05 sip字段说明Word文档格式.docx
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用来表示这个包最多可以被传送多少跳，当此值为0还没有到达目的地时，系统会回483（TooManyHops）；
一般在含有request的源包里面带有这个字段，默认值正常的都是设置为70
User-Agent：
终端设备自己填写的关于设备方面的信息，没有具体用处
From：
源的displayname和源的URI；
&
前面带的是设备号或者是主叫号码，&
后面带的是proxy的地址
To：
目的地的绝对地址，包含被叫displayname和被叫URI；
前面带的是设备号或者是被叫号码，&
Call-ID：
是一个唯一的标识符，在一通呼叫中请求和应答消息中的Call-ID是唯一的
Contact：
包含源的URI信息，用来给响应消息直接和源建立连接用
CSeq：
用来标识命令和命令顺序，用32位无符号整数来表示，要小于2**31
Expires：
在注册包和注册应答包中携带，用来协商URI的有效时间，当为0的时候表示注销设备，没有Expires的时候会被系统拒绝（现在做了修改，如果没有这个字段，系统会把此值当作是3600）
Allow：
允许的命令
Supported：
支持的操作，例如：
replace等
Content-Type：
指明消息体的类型
Content-Length：
指明消息体的字节大小
4．Messagebody
SDP协议版本
会话名，例如：
SIPCALL
ConnectionInformation：
ConnectNetworkType现在只有IN（Internet）；
ConnectionAddressType现在只有IP4和IP6两种；
ConnectionAddress可以为单播地址或多播组地址，如果是多播组地址还必须有一个生存时间（TTL）值，如：
c＝INIP4224.2.1.1/127，表示TTL＝127秒
TimeDescription：
标明会话的开始时间和终止时间
MediaDescription：
包含媒体类型、端口、传送层和格式列表4部分，传送层描述的是MediaProtocol，例如：
RTP/AVP表示IETFRTP协议，udp表示UDP协议；
格式列表列举出支持的codec类型
MediaAttribute：
有两种描述方式：
a=<
属性>
或a=<
：
<
值>
，第一种形式称为特殊属性，无须规定数值，如：
a=recvonly表示该媒体信道是“只收”信道；
第二种形式称为数值属性，例如：
MediaAttributeValue：
18G729/8000这种形式
二、一些功能信令流程
1．Refer（Transfer业务）命令的使用
对于SIP信令的Transfer应用，主要用到的命令就是Refer，在B挂机后会向系统发出Refer命令，系统回应一个Accepted（202）命令，然后系统再会一个Notify命令，B回应200OK后，过程结束，具体的信令流程和信令内容请查看SIPTransfer文档，下面列举如下：
AttendedCallTransfer
Message1
REFERsip:
b@SIP/2.0
Via:
SIP/2.0/UDP;
branch=z9hG4bK2293940223
To:
<
sip:
b@>
From:
a@>
;
tag=193402342
Call-ID:
898234234@
CSeq:
93809823REFER
Max-Forwards:
70
Refer-To:
（whateverURI）
Contact:
sip:
a@
Content-Length:
0
Message2
SIP/2.0202Accepted
tag=4992881234
b@
Message3
NOTIFYsip:
a@SIP/2.0
branch=z9hG4bK9922ef992-25
1993402NOTIFY
Event:
refer
Subscription-State:
active;
expires=（dependsonRefer-ToURI）
Content-Type:
message/sipfrag;
version=2.0普通呼叫的type为：
application/sdp
20
2．Replace的使用
过程如下图所示：
3．EarlyMediaApplications
在SIP的EarlyMedia中使用的是183信令来实现，如下图：
4．SIP自动callback的应用
5．用InstantMessagetoTransferaCall
6．SIPMessageWaiting
7．SIPCallControlinConferencing
三、新功能
1．SigComp
theSignalingCompression（SigComp）add-onmoduleisasolutionforcompressingSIP
signaling.SinceSIPmessagesaretextbased,theyarenotoptimizedintermsofsize.Forexample,
typicalSIPmessagesrangefromafewhundredbytestotwothousandbytesormore（RFC3261）.
Withtheplannedusageoftheseprotocolsinwirelessandcellularhandsets,andaspartofthe3GPP
（ThirdGenerationPartnershipProject）requirementsforIMS（IPMultimediaSubsystem）,thelarge
messagesizeisproblematicandmessagecompressionismandatory.
2．DLA（DynamicLocalAddress）
enablesthedynamicopeningandclosingofthelocalIP
addresses,whichareusedforrequestsendingandreception,atanymomentoftheSIPStacklife
cycle.Thisfeatureistypicallyusedwithmultihomedhost.DLAisusedforbroadband（DSL,cable）,
aswellaswirelessandcellularnetworks,tosupporthandoffsandIPaddresschangesbyservice
providers.
3．IP_TOS
determinesthevalueoftheTypeofServicefieldintheIPheaderofallpacketsthatare
sentovertheoutgoingconnections.（SupportedforIPv4addressesonly.）
4．TransmitterObject
theSIPStackusestransmitterobjectsformessagesending.Eachtransaction
objectholdsasingletransmitterobjectandusesittosendSIPmessagesandmessage
retransmissions.Theapplicationcanusethisnewobjectforsendinganout-of-scoperequestor
responsewithoutusingtheTransactionlayer.
