Improvement of Resilient Packet Ring Fairness
ITS解决方案
深圳键桥通讯技术有限公司ITS解决方案一、系统总体目标、功能与架构 ----------------------------------------------------------------------------- 2二、交通指挥中心集成平台 ----------------------------------------------------------------------------------- 6三、交通信息综合传输平台 ----------------------------------------------------------------------------------- 8四、交通数据采集子系统 ------------------------------------------------------------------------------------- 11五、交通诱导子系统-------------------------------------------------------------------------------------------- 13六、交通信号控制子系统 ------------------------------------------------------------------------------------- 16七、道路图像监控子系统 ------------------------------------------------------------------------------------- 18八、中心大屏幕显示控制子系统 ---------------------------------------------------------------------------- 21九、GIS/GPS子系统-------------------------------------------------------------------------------------------- 239.1地理信息系统GIS ---------------------------------------------------------------------------------- 23 9.2全球卫星定位系统GPS --------------------------------------------------------------------------- 26 十、交通违法监测子系统 ------------------------------------------------------------------------------------- 2910.1视频闯红灯违法监测系统 ---------------------------------------------------------------------- 31 10.2超速视频抓拍违法监测系统 ------------------------------------------------------------------- 33 10.3违法监测中心处理分系统 ---------------------------------------------------------------------- 35 十一、卡口监控子系统 ---------------------------------------------------------------------------------------- 37一、ITS总体目标、功能与架构总体目标:1)建立快速的自动突发事件检测系统。
ptn期末考试题及答案
ptn期末考试题及答案试题:一、选择题(每题2分,共20分)1. PTN(Packet Transport Network)是一种用于什么的网络技术?A. 视频传输B. 数据传输C. 语音传输D. 广播传输2. PTN网络中,哪种技术可以提供高可靠性的数据传输?A. MPLSB. VPNC. RPRD. SDH3. PTN网络中,以下哪个不是其主要特点?A. 高可靠性B. 高带宽C. 低时延D. 低成本4. PTN网络支持哪种类型的网络拓扑?A. 星型B. 环形C. 网状D. 所有以上5. PTN网络中,哪个协议用于确保数据传输的顺序?B. UDPC. IPD. MPLS6. PTN网络中,哪种技术可以提高数据传输的安全性?A. VPNB. MPLSC. RPRD. SDH7. PTN网络中,以下哪个选项是正确的?A. PTN只能用于固定网络B. PTN可以用于移动网络C. PTN不能用于数据传输D. PTN只能用于语音传输8. PTN网络中,哪个术语表示“保护环”?A. VPNB. RPRC. MPLSD. SDH9. PTN网络中,哪种技术可以实现数据的快速恢复?A. TCPB. RPRC. MPLSD. SDH10. PTN网络中,以下哪个不是数据传输的协议?A. TCPC. IPD. PTN二、填空题(每空2分,共20分)11. PTN网络的全称是________。
12. PTN网络的核心技术之一是________。
13. PTN网络的________可以提供数据传输的顺序性。
14. PTN网络的________技术可以提高数据传输的安全性。
15. PTN网络的________技术可以实现数据的快速恢复。
16. PTN网络支持________、________和________三种网络拓扑。
17. PTN网络的________技术可以提供高可靠性的数据传输。
18. PTN网络的________可以提高数据传输的效率。
RPR(弹性分组环)
RPR的简称Resilient Packet Ring弹性分组环(802.17), 从字眼我们可以看出这个技术的三个特点,首先是Resilient(弹性的),这个比较复杂我们后面慢慢谈谈这些弹性的优点。
再次是Packet(包),这个技术基于包的传送。
最后是Ring(环),包的传送要建立在Ring这种拓扑结构上。
而且是一种双环结构,每个环上最大的带宽1.25Gbit/s, 双环最大带宽2.5Gbit/s. 外环携带内环数据包的管理字节,内环携带外环的管理字节。
这样,双环互为保护和备份。
目录我们来谈谈“弹性”带来的优点:RPR关键技术RPR特点与发展现状我们来谈谈“弹性”带来的优点:RPR关键技术RPR特点与发展现状展开编辑本段我们来谈谈“弹性”带来的优点:1、业务分级将业务分为A,B,C3级。
其中A细分为两级,B细分为两级。
数据类型实际上被分为5级,每一级有不同的QoS,保证业务的区分度,分别对应实时业务,非实时业务和尽力传送。
2、拓扑自动发现保证了对环上新增和移去的节点,动态实现拓扑结构更新。
如果要增加或者减少RPR上的总带宽,则可以结合LCAS功能来实现。
使用LCAS可以动态的调整带宽,而不影响原有业务。
3、空间重用RPR单播帧在目的节点剥离的机制,实现了环上带宽的空间重用。
环上带宽可以几个点的业务共用,带宽利用率提高。
4、公平算法RPR内环和外环都支持独立的公平算法。
公平算法保证了低优先级的B_EIR和C类业务在RPR环上的公平接入。
通过设置公平算法的权重,可以使不同的结点具有不同的接入速率。
节点可以分别在外环和内环上设置不同的权重。
5、保护wrapping+string, wrapping相当于断纤处环回,倒换时间快,但是路径不是最优。
String保护模式倒换时间慢,但选择最优路径。
目前,电信业的开放和互联网的发展,致使网络与通信正以前所未有的速度迅猛发展。
住宅用户和各类商业用户对带宽的要求越来越高,且业务的发展和宽带的增加之间相辅相成。
弹性分组环(RPR)协议简介
弹性分组环(RPR)协议简介 ⼀、前⾔ IP技术的发展,使得数据业务逐渐成为主要的通信流量,这对城域⽹(MAN)和⼴域⽹(WAN)都提出了更⾼的带宽要求。
对于建⼀个好的MAN来说,有两个要求:⾸先,要有⼀个价格合理的、扩展性好的解决⽅案来适应不断膨胀的IP流量和光纤带宽的增长;其次,要有新的通⽤功能部件和技术来满⾜现有的需要。
但传统的城域⽹和⼴域⽹是为使⽤SONET/SDH电路交换的话⾳和视频⽽设计和优化的。
在传统的电路交换⽹络上传输数据已被证明不是有效的⽅法,该⽅法复杂⽽且昂贵。
IP领域很早就认识到了环形⽹络结构的价值,并已在这⽅⾯作了⼤量努⼒,发展了象令牌环和光纤分布数字接⼝(FDDI)这样的解决⽅案;但这些⽅案却⽆法满⾜IP流量和光纤带宽增长的需要,也⽆法满⾜在拥塞情况下维持⾼的带宽利⽤率和转发量、保证节点间的平衡、迅速从节点或传输媒体故障中恢复、可即插即⽤等IP传输和业务传递发展的需要。
因此,像令牌环和FDDI这样的环形⽹并不适合⽤于城域⽹。
服务提供商和企业需要⼀种扩展性好、能够健壮地应⽤在城域⽹和⼴域⽹上、以千兆的速度传输IP信息包的技术。
因此,2000年11⽉正式成⽴了IEEE’s 802.17 弹性分组数据环⼯作组(RPRWG),希望开发⼀个RPR (Resilient Packet Rings) MAC标准,优化在LAN、MAN和WAN拓扑环上数据包的传输。
⼆、RPT的主要⽬标 弹性分组数据传送RPT(Resilient Packet Transport)是基于RPR环形结构的⼀种带空间复⽤的传输⽅式,是⼀种全新的千兆IP直接Over光纤技术。
RPT技术吸收了千兆以太⽹的经济性,SDH对延时和抖动严格保障、可靠的时钟和50ms环⽹保护特性。
RPT具有空间复⽤机制,可同MPLS相结合,简化IP前传,同时具有第三层路由功能,基于RPT技术的设备可以承载具有突发性的IP业务,同时⽀持传统语⾳传送,是适⽤于中⼩型城域⽹⾻⼲到接⼊的技术。
IEEE802协议各个标准的介绍(1)
IEEE 802协议各个标准的介绍(1)IEEE 802协议的各类标准的针对类型不同,有的是在之前的演进版本,有的则是特定用户所需要的一个网络协议,下面就这个方面来总结一下。
无线网络的使用已经是司空见惯了。
那么对于IEEE 802协议下的各类标准,你是否清晰呢?现在就让小编在此在为大家总结一下吧。
首先还是来了解一下这个协议的基本含义。
无线局域网最通用的标准是IEEE定义的无线网络通信工业标准——IEEE802.11系列。
开始之前,让我们先来了解什么是IEEE?IEEE是电子和电气工程师协会(Institute of Electrical and Electronics Engineers)的简写,于1963年1月1日由AIEE(美国电气工程师学会)和IRE(美国无线电工程师学会)合并而成,是美国规模最大的专业学会,亦是世界上最大的专业技术组织之一,拥有来自175个国家的36万会员。
目前IEEE在工业界所定义的标准有着极大的影响。
IEEE定位在“科学和教育,并直接面向电子电气工程、通讯、计算机工程、计算机科学理论和原理研究的组织,以及相关工程分支的艺术和科学”。
为了实现这一目标,IEEE承担者多个科学期刊和会议组织者的角色,它也是一个广泛的工业标准开发者。
IEEE制定了全世界电子和电气还有计算机科学领域30%的文献,另外它还制定了超过900个现行工业标准。
每年它还发起或者合作举办超过300次国际技术会议。
IEEE由37个协会组成,还组织了相关的专门技术领域,每年本地组织有规律的召开超过300次会议。
IEEE 出版广泛的同级评审期刊,是主要的国际标准机构(900现行标准,700研发中标准)。
IEEE 802协议定义的常见标准IEEE 802.1──高级接口High Level Interface(Internetworking)IEEE 802.1d──生成树协议(Spanning Tree)IEEE 802.1p──General Registration ProtocolIEEE 802.1q──虚拟局域网(Virtual LANs;VLAN)IEEE 802.1x──基于端口的访问控制(Port Based Network Access Control)IEEE 802.2──逻辑链路控制(Logical Link Control)IEEE 802.3──带冲突检测的载波侦听多路访问协议CSMA/CD(半双工以太网)IEEE 802.3u──快速以太网(Fast Ethernet)IEEE 802.3z──千兆以太网(Gigabit Ethernet)IEEE 802.3ae──万兆以太网(10 Gigabit Ethernet)IEEE 802.4──令牌环总线(Token-Passing Bus)IEEE 802.5──令牌环(Token-Passing Ring)IEEE 802.6──城域网(Metropolitan Area Networks,MAN)IEEE 802.7──宽带局域网(Brandband LAN)IEEE 802.8──光纤局域网IEEE 802.9──集成数据和语音网络(Integrated Voice and Data Networks,VoIP IEEE 802.9a──IsoENET(proposed)IEEE 802.10──网络安全(Network Security)IEEE 802.11──无线以太网IEEE 802.12──100VG-AnyLAN(Voice Grade - Sprache geeignet)IEEE 802.14──有线电视(CATV)IEEE 802.15──无线个人局域网路(Wireless Personal Area Network,WPAN)IEEE 802.17──弹性分组环(Resilient Packet Ring)802.11是IEEE 802协议在1997年为无线局域网(Wireless LAN)定义的一个无线网络通信的工业标准。
计算机三级网络技能技术总结选择题第十套-含答案
精心整理1.下列属于无线接入技术的是(B )。
A)RPRB)AdhocC)EPOND)SDH解析:RPR(弹性分组环,ResilientPacketRing)是一种直接在光纤上高校传输IP 分组的传输技术,用于支持城域光网络。
RPR 采用双环结构,可提供最大长度100km 的光纤传输。
其双环均可以传输数据,高效的利用光纤的带宽。
Adhoc 是一种无线接入技术,主要在无线传感网和无线网格网中运用。
EPON 是一种新型的光纤接入网技术,采用点到多点结构、无源光纤传输,在以太网之上提供多种业务。
SDH 是一种将复接、线路传输及交换功能融为一体、并由统一网管系统操作的综合信息2.解析:802.11a 。
3.A)B)C)D)保证管理、IP 功能。
)4.A)ADSL B)ADSL D)采用解析:ADSL 在现有的用户电话铜双绞线上,以重复和不干扰传统模拟电话业务下,提供告诉数字业务。
由于电话铜双绞线通常用于传输模拟信号,为了传输数字信号,计算机需要在传输信道和计算机直接采用ADSLModem 进行调制解调。
ADSL 技术提供了非对称特性,上行速率在64kbps~640kbps ,下行速率在500kbps~7Mbps 。
用户可以根据需求,采用上行和下行速率。
5.下列关于B/S 模式应用服务器的描述中,错误的是(B )。
A)网络应用建立在Web 服务的基础上B)访问不同的应用服务器需要不同的客户端程序C)浏览器不能直接访问数据库服务器D)采用三层架构解析:B/S 结构(浏览器服务器模式),是兴起后的一种网络结构模式。
