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实验研究复方藤梨汤含药血清对人脑胶质瘤U251细胞增殖、凋亡及上皮间质转化的影响武海博，梁燕，沈雷，范展，傅国惠△摘要：目的探究复方藤梨汤含药血清对人脑胶质瘤U251细胞增殖、凋亡及上皮间质转化的影响。
方法将24只雄性SD大鼠分为对照组和低、中、高剂量组[复方藤梨汤6、12、24g/（kg·d）]，每组6只，制备含药血清处理人脑胶质瘤U251细胞。
采用CCK-8法检测细胞活力，集落形成实验检测细胞克隆形成能力，流式细胞术检测细胞周期分布与细胞凋亡，定量聚合酶链反应检测原癌基因C-myc、细胞周期蛋白D1（CyclinD1）基因表达，Western blot法检测细胞凋亡蛋白［B细胞淋巴瘤-2（Bcl-2）、Bcl-2相关X蛋白（Bax）、胱天蛋白酶（Caspase）-3、Caspase-8］以及β-连环蛋白（β-catenin）、上皮性黏附蛋白（E-cadherin）及波形蛋白（Vimentin）表达。
结果选取体积分数10%的含药血清为最终剂量。
与对照组比较，低、中、高剂量组细胞活力、克隆形成数、C-myc mRNA、CyclinD1mRNA、Vimentin表达水平降低，处于S期细胞比例、Bax/Bcl-2比值、Caspase-3表达水平升高（P＜0.05）；低、高剂量组G1期细胞比例降低（P＜0.05）；中、高剂量组G2期细胞比例、β-catenin表达水平降低，Caspase-8和E-cadherin表达水平升高（P＜0.05）；高剂量组细胞凋亡率升高（P＜0.05）。
结论复方藤梨汤含药血清可促使人脑胶质瘤U251细胞阻滞于S期，抑制细胞增殖，诱导细胞凋亡，通过调节β-catenin、E-cadherin和Vimentin表达抑制上皮间质转化。
关键词：神经胶质瘤；上皮-间质转化；细胞增殖；细胞凋亡；细胞增殖抑制药（中药）；复方藤梨汤含药血清；人脑胶质瘤U251细胞中图分类号：R739.41文献标志码：A DOI：10.11958/20221840Effects of Fufang Tengli Decoction drug-containing serum on proliferation,apoptosis and epithelial-mesenchymal transition of human glioma U251cellsWU Haibo,LIANG Yan,SHEN Lei,FAN Zhan,FU Guohui△Department of Neurology,Nanyang Central Hospital,Nanyang473000,China△Corresponding Author E-mail:Abstract:Objective To explore effects of Fufang Tengli Decoction drug-containing serum on the proliferation, apoptosis and epithelial-mesenchymal transition(EMT)of human glioma U251cells.Methods A total of24male SD rats were divided into the control group,the low-dose,medium-dose and high-dose Fufang Tengli Decoction groups[6,12,24g/ (kg·d)],6rats in each group.After10d of continuous intragastric administration,blood samples was collected to prepare drug-containing serum,and human glioma U251cells were treated for24h.The cells activity was detected by Cell Counting Kit-8.The cell cloning was detected by colony formation assay.The distribution of cells cycles and apoptosis were detected by flow cytometry.The expressions of proto-oncogene C-myc and cyclin D1(CyclinD1)genes were detected by quantitative polymerase chain reaction.The expressions of B-cell lymphoma-2(Bcl-2),Bcl-2associated X protein(Bax),cysteine aspartase-3(caspase-3),caspase-8,β-catenin,epithelial cadherin(E-cadherin)and vimentin(Vimentin)were detected by Western blot assay.Results The drug-containing serum with10%volume fraction was selected as the final dose. Compared with the control group,cells activity,number of clone formation and expression levels of C-myc,CyclinD1mRNA and Vimentin were decreased,while numbers of cells in S phase and expression levels of Bax/Bcl-2and Caspase-3were increased in the low-dose,medium-dose and high-dose Fufang Tengli Decoction groups(P＜0.05).The proportion of cells in G2phase and expression level ofβ-catenin were decreased,while expression levels of Caspase-8and E-cadherin were increased in the medium-dose and high-dose Fufang Tengli Decoction groups(P＜0.05).Cell apoptosis rate was increased in the high-dose Fufang Tengli Decoction group(P＜0.05).Conclusion Fufang Tengli Decoction drug-containing serum can block human glioma U251cells in S phase,inhibit cell proliferation,induce apoptosis,regulate expressions ofβ-catenin,E-cadherin and Vimentin,and inhibit EMT.基金项目：河南省医学科技攻关计划联合共建项目（LHGJ20191452）；河南省科技厅科技攻关项目（202102310408）作者单位：南阳市中心医院神经内科（邮编473000）作者简介：武海博（1988），男，主治医师，主要从事胶质瘤方面研究。
C#中Abstract、Virtual和Override的使⽤及区别1. abstract 修饰符指⽰所修饰的内容缺少实现或未完全实现。
abstract修饰符可⽤于类、⽅法、属性、索引器和事件。
在类声明中使⽤abstract修饰符以指⽰某个类只能是其他类的基类。
标记为抽象或包含在抽象类中的成员必须通过从抽象类派⽣的类来实现。
(1)抽象类具有以下特性：1) 抽象类不能实例化。
2) 抽象类可以包含抽象⽅法和抽象访问器。
3) 不能⽤sealed修饰符修饰抽象类，因为这两个修饰符的含义是相反的。
采⽤sealed修饰符的类⽆法继承，⽽abstract修饰符要求对类进⾏继承。
4) 从抽象类派⽣的⾮抽象类必须包括继承的所有抽象⽅法和抽象访问器的实际实现。
5) 在⽅法或属性声明中使⽤abstract修饰符以指⽰⽅法或属性不包含实现。
(2)抽象⽅法具有以下特性：1) 抽象⽅法是隐式的虚⽅法。
2) 只允许在抽象类中使⽤抽象⽅法声明。
3) 因为抽象⽅法声明不提供实际的实现，所以没有⽅法体；⽅法声明只是以⼀个分号结束，并且在签名后没有⼤括号({ })。
(3)在抽象⽅法声明中使⽤static或virtual修饰符是错误的。
除了在声明和调⽤语法上不同外，抽象属性的⾏为与抽象⽅法⼀样。
在静态属性上使⽤abstract修饰符是错误的。
在派⽣类中，通过包括使⽤override修饰符的属性声明，可以重写抽象的继承属性。
publicabstractclassparent{protectedintx=100;protectedinty = 200;publicabstractvoidfunction();publicabstractintX {get; }publicabstractintY {get; }}publicclassnewperson:parent{publicoverridevoidfunction(){x++;y++;}publicoverrideintX{get{returnx+100; }}publicoverrideintYget{returny+100; }}}staticvoidMain(string[] args){newpersonp =newnewperson();Console.WriteLine(p.X);Console.WriteLine(p.Y);p.function();Console.WriteLine(p.X);Console.WriteLine(p.Y);Console.ReadKey();}2.virtual关键字⽤于修饰⽅法、属性、索引器或事件声明，并使它们可以在派⽣类中被重写。
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常见科技行业缩写中英对照作者：未知文章来源：本站原创点击数：56 更新时间：2005-12-25 DSL数字用户线路CATV有线电视ADSL非对称DSLHDSL高比特速率VDSL极高比特速率SDSL单线DSLRADSL速率自适应ISDNDSLIDSLCDSL用户DSLDS DS0 DS1 DS1C DS2 DS3 DS4DS系列E E1 E2 E3E系列(欧洲标准)CEPT欧洲邮电委员会SDH同步光纤网络STS不清楚SONET同步光纤网络RED随机早期测试SCS结构化综合布线系统ISO,Intenational organization for standardization国际标准化组织ITU-T,International Telecommunication Union国际联盟电信标准T:Telecommunication standardization sector电信标准分会CCITT:international telegraph & telephone consultative committee ITU-T的前身SNMP:Simple network management protocol简单网络管理协议PPP:Point to Point protocol点对点协议RIP:Routing Information protocol路由信息协议WAP:wireless applicaition protocol无线应用协议OSPF:open shortest path control protocol开放的最短路径优先协议HDLC:high level datalink control protocol协议RARP: reverse address resolution protocol知MAC求IP地址CNNIC中国互联网中心history历史ISP:Internet service provider服务商UNINET联通:联通公用计算机互联网xDSL:x digital subscriber line数字用户线路HDSL:high bit rate两对双绞线 E1速率SDSL:symmetric DSL单对双绞线RADSL:rate adaptive DSL速率自适应DSLsettop box机顶盒WAP:wireless markup protocol无线协议IPV6IETP在RFC1550规定policy base networking策略网络MPLS多协议标记交换linux OS操作系统虚拟专用网IPX/SPX:Novell netware客户机使用一种网络协议NETBEUI小型网络上的高速通信协议MTU:maximum transmission unit最大传输单位MSS:maximum segment size最大分段尺寸default receive windows预设接收窗口TTL:time to live留存时间ICQ:I seek you我找你SMTP:simple mail transfer protocol简单邮件传输协议POP3:post office protocol version3POP3的邮局IMAP:Internet message access protocol 协议specify明确、说明special专用role入口AALATM adaptation layerABRAvailable bit rateADPCMadaptive differntial pulse code modulation ADSLasymmtric digital phone systemAMPSadvanced mobile phone systemANSadvanced network and servicesASautonomatic repeat requestASKamplitude shift keyingasynchronous time division multiplexingBERbit error rateBGPborder gateway protocolB-ISDNbroad integrated services digital networkBOOTPbootstrapping protocolBRIbasic rate interfaceBUSbroadcast/unknown serverCATVcable televisionCACconnection admission controlCBRcontinusou bit rateCDMAcode division multiple accessCDPDcellular digital packet dataCDVcell delay variationCLIPATM managerCIDRclassless interDomain RoutingCMIPcommon management information protocolCMIScommon management information serviceCMOTcommon management information service and protocol over TCP/IP CNOMcommittee of network operation&managementCORBAcommon object request broker architectureCPCScommon part convergence sublayerCRcarriage returnconvergence sublayerCSMA/CD冲突检测CSU/DSU频道服务单元/数据服务单元DARPAdefense advanced research project agency DCEdata circuit terminating equipmentDDNdigital data networkDIMEdistributed management environment DPIdot per inchDQDBdistributed queue dual busDEN目录服务DSMAdigital CSMA/CD sense multi-access DVMRPdistance vector multicast routing protocol EGPexterior gateway protocolEMAethernet media adapterFAQfrequently answer questionFCSfast circuit switchingFDDIfiber distributed data interfaceFECforward error correctionFSKfrequency shift keyingFTTC/FTTHfiber to the curb/homeGCRAgeneric cell rate algorithmGGPgateway gateway protocol全球通HECheader error controlHCSheader checked sequenceHDLChigh level data link controlHDTVhigh definition televisionHFChybird fiber coaxHIPPIhigh performance parallel interfaceHTTPhypertext transfer protocolIABinternet architecture boardIAPinternet access provider(ISP)ICCBinternet control & congigruration board ICMPinternet control message protocolICXinter cartridge exchangeIDPinternetwork datagram protocolIDUinterface data unitIEEEInstitute of Electrical& Electronic Engineers IGMPInternet group managament protocolIMPInterface message processorIMTSImproved Mobile Telephone SystemIRTFInternet Research Task ForceISDNIntegrated services digital networkISOinternational organization for standardizaioninternational standard organizaition ITUInternational telecommunications union JPEGJoint photographic experts group LANELAN emulation A TMLAPlink access procedureLDAP目录服务LCPlink control protocolLECLAN emulation client LESLECSLAN emulation configure serviceLEDlow emiiting diiodeLLQlogical link controlMANMAN metropolitan area networkMIBmanagement information baseMOTDmessage of the dayMPEGmotion picture express groupMPOAATMMSCmobile switching centerMTBFmedia time between faultsMTORmedica time of repairMTRmail transfer protocolMTSOmobile telephone switching phone MTTDmedia