How does a SAP LOGON work?

When a SAP GUI process is started on the front end, a command line parameter is sent, indicating one of the following:

  • A specific dispatcher can be accessed directly (go directly to 3)
  • The logon must first be sent to the message server (1) for logon load balancing
  • When logon load balancing is used, the message server returns the IP address and instance number (2) of a specific dispatcher. The number of dispatchers available for a particular logon is configured in the system. Logon load balancing is useful if certain user groups are assigned to work on specific servers.
  • The message server returns the IP address of one of the assigned dispatchers, for example the dispatcher that has shown the best response time during the last five minutes. Response times are stored in the collected workload data.
  • The frontend process then connects to the assigned dispatcher (3), which selects a free dialog work process (4) to compare the logon user data with the user data stored in the database (5, 6).
  • If the logon user data does not agree with the stored user data, no logon is allowed. If the logon is successful, the SAP GUI is established with the user (7-10). This dispatcher and its work processes are used for the duration of the session.
  • If a user logs off and then logs on again to the system, logon load balancing may cause the message server to select another dispatcher for the user to work with.

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