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📁 通讯类的标准。对要开发SS7的朋友有很大帮助的。（通讯协议）
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<META content="MSHTML 6.00.2600.0" name=GENERATOR></HEAD>
<BODY>
<DIV class=pg></DIV><!-- bitmap and vector images are written here -->
<DIV class=im0><IMG height=64 src="003_34.files/right.jpg" width=563 
border=0></DIV>
<DIV class=im1><IMG height=442 src="003_34.files/003_34_2.jpg" width=495 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR><SPAN 
class=ft0>第<SPAN class=em2>3</SPAN>章&nbsp;语音电话的基本呼叫控制</SPAN></NOBR></SPAN> <SPAN 
class=ps1><NOBR><SPAN class=ft1>133</SPAN></NOBR></SPAN> <SPAN 
class=ps2><NOBR><SPAN class=ft2>文档</SPAN></NOBR></SPAN> <SPAN 
class=ps3><NOBR><SPAN class=ft3>图<SPAN class=em3>3-23 
&nbsp;&nbsp;ISUP</SPAN>到<SPAN class=em3>PSTN</SPAN>网关的呼叫终止</SPAN></NOBR></SPAN> 
<SPAN class=ps4><NOBR>当被叫方挂机时，介质网关发送一条<SPAN class=em1>NTFY</SPAN>命令到<SPAN 
class=em1>MGC<SPAN class=em0>，</SPAN></SPAN>通知这个事件。命令语法和图</NOBR></SPAN> <SPAN 
class=ps5><NOBR><SPAN class=ft5>3-21<SPAN class=em0>中基本</SPAN>MGCP<SPAN 
class=em0>呼叫终止中分析的例子类似。</SPAN>MGC<SPAN class=em0>的第一件事情是删除</SPAN>MG<SPAN 
class=em0>和</SPAN>PSTN<SPAN class=em0>网关之</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps6><NOBR>间的连接，清除呼叫场景。<SPAN class=em1>DLCX</SPAN>命令发出后，<SPAN 
class=em1>PSTN</SPAN>网关和<SPAN class=em1>MG</SPAN>用带有性能参数的正<SPAN 
class=em1>ACK</SPAN>确</NOBR></SPAN> <SPAN class=ps7><NOBR>认。同时，<SPAN 
class=em1>MGC</SPAN>向起始交换机发送<SPAN class=em1>ISUP REL</SPAN>命令，以释放呼叫。在<SPAN 
class=em1>OLE</SPAN>中，<SPAN class=em1>REL</SPAN>命令导致</NOBR></SPAN> <SPAN 
class=ps8><NOBR><SPAN class=ft5>DISCONNECT<SPAN 
class=em0>命令被发送到呼叫发起方。信令通过交换</SPAN>RELEASE<SPAN class=em0>和</SPAN>RELEASE 
COMPLETE</SPAN></NOBR></SPAN> <SPAN 
class=ps9><NOBR>结束，这时呼叫场景可以被认为已经清除。</NOBR></SPAN> <SPAN class=ps10><NOBR>当<SPAN 
class=em1>SS7</SPAN>网络上发送<SPAN 
class=em1>REL</SPAN>命令时，计帐和收费信息会停止。在所有的清理工作之后，呼叫代</NOBR></SPAN> <SPAN 
class=ps11><NOBR>理通知<SPAN 
class=em1>MG</SPAN>上的端点，查找新的摘机事件以接受新的呼叫尝试。这时，呼叫终止过程结束。</NOBR></SPAN> <SPAN 
class=ps12><NOBR><SPAN class=ft5>1. PSTN<SPAN class=em4>上</SPAN>SIP<SPAN 
class=em4>和</SPAN>RGW<SPAN class=em4>客户间的呼叫建立</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps13><NOBR>在这种情况下，介质网关控制器的构造支持<SPAN class=em1>SIP</SPAN>客户和<SPAN 
class=em1>MGCP</SPAN>协议控制的<SPAN class=em1>MG</SPAN>上的端点端</NOBR></SPAN> <SPAN 
class=ps14><NOBR>之间的呼叫建立。基本呼叫流信令从<SPAN class=em1>SIP</SPAN>呼叫代理到<SPAN 
class=em1>MGC </SPAN>的<SPAN class=em1>INVITE</SPAN>开始，它被映射为<SPAN 
class=em1>CRCX</SPAN></NOBR></SPAN> <SPAN 
class=ps15><NOBR>命令，并发送到控制被叫端点的介质网关。信令过程如图<SPAN 
class=em1>3-24</SPAN>所示。</NOBR></SPAN> <SPAN class=ps16><NOBR>一旦<SPAN 
class=em1>MGC</SPAN>收到<SPAN class=em1>INVITE</SPAN>消息，必须确定被叫端点的位置。如果<SPAN 
class=em1>MGC</SPAN>没有立即知道被叫方</NOBR></SPAN> <SPAN 
class=ps17><NOBR>的位置，那么可能需要定位服务。它可能和执行一个简单的<SPAN class=em1>DNS</SPAN>查询来翻译<SPAN 
class=em1>URL</SPAN>一样简单，</NOBR></SPAN> <SPAN 
class=ps18><NOBR>也可能实现其他更复杂的服务，作为服务设计的一部分以支持用户移动。一旦端点已被标识，</NOBR></SPAN> <SPAN 
class=ps19><NOBR><SPAN class=ft5>CRCX<SPAN 
class=em0>命令已被发送以说明希望建立呼叫，那么将返回</SPAN>SIP<SPAN class=em0>“</SPAN>trying<SPAN 
class=em0>”</SPAN><SPAN class=em0>信息码到发起端点。当端</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps20><NOBR>点以<SPAN class=em1>ACK</SPAN>应答时，<SPAN 
class=em1>MGC</SPAN>会请求电话振铃，并请求摘机状态的通知。同时将发送<SPAN class=em1>SIP<SPAN 
class=em0>“</SPAN>ringing<SPAN class=em0>”</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps21><NOBR><SPAN class=ft6>PSTN<SPAN 
class=em5>端点</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps22><NOBR><SPAN 
class=ft7>起始本地交换机</SPAN></NOBR></SPAN> <SPAN class=ps23><NOBR><SPAN 
class=ft7>PSTN网</SPAN></NOBR></SPAN> <SPAN class=ps24><NOBR><SPAN 
class=ft7>介质网关</SPAN></NOBR></SPAN> <SPAN class=ps25><NOBR><SPAN 
class=ft7>用户</SPAN></NOBR></SPAN> <SPAN class=ps26><NOBR><SPAN 
class=ft7>挂机</SPAN></NOBR></SPAN> <SPAN class=ps27><NOBR><SPAN 
class=ft7>挂机</SPAN></NOBR></SPAN> <SPAN class=ps28><NOBR><SPAN 
class=ft7>和TGW断开连接</SPAN></NOBR></SPAN> <SPAN class=ps29><NOBR><SPAN 
class=ft7>用户挂机</SPAN></NOBR></SPAN> <SPAN class=ps30><NOBR><SPAN 
class=ft7>性能数据</SPAN></NOBR></SPAN> <SPAN class=ps31><NOBR><SPAN 
class=ft6>(7)</SPAN></NOBR></SPAN> <SPAN class=ps32><NOBR><SPAN 
class=ft7>再次查找摘机</SPAN></NOBR></SPAN> <SPAN class=ps33><NOBR><SPAN 
class=ft7>介质网关控制器</SPAN></NOBR></SPAN> </BODY></HTML>

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