⭐ 欢迎来到虫虫下载站！ | 📦 资源下载 📁 资源专辑 ℹ️ 关于我们
⭐ 虫虫下载站
📤 上传资源

📄 002_31.htm

📁 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
字号:
🔍 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<!-- saved from url=(0059)http://www.chinagk.org/technology/IPTech/002/css/002_31.htm -->
<HTML><HEAD><TITLE>002_31</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: 64px; WIDTH: 530px; POSITION: absolute; TOP: 102px
}
.ps1 {
	LEFT: 37px; WIDTH: 472px; POSITION: absolute; TOP: 123px
}
.ps2 {
	LEFT: 64px; WIDTH: 537px; POSITION: absolute; TOP: 496px
}
.ps3 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 516px
}
.ps4 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 536px
}
.ps5 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 557px
}
.ps6 {
	LEFT: 37px; WIDTH: 27px; POSITION: absolute; TOP: 578px
}
.ps7 {
	LEFT: 64px; WIDTH: 164px; POSITION: absolute; TOP: 599px
}
.ps8 {
	LEFT: 64px; WIDTH: 529px; POSITION: absolute; TOP: 619px
}
.ps9 {
	LEFT: 37px; WIDTH: 557px; POSITION: absolute; TOP: 640px
}
.ps10 {
	LEFT: 37px; WIDTH: 399px; POSITION: absolute; TOP: 661px
}
.ps11 {
	LEFT: 64px; WIDTH: 363px; POSITION: absolute; TOP: 681px
}
.ps12 {
	LEFT: 64px; WIDTH: 529px; POSITION: absolute; TOP: 702px
}
.ps13 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 722px
}
.ps14 {
	LEFT: 37px; WIDTH: 40px; POSITION: absolute; TOP: 743px
}
.ps15 {
	LEFT: 64px; WIDTH: 108px; POSITION: absolute; TOP: 765px
}
.ps16 {
	LEFT: 64px; WIDTH: 536px; POSITION: absolute; TOP: 785px
}
.ps17 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 805px
}
.ps18 {
	LEFT: 37px; WIDTH: 232px; POSITION: absolute; TOP: 826px
}
.ps19 {
	LEFT: 64px; WIDTH: 529px; POSITION: absolute; TOP: 846px
}
.ps20 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 867px
}
.ps21 {
	LEFT: 37px; WIDTH: 556px; POSITION: absolute; TOP: 888px
}
.ps22 {
	LEFT: 371px; WIDTH: 150px; POSITION: absolute; TOP: 54px
}
.ps23 {
	LEFT: 541px; WIDTH: 37px; POSITION: absolute; TOP: 31px
}
.ps24 {
	LEFT: 44px; WIDTH: 43px; POSITION: absolute; TOP: 64px
}
.ps25 {
	LEFT: 90px; WIDTH: 167px; POSITION: absolute; TOP: 469px
}
.ps26 {
	LEFT: 374px; WIDTH: 182px; POSITION: absolute; TOP: 469px
}
.ps27 {
	LEFT: 106px; WIDTH: 141px; POSITION: absolute; TOP: 158px
}
.ps28 {
	LEFT: 152px; WIDTH: 49px; POSITION: absolute; TOP: 169px
}
.ps29 {
	LEFT: 123px; WIDTH: 107px; POSITION: absolute; TOP: 239px
