Synchronous Optical Network Research Articles

A 1-16-Gb/s All-Digital Clock and Data Recovery With a Wideband, High-Linearity Phase Interpolator

An all-digital phase interpolator (PI)-based clock and data recovery (CDR) is proposed in this paper to accommodate any data rate continuously from 1 to 16 Gb/s with quadrature sampling clocks from 4 to 8 GHz. A new low-power two-step PI (TSPI) with high linearity over 4–8 GHz range is presented. The all-digital CDR control loop adopts a multimode phase detection scheme enabling continuous data rate support. The digital architecture not only eliminates the large filtering capacitor but also makes the design more tolerant to process, voltage, and temperature variations. The CDR core occupies 0.088 mm2 in a commercial 65-nm CMOS technology and consumes 73.1 mA at 16 Gb/s from a 1.2 V power supply. The differential nonlinearity of the PI is measured to be within 0.48 LSB. The measurement results show that this CDR can function at the proposed phase detection modes and is able to exceed the synchronous optical networking (SONET) OC-192 jitter tolerance mask at least by 0.2 unit interval at high frequencies (4–100 MHz) with a $2^{31}-1$ pseudorandom binary sequence data pattern at 10 Gb/s and a target bit error rate of $10^{-12}$ .

Development of ultrastable fiber-optic time and frequency reference networks in Africa.

The unparalleled accuracy of modern-day atomic clocks has stimulated the development of time and frequency comparison techniques, with optical frequency transfer over fiber networks emerging as the preferred method. It has been demonstrated that frequency transfer over optical fibers has an order-of-magnitude better stability and accuracy than traditional satellite-based techniques. Precise time has become an essential service for most critical infrastructure and applications. New progress in LTE and 5G will demand more access to precise time with accuracies of under 10 ns. Although this technology exists in Africa, continuous improvements are required. With the arrival of the Square Kilometre Array (SKA) in Africa, the National Metrology Institute of South Africa (NMISA) upgraded its time and frequency infrastructure in order to support the stringent time accuracy requirements of the MeerKAT and SKA telescopes. Over the past five years, the Centre for Broadband Communication at the Nelson Mandela University has been conducting exciting and cutting-edge research looking at new and innovative ways for coherently disseminating high-speed data and clock over optical fiber networks. This paper reports on recent research progress made in developing synchronous optical networks in South Africa and across the African continent. This paper begins by presenting a pioneering all-optical approach for measuring the round-trip latency time along a spooled G.652 single-mode fiber. This has been realized by optically injecting a pulse-per-second (PPS) signal from a distributed feedback laser into the slave mode of a 1550 nm vertical cavity surface emitting laser (VCSEL) located at the receiver end. A round-trip fiber time delay of 113.2 µs was experimentally measured over 22 km. Furthermore, the jitter instability of an optically modulated PPS was measured as a function of temperature. A jitter of 434.82 ps was measured during the night-to-day temperature cycle (5°C-25°C). The impact of polarization fluctuations on jitter stability is presented. A maximum jitter of 417.88 ps was measured for the transmitted PPS along the aerial fiber. Lastly, a novel technique for distributing a stable microwave reference frequency, using an intensity modulated VCSEL, is presented. The novel frequency dissemination and synchronization system proposes the use of a VCSEL-based phase correction actuator together with the inherent chromatic dispersion properties of the fiber. Frequency instabilities of 4.18939×10-12 at 104s without active noise cancellation and 4.86×10-14 at 104s with active noise cancellation were successfully measured across the 26 km G.655 fiber link.

Improving Fibre Optics Transmission with Wave Length Division Multiplex through Routed-Switching Network

The Optics Fiber link is implemented to satisfy various types of networks, with a wide range of transmission capabilities and improved speed in signal delivery. The link carries multiple signals and for adequate transmission, multiplexing of signals, each signal component, is aggregated and transmitted over a common link which is regarded as multiplexing. The wavelength-routed network bridges the gap of the timeshare, which has retardation on speed and efficiency. The wavelength division multiplex (WDM) is a multiplexing technique designed to suit fiber optics and achieves speed demands, as against time-division multiplexing(TDM) for analog continuous signals (CT) and frequency division multiplexing(FDM) for discrete-time signals(DT). The synchronous optical network (SONNET) and synchronous digital hierarchy (SDH) and the Asynchronous transfer mode (ATM) create an inter-switching system using various matrix dimensions, of 2 X 2, 8 X 8 and other multiples to achieve a versatile routing switching technique. Wavelength division Multiplex and it’s a dense modification (DWDM); have greatly improved the quality and speed of signal transmission over all other techniques.

