Understanding Sun's Latest Thin-client Device

If you want to understand how Sun's recently unveiled Sun Ray desktop appliance really works, think of your telephone. And then think of your phone as a thin-client device.

The phone itself is just a means to connect to a network of services - voice applications, such as one-to-one voice communication, a directory, call answering and automatic redial. New applications can be added by the network, but you don't have to change your phone to use them.

Creating such an environment became the goal of a Sun engineering team, headed by Duane Northcutt, that two years ago started work on the next step in thin-client computing. Sun's Java network computer, the JavaStation, was becoming generally available and was being widely deployed within Sun itself. The Sun Ray was intended as the JavaStation replacement and was designed to run on corporate LANs.

Unlike other thin-client models, such as network computers and Windows-based terminals, the Sun Ray has no operating system. For the most part, the client software simply turns the display screen's pixels on and off. Unlike the JavaStation, the Sun Ray can't download and run Java applets. Unlike Windows terminals, it doesn't have a graphics subsystem for graphical user interface processing.

And unlike both other thin clients, the Sun Ray is not recognized by the net as a discrete device assigned to a specific user. It's simply three peripheral devices: keyboard, mouse, display.

"We created a stateless, computeless display device," says Northcutt, who is chief technologist for Sun's Webtop business unit. "You never need to upgrade it."

Sun accomplished this by creating desktop and server software called HotDesk. Sun's engineers shifted nearly all client processing to a server software program. They created an I/O protocol - based on TCP/IP that runs at 12.5M bits per second (bps) - between a small piece of client code on the desktop device and the software on the Sun Ray server.

As users work with the keyboard and mouse, the key and click sequences are sent to the server. There, an application executes or the server connects with another application server on the LAN.

As the application runs and creates changes in the display, the only information being sent back to the Sun Ray device is instructions on what individual pixels to turn on or off.

"We were shocked at how well this repartitioning worked," Northcutt says. "We found we didn't burn that much bandwidth because we're only sending pixel changes over the wire. And most of the pixels don't change from second to second."

Using the smart card option with the Sun Ray, anyone can sit down at any Sun Ray device (or in the future, any HotDesk-based device), be authenticated via his smart card by the network, and then be free to access all of his files, data and applications.

Northcutt illustrates the power of the Sun Ray and HotDesk with a story. He was typing an e-mail on a Sun Ray device when the electricity failed. When the power was restored an hour later, Northcutt at once was able to start working on the uncompleted message without having lost a single keystroke.

Sun plans to license its HotDesk code and the I/O protocol widely so system vendors can add the technologies to their product lines.

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