The maximum number of connections across the LAN, i.e. servers x clients. If you get an "Out Of Sessions" or "Out of Msg Instance, Increase[LAN]Sessions" error, increase the value of this parameter.
A CitectSCADA client uses 3 sessions for the servers (Alarms, Trends, Reports) + 1 session for each of your I/O Servers, so the default parameter setting is good for Clients.
A Server uses 1 session for each client attached, for each type of server it is. So if a computer is a Alarms, Trends, Reports, and I/O Server and you have 20 clients, the server uses 4 x 20 = 80 sessions. You should also allow 50% extra sessions, because during a redundant changeover you get an extra peak loading. So in the example, allow a total of 80 + 40 = 120 sessions.
Allowable Values: 16 to 4000
Default Value: 128