}
.ps30 {
	LEFT: 92px; WIDTH: 171px; POSITION: absolute; TOP: 274px
}
.ps31 {
	LEFT: 135px; WIDTH: 85px; POSITION: absolute; TOP: 289px
}
.ps32 {
	LEFT: 143px; WIDTH: 66px; POSITION: absolute; TOP: 316px
}
.ps33 {
	LEFT: 119px; WIDTH: 114px; POSITION: absolute; TOP: 424px
}
.ps34 {
	LEFT: 117px; WIDTH: 117px; POSITION: absolute; TOP: 353px
}
.ps35 {
	LEFT: 132px; WIDTH: 87px; POSITION: absolute; TOP: 369px
}
.ps36 {
	LEFT: 198px; WIDTH: 43px; POSITION: absolute; TOP: 205px
}
.ps37 {
	LEFT: 395px; WIDTH: 131px; POSITION: absolute; TOP: 265px
}
.ps38 {
	LEFT: 429px; WIDTH: 64px; POSITION: absolute; TOP: 292px
}
.ps39 {
	LEFT: 491px; WIDTH: 43px; POSITION: absolute; TOP: 317px
}
.ps40 {
	LEFT: 491px; WIDTH: 43px; POSITION: absolute; TOP: 395px
}
.ps41 {
	LEFT: 439px; WIDTH: 53px; POSITION: absolute; TOP: 347px
}
.ps42 {
	LEFT: 430px; WIDTH: 71px; POSITION: absolute; TOP: 364px
}
.ft1 {
	FONT-SIZE: 13px; FONT-FAMILY: "Times New Roman",Times,serif
}
.ft2 {
	FONT-STYLE: italic; FONT-FAMILY: ""
}
.ft3 {
	FONT-WEIGHT: bold; FONT-SIZE: 37px; FONT-STYLE: italic; FONT-FAMILY: "Times New Roman",Times,serif
}
.ft4 {
	FONT-SIZE: 21px; COLOR: #000000; FONT-STYLE: italic; FONT-FAMILY: ""
}
.ft5 {
	FONT-SIZE: 12px; COLOR: #000000
}
.ft6 {
	FONT-SIZE: 10px; COLOR: #000000; FONT-FAMILY: "Times New Roman",Times,serif
}
.ft7 {
	FONT-SIZE: 11px; COLOR: #000000
}
.em0 {
	FONT-SIZE: 13px; FONT-FAMILY: "Times New Roman",Times,serif
}
.em1 {
	FONT-SIZE: 13px; FONT-FAMILY: ""
}
.em2 {
	FONT-SIZE: 11px; FONT-FAMILY: ""
}
.em3 {
	FONT-SIZE: 13px; FONT-STYLE: italic; FONT-FAMILY: ""
}
.em4 {
	FONT-STYLE: italic; FONT-FAMILY: "Times New Roman",Times,serif
}
.em5 {
	FONT-SIZE: 11px; FONT-FAMILY: "Times New Roman",Times,serif
}
.em6 {
	FONT-SIZE: 10px; FONT-FAMILY: "Times New Roman",Times,serif
}
.im0 {
	LEFT: 33px; WIDTH: 562px; POSITION: absolute; TOP: 24px
}
.im1 {
	LEFT: 79px; WIDTH: 191px; POSITION: absolute; TOP: 149px
}
.im2 {
	LEFT: 349px; WIDTH: 223px; POSITION: absolute; TOP: 250px
}
</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=64 src="002_31.files/right.jpg" width=563 
border=0></DIV>
<DIV class=im1><IMG height=299 src="002_31.files/002_31_2.jpg" width=191 
border=0></DIV>
<DIV class=im2><IMG height=195 src="002_31.files/002_31_3.jpg" width=223 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR>如图<SPAN 
