## Computing Model

The Sun Ray Administration Tool (Admin GUI) provides an easy way to manage primary Sun Ray objects such as servers, sessions, desktop units, and tokens:

The Sun Ray system provides customers with an interoperable desktop computing solution that reduces the maintenance, upgrade, and operational costs associated with most PC-based fat client environments. The system employs a network-dependent model in which thin clients, called Sun Ray Desktop Units (DTUs), connect to Sun Ray servers. All desktop applications, such as office productivity suites, Web browsers, and the desktop itself, are executed on the servers, while the DTUs simply act as frame buffers, displaying the desktop and forwarding user input to the servers. Sun Ray DTUs have no local disks or locally installed applications or operating systems and are therefore considered stateless. This makes them easy to exchange, inexpensive to maintain, and extremely secure.

To ensure uninterrupted service, several Sun Ray servers can be configured as a failover group, so that whenever a server goes down, the affected DTUs automatically re-connect to the next available Sun Ray server in the failover group. A load balancing algorithm ensures that the DTU connections are equally distributed among the remaining servers, taking into account the current load and capacity of each server. It is important to understand that this model does not include any automatic transfer of a running desktop session to a different server. Any user data or session state that has not been saved will be lost if the original server becomes unavailable. The Sun Ray failover group model ensures high availability in the sense that a user can immediately start a new desktop session (on a different server) without any further outages.

The Sun Ray architecture uses tokens (authentication keys) to associate a desktop session with a user. Typically, the token is presented on a smart card that the user inserts into the DTU's card reader. If a session associated with that token is already running on any Sun Ray server, the DTU is automatically redirected to that server, and the user's most recent session is displayed. While the session continues to reside on the server, it appears to follow the user from one DTU to another. This functionality, called hotdesking or session mobility, enables users to access their sessions from different locations, using any DTU on their network.