SESSION ID allocation in RAC across instances

In Oracle RAC, when each instance creates a connection and allocates a session ID, it looks like a tendency that the same session ID (or close/similar ID) is allocated for the same program.

Below is an example.  We have 3 node RAC and 7 app servers for our application.  When a service (called WCSGATE.exe) running on the app servers connects to RAC, each instance allocates duplicated (or close) SESSION IDs across RAC.

Is there any mechanism for Oracle when it allocate SESSION ID?  Is there any way to make each instance to allocate different range of SESSION IDs?

Jun

     

INST_ID