利用Exosip进行SIP协议通信，对方发送INFO过来，但是我这里一直回复481 Call Leg/Transaction Does Not Exist，请问下大神们产生这个问题可能原因？？
下面是发送的报文信息：
INFO sip:153122387331646674@52.50.64.55:5090 SIP/2.0
Via: SIP/2.0/UDP 52.160.6.60:5061;rport;branch=z9hG4bK1635013705
From: sip:123@52.160.6.60;tag=3748143564
To: sip:153122387331646674@52.50.64.55:5090
Call-ID: 1954869349
CSeq: 20 INFO
Content-Type: Application/IVS_XML
Max-Forwards: 70
User-Agent: eXosip/4.0.0
Content-Length: 244
<?xml version="1.0"?>
FileList991202014-12-11T00:00:00Z2014-12-11T09:25:40Z
SIP/2.0 481 Call Leg/Transaction Does Not Exist
Via: SIP/2.0/UDP 52.160.6.60:5061;rport=5061;branch=z9hG4bK1635013705
From: sip:123@52.160.6.60;tag=3748143564
To: sip:153122387331646674@52.50.64.55:5090;tag=1375850661
Call-ID: 1954869349
CSeq: 20 INFO
User-Agent: Cascade
Content-Length: 0