002_20.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 282 行
HTM
282 行
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from url=(0059)http://www.chinagk.org/technology/IPTech/002/css/002_20.htm -->
<HTML><HEAD><TITLE>002_20</TITLE>
<META http-equiv=Content-Type content="text/html; charset=gb2312">
<STYLE type=text/css>.pg {
LEFT: 0px; WIDTH: 635px; POSITION: absolute; TOP: 0px; HEIGHT: 983px
}
BODY {
FONT-SIZE: 13px; COLOR: #000000; FONT-FAMILY: ""; BACKGROUND-COLOR: #ffffff
}
A {
TEXT-DECORATION: none
}
.ps0 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 102px
}
.ps1 {
LEFT: 38px; WIDTH: 122px; POSITION: absolute; TOP: 123px
}
.ps2 {
LEFT: 65px; WIDTH: 529px; POSITION: absolute; TOP: 143px
}
.ps3 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 163px
}
.ps4 {
LEFT: 38px; WIDTH: 551px; POSITION: absolute; TOP: 184px
}
.ps5 {
LEFT: 38px; WIDTH: 564px; POSITION: absolute; TOP: 206px
}
.ps6 {
LEFT: 38px; WIDTH: 555px; POSITION: absolute; TOP: 226px
}
.ps7 {
LEFT: 38px; WIDTH: 493px; POSITION: absolute; TOP: 245px
}
.ps8 {
LEFT: 546px; WIDTH: 47px; POSITION: absolute; TOP: 247px
}
.ps9 {
LEFT: 38px; WIDTH: 40px; POSITION: absolute; TOP: 265px
}
.ps10 {
LEFT: 65px; WIDTH: 530px; POSITION: absolute; TOP: 286px
}
.ps11 {
LEFT: 38px; WIDTH: 486px; POSITION: absolute; TOP: 306px
}
.ps12 {
LEFT: 65px; WIDTH: 95px; POSITION: absolute; TOP: 328px
}
.ps13 {
LEFT: 65px; WIDTH: 530px; POSITION: absolute; TOP: 349px
}
.ps14 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 367px
}
.ps15 {
LEFT: 38px; WIDTH: 557px; POSITION: absolute; TOP: 388px
}
.ps16 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 408px
}
.ps17 {
LEFT: 38px; WIDTH: 385px; POSITION: absolute; TOP: 429px
}
.ps18 {
LEFT: 436px; WIDTH: 157px; POSITION: absolute; TOP: 430px
}
.ps19 {
LEFT: 38px; WIDTH: 220px; POSITION: absolute; TOP: 451px
}
.ps20 {
LEFT: 65px; WIDTH: 529px; POSITION: absolute; TOP: 469px
}
.ps21 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 490px
}
.ps22 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 510px
}
.ps23 {
LEFT: 38px; WIDTH: 391px; POSITION: absolute; TOP: 531px
}
.ps24 {
LEFT: 65px; WIDTH: 530px; POSITION: absolute; TOP: 553px
}
.ps25 {
LEFT: 38px; WIDTH: 316px; POSITION: absolute; TOP: 571px
}
.ps26 {
LEFT: 65px; WIDTH: 529px; POSITION: absolute; TOP: 593px
}
.ps27 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 612px
}
.ps28 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 633px
}
.ps29 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 653px
