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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=64 src="003_9.files/left.jpg" width=564 
border=0></DIV>
<DIV class=im1><IMG height=3 src="003_9.files/003_9_2.jpg" width=558 
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<DIV class=im2><IMG height=2 src="003_9.files/003_9_3.jpg" width=558 
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<DIV class=im3><IMG height=3 src="003_9.files/003_9_4.jpg" width=558 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR><SPAN 
class=ft0>108&nbsp;&nbsp;<SPAN class=em0>IP </SPAN><SPAN 
class=em5>电话技术：稳定的</SPAN><SPAN class=em0>VoIP</SPAN><SPAN 
class=em5>服务集成</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps1><NOBR><SPAN 
class=ft1>文档</SPAN></NOBR></SPAN> <SPAN class=ps2><NOBR>送信息。</NOBR></SPAN> <SPAN 
class=ps3><NOBR>如图<SPAN class=em1>3-4</SPAN>所示，<SPAN class=em1>MSU</SPAN>是<SPAN 
class=em1>MTP3</SPAN>层的基本信令信息，它包含从用户端接收到的消息。<SPAN 
class=em1>MSU</SPAN>以</NOBR></SPAN> <SPAN class=ps4><NOBR>长度指示器（<SPAN 
class=em1>Length Indicator</SPAN>，<SPAN class=em1>LI</SPAN>）开头，以校验位域（<SPAN 
class=em1>Check Bit Field</SPAN>，<SPAN class=em1>CB</SPAN>）结尾。<SPAN 
class=em1>LI</SPAN>和</NOBR></SPAN> <SPAN class=ps5><NOBR><SPAN class=ft3>CB<SPAN 
class=em2>域由</SPAN>MTP2<SPAN class=em2>产生并添加，然而服务信息域（<SPAN class=em1>Service 
Information Field</SPAN>，<SPAN class=em1>SIF</SPAN>）则由</SPAN>MTP<SPAN 
class=em2>从用</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps6><NOBR>户部件第<SPAN 
class=em1>4</SPAN>层协议接收。<SPAN class=em1>SIF</SPAN>可以多达<SPAN 
class=em1>272</SPAN>个字节。服务信息字节（<SPAN class=em1>Service Information 
Octet</SPAN>，</NOBR></SPAN> <SPAN class=ps7><NOBR><SPAN class=ft3>SIO<SPAN 
class=em2>）</SPAN><SPAN class=em2>用于</SPAN>MTP<SPAN 
class=em2>将消息路由到正确的用户处，其编码如表</SPAN>3-2<SPAN 
class=em2>所示。</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps8><NOBR><SPAN 
class=ft4>表<SPAN class=em3>3-2 &nbsp;&nbsp;MSU</SPAN>服务信息字节（<SPAN 
class=em3>Service Information Octet</SPAN>，<SPAN 
class=em3>SIO</SPAN>）</SPAN></NOBR></SPAN> <SPAN class=ps9><NOBR><SPAN 
class=ft5>子服务域</SPAN></NOBR></SPAN> <SPAN class=ps10><NOBR><SPAN 
class=ft5>意</SPAN></NOBR></SPAN> <SPAN class=ps11><NOBR><SPAN 
class=ft5>义</SPAN></NOBR></SPAN> <SPAN class=ps12><NOBR><SPAN 
class=ft5>子服务域</SPAN></NOBR></SPAN> <SPAN class=ps13><NOBR><SPAN 
class=ft5>意</SPAN></NOBR></SPAN> <SPAN class=ps14><NOBR><SPAN 
class=ft5>义</SPAN></NOBR></SPAN> <SPAN class=ps15><NOBR><SPAN class=ft6>SSF<SPAN 
class=em4>（</SPAN><SPAN class=em4>第</SPAN>8<SPAN class=em4>、</SPAN>7<SPAN 
class=em4>、</SPAN>6<SPAN class=em4>、</SPAN>5<SPAN 
class=em4>位）</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps16><NOBR><SPAN 
