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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_16.files/002_16_1.jpg" width=558 
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<DIV class=im1><IMG height=2 src="002_16.files/002_16_2.jpg" width=558 
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<DIV class=im3><IMG height=64 src="002_16.files/left.jpg" width=564 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR><SPAN 
class=ft0>会碰到与<SPAN class=em1>RTCP</SPAN>通信量生成有关的升级问题。</SPAN></NOBR></SPAN> 
<SPAN class=ps1><NOBR><SPAN class=ft1>IETF<SPAN 
class=em0>工作组已经意识到这个问题，并建议新的</SPAN>SDP<SPAN 
class=em0>扩展，使用带外信令在端点建立</SPAN>RTCP</SPAN></NOBR></SPAN> <SPAN 
class=ps2><NOBR><SPAN class=ft0>带宽。格式是：</SPAN></NOBR></SPAN> <SPAN 
class=ps3><NOBR><SPAN class=ft1>b=RS:&lt;<SPAN class=em0>带宽值</SPAN>&gt;<SPAN 
class=em0>，</SPAN><SPAN class=em0>适用于发送者报告</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps4><NOBR><SPAN class=ft1>b=RR:&lt;<SPAN class=em0>带宽值</SPAN>&gt;<SPAN 
class=em0>，</SPAN><SPAN class=em0>适用于接收者报告</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps5><NOBR><SPAN class=ft0>两个值均以比特每秒为单位，以免使用分数符号。如果信令协议不支持<SPAN 
class=em1>RTCP</SPAN>带宽值，上</SPAN></NOBR></SPAN> <SPAN class=ps6><NOBR><SPAN 
class=ft0>面讨论的缺省说明可以用来在端点为<SPAN class=em1>RTCP</SPAN>包建立最小传输间隔。例如，如果为使用<SPAN 
class=em1>32Kbps</SPAN>的</SPAN></NOBR></SPAN> <SPAN class=ps7><NOBR><SPAN 
class=ft0>语音定义<SPAN class=em1>SDP</SPAN>属性为：</SPAN></NOBR></SPAN> <SPAN 
class=ps8><NOBR><SPAN class=ft1>b=RS</SPAN></NOBR></SPAN> <SPAN 
class=ps9><NOBR><SPAN class=ft0>并且没有设置<SPAN class=em1>RTCP</SPAN>参数，<SPAN 
class=em1>5%</SPAN>准则会分配<SPAN class=em1>1600 bps</SPAN>给<SPAN 
class=em1>RTCP</SPAN>包。</SPAN></NOBR></SPAN> <SPAN class=ps10><NOBR><SPAN 
class=ft1>2. RTP<SPAN class=em6>和用户配置</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps11><NOBR><SPAN class=ft1>RTP<SPAN class=em0>配置最早是在</SPAN>RFC1890<SPAN 
class=em0>中讨论，但是，正在进行的工作已向</SPAN>IETF<SPAN 
class=em0>提交草案，提出增</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps12><NOBR><SPAN 
class=ft0>加原来的规范。</SPAN></NOBR></SPAN> <SPAN class=ps13><NOBR><SPAN 
class=ft0>在本节中将讨论正在进行的一部分工作，它来自<SPAN 
class=em1>AVT</SPAN>工作组“具有最少控制的音频视频</SPAN></NOBR></SPAN> <SPAN 
class=ps14><NOBR><SPAN class=ft0>会议的<SPAN 
class=em1>RTP</SPAN>配置”的提议。我们将要指出，从信令和呼叫管理的角度，不管是跨过公用还是</SPAN></NOBR></SPAN> 
<SPAN class=ps15><NOBR><SPAN class=ft0>专用的独立<SPAN 
class=em1>AS</SPAN>域，在提供端到端基于<SPAN 
class=em1>IP</SPAN>电话的愿望中会出现一些典型问题。我们可能会得出</SPAN></NOBR></SPAN> <SPAN 
