002_14.htm
来自「通讯类的标准。对要开发SS7的朋友有很大帮助的。（通讯协议）」· HTM 代码 · 共 237 行
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<DIV class=im1><IMG height=270 src="002_14.files/002_14_2.jpg" width=456
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class=ps0><NOBR>计质量的有意义的推论。这里的参与者指的是用于连接呼叫中各方的应用程序，以及那些能</NOBR></SPAN> <SPAN
class=ps1><NOBR>够在统计数据说明质量已下降到预先设定的可接收标准之下时，能够采取行动的应用程序。</NOBR></SPAN> <SPAN
class=ps2><NOBR>显然，<SPAN class=em0>RTCP</SPAN>服务需要用它的<SPAN
class=em0>SDES</SPAN>包标识一个用户，在跨越管理边界或不同网络的会话中特</NOBR></SPAN> <SPAN
class=ps3><NOBR>别重要（除了<SPAN class=em0>SDES</SPAN>包之外，信令协议不可能跨越多个<SPAN
class=em0>AS</SPAN>边界，传送明确的用户标识）。</NOBR></SPAN> <SPAN class=ps4><NOBR><SPAN
class=ft1>图<SPAN class=em3>2-10 </SPAN>一个<SPAN
class=em3>RTP</SPAN>混合器</SPAN></NOBR></SPAN> <SPAN
class=ps5><NOBR>和上面潜在的问题类似，读者应该注意</NOBR></SPAN> <SPAN class=ps6><NOBR><SPAN
class=ft2>SS7<SPAN class=em1>中的自动名称识别（ <SPAN class=em0>Automatic
Name</SPAN></SPAN></SPAN></NOBR></SPAN> <SPAN class=ps7><NOBR><SPAN
class=ft2>Identification<SPAN class=em1>，</SPAN>ANI<SPAN
class=em1>）</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps8><NOBR>。使用<SPAN
class=em0>RTP</SPAN>和<SPAN
class=em0>RTCP</SPAN>的新的电话服务将能够识别更多的用户信息，而不仅</NOBR></SPAN> <SPAN
class=ps9><NOBR>仅是它们的名称。</NOBR></SPAN> <SPAN class=ps10><NOBR>在会话中使用<SPAN
class=em0>RTCP</SPAN>需要带宽。如何以简单的方式分配带宽、当会话参与者随着时间改变</NOBR></SPAN> <SPAN
class=ps11><NOBR>时如何升级，这些问题的答案并不是显而易见的。一个想法是当会话参与增加时保持恒定的</NOBR></SPAN> <SPAN
class=ps12><NOBR><SPAN class=ft2>RTCP<SPAN
class=em1>带宽，但是要满足在不同实现间的相互可操作，可接受的</SPAN>RTCP<SPAN
class=em1>包产生间隔的最小值是</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps13><NOBR>多少？正在进行的工作提出了一种算法和它后面的论证，但是仍然有很多没有解答和需要整</NOBR></SPAN> <SPAN
class=ps14><NOBR>理的问题。<SPAN
class=em0>RTP/RTCP</SPAN>的关键问题在于，缺少有意义的应用以及来自已存在的案例分析的性能</NOBR></SPAN> <SPAN
class=ps15><NOBR>数据，这里指的是在跨越大规模和地理范围的拓扑上的应用。</NOBR></SPAN> <SPAN
class=ps16><NOBR>要让<SPAN class=em0>RTCP</SPAN>在网络调度中提供确实增加的价值，端点和网关需要遵照<SPAN
class=em0>RTP</SPAN>包中携带的信息</NOBR></SPAN> <SPAN class=ps17><NOBR>行事。如果<SPAN
class=em0>RTCP</SPAN>统计信息不是端点或网关所好，它们实际上能做什么呢？例如，当抖动使服</NOBR></SPAN> <SPAN
class=ps18><NOBR>务质量减小到可接收水平以下时，网关能够路由正在进行的呼叫吗？当拓扑升级到包括大规</NOBR></SPAN> <SPAN
class=ps19><NOBR>模并且不相同的端到端网段时，这几乎是不可能的。简单地说， <SPAN
class=em0>RTCP</SPAN>看起来最好的用途在于</NOBR></SPAN> <SPAN
class=ps20><NOBR>认识网络的健壮性和动态实现变化，以不断改善传输的服务质量。达到这个目的后，其他信</NOBR></SPAN> <SPAN
class=ps21><NOBR>息可以成为最高目标，以增加对拓扑中出现问题地方的了解。简单的端到端信息不足以告诉</NOBR></SPAN> <SPAN
class=ps22><NOBR>我们，在哪里服务质量会出现问题。</NOBR></SPAN> <SPAN class=ps23><NOBR>对<SPAN
class=em0>RTCP</SPAN>带宽分配起推动作用的概念是会话带宽。这是通过某种未定义方法获得的数字，</NOBR></SPAN> <SPAN
class=ps24><NOBR>尤其是在跨越网络边界的时候。在端到端呼叫的最简单情况下，每个端点的带宽是分配给一</NOBR></SPAN> <SPAN
class=ps25><NOBR>个用户的单向带宽。如果一个端点使用压缩语音，而且用于介质传输的带宽总共是</NOBR></SPAN> <SPAN
class=ps26><NOBR><SPAN class=ft2>Xbps<SPAN
class=em1>时，</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps27><NOBR>最初的建议是为<SPAN
class=em0>RTCP</SPAN>流量分配<SPAN class=em0>X</SPAN>的<SPAN class=em0>5%<SPAN
class=em1>，</SPAN></SPAN>以及一些对它进行划分的警告。分配给<SPAN
class=em0>RTCP</SPAN>的带宽</NOBR></SPAN> <SPAN class=ps28><NOBR><SPAN
class=ft3>70 <SPAN class=em2>IP </SPAN><SPAN
class=em4>电话技术：稳定的</SPAN><SPAN class=em2>VoIP</SPAN><SPAN
class=em4>服务集成</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps29><NOBR><SPAN
class=ft4>文档</SPAN></NOBR></SPAN> <SPAN class=ps30><NOBR><SPAN
class=ft5>信源</SPAN></NOBR></SPAN> <SPAN class=ps31><NOBR><SPAN
class=ft5>信源</SPAN></NOBR></SPAN> <SPAN class=ps32><NOBR><SPAN
class=ft5>信源</SPAN></NOBR></SPAN> <SPAN class=ps33><NOBR><SPAN
class=ft5>介质网关</SPAN></NOBR></SPAN> <SPAN class=ps34><NOBR><SPAN
class=ft5>介质网关</SPAN></NOBR></SPAN> <SPAN class=ps35><NOBR><SPAN
class=ft5>内部网</SPAN></NOBR></SPAN> <SPAN class=ps36><NOBR><SPAN
class=ft5>终端用户</SPAN></NOBR></SPAN> <SPAN class=ps37><NOBR><SPAN
class=ft5>网关混合器</SPAN></NOBR></SPAN> <SPAN class=ps38><NOBR><SPAN
class=ft6>IP<SPAN class=em5>网络</SPAN></SPAN></NOBR></SPAN> </BODY></HTML>
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