5．REFERRFC3515
REFERisaSIPmethoddefinedbyRFC3515（SessionInitiationProtocol
ReferMethod）.TheREFERmethodindicatesthattherecipientoftheREFERrequestshouldcontact
athirdpartyusingthecontactinformationprovidedintheREFERrequest.RFC3515providesa
mechanismallowingthepartythatissendingtheREFERtobenotifiedoftheoutcomeofthe
referencedrequestwithaNOTIFYrequest.Thisimplementationusessubscriptionobjectsfor
REFERimplementation.ItreplacesthepreviousREFERimplementationandisintroduceddueto
standardmodifications.
6．Client-sideforking
inpreviousSIPToolkitversions,ifarequestwasforked,theSIPStackonthe
clientsideautomaticallyconnectedthefirstestablisheddialog,anddidnotallowtheapplicationto
chooseadifferentdialogorconnectmultipledialogs.Inthecurrentversion,theCall-legand
Subscriptionmoduleswereenhancedtoallowthisflexibility.
7．Mergingdisabling
ifaproxyforksarequestandeventuallythetworequestsareterminatedatthesameUserAgentServer（UAS）,theUASneedstomergethemintoonerequest.TherearecaseswheretheUASisagatewayandthereforewillwanttoavoidthemessagemerging.Thisflexibilityiscurrentlyavailable.
8．TransportLayerenhancements
twofunctionalitieswereadded.Anapplicationcannowblockincomingconnectionsevenbeforedatawasreceivedonthem.Thisletstheapplicationimplementawhite/blackIPaddresslistandhandlethedenialofserviceattacksinabetterway.Accesstotheincomingrawbuffersothattheapplicationcandumpbuffertofileordiscardthebuffer,forexample.
9．A-synchronousDNS
DNSfunctionalitywasenhancedandisnowa-synchronous,improvingperformanceespeciallyformulti-sessionapplicationssuchasgatewaysandservers.
10．DNSserverruntimeconfiguration
insomecases,itisrequiredtochangetheDNSserverthatisbeingusedatruntime.ThisisnowpossibleviatheSIPToolkitAPIs.
11．ManualPRACK
theapplicationcannowcontrolthesendingofPRACK/200.Thisisanadditiontotheautomaticfunctionalityavailableinpreviousversions.
12．Primitivescompilationflag
thisnewcompilationflagreplacestheEXTRA_LEANcompilationflag.Itremovesthedialoglayer,allowingapplicationtoworkdirectlyabovetheTransactionlayer.Additionally,itremovesspecificsupportofcertainheaders.Theapplicationcanstillusetheseheadersbyaddingspecificsupportintheapplicationitself.
13．MiddleLayerforlow-levelservices
theRADVISIONoperatingsystemabstractionlayerwaswrappedandsomeofitsAPIsarenowexposedsotheapplicationcanuseservicessuchastimersandselect.
14．Viaheadercontrol
someimplementations,suchaswhenusingaSTUN/TURNserver,requiremanualmodificationoftheViaheaderafterDNSwascompleted.Thiscontrolandflexibilityisnowpossible.
15．Subscriptionhighavailability
theRADVISIONSIPStackprovidesastoreandrestoremechanismthatenablestheapplicationtobackupsubscriptionsintheACTIVEstate.Backingupsubscriptionsletsapplicationdevelopersimplementredundancycapabilitiesintheirsystems,allowingback-upsystemsto“takeover”whentheprimarysystemgoesdown.Whenstoringanactivesubscription,allofthesubscriptionparametersarecopiedintoaconsecutivebuffer.Theapplicationcanthensavethisbufferanduseitwhenrestoringthebackupobject.
16．Authenticationenhancement
theauthenticationmechanismenablesaUserAgentClient（UAC）toproveauthenticitytoserversorproxieswhichrequireauthentication.TheSIPStacksupportsSIPauthenticationusingtheHTTPDigestSchemeasdescribedinRFC3261andRFC2617.Inthecurrentversion,supportofthe“auth-int”qualityofprotection（qop）wasadded.Forserver-sideauthentication,only“auth”qopissupported.
17．RequirementsforEnd-to-MiddleSecurityfortheSessionInitiationProtocol（SIP）【rfc4189】
ASessionInitiationProtocol（SIP）UserAgent（UA）doesnotalways
trustallintermediariesinitsrequestpathtoinspectitsmessage
bodiesand/orheaderscontainedinitsmessage.TheUAmightwantto
protectthemessagebodiesand/orheadersfromintermediaries,except
thosethatprovideservicesbasedonitscontent.Thissituation
requiresamechanismcalled"
end-to-middlesecurity"
tosecurethe
informationpassedbetweentheUAandintermediaries,whichdoesnot
interferewithend-to-endsecurity.Thisdocumentdefinesasetof
requirementsforamechanismtoachieveend-to-middlesecurity
18．TheStreamControlTransmissionProtocol（SCTP）asaTransportfortheSessionInitiationProtocol（SIP）【rfc4168】
ThisdocumentspecifiesamechanismforusageofSCTP（theStream
ControlTransmissionProtocol）asthetransportmechanismbetweenSIP
（SessionInitiationProtocol）entities.SCTPisanewprotocolthat
providesseveralfeaturesthatmayprovebeneficialfortransport
betweenSIPentitiesthatexchangealargeamountofmessages,
includinggatewaysandproxies.AsSIPistransport-independent,
supportofSCTPisarelativelystraightforwardprocess,nearly
identicaltosupportforTCP
19．SessionInitiationProtocol（SIP）-H.323
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