请教

xiong19811209

<p class="MsoNormal" style="MARGIN: 0cm 0cm 3.6pt; TEXT-INDENT: 24pt;"><font size="3"><font face="Times New Roman"><place wst="on"><span lang="EN-US" style="mso-fareast-font-family: 宋体;"><span style="FONT-SIZE: 12pt; LINE-HEIGHT: 140%; FONT-FAMILY: 宋体; mso-font-kerning: 1.0pt; mso-bidi-font-family: &quot;Times New Roman&quot;; mso-ascii-font-family: &quot;Times New Roman&quot;; mso-hansi-font-family: &quot;Times New Roman&quot;; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;">专网用户入公网的</span>LOOP</span></place><span lang="EN-US" style="mso-fareast-font-family: 宋体;">+DTMF，请问这是一个什么概念<p></p></span></font></font></p>