Reliability-aware ring protection link selection in Ethernet ring mesh networks

Ring topology is an appropriate solution to be applied on the carrier Ethernet networks due to its high switching speed when one of the links fails. Meanwhile, the ITU-T G.8032 Ethernet ring protection (ERP) recommendation was developed to compete with the switching speed of synchronous digital hierarchy (SDH)/synchronous optical networking (SONET) rings. Nevertheless, ERP has emerged some new optimization issues that the most important of which is to find the ring protection link (RPL). In addition, this issue should also satisfy the network reliability requirements as a key performance parameter. To cope with this problem, in this paper, a new approach is proposed. The main idea behind the proposed approach is to analyze the impact of network links on the overall network reliability. In this regard, the proposed approach consists of five steps: (1) computing the reliability equation for the network through the spanning tree set method, (2) calculating the reliability importance for each link through the Birnbaum importance measure, (3) sorting links based on reliability importance by investigating numerical results, (4) selecting the most appropriate links as RPL per ring by taking into account two modes of working and protection, and finally (5) choosing a ring hierarchy based on the selected RPLs. Performance evaluations demonstrate that the proposed approach provides significant improvement in network reliability compared to the representative approaches.

Broadband Services Implementation by Using Survivable ATM Architecture

In Communication Networks, connectivity with Data Voice and Video Services are enhanced by means of NXN connectivity. These three domains play a vital role viz interconnection of users (Networking), Transition from one stage to another (Switching) and determining the path connectivity (Routing are main to enhance the single period to multiperiod network services. Survivability techniques focus on improving the network efficiency rather than redundancy. Hence this paper focuses on the General Fiber Network Architecture by using ATM (Asynchronous Transfer Mode) with SONET (Synchronous Optical Network and also enable its support enhancement by using uniform Multiplexing Switched Network (MSN) and Transfer Mode (TM). It refers to the networking, switching and routing by using multiplexing process in end-to- end communication. In the previous era many experiments that use ATM technology, by integrating digital transmission services in a network of fiber optics media (B-ISDN) was used. In this paper ATM standards, switches are used to conduct the experiments by using Optical Cross Connectivity (OCC), Optical Path Protection and Restoration (OPPR), Optical Network Integration Scheme (ONIS) are presented by using Survivable ATM Architecture (SATMA-BS).

Analysis and design of weighted MPC in incoherent synchronous OCDMA network

In this paper, a novel spreading code design in incoherent synchronous Optical Code Division Multiple Access networks is introduced. This new code is designed by remodeling and improvising the existing concept of Modified Prime Code (MPC) sequences. In addition, it has been generated at optimum code weight and sufficient code length with respect to the new MPC, Uniform Cross-Correlation MPC, Double Padded MPC and Enhanced MPC. The proposed new code is named as Weighted MPC (WMPC). The used technique to generate the WMPC sequences is based on XOR operation between code words of MPC and then rearranging between them. Such operation is performed to increase code weight. The proposed coding technique has a capability to provide better correlation results, higher throughput, minimum Multiple User Interference and good network performance. Furthermore, the auto and cross-correlation properties of WMPC sequences were investigated, where the results were compared with the correlation results of other Prime Codes family.

Business Risk-based Redundancy Points Identification in Synchronous Digital Hierarchy Optical Networks

Locating redundancy points in a Synchronous Digital Hierarchy optical network is a challenging task for service managers. Here, we present a model capable of locating suitable points for the application of asset redundancy to reduce disruptions to the operation of the network, based on the risk to the business. The model was implemented by means of an algorithm called Asset Redundancy Location Indicator (ASP), which performs fault analysis based on the dependence between the elements of the network and the risk of failure. The output of the model allows network administrators to make better decisions when defining critical network redundancy points. A case study was carried out using the ARPA2 reference network. The paper also reports on the case study results.

