同步以太网的SSM

OptiX10G（METRO5000）功能与结构介绍OptiX10G是提供STM-64光同步传输能力的高速、大容量SDH光传输设备，它采用了MADM体系结构，是当今以及未来的干线网、城域网建设的主流设备。

一.OptiX10G功能和特点OptiX10G系统可以从10Gbit/s（STM-64）的高等级SDH信号中直接分插各种较低等级的SDH信号，提供2016×2016 VC-12的低阶接入能力，同时提供线路与线路、线路与支路以及支路与支路间业务的灵活交叉调配能力。

OptiX10G设备还提供的VC-4-4c、VC-4-8c、VC-4-16c、VC-4-64c的级联交叉能力和VC-3、VC-12的低阶业务调度。

OptiX10G设备提供数据业务（包括100M/1000M以太网业务）的透明传输和二层交换，实现多业务的汇聚后在SDH网络上传送，进一步缓解日益严重的网络带宽压力。

同时，OptiX10G可以实现各种复杂的网络级和设备级保护，确保网络的安全运营。

OptiX10G设备灵活多样的设备配置功能、大容量的支路接入能力以及大容量交叉功能可以满足多种不同网络运用的需要。

二.OptiX10G功能1.交叉连接和多系统支持能力OptiX10G提供高阶交叉与低阶交叉两种类型交叉板，交叉容量如表8-1所示。

表8-1 OptiX10G交叉板交叉容量注：ATXC不能单独使用，必须与高阶交叉板配合使用。

OptiX10G设备可在单台设备上实现4套STM-64 ADM系统+多套STM-16/4/1 ADM系统，并支持多系统间的业务调度和保护，因此可以作为一个中等容量的本地交叉连接设备使用。

同时，OptiX10G设备提供交叉容量为2016×2016 VC-12的低阶业务调度能力，大大增强了设备的组网能力和网络的调度能力。

2.多种网元类型配置OptiX10G设备的配置相当灵活。

每个网元既可配置为单个的STM-64 REG、TM或ADM系统或其组合，也可配置为STM-1、STM-4、STM-16、STM-64接口组合的多ADM系统；并实现多系统间业务的交叉连接。

通信专业实务（传输与接入-有线）-分组传送网-第4节PTN的关键技术[单选题]1.PWE3属于点到点方式的()，建立的是一个点到点的通道，在分组传送网的两台PE（江南博哥）中，通过隧道模拟CE端的各种二层业务，使CE端的二层数据在分组传送网中透明传递。

A.L2VPNB.OVPNC.MPLSVPND.L3VPN正确答案：A参考解析：PWE3属于点到点方式的L2VP，建立的是一个点到点的通道，在分组传送网的两台PE中，通过隧道模拟CE端的各种二层业务，使CE端的二层数据在分组传送网中透明传递。

[单选题]2.PWE3称为端到端伪线仿真，它是一种端到端的()层业务承载技术。

A.一B.二C.三D.四正确答案：B参考解析：本小题对PWE3技术原理的考查。

PWE3是一种端到端的二层业务承载技术，属于点到点方式的L2VPN，建立的是一个点到点的通道。

在分组传送网的两台PE中，通过隧道模拟CE端的各种二层业务，使CE端的二层数据在分组传送网中透明传递。

PWE3技术的基础是MPLSL2VPN;隧道技术是构建VPN的关键技术，它用来在公共网络上仿真一条点到点的通路;本小题选B。

[判断题]3.PTN组网策略与MSTP相比,最大的变化是汇聚层不再采用线性端到端保护机制,而是选用环网保护方式。

()A.正确B.错误正确答案：B参考解析：本小题是对PTN保障体系进行的考察。

PTN组网保护策略与MSTP网络相比最大变化是汇聚层不再采用环网保护方式，而是选用线性端到端保护机制。

本小题说法错误。

[判断题]4.PTN设备级别保护主要是指对PTN设备的核心单元配置1:1的热备份保护。

()A.正确B.错误正确答案：B参考解析：本小题是对PTN的保护技术的考查。

PTN网络的保护技术分为设备级保护和网络级保护;.设备级保护主要是指对PTN设备的核心单元配置1+1的热备份保护;网络级保护分为网内保护和网间保护:网内保护分为PW保护、线性保护和环网保护:网间保护主要有LAG保护、LMSP保护和TPS保护;本小题说法错误。