class=em0>2-17</SPAN>所示，<SPAN class=em0>RTP</SPAN>域中在会话期间不断发生变化，因此必须用<SPAN 
class=em0>COMPRESSED_UDP</SPAN>包</NOBR></SPAN> <SPAN 
class=ps1><NOBR>格式发送非压缩的<SPAN class=em0>RTP</SPAN>报头。如果<SPAN 
class=em0>IP</SPAN>和<SPAN class=em0>UDP</SPAN>报头不需要更新，则采用报头压缩。</NOBR></SPAN> 
<SPAN class=ps2><NOBR><SPAN class=ft1>RFC 2508<SPAN 
class=em1>定义了以压缩形式编码增量差的方法，但是它也建议使用表驱动的增量编码器，</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps3><NOBR>后者更加健壮，在协商各个会话的编码时也更加灵活。问题在于需要更新时，压缩形式的增</NOBR></SPAN> <SPAN 
class=ps4><NOBR>量序列的长度是多少？在<SPAN 
class=em0>RFC</SPAN>中读者会注意到，增量域中的第一个字节四位组的编码可以用</NOBR></SPAN> <SPAN 
class=ps5><NOBR>来说明增量域的长度。改变值的增量压缩过程在<SPAN class=em0>RFC 2508</SPAN>中说明，它和<SPAN 
class=em0>Huffman</SPAN>编码有些相</NOBR></SPAN> <SPAN 
class=ps6><NOBR>似。</NOBR></SPAN> <SPAN class=ps7><NOBR><SPAN class=ft1>9. <SPAN 
class=em3>错误恢复和场景状态协商</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps8><NOBR>当压缩<SPAN 
class=em0>RTP</SPAN>报头中的顺序域增加值大于<SPAN class=em0>1</SPAN>时，场景变成无效（如果它增加<SPAN 
class=em0>1mod16<SPAN class=em1>，</SPAN></SPAN>解压缩</NOBR></SPAN> <SPAN 
class=ps9><NOBR>器不会注意到错误，除非链路层协议给<SPAN 
class=em0>IP</SPAN>层发通知）。场景失效提示解压缩器返回一个如图<SPAN class=em0>2-</SPAN></NOBR></SPAN> 
<SPAN class=ps10><NOBR><SPAN class=ft1>18<SPAN 
class=em1>所示的</SPAN>CONTEXT_STATE<SPAN 
class=em1>包，并且请求刷新包中场景的顺序域。</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps11><NOBR>如果包中<SPAN class=em0>I=1<SPAN 
class=em1>，</SPAN></SPAN>解压缩器为那个信源请求<SPAN 
class=em0>FULL_HEADER</SPAN>包。</NOBR></SPAN> <SPAN 
class=ps12><NOBR>错误恢复是破坏性的，在网络阻塞的情况下会花一段时间。更具破坏性的是，在低速连</NOBR></SPAN> <SPAN 
class=ps13><NOBR>接上存在多个无效场景时，它的完整更新可能会导致更多的暂时阻塞，直到完成所有的刷新</NOBR></SPAN> <SPAN 
class=ps14><NOBR>为止。</NOBR></SPAN> <SPAN class=ps15><NOBR><SPAN class=ft1>10. 
RTCP<SPAN class=em3>包的压缩</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps16><NOBR><SPAN class=ft1>RTCP<SPAN 
class=em1>包的内容不能被压缩，最好不要处理</SPAN>RTCP<SPAN 
class=em1>包，也不要对其进行压缩。如前所述，</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps17><NOBR>分配给<SPAN class=em0>RTCP</SPAN>的总带宽是会话带宽的<SPAN class=em0>5%<SPAN 
class=em1>，</SPAN></SPAN>或者说通常总是少于<SPAN 
class=em0>5%</SPAN>的一个固定值，所以，压缩</NOBR></SPAN> <SPAN 
class=ps18><NOBR>就节省带宽和效率而言没有多大好处。</NOBR></SPAN> <SPAN 
class=ps19><NOBR>最后，当跨越多个<SPAN 
class=em0>AS</SPAN>域时，可能会碰到包的破碎。原因是大的包携带大的有效载荷，报</NOBR></SPAN> <SPAN 
class=ps20><NOBR>头大小作为整体的一部分对于大包的影响不太显著。我们的建议是，当发送大包时应该完全</NOBR></SPAN> <SPAN 
