CLOSED STATE (i.e., TCB does not exist) If the user does not have access to such a connection, return "error: connection illegal for this process". Otherwise return "error: connection does not exist". LISTEN STATE SYN-SENT STATE SYN-RECEIVED STATE Queue for processing after entering ESTABLISHED state. If there is no room to queue this request, respond with "error: insufficient resources". ESTABLISHED STATE FIN-WAIT-1 STATE FIN-WAIT-2 STATE If insufficient incoming segments are queued to satisfy the request, queue the request. If there is no queue space to remember the RECEIVE, respond with "error: insufficient resources". Reassemble queued incoming segments into receive buffer and return to user. Mark "push seen" (PUSH) if this is the case. If RCV.UP is in advance of the data currently being passed to the user notify the user of the presence of urgent data. When the TCP takes responsibility for delivering data to the user that fact must be communicated to the sender via an acknowledgment. The formation of such an acknowledgment is described below in the discussion of processing an incoming segment. CLOSE-WAIT STATE Since the remote side has already sent FIN, RECEIVEs must be satisfied by text already on hand, but not yet delivered to the user. If no text is awaiting delivery, the RECEIVE will get a "error: connection closing" response. Otherwise, any remaining text can be used to satisfy the RECEIVE. CLOSING STATE LAST-ACK STATE TIME-WAIT STATE Return "error: connection closing".