该结构统一采用Web 浏览器作为客户端。
B/S结构将系统功能实现的核心部分集中到服务器上,使得系统的开发、维护和使用简便化。
Web浏览器通过服务器访问数据库服务器,将复杂的业务逻辑部分集中在服务器上。
6.IP地址的子网掩码可写为(B)。
A)B)C)D)解析:IP地址中的27表示的是子网掩码的长度,也就是说子网掩码是27个1和5和0组成的,即,所以的子网掩码为。
地铁设备系统综合联调方案
关于印发《沈阳地铁二号线一期工程设备系统综合联调方案》的通知各处室、项目部、各直属公司、相关参建单位项目部:现将《沈阳地铁二号线一期工程设备系统综合联调方案》印发给你们,请遵照执行。
二〇一一年八月四日沈阳地铁二号线一期工程设备系统综合联调方案沈阳地铁集团有限公司2011-8-4目录第一章工程概况 (1)一、沈阳地铁二号线一期工程项目概况 (1)二、系统概况 (1)第二章综合联调概况 (26)一、综合联调的定义 (26)二、综合联调的目的 (26)三、综合联调的主要任务 (28)四、综合联调的意义 (29)五、综合联调工作流程图 (29)六、综合联调接口关系矩阵 (31)第三章组织机构及职责 (32)一、综合联调领导小组 (32)二、综合联调办公室 (33)三、安全督导组 (33)四、技术协调组 (34)五、质量检查组 (34)六、调度乘务组 (35)七、综合联调试验组 (35)八、保障组 (36)第四章综合联调实施方案 (39)一、前提条件 (39)二、联调目标 (40)三、调试依据 (40)四、联调工作量及实施计划 (41)五、综合联调实施方案 (46)第五章相关管理办法及制度 (118)第六章应急预案 (119)附录 (135)第一章工程概况一、沈阳地铁二号线一期工程项目概况沈阳地铁二号线工程分为一期工程、北延线工程和南延线工程3部分,其中一期工程与北延线工程同期分步实施,南延线工程为远期工程。
一期工程线路全长21.86km,全部为地下线,设三台子站、陵西站、新乐遗址站、北陵公园站、中医药大学站(与五号线换乘)、岐山路站、沈阳北站站(与国铁换乘)、金融中心站、市府广场站(与三号线换乘)、青年大街站(与一号线换乘)、青年公园站、工业展览馆站(与五号线换乘)、市图书馆站(与四号线换乘)、五里河站、奥体中心站、营盘街站、世纪大厦站、下深沟站、上深沟站共计19座地下(地面厅)车站,平均站间距1.159km,最长站间距1.485 km。
以太网业务在SDH中的应用与配置
以太网业务在SDH中的应用与配置广东省广州市 510000摘要:MSTP(Multi-Service Transport Platform)技术的发展让IP业务(甚至是ATM等)与传统的SDH业务结合起来了,基于SDH平台的以太网业务传送除具有标准SDH节点的所有功能外还同时支持以太网的二层交换和透传,满足了业务承载和专线透传的需求。
基于SDH的以太网业务有四种:实现业务点到点透传的以太网私有专线业务EPL、基于VPN专线的以太网虚拟私有专线业务EVPL、基于二层交换业务,实现多点到多点的以太网私有局域网业务EPLAN和以太网虚拟专用局域网业务EVPLN。
关键字:MSTP、EPL、EVPL、EPLAN、EVPLAN前言随着Internet的高速发展,各种带宽接入和应用也逐渐成熟,同时越来越多的办公地点和场景出现了多元化的需求,需要进行高速互连,而原有的窄带数据通信技术已不能满足带宽的需求。
在此背景下,MSTP(多业务传送平台)技术应运而生,利用MSTP技术可以实现多种类型的以太网业务在SDH平台进行处理和传输。
一、以太网业务在SDH传输的原理1.1以太网单板数据的处理流程以太网数据进入端口后会根据不同的业务形式进行端口业务处理和环路控制,然后进行封装和映射送至SDH交叉连接单元。
其中环路控制的RPR是弹性分组环Resilient Packet Ring的意思,是IEEE 802.17定义用于局域网、城域网和广域网的媒介存取控制(MAC)协议,它采用了现有的物理层规范,逆向双环拓扑结构,外环( Outer Ring )和内环( Inner Ring )都传送数据包和控制包,内环的控制包携带外环数据包的控制信息,反之亦然。
它同时借鉴了SDH的电信级倒换保护的优点和以太网传输高效的特点。
1.2以太网Tag属性具有交换功能的EFS系列单板均可对数据帧中的标签进行处理,而为了区分不同格式的数据帧则是通过Tag属性对信号包进行标示的,Tag是数据帧中如果包含了VLAN ID。
城市轨道交通信号系统项目七 DCS信号子系统
的列车控制子系统都包括标准的
IEEE 802.3(以太网)接口和使用 UDP/IP作为不同设备之间的通信协
议。
项目七 DCS信号子系统
二、DCS子系统系统功能
CBTC各子系统之间双向﹑可靠数据通信
信息冗余传输
采用有效的安全机制保障DCS网络安全性 采用先进的加密算法保证数据安全性 网络管理
项目七 DCS信号子系统
2、系统结构组成 3)轨旁数据接入网络 轨旁接入网络部分,提供各轨旁子系统和轨旁无线设备接入数据通信子系统的接 口。 一般线路非设备集中站都部署一台光口接入交换机
设备集中站及运营控制中心和车辆段分别部署一台轨旁无线设备接入交换机
和有线设备接入交换机,轨旁无线设备和有线设备采用不同的AS交换机接入网络 ,保障轨旁数据接入的高可靠性; 轨旁光口接入交换机和电口接入交换机分别以星型方式千兆上联所属的本区 域骨干交换机; 轨旁光口接入交换机以百兆光纤连接本站区域各轨旁AP,电口接入交换机通 过百兆双绞线为本站内各轨旁有线设备提供接入。
项目七 DCS信号子系统
一、系统组成
2、系统结构组成 5)车载数据通信网络
车载网络系统分别由车头驾驶室网络部分及车尾驾驶室网络部分组成。其中车
头和车尾的驾驶室网络部分由车载无线网络单元、车载天线、车载网络交换机和车 载CBTC系统设备组成。
无线链路 车载无线单元 车载交换机 CBTC系统设备 车尾驾驶室
息、ATP信息、ATO信息能在各系统设备间快速传递,完成ATS、ATP、ATO的各
类功能。 DCS子系统基于开放的业界标准:有线通信部分采用IEEE802.3以太网标准,无 线通信部分采用先进的WLAN技术——IEEE802.11g标准,最大程度地采用成熟的 设备。
核电厂数字化仪控系统通信网络分析
设备管理与维修2018翼9(下)核电厂数字化仪控系统通信网络分析岳春生,王欣(中核核电运行管理有限公司,浙江嘉兴314300)摘要:基于国内核电厂数字化仪控系统应用现状,分析几种控制系统通信网络解决方案。
通过对比网络拓扑结构,得出各核电厂数字化仪控系统通信技术在可靠性设计上的优缺点。
结果表明:采用双环型、双总线型和两种型式相结合拓扑结构的通信网络在可靠性和安全性上满足相关核安全法规和标准的规定。
关键词:核电厂;数字化仪控系统;通信;网络拓扑;可靠性中图分类号:TL48文献标识码:B DOI :10.16621/ki.issn1001-0599.2018.09D.630引言仪器仪表技术的出现和发展极大地推动了工业仪控系统的发展,后者由传统的模拟仪表逐渐朝着数字化设备+模拟仪表组合和全数字化控制系统进化和发展。
现如今,全数字化仪控系统已经开始逐渐取代我国核电厂仪控系统主体所使用的数字化设备+模拟仪表组合。
数字化技术的核心是通信网络,通信网络对控制系统的建立以及各控制站间数据交互的实现起到重要作用。
核电厂仪控系统分为安全级与非安全级,其中安全级系统执行紧急停堆、堆芯冷却、安全壳隔离等重要的核安全功能,对设备和技术的可靠性和安全性要求高,都必须经历严格的成熟验证。
所以,在安全级控制系统的设计方面,也有专门的核安全法规和标准对具体设计作了相应的要求和规范。
通信网络是安全级数字化仪控系统的最为基础和关键的组成部分,其可靠性设计必须遵循以下原则,如冗余性、独立性、多样性、单一故障、故障安全等[1]。
1核电厂数字化仪控系统现状目前国内核电厂数字化仪控系统统计见表1。
2核电厂数字化仪控系统通信网络分析2.1通信网络简介目前,电气和电子工程师协会局域网委员会制定的局域网标准中,主要以令牌环、以太网、令牌总线网等使用较为普遍,上述标准对网络拓扑结构和介质访问方式作了明确规定,并且许多通信协议的建立都依赖于上述标准。
现如今,部分主流通信网络的开发者并未将安全理念贯穿于整开发过程,而只是简单对完成的设计产品进行安全性评价。
你也喜欢打拳吗 英语作文
你也喜欢打拳吗英语作文Title: The Art of Boxing: A Passion Beyond the Ring。
Boxing, a sport revered for its raw power, precision, and discipline, is indeed a passion of mine. Its essence transcends mere physicality; it embodies the virtues of perseverance, strategy, and respect. Through the rhythmic dance of footwork, the thunderous symphony of punches, and the silent language of the ring, boxing weaves a narrative of courage and determination.First and foremost, boxing is a testament to the power of discipline. Every jab, hook, and uppercut is honed through countless hours of relentless training. It demands unwavering commitment, pushing the body and mind to their limits. In the solitude of the gym, amidst the sweat and the strain, one discovers the true meaning of dedication. Each session is not just a test of physical prowess but a journey of self-discovery and growth.Moreover, boxing is a masterclass in strategy. It is not merely about throwing punches haphazardly but about outsmarting your opponent, predicting their moves, and exploiting their weaknesses. Every feint, every dodge, every counter is a calculated maneuver aimed at gaining the upper hand. The mental chess match that unfolds within the confines of the ring is as exhilarating as it is cerebral. It teaches us to think on our feet, to adapt to changing circumstances, and to remain calm under pressure.Beyond the glitz and glamour of the sport lies a deeper lesson in humility and respect. In the ring, there are no shortcuts, no excuses. It is just you and your opponent, stripped of all pretense. Regardless of the outcome, there is a mutual acknowledgment of the courage it takes to step between those ropes. Win or lose, both warriors emerge with a newfound respect for each other, bound by the shared experience of battle.For me, boxing is not just a hobby but a way of life. It instills in me a sense of purpose, a drive to constantly strive for improvement. It teaches me to embrace challengeshead-on, to never back down in the face of adversity. More than anything, it reminds me of the power of resilience, that no matter how many times I may fall, I have the strength to rise again.In conclusion, boxing is a passion that transcends the boundaries of the ring. It is a symphony of sweat, determination, and camaraderie. Through its trials and triumphs, it molds us into stronger, more resilient individuals. So, do I love boxing? Absolutely. It is not just a sport but a way of life, a journey of self-discovery and growth. And for that, I will always be grateful.。
自我提升英语作文120字