time to diagnosemaximum transfer unitNAPnetwork access protocolNCAnetwork computing architecture NCPnetwork control/core protocol NICnetwork information centerNIMnetwork interface moduleN-ISDNISDNNNInetwork network interfaceNRZnon return to zeroNSAPnetwork service access point NVRAMnon volatile RAMNVTnetwork virtual terminalPBXprivate branch exchangePCMpulse code modulationPCNpersonal communications network PCRpeak cell ratePCSpersonal communications service PDApersonal digital assistantPDNpublic data networkPDUprotocol data unitPERpacket error ratePIRpacket insertion ratephysical layer convergence protocol PLRpacket loss ratePMDphysical medium dependent POTSplain old telephone servicePPDpartical packet discardPPMpage per minutePPMProtocl reference modelPRNpacket radio networkPSpacket switchingPSNpacket switching nodePSKphase shift keyingPVCpermanent virtual circuitPVPpermanent virtual path quadratare amplitude modulation QoSquality of serviceRFCrequest for commnentsRPCremote procedure callRTSround trip sampleSAPservice access pointSAPsercie advertising protocolSARsegmentation and reassemblySCRsustained cell rateSDHsynchronous digital hierarchy SDLCsynchronous data link controlSDUservice data unitSSLsecure socket layerSGMPsimple gateway monitor protocol SIPDsimple internet protocol plusSLIPserial line interface protocol SMDSswitched multimegabit data services SMFsingle mode fiberSMIstructer of management informatin SMTstation managment protocolSMTPsimple mail transfer protocolSNRsignal noise ratioSONETsynchronous optical networkSPEsynchronous payload envelope SPPsequential packet protocolSIIserver side includeSTDMstatistical time division multiplexing STMsynchronous transfer modeSTSsynchronous transport signalSVCswitched virtual pairTCtransmission convergenceTCPtransmission control protocol TDMtime division multiplexing TFTPtrival file trnasfer protocolTIPterminal interface processor TSAPtransport service access point TTLtime to liveUBRundefined bit rateUEMuniversal ethernet modeule UDPuser datagram protocolUNIuser network interfaceUPCusage parameter controlUSBuniversal serial busUUCPunix to unix copy programV ANvalue added networkVBRvariable bit rateVCCvirtual channel connectionV-Dvector distance/bellman-ford VLANvirtual LANVPNvirtual private networkVODvideo on demandVPCvirtual path connectionVRMLvirtual reality modeling language WDM。
C#中abstract的⽤法详解参考：abstract可以⽤来修饰类,⽅法,属性,索引器和时间,这⾥不包括字段. 使⽤abstrac修饰的类,该类只能作为其他类的基类,不能实例化,⽽且abstract修饰的成员在派⽣类中必须全部实现,不允许部分实现,否则编译异常. 如:using System;namespace ConsoleApplication8{ class Program { static void Main(string[] args) { BClass b = new BClass(); b.m1(); } } abstract class AClass { public abstract void m1(); public abstract void m2(); } class BClass : AClass { public override void m1() { throw new NotImplementedException(); } //public override void m2() //{ // throw new NotImplementedException(); //} }}Abstract classes have the following features:抽象类拥有如下特征:1,抽象类不能被实例化, 但可以有实例构造函数, 类是否可以实例化取决于是否拥有实例化的权限 (对于抽象类的权限是abstract, 禁⽌实例化),即使不提供构造函数, 编译器也会提供默认构造函数;2,抽象类可以包含抽象⽅法和访问器;3,抽象类不能使⽤sealed修饰, sealed意为不能被继承;4,所有继承⾃抽象类的⾮抽象类必须实现所有的抽象成员,包括⽅法,属性,索引器,事件;abstract修饰的⽅法有如下特征:1,抽象⽅法即是虚拟⽅法(隐含);2,抽象⽅法只能在抽象类中声明;3,因为抽象⽅法只是声明, 不提供实现, 所以⽅法只以分号结束,没有⽅法体,即没有花括号部分;如public abstract void MyMethod();4,override修饰的覆盖⽅法提供实现,且只能作为⾮抽象类的成员;5,在抽象⽅法的声明上不能使⽤virtual或者是static修饰.即不能是静态的,⼜因为abstract已经是虚拟的,⽆需再⽤virtual强调.抽象属性尽管在⾏为上与抽象⽅法相似,但仍有有如下不同:1,不能在静态属性上应⽤abstract修饰符;2,抽象属性在⾮抽象的派⽣类中覆盖重写,使⽤override修饰符;抽象类与接⼝:1,抽象类必须提供所有接⼝成员的实现;2,继承接⼝的抽象类可以将接⼝的成员映射位抽象⽅法.interface I{void M();}abstract class C: I{public abstract void M();}抽象类实例:// abstract_keyword.cs// 抽象类using System;abstract class BaseClass // 抽象类{protected int _x = 100; //抽象类可以定义字段,但不可以是抽象字段,也没有这⼀说法.protected int _y = 150;public BaseClass(int i) //可以定义实例构造函数,仅供派⽣的⾮抽象类调⽤; 这⾥显式提供构造函数,编译器将不再提供默认构造函数. {fielda = i;}public BaseClass(){}private int fielda;public static int fieldsa = 0;public abstract void AbstractMethod(); // 抽象⽅法public abstract int X { get; } //抽象属性public abstract int Y { get; }public abstract string IdxString { get; set; } //抽象属性public abstract char this[int i] { get; } //抽象索引器}class DerivedClass : BaseClass{private string idxstring;private int fieldb;//如果基类中没有定义⽆参构造函数,但存在有参数的构造函数,//那么这⾥派⽣类得构造函数必须调⽤基类的有参数构造函数,否则编译出错public DerivedClass(int p): base(p) //这⾥的:base(p)可省略,因为基类定义了默认的⽆参构造函数{fieldb = p;}public override string IdxString //覆盖重新属性{get{return idxstring;}set{idxstring = value;}}public override char this[int i] //覆盖重写索引器{get { return IdxString[i]; }}public override void AbstractMethod(){_x++;_y++;}public override int X // 覆盖重写属性{get{return _x + 10;}}public override int Y // 覆盖重写属性{get{return _y + 10;}}static void Main(){DerivedClass o = new DerivedClass(1);o.AbstractMethod();Console.WriteLine("x = {0}, y = {1}", o.X, o.Y); }}。
C++中abstract修饰类的用法1. 概述在C++中，我们经常会听到关于abstract类的概念。
那么，abstract 类到底是什么？它又有什么作用呢？2. 什么是abstract类在C++中，我们可以使用关键字“abstract”来修饰一个类，使其成为一个“abstract类”。
一个abstract类是一种不能被实例化的类，即不能创建它的对象。
abstract类通常用于定义接口和抽象的行为，它的目的是为了让其他类继承并实现它的纯虚函数。
3. abstract类的定义要定义一个abstract类，我们可以在类中声明纯虚函数。
纯虚函数是指在类中声明但没有实现的虚函数。
通过在函数声明后面加上“= 0”来将一个虚函数声明为纯虚函数。
例如：```C++class AbstractClass {public:virtual void pureVirtualFunction() = 0;};```4. abstract类的作用abstract类的作用主要有以下几点：- 定义接口：abstract类定义了一组接口，表示了一种抽象的行为。
其他类可以继承并实现这些接口。
这样一来，我们就可以通过基类指针来调用派生类的函数。
- 特定行为的约束：abstract类可以约束其派生类必须实现某些特定的行为。
这样一来，我们就可以确保派生类都具有相同的接口，从而提高代码的一致性和可维护性。
- 防止实例化：abstract类的对象不能被创建，这可以防止程序员错误地使用该类，从而避免一些潜在的错误。
5. 如何使用abstract类在C++中，我们可以通过继承abstract类并实现其中定义的纯虚函数来使用abstract类。
例如：```C++class ConcreteClass : public AbstractClass {public:void pureVirtualFunction() override {// 实现纯虚函数的具体逻辑}};```在上面的例子中，ConcreteClass继承了AbstractClass，并实现了其中定义的纯虚函数pureVirtualFunction。
10档案与建设ARCHIVES & CONSTRUCTION2023年 第11期基于《档号编制规则》（DA/T 13-2022）的档号编制问题研究黄新荣 曹天帆（西北大学公共管理学院，陕西西安，710127）摘 要：新修订的《档号编制规则》适合现今档案管理要求，可适应不同的档案管理环境，还增添了可操作性示例，但也存在概念表述不清、分隔符号设置复杂、全宗号不宜必选、全宗号不宜首选的问题。
其背后是《档号编制规则》本身的局限性和《规则》背后的分类思维局限性。
建议在修订《档号编制规则》时，考虑采纳发展性、包容性、完整性、参考性原则。
关键词：档号编制规则；档案分类；档号；全宗号；元数据分类号：G272.6Research on the Problem of Reference Code Compilation Based onCompilation Rules for Reference Codes (DA/T 13-2022)Huang xinrong, Cao tianfan( School of public administration, Northwestern University, xi’an, shanxi, 710127 )Abstract: the newly revised Compilation Rules for Reference Codes adapts to the current file management requirements, adapts todifferent file management environments, and adds operational examples. However, there are some problems in the new Rules , such as unclear concept expression, complex separator symbol setting, and not mandatory or preferred fonds number. Behind it is the limitation of the Compilation Rules for Reference Codes itself and the limitation of classification thinking behind the Rules . It is suggested that the principles of development, inclusiveness, integrity and reference should be adhered to when improving the Compilation Rules for Reference Codes .Keywords: t he Compilation Rules for Reference Codes;Archival Classification;Reference Codes;Fonds Number; Metadata档号是固化档案分类结果的一组代码，无论是在实体档案还是电子文件的管理中，档号都占据着非常重要的地位。
Reference number ISO 11898-3:2006(E)© ISO 2006INTERNATIONAL STANDARD ISO 11898-3First edition 2006-06-01Road vehicles — Controller area network (CAN) —Part 3:Low-speed, fault-tolerant, medium-dependent interfaceVéhicules routiers — Gestionnaire de réseau de communication (CAN) —Partie 3: Interface à basse vitesse, tolérant les pannes, dépendante du supportCopyright International Organization for Standardization Provided by IHS under license with ISONo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---ISO 11898-3:2006(E)PDF disclaimerThis PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. 