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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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<DIV class=pg></DIV><!-- bitmap and vector images are written here -->
<DIV class=im0><IMG height=3 src="002_17.files/002_17_1.jpg" width=558 
border=0></DIV>
<DIV class=im1><IMG height=2 src="002_17.files/002_17_2.jpg" width=558 
border=0></DIV>
<DIV class=im2><IMG height=3 src="002_17.files/002_17_3.jpg" width=558 
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<DIV class=im6><IMG height=2 src="002_17.files/002_17_7.jpg" width=134 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR>(<SPAN 
class=em4>续</SPAN>)</NOBR></SPAN> <SPAN class=ps1><NOBR><SPAN 
class=ft1>介质编码</SPAN></NOBR></SPAN> <SPAN class=ps2><NOBR><SPAN 
class=ft1>每个样本的</SPAN></NOBR></SPAN> <SPAN class=ps3><NOBR><SPAN 
class=ft1>缺省的</SPAN></NOBR></SPAN> <SPAN class=ps4><NOBR>RTP<SPAN 
class=em5>有效</SPAN></NOBR></SPAN> <SPAN class=ps5><NOBR>S=<SPAN 
class=em5>样本</SPAN>F=<SPAN class=em5>帧</SPAN></NOBR></SPAN> <SPAN 
class=ps6><NOBR><SPAN class=ft1>比特率</SPAN></NOBR></SPAN> <SPAN 
class=ps7><NOBR><SPAN class=ft1>采样速率</SPAN></NOBR></SPAN> <SPAN 
class=ps8><NOBR><SPAN class=ft1>帧速率</SPAN></NOBR></SPAN> <SPAN 
class=ps9><NOBR><SPAN class=ft1>包速率</SPAN></NOBR></SPAN> <SPAN 
class=ps10><NOBR><SPAN class=ft1>载荷类型</SPAN></NOBR></SPAN> <SPAN 
class=ps11><NOBR>GSM-HR(f)</NOBR></SPAN> <SPAN class=ps12><NOBR>8 
KHz</NOBR></SPAN> <SPAN class=ps13><NOBR>20ms</NOBR></SPAN> <SPAN 
class=ps14><NOBR><SPAN class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps15><NOBR>GSM-EFR(f)</NOBR></SPAN> <SPAN class=ps16><NOBR>8 
KHz</NOBR></SPAN> <SPAN class=ps17><NOBR>20ms</NOBR></SPAN> <SPAN 
class=ps18><NOBR><SPAN class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps19><NOBR>L8(s)</NOBR></SPAN> <SPAN class=ps20><NOBR>8</NOBR></SPAN> 
<SPAN class=ps21><NOBR><SPAN class=ft1>可变</SPAN></NOBR></SPAN> <SPAN 
class=ps22><NOBR>L16(s)</NOBR></SPAN> <SPAN class=ps23><NOBR>16</NOBR></SPAN> 
<SPAN class=ps24><NOBR><SPAN class=ft1>可变</SPAN></NOBR></SPAN> <SPAN 
class=ps25><NOBR>2<SPAN class=em5>信道时是</SPAN>10</NOBR></SPAN> <SPAN 
class=ps26><NOBR>1<SPAN class=em5>信道时是</SPAN>11</NOBR></SPAN> <SPAN 
class=ps27><NOBR><SPAN class=ft1>二者都在<SPAN 
class=em0>44100KHz</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps28><NOBR>LPC(f)</NOBR></SPAN> <SPAN class=ps29><NOBR>8 KHz</NOBR></SPAN> 
<SPAN class=ps30><NOBR>20ms</NOBR></SPAN> <SPAN class=ps31><NOBR>7</NOBR></SPAN> 
<SPAN class=ps32><NOBR>MPA(f)</NOBR></SPAN> <SPAN class=ps33><NOBR><SPAN 
class=ft1>可变</SPAN></NOBR></SPAN> <SPAN class=ps34><NOBR>90KHz<SPAN 