class=ps21><NOBR>避免压缩，保持总包长度达到<SPAN 
class=em0>AS</SPAN>所支持的最小长度（就是说，也要避免破碎）。由于碎片出</NOBR></SPAN> <SPAN 
class=ps22><NOBR><SPAN class=ft2>第<SPAN 
class=em4>2</SPAN>章&nbsp;包网络的介质传输</SPAN></NOBR></SPAN> <SPAN 
class=ps23><NOBR><SPAN class=ft3>87</SPAN></NOBR></SPAN> <SPAN 
class=ps24><NOBR><SPAN class=ft4>文档</SPAN></NOBR></SPAN> <SPAN 
class=ps25><NOBR><SPAN class=ft5>图<SPAN class=em5>2-17 
&nbsp;&nbsp;</SPAN>压缩<SPAN class=em5>UDP</SPAN>报头和包格式</SPAN></NOBR></SPAN> <SPAN 
class=ps26><NOBR><SPAN class=ft5>图<SPAN class=em5>2-18 
&nbsp;&nbsp;CONTEXT_STATE</SPAN>包格式</SPAN></NOBR></SPAN> <SPAN 
class=ps27><NOBR><SPAN class=ft6>CID<SPAN class=em2>的</SPAN>MSB(<SPAN 
class=em2>如果</SPAN>CID<SPAN class=em2>为</SPAN>16<SPAN 
class=em2>比特</SPAN>)</SPAN></NOBR></SPAN> <SPAN class=ps28><NOBR><SPAN 
class=ft6>CID<SPAN class=em2>的</SPAN>LSB</SPAN></NOBR></SPAN> <SPAN 
class=ps29><NOBR><SPAN class=ft6>UDP<SPAN 
class=em2>校验和如果有的话</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps30><NOBR><SPAN 
class=ft6>RANDOM(<SPAN class=em2>用于包中有多个</SPAN>IPv4<SPAN 
class=em2>报头</SPAN>)</SPAN></NOBR></SPAN> <SPAN class=ps31><NOBR><SPAN 
class=ft7>发送时不会被压缩</SPAN></NOBR></SPAN> <SPAN class=ps32><NOBR><SPAN 
class=ft6>IPv4 ID<SPAN class=em2>的增量</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps33><NOBR><SPAN class=ft6>PAD<SPAN class=em2>，</SPAN><SPAN 
class=em2>如果</SPAN>RTP<SPAN class=em2>需要的话</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps34><NOBR><SPAN class=ft7>带有未压缩的<SPAN 
class=em6>RTP</SPAN>报头和</SPAN></NOBR></SPAN> <SPAN class=ps35><NOBR><SPAN 
class=ft7>有效载荷的<SPAN class=em6>UDP</SPAN>包</SPAN></NOBR></SPAN> <SPAN 
class=ps36><NOBR><SPAN class=ft7>链路顺序</SPAN></NOBR></SPAN> <SPAN 
class=ps37><NOBR><SPAN class=ft6>1(8<SPAN class=em2>比特</SPAN>CID)<SPAN 
class=em2>或</SPAN>2(16<SPAN class=em2>比特</SPAN>CID)</SPAN></NOBR></SPAN> <SPAN 
class=ps38><NOBR><SPAN class=ft7>包中的场景数</SPAN></NOBR></SPAN> <SPAN 
class=ps39><NOBR><SPAN class=ft7>链路顺序</SPAN></NOBR></SPAN> <SPAN 
class=ps40><NOBR><SPAN class=ft7>顺序编号</SPAN></NOBR></SPAN> <SPAN 
class=ps41><NOBR><SPAN class=ft7>会话<SPAN class=em6>CID <SPAN 
class=em2>１</SPAN></SPAN></SPAN></NOBR></SPAN> <SPAN class=ps42><NOBR><SPAN 
class=ft6>(1<SPAN class=em2>个或</SPAN>2<SPAN 
class=em2>个字节</SPAN>)</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
切换主题 Ctrl + Shift + D
显示快捷键 ?
增大字号 Ctrl + =
减小字号 Ctrl + -