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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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<BODY>
<DIV class=pg></DIV><!-- bitmap and vector images are written here -->
<DIV class=im0><IMG height=64 src="002_25.files/right.jpg" width=563 
border=0></DIV>
<DIV class=im1><IMG height=25 src="002_25.files/002_25_2.jpg" width=230 
border=0></DIV>
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<DIV class=im4><IMG height=36 src="002_25.files/002_25_5.jpg" width=362 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR>传输<SPAN 
class=em0>DTMF</SPAN>、其他音调和信令事件的另一种可能方法是，让信令协议用带外信令完成。这</NOBR></SPAN> <SPAN 
class=ps1><NOBR>种方法自身也有问题，在跨越不同域时可能不被支持，这种情况似的带内</NOBR></SPAN> <SPAN 
class=ps2><NOBR><SPAN class=ft1>DTMF<SPAN 
class=em1>有效载荷成</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps3><NOBR>为跨越边界的惟一选择。即使这样，动态分配的带内有效载荷类型也可能是不相同的，或者</NOBR></SPAN> <SPAN 
class=ps4><NOBR>是跨域可协商的，这会引起建立呼叫或<SPAN 
class=em0>DTMF</SPAN>端到端信令时的重大问题。显然，现在对于所</NOBR></SPAN> <SPAN 
class=ps5><NOBR>有的<SPAN class=em0>5</SPAN>类特性激活<SPAN 
class=em2>/</SPAN>停用，本地交换机都需要看到<SPAN 
class=em0>DTMF</SPAN>数字，或者是带内的，或者通过带外信</NOBR></SPAN> <SPAN 
class=ps6><NOBR>令。在两种情况下都要用它可理解的方式。</NOBR></SPAN> <SPAN 
class=ps7><NOBR>一般的音调识别和传输中可能的警告是，在向端点的边缘网络上存在<SPAN 
class=em0>MF</SPAN>信令干线。在这</NOBR></SPAN> <SPAN class=ps8><NOBR>种情况下，数字会以带内<SPAN 
class=em0>MF</SPAN>对编码方式出现。<SPAN 
class=em0>MF</SPAN>干线没有带外信令协议，网关除了把带内</NOBR></SPAN> <SPAN 
class=ps9><NOBR>到达的<SPAN class=em0>DTMF</SPAN>数字作为<SPAN 
class=em0>RTP</SPAN>有效载荷、在<SPAN class=em0>PSTN</SPAN>干线上以精确持续时间的<SPAN 
class=em0>MF</SPAN>音调发送出去外，</NOBR></SPAN> <SPAN 
class=ps10><NOBR>别无选择。这意味着需要知道网关在干线上的带内信令需要，还要使有效载荷中表示的</NOBR></SPAN> <SPAN 
class=ps11><NOBR><SPAN class=ft1>DTMF<SPAN class=em1>数字同步适应相应的</SPAN>MF<SPAN 
class=em1>音调同步。</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps12><NOBR><SPAN 
class=ft1>6. RTP<SPAN class=em3>抖动和延迟计算</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps13><NOBR>抖动是<SPAN 
class=em0>RTCP</SPAN>发送者和接收者报告传送的统计数据之一。抖动的定义是一个事件实际发生</NOBR></SPAN> <SPAN 
class=ps14><NOBR>和期望发生之间的时间差。<SPAN 
class=em0>RTP</SPAN>包的抖动值是通过平滑包到达间延迟的连续平均值得到的。</NOBR></SPAN> <SPAN 
class=ps15><NOBR>图<SPAN class=em0>2-12</SPAN>可以帮助计算抖动。</NOBR></SPAN> <SPAN 
class=ps16><NOBR><SPAN class=ft2>图<SPAN class=em4>2-12 
&nbsp;&nbsp;</SPAN>计算<SPAN class=em4>RTP</SPAN>到达间抖动</SPAN></NOBR></SPAN> <SPAN 
class=ps17><NOBR>关于包的传送时间，接收者最先了解到的是它的时间戳和接收者当前时间之间的差值。</NOBR></SPAN> <SPAN 
class=ps18><NOBR>该差值是：</NOBR></SPAN> <SPAN 
class=ps19><NOBR>表示从包被盖上戳开始，到它在信源的输出链路上被实际发送为止，其中的传送时间和某</NOBR></SPAN> <SPAN 
class=ps20><NOBR>个机器时间。<SPAN class=em0>RFC 1889</SPAN>建议使用<SPAN 
class=em0>NTP</SPAN>来完成端点的端到端同步，但是也有非同步端点实现存在。</NOBR></SPAN> <SPAN 
class=ps21><NOBR>包<SPAN class=em0>N</SPAN>和<SPAN 
class=em0>N-1</SPAN>之间增加的延迟差（二阶效应）是：</NOBR></SPAN> <SPAN 
class=ps22><NOBR>包抖动保持为平稳后的连续和：</NOBR></SPAN> <SPAN class=ps23><NOBR>图<SPAN 
class=em0>2-13a</SPAN>和图<SPAN 
class=em0>2-13b</SPAN>中是两个来自典型抖动测量的跟踪记录。</NOBR></SPAN> <SPAN 
class=ps24><NOBR><SPAN class=ft3>第<SPAN 
class=em5>2</SPAN>章&nbsp;包网络的介质传输</SPAN></NOBR></SPAN> <SPAN 
class=ps25><NOBR><SPAN class=ft4>81</SPAN></NOBR></SPAN> <SPAN 
class=ps26><NOBR><SPAN class=ft5>文档</SPAN></NOBR></SPAN> <SPAN 
class=ps27><NOBR><SPAN class=ft6>发送第<SPAN 
class=em6>N-1</SPAN>个包</SPAN></NOBR></SPAN> <SPAN class=ps28><NOBR><SPAN 
class=ft6>接收第<SPAN class=em6>N-1</SPAN>个包</SPAN></NOBR></SPAN> <SPAN 
class=ps29><NOBR><SPAN class=ft6>接收第<SPAN 
class=em6>N-1</SPAN>个包</SPAN></NOBR></SPAN> <SPAN class=ps30><NOBR><SPAN 
class=ft6>第<SPAN class=em6>N-1</SPAN>个包</SPAN></NOBR></SPAN> <SPAN 
class=ps31><NOBR><SPAN class=ft6>第<SPAN 
class=em6>N</SPAN>个包</SPAN></NOBR></SPAN> <SPAN class=ps32><NOBR><SPAN 
class=ft6>发送第<SPAN class=em6>N</SPAN>个包</SPAN></NOBR></SPAN> <SPAN 
class=ps33><NOBR><SPAN class=ft6>传输时间</SPAN></NOBR></SPAN> <SPAN 
class=ps34><NOBR><SPAN class=ft6>传输时间</SPAN></NOBR></SPAN> </BODY></HTML>

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