class=em5>时是</SPAN>14</NOBR></SPAN> <SPAN class=ps35><NOBR>PCM 
ALaw(s)</NOBR></SPAN> <SPAN class=ps36><NOBR>8</NOBR></SPAN> <SPAN 
class=ps37><NOBR><SPAN class=ft1>可变</SPAN></NOBR></SPAN> <SPAN 
class=ps38><NOBR>8</NOBR></SPAN> <SPAN class=ps39><NOBR>PCM 
&micro;Law(s)</NOBR></SPAN> <SPAN class=ps40><NOBR>8</NOBR></SPAN> <SPAN 
class=ps41><NOBR><SPAN class=ft1>可变</SPAN></NOBR></SPAN> <SPAN 
class=ps42><NOBR>0</NOBR></SPAN> <SPAN class=ps43><NOBR>QCELP(f)</NOBR></SPAN> 
<SPAN class=ps44><NOBR>8KHz</NOBR></SPAN> <SPAN 
class=ps45><NOBR>12</NOBR></SPAN> <SPAN 
class=ps46><NOBR>SX7300P(f)</NOBR></SPAN> <SPAN 
class=ps47><NOBR>8KHz</NOBR></SPAN> <SPAN class=ps48><NOBR>30ms</NOBR></SPAN> 
<SPAN class=ps49><NOBR><SPAN class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps50><NOBR>SX8300P(f)</NOBR></SPAN> <SPAN 
class=ps51><NOBR>8KHz</NOBR></SPAN> <SPAN class=ps52><NOBR>30ms</NOBR></SPAN> 
<SPAN class=ps53><NOBR><SPAN class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps54><NOBR>SX9600P(f)</NOBR></SPAN> <SPAN 
class=ps55><NOBR>8KHz</NOBR></SPAN> <SPAN class=ps56><NOBR>30ms</NOBR></SPAN> 
<SPAN class=ps57><NOBR><SPAN class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps58><NOBR>VDVI(s)</NOBR></SPAN> <SPAN class=ps59><NOBR><SPAN 
class=ft1>可变</SPAN></NOBR></SPAN> <SPAN class=ps60><NOBR><SPAN 
class=ft1>可变</SPAN></NOBR></SPAN> <SPAN class=ps61><NOBR><SPAN 
class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN class=ps62><NOBR>RED</NOBR></SPAN> 
<SPAN class=ps63><NOBR><SPAN class=ft1>参见文本说明</SPAN></NOBR></SPAN> <SPAN 
class=ps64><NOBR><SPAN class=ft1>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps65><NOBR><SPAN class=ft2>①<SPAN class=em0>a. n=0</SPAN><SPAN class=em1> 
</SPAN><SPAN class=em0>3</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps66><NOBR><SPAN class=ft2>②&nbsp;<SPAN class=em0>b</SPAN>.<SPAN 
class=em0>n=0</SPAN><SPAN class=em1> </SPAN><SPAN 
class=em0>3</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps67><NOBR><SPAN 
class=ft3>包语音技术的一个主要问题是由于编码和打包而造成的最小端到端延迟。图</SPAN></NOBR></SPAN> <SPAN 
class=ps68><NOBR><SPAN class=ft4>2-11<SPAN 
class=em2>中是一</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps69><NOBR><SPAN 
class=ft3>个简单参考模型，它可以用来计算端到端延迟、确定典型点对点或会议呼叫中的可接收值。</SPAN></NOBR></SPAN> <SPAN 
class=ps70><NOBR><SPAN 
class=ft3>语音质量和用户总体感受会受到编码和转换编码（介质转换）点，以及核心网络引入的</SPAN></NOBR></SPAN> <SPAN 
class=ps71><NOBR><SPAN class=ft3>延迟的影响。需要考察两种情况：</SPAN></NOBR></SPAN> <SPAN 
class=ps72><NOBR><SPAN class=ft4>1) <SPAN 
class=em2>跨越网段的呼叫，在端到端呼叫中不需要介质转换编码。</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps73><NOBR><SPAN class=ft4>2) <SPAN 
