OPEN Call

    CLOSED STATE (i.e., TCB does not exist)

      Create a new transmission control block (TCB) to hold connection
      state information.  Fill in local socket identifier, foreign
      socket, precedence, security/compartment, and user timeout
      information.  Note that some parts of the foreign socket may be
      unspecified in a passive OPEN and are to be filled in by the
      parameters of the incoming SYN segment.  Verify the security and
      precedence requested are allowed for this user, if not return
      "error:  precedence not allowed" or "error:  security/compartment
      not allowed."  If passive enter the LISTEN state and return.  If
      active and the foreign socket is unspecified, return "error:
      foreign socket unspecified"; if active and the foreign socket is
      specified, issue a SYN segment.  An initial send sequence number
      (ISS) is selected.  A SYN segment of the form <SEQ=ISS><CTL=SYN>
      is sent.  Set SND.UNA to ISS, SND.NXT to ISS+1, enter SYN-SENT
      state, and return.

      If the caller does not have access to the local socket specified,
      return "error:  connection illegal for this process".  If there is
      no room to create a new connection, return "error:  insufficient
      resources".

    LISTEN STATE

      If active and the foreign socket is specified, then change the
      connection from passive to active, select an ISS.  Send a SYN
      segment, set SND.UNA to ISS, SND.NXT to ISS+1.  Enter SYN-SENT
      state.  Data associated with SEND may be sent with SYN segment or
      queued for transmission after entering ESTABLISHED state.  The
      urgent bit if requested in the command must be sent with the data
      segments sent as a result of this command.  If there is no room to
      queue the request, respond with "error:  insufficient resources".
      If Foreign socket was not specified, then return "error:  foreign
      socket unspecified".

    SYN-SENT STATE
    SYN-RECEIVED STATE
    ESTABLISHED STATE
    FIN-WAIT-1 STATE
    FIN-WAIT-2 STATE
    CLOSE-WAIT STATE
    CLOSING STATE
    LAST-ACK STATE
    TIME-WAIT STATE

      Return "error:  connection already exists".