}
.ps30 {
LEFT: 38px; WIDTH: 162px; POSITION: absolute; TOP: 673px
}
.ps31 {
LEFT: 65px; WIDTH: 529px; POSITION: absolute; TOP: 695px
}
.ps32 {
LEFT: 38px; WIDTH: 564px; POSITION: absolute; TOP: 714px
}
.ps33 {
LEFT: 38px; WIDTH: 256px; POSITION: absolute; TOP: 736px
}
.ps34 {
LEFT: 65px; WIDTH: 309px; POSITION: absolute; TOP: 757px
}
.ps35 {
LEFT: 65px; WIDTH: 530px; POSITION: absolute; TOP: 775px
}
.ps36 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 796px
}
.ps37 {
LEFT: 38px; WIDTH: 548px; POSITION: absolute; TOP: 816px
}
.ps38 {
LEFT: 65px; WIDTH: 530px; POSITION: absolute; TOP: 837px
}
.ps39 {
LEFT: 38px; WIDTH: 556px; POSITION: absolute; TOP: 857px
}
.ps40 {
LEFT: 53px; WIDTH: 259px; POSITION: absolute; TOP: 31px
}
.ps41 {
LEFT: 547px; WIDTH: 43px; POSITION: absolute; TOP: 64px
}
.ps42 {
LEFT: 89px; WIDTH: 64px; POSITION: absolute; TOP: 896px
}
.ps43 {
LEFT: 157px; WIDTH: 98px; POSITION: absolute; TOP: 896px
}
.ft1 {
FONT-SIZE: 11px; FONT-FAMILY: "Times New Roman",Times,serif
}
.ft2 {
FONT-WEIGHT: bold; FONT-SIZE: 37px; FONT-STYLE: italic; FONT-FAMILY: "Times New Roman",Times,serif
}
.ft3 {
FONT-SIZE: 21px; COLOR: #000000; FONT-STYLE: italic; FONT-FAMILY: ""
}
.ft4 {
FONT-SIZE: 9px; FONT-FAMILY: "Times New Roman",Times,serif
}
.ft5 {
FONT-SIZE: 11px
}
.em0 {
FONT-SIZE: 11px; FONT-FAMILY: "Times New Roman",Times,serif
}
.em1 {
FONT-SIZE: 13px; FONT-FAMILY: ""
}
.em2 {
FONT-WEIGHT: normal; FONT-SIZE: 13px; FONT-STYLE: italic
}
.em3 {
FONT-SIZE: 13px; FONT-STYLE: italic; FONT-FAMILY: ""
}
.em4 {
FONT-WEIGHT: normal; FONT-SIZE: 13px; FONT-STYLE: italic; FONT-FAMILY: ""
}
.em5 {
FONT-SIZE: 11px; FONT-FAMILY: ""
}
.im0 {
LEFT: 161px; WIDTH: 7px; POSITION: absolute; TOP: 385px
}
.im1 {
LEFT: 36px; WIDTH: 564px; POSITION: absolute; TOP: 24px
}
.im2 {
LEFT: 66px; WIDTH: 8px; POSITION: absolute; TOP: 895px
}
.im3 {
LEFT: 36px; WIDTH: 134px; POSITION: absolute; TOP: 885px
}
</STYLE>
<META content="MSHTML 6.00.2600.0" name=GENERATOR></HEAD>
<BODY>
<DIV class=pg></DIV><!-- bitmap and vector images are written here -->
<DIV class=im0><IMG height=7 src="002_20.files/002_20_1.jpg" width=7
border=0></DIV>
<DIV class=im1><IMG height=64 src="002_20.files/left.jpg" width=564
border=0></DIV>
<DIV class=im2><IMG height=9 src="002_20.files/002_20_3.jpg" width=8
border=0></DIV>
<DIV class=im3><IMG height=2 src="002_20.files/002_20_4.jpg" width=134
border=0></DIV><!-- text starts here --><SPAN
class=ps0><NOBR>将网络中的抖动控制在很小的数值，在每个端点都可以实现两个包去除抖动的缓冲，这样会</NOBR></SPAN> <SPAN
