Thank you for suggestions.<br>
    I test it again, and the callee answers as soon as possible.<br>
    The result is:<br>
        1. caller---(24028)---&gt;(24038)FS---(21679)---&gt;(21679)callee. The call duration is 8 minutes. The drop rate is 9.8%.<br>
        2. 
caller---(27042)---&gt;(27054)FS---(24670)---&gt;(24670)callee. The call
 duration is 9 minutes. The drop rate is 8.8%.<br>
    The drop rate reduces actually. But I still hear the <span lang="EN-US"> voice which keeps off and on</span>. I will try another test in different network structure to check if it is cause by the network traffic.<br>

<div style="text-align: right;">Sincerely yours,<br>
thisjoy.<br>
</div>
<br><div class="gmail_quote">On Fri, Mar 18, 2011 at 4:27 PM, Steven Ayre <span dir="ltr">&lt;<a href="mailto:steveayre@gmail.com">steveayre@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
Some
 RTP packets will be dropped because they either arrive before the 
signalling starts the media (on 18x or 200), or they arrive after the 
hangup.<br><br>How long was the call you made? 2380 suggests under a 
minute? Try a much longer call and see whether you&#39;re still seeing the 
same amount of loss.<br>

<br>-Steve<br><br>
</blockquote></div><br>