自我提升英语作文120字Self-improvement is a journey that everyone should embark on. It is the process of constantly striving to become a better version of oneself. In the context of learning English, self-improvement is crucial for mastering the language and becoming proficient in it. There are several ways to achieve self-improvement in English, and they can be approached from various perspectives.Firstly, one can focus on enhancing their language skills through consistent practice. This can be done by reading English books, watching English movies, and listening to English podcasts. By immersing oneself in the language, one can improve their vocabulary, grammar, and overall comprehension. Additionally, practicing speaking and writing in English regularly can significantly contribute to self-improvement.Secondly, setting specific and achievable goals is essential for self-improvement in English. By establishingclear objectives, such as learning a certain number of new words each week or completing a certain number of writing exercises, individuals can track their progress and stay motivated. This sense of accomplishment can fuel further self-improvement and maintain momentum in the learning process.Furthermore, seeking feedback and guidance from others can be invaluable for self-improvement in English. Whether it is through joining a language exchange program, taking language classes, or working with a tutor, receiving constructive criticism and support from others can help individuals identify areas for improvement and make necessary adjustments in their learning approach.In addition, adopting a positive mindset and being persistent in the face of challenges is crucial for self-improvement in English. Learning a new language can be daunting at times, but maintaining a positive attitude and persevering through difficulties can ultimately lead to success. Embracing mistakes as learning opportunities and staying resilient in the face of setbacks are essentialaspects of self-improvement.Moreover, utilizing technology and resourceseffectively can aid in self-improvement in English. There are numerous language learning apps, online resources, and interactive platforms that can supplement traditional learning methods. Leveraging these tools can make the learning process more engaging and accessible, ultimately contributing to self-improvement.Lastly, self-reflection and self-assessment areintegral to self-improvement in English. Taking the time to evaluate one's strengths and weaknesses in language learning can help individuals tailor their approach to better suit their needs. By identifying areas that require improvement and devising strategies to address them, individuals can make significant progress in mastering the English language.In conclusion, self-improvement in English is a multifaceted endeavor that encompasses various strategies and perspectives. By focusing on consistent practice, goal-setting, seeking feedback, maintaining a positive mindset, utilizing resources, and engaging in self-reflection, individuals can effectively enhance their language skills and achieve proficiency in English. Ultimately, self-improvement is a continuous process that requires dedication, perseverance, and a willingness to embrace growth and learning.。
The Importance of Goals
The Importance of GoalsGoals are an essential part of life, providing direction, motivation, and a sense of purpose. They give us something to strive for, a target to aim at, and a reason to push ourselves beyond our limits. Without goals, we may feel lost, unmotivated, and unsure of what we want to achieve in life. Whether they areshort-term or long-term, personal or professional, goals play a crucial role in shaping our lives and driving us towards success. In this essay, we will explore the importance of goals from various perspectives, including their impact on personal growth, professional development, and overall well-being. From a personal growth perspective, setting and working towards goals can be incredibly empowering. When we have a clear vision of what we want to achieve, we are more likely to take action and make choices that align with our aspirations. This sense of purpose and direction can boost our self-confidence and self-esteem, as we see ourselves making progress and achieving the things that matter to us. Whether it's learning a new skill, improving our health, or pursuing a passion, having goals gives us a sense of control over our lives and a reason to keep moving forward. Furthermore, goals can also serve as a source of motivation during challenging times. When we face obstacles or setbacks, having a clear goal in mind can provide the strength and determination to persevere. It gives us something to focus on and reminds us of the bigger picture, helping us to stay resilient and push through adversity. This resilience is crucial for personal growth, as it allows us to learn from our experiences, adapt to change, and ultimately become stronger individuals. In addition to personal growth, goals also play a significant role in professional development. In a professional setting, setting clear and achievable goals can enhance productivity, drive innovation, and foster a culture of continuous improvement. When individuals and teams have specific objectives to work towards, they are more likely to stay focused, prioritize their tasks, and collaborate effectively to achieve success. This not only benefits the organization but also provides employees with a sense of purpose and fulfillment in their work. Moreover, goals can also serve as a benchmark for measuring progress and performance. By setting specific targets and milestones, individuals can track their accomplishments, identify areas for improvement, and celebratetheir successes. This feedback loop is essential for professional development, asit allows individuals to reflect on their work, set new goals, and continuously strive for excellence. It also provides a sense of direction and clarity, guiding individuals towards their desired career path and helping them make informed decisions about their future. From a broader perspective, goals are also crucial for overall well-being and life satisfaction. When we have meaningful goals to pursue, we are more likely to experience a sense of fulfillment and happiness.This is because goals give us a sense of purpose and meaning in our lives,allowing us to focus on what truly matters to us. Whether it's building meaningful relationships, contributing to our community, or achieving personal milestones, having goals can enrich our lives and provide a sense of fulfillment. Furthermore, goals can also contribute to a sense of balance and well-being by helping us manage our time and energy effectively. When we have clear priorities and objectives, we are better able to allocate our resources in a way that supportsour overall well-being. This can help us avoid burnout, reduce stress, andmaintain a healthy work-life balance. By setting boundaries and pursuing goalsthat align with our values, we can create a sense of harmony and contentment inour lives. In conclusion, goals are an integral part of personal growth, professional development, and overall well-being. They provide us with direction, motivation, and a sense of purpose, driving us towards success and fulfillment. Whether they are short-term or long-term, personal or professional, goals play a crucial role in shaping our lives and guiding us towards a meaningful and purposeful existence. By setting clear objectives, staying resilient in the faceof challenges, and striving for continuous improvement, we can unlock our full potential and lead a life that is rich, fulfilling, and aligned with our deepest aspirations.。
