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border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR><SPAN
class=ft0>第<SPAN class=em4>3</SPAN>章 语音电话的基本呼叫控制</SPAN></NOBR></SPAN> <SPAN
class=ps1><NOBR><SPAN class=ft1>131</SPAN></NOBR></SPAN> <SPAN
class=ps2><NOBR><SPAN class=ft2>文档</SPAN></NOBR></SPAN> <SPAN
class=ps3><NOBR><SPAN class=ft3>(<SPAN class=em5>续</SPAN>)</SPAN></NOBR></SPAN>
<SPAN class=ps4><NOBR>指令<SPAN class=em2>/</SPAN>响应</NOBR></SPAN> <SPAN
class=ps5><NOBR>参</NOBR></SPAN> <SPAN class=ps6><NOBR>数</NOBR></SPAN> <SPAN
class=ps7><NOBR>语法说明</NOBR></SPAN> <SPAN
class=ps8><NOBR>在这一点上,两部分都准备发送和接收其他呼叫,两个端点并没有附加的获利。但是该例中的呼叫信息流在单纯</NOBR></SPAN>
<SPAN class=ps9><NOBR>化这一点上并没有变复杂,即使是如今<SPAN
class=em2>SS7</SPAN>电话支持的一些更加复杂的特性,这个话题在本文的后面会继续讨论。</NOBR></SPAN> <SPAN
class=ps10><NOBR><SPAN
class=ft5>这个呼叫流的例子不应该使读者对实际提供电话服务的复杂性产生误解。实现电话特性</SPAN></NOBR></SPAN> <SPAN
class=ps11><NOBR><SPAN class=ft5>的呼叫流非常复杂。即使我们以最大胆的方式假定<SPAN
class=em0>PSTN</SPAN>已经消失,仍然需要替换当前电话网</SPAN></NOBR></SPAN> <SPAN
class=ps12><NOBR><SPAN class=ft5>络中支持的特性集。在这个考虑中还包括<SPAN
class=em0>99.999%</SPAN>的网络可靠度,这正是我们到现在为止一直</SPAN></NOBR></SPAN> <SPAN
class=ps13><NOBR><SPAN
class=ft5>享有的可靠度。这是一个很难满足的要求,但是除非可靠性和可依赖性已被证实,否则可行</SPAN></NOBR></SPAN> <SPAN
class=ps14><NOBR><SPAN class=ft5>的<SPAN
class=em0>VoIP</SPAN>和集成服务将不会得到广泛应用。</SPAN></NOBR></SPAN> <SPAN
class=ps15><NOBR><SPAN
class=ft5>主要的线路电话服务受联邦政府控制。如果供应商希望出售本地电话服务,它必须无异</SPAN></NOBR></SPAN> <SPAN
class=ps16><NOBR><SPAN class=ft5>议地同意管理要求。管理要求的一些条款包含了操作员服务、<SPAN
class=em0>911</SPAN>紧急呼叫、法律强制的监听、</SPAN></NOBR></SPAN> <SPAN
class=ps17><NOBR><SPAN class=ft5>允许的网络停工期等。<SPAN
class=em0>PSTN</SPAN>也包含世界的其他部分,任何新的信令方法都必须和国际网络内</SPAN></NOBR></SPAN> <SPAN
class=ps18><NOBR><SPAN
class=ft5>的信令协作进行交互信令,而它们也受到本地政府的管理。当我们在这个全景图中加入未来</SPAN></NOBR></SPAN> <SPAN
class=ps19><NOBR><SPAN class=ft5>的智能网络(<SPAN class=em0>Intelligent
Network</SPAN>,<SPAN
class=em0>IN</SPAN>)的要求时,前面的呼叫流仅仅是无数复杂的呼叫流中</SPAN></NOBR></SPAN> <SPAN
class=ps20><NOBR><SPAN
class=ft5>一个非常基本的例子,随着平台设计过程中的变化会导致无数呼叫流的出现。</SPAN></NOBR></SPAN> <SPAN
class=ps21><NOBR><SPAN class=ft6>3.4 <SPAN
class=em6>异类呼叫建立——将</SPAN>SS7<SPAN class=em6>映射到基于</SPAN>IP<SPAN
class=em6>的呼叫控制</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps22><NOBR><SPAN
