argue that an underlying control plane foundation, with its routing and signaling infrastructure, gives tremendous flexibility to the operator to build new value-added services that can significantly improve network efficiency. Consequently, once deployed, these novel services can provide alternate avenues for revenue and capital expenditure (CapEx) savings in the long term. To that end, we present two applications — link defragmentation for legacy traffic and Ethernet mesh restoration — that leverage virtual concatenation in next-generation synchronous optical network (SONET) standards. We highlight our implementation experiences and show that the underlying control plane infrastructure is key to a low overhead deployment. We quantify the savings and conclude that in the current environment, these new customizable value-added services provide a prudent strategy for increasing service provider traction, especially with respect to long-term CapEx savings.

Impact of interferometer optical path difference speed profile on the Fourier-transform-spectrometry-derived spectrum of a telecommunications signal

The impact of the interferometer optical path difference (OPD) speed profile on the spectrum, derived through the use of Fourier-transform spectrometry (FTS), of a synchronous optical network (SONET) signal is found. The SONET signal carries high-speed data traffic. It also may be modulated by low-frequency intensity or frequency modulation. It is found that the SONET header, high-speed data traffic and low-frequency modulation all manifest themselves as artifacts in the FTS-derived spectrum of the SONET signal. It is shown that a nonconstant OPD speed profile can smooth out these artifacts, making it unlikely that they will be mistaken for carrier signal peaks. However, it is found that smoothing out these artifacts lessens the achievable dynamic range of the FTS instrument in the frequency range of interest, the International Telecommunications Union common (C) and long (L) bands.

Convergence in Optical Transport Networks

Optical transport networks interconnect switches and routers in the network core, or connect high-speed, typically business/enterprise, users to the network (access). These networks are almost entirely based on the Synchronous Digital Hierarchy (SDH) standards today (or the equivalent Synchronous Optical Network (SONET) standard in North America).Traditionally, SDH has been the sole transport network and thus has carried all of the telecommunication service provider's traffic, including voice and data. So, SDH has, in a sense, provided “converged” transport, all along. However, the interfaces provided by SDH equipment for the first 10 years or so (since about 1990 to 2002) were restricted to the rates used by the older plesiochronous digital hierarchy (PDH) systems, namely, 2/34/140 Mbps, or the standard SDH rates, 155/622/2488 Mbps. Data typically originates within an enterprise local area network (LAN), invariably Ethernet at 10, 100 or 1000 Mbps, and had to adapted to a “standard” PDH or SDH data rate, typically using a router within the enterprise. (This application of a router is so prevalent that the PDH interface on a router is called the wide- area network, WAN, interface.)The first step that the SDH standards, and equipment vendors, took to support a data-friendly network was to provide Ethernet interfaces (10/100/1000 Mbps) on the SDH equipment in addition to PDH and SDH interfaces. The provision of Ethernet interfaces on SDH equipment is based on the Generic framing Procedure (GFP), Virtual Concatenation (VCAT) and Link Capacity Adjustment Scheme (LCAS) standards that were published and refined in 2001–03, and which are collectively referred to as the “Ethernet-over-SDH/SONET” or EoS standards. “Next-generation” SDH equipment supporting these EoS standards has been deployed since early 2003; Tejas' first shipment of standards-based EoS equipment to carry commercial traffic was in January 2003.

VCAT-LCAS in a clamshell

Virtual concatenation (VCAT) is a standardized layer 1 inverse multiplexing technique that can be applied to the optical transport network (OTN), synchronous optical network (SONET), synchronous digital hierarchy (SDH), and plesiochronous digital hierarchy (PDH) component signals. By inverse multiplexing, it combines multiple links at a particular layer into aggregate links to achieve a commensurate increase in available bandwidth on the aggregate link. While any inverse multiplexing scheme is about "more bandwidth", the VCAT/LCAS is a general technique that can enable a fairly broad range of network features such as (1) right sizing bandwidth for data applications, (2) bandwidth extraction from a mesh network, (3), bandwidth on demand and IP traffic engineering, and (4) provides new forms of protection-restoration and graceful degradation. In this paper, the authors have given a quick overview of VCAT/LCAS technology and just a few examples of its applications

Analytical formula for radio-frequency spectral monitoring of the SONET frame alignment header

An analytical formula is developed for a previously reported radio-frequency (RF) spectral monitoring of the Synchronous Optical Network (SONET) frame alignment header (FAH), where special RF filters are used before RF power detection to obtain pulses corresponding to the FAH with the pulse amplitude reflecting the in-band signal-to-noise ratio of the channel. As a result, spectrally resolved signal power as well as noise power is derived. The theoretical analysis explains the previous experimental results.