class=ft6>SI<SPAN class=em4>（</SPAN><SPAN class=em4>第</SPAN>4<SPAN 
class=em4>、</SPAN>3<SPAN class=em4>、</SPAN>2<SPAN class=em4>、</SPAN>1<SPAN 
class=em4>位）</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps17><NOBR><SPAN 
class=ft6>0000</SPAN></NOBR></SPAN> <SPAN class=ps18><NOBR><SPAN 
class=ft5>国际网络</SPAN></NOBR></SPAN> <SPAN class=ps19><NOBR><SPAN 
class=ft6>0000</SPAN></NOBR></SPAN> <SPAN class=ps20><NOBR><SPAN 
class=ft5>信令网络管理</SPAN></NOBR></SPAN> <SPAN class=ps21><NOBR><SPAN 
class=ft6>0010</SPAN></NOBR></SPAN> <SPAN class=ps22><NOBR><SPAN 
class=ft5>未使用</SPAN></NOBR></SPAN> <SPAN class=ps23><NOBR><SPAN 
class=ft6>0001</SPAN></NOBR></SPAN> <SPAN class=ps24><NOBR><SPAN 
class=ft5>信令网络测试和维护</SPAN></NOBR></SPAN> <SPAN class=ps25><NOBR><SPAN 
class=ft6>1010</SPAN></NOBR></SPAN> <SPAN class=ps26><NOBR><SPAN 
class=ft5>国际网络</SPAN></NOBR></SPAN> <SPAN class=ps27><NOBR><SPAN 
class=ft6>0010</SPAN></NOBR></SPAN> <SPAN class=ps28><NOBR><SPAN 
class=ft5>未使用</SPAN></NOBR></SPAN> <SPAN class=ps29><NOBR><SPAN 
class=ft6>11xx</SPAN></NOBR></SPAN> <SPAN class=ps30><NOBR><SPAN 
class=ft5>保留</SPAN></NOBR></SPAN> <SPAN class=ps31><NOBR><SPAN 
class=ft6>0011</SPAN></NOBR></SPAN> <SPAN class=ps32><NOBR><SPAN 
class=ft6>SCCP(TCAP<SPAN class=em4>、</SPAN>ISUP)<SPAN 
class=em4>等</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps33><NOBR><SPAN 
class=ft6>0100</SPAN></NOBR></SPAN> <SPAN class=ps34><NOBR><SPAN 
class=ft6>TUP</SPAN></NOBR></SPAN> <SPAN class=ps35><NOBR><SPAN 
class=ft6>0101</SPAN></NOBR></SPAN> <SPAN class=ps36><NOBR><SPAN 
class=ft6>ISUP</SPAN></NOBR></SPAN> <SPAN class=ps37><NOBR>举个例子，同路传送的<SPAN 
class=em1>ISUP</SPAN>消息可能有<SPAN class=em1>SI=10100101<SPAN 
class=em2>，</SPAN></SPAN>但是端对端的用户消息通过<SPAN class=em1>SCCP</SPAN></NOBR></SPAN> 
<SPAN class=ps38><NOBR>使用<SPAN class=em1>ISUP</SPAN>则可能有如下编码：<SPAN 
class=em1>SI=10100011</SPAN>。</NOBR></SPAN> <SPAN class=ps39><NOBR><SPAN 
class=ft3>SIF<SPAN class=em2>的路由标记（<SPAN class=em1>Routing Label</SPAN>，<SPAN 
class=em1>RL</SPAN>）在北美</SPAN>ANSI<SPAN class=em2>版的</SPAN>SS7<SPAN 
class=em2>中是</SPAN>56<SPAN class=em2>位域（在</SPAN>ITU-T<SPAN 
class=em2>的版本</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps40><NOBR>中为<SPAN 
class=em1>32</SPAN>位域），并分为三部分：</NOBR></SPAN> <SPAN class=ps41><NOBR><SPAN 
class=ft3>&#8226; <SPAN class=em2>前</SPAN>24<SPAN 
class=em2>位（三个字节）是终端或相邻信令节点的目标点码（<SPAN class=em1>Destination Point 
Code</SPAN>，<SPAN class=em1>DPC</SPAN>）</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps42><NOBR>。</NOBR></SPAN> <SPAN class=ps43><NOBR>该编码在<SPAN 
class=em1>ITU</SPAN>版本的<SPAN class=em1>SS7<SPAN class=em2>（</SPAN>ITU No 7<SPAN 
class=em2>）</SPAN></SPAN>中只占<SPAN class=em1>14</SPAN>比特。</NOBR></SPAN> <SPAN 