class=ps16><NOBR><SPAN 
class=ft0>结论：实际上，用于建立、维护和终止这样的多用户会议的控制到底没有预期的那么少。</SPAN></NOBR></SPAN> <SPAN 
class=ps17><NOBR><SPAN class=ft0>如前所述，<SPAN 
class=em1>RTP</SPAN>配置是介质编码到有效载荷格式的映射，但是配置仍然有其他隐含的因素</SPAN></NOBR></SPAN> <SPAN 
class=ps18><NOBR><SPAN class=ft0>需要考虑。我们在<SPAN 
class=em1>RTCP</SPAN>控制包通信量生成部分已经讨论过其中一些了。其他的因素主要处理</SPAN></NOBR></SPAN> <SPAN 
class=ps19><NOBR><SPAN 
class=ft0>基本双方呼叫的主观语音质量，而当会议中并非所有端点支持相同介质编码时，多用户会议</SPAN></NOBR></SPAN> <SPAN 
class=ps20><NOBR><SPAN 
class=ft0>中语音传输的可测量的服务质量使问题更加复杂。我们首先列出在写作本书时，介质编码支</SPAN></NOBR></SPAN> <SPAN 
class=ps21><NOBR><SPAN class=ft0>持的所有有效载荷格式。表<SPAN 
class=em1>2-2</SPAN>中的项说明为了找到最低比特率编码，并传输可能的最大用户</SPAN></NOBR></SPAN> <SPAN 
class=ps22><NOBR><SPAN class=ft0>感知质量，研究团体付出了巨大的努力。这里的关键词是“感知（&nbsp;<SPAN 
class=em1>perceived</SPAN>）”，在第<SPAN class=em1>4</SPAN>章中测</SPAN></NOBR></SPAN> 
<SPAN class=ps23><NOBR><SPAN 
class=ft0>量由于包网络中经常发现的损耗对语音质量的影响时，我们将再次讨论这个主题。在公用网</SPAN></NOBR></SPAN> <SPAN 
class=ps24><NOBR><SPAN 
class=ft0>上的包语音中，语音清晰性是最重要的问题，但是延迟和抖动也是影响语音感知质量的因素。</SPAN></NOBR></SPAN> <SPAN 
class=ps25><NOBR><SPAN class=ft0>传输质量是在公用网中的全部问题，所以，这也是基于<SPAN 
class=em1>IP</SPAN>的包网络中研究和开发的主要领域。</SPAN></NOBR></SPAN> <SPAN 
class=ps26><NOBR><SPAN class=ft2>表<SPAN class=em7>2-2 
&nbsp;&nbsp;</SPAN>主要语音流编码和基本特性</SPAN></NOBR></SPAN> <SPAN 
class=ps27><NOBR><SPAN class=ft3>介质编码</SPAN></NOBR></SPAN> <SPAN 
class=ps28><NOBR><SPAN class=ft3>每个样本的</SPAN></NOBR></SPAN> <SPAN 
class=ps29><NOBR><SPAN class=ft3>缺省的</SPAN></NOBR></SPAN> <SPAN 
class=ps30><NOBR>RTP<SPAN class=em2>有效</SPAN></NOBR></SPAN> <SPAN 
class=ps31><NOBR>S=<SPAN class=em2>样本</SPAN>F=<SPAN 
class=em2>帧</SPAN></NOBR></SPAN> <SPAN class=ps32><NOBR><SPAN 
class=ft3>比特率</SPAN></NOBR></SPAN> <SPAN class=ps33><NOBR><SPAN 
class=ft3>采样速率</SPAN></NOBR></SPAN> <SPAN class=ps34><NOBR><SPAN 
class=ft3>帧速率</SPAN></NOBR></SPAN> <SPAN class=ps35><NOBR><SPAN 
class=ft3>包速率</SPAN></NOBR></SPAN> <SPAN class=ps36><NOBR><SPAN 
class=ft3>载荷类型</SPAN></NOBR></SPAN> <SPAN class=ps37><NOBR>1016(f)</NOBR></SPAN> 
<SPAN class=ps38><NOBR>8KHz</NOBR></SPAN> <SPAN 
class=ps39><NOBR>30ms</NOBR></SPAN> <SPAN class=ps40><NOBR>30ms</NOBR></SPAN> 
<SPAN class=ps41><NOBR>1</NOBR></SPAN> <SPAN 
class=ps42><NOBR>CN(f)</NOBR></SPAN> <SPAN class=ps43><NOBR><SPAN 
class=ft3>可变的<SPAN class=em8>8KHz</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps44><NOBR><SPAN class=ft3>安慰噪声</SPAN></NOBR></SPAN> <SPAN 
class=ps45><NOBR>19</NOBR></SPAN> <SPAN class=ps46><NOBR>DVI4(s)</NOBR></SPAN> 
