Siemens SIMATIC PCS7 Manual page 165

Client request for
user input (2)
Opening
transitions (3)
Redundant access
to the OS data
manager (4)
Server failure
Batch flexible , Manual
C79000-G7076-C650-02
All requests for user inputs will be sent by the clients to the server which
carries them out and a message will be returned to all clients which visualize
this change. The server always retains control.
When a transition is opened for visualization this is reported to the server.
Here the variables are reported to the OS for monitoring and in the case of
OS modification messages sent to the client(s).
A condition of redundant access is that the computer in which the OS client
is installed also has an OS data manager running with the same Runtime
project.
If there is a server failure there are 3 ways of restarting:
1. If the server is active as the only batch control and batches are still
running, are paused or are in 'error' condition, batch control will start
again automatically after stopping and will continue processing the
batches.
2. Every BATCH flexible application is notified when an application is
started or finished. If a client is informed that a batch control instance has
finished, the client will check to see whether any other instances of batch
control are running and if they include a server. If a server is not found,
each one of the batch control instances running will check whether it
should become the server. If this is the case, a connection with WinCC
will be set up. If this attempt fails, this client will be shut down as well.
3. Each client checks regularly to make sure it still detects the server and is
able to send it messages. If this is not the case, checking comes into effect
(as described under 2.) with the aim of making a suitable client into the
server.
Batch control
5-29