TN时钟同步技术1588v2和SyncE的应用当运营商对分组传送网(PTN)取代传统时分复用(TDM)传输网的需求日益明显时，如何解决时钟同步成为重要问题之一。

对分组传送网的同步需求有两个方面：一是可以承载TDM 业务并提供TDM业务时钟恢复的机制，使得TDM业务在穿越分组网络后仍满足一定的性能指标(如ITU-T G.823/G.824规范)；二是分组网络可以像TDM网络一样，提供高精度的网络参考时钟，满足网络节点(如基站)的同步需求。

1同步技术时钟同步包括：频率同步和时间同步。

频率同步要求相同的时间间隔，时间同步要求时间的起始点相同和相同的时间间隔。

无线技术不同制式对时钟的承载有不同的需求，GSM/WCDMA采用的是异步基站技术，只需要做频率同步，精度要求0.05 ppm，而TD-SCDMA/CDMA2000需要时间同步，TD- SCDMA的精度要求为±1.5 μs。

从2004年开始，国际电信联盟电信标准部门(ITU-T)Q13/SG15开始逐步制订关于分组网同步技术的系列建议书，主要有：G.8261(定义总体需求)、G.8262(定义设备时钟的性能)、G.8264(主要定义体系结构和同步功能模块)。

IEEE在2002年发布了IEEE 1588标准，该标准定义了一种精确时间同步协议(PTP)。

IEEE 1588是针对局域网组播环境制订的标准，在电信网络的复杂环境下，应用将受到限制。

因此在2008年又发布了IEEE 1588v2(以下简称1588v2)，该版本中增加了适应电信网络应用的技术特点[1-5]。

因特网工程任务组(IETF)网络时间同步协议(NTP)实现了Internet上用户与时间服务器之间时间同步。

2同步以太网技术物理层同步技术在传统同步数字体系(SDH)网络中应用广泛。

每个节点可从物理链路提取线路时钟或从外部同步接口获取时钟，从多个时钟源中进行时钟质量选择，使本地时钟锁定在质量最高的时钟源，并将锁定后的时钟传送到下游设备。

ENT-AN1108-4.0Application Note SyncE Software Configuration GuideReleasedJanuary20191Revision History (1)2Synchronous Ethernet (2)3Synchronization Messaging (3)4Clock Selection Algorithm (4)5Clock Source Configuration (5)5.1Configuring Clock Recovery (5)5.2Configuring Clock Redundancy (6)5.3Configuring Clock Selection Modes (7)5.4Clock Redundancy with Input Fail (8)5.5Configuring WTR and Hold Off Timers (8)5.6Configuring ANEG Mode (9)5.7Configuring the Station Clock (9)5.8PTP as Clock Source (10)5.8.1Prerequisites (10)5.8.2Configuring PTP as a Clock Source (10)6Troubleshooting (12)Figure1•Basic SyncE Settings (5)Figure2•Clock Redundancy (6)Figure3•Selected Source Failure in Manual Mode with No Switch Over (7)Figure4•Selected Clock Source Failure (8)Figure5•Active WTR (8)Figure6•Set SSM Overwrite Quality Level (10)Figure7•Output Frequency Measured (10)Figure8•SyncE Configuration (11)Figure9•Clock Hardware ID Undetected (12)1Revision HistoryThe revision history describes the changes that were implemented in the document.The changes are listed by revision,starting with the most current publication.Revision 1.0Revision 1.0was published in January 2019.It was the first publication of this document.Revision History2Synchronous EthernetSynchronous Ethernet (SyncE)uses a physical layer interface to pass timing from one node to the other in the same manner as timing is passed in SONET or SDH.SyncE,as defined by ITU-T standards,such as G.8261,G.8262,G.8264,and G.781,leverages the physical layer of Ethernet to transmit frequency to remote sites.This synchronous transmission of frequency over Ethernet provides a cost-effective alternative for network designers.For SyncE to work,each network element along the synchronization path must support SyncE.Synchronous Ethernet3Synchronization MessagingNetwork elements use synchronization status messages (SSM)to inform the neighboring elements about the quality level (QL)of the clock.SSM is used by non-Ethernet interfaces,such as the optical interfaces and the SONET/T1/E1SPA framers.SSM functionality provides the following key benefits.•Prevents timing loops•Provides fast recovery when a part of the network fails•Ensures that a node derives timing from the most reliable clock sourceTo maintain a logical communication channel in synchronous network connections,Ethernet relies on a channel called the Ethernet synchronization messaging channel (ESMC),based on IEEE 802.3organization-specific slow protocol standards.ESMC relays the SSM code that represents the quality level of the Ethernet equipment clock (EEC)in a physical layer.The ESMC packets are received only for those ports configured as clock sources and transmitted on all SyncE interfaces in the system.These packets are then processed by the clock selection algorithm and used to select the best clock.The transmitted frame is generated based on the QL value of the selected clock source and sent to all the enabled SyncE ports.Synchronization Messaging4Clock Selection AlgorithmThe clock selection algorithm selects the best available synchronization source from the nominated sources.The clock selection algorithm has a non-revertive behavior among clock sources with the same QL value and priority.It always selects the signal with the best QL value.The following parameters contribute to the selection process.