Digital Cross-connect Systems Research Articles

Optical Network Management and Control

While dense wavelength division multiplexing equipment has been deployed in networks of major telecommunications carriers for over a decade, the capabilities of its networking and associated network control and management have not caught up to those of digital cross-connect systems and packet-switched counterparts in higher layer networks. We shed light on this situation by examining the current structure of the optical layer, its relationship to other network technology layers, and current network management and control implementations. We provide additional insight by explaining how a combination of business and technical perspectives has driven evolution of the optical layer. We conclude by exploring activities to close this gap in the future.

The WaveStar™ BandWidth Manager: The key building block in the next-generation transport network

The WaveStar™ BandWidth Manager (BWM) is Lucent Technologies' flagship product platform for providing bandwidth management within network nodes. It provides broadband (OC-3/12/48/192 and STM-1/4/16/64), asynchronous transfer mode (ATM), and Internet protocol (IP) bandwidth management within a highly-integrated, scalable, single network element. The WaveStar BWM's broadband synchronous transfer mode (STM) fabric scales from 1152 STS-1/384 STM-1 (60 Gb/s) to 9216 STS-1/3072 STM-1 (480 Gb/s) port capacity. With such a high range in capacity scalability across the broadband STM fabric, the BWM can be sized to meet most carriers' growth projections while protecting them from unforeseen growth within network nodes. The WaveStar BWM also addresses the growing need for enhanced bandwidth management capabilities within central offices. It integrates all access and transport facilities within a network node and efficiently manages bandwidth among these facilities via a cost-effective, scalable, multiservice switching architecture. The BWM facility interfaces, which feature integrated self-healing rings, eliminate the need for stand-alone add/drop multiplexer (ADM) ring terminals in the central office. Furthermore, the switching architecture, which includes an STM fabric as well as ATM and IP functionality, replaces the need for stand-alone broadband digital cross-connect systems (BDCSs) and ATM and IP core switches/routers. The WaveStar BWM also supports direct integration of Lucent's dense wavelength division multiplexing (DWDM) systems — the WaveStar optical line system (OLS) 400G and the WaveStar OLS 40G.

Traffic generation algorithm for sdh digital cross‐connects

AbstractData in Synchronous Digital Hierarchy (SDH) networks may be routed, managed, and regulated by digital cross‐connect systems (DCSs). The adequacy and performance of current and proposed DCSs are determined through simulations, which require realistic connection requests or traffic. This work entailed the creation and analysis of a traffic generation algorithm for SDH DCSs. The algorithm accepts any valid configuration of desired traffic characteristics, and it produces connection and disconnection requests according to the provided configuration. The algorithm incorporates a probabilistic approach that allows the statistics of the configuration to determine the distributions of the types of connections and disconnections that are attempted. Special considerations are made to maintain the requested output load, to apportion the payloads, and to create opportunities for bidirectional connections. This paper includes an analysis of factors that may affect traffic generation.

Assignment of add–drop multiplexer (ADM) rings and digital cross-connect system (DCS) mesh in telecommunication networks

This paper discusses a design of a hybrid ring–mesh network in a survivable communication network. Given a set of traffic demands, the problem is to assign each traffic demand to rings and mesh such that the cost of add–drop multiplexer (ADM) and digital cross-connect system (DCS) equipment required is minimized. This assignment problem can be considered together with the fibre routing of nodes on rings and mesh. As a solution procedure, a tabu search is developed with recency-based short-term and frequency-based long-term memory structures. In computational experiments, the proposed tabu search is compared with the solutions obtained by the branch and bound procedure of CPLEX. We see that the tabu search provides a nearly optimal solution within sufficiently short time periods for all test problems with a gap of approximately 1–4% from the lower bound.

Assignment of add–drop multiplexer (ADM) rings and digital cross-connect system (DCS) mesh in telecommunication networks

Assignment of add–drop multiplexer (ADM) rings and digital cross-connect system (DCS) mesh in telecommunication networks

Efficient parallel time-slot interchanger for high-performance SDH/SONET digital crossconnect systems

A parallel design of time-slot interchangers is refined in order to scale the interchangers' capacity in an efficient manner. Performance analysis shows that this design scheme requires significantly less memory compared with a conventional parallel design because of newly implemented load-balancing switches, while keeping its switching control complexity to a minimum.

