User manual

Hot Standby
33002479 06 07/2008 321
Network Effects of Modicon Quantum Hot Standby with Unity Solution
Overview The Modicon Quantum Hot Standby with Unity Pro solution is a powerful feature of
NOEs, a feature that increases the reliability of your installation. Hot Standby uses
a network, and using the Hot Standby feature over a network can affect the behavior
of:
z browsers
z remote and local clients
z I/O scanning service
z global data service
z FTP/TFTP server
The following are factors you may encounter while using the Modicon Quantum Hot
Standby with Unity solution.
Browsers
If a browser requests a page and during the process of downloading that page an IP
address switchover occurs, the browser will either hang or time out. Click the
Refresh or Reload button.
Remote Clients Hot Standby switchover affect remote clients.
An NOE will reset under the following conditions:
Remote Connection Request during Hot Standby : If a remote client establishes
a TCP/IP connection during a Hot Standby switchover, the server closes the
connection using a TCP/IP reset.
Hot Standby Switchover during Remote Connection Request : If a remote
client makes a connection request and a Hot Standby switchover occurs during
the connection request, the sever rejects the TCP/IP connection by sending a
reset.
Outstanding Requests : If there is an outstanding request, the NOE will not
respond to the request, but the NOE will reset the connection.
The NOE will do a Modbus logout if any connection has logged in.
Local Clients During a switchover, the NOE will reset all client connections using a TCP/IP reset.
Note: In Modicon Quantum Hot Standby with Unity Pro configuration, the NOE’s I/
O Scanner must be enabled.