•Quality level•Signal fail (QL-FAILED)•Priority•External commands (manual,auto-revertive,and so on)Clock Selection AlgorithmThe following sections describe how to configure the clock source.5.1Configuring Clock RecoveryTo configure a clock source,perform the following step.•Click Configuration>SyncE,and then configure the following parameters as shown in the following figure.1.Under the Clock Source Nomination and State section,select the required Nominated option forthe clock source to be nominated.2.To set the priority of the source,under the Clock Source Nomination and State section,select theappropriate option from the Priority list.3.To enable the reception of SSM,under the SyncE Ports section,select the SSM Enable optionagainst the required ports.Figure1•Basic SyncE SettingsNote:If the clock source does not send SSM,it is possible to set a QL using the SSMoverwrite.In the previous figure,the state under the Clock Selection Mode and State section is shown as Locked,implying that all the Ethernet ports are transmitting with the frequency of the selected clock source,Port25in the configuration.The LOCS shows green when the nominated clock source is available,the SSM shows red when no SSMquality level is received,and DHOLD shows green after a while in the locked state.DHOLD is a digital holdcondition for the PLL that indicates a valid holdover frequency has been calculated.The SSM transmitted on enabled ports reflects the locked condition.On the port used as the clock source,the Tx-SSM is QL-DNU,meaning quality level"do not use".This is to avoid timing loops.A receiver of theQL-DNU SSM does not use this clock as a timing source.On other ports,the QL-PRC is transmitted,indicatingthe quality level of the clock.# conf t(config)# network-clock clk-source 1 nominate interface 10GigabitEthernet 1/1!!(config)# interface 10GigabitEthernet 1/1(config-if)# network-clock synchronization ssm! Show SyncE status# show network-clockSelector State is: Locked to 1Alarm State is:Clk: 1 2 3LOCS: FALSE TRUE TRUESSM: FALSE FALSE FALSEWTR: FALSE FALSE FALSELOL: FALSEDHOLD: FALSESSM State is:Interface Tx SSM Rx SSM Mode10GigabitEthernet 1/1 QL_DNU QL_EEC1 Master10GigabitEthernet 1/4 QL_PRC QL_EEC1 Master5.2Configuring Clock RedundancyIt is possible to configure up to three clock sources:two sources from any of the Ethernet ports and thethird from an external clock input.Based on the priority and QL of these clock sources,the best source isselected.Note:QL overrides the priority.If port3receives QL-PRC and port2receives only QL-EEC1,butport2has higher priority(lowest number,0),then port3is selected.To configure clock redundancy,perform the following step.•Click Configuration>SyncE,and then configure the following parameters as shown in the following figure.◦Under the Clock Source Nomination and State section,select the required Nominated option for the clock source to be nominated;and from the Priority list,select the priority.◦To enable the reception of SSM,under the SyncE Ports section,select the SSM Enable check boxes against the required ports.Figure2•Clock Redundancy# conf t(config)# network-clock clk-source 1 nominate interface 10GigabitEthernet 1/1(config)# network-clock clk-source 2 nominate interface 10GigabitEthernet 1/4(config)# network-clock clk-source 1 priority 0(config)# interface 10GigabitEthernet 1/1,4(config-if)# network-clock synchronization ssm5.3Configuring Clock Selection ModesThe definition of the best clock source is the one with the highest QL and the highest priority among theones with equal QL.The following table lists the available clock selection modes.Table1•Clock Selection ModeModeDescriptionManualNo clock selection occurs as the clock source is strictly what isstated in the Source field.This is used to