Simple about SAP basis: Logon Load Balancing in SAP R/3, Logon Groups, SMLG and CCMS Configuration for Basis Admins

What is SAP Logon Load Balancing?

SAP R/3 Logon load balancing enables a SAP Basis admin to create various log on groups.
Logon groups are logical groups of users that can be assigned to one or more SAP instances.
A group GroupX, Once assigned to an instance I, all users who login using that group in the SAP log on pad client, will automatically login into the instance.
If you have two instances I1, I2 then you can create two groups GroupX and GroupY and assign them to I1 and I2 respectively. You can also divide your users according to some criterion (such as Floor1 thru 5 will use GroupX and floor 6 thru 10 will use GroupY) and ask them to use only those groups.
In SAP Logon Pad, you can create and delete logon group entries, remove instances from groups, and delete entire logon groups.
When you call transaction SMLG, the CCMS: Maintain Logon Groups screen shows a table with entries for logon groups and the associated instances. An entry in this table, which is characterized by an instance and a logon group, is known as an assignment.
A logon group to which multiple instances belong therefore consists of multiple assignments in this table, where an assignment contains one instance in each case.

Choose CCMS® Configuration logon Groups, or call transaction SMLG.
Choose (Create Assignment), and specify the desired name of the logon group in the Logon Group input field. Enter the name of the desired Instance that is to belong to the logon group. The logon group SPACE is reserved for SAP; therefore, do not use this name.
Repeat the last step until you have entered all instances that are to belong to the logon group.
You can assign one group to one or more instances.
Save your changes.

Choose CCMS® Configuration ® Logon Groups, or call transaction SMLG.
Select any assignment for the logon group that you want to delete or from which you want to remove an instance.
To remove an instance from the selected logon group, choose Remove Instance, enter the desired instance on the next screen, and confirm your choice by choosing (Delete).
To delete the desired log on group, choose Delete Group and confirm your choice by choosing (Delete) on the next screen.
Save your changes.

Choose CCMS® Configuration ® Logon Groups, or call transaction SMLG.
To change the properties of an assignment, double-click the assignment, and switch to the Properties tab page.
You can change the following properties:
IP address of the application server: Only enter a value in this field if the application server associated with the instance needs to be addressed by the front end with a different IP address to the one used for application server-internal communication. This value applies only for the selected assignment.
Settings for external RFC call: You can use this indicator to determine whether logon using an external RFC connection is to be permitted. This value applies to the selected logon group.
Threshold values for dialog response time and number of users logged on

If you log on using a logon group, the logon is automatically performed using the instance of the group that currently has the best dialog quality. This quality is a key figure that is calculated from the number of users logged on and the average dialog response time.
To allow the different prerequisites of different instance to be taken into account in this calculation, you can set threshold values for the dialog response time and the number of users yourself. The larger the actual values for response time and the number of users are in comparison to the threshold values set, the lower the quality. These figures apply for the selected instance.
The values for Response Time and Users are not absolute limits, but rather thresholds. Even if the current value for response time or number of users is higher than this threshold value, it is possible to log on to another instance. The threshold values only influence the calculation of the current logon server of the logon groups.
You can use a preview to see how the settings of the threshold values can affect the quality calculation, based on the current performance data. Choose test to do this. In a logon group, the instance with the highest quality key figure is always selected for the logon.
Choose Copy, and save your changes.