Metro Transport Networks Research Articles

Construction and Characteristics Analysis of the Xi’an Public Transport Network Considering Single-Mode and Multi-Mode Transferring

The connectivity of the urban public transport network and the convenience of transfers between modes of transit are important factors that affect whether passengers choose public transport. Identifying the key nodes that affect network connectivity, direct access, transfers, and clarifying the main factors that restrict the network efficiency play important roles in improving the efficiency of the public transport network and establishing a “green city”. On this premise, this paper constructs two single-layer networks and a composite network that can reflect the transfer relationship between ‘bus–bus’, ‘metro–metro’, and ‘metro–bus’ based on the method of Space-P. The composite network realizes the integration study of homogeneous and heterogeneous stops, lines, and transfer relationships in the public transport network. At the same time, five kinds of centrality indexes are applied to the transport transfer network, and the significance of these indexes in the network is explained. Through the comprehensive analysis of these five types of indexes, the key nodes affecting the network connectivity, direct access and transfer efficiency, can be identified more accurately. Taking the public transport network of Xi’an as an example, the structural characteristics of the networks, including scale-free and small-world characteristics, were empirically analyzed. The main stops that play important roles in networks were identified based on the integrated centrality, degrees, and weight degrees. The research results showed the following: (1) Xi’an’s metro network, bus network, and metro–bus composite network all have scale-free and small-world characteristics. (2) The influence of the key stops of the metro network is concentrated, while the influence of the key stops of the bus network is scattered. (3) The public transport network in the first ring road area of Xi’an has the highest degree of direct access, and the core areas of the south, west, and north of Xi’an also have high direct access. However, the direct access in the area east of Xi’an is slightly lower. (4) Xi’an’s bus transport network covers a large area, showing the characteristics of a dual-core “central + southern” network. (5) The metro–bus composite network demonstrates a closer connection between stops and a more balanced network. (6) Finally, the degree of direct access to stops in the bus transport network and metro transport network shows the characteristics of “the single core is dominant, and the circle diffusion weakens step by step”.

Disaggregated edge-enabled C+L-band filterless metro networks

The recent interest in the upgrade and enhancements of metro transport networks and the availability of transponder cards with coherent receivers is opening the way to filterless solutions employing only passive splitters/couplers and optical amplifiers, potentially achieving significant capital expeditures and operating expenditures savings. However, the filterless option suffers from inefficiencies, mainly due to the broadcasting constraint and the reduced optical reach. To overcome such limitations, this paper proposes three complementary strategies to upgrade optical filterless metro networks (FMN). First, the number of supported channels is incremented by exploiting the full C + L -band. To this end, two design architectures (i.e., Single and Dual Region) are proposed and evaluated, targeting double capacity with respect to the standard C-band and an upgrade to cost reduction. Second, we investigate a dual-architecture solution, extending metro deployments with a low-cost filterless and unamplified L-band system. Its design trade-offs are evaluated to determine its suitability in providing direct low-latency connectivity between metro-access nodes with the aim of supporting edge-computing platforms. Finally, the flexibility of the FMN is extended by introducing disaggregated transponders with different bitrates (i.e., 100 Gbps and 400 Gbps) and configurable transmission parameters, such as the modulation format and the forward error correction). Such flexibility is exploited through the extension of the OpenConfig YANG model of the optical line system, thus enabling automatic spectrum and transmission parameter assignment by means of a centralized software-defined-network controller and achieving better resource utilization. Simulation and experimental results are provided, showing the effectiveness and the potential impact of filterless metro solutions in future deployments and low-cost network upgrades supporting edge/fog clusters and 5G.

Recent Development in Public Transport Network Analysis From the Complex Network Perspective

A graph, comprising a set of nodes connected by edges, is one of the simplest yet remarkably useful mathematical structures for the analysis of real-world complex systems. Network theory, being an application-based extension of graph theory, has been applied to a wide variety of real-world systems involving complex interconnection of subsystems. The application of network theory has permitted in-depth understanding of connectivity, topologies, and operations of many practical networked systems as well as the roles that various parameters play in determining the performance of such systems. In the field of transportation networks, however, the use of graph theory has been relatively much less explored, and this motivates us to bring together the recent development in the field of public transport analysis from a graph theoretic perspective. In this paper, we focus on ground transportation, and in particular the bus transport network (BTN) and metro transport network (MTN), since the two types of networks are widely used by the public and their performances have significant impact to people's life. In the course of our analysis, various network parameters are introduced to probe into the impact of topologies and their relative merits and demerits in transportation. The various local and global properties evaluated as part of the topological analysis provide a common platform to comprehend and decipher the inherent network features that are partly encoded in their topological properties. Overall, this paper gives a detailed exposition of recent development in the use of graph theory in public transport network analysis, and summarizes the key results that offer important insights for government agencies and public transport system operators to plan, design, and optimize future public transport networks in order to achieve more efficient and robust services.

