This subject is probably too long to cover in detail in this Community, though here is a a brief summary:
The Expedition flow uses a database (the iCDB) to store the schematic (logical) and constraint data and to manage concurrent acces to the data for multiple users, it is also used used by Expedition PCB to extract the logical definition of the design. To enable this concurrent access there are a number of process that run on the systems accessing the data. One process is the iCDBNetServer that manages access to the iCDB and another is the iCDBNetLauncher that manages client requests for access to the iCDBNetServer. When a project is opened it starts the iCDBNetServer process and all clients access the database using this process (you will see an iCDBNetServer.exe running, this is sometimes refered to as the iCDB Server). For concurrent usage this process needs to run in concurrent mode in which case the Remote Server Configuration Manager service is used (this service runs as the iCDBNetLauncher.exe on the system). The iCDBNetLauncher listens for clients (applications) attempting to connect to the iCDB (open a project), the first client triggers the iCDBNetLauncher to start the iCDBNetServer.exe and open the database for edit. Additional clients requesting access to the database are directed via the iCDBNetLauncher.exe to connect to the already running iCDBNetServer and thus join the project. Projects have a setting that tells them to run in concurrent mode (Enable concurrent design in Setup - Settings in DxDesigner) and they connect to the project database through the iCDBNetLauncher.exe process.
XtremePCB has its own processes to allow access to the PCB Layout, the Xtreme Service and Xtreme Design Session, these are analogous to the iCDBNetLauncher and iCDBNetServer. However, the project also needs access to the iCDB for the front-end tools (DxDesigner) and Constraint Management so both 'servers' need to be configured for full concurrent access.
For conccurrent design the Remote Server Configuration Manager must be installed and configured and for XtremePCB the Xtreme Service must be installed. Generally this is done by a Systems Administrator and end-users do not need to understand the details. If you are the administrator or need a better understanding then your best source of information is the 'Remote Server Configuration Manager and Server Manager Administrator's Guide' and the 'XtremePCB Administrator's Guide' both delivered with the documentation.
Note that in the EE7.9.4 release of software these two guides have been combined into the 'Concurrent Design Administrator’s Guide'
I would like to know whehther client & administrator need to have same OS for xtreme session?
Also if version between the client & administrator gets change it will affect the xtreme session?
XtremePCB is supported in a mixed platform environment, see the section on 'Setting up path mapping for mixed-platform configurations' in the on-line documentation. The client/server must use the same version of iCDB server but you can configure the server machine to run multiple versions in parallel, again this is documented in the on-line help.
How to know what is the ICDB version?
Why ICDB differ?
The iCDB is tied to the release, as we enhance functionality it is sometimes necessary to revise the database structures. Providing the server and client are running the same versions of the software they will be compatible, however a design should not be considered backward's compatible between a release. So if the client/server are both running 7.9.3 and the design has been opened in 7.9.3 then there will be no issues. If the design has been 'upgraded' to 7.9.4 then the client/server must be running the 7.9.4 version of the software to open the design.