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Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester.ISO copyright officeCase postale 56 • CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyright@Web Published in Switzerlandii © ISO 2006 – All rights reserved Copyright International Organization for StandardizationProvided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHSISO 11898-3:2006(E)© ISO 2006 – All rights reservediiiContents PageForeword............................................................................................................................................................iv Introduction........................................................................................................................................................v 1 Scope.....................................................................................................................................................1 2 Terms and definitions...........................................................................................................................1 3 Abbreviated terms................................................................................................................................3 4 OSI reference model.............................................................................................................................4 5 MDI specification ..................................................................................................................................4 5.1 Physical medium...................................................................................................................................4 5.2 Physical signalling................................................................................................................................8 5.3 Electrical specification.......................................................................................................................10 5.4 Network specification.........................................................................................................................12 6 Physical medium failure definition ...................................................................................................14 6.1 Physical failures..................................................................................................................................14 6.2 Failure events......................................................................................................................................15 7 PMA specification...............................................................................................................................16 7.1 General.................................................................................................................................................16 7.2 Timing requirements..........................................................................................................................16 7.3 Failure management...........................................................................................................................20 7.4 Operating modes .. (23)Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---ISO 11898-3:2006(E)iv© ISO 2006 – All rights reservedForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.ISO 11898-3 was prepared by Technical Committee ISO/TC 22, Road vehicles , Subcommittee SC 3, Electrical and electronic equipment .This first edition of ISO 11898-3 cancels and replaces ISO 11519-2:1994, which has been technically revised. ISO 11898 consists of the following parts, under the general title Road vehicles — Controller area network (CAN):⎯ Part 1: Data link layer and physical signalling ⎯ Part 2: High-speed medium access unit⎯ Part 3: Low-speed, fault-tolerant, medium-dependent interface ⎯ Part 4: Time triggered communication⎯ Part 5: High-speed medium access unit with low-power modeCopyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---ISO 11898-3:2006(E)© ISO 2006 – All rights reservedvIntroductionISO 11898, first published in November 1993, covered the controller area network (CAN) data link layer as well as the high-speed physical layer. In the reviewed and restructured ISO 11898:⎯ ISO 11898-1 describes the data link layer protocol as well as the medium access control;⎯ ISO 11898-2 specifies the high-speed medium access unit (MAU) as well as the medium dependentinterface (MDI). ISO 11898-1:2003 and ISO 11898-2:2003 cancel and replace ISO 11898:1993.In addition to the high-speed CAN, the development of the low-speed CAN, which was originally covered by ISO 11519-2, gained new means such as fault tolerant behaviour. The subject of this part of ISO 11898 is the definition and description of requirements necessary to obtain a fault tolerant behaviour as well as the specification of fault tolerance itself. In particular, it describes the medium dependent interface and parts of the medium access control.Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`-----`,,```,,,,````-`-`,,`,,`,`,,`---Copyright International Organization for StandardizationProvided by IHS under license with ISONot for Resale No reproduction or networking permitted without license from IHSINTERNATIONAL STANDARD ISO 11898-3:2006(E)© ISO 2006 – All rights reserved1Road vehicles — Controller area network (CAN) — Part 3:Low-speed, fault-tolerant, medium-dependent interface1 ScopeThis part of ISO 11898 specifies characteristics of setting up an interchange of digital information between electronic control units of road vehicles equipped with the controller area network (CAN) at transmission rates above 40 kBit/s up to 125 kBit/s. The CAN is a serial communication protocol which supports distributed control and multiplexing.This part of ISO 11898 describes the fault tolerant behaviour of low-speed CAN applications, and parts of the physical layer according to the ISO/OSI layer model. The following parts of the physical layer are covered by this part of ISO 11898:⎯ medium dependent interface (MDI); ⎯ physical medium attachment (PMA).In addition, parts of the physical layer signalling (PLS) and parts of the medium access control (MAC) are also affected by the definitions provided by this part of ISO 11898.All other layers of the OSI model either do not have counterparts within the CAN protocol and are part of the user’s level or do not affect the fault tolerant behaviour of the low speed CAN physical layer and therefore are not part of this part of ISO 11898.2 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.2.1 bustopology of a communication network where all nodes are reached by passive links which allow transmission in both directions2.2bus failurefailures caused by a malfunction of the physical bus such as interruption, short circuits 2.3bus valueone of two complementary logical values: dominant or recessiveNOTE The dominant value represents a logical “0” the recessive represents a logical “1”. During simultaneous transmission of dominant and recessive bits, the resulting bus value will be dominant.2.4bus voltagevoltage of the bus line wires CAN_L and CAN_H relative to ground of each individual CAN nodeNOTEV CAN_L and V CAN_H denote the bus voltage.Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---ISO 11898-3:2006(E)2© ISO 2006 – All rights reserved2.5differential voltage V diffvoltage seen between the CAN_H and CAN_L linesNOTEV diff = V CAN_H − V CAN_L2.6fault free communicationmode of operation without loss of information2.7fault toleranceability to operate under specified bus failure conditions at least with a reduced performanceEXAMPLEReduced signal to noise ratio.2.8transceiver loop time delaydelay time from applying a logical signal to the input on the logical side of the transceiver until it is detected on the output on the logical side of the transceiver 2.9low power modeoperating mode with reduced power consumptionNOTEA node in low power mode does not disturb communication between other nodes.2.10 nodeassembly, connected to the communication line, capable of communicating across the network according to the given communication protocol specification2.11normal modeoperating mode of a transceiver which is actively participating (transmitting and/or receiving) in network communication2.12operating capacitance C OPoverall capacitance of bus wires and connectors seen by one or more nodes, depending on the topology and properties of the physical media2.13physical layerelectrical circuit realization that connects an ECU to the bus 2.14physical medium (of the bus)pair of wires, parallel or twisted, shielded or unshieldedNOTEThe individual wires are denoted as CAN_H and CAN_L.2.15 receiverdevice that transforms physical signals used for the transmission back into logical information or data signalsCopyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---ISO 11898-3:2006(E)© ISO 2006 – All rights reserved32.16transmitterdevice that transforms logical information or data signals to electrical signals so that these signals can be transmitted via the physical medium2.17transceiverdevice that adapts logical signals to the physical layer and vice versa3 Abbreviated termsACK AcknowledgeCAN Controller Area Network CRC Cyclic Redundancy Check CSMA Carrier Sense Multiple Access DLC Data Length Code ECUElectronic Control UnitEOF End of FrameFCE Fault Confinement Entity IC Integrated Circuit LAN Local Area Network LLC Logical Link Control LME Layer Management Entity LPDU LLC Protocol Data Unit LSB Least Significant BitLSDU LLC Service Data Unit LS-MAU Low-Speed Medium Access UnitMAC Medium Access Control MAU Medium Access Unit MDI Medium Dependent Interface MPDU MAC Protocol Data Unit MSB Most Significant Bit MSDUMAC Service Data UnitNRZ Non-Return-to-ZeroOSI Open System Interconnection PL Physical Layer PLS Physical Layer Signalling PMA Physical Medium Attachment RTRRemote Transmission RequestSOF Start of FrameCopyright International Organization for StandardizationProvided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---ISO 11898-3:2006(E)4© ISO 2006 – All rights reserved4 OSI reference modelAccording to the OSI reference model shown in Figure 1, the CAN architecture represents two layers: ⎯ data link layer; ⎯ physical layer.This part of ISO 11898 describes the physical layer of a fault tolerant low-speed CAN transceiver. Only a few influences to the data link layer are given.Figure 1 — OSI reference model/CAN layered architecture5 MDI specification5.1 Physical media5.1.1 GeneralThe physical media used for the transmission of CAN broadcasts shall be a pair of parallel (or twisted) wires, shielded or unshielded, dependent on EMC requirements. The individual wires are denoted as CAN_H and CAN_L. In dominant state, CAN_L has a lower voltage level than in recessive state, and CAN_H has a higher voltage level than in recessive state. 