A variation of client-server computing is , in which software that allows for applications are installed on servers and then accessed and executed through desktop clients, instead of installing applications on each individual client computer.

Terminal services

Explanation:

Terminal services are multiuser, lean client environment from Microsoft which was built for Windows servers. It was first launched on the Windows NT 4.0 in 1996, as of the 2009 the launch of Windows Server 2008 R2, it became part of Remote Desktop Services (RDS), and exclusively, the "shared sessions" method in RDS.

Just like in the old times of mainframes, Terminal Services supports numerous users connected to a central computer. The user's device can be a compact PC, bare-bones PC or a dedicated terminal, and all of them are to function as input/output (I/O) terminals and use the same OS and applications running in the server. Terminal Services utilizes the Microsoft's Remote Desktop Protocol (RDP) to govern mouse, keyboard and screen transfer.

answer; its the top layer;