Enhancing Fault Tolerance and Resource Utilization in Unidirectional Quorum-Based Cycle Routing

Cycle-based optical network routing, whether using synchronous optical networking rings or p-cycles, provides sufficient reliability in the network. Light trails forming a cycle allow broadcasts within a cycle to be used for efficient multicasts. Optimal communication quorum sets forming optical cycles based on light trails have been shown to flexibly and efficiently route both point-to-point and multipoint-to-multipoint traffic requests. Commonly, cycle routing techniques use pairs of cycles to achieve both routing and fault tolerance, which use substantial resources and create the potential for underutilization. Instead, we intentionally utilize $R$ redundancy within the quorum cycles for fault tolerance such that every point-to-point communication pairs occur in at least $R$ cycles. We develop a generalized $R$ redundancy cycle technique that provides optical networks high fault-tolerant communications capability. When applied using only the single unidirectional cycles rather than the standard paired cycles, the generalized $R$ redundancy technique has been shown to almost halve the necessary light-trail resources in the network. However, due to unidirectional nature, a small percentage of node pairs for one-to-one communication may not have exactly two paths. For this reason, we further develop a greedy cycle direction heuristic and show a reduction of missing pairs. More importantly, we show that the resource requirement is reduced while maintaining the fault tolerance and dependability expected from cycle-based routing. The result is a set of cycles with 96.6%–99.37% fault coverage, while using 42.9%–47.18% fewer resources.

A New Prime Code for Synchronous Optical Code Division Multiple-Access Networks

A new spreading code based on a prime code for synchronous optical code-division multiple-access networks that can be used in monitoring applications has been proposed. The new code is referred to as “extended grouped new modified prime code.” This new code has the ability to support more terminal devices than other prime codes. In addition, it patches subsequences with “0s” leading to lower power consumption. The proposed code has an improved cross-correlation resulting in enhanced BER performance. The code construction and parameters are provided. The operating performance, using incoherent on-off keying modulation and incoherent pulse position modulation systems, has been analyzed. The performance of the code was compared with other prime codes. The results demonstrate an improved performance, and a BER floor of 10−9 was achieved.

Complete Power Management System for an Industrial Refinery

Islanded power systems for critical facilities require a robust, secure, and reliable power management system (PMS) that can respond to system disturbances and avoid blackouts to ensure process survivability. A facility in Saudi Arabia with four gas-oil separation plants and one natural gas liquids’ recovery facility operates with a total installed generation capacity of approximately two gigawatts and no utility interconnections. This paper discusses PMS components, such as automatic generation control (power and frequency), volt/VAR control systems (reactive power and voltage), intertie power factor control, high-speed generation shedding, and runback, and high-speed load shedding, along with an overview of the overall system architecture and the state-of-the-art dual-ring time-division multiplexing synchronous optical network communications networks at this facility. High-speed generation-shedding and load-shedding systems are designed with overfrequency- and underfrequency-based secondary backup protection schemes to provide additional system reliability. This paper also introduces a transient-level computer model of the facility power system, which is used for functional testing of the PMS components.

Bang‐bang cycle‐slip detector improves jitter‐tolerance in SONET PLL/DLL CDR

SummaryThe phase‐locked loop circuit (PLL) cycle‐slips (CS) phenomenon is a problem in two‐level baseband clock and data recovery (CDR) data‐synchronization. A singular example is that of a CDR synchronizer that uses a PLL in cascaded with delay‐lock‐loop (P/DLL) architecture. The CS issue is most evident when testing jitter‐tolerance to sine‐modulated jitter, particularly for sine‐modulated jitter‐frequencies near the PLL bandwidth. Reuse of a bang‐bang frequency‐detector, already on board of reference‐less CDRs, does CS detection and provides for suppression producing a clean demodulation. In the cascaded‐DLL of Rhee's P/DLL [1], this CS‐suppressed PLL‐clock assures proper DLL operation to broadband the jitter‐tolerance recommendation of the synchronous optical network (SONET). Copyright © 2016 John Wiley & Sons, Ltd.