class=ps44><NOBR><SPAN class=ft3>&#8226; <SPAN class=em2>后</SPAN>24<SPAN 
class=em2>位（三个字节）是初始信令节点的源点码（<SPAN class=em1>Source Point Code</SPAN>，<SPAN 
class=em1>SPC</SPAN>）</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps45><NOBR>。类似地，该</NOBR></SPAN> <SPAN class=ps46><NOBR>编码在<SPAN 
class=em1>ITU</SPAN>版本的<SPAN class=em1>SS7</SPAN>中只占<SPAN 
class=em1>14</SPAN>比特。</NOBR></SPAN> <SPAN class=ps47><NOBR><SPAN class=ft3>&#8226; 
RL<SPAN class=em2>域的最后</SPAN>5<SPAN class=em2>位是信令链路选择码（<SPAN 
class=em1>Signaling Link Selection Code</SPAN>，<SPAN 
class=em1>SLSC</SPAN>）</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps48><NOBR>。在<SPAN class=em1>ITU</SPAN>版本</NOBR></SPAN> <SPAN 
class=ps49><NOBR>的<SPAN class=em1>SS7</SPAN>中，<SPAN class=em1>SLS</SPAN>码是<SPAN 
class=em1>4</SPAN>比特。</NOBR></SPAN> <SPAN class=ps50><NOBR>信令单元之间的负载共享由<SPAN 
class=em1>MSU</SPAN>中的信令链路选择（<SPAN class=em1>Signaling Link 
Selection</SPAN>，<SPAN class=em1>SLS</SPAN>）码</NOBR></SPAN> <SPAN 
class=ps51><NOBR>来实现。通过将交换机上的语音干线数对信令链路数取模平衡，就可以得到该编码。一个电</NOBR></SPAN> <SPAN 
class=ps52><NOBR>路识别码（<SPAN class=em1>Circuit Identification Code</SPAN>，<SPAN 
class=em1>CIC</SPAN>）模<SPAN class=em1>32</SPAN>的除法运算为每条干线产生一个编码，这</NOBR></SPAN> 
<SPAN class=ps53><NOBR>样每个编码就映射为<SPAN class=em1>32</SPAN>条干线。编码的每个比特能被<SPAN 
class=em1>SSP</SPAN>和<SPAN class=em1>STP</SPAN>用来选择通往目的地的输出链</NOBR></SPAN> <SPAN 
class=ps54><NOBR>路。<SPAN class=em1>ITU No 7</SPAN>的<SPAN 
class=em1>SLS</SPAN>提供模<SPAN class=em1>16</SPAN>的分解来进行负载平衡。</NOBR></SPAN> <SPAN 
class=ps55><NOBR><SPAN class=ft3>STP<SPAN 
class=em2>能改变信令链路选择的算法，这样当网络出现拥塞或链路不稳定时，它能把通信量映</SPAN></SPAN></NOBR></SPAN> 
<SPAN class=ps56><NOBR>射到别的出口链路上。在下一节将讨论这个过程。</NOBR></SPAN> <SPAN 
class=ps57><NOBR><SPAN class=ft3>3. SS7<SPAN 
class=em6>中的流控制和错误恢复</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps58><NOBR><SPAN 
class=ft3>SS7<SPAN class=em2>中的流控制由</SPAN>MTP2<SPAN 
class=em2>子层负责。基本的流控制概念十分简单，当缓冲即将溢出或别的</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps59><NOBR>处理环境阻止了<SPAN class=em1>STP</SPAN>跟上消息流时，流控制便使用<SPAN 
class=em1>LSSU</SPAN>消息对发送端进行调速。在包电话中，</NOBR></SPAN> <SPAN 
class=ps60><NOBR>基于<SPAN class=em1>IP</SPAN>的协议有望代替<SPAN 
class=em1>SS7</SPAN>的低层，它将在几个地方代为实现<SPAN 
class=em1>MTP</SPAN>的任务。在体系结构中，基</NOBR></SPAN> <SPAN class=ps61><NOBR>于<SPAN 
class=em1>IP</SPAN>的协议层代替部分<SPAN 
class=em1>MTP</SPAN>的具体位置还没有标准化，需要在新的公用网络的健壮性和可靠</NOBR></SPAN> <SPAN 
class=ps62><NOBR>性等领域进行很多研究。</NOBR></SPAN> <SPAN class=ps63><NOBR><SPAN 
class=ft3>MTP2<SPAN class=em2>在</SPAN>LSSU<SPAN 
class=em2>的链路状态标记域中使用</SPAN>BUSY<SPAN class=em2>（</SPAN><SPAN 
class=em2>忙）标记来说明它已无法处理消息到达的</SPAN></SPAN></NOBR></SPAN> </BODY></HTML>
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