How XenApp or XenDesktop Logon Process Works?

Pictorial representation:

Step-by-Step Explanation:

Step	XenApp	XenDesktop
1	User requests a connection to a desktop or application. Users initiate the process by launching an application or desktop through the Citrix client, a shortcut create by Receiver, or a link on Web Interface.
2	Web Interface queries the XenApp Zone Data Collector (ZDC). The Web Interface passes the request to the appropriate controller, along with authentication and user information.	Web Interface queries the XenDesktop Controller (XDC). The Web Interface passes the request to the appropriate controller, along with authentication and user information.
3	ZDC returns best server information. Using load information, available servers, zone preferences and access rights, the	XDC returns best desktop information. Using available desktop and access rights, the controller server returns the best desktop

Reference: Citrix Optimization Guide: User Logon