class=ps1><NOBR>使端到端延迟最小。</NOBR></SPAN> <SPAN class=ps2><NOBR>从健壮性角度来看，<SPAN
class=em0>PSTN</SPAN>实例存在其他和跨越不同网络信令有关的问题。它主要涉及</NOBR></SPAN> <SPAN
class=ps3><NOBR>载波在它们的域内（服务于它们的用户）提供<SPAN
class=em0>VoIP</SPAN>服务的能力，以通过信令方法为其他竞</NOBR></SPAN> <SPAN
class=ps4><NOBR>争载波的用户提供电话特性。如果中间是使用<SPAN class=em0>SS7</SPAN>信令的<SPAN
class=em0>PSTN<SPAN class=em1>，</SPAN></SPAN>那么最常用的特性集合是</NOBR></SPAN> <SPAN
class=ps5><NOBR><SPAN class=ft1>SS7<SPAN
class=em1>所支持的那些特性，以及载波之间通过高级智能网络（ <SPAN class=em0>Advanced Intelligent
Network</SPAN>，</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps6><NOBR><SPAN
class=ft1>AIN<SPAN class=em1>）</SPAN><SPAN
class=em1>支持的任何常用特性。在任何情况下，每种载波会以标准的和专用的方法，甚至通</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps7><NOBR>过电缆调制解调器提供的电话服务，在混合载波拓扑中很大程度地支持最常使用的</NOBR></SPAN> <SPAN
class=ps8><NOBR><SPAN class=ft1>5<SPAN class=em1>类电话</SPAN></SPAN></NOBR></SPAN>
<SPAN class=ps9><NOBR>特性。</NOBR></SPAN> <SPAN
class=ps10><NOBR>涉及呼叫建立、拨号后延迟、<SPAN
class=em0>FCAPS</SPAN>、记帐和跨越混合网络支持无线服务的健壮性考虑</NOBR></SPAN> <SPAN
class=ps11><NOBR>都是有根据的。在建立相互可操作的实现之前，标准组织需要进行进一步的工作。</NOBR></SPAN> <SPAN
class=ps12><NOBR><SPAN class=ft1>3. <SPAN
class=em3>关于编码格式</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps13><NOBR><SPAN
class=ft1>Monoli<SPAN class=em1>（</SPAN>[21]<SPAN class=em1>）</SPAN><SPAN
class=em1>在分析各种语音编码方案方面做出了很好的工作。支持所有已定义类型的</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps14><NOBR>端点在近期内是不可能的，尽管你的<SPAN class=em0>PC</SPAN>已经有了很好的选择。和<SPAN
class=em0>PSTN</SPAN>上一样，长途电话质量</NOBR></SPAN> <SPAN class=ps15><NOBR>的语音能够用<SPAN
class=em0>PCMU</SPAN>、<SPAN class=em0>PCMA</SPAN>、<SPAN
class=em0>ADPCM</SPAN>编码以最小网络损耗传输。<SPAN class=em0>ADPCM</SPAN>是通过<SPAN
class=em0>G.726-32</SPAN></NOBR></SPAN> <SPAN class=ps16><NOBR>或<SPAN
class=em0>G.727-32</SPAN>支持的。这两种格式在比特级别上是互不相容的，但是由于<SPAN
class=em0>G.727</SPAN>能够吸收网络环</NOBR></SPAN> <SPAN
class=ps17><NOBR>境导致的包丢失，因此在高语音质量方面提供了更高的健壮性。</NOBR></SPAN> <SPAN
class=ps18><NOBR><SPAN class=ft1>G.726<SPAN class=em1>和</SPAN>G.727<SPAN
class=em1>的范围是从</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps19><NOBR><SPAN
class=ft1>16Kbps ~ 40Kbps<SPAN class=em1>，</SPAN><SPAN
class=em1>每次增加</SPAN>8Kbps<SPAN class=em1>。</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps20><NOBR>读者不要把低延迟编码格式与会话中规定的打包延迟混为一谈。编码样本的生成能够很</NOBR></SPAN> <SPAN
class=ps21><NOBR>快完成，但是包的产生是延迟计算中的主要因素。如果网络设计想使用额外的带宽来使延迟</NOBR></SPAN> <SPAN
class=ps22><NOBR>最小化，那么低延迟算法更适合于这项工作。但是，打包的介质所获得的效率大部分会同时</NOBR></SPAN> <SPAN
class=ps23><NOBR>丧失掉，而网关和交换机之间的连接的网络工程会变得更加复杂。</NOBR></SPAN> <SPAN