White Rabbit Precision Time Protocol on Long-Distance Fiber Links.

The application of White Rabbit precision time protocol (WR-PTP) in long-distance optical fiber links has been investigated. WR-PTP is an implementation of PTP in synchronous Ethernet optical fiber networks, originally intended for synchronization of equipment within a range of 10km. This paper discusses the results and limitations of two implementations of WR-PTP in the existing communication fiber networks. A 950-km WR-PTP link was realized using unidirectional paths in a fiber pair between Espoo and Kajaani, Finland. The time transfer on this link was compared (after initial calibration) against a clock comparison by GPS precise point positioning (PPP). The agreement between the two methods remained within [Formula: see text] over three months of measurements. Another WR-PTP implementation was realized between Delft and Amsterdam, the Netherlands, by cascading two links of 137km each. In this case, the WR links were realized as bidirectional paths in single fibers. The measured time offset between the starting and end points of the link was within 5ns with an uncertainty of 8ns, mainly due to the estimated delay asymmetry caused by chromatic dispersion.

An Efficient Way to Optimize Bandwidth using Dedicated Path Protection for Sonet/SDH Network

SONET stands for synchronous optical network which is a time-division multiplexing process (TDMA) for providing bandwidth Services for the end users which works at application level. High Speed data communication and telecommunication traffic are handled with the use of time division technology. For providing efficient high capacity networks required by telecommunication and data services the SONET/SDH standard is used since it uses TDMA for bandwidth services. The Service providers are looking forward to find automatic ways of commissioning the channels associated with the SONET/SDH since manual provisioning is not possible due to high bandwidth requirement. Another thing which is most important is to cover the protection of the optical network in case of failure of any path used for data transfer. An Automatic Path protection algorithm is implemented and moreover analyzed. The algorithm is works for LCAS, VCAT like issues. The Dedicated and shared path protection mechanism has been used for the efficient use of the SONET/SDH network. In this research the basic parameters like probability error, QOS of network, Accepted request and Rejected request have been analyzed by our algorithm. We also investigated the Bandwidth constraint. Using proposed algorithm we have improved the bandwidth utilization.

A Study on Sonet and SDH with their Defects in Optical Network

Background Objectives: Data transmission over a communication channel, should provide important facilities to be added, including data framing, error checking and to manage the channel. Methods/Stastical Analysis: This is a complete review paper and theoretically we intend to explain the basics of SONET / SDH, Architecture, Bit rates, Netowork configurations etc. All these are standardised and approved by ANSI. Conclusion: One would get to know what Synchronous Optical Network / Synchronous Digital Hierarchy (SONET/SDH) is all about and how exactly are they used through this paper. Also, the merits and de-merits are completely analysed.

A Combinatorial Optimization Approach to Solve the Synchronous Optical Network (SONET) Problem

Synchronous Optical Network (SONET) is a network with a fast service capability. Most of businesses that deal with finance are will-ing to pay high rates of money just to get reliable continuous connections. The problem is one of assigning each customer to a ring without violating the capacity constraints. The goal is to minimize the size of each ring without sacrificing each customer demands. This paper is to introduce a new effective mathematical approach to optimize the SONET network. The main idea is to transform SONET problem formulation to the capacitated vehicle routing problem.

Highly Reliable and Large-Capacity Packet Transport Networks: Technologies, Perspectives, and Standardization

With the recent prevalence of Internet protocol-based services, packet traffic is rapidly becoming the mainstream of data traffic. This has increased the demand for transport network technology that can efficiently accommodate the large capacity of both packet-based and circuit-based traffic while achieving high reliability, sufficient operation, and maintenance capability comparable to that of traditional transport networks such as synchronous digital hierarchy or optical transport networks. This study gives an overview of packet transport technologies including Ethernet and multiprotocol label switching (MPLS), and provides details of MPLS-TP (transport profile), recently developed as a promising next-generation packet transport technology. Its standardization in International Telecommunication Union, Telecommunication Standardization Sector and Internet Engineering Task Force is also described. Then, further perspectives are given on MPLS-TP applications including layer convergence of transport networks for cost-effective and simple operation.

