通过电路仿真降低无线回程成本

无线收发器基站(BTS)回程连接的数据速率要求在不断增长,而千兆以太网连接的成本不断下降。结果,IP/以太网回程技术成为新基站的首选。然而,对于采用了时分复用(TDM)连接的大量基站,运营商不得不支付高昂的TDM线路租费,但是,可以使用电路仿真服务(CES),通过在相对低廉的以太网上传送信号来降低成本。对于任何CES应用,链路远端的时钟恢复都是很大的挑战,网间功能(IWF)模块需要支持差分以及自适应时钟恢复。对于要求更高的应用,例如无线基站同步,运营商可以采用混合时序发生器(HTG)技术。本文详细讨论CES相关协议,介绍CES解决方案的时钟恢复、网络、节点和器件体系结构。文章还探讨了用FPGA技术实现的优势。     

音视频实时传输技术AVB及飞思卡尔汽车应用参考方案

正1以太网AVB技术概述以太网音视频桥接技术(Ethernet Audio/Video Bridging,以下简称Ethernet AVB)是一项新的IEEE802标准。其在传统以太网络的基础上,通过保障带宽,限制延迟和精确时钟同步,提供完美的服务质量,以支持各种基于音频、视频的网络多媒体应用。Ethernet AVB致力于提供一套基于标准的方案来为演播室、影剧院、音乐会现场及娱乐系统等提供稳定可靠的音视频服务,以及提供低延时、供家庭及企业使用的同步音视频网络。其关注于增强传统以太网的实时音视频性能,同时又能够100%向后兼容传统以太网,是极具发展潜力的下一代网络音视频实时传输技术。它是一种架构在以太网三层网络     

IXIA向电信级以太网移动同传网络引入时钟协议

电信级IP以太网可替代传统的TDM网络,经济高效．可灵活处理移动回传网络上极需带宽的数据流量。但是,电信级以太网必须满足25／3G无线移动回传严格的时钟要求。     

IEEE1588协议及其在路由交换平台中的实现技术

下一代网络（NGN）是一种融合了IP技术和多媒体通信技术的全新网络,然而当涉及到传统TDM业务应用及需要进行时钟同步分配时,基于IP技术的全新网络则需要具备完善的时钟同步能力来满足相关业务的同步需求。IEEE1588协议标准的出现正好解决了在新一代路由交换平台中的时钟同步问题。这里分析了IEEE1588协议的偏移测量和延时测量时钟同步过程,并给出了IEEE1588协议在路由交换平台中的具体实现过程。     

一种基站同步以太网时钟故障分析算法

在无线通信领域中,随着同步以太网时钟在基站上广泛应用,出现了大量与该时钟相关的时钟同步故障。针对这种情况,提出一种基于概率统计的故障分析算法。该算法通过分析基站时钟频率偏差变化数据的概率分布,结合基站时钟同步架构和器件特性,对故障点做出判断。该算法既能实现故障的远程分析定位,又能提前发现故障隐患。     

IXIA：测试电信级以太网移动回传网络时钟协议

阻止运营商转向IP/以太网回传网络的最大障碍之一便是移动语音流量所需的时钟和同步功能。Ixia的产品可帮助移动运营商和回传传输提供商实现该功能测试     

一种TDM／TDMA点地多点系统时钟同步方法

针对TDM/TDMA点对多点系统传输信号特点,提出了一种系统时钟同步方法,介绍了电路的组成及原理。该方法能有效地抑制多级中继时系统的时钟抖动,提高TDM/TDMA通信系统的传输性能。     

分组传送网中时钟同步技术的研究

随着下一代网络(NGN)和3G网络的大规模应用,传统的以电路交换为主的公共交换电话网(PSTN)逐渐转向以分组交换为主.在从传统网络向未来网络转换的过程中,时钟同步仍然是其中面临的一大难题.文章研究和分析了分组传送网(PTN)中应用同步的两种技术,即同步以太网技术和IEEE 1588 V2技术,并且阐述了其相关原理和在PTN时钟同步中的应用.     

基于精确时钟协议的多时钟源时钟同步实现

精确时钟协议(precision time protocol,PTP)由网络测量和控制系统的精确时钟同步协议标准(IEEE 1588)定义,借助网络通信和本地计算等技术实现分布式系统中的高精度时钟同步.虽然PTP系统可以通过纯软件的方式在局域网络内实现亚微秒级的时钟同步,却难以满足对时钟同步性能有更高要求的通信传输网络...     