class=ft5>跨过<SPAN class=em0>PSTN</SPAN>的呼叫建立涉及到基于<SPAN
class=em0>IP</SPAN>的信令栈到<SPAN class=em0>SS7/ISUP</SPAN>协议的映射。在图<SPAN
class=em0>3-22</SPAN>中的呼叫</SPAN></NOBR></SPAN> <SPAN class=ps23><NOBR><SPAN
class=ft5>流例子 里,能够发出<SPAN class=em0>PRI</SPAN>命令的用户设备(例如<SPAN
class=em0>PBX<SPAN
class=em1>)</SPAN></SPAN>正在为一个用户服务,该用户正在向</SPAN></NOBR></SPAN> <SPAN
class=ps24><NOBR><SPAN class=ft5>一个基于<SPAN
class=em0>IP</SPAN>的介质网关控制器管理的端点发出呼叫。这个实例的呼叫建立部分只显示了最基</SPAN></NOBR></SPAN>
<SPAN class=ps25><NOBR><SPAN class=ft5>本的<SPAN class=em0>ISUP</SPAN>消息<SPAN
class=em0>IAM</SPAN>、<SPAN class=em0>ACM</SPAN>和<SPAN
class=em0>ANM</SPAN>。在建立和管理呼叫的过程中,信令网络可能会在发送方</SPAN></NOBR></SPAN> <SPAN
class=ps26><NOBR><SPAN class=ft5>的本地交换机和终止呼叫代理之间使用更大的<SPAN
class=em0>ISUP</SPAN>消息集。因此,信令平台实现被寄希望于</SPAN></NOBR></SPAN> <SPAN
class=ps27><NOBR><SPAN class=ft5>支持基于<SPAN class=em0>ANSI</SPAN>和国际网络的<SPAN
class=em0>ISUP</SPAN>信息全集。</SPAN></NOBR></SPAN> <SPAN class=ps28><NOBR><SPAN
class=ft5>表<SPAN class=em0>3-10</SPAN>是图<SPAN
class=em0>3-22</SPAN>中呼叫流的事务的排练。</SPAN></NOBR></SPAN> <SPAN
class=ps29><NOBR><SPAN class=ft7>表<SPAN class=em7>3-10 </SPAN>从<SPAN
class=em7>PSTN</SPAN>到<SPAN class=em7>RGW</SPAN>的呼叫设置信令</SPAN></NOBR></SPAN>
<SPAN class=ps30><NOBR>事务处理</NOBR></SPAN> <SPAN class=ps31><NOBR>参</NOBR></SPAN>
<SPAN class=ps32><NOBR>数</NOBR></SPAN> <SPAN
class=ps33><NOBR>注意和解释</NOBR></SPAN> <SPAN class=ps34><NOBR>安装(从<SPAN
class=em2>PSTN</SPAN></NOBR></SPAN> <SPAN class=ps35><NOBR>用户到当地交换</NOBR></SPAN>
<SPAN class=ps36><NOBR>机的<SPAN class=em2>PRI</SPAN>信息)</NOBR></SPAN> <SPAN
class=ps37><NOBR>(<SPAN class=em2>1</SPAN>)</NOBR></SPAN> <SPAN
class=ps38><NOBR><SPAN class=ft3>IAM</SPAN></NOBR></SPAN> <SPAN
class=ps39><NOBR>(从<SPAN class=em2>OLE</SPAN>到相邻交</NOBR></SPAN> <SPAN
class=ps40><NOBR>换机的<SPAN class=em2>SS7</SPAN>消息)</NOBR></SPAN> <SPAN
class=ps41><NOBR>(<SPAN class=em2>2</SPAN>)</NOBR></SPAN> <SPAN
class=ps42><NOBR>改编自<SPAN class=em2>Huitema</SPAN>、<SPAN
class=em2>Andreasen</SPAN>、<SPAN class=em2>Arango</SPAN>和<SPAN
class=em2>Prakash</SPAN>的一个例子。</NOBR></SPAN> <SPAN class=ps43><NOBR>一接收到<SPAN
class=em2>SETUP</SPAN>消息,源当地</NOBR></SPAN> <SPAN class=ps44><NOBR>交换机(<SPAN
class=em2>OLE</SPAN>)会首先执行<SPAN class=em2>LNP</SPAN></NOBR></SPAN> <SPAN
class=ps45><NOBR>查询(但不显示),然后开始启动</NOBR></SPAN> <SPAN class=ps46><NOBR><SPAN