A Zoom-In Approach to Design SDH Mesh Restorable Networks

Mesh restorable networks based on SONET (Synchronous Optical Network, standard optical transmission technology widely accepted and implemented in North America) or SDH (Synchronous Digital Hierarchy, the European standard currently adopted by the major European telecom operators) are an economically attractive solution in areas where high demand and high connectivity are involved (Wu, 1995). In these networks, the reconfiguration capability of the digital cross connect systems (DCS) allows to reroute the demand affected by network failures. The degree of sharing of spare capacity in networks based on this architecture is high. This paper presents a heuristic algorithm for solving the near-optimal design of SDH mesh-type link restorable networks, i.e. determining the network topology and assigning the capacity to transport the demand in normal situations and to allow full link restorability in case of single link failures. The algorithm is based on a Zoom-In technique, a novel approach which forms a compromise between sequential and integrated techniques. The different building blocks of the algorithm are tested extensively and compared with other results mentioned in literature. Comparison of the simulation results for the overall design problem with other solution techniques indicates that the Zoom-In method is a quite promising approach, able to combine the accuracy of integrated approaches with the calculation speed of sequential approaches.

Applying tabu search to spare capacity planning for network restoration

This paper employs tabu search to solve the network spare capacity planning problem. Our study involves the determination of the necessary spare capacity on each link of a network required to achieve a certain desired level of restoration at minimum cost during network failure. We have developed here a procedure based on tabu search. The computational results show that the proposed tabu search algorithm offers an effective and efficient way for handling this network restoration problem. Scope and purpose Telecommunication network plays a crucial role in modern communication. An ever increasing number of end users are completely relying on telecommunication in their business activities today. The use and integration of computers with telecommunication have created a new information era. In order to provide the much desired broadband services, high capacity transport systems are widely adopted in the transmission network. While these systems offer great economic advantages through multiplexing and sharing of transmission facilities, they also increase the vulnerability of the telecommunication services dependent on them. If a failure occurs on a high speed facility of such a network, all the related services get affected. Network survivability has, therefore, become a major concern in broadband network planning. One of the methods to improve network survivability is to keep redundant or spare capacity for Digital Cross-Connect System (DCS) to restore failed services. However, the problem of spare capacity deployment on the links of a restorable network is NP-hard, implying exponential growth in execution time with network size for an exact solution. In this paper, an algorithm based on tabu search is proposed to find an approximate optimal solution for this problem.

Spare capacity assignment in telecom networks using path restoration and further improvement using traffic splitting

Link restoration and path restoration are the two major techniques used for telecom network restoration in DCS (Digital Cross-connect System) mesh networks. Upon any link failure, for rerouting to be possible, sufficient spare capacity must exist in the links of the chosen alternate paths. Path restoration results in lower additional cost compared to link restoration. Path restoration planning corresponds to the multi-commodity flow problem, which is computationally NP-hard. In this paper, we present the details of an approximation scheme for the path based restoration planning problem and compare the performance of link and path restoration schemes. These schemes have been incorporated into the network planning tool developed at Alcatel Network Systems. Traffic splitting can be used to further reduce the additional cost. There are several methods of performing traffic splitting. We have chosen to study even-splitting and best-splitting methods. We have evaluated traffic splitting techniques by enhancing the link and path restoration modules of the Restoration Network Planning Tool developed by Alcatel Network Systems. We have observed, through several experiments, that traffic splitting results in significant reduction in the spare capacity and the corresponding augmentation cost.

Economic spare capacity planning for DCS mesh-restorable networks

This paper considers an integer programming (IP) based optimization algorithm to solve the Spare Channel Assignment Problem (SCAP) for the new synchronous transmission networks that use a Digital Cross-Connect System (DCS) for each node of the network. Given predetermined working channels on each link of the network, the problem is to determine the spare capacity that should be added on each link to ensure rerouting of the traffic in case of a link failure. We propose an IP model which determines not only the spare capacity on each link but also the number of each link facility needed to be installed on each link to meet the aggregated requirements of working and spare channels. The objective is to minimize the total installation cost. We propose a branch-and-cut algorithm to solve the SCAR To solve the linear programming (LP) relaxation of the problem, an efficient constraint generation routine was devised. Moreover, some strong valid inequalities were found and used to strengthen the formulation. Computational results show that the algorithm can solve real world problems to optimality within a reasonable time.

