📄 003_12.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）
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<DIV class=im0><IMG height=64 src="003_12.files/right.jpg" width=563 
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<DIV class=im1><IMG height=7 src="003_12.files/003_12_2.jpg" width=7 
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<DIV class=im4><IMG height=253 src="003_12.files/003_12_5.jpg" width=486 
border=0></DIV><!-- text starts here --><SPAN class=ps0><NOBR><SPAN 
class=ft0>第<SPAN class=em2>3</SPAN>章&nbsp;语音电话的基本呼叫控制</SPAN></NOBR></SPAN> <SPAN 
class=ps1><NOBR><SPAN class=ft1>111</SPAN></NOBR></SPAN> <SPAN 
class=ps2><NOBR><SPAN class=ft2>文档</SPAN></NOBR></SPAN> <SPAN 
class=ps3><NOBR>图<SPAN class=em0>3-12</SPAN>中的情况说明了当链路不可用，目标不能通过特定的<SPAN 
class=em0>STP</SPAN>到达时，<SPAN class=em0>MTP</SPAN>所采取的动</NOBR></SPAN> <SPAN 
class=ps4><NOBR>作。它描述了当<SPAN class=em0>STP D</SPAN>由于<SPAN class=em0>STP 
B</SPAN>或它的链路的故障而不能到达时，通过<SPAN class=em0>STP C</SPAN>的信令消息的</NOBR></SPAN> <SPAN 
class=ps5><NOBR>雪崩效应，所有的信令端点，也就是和<SPAN class=em0>STP A</SPAN>和<SPAN 
class=em0>B</SPAN>对连接的交换机，从<SPAN class=em0>STP B</SPAN>接收到传输禁止</NOBR></SPAN> 
<SPAN class=ps6><NOBR>（<SPAN class=em0>TransFer Prohibited</SPAN>，<SPAN 
class=em0>TFP</SPAN>）消息，从而导致所有到<SPAN class=em0>STP 2</SPAN>的信令被路由为通过<SPAN 
class=em0>STP A</SPAN>。</NOBR></SPAN> <SPAN class=ps7><NOBR><SPAN 
class=ft4>图<SPAN class=em3>3-12 &nbsp;&nbsp;</SPAN>传输禁止和传输受控在<SPAN 
class=em3>SS7</SPAN>中的使用</SPAN></NOBR></SPAN> <SPAN 
class=ps8><NOBR>根据信令失败的性质，到达<SPAN class=em0>STP C</SPAN>的消息数可以超过<SPAN 
class=em0>MTP</SPAN>的第<SPAN class=em0>2</SPAN>层或第<SPAN 
class=em0>3</SPAN>层，从而导致<SPAN class=em0>STP</SPAN></NOBR></SPAN> <SPAN 
class=ps9><NOBR><SPAN class=ft5>C<SPAN class=em1>和</SPAN>SSP 2<SPAN 
class=em1>之间链路的拥塞问题。这种情况还会导致</SPAN>STP C<SPAN class=em1>向起始交换机的</SPAN>MTP<SPAN 
class=em1>发回传输受控</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps10><NOBR>（<SPAN 
class=em0>TransFer Controlled</SPAN>，<SPAN 
class=em0>TFC</SPAN>）消息。这种后向作用将使信令流最终停止在<SPAN class=em0>STP 
C</SPAN>在其限制内能</NOBR></SPAN> <SPAN class=ps11><NOBR>够处理的那一层&nbsp;。</NOBR></SPAN> 
<SPAN class=ps12><NOBR>当<SPAN class=em0>SSP 1</SPAN>试图通过<SPAN class=em0>STP 
B</SPAN>到达<SPAN class=em0>SSP 2</SPAN>时会出现一个问题，那就是它仍然会收到<SPAN 
class=em0>TFP</SPAN>。<SPAN class=em0>STP B</SPAN></NOBR></SPAN> <SPAN 
class=ps13><NOBR>已经和<SPAN class=em0>SSP 2</SPAN>断开连接，因此它不可能再访问<SPAN 