force the selection ofa specific source.If this manually selected clock source is failing,then the clock selector goes into the holdover state.Manual To SelectedThis is same as the Manual mode where the port selected clocksource becomes the source.This is used to freeze the currentclock source in case of a failure upon switchover.Auto NonRevertiveThe clock selection of the best clock source is only done whenthe selected clock fails.Auto RevertiveThe clock selection of the best clock source is constantly done.This is the default setting.Force Hold OverThe clock selector is forced to hold over state.The clock selector is forced to free run state.Force Free RunTo configure the clock selection modes,perform the following step.•Click Configuration>SyncE,and then under the Clock Selection Mode and State section,from the Mode list,select the required mode.Figure3•Selected Source Failure in Manual Mode with No Switch OverNote:As also seen in the previous figure,if the Mode is set to Manual and the source isfailing,the clock selector goes into the Holdover state.The equivalent ICLI commands are:# conf t(config)# network-clock selector manual clk-source 05.4Clock Redundancy with Input FailIn the following example of the default clock selection mode,Auto Revertive,if the selected source fails,another source is selected.As shown in the following figure,when Source1is failing,the Clock selectorstarts using Source2.If the selected source fails,the other source is selected because the default modesetting is Auto-revertive.Figure4•Selected Clock Source FailureWhen port25is restored,the wait to restore(WTR)timer is started as shown in the following figure.Whenthe WTR timer expires,the primary port is elected again.Figure5•Active WTR5.5Configuring WTR and Hold Off TimersThere are two timers:•WTR(wait to restore)timer•Hold off timerThe WTR timer is activated on the falling edge of a clock source failure(in revertive mode).This means thatthe clock source is first available for clock selection after the WTR timer is cleared.The hold off timer delays the active loss of clock by a specific amount of time.The clock selector will notchange clock source if the loss of clock condition is cleared within this time.To configure a WTR of1minute and a hold-off on clock source1to300ms,perform the following step.•Click Configuration>SyncE,and then(refer to Figure3•Selected Source Failure in Manual Mode with No Switch Over on page7):◦Under the Clock Selection Mode and State section,from the WTR Time list,select1M.◦Under the Clock Source Nomination and State section,from the Hold Off list,select300ms.The equivalent ICLI commands are# conf t(config)# network-clock wait-to-restore 1(config)# network-clock clk-source 1 hold-timeout 35.6Configuring ANEG ModeAuto negotiation(ANEG)mode is relevant for1000BaseT ports only.To recover the clock from a port,itmust be negotiated to the slave mode.To distribute the clock,the port must be negotiated to master mode.The following ANEG modes can be activated on a clock source port.•Prefer Slave—the port is negotiated to slave mode if possible.•Prefer Master—the port is negotiated to master mode if possible.•Forced Slave—the port is forced to master mode.Note:If possible,the selected port in the locked state is always negotiated as slave mode.To configure the nominated port as Prefer Slave,perform the following step.•Click Configuration>SyncE,and then under the Clock Source Nomination and State section,in the ANEG Mode list select the required mode(refer to Figure3•Selected Source Failure in Manual Modewith No Switch Over on page7).The equivalent ICLI commands are:# conf t(config)# network-clock clk-source 1 aneg-mode slave5.7Configuring the Station ClockIt is possible to select an input clock signal and to generate an output clock signal.Both signals can be1.544MHz,2.048MHz,or10MHz(individually selected).The input clock signal can be used as the clock source and is always nominated as clock source3.The portselection in this case is S-CLK(clk-in).As this input clock signal carries no SSM,an SSM overwrite quality level must be set.To set an SSM overwrite quality level using the input clock signal as clock source,perform the followingstep.