--- channels/chan_sip.c.orig	2010-07-08 14:51:53.000000000 +0000
+++ channels/chan_sip.c	2010-07-08 14:53:51.000000000 +0000
@@ -22085,6 +22085,25 @@
 		}
 	}
 	p->recv = *sin;
+        if(!p->owner) { 
+                char *e; 
+                int respid;      
+ 
+                e = ast_skip_blanks(REQ_OFFSET_TO_STR(req, rlPart2)); 
+ 
+                if (!ast_strlen_zero(e)) { 
+                        if (sscanf(e, "SIP/2.0 %30u", &respid) == 1) { 
+                                if((respid == 180)||(respid == 100)) { 
+                                        transmit_request(p, SIP_CANCEL, p->lastinvite, XMIT_RELIABLE, FALSE); 
+                                        p->needdestroy = 0; 
+                                        sip_scheddestroy(p, DEFAULT_TRANS_TIMEOUT); 
+                                        sip_pvt_unlock(p); 
+                                        return 1; 
+ 
+                                } 
+                        }
+                }
+        }
 
 	if (p->do_history) /* This is a request or response, note what it was for */
 		append_history(p, "Rx", "%s / %s / %s", req->data->str, get_header(req, "CSeq"), REQ_OFFSET_TO_STR(req, rlPart2));