文档介绍：VoLTE呼叫SIP信令分析 VoLTE主叫与网络侧交互流程1     INVITE   /**UE向网侧发起INVITE请求,sip:*************@**********是被叫的号码,SIP/*/INVITEsip:*************@.;user=phoneSIP//**电话是**********呼出的,*/From:<sip:+86*************@ims.>;ecbow /**被叫电话是***********/To:"**********"<sip:*************@.;user=phone>P-Preferred-Identity:<sip:+86*************@ims.>Contact:<sip:******@:5060>;+="<urn:gsma:imei:86527602-000237-4>";+-ref="urn%%3Aurn-7%%3A3gpp-";+-call;+.-alerting;ept-Contact:*;+-ref="urn%%3Aurn-7%%3A3gpp-"Request-Disposition:fork/**E-UTRAN表示4GTDD是TDD制式,现在支持TDD和FDD的4G通话*/P-work-Info:3GPP-E-UTRAN-TDD;utran-cell-id-3gpp="460600000000A06A"/**打开了precondition*/Supported:100rel,join,norefersub,precondition,replaces,timerAllow:INVITE,ACK,BYE,CANCEL,UPDATE,INFO,PRACK,SUBSCRIBE,NOTIFY,REFERSession-Expires:1800Min-SE:90Call-ID:******@:1INVITE/**VoLTE呼叫经过的网络节点数最大值*/Max-Forwards:70User-Agent:RCS-client/-VxW/:SIP/.:5060;branch=z9hG4bKddecbowMmawMmxhaaGL2;rportContent-Type:application/sdpContent-Length:833v=0o==-c==00m=audio31004RTP/AVP108106101102/***********************AMB-WB宽带,a开头的字段是详细解释有4种编码方式:宽带108窄带101宽带DTMF描述101宽带DTMF描述102*/a=rtpmap:108AMR-WB/16000/1a=fmtp:108mode-change-capability=2;max-red=0/************************AMR就表示AMR-NB(窄带)********************/a=rtpmap:106AMR/8000/1a=fmtp:106mode-change-capability=2;max-red=0a=rtpmap:101telephone-event/16000a=fmtp:1010-15a=rtpmap:102telephone-event/8000a=fmtp:1020-15/**************表示1帧/20ms***************/a=ptime:20/***************表示1帧/240秒是个界限,网络侧不能低于这个速率*****************/a=maxptime:240/***************SDP协商****************/a=sendrecv/****************curr:当前状态Preconditiontype:qosstatustype:local****************/a=curr:qoslocalnonea=curr:qosremotenone/****************des:期望derectiontag:sen