5.1.2 Node bus connectionThe two wires CAN_H and CAN_L are terminated by a termination network, which shall be realized by the individual nodes themselves. The overall termination resistance of each line should be greater than or equal to 100 Ω. However, the termination resistor’s value of a designated node should not be below 500 Ω, due to the semiconductor manufacturers’ constraints. To represent the recessive state CAN_L is terminated to V CC and CAN_H is terminated to GND. Figure 2 illustrates the normal termination of a designated bus node.Copyright International Organization for StandardizationProvided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---© ISO 2006 – All rights reserved5Keya Optional.Figure 2 — Termination of a single bus nodeIn Figure 2, the termination resistors are denoted as optional. That means that under certain conditions not all nodes need an individual termination, if the requirements of proper overall termination are fulfilled. 5.1.3 Operating capacitanceThe following specifications are valid for a simple wiring model which in general is used in automotive applications. It consists of a pair of twisted copper cables which are connected in a topology described in 5.1.4. The following basic model shown in Figure 3 and 4 is used for the calculations.Keya Driver.b Wire.Figure 3 — Substitute circuit for bus lineCopyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---6© ISO 2006 – All rights reservedKeya Symmetric axis.b Ground.Figure 4 — Operating capacitance referring to network length lThe operating capacitance is calculated using Equation 1.C OP = l (C ′ + 2C ′12) + n C node + k C plug (1) whereC OP is the operating capacitance;C ′ is the capacitance between the lines and ground referring to the wire length in metres (m); C ′12 is the capacitance between the two wires (which is assumed to be symmetrical) referring to thewire length in metres (m);C node is the capacitance of an attached bus node seen from the bus side; C plug is the capacitance of one connecting plug; l is the overall network cable length; n is the number of nodes; kis the number of plugs.EXAMPLE A typical value for the operating capacitance referring to the overall network cable length in respect to the exemplary network described below is given by:()[]122120pF/m C C ′′+= 5.1.4 Medium timingThe maximum allowed operating capacitance is limited by network inherent parameters such as: ⎯ overall termination resistance R term ; ⎯ wiring model and topology; ⎯ communication speed;⎯ sample point and voltage thresholds; ⎯ ground shift, etc.Copyright International Organization for StandardizationProvided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---© ISO 2006 – All rights reserved7The following equation provides a method to estimate the maximum allowed operating capacitance.pl sync bitterm OP C0GND th2In()ln s t t f R C V V V τ−−==+− (2) whereR term is the overall network termination resistor (approx. 120 Ω); C OPis the operating capacitance, specified in Equation (1); τCis the time constant of bus wire;s p is the sampling point within a bit, in percent (%);ƒbit is the bit frequency or physical communication speed in bits per second (bit/s); t l is the overall loop delay time of a transceiver device;t sync is the maximum possible synchronization delay between two nodes; V 0 is the maximum voltage level of a bus line (approx. 5 V); V th is the sampling voltage threshold (approx. < 0,5 V);V GNDdenotes the maximum allowed effective groundshift (max. 3 V).The calculation of τC leads to the graph in Figure 5.Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---8© ISO 2006 – All rights reservedKeyX τC (µs) Y sample point (%) Zcommunication speed (kBit/s)Conditions:V 0 is assumed to 5 V. V th is assumed to 0,2 V.No groundshift is assumed.The total internal loop delay is assumed to 1,5 µs.Figure 5 — Maximum communication speed versus τC and the sample pointAs a rule of thumb, the possible maximum time constant τC can be calculated using Equation (3).C bit16f τu(3)where f bit denotes the bit frequency or physical communication speed in bit/s.5.2 Physical signallingThe bus line can have one of the two logical states recessive and dominant (see Figure 6). To distinguish between both states a differential voltage V is used.V diff = V CAN_H − V CAN_L(4)Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---© ISO 2006 – All rights reserved9whereV CAN_H is the voltage level of the CAN_H wire; V CAN_L is the voltage level of the CAN_L wire.In recessive state the CAN_L line is fixed to a higher voltage level than the CAN_H line. In general, this leads to a negative differential voltage V diff . The recessive state is transmitted during bus idle or during recessive bits.The dominant state is represented by a positive differential voltage V diff , which means that the CAN_H line is actively fixed to a higher voltage level and the CAN_L line is actively fixed to a lower voltage level. The dominant state overrides a recessive state and is transmitted during dominant bits.Keya Recessive.b Dominant.Figure 6 — Physical bit representationCopyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---10© ISO 2006 – All rights reserved5.3 Electrical specification5.3.1 Electrical boundary voltages for ECUThe parameters given in Table 1 should be valid for maximum node connecting voltages.Table 1 — Ratings of V CAN_L and V CAN_H of an ECU in 12 V and 42 V systemsVoltageNotationmin. aVmax. VV CAN_L −27,0 40,0 12 V systemV CAN_H −27,0 40,0 V CAN_L −58,0 58,0 42 V systemV CAN_H−58,0 58,0No destruction of transceiver occurs.The transceiver should not affect communication on the net. The voltage levels may be applied without time restrictions.a Possible if VGND is disconnected or during jump start conditions.The common mode bus voltage, V COM , is:CAN_L CAN_HCOM 2V V V +=(5)whereV CAN_L is the CAN_L wire voltage level; V CAN_H is the CAN_H wire voltage level.The common mode voltage, V COM , for an undisturbed system in normal mode must be ensured within theratings specified in Table 2.Table 2 — Common mode voltage, for undisturbed system in normal modeValueParameter Notation Unitmin. nominal max.Common mode voltageV COM V −1 2,5 65.3.2 DC parameters for physical signallingSee Tables 3 to 5.Copyright International Organization for StandardizationProvided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---© ISO 2006 – All rights reserved11Table 3 — DC parameters for the recessive state of an ECU connectedto the termination network via bus lineValueParameter Notation Unitmin. nominal max.V CAN_L V V CC − 0,3 a ——Bus voltageV CAN_H V — — 0,3 Differential bus voltage bV diff V −V CC — −V CC + 0,6a VCC is nominal 5 V.bThe differential voltage is determined by the input load of all ECUs during the recessive state. Therefore, V diff decreases slightly asthe number of ECUs connected to the bus increases.Table 4 — DC parameters for the dominant state of an ECU connectedto the termination network via bus lineValueParameter Notation Unitmin. nominal max.V CAN_L V — — 1,4 Bus voltageV CAN_H V V CC − 1,4 a — — Differential bus voltageV diffVV CC − 2,8—V CCaV CC is nominal 5 V.Table 5 — DC parameters for the low power mode of an ECU connectedto the termination network via bus lineValueParameter Notation Unitmin. nominal max.V CAN_L V 5— —Bus voltageV CAN_H V — —15.3.3 DC parameters for comparatorsSee Tables 6 and 7.Table 6 — DC threshold of dominant, recessive and failure detection innormal mode and vice versaValueParameter Notation Unitmin. nominal max.V thCAN_L_N V 2,5 — 3,9 Single ended bus receiver V thCAN_H_N V 1,5 — 