Numerical study on the transient operation characteristics of the heat pipe cooling system with the multiple uniform heating components for broadband digital cross-connect system

A numerical study t predict the characteristics on transient operation of the heat pipe cooling system with multiple heaters for electronic system has been performed. The heat pipe cooling system of 45 cm length and 16 mm diameter was composed of evaporator section with four heaters which simulate electronic components, insulated transport section, and condenser section with a conductor which was cooled under the constant heat flux boundary condition. Two test cases were investigated in present study; Case 1 indicated that the 1st and 2nd heaters among four heaters were heated off, while the 3rd and the 4th heaters were heated on. Case 2 was the inverse situation switched from heating locations of Case 1. Case 3 indicated that the 1st and 4th heaters among four heaters were heated off, while the 2nd and 3rd heaters were heated on. The results showed that the transient time to reach the steady state is shorter for Case 1 than for Case 2. Especially, the maximum temperature among the heaters which simulate electronic components during switching operation is relatively small compared to the maximum allowable operating temperature in electronic system. It is concluded that the heat pipe cooling system in present study operate with the good thermal reliability even for sudden switching situation of the heaters.

Reliability evaluation of large telecommunication networks

In this paper, we describe an approximation method to evaluate the reliability of large telecommunication networks based on optic fibre and digital cross-connect systems (DCS). The reliability measures are defined as the availability and the expected lost traffic. Their evaluation is decomposed into the rerouting calculation and the probabilistic calculation. The rerouting calculation (restoration from failures) is accomplished by a heuristic method using the K-shortest paths. It is made very rapidly, thanks to a sophisticated data structure. The probabilistic calculation is based on the stratified sampling which results in computational savings of several orders of magnitude and is well suited to very large networks with high reliability components.

Towards Fault Recovery and Management inCommunication Networks

Society’s growing use of communication networks in both the public and private sector has led to an increased focus on reliability and survivability. Over the last decade, widely publicized network outages illustrated that a disruption of communications services can be very expensive to businesses and critical services (such as 911 service). The growing vulnerability of the public switched telephone network in the United States was initially discussed in 1989 by the National Research Council which noted a As we become more dependent on network, the consequences of network failure become greater and the need to reduce network vulnerabilities increases commensurately.o With the popularity of the Internet, a variety of network failures has surfaced in the recent years. It is clear that fault management will grow in importance for the foreseeable future. A variety of network failures are possible with typical events resulting in a failure being accidental cable cuts, hardware malfunctions, software errors, natural disasters (e.g., ® re, hurricane, earthquake), human error (e.g., incorrect maintenance), and malicious attack (both hardware and software). Broadly, we can classify the failures as physical-type failures and software-type failures. First we discuss physical failures in this context. Consider, a ® ber cable cut in a selfhealing ring in a metropolitan area telecommunication network; the failure can be restored in milliseconds by changing the direction of ow (with appropriate availability of capacity). However, using such a ring approach on a national or an international scale is likely to be cost prohibitive. This may lead to an approach which allows a combination of ring and digital cross-connect systems for transmission layer restoration, although it should be kept in mind that the spare capacity provided for such restoration is unused during normal network

Simulating Seismic Response Behavior of Telecommunications Equipment

Over the past four years, Lucent Technologies (formerly AT&T Bell Laboratories) has funded a research project that is aimed at determining the feasibility of using a computer to simulate the dynamic response of its digital access and cross-connect systems when subjected to design earthquake loadings. In this work, coarse finite element models are demonstrated to be accurate in calculating the resonant frequencies and corresponding modes of vibration for these structural systems. Through further comparisons with actual shake table tests performed at Wyle Laboratories in Huntsville, Ala., this technology is also proven adequate in calculating earthquake response behavior. It is expected that the research summarized in this paper will provide structural and mechanical engineers in the telecommunications field a basis for applying computer simulation as an earthquake design tool.