class=ft3>SS7<SPAN class=em3>信号</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps47><NOBR>在<SPAN class=em2>ISUP</SPAN>组中,这是最综合和</NOBR></SPAN> <SPAN
class=ps48><NOBR>复杂的消息。此例显示了横越从</NOBR></SPAN> <SPAN class=ps49><NOBR><SPAN
class=ft3>OLE<SPAN class=em3>到掌握</SPAN>VoIP<SPAN
class=em3>媒质网关控制器的</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps50><NOBR>交换机间的中续断。通常,在到达</NOBR></SPAN> <SPAN
class=ps51><NOBR>终止交换机之前,有多个中续断</NOBR></SPAN> <SPAN class=ps52><NOBR><SPAN
class=ft3>IAM<SPAN class=em3>携带着正向电路信息,</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps53><NOBR>载流子鉴定代码,被叫方号码,</NOBR></SPAN> <SPAN
class=ps54><NOBR>和可选参数,例如为电路的连续</NOBR></SPAN> <SPAN
class=ps55><NOBR>性测试和可能的呼叫方号码的</NOBR></SPAN> <SPAN
class=ps56><NOBR>请求</NOBR></SPAN> <SPAN class=ps57><NOBR><SPAN
class=ft3>Q.931<SPAN class=em3>信息启动呼叫建立。他</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps58><NOBR>尽可能少地携带关于呼叫所需求</NOBR></SPAN> <SPAN
class=ps59><NOBR>的电路类型的信息</NOBR></SPAN> <SPAN class=ps60><NOBR>在<SPAN
class=em2>CAS</SPAN>信号的例子中,<SPAN class=em2>OLE</SPAN>将发送信号通知<SPAN
class=em2>CPE</SPAN>收集数字。在<SPAN
class=em2>OLE</SPAN>分析完数字后,流动信号能应用,并且其</NOBR></SPAN> <SPAN
class=ps61><NOBR>准备发送<SPAN class=em2>ISUP</SPAN>初始地址消息</NOBR></SPAN> <SPAN
class=ps62><NOBR>流动呼叫中的步骤<SPAN class=em2>3</SPAN>到<SPAN
class=em2>10</SPAN>代表一基本的<SPAN class=em2>MGCP</SPAN>呼叫设置,就如同在图<SPAN
class=em2>3-20</SPAN>所看的例子。<SPAN class=em2>MGC</SPAN>仅仅建立被叫端点</NOBR></SPAN>
<SPAN class=ps63><NOBR>和<SPAN
class=em2>PSTN</SPAN>网关上的端点间的连接,此连接映射接收引入呼叫的电路。若需要任何媒质的转换代码,网关会完成。当确</NOBR></SPAN>
<SPAN class=ps64><NOBR>认了请求<SPAN class=em2>MG</SPAN>拨被叫方的电话号码(端点)的消息后,在步骤<SPAN
class=em2>11</SPAN>中<SPAN class=em2>MGC</SPAN>会发送<SPAN
class=em2>ISUP</SPAN>地址完整消息(<SPAN class=em2>ACM</SPAN>)到交换机,</NOBR></SPAN> <SPAN
class=ps65><NOBR>交换机发送<SPAN class=em2>IAM<SPAN
class=em3>(</SPAN></SPAN>在此例中是<SPAN class=em2>OLE<SPAN
class=em3>)</SPAN></SPAN>。<SPAN class=em2>ACM</SPAN>表明成功地传送了<SPAN
class=em2>IAM<SPAN class=em3>,</SPAN></SPAN>而且若一切运行良好的话,电话正在振铃。现在</NOBR></SPAN>
<SPAN class=ps66><NOBR>等待某人来接电话。一旦<SPAN class=em2>OLE</SPAN>接收<SPAN
class=em2>ACM<SPAN class=em3>,</SPAN></SPAN>他发送<SPAN class=em2>Q.931
ALERTING</SPAN>消息到发呼叫方。那时,打电话者听到铃响</NOBR></SPAN> </BODY></HTML>
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