2,3 Differential bus receiver V thDiff_N V −3,9 — −2,5 CAN_L to BAT detector V thLxBAT_N V 6,5 — 8,0 CAN_H to BAT detectorV thHxBAT_NV 6,5 — 8,0Copyright International Organization for StandardizationProvided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---12© ISO 2006 – All rights reservedTable 7 — DC threshold for wake-up and failure detection in low power modeValueParameter Notation Unitmin. nominal max.V th(wake)L V 2,5 3,2 3,9 Wake-up thresholdV th(wake)H V 1,1 1,8 2,5 Wake-up threshold difference∆V th(wake) V 0,8 1,4 —5.4 Network specification5.4.1 Network topologyIndividual CAN nodes can be connected to a communication network either by a bus or star topology (seeFigures 7 and 8).Key1 node 12 node 2Figure 7 — Connecting model; bus structure with stub linesHowever, for any connecting concept, the following requirements shall be fulfilled, in order to provide the fault tolerant means:⎯ The overall network termination resistor shall be in a range of about 100 Ω (but not less than 100 Ω). Fora detailed description of the termination concept please refer to 5.4.2. ⎯ The maximum possible number of participating nodes should not be less than 20 (at 125 kBit/s and aoverall network length of 40 m). The actual number of nodes varies due to communication speed, capacitive network load, overall line length, network termination concept, etc. ⎯ To provide a maximum communication speed of 125 kBit/s, the overall network length should not exceed40 m. However, it is possible to increase the overall network length by reducing the actual communication speed.Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---© ISO 2006 – All rights reserved13Key1 node 12 node 23 node 34 node 45 node 56 node 67 node nFigure 8 — Connecting model, star point structureFor a star point configuration, some additional constraints are given by the following:⎯ The individual nodes are connected to one or more “passive” star points, which themselves areconnected via a normal bus structure. ⎯ Even some connecting lines (star connector to node) might be extended to several meters; no stub linesare recommended. ⎯ Both the overall network length (all star connection line lengths added) and the maximum node to nodedistance affect the network communication.EXAMPLEFor most of the examples given in this part of ISO 11898, the following network topology is used:⎯ The star point connection method is with two star points. ⎯ The network is terminated with an overall resistance of 100 Ω. ⎯ The node number is about 20.⎯ The overall network length is about 40 m. ⎯ The maximum node to node distance is 20 m.⎯ The wire capacitance related to the length is about 120 pF/m.Copyright International Organization for Standardization Provided by IHS under license with ISONot for ResaleNo reproduction or networking permitted without license from IHS--`,,```,,,,````-`-`,,`,,`,`,,`---。
Network Working Group(网络工作组) R. Fielding Request for Comments: 2616 UC Irvine Obsoletes(过时弃用）: 2068 J. Gettys Category: Standards Track （类别:标准组） Compaq/W3CJ. MogulCompaqH. FrystykW3C/MITL. MasinterXeroxP. LeachMicrosoftT. Berners-LeeW3C/MITJune 1999超文本传输协议-HTTP/1.1本备忘录状况本文档说明了用于互联网社区的标准化跟踪协议，但还需要讨论和建议以便更加完善。
请参考"互联网官方协议标准"（STD1）来了解本协议的标准化状态。
分发散布本文是不受限制的。
版权声明Copyright (C) The Internet Society (1999). All Rights Reserved.摘要超文本传输协议（HTTP）是一种应用于分布式、协作式、超媒体信息系统的应用层协议。
它是一种通用的，状态无关的协议，可以用于除了超文本以外，还可以通过扩展它的请求方法，错误代码和报头[47]来完成更多任务，比如名称服务和分布对象管理系统。
HTTP的一个特点是数据表示方式的典型性（可输入的）（typing）和可协商性，允许建立独立于被传输数据的系统。
HTTP在1990年WWW全球信息刚刚起步的时候就得到了应用。
本规范定义了HTTP/1.1协议，这是RFC 2068的升级版[33]。
[页码1]------------------------------------------------------------------------目录1 Introduction （介绍） (7)1.1 Purpose（目的） (7)1.2 Requirements （要求） (8)1.3 Terminology （术语） (8)1.4 Overall Operation （概述） (12)2 Notational Conventions and Generic Grammar（标志转换及通用语法） (14)2.1 Augmented BNF （扩充的范式） (14)2.2 Basic Rules （基本规则） (15)3 Protocol Parameters （协议参数） (17)3.1 HTTP Version （版本） (17)3.2 Uniform Resource Identifiers （统一资源标识） (18)3.2.1 General Syntax （通用语法） (19)3.2.2 http URL (19)3.2.3 URI Comparison （URI对比） (20)3.3 Date/Time Formats （时间日期格式） (20)3.3.1 Full Date （完整日期） (20)3.3.2 Delta Seconds (21)3.4 Character Sets （字符集） (21)3.4.1 Missing Charset （不见了的字符集） (22)3.5 Content Codings （内容编码） (23)3.6 Transfer Codings （传输编码） (24)3.6.1 Chunked Transfer Coding （大块数据传输编码） (25)3.7 Media Types （媒介类型） (26)3.7.1 Canonicalization and Text Defaults (27)3.7.2 Multipart Types （复合类型） (27)3.8 Product Tokens （产品记号） (28)3.9 Quality Values （质量值） (29)3.10 Language Tags （语言标签） (29)3.11 Entity Tags （实体标签） (30)3.12 Range Units （范围单位） (30)4 HTTP Message （HTTP 消息） (31)4.1 Message Types （消息类型） (31)4.2 Message Headers （消息头） (31)4.3 Message Body （消息主体） (32)4.4 Message Length （消息长度） (33)4.5 General Header Fields （通用头字段） (34)5 Request （请求） (35)5.1 Request-Line （请求行） (35)5.1.1 Method （方法） (36)5.1.2 Request-URI （请求-URI） (36)5.2 The Resource Identified by a Request (38)5.3 Request Header Fields （请求头字段） (38)6 Response （应答） (39)6.1 Status-Line （状态行） (39)6.1.1 Status Code and Reason Phrase （状态码和原因短语） (39)6.2 Response Header Fields （应答头字段） (41)[页码2]------------------------------------------------------------------------7 Entity （实体） (42)7.1 Entity Header Fields （实体头字段） (42)7.2 Entity Body （实体主体） (43)7.2.1 Type （类型） (43)7.2.2 Entity Length （实体长度） (43)8 Connections （连接） (44)8.1 Persistent Connections （持久连接） (44)8.1.1 Purpose （目的） (44)8.1.2 Overall Operation（概述） (45)8.1.3 Proxy Servers （代理服务器） (46)8.1.4 Practical Considerations （实践中的考虑） (46)8.2 Message Transmission Requirements （消息传送请求） (47)8.2.1 Persistent Connections and Flow Control（持久连接和流程控制） (47)8.2.2 Monitoring Connections for Error Status Messages（出错状态消息的监测连接） (48)8.2.3 Use of the 100 (Continue) Status（状态号100的使用） (48)8.2.4 Client Behavior if Server Prematurely Closes Connection（如果服务器过早关闭连接，客户端的行为） (50)9 Method Definitions （方法的定义） (51)9.1 Safe and Idempotent Methods （安全和幂等方法） (51)9.1.1 Safe Methods （安全方法） (51)9.1.2 Idempotent Methods （幂等方法） (51)9.2 OPTIONS （选项） (52)9.3 GET （命令：GET） (53)9.4 HEAD （命令：HEAD） (54)9.5 POST （命令：POST） (54)9.6 PUT （命令：PUT） (55)9.7 DELETE （命令：DELETE） (56)9.8 TRACE （命令：TRACE） (56)9.9 CONNECT （命令：CONNECT） (57)10 Status Code Definitions （状态码定义） (57)10.1 Informational 1xx （报告：1XX） (57)10.1.1 100 Continue （100 继续） (58)10.1.2 101 Switching Protocols（交换协议） (58)10.2 Successful 2xx （成功：2XX） (58)10.2.1 200 OK （200 正常） (58)10.2.2 201 Created （201 已建立） (59)10.2.3 202 Accepted （202 已接受） (59)10.2.4 203 Non-Authoritative Information （无认证信息） (59)10.2.5 204 No Content （无内容） (60)10.2.6 205 Reset Content （重置内容） (60)10.2.7 206 Partial Content （部分内容） (60)10.3 Redirection 3xx （3XX 重定向） (61)10.3.1 300 Multiple Choices （复合选择） (61)10.3.2 301 Moved Permanently （永久转移） (62)10.3.3 302 Found （找到） (62)10.3.4 303 See Other （访问其他） (63)10.3.5 304 Not Modified （304 没有更改） (63)10.3.6 305 Use Proxy （305 使用代理） (64)10.3.7 306 (Unused) （306 未使用） (64)[页码3]------------------------------------------------------------------------10.3.8 307 Temporary Redirect （暂时重定向） (65)10.4 Client Error 4xx （客户端错误） (65)10.4.1 400 Bad Request （错误请求） (65)10.4.2 401 Unauthorized （未认证） (66)10.4.3 402 Payment Required （支付请求） (66)10.4.4 403 Forbidden （禁止） (66)10.4.5 404 Not Found （没有找到） (66)10.4.6 405 Method Not Allowed （方法不容许） (66)10.4.7 406 Not Acceptable （不可接受） (67)10.4.8 407 Proxy Authentication Required （要求代理认证） (67)10.4.9 408 Request Timeout （请求超时） (67)10.4.10 409 Conflict （冲突） (67)10.4.11 410 Gone （离开） (68)10.4.12 411 Length Required （长度请求） (68)10.4.13 412 Precondition Failed （预处理失败） (68)10.4.14 413 Request Entity Too Large （请求的实体太大了） (69)10.4.15 414 Request-URI Too Long （请求URI太长了） (69)10.4.16 415 Unsupported Media Type （不支持的媒提类型） (69)10.4.17 416 Requested Range Not Satisfiable （请求范围未满足） (69)10.4.18 417 Expectation Failed （期望失败） (70)10.5 Server Error 5xx （服务器错误 5XX） (70)10.5.1 500 Internal Server Error （内部错误） (70)10.5.2 501 Not Implemented （未实现） (70)10.5.3 502 Bad Gateway （错误网关） (70)10.5.4 503 Service Unavailable （服务不可用） (70)10.5.5 504 Gateway Timeout （网关超时） (71)10.5.6 505 HTTP Version Not Supported （版本不支持） (71)11 Access Authentication （访问认证） (71)12 Content Negotiation （内容协商） (71)12.1 Server-driven Negotiation （服务器驱动协商） (72)12.2 Agent-driven Negotiation （客户端驱动协商） (73)12.3 Transparent Negotiation （透明协商） (74)13 Caching in HTTP （缓存） (74)13.1.1 Cache Correctness （缓存正确性） (75)13.1.2 Warnings （警告） (76)13.1.3 Cache-control Mechanisms （缓存控制机制） (77)13.1.4 Explicit User Agent Warnings （直接用户代理警告） (78)13.1.5 Exceptions to the Rules and Warnings （规则和警告的异常）.78 13.1.6 Client-controlled Behavior（客户控制的行为） (79)13.2 Expiration Model （过期模式） (79)13.2.1 Server-Specified Expiration （服务器指定过期） (79)13.2.2 Heuristic Expiration （启发式过期） (80)13.2.3 Age Calculations （年龄计算） (80)13.2.4 Expiration Calculations （过期计算） (83)13.2.5 Disambiguating Expiration Values （消除歧义的过期值） (84)13.2.6 