Dynamic bandwidth-allocation and path-restoration in SONET self-healing networks

This paper presents a new scheme for real-time bandwidth allocation and path restoration (BARS) in mesh networks via SONET wideband digital cross-connect systems (WDCSs) in response to demand and load dynamics and link and/or node failure(s). The scheme dynamically maximizes bandwidth allocation while ensuring full service restorability. Since the physical network capacity is limited, sometime not all the demand can be accommodated under the full restorability requirement. This demand in SONET BARS is rejected fairly at the network boundary even if capacity for allocation is available. Bandwidth allocation and fair demand admission are optimized jointly under the full restorability requirements. The implementation of SONET WDCS does not need excessive storage. An efficient parallel algorithm for solving the optimization problem is also presented. The algorithm produces superior spare capacity assignments compared to the results in the literature.

Decision models for designing and planning private communication networks

We consider the recently developed reconfigurable digital data networks consisting of T1/T3 circuits and Digital Crossconnect Systems (DCSs). A DCS is a device to patch base channels electronically from one T1/T3 circuit to another with a negligible queuing delay at the connecting node. We present new decision models for the design and circuit leasing policies of such digital backbone networks. Our model takes advantage of the special capabilities of the DCS technology and is likely to result in remarkable economic gains for the private network users. The formulation and analyses presented here simultaneously address the following problems: physical link and capacity selection, logical network configuration and channel assignment, and traffic routing on the logical network. The problem formulation results in a large-scale non-linear mixed integer program, and we propose an efficient solution methodology employing Lagrangean relaxation and subgradient optimization. Several numerical results illustrate the utility of our approach for these complex problems. We show that the economies of scale built into the tariff structure of these digital networks can be successfully exploited, and that the inherent flexibility of DCSs leads to logical networks that are dramatically different from their underlying physical topologies.

Optical digital cross‐connect system using photonic switch matrices and optical amplifiers

AbstractAn optical digital cross‐connect system (DCS) comprised of both photonic switching networks and electric DCSs is proposed for applications in network‐failure restorations. Optical DCSs exhibit excellent characteristics in restorations of multiple failures and when compared against their electrical counterparts, size‐reduced apparatus can be expected. the design of DCSs for applications in metropolitanarea networks are investigated and it is shown that such DCSs can be realized using LiNbO3 photonic switch matrices together with traveling wave optical amplifiers (TWA).With respect to the problem arising from the polarization dependency of TWA gain, it was solved using the output power controller (APC) which is shown theoretically to cause no difficulty in the noise characteristics. the optical DCS is designed and manufactured using LiNbO3 switch matrices and TWA, by which its basic operation properties are verified. Using this trial system, it is confirmed that the network failures can be restored by changing the optical routes.

Restoration strategies for future networks

The prospect of broadband telecommunication networks loaded with massive quantities of information due to the wide range of services being supported stimulates extra concern for network survivability. As the effect of span or node failures could be drastic, rapid restoration strategies are imperative. This paper describes restoration techniques involving the control of digital crossconnect systems, and the exploitation of spare capacity which has been economically planned into the network. This represents a more extensive approach to survivability than straightforward protection switching, thus improving network reliability.

Bandwidth allocation in ATM networks

In an ATM network, bandwidth is allocated at different levels and in different stages. At the physical level, the ATM topology can be dynamically reconfigured by adding/removing truns between ATM switches. This allocation of bandwidth is made possible by the SONET Synchronous Transfer Mode (STM) infrastructure equipped with Digital Cross Connect Systems (DCSs). We will refer to this allocation asSTM allocation. At the ATM level, we can allocate bandwidth to individual Virtual Circuits (ATM-VC allocation) as well as to Virtual Paths (ATM-VP allocation). For example, in order to implement the Connectionless Network Access layer functions we find it convenient to organize the Virtual Paths in a Connectionless Overlay Network. This introduces another type of bandwidth allocation (CLS allocation). In this paper, we address and formulate the above bandwidth allocation problems, and propose efficient techniques for their solution. We illustrate these techniques with examples based on STM and CLS allocation, respectively.

Multiwavelength line-rate-independent optical digital cross-connects based on low-gain fiber amplifiers

We experimentally demonstrated a multiwavelength, line-rate independent optical digital cross-connect system (DCS) by using cascaded low-gain erbium-doped fiber amplifiers as the switching elements in a dilated Benes architecture.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>