Connection and Authorisation
In order to access the Server, a Client must log into the system and establish a session. This is accomplished by sending a Login message.
Depending on how the System has been configured, a UserId may be allowed more than one simultaneous login. Each such login is called a session. Each session for a UserId operates independently. For example, if the maximum number of simultaneous logins for each user is set to 5, then each user may have up to five active logins (sessions) at any time and each session may be dealing with different functions and messages.
Sessions are numbered sequentially from 1.
The SessionId field in the Login request specifies which session number should be used for the login. SessionId may have a value from 1 through to the maximum number of simultaneous sessions allowed in the System. The user will be logged in to the System using the specified session number. If the user already had an active login on that session number, the new login will replace the previous one and any activity from the process or program that was logged in previously will fail from that point (since that process or program will effectively have been logged out from the System).
SessionId may also have the value 0, in which case the user will be logged in with the next available free (not currently used) session for the UserId. If there are no free sessions (the user has the maximum number of simultaneous sessions allowed), the Login transaction will fail
Role message documentation not provided in this specification.