Disambiguating Multiple Responses （消除歧义的复合应答）..84 13.3 Validation Model （确认模式） (85)13.3.1 Last-Modified Dates （最后更改日期） (86)[页码4]------------------------------------------------------------------------13.3.2 Entity Tag Cache Validators （实体标签缓存确认） (86)13.3.3 Weak and Strong Validators （强弱确认） (86)13.3.4 Rules for When to Use Entity Tags and Last-Modified Dates当使用实体标签和最后更改日期字段时候的规则 (89)13.3.5 Non-validating Conditionals （不可确认的条件） (90)13.4 Response Cacheability （应答缓存功能） (91)13.5 Constructing Responses From Caches （从缓存构造应答） (92)13.5.1 End-to-end and Hop-by-hop Headers （端对端和逐跳的头） (92)13.5.2 Non-modifiable Headers （不可以更改的报头） (92)13.5.3 Combining Headers （组合报头） (94)13.5.4 Combining Byte Ranges （组合字节范围） (95)13.6 Caching Negotiated Responses （缓存协商过的应答） (95)13.7 Shared and Non-Shared Caches （共享和非共享缓存） (96)13.8 Errors or Incomplete Response Cache Behavior（错误或不完整应答缓存行为） (97)13.9 Side Effects of GET and HEAD （GET和HEAD的单方影响） (97)13.10 Invalidation After Updates or Deletions（更新和删除后的失效） (97)13.11 Write-Through Mandatory （强制写通过） (98)13.12 Cache Replacement （缓存替换） (99)13.13 History Lists （历史列表） (99)14 Header Field Definitions （头字段定义） (100)14.1 Accept （接受） (100)14.2 Accept-Charset （接受的字符集） (102)14.3 Accept-Encoding （接受的编码方式） (102)14.4 Accept-Language （接受的语言） (104)14.5 Accept-Ranges （接受的范围） (105)14.6 Age （年龄，生存期） (106)14.7 Allow （容许） (106)14.8 Authorization （认证） (107)14.9 Cache-Control （缓存控制） (108)14.9.1 What is Cacheable （什么可以缓存） (109)14.9.2 What May be Stored by Caches （什么将被缓存存储） (110)14.9.3 Modifications of the Basic Expiration Mechanism基本过期机制的更改 (111)14.9.4 Cache Revalidation and Reload Controls缓存重确认和重载控制 (113)14.9.5 No-Transform Directive （不可转换指示） (115)14.9.6 Cache Control Extensions （缓存控制扩展） (116)14.10 Connection （连接） (117)14.11 Content-Encoding （内容编码） (118)14.12 Content-Language （内容语言） (118)14.13 Content-Length （内容长度） (119)14.14 Content-Location （内容位置） (120)14.15 Content-MD5 （内容的MD5校验） (121)14.16 Content-Range （内容范围） (122)14.17 Content-Type （内容类型） (124)14.18 Date （日期） (124)14.18.1 Clockless Origin Server Operation （无时钟服务器操作）..125 14.19 ETag （标签） (126)14.20 Expect （期望） (126)14.21 Expires （过期） (127)14.22 From （来自） (128)[页码5]------------------------------------------------------------------------14.23 Host （主机） (128)14.24 If-Match （如果匹配） (129)14.25 If-Modified-Since （如果自从某个时间已经更改） (130)14.26 If-None-Match （如果没有匹配） (132)14.27 If-Range （如果范围） (133)14.28 If-Unmodified-Since （如果自从某个时间未更改） (134)14.29 Last-Modified （最后更改） (134)14.30 Location （位置） (135)14.31 Max-Forwards （最大向前量） (136)14.32 Pragma （语法） (136)14.33 Proxy-Authenticate （代理鉴别） (137)14.34 Proxy-Authorization （代理授权） (137)14.35 Range （范围） (138)14.35.1 Byte Ranges （字节范围） (138)14.35.2 Range Retrieval Requests （范围重获请求） (139)14.36 Referer （引用自） (140)14.37 Retry-After （一会重试） (141)14.38 Server （服务器） (141)14.39 TE (142)14.40 Trailer （追踪者） (143)14.41 Transfer-Encoding（传输编码） (143)14.42 Upgrade （改良） (144)14.43 User-Agent （用户代理） (145)14.44 Vary （变更） (145)14.45 Via （经由） (146)14.46 Warning （警告） (148)14.47 WWW-Authenticate （WWW鉴别） (150)15 Security Considerations （对安全的考虑） (150)15.1 Personal Information（个人信息） (151)15.1.1 Abuse of Server Log Information （服务日志信息的滥用） (151)15.1.2 Transfer of Sensitive Information （敏感信息传输） (151)15.1.3 Encoding Sensitive Information in URI's（对URI中的敏感信息编码） (152)15.1.4 Privacy Issues Connected to Accept Headers（可接受头的秘密问题） (152)15.2 Attacks Based On File and Path Names基于文件名和路径的攻击 (153)15.3 DNS Spoofing （DNS欺骗） (154)15.4 Location Headers and Spoofing （位置头和欺骗） (154)15.5 Content-Disposition Issues （内容部署问题） (154)15.6 Authentication Credentials and Idle Clients（信用鉴定与空闲客户） (155)15.7 Proxies and Caching （代理与缓存） (155)15.7.1 Denial of Service Attacks on Proxies（对代理的服务拒绝攻击） (156)16 Acknowledgments （致谢） (156)17 References （参考） (158)18 Authors' Addresses （作者地址） (162)19 Appendices （附录） (164)19.1 Internet Media Type message/http and application/http（网络媒体类型：消息/HTTP和应用/HTTP） (164)19.2 Internet Media Type multipart/byteranges（网络媒体类型：多部分/字节范围） (165)19.3 Tolerant Applications （容错的应用） (166)19.4 Differences Between HTTP Entities and RFC 2045 Entities（HTTP的实体和RFC2045中实体的区别） (167)[页码6]------------------------------------------------------------------------19.4.1 MIME-Version （MIME版本） (167)19.4.2 Conversion to Canonical Form （语言形式转变） (167)19.4.3 Conversion of Date Formats （日期格式的转变） (168)19.4.4 Introduction of Content-Encoding （内容编码的介绍） (168)19.4.5 No Content-Transfer-Encoding （不要内容传输编码） (168)19.4.6 Introduction of Transfer-Encoding （传输编码的介绍） (169)19.4.7 MHTML and Line Length Limitations（MHTML与行长度限制） (169)19.5 Additional Features （附加的一些性质） (169)19.5.1 Content-Disposition （内容部署） (170)19.6 Compatibility with Previous Versions （与久版本的兼容性） (170)19.6.1 Changes from HTTP/1.0 （自HTTP/1.0的更改） (171)19.6.2 Compatibility with HTTP/1.0 Persistent Connections（与HTTP/1.1持久连接的兼容性） (172)19.6.3 Changes from RFC 2068 （自RFC268的更改） (172)20 Index （索引） (175)21 Full Copyright Statement （完整版权声明） (176)1 概述1.1 目的超文本传输协议（HTTP）是一种应用于分布式、合作式、多媒体信息系统的应用层协议。
abstract关键字用法
abstract关键字用法有以下几种：
1. 抽象类的声明：在类的声明前加上abstract，表示该类是抽象类，不能直接实例化，只能被继承。
2. 抽象方法的声明：在方法的声明前加上abstract，表示该方法是抽象方法，没有具体的实现，需要子类去实现。
抽象方法没有方法体，用分号代替。
3. 抽象属性的声明：在成员变量的声明前加上abstract，表示该成员变量是抽象属性，没有具体的实现，需要子类去实现。
4. 接口的声明：接口中的所有方法默认都是抽象方法，所有成员变量默认都是public、static、final类型，可以不用声明为abstract。
5. 抽象类的继承：一个非抽象类可以继承一个抽象类，但必须实现该抽象类的所有抽象方法。
总的来说，abstract关键字的作用是定义抽象类、抽象方法或抽象属性，通过继承和实现来完成具体的操作。
网络管理习题参考答案习题 11．什么是网络管理？网络管理的目标是什么？[解答] 网络管理是指对网络的运行状态进行监测和控制，并能提供有效、可靠、安全、经济的服务。
网络管理的目标是使网络的性能达到最优化状态。
通过网络管理，要能够预知潜在的网络故障，采取必要的措施加以预防和处理，达到零停机；通过监控网络性能，调整网络运行配置，提高网络性能；借助有效的性能尺度和评估方法，扩充和规划网络的发展。
所以网络管理的根本目标就是最大限度地满足网络管理者和网络用户对计算机网络的有效性、可靠性、开放性、综合性、安全性和经济性的要求。
2．网络管理标准有哪些？[解答] 网络管理的主要标准分别是OSI参考模型、TCP/IP参考模型、TMN参考模型、IEEE LAN/WAN以及基于Web的管理。
3．ISO制定的网络管理标准有哪些文件？其内容是什么？[解答] ISO在1989年颁布了ISO DIS7498-4（X.700）文件，定义了网络管理的基本概念和总体框架；之后在1991年发布的两个文件中规定了网络管理提供的服务和网络管理协议，即ISO 9595公共管理信息服务定义（Common Management Information Service，CMIS）和ISO 9596公共管理信息协议规范（Common Management Information Protocol，CMIP）；在1992年公布的ISO 10164文件中规定了系统管理功能（System Management Functions，SMFs），而ISO 10165文件则定义了管理信息结构（Structure of Management Information，SMI）。
这些文件共同组成了ISO的网络管理标准。
4．TCP/IP网络管理标准有哪些主要的RFC文件？其内容是什么？[解答]TCP/IP网络管理在1987年11月提出的简单网关监控协议（Simple Gateway Monitoring Protocol，SGMP），并在此基础上发展为简单网络管理协议第一版（Simple Network Management Protocol，SNMPv1），陆续公布在1990和1991年的几个RFC（Request For Comments）文件中，即RFC 1155（SMI）、RFC 1157（SNMP）、RFC 1212（MIB定义）和RFC 1213（MIB-2规范）。
abstractmethoderror案例1. 引言abstractmethoderror是Python中的一个常见错误类型，通常在使用抽象基类或继承的过程中发生。
在本文中，我们将深入探讨abstractmethoderror的定义、原因、解决方法，并通过案例分析来帮助读者更好地理解和避免这一错误。
2. 什么是abstractmethoderror？abstractmethoderror是指在Python中使用抽象基类（Abstract Base Classes, ABCs）或继承时，如果未实现抽象方法就会触发的错误。
在面向对象编程中，抽象基类是指包含抽象方法的类，这些方法必须在子类中被具体实现。
如果子类没有实现所有抽象方法，就会导致abstractmethoderror。
3. 导致abstractmethoderror的原因导致abstractmethoderror的原因通常有两种：3.1. 没有实现抽象方法：在子类中没有实现抽象基类中定义的抽象方法。
3.2. 调用未实现的抽象方法：在子类中调用了抽象基类中定义的但未被实现的抽象方法。
4. 解决abstractmethoderror的方法为了避免abstractmethoderror，我们可以采取以下方法来解决：4.1. 实现抽象方法：在子类中必须实现所有抽象基类中定义的抽象方法，确保不会出现未实现的情况。
4.2. 使用@abstractmethod装饰器：在抽象基类中使用@abstractmethod装饰器来标记抽象方法，以确保子类必须实现这些方法。
5. 案例分析让我们通过一个简单的案例来更好地理解abstractmethoderror。
假设我们有一个抽象基类Animal，其中定义了一个抽象方法speak()，我们再定义一个子类Dog，但在Dog类中忘记实现speak()方法。
当我们调用Dog类的speak()方法时，就会触发abstractmethoderror。
scintilla 代码结构
Scintilla是一个用C++编写的文本编辑器控件，它的代码结构可以从多个角度来理解。
首先，从功能模块的角度来看，Scintilla的代码结构包括文本编辑、语法高亮、代码折叠、自动完成、多窗口管理等多个功能模块。
每个功能模块都有相应的代码文件来实现其功能，这些文件按照功能模块的不同进行组织和管理。
其次，从代码文件的角度来看，Scintilla的代码结构包括核心编辑器代码、语法定义文件、样式定义文件、配置文件等。
核心编辑器代码包括处理文本编辑、绘制文本、处理用户输入等功能的代码文件；语法定义文件用于定义不同编程语言的语法规则和关键字；样式定义文件用于定义文本的显示样式；配置文件用于配置编辑器的行为和外观等。
此外，Scintilla的代码结构还包括跨平台支持，它可以在不同的操作系统上运行，并且代码结构中包含了针对不同操作系统的适配代码，以实现跨平台的支持。
总的来说，Scintilla的代码结构是一个复杂而完整的系统，它包括多个功能模块、多个代码文件以及跨平台支持，这些都构成了Scintilla代码结构的重要组成部分。
abstract在c语言中的用法
在C语言中，abstract是用来描述抽象数据类型的关键字。
抽象数据类型是一种数据类型，它的行为仅由其操作定义，而不依赖于其实现方式。
这种抽象性允许程序员将数据类型的实现和使用分开。
在C语言中，我们可以使用struct关键字来定义抽象数据类型。
定义一个struct后，我们可以在其后面使用typedef来定义一个新的类型名，使其更加易用。
在使用抽象数据类型时，我们通常会将类型的实现细节放在一个源文件中，然后将接口(也就是操作)定义在一个头文件中。
这样，在使用该类型的程序中，我们只需要包含该头文件即可使用该类型的操作，而不需要了解其实现细节。
总的来说，abstract在C语言中的用法是为了定义抽象数据类型，将类型的实现与使用分开，并提供一个清晰的接口供使用者使用。
