<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div><blockquote type="cite">What is the reason for such response?</blockquote><div><br class="webkit-block-placeholder"></div><div><blockquote type="cite">SIP/2.0 491 Request Pending<br>Via: SIP/2.0/UDP <a href="http://192.168.129.74:5160">192.168.129.74:5160</a>;branch=z9hG4bK17c3.17db29e7.0;received=<a href="http://192.168.129.74">192.168.129.74</a><br>Via: SIP/2.0/UDP <a href="http://192.168.129.74">192.168.129.74</a> ;branch=z9hG4bK17c3.23083974.0<br>Via: SIP/2.0/UDP <a href="http://192.168.129.74:5070">192.168.129.74:5070</a>;branch=z9hG4bK5b33ae78;rport=5070<br>From: "IPFon" <<a href="sip:0225761853@192.168.129.74:5070">sip:0225761853@192.168.129.74:5070</a>>;tag=as7217acbc <br>To: <<a href="mailto:sip:tzl@voip.touk.pl">sip:tzl@voip.touk.pl</a>>;tag=as7217acbc<br>Call-ID: <a href="mailto:307fda656066a7e264e85cea0742e601@192.168.129.74">307fda656066a7e264e85cea0742e601@192.168.129.74</a> <br>CSeq: 102 INVITE<br>User-Agent: Asterisk PBX<br>Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY<br>Supported: replaces<br>Content-Length: 0<br>X-Asterisk-HangupCause: Normal Clearing<br>X-Asterisk-HangupCauseCode: 16 <br></blockquote></div><div><br class="webkit-block-placeholder"></div><div>Asterisk will send a 491 Request Pending when it is currently processing an INIVTE on a particular call and it gets another INVITE that isn't a retransmission.</div><div><br class="webkit-block-placeholder"></div></div></body></html>