Index: channels/chan_sip.c
===================================================================
--- channels/chan_sip.c	(revision 47646)
+++ channels/chan_sip.c	(working copy)
@@ -4350,6 +4350,10 @@
 	const char *from = get_header(req, "From");
 	const char *to = get_header(req, "To");
 	const char *cseq = get_header(req, "Cseq");
+	const char *their_local_tag;
+	const char *their_remote_tag;
+	int found = FALSE;
+	int chan_is_outgoing = ast_test_flag(&p->flags[0], SIP_OUTGOING);
 
 	/* Call-ID, to, from and Cseq are required by RFC 3261. (Max-forwards and via too - ignored now) */
 	/* get_header always returns non-NULL so we must use ast_strlen_zero() */
@@ -4389,39 +4393,58 @@
 
 	dialoglist_lock();
 	for (p = dialoglist; p; p = p->next) {
-		/* In pedantic, we do not want packets with bad syntax to be connected to a PVT */
-		int found = FALSE;
-		if (req->method == SIP_REGISTER)
-			found = (!strcmp(p->callid, callid));
-		else 
-			found = (!strcmp(p->callid, callid) && 
-			(!pedanticsipchecking || !tag || ast_strlen_zero(p->theirtag) || !strcmp(p->theirtag, tag))) ;
-
-		if (option_debug > 4)
-			ast_log(LOG_DEBUG, "= %s Their Call ID: %s Their Tag %s Our tag: %s\n", found ? "Found" : "No match", p->callid, p->theirtag, p->tag);
-
-		/* If we get a new request within an existing to-tag - check the to tag as well */
-		if (pedanticsipchecking && found  && req->method != SIP_RESPONSE) {	/* SIP Request */
-			if (p->tag[0] == '\0' && totag[0]) {
-				/* We have no to tag, but they have. Wrong dialog */
-				found = FALSE;
-			} else if (totag[0]) {			/* Both have tags, compare them */
-				if (strcmp(totag, p->tag)) {
-					found = FALSE;		/* This is not our packet */
-				}
+		/* try and find a channel with a matching callid */
+		/* if pedantic check the tags as well */
+		if (strcmp(p->callid, callid)) {
+			continue;
+		}
+		if (!pedanticsipchecking) {
+			found = TRUE;
+			break;
+		}
+		/* Cancel sometimes has no to tag, if this channel didn't send it we have found the right one */
+		if ( req->method == SIP_CANCEL && totag[0] == '\0'  && strcmp(p->tag, fromtag)) {
+			found = TRUE;
+			if (option_debug > 4 ) {
+				ast_log(LOG_DEBUG, "Found dialog for CANCEL callid: %s from: %s\n", callid, from);
 			}
-			if (!found && option_debug > 4)
-				ast_log(LOG_DEBUG, "= Being pedantic: This is not our match on request: Call ID: %s Ourtag <null> Totag %s Method %s\n", p->callid, totag, sip_methods[req->method].text);
+			break;
 		}
-
-
-		if (found) {
-			/* Found the call */
-			sip_pvt_lock(p);
-			dialoglist_unlock();
-			return p;
+		if (req->method == SIP_RESPONSE) {
+			their_local_tag = totag;
+			their_remote_tag = fromtag;
+		} else {
+			their_local_tag = fromtag;
+			their_remote_tag = totag;
 		}
+		/* see if we match both sets of tags. we have already filtered the request to make sure it */
+		/* has the required tags for it's type, responses outside a dialog like 100 trying will find the */
+		/* right channel because p->theirtag will also be empty */
+		if ( strcmp(p->tag, their_remote_tag) ) {
+			continue;
+		}
+		if ( !strcmp(p->theirtag, their_local_tag)) {
+			if (option_debug > 4 ) {
+				ast_log(LOG_DEBUG, "%s callid:  %s found channel: %p , local tag: %s remote tag: %s\n", sip_methods[req->method].text , callid ,p , p->tag, p->theirtag );
+			}
+			found = TRUE;
+			break;
+		}
+		/* UAC channel does not have a dialog yet. reponse has a to tag establishing a new dialog */
+		if ( p->theirtag[0] == '\0' && chan_is_outgoing && ( req->method == SIP_RESPONSE )) {
+			if (option_debug > 4 ) {
+				ast_log(LOG_DEBUG, "%s callid: %s found channel, response with new dialog, local tag: %s remote tag: %s\n", sip_methods[req->method].text , callid , p->tag, their_local_tag );
+			}
+			found = TRUE;
+			break;
+		}
 	}
+	if (found) {
+	/* Found the call */
+		sip_pvt_lock(p);
+		dialoglist_unlock();
+		return p;
+	}
 	dialoglist_unlock();
 	
 	/* See if the method is capable of creating a dialog */