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A Medium Access Control Protocol for Radio over FiberWireless LAN operating in the60-GHz BandHong Bong Kim,Hagen Woesner,Adam WoliszTelecommunication Networks GroupDepartment of Electrical and Computer EngineeringTechnische Universit¨a t BerlinSekr.FT5-2,Einsteinufer25,10587Berlin,Germany.E-mail:hbkim,woesner,wolisz@ee.tu-berlin.deAbstractRadio overfiber(RoF)technology has been suggested as a cost-effective solution to meet modern ever in-creasing user bandwidth demands and mobility.A system based on this technology has properties quite different from those of conventional WLAN systems in that every room in a building hosts at least one pico-cell having its own base station(BS).Thus a challeng-ing problem lies in the medium access control(MAC) protocol design so that it can support QoS require-ments as well as a fast and simple handover.In this paper a MAC protocol based on frequency switching (FS)codes is proposed,and constraints on some im-portant parameters of it are examined.Six variants of the MAC protocol are proposed and discussed.1IntroductionIn order to meet the increasing user bandwidth de-mands and mobility,wireless networks using radio overfiber(RoF)technology have been suggested as a promising solution.Because of the huge amount of license-free spectrum around60GHz,much of the research in thisfield was concentrated on components for this frequency band[3]–[6].The properties of mil-limeter waves,however,are quite different from those in the usual wireless LAN(WLAN)bands(2.4or5 GHz).The size of the picocells is limited to at most a room in an indoor environment,thus leading to a very large number of base stations(BS)and frequent han-dovers of mobile hosts(MH)between cells.In result one can observe the continuation of a trend:higher and higher bit rates in ever smaller cells.For medium access control(MAC)protocol design this means that less effort has to be paid on“squeezing out the last bit”of the channel in exchange for an efficient han-dover support.While handovers are rather rare events in a GSM or conventional WLAN environment,even a slight movement inside a building may provoke a handover in a60GHz RoF network.Moreover,as will be clear later due to the unknown propagation delay between the control station(CS)and BSs and high data rate Ethernet-like MAC protocol is not ap-propriate.In this paper,a MAC protocol for a RoF WLAN system is proposed that aims at the support of fast and easy handover,while hiding most of the complexity of the system from the MH.A mecha-nism to support QoS requirements is also provided. The MAC protocol is based on frequency switching (FS)codes.Adjacent picocells employ orthogonal FS codes to avoid possible co-channel interference.This mechanism allows a MH to stay tuned to its frequency during handover,which is a major characteristic of the proposed MAC protocol.The paper starts with a brief discussion of options in the physical layer.In section 3operations of the proposed MAC protocol are de-scribed.Its major parameters and some constraints on them are discussed in section4.Section5summa-rizes the work.2Options in the Physical Layer In the last years,the60GHz band received much at-tention because a large spectrum has been allocated worldwide(3-5GHz)for short-range wireless local communication[1].In a building,every room has to be equipped with its own BS,because the millimeter-wave cannot penetrate normal size walls.Thus,devel-opment of cost-effective BSs is essential for the suc-cess of the system.Recently,a lot of research activities have been carried out to develop millimeter-wave generation and transport techniques,which include the optical generation of low phase noise wireless signals and their transport overcoming the chromatic dispersion infiber.Several techniques have been investigated so far which are classified into the following four cat-egories.For more detailed discussion of the advan-tages and disadvantages of the techniques refer to[2] [7].1.Optical Self-heterodyning.In the optical self-heterodyning technique,two wavelengths are carried over an opticalfiber to a BS in which one wavelength acts as a reference and the other carries signals modulated by user data,and the difference between them is the frequency of the millimeter-wave emitted from the BS antenna.A benefit of this approach is that it overcomes theappeared in 5th European Personal Mobile Communications Conference (EPMCC), April 2003chromatic dispersion effect.2.External Modulation.External modulation isdone by a high speed external modulator such as the electro-absorption modulator(EAM).Its configuration is simple,but it has some disad-vantages such asfiber dispersion effect and high insertion loss.3.Up-and Down-conversion.In this technique alower intermediate frequency(IF)(10GHz)is carried over the opticalfiber and the millimeter wave is made at the BS.Although this technique can avoid the optical chromatic dispersion effect it needs a more complex BS structure.4.Optical Transceiver.The simplest BS structurecan be implemented with optical transceivers such as the electro-absorption transceiver(EAT).Two wavelengths are transmitted over an optical fiber from the CS to the BS.One wavelength for the down-link is modulated by user data and the other for the up-link is unmodulated.The un-modulated wavelength is modulated by up-link data at the BS and returns to the CS.It suffers from chromatic dispersion problem.A MAC protocol applicable to a system using the above techniques is proposed in the next section.3MAC protocol3.1System setupThe simple structure of the BS and60GHz wave char-acteristics leads to a centralized network architecture with many picocells,where most of the BS functions of conventional WLANs are shifted to the CS.Every room in a building is covered by at least one pico-cell,each having its own BS(Fig.1(a)).It becomes immediately obvious,that in such system with high number of very small cells,the issue of efficient mo-bility management has a very special significance. We assume that the system works in frequency di-vision duplex(FDD)mode,since most optic-wireless converters developed thus far support this mode[4]–[6].By subdividing the total system bandwidth, (frequency)channels are obtained(Fig.1(b)), where channels are used for down-link transmission and the other channelsfor up-link transmission.A pair of frequency channels are used to-gether to support FDD operation,where, ()are for down-and up-link transmis-sion,respectively.Note that the bandwidth–i.e.the frequency spectrum–assigned to the uplink and to the downlink does NOT have to be identical,making it possible to support asymmetric traffic.In addition, the time axis is also subdivided into time slots of equal length and time slots are grouped into a frame.(d)f mf mf mf mf mfffffsDown-linkUp-linkFigure1:System description.(a)A RoF WLAN sys-tem operating in the millimeter-wave band,(b)The total system bandwidth is subdivided into chan-nels,where,and are the to-tal system bandwidth,the channel bandwidth and the guard bandwidth,respectively,(c)and(d)show fre-quency switching(FS)patterns for down-and up-link when the number of channels isfive.3.2Basic operationThe MH is assigned a pair of channelsand a pair of time slotsfor communication.Only after having re-ceived a permit from the downlink channel during the time slot,the MH may transmit uplink packets over the uplink channel during the next time slot.Every BS supports all channels,each of them,how-ever,being supported in each proper time slot.Fig.1 (c)and(d)show FS patterns for down-and up-link, respectively,when isfive.During every frame time,each of the time slots and channels is utilized once and only once.Note that the picture resembles a chess board,we shall therefore refer to the MAC protocol introduced in this paper as Chess Board Protocol,shortly CheBo Protocol.An impor-tant issue is that adjacent picocells must not use iden-tical FS patterns to avoid possible co-channel inter-ference.And one FS pattern can be used in several picocells if they are spaced far enough that there is no co-channel interference between them.For proper operations using FS patterns,we assume that the sys-tem is synchronous,i.e.all system components,es-pecially the CS and the MH have the same notion of the time slots.The synchronous operation of all cells,however,is enabled by the centralized architec-ture.A sketch of the operation may be the following. Since the CS may initially measure the round-trip-time(RTT)to any BS,it is then possible to transmit downlink slots towards that BS in advance. This leads to a fully slotted system.In order to explain the CheBo operation in detailwe willfirst discuss the slot format.Fig.2shows down-and up-link slot formats and essentially,they have the same format.The down-link slot begins with a MAC address indicating the destination of the slot. Besides individual MAC addresses an additional ad-dress ANY having the semantic of a broadcast address to all MHs in the picocell which happen to listen to the given channel and slot is introduced(please note, that as NOT all the stations will follow each channel and slot,there is no obligation to listen to slots with the ANY address).This MAC address is followed by a permissionfield,which authorizes transmission of the MH specified in the MAC Address in the follow-ing up-link slot.The nextfield is for down-link payload,destined to the