GFP协议
GFP协议GFP(Generic Framing Procedure,通用成帧规程)是一种通用映射技术,它可将变长或定长的数据分组,进行统一的适配处理,实现数据业务在多种高速物理传输通道中的传输。
一方面,GFP采用灵活的帧封装以支持固定或可变长度的数据,GFP能对可变长度的用户PDU(Protocol Data Unit,协议数据单元)进行全封装,免去对数据的拆分、重组及对帧的填充,简化了系统的操作,提高了系统的处理速度和稳定度;另一方面,GFP不像LAPS以特定字符7E填充帧头来确定帧边界,GFP使用类似于ATM中基于差错控制的帧定界方式,以HEC(Head Error Check,帧头错误检验)为基础,通过两字节当前帧的净荷长度和两字节的帧头错误检验来确定帧的边界,这种显示帧长度指示的方式可减少边界搜索处理时间,对于有较高同步需求的数据链路来说相当重要,同时它克服了靠帧标志定位带来的种种缺点,进一步加快了处理速度,适应下一代SDH高速的要求。
GFP 标准定义了两种模式:透传模式和帧映射模式。
GFP—T(透明映射的GFP)是一种面向块状码的数据流模式,实现对时延敏感的SAN网(Storage Area Network,存储区域网)的线路码的高效和透明地传输,它面对的是Fiber Channel(光纤通道)、FICON和ESCON接口的数据流.GFP—F(帧映射的GFP)是一种面向PDU的数据流模式,用作传输IP协议、多协议标记交换(MPLS)和以太网的数据流.在这里我们主要介绍适用于传输以太网数据的GFP—F模式。
(1)GFP帧结构GFP协议定义了两种类型的GFP帧:GFP客户帧和GFP管理帧.GFP的帧结构如图1所示,按字节排列,它包括GFP帧头(Core Header)和GFP净荷区(GFP Payload Area)两部分。
GFP帧头包括帧长度标识(PLI ,Payload Length Indicator)和帧头错误检验(Core HEC)。
2021年 NCRE三级网络技术 三级网络工程 内部真考题库第七套
1、(网络技术-选择题)下列属于无线接入技术的是()。
A.RPRB.Ad hocC.EPOND.SDH参考答案: B【解析】RPR(弹性分组环,Resilient Packet Ring)是一种直接在光纤上高校传输IP分组的传输技术,用于支持城域光网络。
RPR采用双环结构,可提供最大长度100km的光纤传输。
其双环均可以传输数据,高效的利用光纤的带宽。
Ad hoc是一种无线接入技术,主要在无线传感网和无线网格网中运用。
EPON是一种新型的光纤接入网技术,采用点到多点结构、无源光纤传输,在以太网之上提供多种业务。
SDH 是一种将复接、线路传输及交换功能融为一体、并由统一网管系统操作的综合信息传送网络,运用于美国贝尔通信技术研究所的同步光网络。
2、(网络技术-选择题)传输速率为54Mbps 的WLAN 标准是()。
A.802.11aB.802.11bC.802.11jD.802.11n参考答案: A【解析】802.11a 是无线网络标准,指定了最大数据传输速率为54Mbps 和工作频段为5GHz,采用了多载波调制技术。
802.11b 是802.11a 的先行版本,最大数据传输速率为11Mb/s,主要为个人电脑提供完全的网络服务。
802.11j 在 4.9 GHz 到 5.0 GHz 之间的这个无线频率范围内增加信道,是802.11a 的补充。
802.11n将WLAN的传输速率由目前802.11a 及802.11g 提供的54Mbps,提高到300Mbps。
3、(网络技术-选择题)下列关于宽带城域网技术的描述中,错误的是()。
A.能够为用户提供带宽保证,实现流量工程B.可以利用NAT 技术解决IP 地址资源不足的问题C.可以利用SNMP 实现带外网络管理D.保证QoS 的主要技术有RSVP、DiffServ 和MSTP参考答案: D【解析】宽带城域网的汇聚层,根据接入层的用户流量,进行本地路由、流量均衡、QoS 管理、IP地址转换等,宽带城域网技术的交换层实现与主干网络的互联,提供城市的宽带IP数据出口。
改善改进之处的英语作文
改善改进之处的英语作文标题,Improving Improvements: The Path to Progress。
In today's rapidly changing world, the quest for improvement is constant. Whether it's in personal endeavors or societal structures, the desire to enhance and refine is ever-present. However, improvement itself is a dynamic concept, requiring adaptation and innovation. In this essay, we will explore the various dimensions of improvement, its significance, and effective strategies to achieve it.First and foremost, improvement is essential for growth and development. It enables individuals, organizations, and communities to reach their full potential. Without continuous improvement, stagnation sets in, leading to inefficiency and decline. Moreover, in a competitive global landscape, those who embrace improvement gain a competitive edge, driving progress and innovation.One area where improvement is particularly crucial iseducation. As the foundation of society, education shapes the future generation and influences societal progress. Therefore, constant efforts to enhance teaching methods, curriculum design, and educational accessibility are imperative. By integrating technology, adopting interactive learning approaches, and fostering critical thinking skills, we can create a more effective and inclusive educational system.Similarly, in the realm of healthcare, improvement is a matter of life and death. Advances in medical research, technology, and healthcare delivery have significantly improved health outcomes and increased life expectancy. However, challenges such as healthcare disparities and access barriers persist. Therefore, ongoing efforts to enhance healthcare infrastructure, promote preventive care, and address systemic inequalities are essential for achieving equitable health outcomes for all.Moreover, improvement extends beyond individual domains to encompass broader societal issues such as environmental sustainability and social justice. Climate change, resourcedepletion, and environmental degradation threaten the very foundation of our planet. To mitigate these challenges, concerted efforts to promote renewable energy, reduce carbon emissions, and preserve natural ecosystems are imperative. Likewise, addressing social injustices such as discrimination, inequality, and poverty requires sustained advocacy, policy reform, and community empowerment.In the realm of technology and innovation, improvement is synonymous with progress. The rapid pace of technological advancement has revolutionized virtually every aspect of human life. However, with technological progress comes ethical considerations and unintended consequences. Therefore, responsible innovation, ethical guidelines, and regulatory frameworks are essential to ensure that technological advancements benefit society as a whole while minimizing potential harms.Furthermore, improvement in governance and publicpolicy is fundamental for fostering a just and equitable society. Transparent and accountable governance, responsive public institutions, and citizen participation areessential pillars of democracy. By promoting political reforms, strengthening democratic institutions, and combating corruption, we can build more resilient and inclusive societies.In conclusion, improvement is not merely a goal but a journey—a continuous process of refinement and adaptation. Whether in education, healthcare, environmental sustainability, or governance, the pursuit of improvementis essential for shaping a better future. By embracing innovation, fostering collaboration, and prioritizing the common good, we can overcome challenges and create a more just, prosperous, and sustainable world for future generations. As we embark on this journey of improvement, let us remember that the road to progress may be long and arduous, but the destination is worth the effort.。
The Importance of Resilience
