Visara CNA-8000 - Manual (Page 89)

CNA-8000 Users Guide and Maintenance Manual
707157-001 5-1
Chapter 5. TN3270 Management
TN3270E Server Overview
TN3270E clients connect to the CNA-8000 attempting to get sessions to VTAM and the
applications supported by VTAM. TN3270E connections result in an assignment by the
CNA-8000 of the client to an SNA LU. SNA LUs are grouped into Host Circuits on the
CNA-8000, each representing an SNA PU. Prior to establishing LU sessions, the Host
Circuit (PU) must be activated from VTAM. Following the PU activation, VTAM must
then activate the individual LUs.
One configuration option on the CNA-8000 is to limit TN3270E clients connecting only
to LUs that have been activated. This option should result in clients only getting sessions
that are ready to go. Clients attempting to connect to a LU that has not been activated,
should result in the client getting a message written to their screen indicating that the
resource is not currently available.
The TN3270E protocol does not require the client and the server to send messages back
and forth once a connection is made unless there is actual session level communication
that needs to be passed. This means that if a client stops communicating to the CNA-
8000, the CNA-8000 would not know it until such time as the host attempted to contact
the client for some reason. Keepalive is a method used by the CNA-8000 to determine
whether a TN3270E client that has connected to the CNA-8000 is still connected.
Periodically the CNA-8000 will send a ‘Do-Timing-Mark’ keepalive packet to the client
that requires a response from the client. If no response to this ‘keepalive’ message is
received within the prescribed time, then the client session will be terminated and the
resource freed up. If the client was in session with an application, the application will be
notified that the client is no longer there. VTAM will also be notified that the client has
‘powered off’. Keepalive timeouts may be logged in the event log. The keepalive
function is configurable on the Configure Server panel.
Another option to disconnect clients exists in the CNA-8000; the configurable option to
‘Disconnect Client on Unbind’. When a client connects up, they typically get a VTAM
logon screen (unless the LU is genned to automatically log them on to an application).
The user is allowed to log on to a session with an application. If the user logs off the
application, or if the application logs the user off, such as because of inactivity for a
predetermined time, then rather than painting the log on screen back on the clients screen,
the client will be disconnected from the CNA-8000. Note that if the client’s TN3270E
emulation is configured to automatically reconnect after a disconnection, then it may not
be obvious that the CNA-8000 has disconnected the client, since the client may connect
back up within seconds.
The CNA-8000 has tools to check the status of its Host Circuits and the LU sessions
assigned to them.