MH specified by the MAC address.Finally the lastfield,consisting of another MAC address and reservation confirmation has a more complex mean-ing:it confirms the request for bandwidth assignment obtained by the CS from the addressed MH,but with-out immediate authorization for sending.The up-link slot consists of two parts.Thefirst one is used for uplink data transmission and it consists of MH’s MAC address,PIGGYBACKfield,and PAY-LOADfield.The second part is for reservation and it must not be used by the MH currently using the thefirst part but may be used by any other MHs hav-ing data to send,and not being assigned bandwidth in this channel so far.If the PIGGYBACKfield is set,it means that MH still has more data to send and requests assignment of one more slot,and non-setting thisfield indicates that no further usage of the channel is requested.Each PAYLOADfield(both up-link and down-link) consists of at least one,possibly several packets.Each packet has a datafield and a frame check sequence (FCS)field.Several small-size data packets can be packed into an up-link slot.On the other hand large data units may have to be fragmented into several up-link slots.To request a permit for up-link transmission on some channel,the MH sends a request to the CS, using the reservationfield in any slot in this chan-nel(Fig.2).The reservation request must include the MAC address of the requesting host,and,optionally, a requested bit rate.Specifying the bit rate allows the CS to make proper long term reservation.Not spec-ifying the bit rate states a request for one single slot (please note,that while using this single slot,another one,not necessarily adjacent,might be requested by setting the PIGGYBACKfield,just allowing to re-quest a series of slots on a per demand basis,rather than based on a priori bit rates).After having sent a request the MH expects the reservation result in one frame time from the down-link channel.This reservation result can have one of three possible forms.Either an immediate permit to send is given,or a reservation confirmation without permit to transmit can be made.The latter one might include a channel identifier,meaning that the request will be satisfied but in a different channel than the oneDOWNUPFigure2:Slot formats for the down-and up-link data transmission.in which it has been requested.In this case the MH has to tune to the channel,and wait there for the per-mit to transmit.Finally the third option-a reservation reject denotes that the request cannot be satisfied.In this case the MH might decide to make another re-quest some time later.This should be a rare event, only in the case of system approaching temporarily capacity saturation.If neither of this happens,the MH assumes that the reservation has not been received by the CS.More precisely it might indicate one of several possible events,e.g.,collision of the requests or a transmission error of the request.In that case the MH will retrans-mit a request following a collision resolution scheme such as-persistent algorithm.Details of this colli-sion resolution scheme will not be discussed here.Once a MH has been allocated a channel,it can keep using it by setting the piggybackfield until its transmission buffer is empty provided it stays in the same picocell.Notice that the MAC protocol allows more than one BS using different FS codes to be employed in a pic-ocell to increase system capacity.A MH could use more than one up-link slot in a frame time in this case.3.3Mobility supportLet us now discuss the mobility support.Please note, that as long as a MH remains tuned to a certain chan-nel(frequency pair)and time slot pair,i.e.,listening on the down-link channel,the MH knows precisely that a slot from the CS should appear every frame time so that it can expect the time instances at which down-link slots arrive.However,when it moves into an adjacent picocell using a different FS pattern,the MH will receive the down-link slot in an unexpected time instance.Thus the MH can easily realize–within at most a single frame time()!–that it moved into another pic-ocell.Furthermore,using the following slot for the uplink transmission the MH can and should make a request for transmit permission/reservation in the new pair of time slots!Please note,that the CS knows that the MH with this MAC address has been transmitting previously in a different picocell,so it is possible a) to treat such request with higher priority than requests for new reservations and b)release any possible reser-Table1:Six variants of the MAC protocol for RoF WLAN operating in60GHz band.Request when theduring operationGroup 1blockedNO A 3sharedassigned if any,assigned if any,YES Bassigned if any,vation in the old picocell.3.4InitializationWhen a new MH comes into the system thefirst action it has to take is to select a channel randomly and keep listening on the down-link frequency.Within at most ,it will receive a down-link data.After having that it can send in a following slot on an up-link afirst reservation request for up-link transmission permits.3.5Six variants of the MAC protocol Six variants of the MAC protocol,classified into two groups,are considered in the paper as shown in Table 1.In thefirst group(group A),MHs are assumed not to have a capability to change channels during opera-tion,whereas MHs in group B are assumed to be able to change channels.MAC1is the simplest in which the CS allows a sin-gle channel to be used by only one MH,and it has no queue for requests.When the channel is being used, further requests are blocked.In particular,if a MH moves to a picocell in which“its”channel is already used,there is no way to continue transmission,and the MH has to behave like it would enter the system -meaning stochastic selection of another channel and trial.The second MAC–MAC2–is similar with the only difference,that the CS does store requests for “busy”channels rather than rejecting the request,and when the channel is released the CS assigns it to a MH waiting in the queue,under thefirst-comefirst-served policy.In MAC3interleaved usage of slots in a single channel by several MHs is possible.Slots might be assigned using a simple round-robin fashion thereby assuring equal portion of the capacity to each candidate MH,or following a weighted round robin, with respect to the reservation parameter. Essentially group B MACs are similar to those in group A,with the difference,that in the case of group B MACs attempt tofind capacity in other channels, not only in the channel on which the request has been issued.It can be expected that group B MACs will outperform group A MACs on the expense of in-creased complexity.Figure3:The maximum number of channels vs. user data rate.4Parameters of the MAC proto-colThe proposed MAC protocol has two major parame-ters:(1)the number of channels and(2)the slot size.Some constraints on the two parameters are discussed in this section.4.1The number of channelsWe can consider an upper bound for the number of channels.It comes from the relationship in the frequency domain between the total system band-width,the channel bandwidth and the guard band-width(Fig.1(b)),and it is given by(1)For a given total system bandwidth of5GHz and a desired user data rate()being equal to 100Mbit/s(assuming a1bit/Hz coding efficiency,,and),1.Fig.3indicates the maximum number of channels vs.the user data rate with different.4.2Slot lengthFrom the assumption that a MH receives the reserva-tion result in the next frame after it sends a request,we can derive a simple relation for the slot length given by1Assuming.This may not be too unrealistic,when the FS code is chosen carefully.Per user data rate (BTdata) (Mbps)M i n i m u m S l o t S i z e (b y t e )Figure 4:The minimum slot length er data rate.is the maximum number of channels.Suppose a MH sends a request at the end of an up-link slot to the CS at time ,then the CS receives the whole packet at time .Note here that the reser-vation result must be available at the MH before therestpackets are transmitted.After process-ing for reservation the CS transmits down-link packet,which will be received completely at timeby the MH.This value mustbe smaller than or equal to ,which results in Eq.(2).Fig.4shows a relationship between the minimum slot length and the user data rate with dif-ferent total system bandwidth where and are assumed.Notice that must always be of integer value and greater than two,which explains discontinuities and cutoff in the figure.4.3Handover latencyWhen a MH moves into an adjacent picocell,it will realize the handover within at most .Then it sends a request in the next and receives the reservation result in the next next .Thus it takes at least to complete handover,which is represented by。