E1 over EPON的时钟同步技术

文章介绍了E1 over 基于以太网的无源光网络(EPON)的关键技术中时钟同步的实现方法,通过对自适应法的研究和改进,优化了时钟输出抖动的指标,有效地保障了EPON系统的服务质量(QoS)指标.相对于时间标签法,自适应法在分组网络中进行时钟同步方面具有更广泛的适用空间.     

略谈通信网时频同步技术演进趋势

根据ITU-T近期发布的通信同步技术标准建议书，纵观电信运营商对于同步网发展所做的努力，分析国内外厂商和研究单位的代表性新产品，尝试探讨通信同步网和网同步的演进趋势，归纳其特点是：为了迎接5G移动通信等新挑战，通信网时频同步性能指标在明显提升，尤其是高精度时间同步受到更大的重视，需要采用新技术改变传统同步方式，需要研制和运用新的同步设备和检测仪表，新的同步技术标准也彰显了中国在国际的引领作用和影响。     

Service convergence using MPLS multiservice networks

Enterprises are increasingly using virtual private networks to interconnect remote sites. Traditionally, service providers have used ATM core networks to deliver layer 2 services such as frame relay, ATM, or TDM private lines, which enterprise customers have then used to build their corporate network infrastructure. Such services account for the majority of data service revenues today. However, pressure has increased on service providers to combine increased flexibility with reduced costs in the context of a highly dynamic telecommunications market. Service providers also need to generate new revenues from their IP network infrastructure, through new opportunities such as IP VPNs and virtual private LAN services, while simultaneously achieving operational efficiencies through the convergence of all of their services on a common MPLS backbone. New access and metro network technologies, such as Ethernet, are also emerging that can be used to deliver these new services to enterprise customers alongside ATM and frame relay access. This must be achieved while also supporting existing technologies such as ATM, which continue to deliver highly profitable services. This article discusses the technical challenges in meeting the often conflicting requirements of delivering both traditional layer 2 services and new layer 3 services on a converged MPLS network. We show how both network and service interworking are required, and how these must operate at the user, control, and management planes to enable profitable services to be delivered over the new converged network. The different solutions being defined in the standards bodies are described, and the distinct scenarios they address are explained.     

Synchronous ethernet: a method to transport synchronization

This article discusses the evolving transport architecture, covering some of the synchronization distribution problems to many endpoints where mobile backhaul and TDM emulation occur. It shows how Synchronous Ethernet fits into both the Ethernet and synchronization architectures, and discusses how this helped development in standardization bodies. Standardization allows the key building blocks of Ethernet silicon and specific timing devices to be developed, which allows a robust system implementation to be constructed while allowing interworking with and migration from existing SONET/SDH-based transport infrastructure. Finally, results are shown that indicate a very high level of performance is achievable with Synchronous Ethernetnot subject to the normal packet delay variation and traffic load conditions that can occur in packet based networks.     

Circuit emulation services over Ethernet—Part 2: Prototype and experimental results

This paper describes a prototype implementation and experimental results for unstructured circuit emulation service (UCES) of T3 data stream over Ethernet. As explained in Part 1 of this paper,¹ packet‐switched networks such as Ethernet are not designed to transport TDM data and so have no inherent clock distribution and synchronization mechanisms. Thus, to allow the frequency of the source TDM stream to be regenerated at the receiver, the prototype employed the clock synchronization scheme described in Part 1 of this paper. Our experiments showed that the recovered clock conforms to ITU‐T G.824 requirements² even for networks that introduce high jitter and packet loss. Copyright © 2004 John Wiley & Sons, Ltd.     

Hybrid transport solutions for TDM/data networking services

There is a growing demand for native data transport services for enterprises and corporations across public transport networks. Equipment vendors have begun to incorporate a variety of LAN and storage area network interfaces, notably Ethernet, Fibre Channel/FICON, and ESCON, on traditional metro and long-haul transport equipment. Embracing Ethernet and SAN technology enables the introduction of flexible high-capacity transport services optimized for data networking. Transport operators may thus offer both enterprise-centric connectivity services, such as transparent LAN connectivity and virtual LAN services, as well as traditional bandwidth services, such as private lines, while preserving the operations and management infrastructure of the existing public networks. We discuss the benefits of a hybrid Ethernet/TDM transport solution     