class=ps24><NOBR><SPAN class=ft1>G.723.1<SPAN
class=em1>系列规定了两种编码，一种是</SPAN>5.3Kbps<SPAN class=em1>，</SPAN><SPAN
class=em1>另一种是</SPAN>6.3Kbps<SPAN
class=em1>。如果端点允许在信令</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps25><NOBR>过程中选择<SPAN class=em0>G.723.1<SPAN
class=em1>，</SPAN></SPAN>那么它必须同时支持两种编码。</NOBR></SPAN> <SPAN
class=ps26><NOBR><SPAN class=ft1>RED<SPAN
class=em1>通过发送以前的样本以一种巧妙的方式获得冗余性，但是它的压缩程度更大，并对</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps27><NOBR>编码后的语音重新进行采样。如果端点足够幸运，当实际的包还没到达时就得到了那些更大</NOBR></SPAN> <SPAN
class=ps28><NOBR>程度压缩的样本中的一个，那么它可以从后来的包中估计出语音波形，从而产生更好的用户</NOBR></SPAN> <SPAN
class=ps29><NOBR>感受。这听起来（并且确实）难于实现，在跨越不同的<SPAN
class=em0>AS</SPAN>域时更难保证其有效性。由于存在</NOBR></SPAN> <SPAN
class=ps30><NOBR>包重复，它也很耗费带宽。</NOBR></SPAN> <SPAN class=ps31><NOBR><SPAN
class=ft1>SX<SPAN class=em1>家族的编码解码方案产生</SPAN>120<SPAN class=em1>个样本（<SPAN
class=em0>15ms</SPAN>间隔）的编码，每个编码字节块具有可变</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps32><NOBR>的字节数。<SPAN class=em0>SX7300</SPAN>每字节块产生<SPAN
class=em0>14</SPAN>字节，即<SPAN class=em0>7467bps <SPAN
class=em1>，</SPAN>SX8300</SPAN>产生<SPAN class=em0>16</SPAN>字节，即<SPAN
class=em0>8533bps<SPAN class=em1>，</SPAN></SPAN></NOBR></SPAN> <SPAN
class=ps33><NOBR><SPAN class=ft1>SX9600<SPAN class=em1>产生</SPAN>18<SPAN
class=em1>字节，即</SPAN>9600bps<SPAN class=em1>的比特率。</SPAN></SPAN></NOBR></SPAN>
<SPAN class=ps34><NOBR><SPAN class=ft1>4. <SPAN class=em3>携带</SPAN>DTMF<SPAN
class=em3>数字、音调和事件的</SPAN>RTP<SPAN class=em3>有效载荷格式</SPAN></SPAN></NOBR></SPAN>
<SPAN class=ps35><NOBR>在<SPAN class=em0>PSTN</SPAN>中，<SPAN
class=em0>DTMF</SPAN>数字是作为带内音调从电话传送到本地交换机。在<SPAN class=em0>VoIP</SPAN>网络中，<SPAN
class=em0>DTMF</SPAN></NOBR></SPAN> <SPAN
class=ps36><NOBR>数字是在被介质网关识别、收集、甚至可能分析之后，在<SPAN
class=em0>RTP</SPAN>包中传送的。一般情况下，编码</NOBR></SPAN> <SPAN
class=ps37><NOBR>解码方案很难理解压缩的<SPAN class=em0>DTMF</SPAN>音调。这个问题导致了在端点间带外传输<SPAN
class=em0>DTMF</SPAN>音调的需要。</NOBR></SPAN> <SPAN class=ps38><NOBR>基本想法是在<SPAN
class=em0>RTP</SPAN>包中编码<SPAN
class=em0>DTMF</SPAN>数字和音调时，使用和编码语音数据时相同的属性。假</NOBR></SPAN> <SPAN
class=ps39><NOBR>定同步校正对于语音包不是绝对严格， <SPAN
class=em0>RTP</SPAN>包使用和语音包相同的顺序编号。其缺点在于为</NOBR></SPAN> <SPAN
class=ps40><NOBR><SPAN class=ft2>76 <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=ps41><NOBR><SPAN
class=ft3>文档</SPAN></NOBR></SPAN> <SPAN class=ps42><NOBR><SPAN
class=ft4>PCMU<SPAN class=em5>是</SPAN>µLaw</SPAN></NOBR></SPAN> <SPAN
class=ps43><NOBR><SPAN class=ft5>编码的另一个名称。</SPAN></NOBR></SPAN> </BODY></HTML>
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?