The Importance of Resilience Resilience is a crucial quality that enables individuals to navigate through life's challenges and setbacks. It is the ability to bounce back from adversity,to adapt to change, and to overcome obstacles. The importance of resilience cannot be overstated, as it plays a significant role in one's mental, emotional, and physical well-being. In this essay, we will explore the significance of resilience from various perspectives, including its impact on mental health, its role in personal development, and its relevance in the workplace. From a mental health perspective, resilience is essential for coping with stress, trauma, and adversity. In today's fast-paced and unpredictable world, individuals are constantly faced with various stressors, such as work pressure, financial difficulties, and relationship challenges. Without resilience, these stressors can take a toll onone's mental health, leading to anxiety, depression, and other psychological issues. However, individuals who possess resilience are better equipped to cope with these challenges, as they are able to maintain a positive outlook, seek support when needed, and bounce back from setbacks. Research has shown thatresilient individuals are less likely to develop mental health problems and are more likely to experience greater psychological well-being. Moreover, resilience plays a crucial role in personal development. When individuals face adversity,they are presented with an opportunity for growth and self-improvement. Resilience enables individuals to learn from their experiences, develop problem-solving skills, and build emotional strength. By overcoming obstacles, individuals become more confident in their abilities and develop a sense of mastery over their lives. This, in turn, fosters a greater sense of self-efficacy and empowerment, leadingto overall personal growth and development. Without resilience, individuals may become overwhelmed by challenges and struggle to move forward in their lives. In the workplace, resilience is a highly valued trait that is sought after by employers. In today's competitive and fast-paced work environment, employees are often required to deal with high levels of stress, uncertainty, and change. Those who possess resilience are better able to adapt to these challenges, remainfocused and productive, and maintain a positive attitude. Resilient employees are also more likely to persevere in the face of setbacks, take on leadership roles,and contribute to a positive work culture. As a result, resilient individuals are often more successful in their careers and are able to thrive in challenging work environments. From a societal perspective, resilience is crucial for building strong and resilient communities. In the face of natural disasters, economic downturns, and other crises, resilient communities are better able to come together, support one another, and recover from adversity. Resilient communities also have the capacity to adapt to change, innovate, and create sustainable solutions to complex problems. By fostering resilience at the community level, societies can build a more cohesive and supportive environment that is better equipped to deal with the challenges of the modern world. In conclusion, resilience is a vital quality that has far-reaching implications for individuals, communities, and societies as a whole. It is essential for maintaining mental health, fostering personal development, succeeding in the workplace, and building strong communities. By recognizing the importance of resilience and cultivating this quality in ourselves and others, we can better prepare for the challenges that life presents and lead more fulfilling and meaningful lives.。
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Improvement of Resilient Packet Ring FairnessFredrik Davik Simula Research Laboratory University of Oslo Ericsson Research Norway Email:bjornfd@simula.noAmund KvalbeinSimula Research LaboratoryEmail:amundk@simula.noStein GjessingSimula Research LaboratoryEmail:steing@simula.noAbstract—Resilient Packet Ring(RPR,IEEE std.802.17-2004)is a recent networking standard developed by the IEEE LAN/MAN working group.RPR is an insertion buffer,dual ring technology,utilizing a back pressure based fairness algorithm to distribute bandwidth when congestion occurs.In its attempt to control a set of nodes’sending behavior over a congested link,the RPR fairness algorithm suffers from some severe performance deficiencies.One concerns how the node closest to a congested link calculates a fair rate estimate,the other deficiency relates to the distribution of this fair rate estimate to nodes upstream from the congested node.In this paper,we analyze these deficiencies and propose improvements to resolve them.Keywords:Resilient Packet Ring,Fairness,Performance evaluation.I.I NTRODUCTION AND MOTIVATIONRPR is a ring topology network,developed mainly for MAN environments[1],[8].By the use of two rings(also called ringlets),resilience is ensured;if one link fails,any two nodes connected to the ring still have a viable communication path between them.When a node wants to send a packet to another node on the ring,it sends the packet onto one of the two ringlets.For bandwidth efficiency,the ringlet that gives the shortest path is used by default.When the packet travels on the ring,it transits all nodes between the sender and the receiver.When it reaches the destination,the packet is removed(stripped)from the ring.Hence the bandwidth that would otherwise be consumed by the packet on its way back to the sender(as is the case in a Token Ring),can be used by other communications.Such destination stripping of packets leads to what is commonly known as spatial reuse.RPR uses insertion buffer(s)for collision avoidance[2],[3]. When a packet in transit arrives at a node that is currently sending a packet to the ring,the transiting packet is tempor-arily stored in an insertion buffer,called a transit queue in RPR.In a buffer insertion ring like RPR,a fairness algorithm is needed to divide the bandwidth fairly between contending nodes,when congestion occurs[4],[5].The main contribution of this paper is the analysis and improvement of two major performance deficiencies in the RPR fairness algorithm.These deficiencies are caused by the way the rate value of so called fairness messages are calculated and distributed to nodes sending traffic over a congested link. First,we address a deficiency in the method used by the node closest to the congested link to calculate a fair rate estimate. Secondly,we address a deficiency in the method used for the distribution of this calculated rate value to nodes upstream of the congested node.In this paper,we present only the most important parts of the problem discussion and our proposed modifications,together with some general examples.For an in-depth analysis of the two problems,refer to[6],[7].The rest of this paper is organized as follows:in section II,we give a brief introduction to the RPR fairness algorithm. Then,in section III,we present the two RPR performance deficiencies mentioned above.Next,in