MOUNTAIN VIEW, Calif. — Sun Microsystems has sketched out a set of Java programming guidelines and source code that it claims could make it easier for users to install devices or access services over a network, pushing closer to the company's long-held vision of distributed computing. But like Java itself, the approach to create a kind of plug-and-play networking environment will require widespread adoption by systems and services companies if it is to be successful. The effort is also subject to the same performance questions that have dogged Java generally.

Sun claims it is working with as many as 20 companies — including announced partners Canon, Ericsson, Federal Express, Novell, Seagate and Quantum — on the 18-month-old R&D project Sun calls Jini (pronounced gee-nee). This fall, Sun will release source code for free downloading over the Internet for implementing the Jini guidelines. Specifications for Jini will be detailed in documents the company plans to post on its Web site today.

"It's a very simple set of conventions," said Jim Waldo, a senior staff engineer at Sun's Chelmsford, Mass., office and an architect of Jini. "It's an aggressive use of technology that has existed in Java that people haven't used all that much—the ability to move code around."

Waldo described Jini as similar to the concept of downloadable Java applets that has existed from the genesis of Java. Sun has now pushed it "to the extent that it really gives you a different approach to a network."

Jini is essentially a set of guidelines and conventions for devices and services to automatically communicate with one another over a network via a Java-based lookup service. The lookup service acts as a kind of database or registry of devices and services on the net. In this way, Jini can work with any existing environment, but is intended to provide an alternative to the traditional use of operating systems and their related applications and device drivers as a means of linking systems and services on a net.

When new Jini devices or services plug into a network, they broadcast a unique byte pattern over the network to locate a lookup service. The service responds by sending back code based on Sun's Remote Method Invocation — a form of remote procedure call particular to Java& #0151; that allows Java modules to communicate by dynamically loading pieces of Java code. The devices and services also register themselves with the lookup service by identifying their key attributes as described in pre-defined Java types or interfaces. When a client system wants a service, it queries the lookup service and retrieves the appropriate Java interface — a chunk of Java code that lets the client talk directly to the service or device it is requesting.

"If you have a standard directory service, you can get a reference to an object, but then you have to figure out what the programmatic interface is that lets you talk to the object," said Waldo. "What we've done is merge those two because we are living in a Java world, so that the way you identify the object is based on the capabilities of the object which are described by its Java type. So instead of saying, 'I want a printer' and then figuring out how to make calls to it, you say, 'I want something that supports the Java printer interface.'"

Sun will deliver source code for a lookup service as well as modules for discovering and registering devices and services with such lookup services as part of its Jini release this fall. However, the company expects third parties might develop their own modules, similar to programmers writing their own Java Virtual Machines today.

Waldo said the Jini source and binary code, which includes a lookup service and other models, fits on a single 1.44-Mbyte floppy. JavaSpaces, a demo service Sun created that manages a bulletin board of Java objects, requires less than 20,000 lines of Java code. A client system requires a minimum of 45 kbytes of compiled code to implement the basic Jini features.

The system relies on features found in an upcoming version 1.2 of the Java Developers Kit that will be released in the fall.

Performance and uptake
Waldo said the Jini approach would not generate any significant network overheads other than those created by the services themselves. And he said the performance issues that have dogged Java generally were improving as the Java Virtual Machines themselves improved.

However, at least one of Sun's partners noted some hurdles the Jini approach must broach. Paul Borill, a chief architect at Quantum Corp., said he is upbeat about the technique. However, he expects to use it only on 100-Mbit/s Ethernet networks for the kinds of networked tape and disk drives his company is developing.

"We haven't seen any problem in bandwidth, but we don't know if it's going to be a problem," said Borill. He said Sun claimed devices such as he is trying to define would work on 10-Mbit/s Ethernet networks without significant performance degradation. "If you don't want to see any performance degradation you really ought to use 100 Mbit/s Ethernet," Borill added.

Waldo said the performance issues were more likely tied to the requirements of networked storage than Jini itself.

"The demo I saw was not slow at all," said Tim Bajarin, a market analyst with Creative Strategies (San Jose, Calif.). He described a Jini demo in which a printer, camera, hard disk and Palm Pilot handheld computer communicated via Jini.

Jini relies on techniques such as Dynamic Host Configuration protocol to assign IP addresses for Jini devices. However, "it still requires a sophisticated administrator to set up the IP address tables," Borill said.

Nevertheless, he praised Jini as "a computing environment that configures itself in real time dynamically."

Significant work has gone into generating a specification that is "a foot thick," Borill added. "We believe the specifications are well nailed down and we haven't seen any fundamental robustness problems."

Sun will need all the support it can muster if Jini is to fly, said Bajarin. "They will need a tremendous amount of industry buy-in to make this work."