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<div>We have been working on a strange Issue with TAC , We have CUCM 6.0.1.1000.37 , The <span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Problem which we are facing is that when we make a PSTN call from a SIP phone 3951 to a cell phone or PSTN Phone, Ring back tone is played on 3951 IP phone even if the mobile phone at other end is switched OFF & PSTN is busy, A 7970 sip phone does not behave this way. I have sniffer capture for this and I am not good at understanding SIP messages. TAC engineer has told me to enable <font size="2">PRACK message , can any one tell me what does this SIP message does and how to enable it on CUCM.</font></span></div>
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<div><span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">TIA</span></div>
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<div><span style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">Aman</span></div>
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