section IV,we present our improvements which resolves these deficiencies.Then in section V,we present our simulation results comparing the performance of our proposed improvements to that of the original fairness algorithm.Finally,in sections VI and VII, we conclude and point out directions for future work.II.T HE RPR F AIRNESS A LGORITHMBoth modes(aggressive and conservative)of the RPR fairness algorithm work with a concept known as a congestion domain.A congestion domain defines a consecutive collection of nodes,of which some or all contribute to a sustained congestion state for a given link.The congestion domain is confined within a region specified by two boundary nodes,see Fig.1.At one end of the region resides a node,denoted the head,which is attached upstream of the most congested link in the region.At the opposite end of the region resides a node, denoted the tail.Nodes upstream of the tail are considered as not being contributors to the congestion situation at the head. The declaration and operation of a congestion domain can be considered a two-part problem.Thefirst part of the problem,consists of making a node assume the role of the head.The head is responsible for,the periodic(every agin-gInterval)calculation and distribution of fair rate estimates upstream(by use of fairness messages).The second part of the problem,consists of making a node assume the role of the tail,responsible for stopping further propagation of fairness messages,received from the head.In the case of aggressive mode fairness,the fair rate estimate is the head’s own send rate.In the case of conservative mode fairness,the fair rate estimate is calculated by the head,independent of its send-rate.Regardless of the fairnessmode used,the goal is to arrive at the RIAS (Ring Ingress Aggregated with Spatial Reuse)fair sharing of bandwidth over the congested link [8].That is,when there is acongestion on a link,the capacity of that link is shared equally 1between the nodes sending traffic over this link.The behavior of the RPR conservative and aggressive fairness modes has been studied by several [1],[8]–[12].Head induced Tail Congestion domainHeadTailoscillations(when head is modest)induced oscillations(when tail node changes)(Tail)Fig.1.Nodes 0,1,2and 3are all sending so much data to node4that the link between nodes 3and 4becomes congested.Then node 3becomes the head of a congestion domain and calculates and distrubutes a fair rate estimate.The node furthest away and upstream from the head,contributing to the congestion,is called the tail of the congestion domain.Because of unstability in the control system,the possition of the tail node may vary between nodes 0and 1.III.F AIRNESS A LGORITHM P ERFORMANCE D EFICIENCIES A.Problem 1-Congestion Domain Fair Rate Calculation In a congestion scenario,the sending pattern of the in-dividual nodes may vary from modest (the node’s demand is less than its fair share)to greedy (the node sends as much as the available bandwidth allows).Regardless of the demand of the individual nodes,the fairness algorithm should perform equally well.For aggressive mode fairness,several papers have reported severe performance deficiencies for so called unbalanced traffic scenarios [13].The unbalanced traffic scenario is characterized by a congestion domain,where the head is a modest sender,while its upstream neighbors have a greedy sending behavior.Fig.1may be used to illustrate an unbalanced traffic scen-ario.Assume all nodes start sending traffic to node 4,and that nodes 0,1and 2have a greedy sending behavior,while node 3,using the aggressive mode fairness algorithm,has a modest sending behavior.As long as node 3is uncongested (its transit1TheRIAS reference model does not include the use of different weightsfor the individual nodes as supported by RPR.However,for the general fairness discussion in this paper,we assume equal node weights.Thus the RIAS fairness definition can be used.buffer (STQ )occupancy is below a threshold termed low ),it sends full-rate messages (i.e.fairness messages containing a rate value of full-rate )upstream,allowing upstream nodes to increase their send rate.As a result,at some future time node 3becomes congested (the STQ occupancy exceeds the low threshold).When this happens,node 3starts sending fairness messages containing its fair rate estimate (which for the aggressive mode is the node’s own send rate).As node 3sends less than its fair share of traffic,the send rate of node 3will always be lower than the (RIAS)fair rate.Thus,the resulting aggregate rate reduction by the upstream nodes will be too high (i.e.the STQ occupancy falls below the low threshold before becoming empty).Once this happens,the head is by (aggressive mode)definition no longer congested and it starts to send full-rate messages upstream.By this,we are back to the starting point.Thus we have a cyclic behavior,leading to large oscillations in the throughput of traffic from nodes upstream of the head,as well as reduced link-utilization.We call this Head induced oscillations (Fig.1).Other groups,having looked into the problems described for the unbalanced traffic scenario,have mostly solved the problem by proposing alternate fairness algorithms that would have to replace the current RPR fairness algorithm [9],[12],[17].Some work has presented results that seems to fit within the framework given by the RPR standard [10].In that work however,the effect of the proposed modifications is to reduce the symptoms (oscillations)rather than removing them.B.Problem 2-Congestion Domain Fair Rate Propagation In an RPR network,a node will assume the responsibility of the tail for two reasons (denoted TA,as a shorthand for Tail Appointment Condition).For both cases,we assume the node is aware of the presence of a downstream head:TA 1:When a node finds itself more congested than the downstream head.In this case,the node becomes tail of the congestion domain that starts at the downstream head.Additionally,it becomes head of a new congestion domain that extends from this node and upstream.TA 2:When a node,based on measurements of traffic rates from upstream nodes,decides that the aggregate of traffic from upstream nodes,traversing the congested link,does not contribute to the downstream congestion.The self-appointment of the tail responsibility,according to the rule specified in TA1,appears problem-free.The self-appointment of the tail responsibility according to the rule specified in TA2,however,has shown to degrade the network performance for some scenarios.The normal operation of the aggressive fairness mode has a behavior,where,to maintain the STQ occupancy constant