The influence of CDN sinking on metro transmission network

With the rise of VR/AR and 4K/8K video services, users have higher requirements for personal experience. Promotion of user experience is an important factor to attract end-users. Compared with traditional website access, the deployment of CDN has advantages of improving access speed, solving the problem of high traffic and large concurrency, improving the reliability of data sources. CDN’s basic characteristics can be summarized as: cache contents in different locations, and load requests of users to the most appropriate cache server through load balancing technology. The traditional networking mode deployed CDN on the core layer leads to contents away from the end users. This means the probability of occurrence of congestion increased, and the end-to-end delay enhanced. Therefore, CDN sink to the convergence layer and even edge layer can be considered to solve problems such as web browsing slow, video buffer in slow and so on. The sinking of CDN has a profound impact on the network structure, basic resources and network intellectualization. Large capacity PTN/OTN equipment should be deployed on each layer. The sinking of CDN leads to the flattening of the network. The basic resources of metro transport network such as computer room space, air conditioning, power supply must ensure the normal operation of the sinking CDN equipments and transmission equipments. SDN/NFV technology should be introduced to transmission network in the future.

Facing the traffic explosion in metro transport networks with energy-sustainable architectures

The continuous growth of traffic volumes is making the consumed energy, in telecommunication networks, a critical issue. In this context, the implementation of new content distribution solutions will speed up this traffic increase. In particular, these solutions will significantly impact the traffic profile in metro networks. The current centralized traffic scenario will move toward a scenario in which the traffic exchanges would be distributed among all the nodes of the metro network. In this work, starting from a real traffic scenario, we estimate a possible traffic evolution, and we design the metro networks, according to different architectures, using integer linear programming formulations. The aim was to understand which architecture can better face the considered traffic evolution. The comparison is performed considering the energy consumption, the network setup and management, and the quality of service ensured by the architectures.

Modeling Critical Infrastructure Interdependency: The Case of the Mexico City Metro Transport System

ABSTRACT“Critical infrastructures” are exceedingly complex and highly interconnected. In order to gain a full understanding and comprehensive awareness of the risks associated with critical infrastructures it becomes essential to consider in a coherent way all the aspects that may cause a failure of such systems. That is, there is a need for a systemic approach to interdependencies among critical infrastructures. The article presents the application of a systemic safety management system (SSMS) model to interdependency modeling for the case of the Mexico City Metro transport network. The model has highlighted that interdependencies occur vertically and horizontally. Horizontal interdependency occurs at every level of recursion and can be: operational, managerial, and environmental. Vertical interdependency, on the other hand, occurs between two levels of recursion only. The SSMS model has shown the potential to be used to model interdependencies among critical infrastructures. It is hoped that the approach presented may help to gain a better understanding of critical infrastructure interdependency.

Stability of FIPP $p$-Cycles Under Dynamic Traffic in WDM Networks

Application opportunities associated with video, voice, and data triple-play result in a dramatic demand increase in metro transport networks, with traffic patterns becoming increasingly dynamic and difficult to predict. This is driving the need of core networks with a high degree of flexibility and multigranularities to carry traffic. We propose to investigate the question of what this means in terms of dynamic protection provisioning. In other words, we want to study how stable are the protection structures under dynamic traffic, i.e., how much and how often they need to be updated in a dynamic survivable WDM network. While most studies on the stability of protection structures have been conducted on p-cycles and link shared protection, we propose to investigate here the stability of failure-independent path-protecting (FIPP) p-cycles under dynamic traffic. For doing so, we design and develop an original scalable mathematical model that we solve using large-scale optimization tools. Numerical results show that FIPP p-cycles are remarkably stable under the evaluation of the number of required optical bypass reconfigurations under dynamic traffic.

Demonstration of error-free 25Gb/s duobinary transmission using a colourless reflective integrated modulator

To realise novel, low-cost, photonic technologies that can support 100Gb/s Ethernet in next-generation dense wavelength-division-multiplexed metro transport networks, we are developing arrayed photonic integrated circuits that leverage colourless reflective modulators. Here, we demonstrate a single-channel, hybrid reflective electroabsorption modulator-based device, showing error-free 25.3Gb/s duobinary transmission with bit-error rates less than 1 × 10(-12) over 35km of standard single-mode fibre. We further confirm the modulator's colourless operation over the ITU C-band, with a 1.2dB variation in required optical signal-to-noise ratio over this wavelength range.

100 Gigabit-per-second: Ultra-high transmission bitrate for next generation optical transport networks

Abstract Modern telecommunication networks have to provide enormous data transport capacity in order to enable the dramatic annual internet traffic growth rates. As an illustration, today some internet exchange nodes partly exhibit annual peak traffic growth rates of more than 200% due to strongly emerging data and broadband video services. This explosion of internet data and video traffic can only be assured by the implementation of the most advanced optical metro and core transport network technologies. It is likely that next generation telecommunication transport networks will be based on 100 Gigabit/s Ethernet (100 GbE) interconnections. Here we will report on the technical challenges and achievements associated with the development of ultra-high speed components and systems for serial 100 Gbit/s optical transmission. To cite this article: G. Veith et al., C. R. Physique 9 (2008).

