[求助]急，请老师帮助。。。。。。

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<P>请问老师<BR>Which WAN protocol is used for out-of-band signaling?<BR>A. NCP<BR>B. HDLC<BR>C. LAPB<BR>D. LAPD<BR>Answer: D<BR>out-of-band signaling 是什么意思啊？</P><P><FONT color=#ff0000>out-of-band signaling&nbsp;: 带外信令；网络中，任何使用与平常用于数据传输的信道或频率相分离的传输。</FONT></P><P><FONT color=#ff0000>控制信道和数据信道共享同样的链路,就称为in-band，使用一个分离的信道专门用于控制用，就称为out-of-band ，再看下面对于LAPB和LAPD的解释，我想你就能明白了．为什么选Ｄ答案．</FONT></P><P><FONT color=#ff0000>&nbsp;LAPB：均衡式链路存取规程（Link Access Procedure, Balanced ，LAPB），是一个工作在数据链路层的面向连接的协议，被X.25使用。它同样能够提供简单的数据传输连接。因为LAPB有着严格的超时和窗口机制，使得它得开销极其巨大。<BR><BR>LAPD：D通道链路存取规程（Link Access Procedure, D-Channel ，LAPD）是ISDN在数据链路层为D通道使用的一个协议。LAPD是从LAPB中派生出来的，它主要用来平衡基本ISDN访问的信号要求。<BR></FONT></P><P>&nbsp;</P><p>［此帖子已被 rainypan 在 2005-8-14 15:30:56 编辑过］

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<P>Which of the following statements correctly describes the characteristics of a Frame<BR>Relay point-to-point subinterface? (Select two answer choices)<BR>A. Needs to use Inverse ARP.<BR>B. Maps a single IP subnet per DLCI.<BR>C. Maps a single IP subnet across multiple DLCIs.<BR>D. Resolves NBMA (non broadcast multi access) split horizon<BR>issues.<BR>E. Requires use of the frame-relay map command.<BR>F. None of the above<BR>这题是选BD吗 为什么<BR></P><P><FONT color=#ff0000>帧中继的Point-to-point要求每个子网要有属于自己的DLCI号，默认情况下，只有主接口才会识别DLCI，因而要给子接口分配相应的DLCI．而且这种类型可以解决水平分割的问题．ＢＤ答案是正确的．</FONT></P><P>&nbsp;</P><p>［此帖子已被 rainypan 在 2005-8-14 15:58:13 编辑过］

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<P>Which of the following correctly describe characteristics of PPP? (Select all valid<BR>answer choices)<BR>A. Encapsulates several different types of routing protocols.<BR>B. Supports only IP.<BR>C. Can be used over analog circuits.<BR>D. Is proprietary to Cisco<BR>E. Supports error<BR>是选CE吗&nbsp; C是什么意思？</P><P><FONT color=#ff0000>ＡＣＥ，PPP只是用来封装用，支持多种的三层路由协议，Ｃ选项是说可以用于模拟线路，比如说电话播号等程控封装．并且提供了错误检测的能力，最后一个答案．</FONT></P><P>&nbsp;</P><p>［此帖子已被 rainypan 在 2005-8-14 16:14:40 编辑过］

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<P>Regarding PAR (Positive Acknowledgement and Re-transmission), which of the<BR>answer choices below are correct? (Select all that apply.)<BR>A. The source device will only retransmit lost packets on the request of<BR>the destination device.<BR>B. The source device starts a timer when it sends a segment and retransmits if<BR>an acknowledgment is not received before the timer expires.<BR>C. The destination device acknowledges receipt of a segment by sending a<BR>packet with a new sequence number and the ACK bit sent.<BR>D. The destination device acknowledges receipt of a segment by sending a<BR>packet that indicates the next sequence number it expects.<BR>E. If the destination device does not receive a segment, all segments<BR>are retransmitted.<BR>F. The source device keeps a record of all segments sent and expects<BR>and acknowledgment of each.<BR>这题该选什么呢<BR></P><P><FONT color=#ff0000>Positive Acknowledgement and Re-transmission 带确认的肯定重传，要求接收方机器在收到数据时，通过向发送方回送一个确认消息，来与发送发机器保持通信．发送方将它所收到的每个数据段都记录下来，并在发送下一个数据段之前，等待对它们的确认．当发送一个数据段时，发送方机器启动一个计时器，如果在收到从接收方返回的确认之前计时器到期了，就重传这个数据段．</FONT></P><P>正确答案　ＢＤＦ</P><p>［此帖子已被 rainypan 在 2005-8-14 16:27:26 编辑过］

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<P>When selecting a Network Interface Card (NIC), which of the following factors need<BR>to be considered? Select three<BR>A. The type of application used on the network<BR>B. The type of system bus used by the computers<BR>C. The type of memory installed in each computer<BR>D. The type of media used in the network topology<BR>E. The type of protocols used in the network<BR>F. The physical layout of the network hosts<BR>这题选什么呢 </P><P><FONT color=#ff0000>这题主要考察网卡的问题了．答案是ＢＤＥ．系统总线，媒体类型，网络协议（一般都是TCP/IP）</FONT></P><p>［此帖子已被 rainypan 在 2005-8-14 15:47:18 编辑过］

chinamoon

<P>well done!</P>

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<P>真的不知道说什么。。。</P><P>太感谢了！！！</P>

single

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