at the high threshold,rate adjustments are done in an mono-tonically increasing/decreasing fashion [14].This behavior,in combination with the enforcement of TA2introduces an unwanted side-effect.Consider the scenario shown in Fig.1,having all(nodes0-3)greedy senders.In this scenario,the amount(rate)of transit traffic for all nodes downstream of node1,will always be larger than the fair rate.Node1only transits traffic from one upstream node.Thus,because of the oscillatory behavior of the fair rate estimate,there may be periods where the amount of transit traffic falls below the fair rate estimate.For the duration of these periods,node1assumes tail responsibility according to TA2.When this happens,node1 sends full-rate messages upstream.Upon reception of these rate-messages,node0increases its send-rate,restricted up-wards only by the link-rate.Thus node0will have an excessive sending of traffic,which will persist until node1,once again discover,according to TA2,that node0indeed is a contributor to the downstream congestion.If the delay between node1and node0is too large,this excessive sending behavior will happen every time we have a transition from a series of monotonically decreasing to a series of monotonically increasing fair rate estimates.The result is that the fair rate calculation process does not converge and there will be sustained large oscillations in throughput for the nodes in the congestion domain.We call this Tail induced oscillations.In addition,node0will,on average,be sending more than its downstream neighbors,hence we do not achieve RIAS fairness.For the conservative mode fairness,a similar behavior may be observed,but in this case,the side-effect is not as serious, as rate adjustments at the head usually are performed much slower than for aggressive mode fairness.IV.I MPROVING THE F AIRNESS A LGORITHMA.Rate Calculation ImprovementIn this chapter,we propose a novel fairness mode for use in Resilient Packet Rings,which we have called the moderate fairness mode.The goals we seek to meet in designing the moderate fairness mode are shown below.1)Remove the oscillatory behavior in the presence of ahead with a modest sending behavior.2)Retain the behavior of the original algorithm in thepresence of a head with a greedy sending behavior. 3)Minimize the changes(state information,code and pro-cessing requirements)to the current algorithm.4)Fit our modifications into the framework given by theRPR standard.Let us assume we have an established congestion domain on the ring.When the head calculates a fair rate estimate to be distributed to its upstream neighbors,we know that at some future time,the resulting aggregate traffic from the upstream nodes is either too high(the STQ occupancy in the head will increase),too low(the STQ occupancy will decrease) or correct2(the STQ occupancy remains constant).2A STQ occupancy that remains constant at0or at the high-threshold is not an indication of a correct fair rate estimate.But these are special cases that requires special handling.Just as for the aggressive and conservative fairness modes,in the moderate mode,a node(that was previously not congested) becomes congested when the STQ-occupancy exceeds the low-threshold.As previously discussed,the use of the head’s own send-rate as a fair rate estimate,does not work for unbalanced traffic scenarios.Thus,in the moderate fairness mode,just as in the conservative mode fairness,we introduce a new rate estimate.In the moderate mode,we call this rate estimate mRate(moderate Rate estimate).We also maintain aged and low-passfiltered versions of this variable,denoted respectively ageMRate and lpMRate.The value of lpMRate is the value (i.e.the fair rate estimate)that is distributed to the upstream neighbors during congestion.lpCoef1Fig.2.Z-domain representation of the2-stage second-order low pass filter used by the fairness algorithm.We use the same two-stage second-order low-passfilter construct,used by both the aggressive and the conservative modes as shown in Fig.2.We have previously shown that for the values used for the configuration settings ageCoef and lpCoef(p1=ageCoef−1(mRateMin).Once the fair rate estimate has been sufficiently reduced,the STQ occupancy will start to decrease.At this point,for the given load,we know that in the future,the fair rate estimate should not be set lower than its current value. Thus,we set mRateMin to the current fair rate estimate. Next,to oppose the decreasing STQ occupancy,we increase the fair rate estimate towards the maximum value of the rate interval(mRateMax).Once the fair rate estimate has beensufficiently increased,the STQ occupancy will start to increase. At this point,for the given load,we know that in the future,the fair rate estimate should not be set higher than its current value. Thus,we set mRateMax to the current fair rate estimate.By this,the cycle is concluded and we are back to the starting point.For each iteration of this cycle,the size of the rate interval is improved(reduced).The actual increase/decrease behavior follows an exponen-tial ramp function,given by the properties of the second-order low-passfilter.During the periods of increasing STQ occupancy,thefilter-input is set to mRateMin,thus ensuring a monotonically decreasing(towards mRateMin)fair-rate estimate.Correspondingly,during the periods of decreasing STQ occupancy,thefilter-input is set to mRateMax,thus ensuring a monotonically increasing(towards mRateMax) fair-rate estimate.The exponential ramp function ensures that the time,used to adjust the fair-rate estimate between the max/min values, remains constant,regardless of the size of the rate-interval. Thus,during the convergence process,the narrower the rate interval gets around the RIAS fair rate,the slower the fair rate estimate is adjusted.This way,the variations in throughput during steady-state are minimized.For the simple scenario shown in Fig.1,with3greedy and one modest sender,we show the convergence process of our moderate fairness mode.In the scenario,we assume a stable demand by the individual nodes.The example illustrates, without loss of generality,the convergence for the transition between a no-load situation,and a max-load situation(i.e.a worst-case situation).For a dynamic scenario,the load-change typically is much smaller.Thus in this case,the task of the fairness mode is to shift the established rate region higher or lower,so that the new RIAS fair rate is included in the interval. This is done by expanding the rate interval on one side before continuing the convergence cycle.Fig.3a shows the convergence of the head’s fair rate estimate,lpMRate,and the rate interval