•Click Configuration>SyncE,and then under the Clock Source Nomination and State section:◦Select the Nominated option for the Clock Source3.◦From the Port list,select S-CLK option◦From the SSM Overwrite list,select a valid quality level(for example,QL-ECC1)◦Under the Station Clock Configuration and Clock Hardware section,from the Clock Input Frequency and Clock Input Frequency lists select the desired clock input and output frequencies.Figure6•Set SSM Overwrite Quality LevelThe equivalent ICLI commands are:# conf t(config)# network-clock input-source 10mhz(config)# network-clock output-source 2048khz(config)# network-clock clk-source 3 nominate clk-in(config)# network-clock clk-source 3 ssm-overwrite eec1The following illustration shows the output frequency.•Channel1is the remote node used as source•Channel2is the local node that is locked to remote nodeNote:SyncE provides frequency synchronization,not phase,so the phase between the twonodes is arbitrary.Figure7•Output Frequency Measured5.8PTP as Clock SourceIt is also possible to use a PTP instance as a clock source.5.8.1PrerequisitesEnsure that the PTP is configured using the G.8265.1profile.For more details,see ENT-AN1039,IEEE1588and NTP Software Configuration Guide.5.8.2Configuring PTP as a Clock SourceTo configure PTP as a clock source,perform the following steps.1.Click Configuration>SyncE,and then under the Clock Source Nomination and State section,select theNominated option for the clock source1.2.Under the Clock Source Nomination and State section,from the Port list,select one of the four PTPinstances.Figure8•SyncE ConfigurationThe status of the PTP instance is shown in the PTP ports(G.8265.1)•RX SSM—the quality level of the PTP clock class converted to SyncE QL.For example,PTP clock class 84=QL PRC•Packet timing signal fail(PTSF):◦None—no error◦Unusable—too low quality◦LossAnn—no announce message received◦LossSync—loss of synchronization6TroubleshootingWhen configuring SyncE,check whether the hardwares are able to detect a PLL.If the hardware supports SyncE but cannot lock to the clock source select,then check the clock source.For SyncE to be able to lock to a clock source,the frequency of the clock source must be within 12ppb of the frequency of the board.Standard Ethernet requires only a clock of 100ppm.Figure 9•Clock Hardware IDUndetectedTroubleshootingMicrosemi makes no warranty,representation,or guarantee regarding the information contained herein or the suitability of its products and services for any particular purpose,nor does Microsemi assume any liability whatsoever arising out of the application or use of any product or circuit.The products sold hereunder and any other products sold by Microsemi have been subject to limited testing and should not be used in conjunction with mission-critical equipment or applications.Any performance specifications are believed to be 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目录修订记录Revision record .............................................................. E rror! Bookmark not defined.同步以太技术白皮书 .. (iv)1 背景 (1)2 同步以太的同步原理 (2)3 同步以太的SSM功能 (5)3.1 同步以太的SSM质量等级定义 (5)3.2 同步以太如何传递SSM信息 (6)3.3 同步以太的SSM协议如何工作 (8)3.4 在什么情况下会成环 (10)4 同步以太的设备模型 (13)5 同步以太的组网要求 (14)6 同步以太技术的总结 (15)7 参考标准 (16)插图目录图2-1 同步以太示意图 (2)图3-1 SyncE中的SSM信息传递 (8)图3-2 SSM协议工作原理 (9)图3-3 SSM协议状态机 (10)图3-4 无SSM的场景 (11)图3-5 有SSM的场景 (11)图5-1 G.803推荐的物理层同步组网要求 (14)表格目录表2-1 以太接口的同步以太支持能力 (3)表3-1 表－ESMC报文格式 (6)表3-2 表：QL TLV格式 (7)同步以太技术白皮书同步以太技术白皮书同步以太技术白皮书关键词：同步以太,SyncE、SSM摘要：本文主要介绍同步以太和NTR技术，包括同步以太和NTR的同步原理、SSM保护倒换原理以及相关的标准体系等内容。

缩略语：同步以太技术白皮书 1 背景1 背景全IP化是未来网络和业务发展的趋势，这已被业界公认，移动网络也是如此。

在移动网络向全IP逐步推进的过程中，也对如何实现时钟同步提出了新的需求和挑战。

众所周知，分组交换网络用于突发性数据通信的传输，其中信息在源处封装成分组，这些分组通过网络节点(如交换机和路由器)以存储转发的方式传输，直至到达目的地。

因此分组网络和原来的电路交换网络有着很大不同，在本质上是异步的。