class=em2>在网段边界可能需要转换编码的混合拓扑。</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps74><NOBR><SPAN 
class=ft3>第一种情况可能是最佳情况，因为单向延迟包括每个信源的采样和打包间隔，缓冲足够</SPAN></NOBR></SPAN> <SPAN 
class=ps75><NOBR><SPAN 
class=ft3>的包可以在每个端点去除到达流的抖动。传输延迟可能是由于距离和网络路由器的包处理造</SPAN></NOBR></SPAN> <SPAN 
class=ps76><NOBR><SPAN 
class=ft3>成。如果使用了压缩和用户多路复用，路由器会增加延迟。如果实现了</SPAN></NOBR></SPAN> <SPAN 
class=ps77><NOBR><SPAN class=ft4>QoS<SPAN 
class=em2>路由方法，如</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps78><NOBR><SPAN 
class=ft4>RSVP<SPAN class=em2>，</SPAN><SPAN 
class=em2>那么会引起进一步的延迟。</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps79><NOBR><SPAN 
class=ft3>混合网络拓扑可能是两个子情况中的一个：</SPAN></NOBR></SPAN> <SPAN class=ps80><NOBR><SPAN 
class=ft4>A. <SPAN class=em2>基于</SPAN>IP<SPAN 
class=em2>的端到端拓扑，在网段边界使用不同的介质编码和信令协议。例如，这种情况</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps81><NOBR><SPAN class=ft3>可能是：<SPAN class=em3>A</SPAN>是一个<SPAN 
class=em3>MGCP</SPAN>域，网关<SPAN class=em3>B</SPAN>在<SPAN 
class=em3>H.323</SPAN>域，而连接它们的核心网络使用<SPAN 
class=em3>RTP</SPAN>介质传输，用</SPAN></NOBR></SPAN> <SPAN class=ps82><NOBR><SPAN 
class=ft4>RTCP<SPAN class=em2>分发统计数据。</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps83><NOBR><SPAN class=ft4>B. <SPAN class=em2>核心网络是现在的</SPAN>PSTN<SPAN 
class=em2>。</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps84><NOBR><SPAN 
class=ft3>在子情况<SPAN class=em3>A</SPAN>下，建立可互操作呼叫模型的问题，和初始化会话的信令机制、用户<SPAN 
class=em3>A</SPAN>支持的</SPAN></NOBR></SPAN> <SPAN class=ps85><NOBR><SPAN 
class=ft3>介质编码选项是否也被<SPAN class=em3>B</SPAN>支持、若用户<SPAN 
class=em3>B</SPAN>不支持该怎么办等等问题都是相关的。作为常识，在</SPAN></NOBR></SPAN> <SPAN 
class=ps86><NOBR><SPAN class=ft3>基于包的电话网络中，所有端点必须能够使用通常支持的编码格式中的一小列。<SPAN 
class=em3>G.711</SPAN>可以作</SPAN></NOBR></SPAN> <SPAN class=ps87><NOBR><SPAN 
class=ft3>为常用格式，但是如前所述，在<SPAN class=em3>RTP/UDP/IP/LLP</SPAN>上的<SPAN 
class=em3>G.711</SPAN>是一个浪费带宽的方案。<SPAN 
class=em3>RTP</SPAN>配</SPAN></NOBR></SPAN> <SPAN class=ps88><NOBR><SPAN 
class=ft3>置建议用<SPAN class=em3>DIV4</SPAN>作为第二选项提供给端点（它已经被<SPAN 
class=em3>MAC</SPAN>计算机支持），但是在设计<SPAN 
class=em3>VoIP</SPAN>网络</SPAN></NOBR></SPAN> <SPAN class=ps89><NOBR><SPAN 
class=ft3>的接入部分时，<SPAN class=em3>ITU-T</SPAN>建议的<SPAN 
class=em3>G</SPAN>系列的另一种编码格式是个更好的选择。</SPAN></NOBR></SPAN> <SPAN 
class=ps90><NOBR><SPAN class=ft5>第<SPAN 
class=em6>2</SPAN>章&nbsp;包网络的介质传输</SPAN></NOBR></SPAN> <SPAN 
class=ps91><NOBR><SPAN class=ft6>73</SPAN></NOBR></SPAN> <SPAN 
class=ps92><NOBR><SPAN class=ft7>文档</SPAN></NOBR></SPAN> <SPAN 
class=ps93><NOBR>LLP<SPAN class=em5>式携带</SPAN>IP<SPAN 
class=em5>的链路层协议。</SPAN></NOBR></SPAN> </BODY></HTML>
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