mRateMin, mRateMax .The corresponding STQ occupancy for the head during the same period is shown in Fig.3b.B.Rate Distribution ImprovementFrom section III-B,it is clear that the exclusion of nodes from a congestion domain,having a demand larger than their fair share,has a negative influence on the convergence process. Further,as long as nodes upstream of the tail are sending traffic over the(nearest)congested link,there is no reason to conceal rate restrictions in effect over the same link.Thus, we propose to alter the responsibility of the tail,so that it5000100001500020000250001.1 1.45[bytes/(ageCoef*agingInterval)]Time [s]mRateMaxmRateMinlpMRatea)Fair Rate Estimate200004000060000800001000001.1 1.45[bytes]Time [s]lowThresholdstqDepthb)STQ OccupancyFig.3.Illustration of the fair rate calculation convergence process for our moderate fairness mode for the scenario shown in Fig.1with3greedy and one modest sender.lpCoef=32,link-length=410µs(82km).is no longer its responsibility to stop the propagation of fair rate estimates received from the head.However,to allow for the establishment of more than one congestion domain on the ring(which is the case for the original fairness algorithm), we remove the fairness message once it reaches a(new) congestion domain head.Thus,the challenge becomes to allow for a congested node to decide whether a fairness message has passed through a downstream tail or not.If the fairness message has passed through a downstream tail,the node will remove the message from the ring and become head of a new fairness domain. Otherwise,the node will assume head(and tail)responsibility as defined by the rules of the original fairness algorithm. The RPR fairness frame format contains13reserved and currently unused bits.We propose using one of these as a passedTail bit.When the fairness message reaches the tail, the tail sets this bit to one to indicate that the fairness frame contains a fair rate that has been propagated beyond a congestion tail.Fairness messages with the passedTail bit set,are terminated once they reach a head node.By this simple improvement,we avoid the problem de-scribed in section III-B where the active node,furthest away from the head,gets to send excessive amounts of traffic during the periods when its downstream neighbor stops the propagation of fairness messages from the head.V.P ERFORMANCE E VALUATIONIn this section,we have picked some particular scenarios we believe represent the general behavior of our proposed improvements.The scenarios picked,are a subset of those contained in[6],[7].First,in section V-A,we show the improved properties from the modified behavior of congestion domain tails applied to the aggressive mode fairness algorithm. Secondly,in section V-B,we present the properties of our moderate fairness mode,which includes both the improved rate calculation method for the head as well as the modified behavior of the tail.The simulation scenarios are run using our RPR discrete event simulator models,implemented within the J-Sim and OPNET modeler frameworks[15],[16].A.Congestion Domain Tail ScenarioIn this section,we present a simulation scenario illustrat-ing the convergence of the aggressive mode algorithm as a function of network size and setting of the lpCoef parameter, with and without the modified tail behavior.It shows that the propagation of the fair rate estimate beyond the congestion tail allows the fairness algorithm to converge with a lower value of the lpCoef parameter than would otherwise be needed, thus providing a shorter convergence time for the fairness algorithm.In this scenario,we have a64node ring with40km links. The link capacity is1Gbit/s.Nodes0,10and20send traffic at their maximum allowed rate to node30,making node20the head and node0the tail.They all start sending simultaneously, at time0.1s.The value of lpCoef is set to128.Fig.5shows the throughput of traffic,received at node 30from each source node.Fig.5a shows the results for the aggressive fairness mode,while Fig.5b shows the result when the fair rate estimate calculated at node20(the head) is propagated beyond the congestion tail with the passedTail bit set.We see that with the original RPR implementation, the sending rate of each active node fails to stabilize at the RIAS fair rate(fairRate=1Gbit/s2e+084e+08 6e+08 8e+08 1e+09 0.1 0.150.2 0.25 0.3 0.35[b i t s /s ]Time [s]Node 0Node 10Node 202e+084e+08 6e+08 8e+08 1e+09 0.1 0.150.2 0.25 0.3 0.35[b i t s /s ]Time [s]Node 0Node 10Node 202e+084e+08 6e+08 8e+08 1e+09 0.1 0.150.2 0.25 0.3 0.35[b i t s /s ]Time [s]Node 0Node 10Node 20Aggressive mode fairness,lpCoef=128Tail modification,lpCoef=128Aggressive mode fairness,lpCoef=256Fig.5.Throughput of traffic received at node ing a lpCoef of 128,the traffic from the different sources does not stabilize withoutpropagation of fair rate beyond the congestion tail.Increasing the lpCoef to 256gives a stable system with the original RPR algorithm,but with a longer convergence time.VI.C ONCLUSIONIn this paper we have analyzed and proposed improvements for two major deficiencies in the RPR fairness algorithm.The first deficiency relates to the calculation of the fair rate estimate by the head of a congestion domain.For some so-called unbalanced traffic scenarios,the operation of the aggressive mode algorithm results in non-convergence of the fairness algorithm,leading to sustained,large oscillations and reduced link utilization.With our moderate mode algorithm,this behavior is avoided and we do not incur reduced link-utilization.Additionally,the algorithm convergences faster and provides better link-utilization than the conservative mode.Although not shown here (but in the in-depth analysis in [6],[7]),our algorithm meets the 4design goals specified in section IV-A.The second deficiency relates to the propagation of the fair rate estimates calculated by the head,to upstream nodes in a congestion domain.For the method used by the standard,the stability of the fairness algorithms is seriously affected.With our simple proposed modification,we can,for a given configuration of the lpCoef parameter,provide stable opera-tion of the fairness algorithm for networks twice (aggregate propagation delay)the size of that possible with the original algorithm.VII.F URTHER W ORKThe configuration of the RPR fairness algorithm is com-plicated and requires a thorough knowledge by the network operator to be configured in a safe and cost-efficient manner.The use of dynamic measurement and configuration methods (not discussed in this paper)in the conservative fairness mode eases the task of the operator 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