diff --git a/callagent/SIPCall.st b/callagent/SIPCall.st
index fe9012e..f0b9a06 100644
--- a/callagent/SIPCall.st
+++ b/callagent/SIPCall.st
@@ -17,7 +17,7 @@
 "
 
 Object subclass: SIPCall [
-    | initial_dialog dialog sdp_offer invite state ua next_cseq |
+    | initial_dialog dialog sdp_offer sdp_result invite state ua next_cseq |
     <category: 'SIP-Call'>
     <comment: 'I am a high level class to deal with transactions,
 sessions and calls. Right now I do not support forking proxies and
@@ -30,6 +30,7 @@ will simply ignore everything but the first dialog.'>
     SIPCall class >> stateCancel  [ <category: 'states'> ^ #cancel  ]
     SIPCall class >> stateHangup  [ <category: 'states'> ^ #hangup  ]
     SIPCall class >> stateRemoteHangup [ <category: 'states'> ^ #remoteHangup ]
+    SIPCall class >> stateFailed  [ <category: 'states'> ^ #failed ]
 
     LegalStates := nil.
 
@@ -91,6 +92,13 @@ will simply ignore everything but the first dialog.'>
 
     createCall: aSDPOffer [
         <category: 'call'>
+
+        (self moveToState: self class stateInvite) ifFalse: [
+            self logError: 'Call failed to start.' area: #sip.
+            ^ false
+        ].
+
+
         sdp_offer := aSDPOffer.
 
         next_cseq := initial_dialog cseq + 1.
@@ -124,23 +132,69 @@ will simply ignore everything but the first dialog.'>
         ].
     ]
 
+    check: aDialog [
+        <category: 'private'>
+        "I check if this enters a new confirmed dialog or if this is the
+        confirmed dialog."
+
+        "We have no confirmed dialog, accept it"
+        ^ dialog isNil
+            ifTrue: [
+                aDialog isConfirmed ifTrue: [
+                    dialog := aDialog.
+                    self logError: 'SIPCall dialog is confirmed now.' area: #sip.
+                ].
+                true]
+            ifFalse: [
+                "We could fork things here. For multi party call"
+                dialog to_tag = aDialog to_tag].
+    ]
+
     callTimedOut [
         <category: 'call-result'>
         self logError: 'Call timed-out.' area: #sip.
+
+        (self moveToState: self class stateTimeout) ifFalse: [
+            ^ self logError: 'Call failed to move to timeout.' area: #sip.
+        ].
     ]
 
     callSuccess: aResponse dialog: aDialog [
         <category: 'call-result'>
-        self logError: 'Call session etsablished.' area: #sip.
+        (self check: aDialog) ifFalse: [
+            self logError: 'Call can only have one session. Ignoring.' area: #sip.
+            ^ false
+        ].
+
+        (self moveToState: self class stateSession) ifTrue: [
+            self logError: 'Call session etsablished.' area: #sip.
+            sdp_result := aResponse sdp.
+            self newSession.
+            ^ true
+        ].
+        ^ false
     ]
 
     callFailure: aResponse dialog: aDialog [
         <category: 'call-result'>
-        self logError: 'Call Failure.' area: #sip.
+        (self check: aDialog) ifFalse: [
+            self logError: 'Call can only have one session. Ignoring failure.' area: #sip.
+            ^ false
+        ].
+
+        (self moveToState: self class stateFailed) ifTrue: [
+            self logError: 'Call Failure.' area: #sip.
+            self newFailed.
+        ].
     ]
 
     callNotification: aResponse dialog: aDialog [
         <category: 'call-result'>
+        (self check: aDialog) ifFalse: [
+            self logError: 'Call can only have one session. Ignoring notification.' area: #sip.
+            ^ false
+        ].
+
         self logError: 'Call Notification.' area: #sip.
     ]
 
@@ -151,18 +205,37 @@ will simply ignore everything but the first dialog.'>
 
     hangupSuccess: aResponse dialog: aDialog [
         <category: 'hangup-result'>
+        (self check: aDialog) ifFalse: [
+            self logError: 'Call can only have one session. Ignoring failure.' area: #sip.
+            ^ false
+        ].
+
         self logError: 'Hang-Up success.' area: #sip.
     ]
 
     hangupFailure: aResponse dialog: aDialog [
         <category: 'hangup-result'>
+        (self check: aDialog) ifFalse: [
+            self logError: 'Call can only have one session. Ignoring failure.' area: #sip.
+            ^ false
+        ].
+
         self logError: 'Hang-Up failure.' area: #sip.
     ]
 
+    newSession [
+        <category: 'callback'>
+    ]
+
+    newFailed [
+        <category: 'callback'>
+    ]
+
     nextCSeq [
         | res |
         <category: 'accessing'>
         res := next_cseq.
-        ^ (next_cseq := next_cseq + 1)
+        next_cseq := next_cseq + 1.
+        ^ res
     ]
 ]
diff --git a/callagent/SIPTransactions.st b/callagent/SIPTransactions.st
index 0f9ee5c..9916066 100644
--- a/callagent/SIPTransactions.st
+++ b/callagent/SIPTransactions.st
@@ -130,8 +130,9 @@ Object subclass: SIPTransaction [
         <category: 'private-dispatch'>
 
         useragent removeTransaction: self.
-        success ifNotNil: [
-            success value: aReq value: aDialog]
+        ^ success isNil
+                ifTrue: [true]
+                ifFalse: [success value: aReq value: aDialog].
     ]
 
     respFailure: aReq dialog: aDialog [
@@ -143,18 +144,31 @@ Object subclass: SIPTransaction [
     ]
 
     newData: aReq [
-        | code dialog |
+        | code dialog new_cseq |
         <category: 'private-dispatch'>
 
         ('Found response %1 %2' % {aReq code. aReq phrase}) printNl.
-        sem critical: [
-            retransmit_time cancel.
-            fail_time cancel.
+        "Compare the sequence number"
+        new_cseq := (aReq parameter: 'CSeq' ifAbsent: [
+            self logError: '%1(%2) response lacks CSeq.'
+                    % {self class. self branch} area: #sip.
+            ^ false
+        ]) number.
+
+        cseq = new_cseq ifFalse: [
+            self logError: '%1(%2) wrong cseq:. %1 %2.'
+                    % {self class. self branch. cseq. new_cseq} area: #sip.
+            ^ false
         ].
 
         "Store all dialogs.... and match them..."
         dialog := initial_dialog newFromRequest: aReq.
 
+        sem critical: [
+            retransmit_time cancel.
+            fail_time cancel.
+        ].
+
         code := aReq code asInteger.
         code < 200 ifTrue: [
             ^ self respNotification: aReq dialog: dialog
@@ -285,9 +299,12 @@ SIPTransaction subclass: SIPInviteTransaction [
         | branch |
         branch := useragent class generateBranch.
         self changeState: self class stateTerminated.
-        self queueData: (self createAck: branch dialog: aDialog) asDatagram
-                dialog: aDialog.
-        ^ super respSuccess: aReq dialog: aDialog.
+
+        "TODO: We probably want to accept and then release/BYE it"
+        (super respSuccess: aReq dialog: aDialog) ifTrue: [
+            self queueData: (self createAck: branch dialog: aDialog) asDatagram
+                    dialog: aDialog.
+        ]
     ]
 
     respFailure: aReq dialog: aDialog [