基于工业网络的分布式时钟同步算法研究

为了实现工业控制过程中的时钟同步,基于以太网的网络通信协议IEEE1588标准,作为以太网中使用最广的时钟同步算法,已经具有十分精确的同步性。IEEE1588使用集中式同步方法,导致如果有一个发送给主时钟的结点发生故障时,将会影响到网络中其余结点的同步性能,某些结点的时钟出现不同步会引起同步控制系统的瘫痪。采用把IEEE1588与FlexRay同步算法结合的分布式同步方法实现时钟同步的机制,结果证明该算法更加适合于工业通信协议的时钟同步。     

Operation, administration, and maintenance in MPLS networks

The boundaries between packet and circuit networks have long disappeared, with many traditional circuit-switched applications such as voice and video now being carried over packet-switched IP/MPLS or Ethernet networks. However, this transition has happened so fast that many OAM functions supported by circuit-switched networks such as SONET/SDH are still unmatched in packet networks. In order to match the quality sustained by circuit-switched networks, OAM functions must also be developed for such packet networks. A number of recent efforts have started to address OAM functions for IP/MPLS and Ethernet packet technologies. Service providers and carriers alike are the driving force behind the work, as there is general recognition that to generate sustained revenues, services must be efficiently managed. In this article we discuss issues in providing OAM features and capabilities for MPLS-based packet networks.     

Clock synchronization for packet networks using a weighted least‐squares error filtering technique and enabling circuit emulation service

Circuit emulation service (CES) allows time‐division multiplexing (TDM) services (T1/E1 and T3/E3 circuits) to be transparently extended across a packet network. With circuit emulation over IP, for instance, TDM data received from an external device at the edge of an IP network is converted to IP packets, sent through the IP network, passed out of the IP network to its destination, and reassembled into TDM bit stream. Clock synchronization is very important for CES. This paper presents a clock synchronization scheme based on a double exponential filtering technique and a linear process model. The linear process model is used to describe the behaviour of clock synchronization errors between a transmitter and a receiver. In the clock synchronization scheme, the transmitter periodically sends explicit time indications or timestamps to a receiver to enable the receiver to synchronize its local clock to the transmitter's clock. A phase‐locked loop (PLL) at the receiver processes the transmitted timestamps to generate timing signal for the receiver. The PLL has a simple implementation and provides both fast responsiveness (i.e. fast acquisition of transmitter frequency at a receiver) and significant jitter reduction in the locked state. Copyright © 2006 John Wiley & Sons, Ltd.     

The evolution of transport network survivability

The bandwidth explosion ushered in by the popularity of the Internet has spurred the acceleration in the development and deployment of equipment supporting packet-based services. This-coupled with the widespread deployment of dense wavelength-division multiplexed systems in the core transport network to satisfy the corresponding increase in capacity demand-has led network planners to reconsider traditional approaches to network survivability. Existing architectures for transport network survivability were developed based on a ubiquitous circuit-switched/TDM network paradigm. As tariffed services increasingly migrate from circuit-switched/TDM to packet-switched/DWDM networks, survivability architectures must also evolve to meet the service requirements of this “new” packet-switched/DWDM network paradigm. We begin with an overview of existing strategies for providing transport network survivability, followed by an analysis of how the architectures for network survivability may evolve to satisfy the requirements of emerging networks     

Network high availability for ethernet services using IP/MPLS networks

Enterprises are increasingly using Ethernet as the foundation for transforming their networks to Internet Protocol. Simultaneously, service providers are deploying Ethernet to exploit the demand for wide-area Ethernet services and as the infrastructure for new residential services such as IPTV. This is due to Ethernet's low cost per bit and ubiquity in local area networks. Recent years have seen the widespread deployment of IP/MPLS networks to address this opportunity. IP/MPLS enables enhanced flexibility over the same converged network for IP and legacy services, avoiding the need to build separate per-service networks. It also adds carrier- grade capabilities such as quality of service, traffic engineering, and resiliency, thereby enabling new multipoint services such as virtual private LAN service. However, using Ethernet for ";always-on"; and other mission-critical services has resulted in new resiliency requirements, in both the access and the network core. Two novel developments address these high expectations by enabling significant improvements in service availability. These are pseudowire redundancy and Ethernet multi-chassis link aggregation. This article reviews the current redundancy mechanisms typically deployed in Ethernet and MPLS networks. We show how additional enhancements are required in both the network core and the access to the Ethernet service. We describe new pseudowire redundancy and MC- LAG mechanisms, showing how they work together to enable end-to-end protection for Ethernet virtual private wire services and VPLS.