On the resource efficiency of virtual concatenation in SDH/SONET mesh transport networks bearing protected scheduled connections

Virtual concatenation (VCAT) is a Synchronous Digital Hierarchy (SDH)/Synchronous Optical Network (SONET) network functionality recently standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). VCAT provides the flexibility required to efficiently allocate network resources to Ethernet, Fiber Channel (FC), Enterprise System Connection (ESCON), and other important data traffic signals. In this article, we assess the resources' gain provided by VCAT with respect to contiguous concatenation (CCAT) in SDH/SONET mesh transport networks bearing protected scheduled connection demands (SCDs). As explained later, an SCD is a connection demand for which the set-up and tear-down dates are known in advance. We define mathematical models to quantify the add/drop and transmission resources required to instantiate a set of protected SCDs in VCAT- and CCAT-capable networks. Quantification of transmission resources requires a routing and slot assignment (RSA) problem to be solved. We formulate the RSA problem in VCAT- and CCAT-capable networks as two different combinatorial optimization problems: RSA in VCAT-capable networks (RSAv) and RSA in CCAT-capable networks (RSAc), respectively. Protection of the SCDs is considered in the formulations using a shared backup path protection (SBPP) technique. We propose a simulated annealing (SA)-based meta-heuristic algorithm to compute approximate solutions to these problems (i.e., solutions whose cost approximates the cost of the optimal ones). The gain in transmission resources and the cost structure of add/drop resources making VCAT-capable networks more economical are analyzed for different traffic scenarios.

Design for Stability of High-Speed Integrated Photoreceivers: A Tutorial

We propose a Design for Stability (DFS) methodology dedicated to the design of reliable high-speed integrated photoreceiver front-ends. This methodology based on the stability factor, S-parameters and Z-parameters analysis is made of four rules that high-speed designers will apply during the stability check of their design. To demonstrate its effectiveness, the proposed DFS methodology was applied to build a transimpedance amplifier (TIA) compliant to Synchronous Optical Network (SONET) OC-192 (10-Gb/s) standard. Experimental results in agreement with initial design specifications show excellent performances such as: 11 GHz bandwidth, ?20 dBm sensitivity measured at 10-Gb/s for a Bit Error Rate (BER) of 10? 9 and 10 ps peak-to-peak jitter.

A Lagrangian-Relaxation Based Network Profit Optimization For Mesh SONET-Over-WDM Networks

In Wavelength Division Multiplexing (WDM) networks, the huge capacity of wavelength channels is generally much larger than the bandwidth requirement of individual traffic streams from network users. Traffic grooming techniques aggregate low-bandwidth traffic streams onto high-bandwidth wavelength channels. In this paper, we study the optimization problem of grooming the static traffic in mesh Synchronous Optical Network (SONET) over WDM networks. The problem is formulated as a constrained integer linear programming problem and an innovative optimization objective is developed as network profit optimization. The routing cost in the SONET and WDM layers as well as the revenue generated by accepting SONET traffic demands are modelled. Through the optimization process, SONET traffic demands will be selectively accepted based on the profit (i.e., the excess of revenue over network cost) they generate. Consiering the complexity of the network optimization problem, a decomposition approach using Lagrangian relaxation is proposed. The overall relaxed dual problem is decomposed into routing and wavelength assignment and SONET traffic routing sub-problems. The subgradient approach is used to optimize the derived dual function by updating the Lagrange multipliers. To generate a feasible network routing scheme, a heuristic algorithm is proposed based on the dual solution. A systematic approach to obtain theoretical performance bounds is presented for an arbitrary topology mesh network. This is the first time that such theoretical performance bounds are obtained for SONET traffic grooming in mesh topology networks. The optimization results of sample networks indicate that the roposed algorithm achieves good sub-optimal solutions. Finally, the influence of various network parameters is studied.

Design for networks-The ultimate design for X

The true test of how a vendor's systems work is how they work with the service provider's existing systems and with other vendors' systems in operating networks. In this paper, we present various concepts, including design for X (DFX), and introduce the concept of design for networks (DFN), the objective of which is a working, revenue-generating network that meets or exceeds the customer's expectations. In a series of case studies involving optical networks, we show what can go wrong when DFN considerations are not part of the product, network, and service design process. We also discuss such network considerations as synchronization, data communications networks (DCNs), management, and synchronous optical network (SONET)/synchronous digital hierarchy (SDH) interfacing, and we introduce an expansive definition of product and design. Finally, we show how to transform the lessons learned in the field into feedback for the design process so as to improve the end result for both vendor and customer.

Network capacity recovery and efficient capacity deployment in switching centers

One way for service providers to reduce their costs is through network capacity recovery. We describe the problem of recovering capacity by minimizing the switching overhead incurred by multiple switches in a switching center. We also describe the Multiple ATM Switch Configuration Optimization Tool (MASCOT), which addresses this problem. Initially developed for asynchronous transfer mode (ATM) switches, the tool applies flexibly to other devices such Synchronous Optical Network (SONET) cross connects or Multiprotocol Label Switching (MPLS) routers. New services enabled by this tool include (1) reconfiguration of an existing switching center to increase the number of available switch ports and (2) efficient green field design for migrating to new hardware. Given the set of external trunks and the traffic demands between them, MASCOT searches for a switching center topology that minimizes the traffic carried on internal trunks. MASCOT handles a wide variety of switch types with hierarchical constraints imposed by components such as interface cards, processor cards, and slots.