Packet Transport System에 의한 효율적인 IPTV 분배망 구축 방안

방송과 통신의 대표적 융합서비스인 IPTV 서비스는 네트워크 상에서 QoS 보장, 멀티캐스팅 효율성, 높은 대역폭이 요구된다. 전형적인 TDM 중심의 메트로 전송 네트워크는 안정적이고 복구가 가능한 방식으로 고정된 음성 트래픽을 전송할 수 있게끔 설계되었기 때문에 폭주 특성을 지니는 데이타 트래픽을 수용하기에는 병목현상과 대역폭 낭비의 단점이 있다. 그리고 고급 하이엔드 서비스와 Best Effort의 로우엔드 서비스를 분별하지 못하여 전송 네트워크에서는 모든 데이타를 동일하게 취급을 한다. 이러한 폭주 트래픽의 증가와 QoS를 근본적으로 해결하기 위해서는 무엇보다도 새로운 전송 네트워크 설계가 절실히 요구된다. 논문에서는 TDM 중심의 메트로 전송 네트워크를 패킷 중심의 전송 네트워크로 변화 방법을 제시하고 또한 패킷 중심의 전송 네트워크의 장점과 실효성도 함께 제시한다. 그리고 패킷 중심의 전송 네트워크인 Packet Transport System 방법에 관한 기술요소와 특징들에 대해서도 함께 제시한다. 연구결과 패킷 중심의 전송 네트워크인 Packet Transport System은 기존의 TDM 특성을 수용할 뿐 아니라 QoS, 멀티캐스트, 높은 대역폭의 수용으로 효과적인 대역폭 운용과 안정적인 패킷 전송성능을 가지고 있으며, 또한 광 경로 상의 장애 발생 시 트래픽의 생존성 확보를 위한 보호 메커니즘을 고려한 알고리즘을 통해서 각 서비스 클래스별 차등화된 QoS를 보장할 수 있다. IPTV Services that is representative union service of broadcasting and telecommunication need guarantee of QoS, efficiency of multicasting, and hish bandwidth on the network. Because typical TDM based metro transport network was designed by transporting fixed voice traffic with stable and recovering method, it has a defect of bottleneck and a waste of bandwidth for acceptance of data traffic with burst feature and then all of data are treated equally at the transport network because it cannot classify between advanced high end service and best effort low end service. for completely resolving this kind of problem about increasing burst traffic and QoS issues, firstly we need to new design for transport network. This paper presents transformation method from TDM based metro transport network to packet based transport network and advantage and effectiveness of packet based transport network and also indicates technical factor and characters about method of packet transport system. As a result of research, the Packet Transport System, which is a transmission network for packet delivery, take in not only a specific character of legacy TDM but QoS, Multicast and high bandwidth, then, it is able to keep an effective bandwidth and a stabilized performance of packet transmissions. Additionally, if a fault be occurred on an optical link, the system is able to guarantee a differential QoS by an each service class using an algorithm to make certain of a traffic existence and contain a protective mechanism.

Same Wavelength Packet Switching in Optical Label Switched Networks

The authors propose a novel optical-label-swapping scheme for the same wavelength packet switching using optical carrier suppression and separation technique and without requiring any conventional wavelength converter in a scalable optical-label-switched network that carries a differential phase-shift keying modulated payload and an on-off keying modulated label. The performance of the proposed scheme is investigated using both experimental demonstration and numerical simulation. These experimental and simulation results show that the proposed optical-label-swapping scheme is suitable for the same wavelength packet switching in future scalable metro and core optical transport networks

Routing Framework for All-Optical DWDM Metro and Long-Haul Transport Networks With Sparse Wavelength Conversion Capabilities

In this paper, we propose a novel routing framework for all-optical dense wavelength-division-multiplexing transport networks with sparse wavelength conversion capabilities. The routing framework includes an integer linear programming formulation to handle the static lightpath establishment problem and a novel open shortest path first protocol extension that advertises the availability of wavelength usage and wavelength conversion resources. Our routing framework addresses the limitations of the extensions presented in the literature because it also includes: 1) an efficient flooding protocol that is suitable for the dynamic nature of these networks and 2) an efficient route and wavelength computation engine that minimizes connection costs without hindering the blocking probability.

INTEGRATING INTERCITY AND URBAN RAILWAYS IN BARCELONA

Railway traffic has been continuously growing in large cities in recent years, as part of the global mobility of the city. In Barcelona, for example, commuter rail demand grew from 220,000 passengers/day in 1993 to 305,000 passenger/day in 1998. To accommodate this growth (38%), several physical aspects had to improve to allow for better quality of service: a clear and urgent action needs to be undertaken in Barcelona was the remodeling of the terminal stations in the city. In 2004 a new rail infrastructure, the high speed train, will arrive and support an incremental traffic of 10 million passengers/year. Both commuter and high speed rail need a global vision and solution so that each type of service can reinforce its potential with their complementarities. This paper presents the context of rail services and network in the city of Barcelona (conventional rail and the connection with metro and public transport network), the methodology adopted for the solution (including topology and accessibility indicators, demand modeling and social cost/benefit analysis), and the conclusions of the study that define and make possible the implementation of the new network are also presented.