class=em0>STP C</SPAN>和<SPAN class=em0>STP D</SPAN>。如果它不是<SPAN class=em0>STP 
A</SPAN>和<SPAN class=em0>STP D</SPAN>之间</NOBR></SPAN> <SPAN 
class=ps14><NOBR>的桥接链路（<SPAN class=em0>3</SPAN>）的话，这种情况将使得<SPAN class=em0>SSP 
2</SPAN>不能到达。<SPAN class=em0>STP A</SPAN>可以重新路由消息。如果拥塞</NOBR></SPAN> <SPAN 
class=ps15><NOBR>持续并影响呼叫建立期间的服务质量，那么<SPAN class=em0>SSP 1</SPAN>和<SPAN 
class=em0>SSP 2</SPAN>之间的所有信令可以被路由为通过</NOBR></SPAN> <SPAN class=ps16><NOBR><SPAN 
class=ft5>STP A<SPAN class=em1>和</SPAN>D<SPAN class=em1>。一种实现纠错的方式是改变命令（<SPAN 
class=em0>ChangeOver Order</SPAN>，<SPAN 
class=em0>COO</SPAN>）</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps17><NOBR>。根据<SPAN class=em0>STP C</SPAN>的判断，</NOBR></SPAN> <SPAN 
class=ps18><NOBR>它可以直接通过连接的<SPAN class=em0>B</SPAN>链路，或者间接通过<SPAN class=em0>STP 
D</SPAN>发送给<SPAN class=em0>STP A<SPAN class=em1>，</SPAN></SPAN>通知<SPAN 
class=em0>STP A</SPAN>使用<SPAN class=em0>B</SPAN>链路连接</NOBR></SPAN> <SPAN 
class=ps19><NOBR><SPAN class=ft5>STP &nbsp;D<SPAN 
class=em1>。在这种情况下，一旦拥塞结束，需要从</SPAN></SPAN></NOBR></SPAN> <SPAN 
class=ps20><NOBR><SPAN class=ft5>STP &nbsp;C<SPAN 
class=em1>发送一条特定的改变回命令</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps21><NOBR>（<SPAN 
class=em0>ChangeBack Order</SPAN>）到<SPAN class=em0>STP A&nbsp;<SPAN 
class=em1>，</SPAN></SPAN>以恢复它们之间的直接链路上的路由。</NOBR></SPAN> <SPAN 
class=ps22><NOBR>在所有的包交换网络中实现拥塞链路的纠错过程时，必须注意避免链路振动。这是一个</NOBR></SPAN> <SPAN 
class=ps23><NOBR>很困难的设计问题，涉及到触发拥塞和其他链路纠错情况的缓冲区阈值的实现。</NOBR></SPAN> <SPAN 
class=ps24><NOBR>在最简单的情况下，没有向其他路由的转变，当<SPAN class=em0>STP C</SPAN>和<SPAN 
class=em0>SSP 2</SPAN>之间的拥塞回落到可接受</NOBR></SPAN> <SPAN 
class=ps25><NOBR>的水平时，<SPAN class=em0>STP</SPAN>发送传输允许（<SPAN class=em0>TransFer 
Allowed</SPAN>，<SPAN class=em0>TFA</SPAN>）消息，向它的邻居表明它又处于健</NOBR></SPAN> <SPAN 
class=ps26><NOBR>康的状态，可以继续在它的链路上传输信令。</NOBR></SPAN> <SPAN class=ps27><NOBR><SPAN 
class=ft5>5. <SPAN class=em4>基本的</SPAN>ISUP<SPAN 
class=em4>呼叫建立</SPAN></SPAN></NOBR></SPAN> <SPAN class=ps28><NOBR>图<SPAN 
class=em0>3-13</SPAN>中说明了和<SPAN class=em0>ISDN</SPAN>用户的呼叫建立和终止的基本呼叫流，以及<SPAN 
class=em0>PSTN</SPAN>上基本<SPAN class=em0>ISUP</SPAN>消</NOBR></SPAN> <SPAN 
class=ps29><NOBR>息的用法。表<SPAN class=em0>3-3</SPAN>中是<SPAN class=em0>ISDN/Q.931 
PRI</SPAN>呼叫处理消息的快速指南。同样地，表<SPAN class=em0>3-4</SPAN>列出了<SPAN 
class=em0>ISUP</SPAN></NOBR></SPAN> <SPAN class=ps30><NOBR><SPAN 
class=ft6>关于链路拥塞管理和节点拥塞状态分配，请参阅参考文献。</SPAN></NOBR></SPAN> </BODY></HTML>
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