Optimal Algorithms for Near-Hitless Network Restoration via Diversity Coding

Coding-based restoration techniques have proactive restoration which results in time savings over other state-of-the-art restoration techniques. Diversity coding is a coding-based recovery technique which offers near-hitless restoration with a competitive spare capacity requirement with respect to other techniques. In this paper, we show that diversity coding can achieve sub-ms restoration time. In addition, we develop two optimal algorithms for pre-provisioning of the static traffic and one for the dynamic provisioning of the traffic on-demand. There is one algorithm for systematic and one for non-systematic diversity coding in pre-provisioning. An MIP formulation and an ILP formulation are developed for systematic and non-systematic cases, respectively. The MIP formulation of the systematic diversity coding requires much fewer integer variables and constraints than similar optimal coding-based formulations. In dynamic provisioning, an ILP-based algorithm covers both of the systematic and non-systematic diversity coding. In all scenarios, diversity coding results in smaller restoration time, higher transmission integrity, and much reduced signaling complexity than the existing techniques in the literature. Simulation results indicate that diversity coding has significantly higher restoration speed than Shared Path Protection (SPP) and p-cycle techniques from the literature as well as Synchronous Optical Network (SONET) rings, which are commonly deployed by service providers today. In terms of capacity efficiency, it outperforms SONET rings and 1+1 APS, whereas it may require more extra capacity than the p-cycle technique and SPP. Diversity coding offers a preferable tradeoff which offers two orders of magnitude increase in restoration speed at the expense of less than 26% extra spare capacity.

Experimental validation of domain-level gradient-based and hierarchical PCE-based routing and control in heterogeneous optical networks

A domain-level gradient-based routing (DLR) algorithm for heterogeneous optical networks with synchronous digital hierarchy and optical transport network domains is proposed and experimentally validated. This algorithm classifies domains into groups with incremental levels on the basis of domain-level partitioning, and guides paths level by level along a gradient on the basis of interdomain routing tree evolution. The proposed algorithm is implemented in the hierarchical path computation element-based control architecture for connection provisioning. Testbeds with commercial and emulated nodes are established to verify the feasibility and performance of the algorithm. Experimental and emulation results show that DLR effectively performs in terms of network blocking probability, real time characteristics, and scalability.

Optimal Capacity Provisioning for Survivable Next Generation Ethernet Transport Networks

Ethernet ring protection (ERP) has recently emerged to provide protection switching for Ethernet ring topologies with sub-50-ms failover capabilities. ERP's promise to also provide protection in multi-ring mesh packet transport networks will position Ethernet as a serious competitor to conventional synchronous optical networking (SONET)/synchronous digital hierarchy (SDH) and the technology of choice for carrier networks. Operating ERP in multi-ring mesh networks, however, comes with unique challenges. This paper reveals some limitations of prior work which relied on exhaustive enumeration and proposes some modifications to overcome these subtle limitations. We also present an optimal ERP design formulation by jointly solving the problem of ring protection link placement and ring hierarchy selection whose objective is to minimize the overall capacity requirement. Our design approach is formulated as an integer linear program, which is shown to provide optimal capacity provisioning and be computationally scalable.

Data Transport Networks: Case Studies in a Public Transit Environment

Ethernet has become the de facto standard for providing data transport not only throughout the Internet but also for numerous private and industrial networks. Before Ethernet's dominance, circuit-switched networks (or time-division multiplexed networks such as synchronous optical network (SONET) are popular choices for applications that require flexible and reliable data transport. Over the past ten years, packet-switched networks in general (and Ethernet in particular) usurped the role formerly played by these circuit-switched networks. But is this a good development given that not all applications that require data transport are created equally? This article explores the current trend of using packet-switched as opposed to circuit-switched networks in the context of providing data transport for rail-based public transit agencies and, after examining five case studies, draws conclusions that are relevant for public transit agencies.