<SPAN class=ps47><NOBR>4</NOBR></SPAN> <SPAN class=ps48><NOBR><SPAN 
class=ft3>可变或<SPAN class=em8>16KHz</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps49><NOBR>20ms</NOBR></SPAN> <SPAN class=ps50><NOBR>8KHz<SPAN 
class=em2>时是</SPAN>5</NOBR></SPAN> <SPAN class=ps51><NOBR>16KHz<SPAN 
class=em2>时是</SPAN>6</NOBR></SPAN> <SPAN class=ps52><NOBR>22.050KHz<SPAN 
class=em2>时是</SPAN>17</NOBR></SPAN> <SPAN 
class=ps53><NOBR>G.722(s)</NOBR></SPAN> <SPAN class=ps54><NOBR>8</NOBR></SPAN> 
<SPAN class=ps55><NOBR>16 KHz</NOBR></SPAN> <SPAN 
class=ps56><NOBR>20ms</NOBR></SPAN> <SPAN class=ps57><NOBR>9</NOBR></SPAN> <SPAN 
class=ps58><NOBR>G.723(f)</NOBR></SPAN> <SPAN class=ps59><NOBR>8 
KHz</NOBR></SPAN> <SPAN class=ps60><NOBR>30ms</NOBR></SPAN> <SPAN 
class=ps61><NOBR>30ms</NOBR></SPAN> <SPAN class=ps62><NOBR>4</NOBR></SPAN> <SPAN 
class=ps63><NOBR>G.726(16+8n<SPAN class=em4><SUP>a</SUP></SPAN>)<SPAN 
class=em5><SUP>①</SUP></SPAN></NOBR></SPAN> <SPAN 
class=ps64><NOBR>2+n</NOBR></SPAN> <SPAN class=ps65><NOBR>8 KHz</NOBR></SPAN> 
<SPAN class=ps66><NOBR>20ms</NOBR></SPAN> <SPAN class=ps67><NOBR>2<SPAN 
class=em2>，</SPAN><SPAN class=em2>只对</SPAN>G.726-32</NOBR></SPAN> <SPAN 
class=ps68><NOBR>Kbps(s)</NOBR></SPAN> <SPAN class=ps69><NOBR>G.727(16+8n<SPAN 
class=em4><SUP>b</SUP></SPAN>)<SPAN class=em5><SUP>②</SUP></SPAN></NOBR></SPAN> 
<SPAN class=ps70><NOBR>2+n</NOBR></SPAN> <SPAN class=ps71><NOBR>8 
KHz</NOBR></SPAN> <SPAN class=ps72><NOBR>20ms</NOBR></SPAN> <SPAN 
class=ps73><NOBR><SPAN class=ft3>由信令分配</SPAN></NOBR></SPAN> <SPAN 
class=ps74><NOBR>Kbps(s)</NOBR></SPAN> <SPAN 
class=ps75><NOBR>G.728(f)</NOBR></SPAN> <SPAN class=ps76><NOBR>8 
KHz</NOBR></SPAN> <SPAN class=ps77><NOBR>2.5ms</NOBR></SPAN> <SPAN 
class=ps78><NOBR>20ms</NOBR></SPAN> <SPAN class=ps79><NOBR>15</NOBR></SPAN> 
<SPAN class=ps80><NOBR>G.729(f)</NOBR></SPAN> <SPAN class=ps81><NOBR>8 
KHz</NOBR></SPAN> <SPAN class=ps82><NOBR>20ms</NOBR></SPAN> <SPAN 
class=ps83><NOBR>18</NOBR></SPAN> <SPAN class=ps84><NOBR>GSM(f)</NOBR></SPAN> 
<SPAN class=ps85><NOBR>8 KHz</NOBR></SPAN> <SPAN 
class=ps86><NOBR>20ms</NOBR></SPAN> <SPAN class=ps87><NOBR>3</NOBR></SPAN> <SPAN 
class=ps88><NOBR><SPAN class=ft5>72&nbsp;&nbsp;<SPAN class=em3>IP </SPAN><SPAN 
class=em9>电话技术：稳定的</SPAN><SPAN class=em3>VoIP</SPAN><SPAN 
class=em9>服务集成</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps89><NOBR><SPAN 
class=ft6>文档</SPAN></NOBR></SPAN> </BODY></HTML>
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