Dr. Fumio Kanehiro and his colleagues in the Intelligent Systems Research Institute (ISI) of the National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institution, implemented real time communications on Ethernet in collaboration with Mr. Yoichi Ishiwata, a director of the MovingEye Corporation. (to be designated as MovingEye) using ART-Linux, a real time extension of Linux developed by the AIST, former Electrotechnical Laboratory (ETL).

The Ethernet has been widely used for personal computers (PCs) as communications network of global standards, but lacks real time communication capability. Here. the real-time communication refers to communication to be finished within a specified time span, or in another word, that imposed with a deadline. While the real time communication is not needed for PCs in office applications, it is indispensable for applications requiring time-limited processing, such as range finding and engine control. Up to now, the real time communications have been implemented by using a costly dedicated network. The present work has made it possible to use the Ethernet characterized by low cost and high baud rate for built-in equipment needing real time communications, and to interconnect built-in equipment via a communications network just like a server PC.

The newly developed real time communications is implemented on a new protocol installed in the data-link layer, without using upper layer protocol such as TCP/IP. The upper layer protocol is realized by providing a packet relay and a communication route switching. While the real time communication is not used, the ordinary TCP/IP protocol can be used to facilitate software development.

The configuration of newly developed real time Ethernet is compared with that of the conventional Ethernet below.

Conventional Ethernet		Real Time Ethernet
Application TCP IP Non-Real Time Data-Link Ethernet 10BASE5		Application Packet relay Route switching Real Time Data-Link Ethernet 100BASE-T

There have been two attempts for implementing real time communications on the Ethernet: to ensure communication bandwidth for multimedia applications, and to ensure finish time of communications through the modification of OS kernel and the development of dedicated device driver. The former attempt has a demerit of lacking real time communication capability needed for the robot control, while the latter has a difficulty in reuse of software.

Generally speaking, the spread of newly developed communication protocol is hindered by the need of extensive modification on the part of existing software. In order to ensure the compatibility with the existing protocol, an application layer protocol GIOP for the middle ware CORBA has been installed on the real time communication protocol. With this arrangement, the CORBA user can utilize CORBA implemented on the real time communications without changing the existing software extensively. For the installation of CORBA, Japan IONA Technologies’ Orbix/E, a version of CORBA adapted for built-in applications is used.

CORBA on conventional Ethernet		CORBA on realtime Ethernet
GIOP TCP IP Non-Real Time Data-Link Ethernet 10BASE5		GIOP routing Real Time Data-Link Ethernet 100BASE-T

The installation of GIOP on the newly developed real time Ethernet is compared with that of the conventional Ethernet in a diagram shown below.

As is evident from the illustration, it is possible to utilize software having worked on the GIOP without any modification owing to the compatibility on the GIOP level. The difference is created by the guarantee of deadline in communication time.

The newly developed software is operable on the ordinary PCs and card-sized boards. The performance test with PCs demonstrated that the shortest period of cyclic communications realizable was 100 µs with data-link layer protocol, and that with CORBA 500 µs.

The ISI-AIST is going to utilize the newly developed software for the next model of humanoid robot being developed in collaboration with the Kawada Industries, Inc., and for the Project “Consolidation of Software Infrastructure for Robot Development (FY 02-04)” entrusted by the New Energy and Industrial Technology Development Organization (NEDO).

The R&D works are shared by collaborative partners in the following way: basic structure of communications and evaluation for robot controller by the ISI-AIST, and practical application of communications by the MovingEye. The ART-Linux is a real time version of Linux developed by Dr. Ishiwata and his colleagues while he was working with the ETL and characterized by real time extension implemented in the user space, allowing the use of device driver without modification, in contrast to other versions of real time Linux.

The Ethernet has been widely used for personal computers (PCs) as communications network of global standards, but lacks real time communication capability. While the real time communication is not needed for PCs in office applications, it is indispensable for applications requiring time-limited processing, such as range finding and engine control. Up to now, the real time communications have been implemented by using a costly dedicated network. For the purpose of reducing the cost of built-in type equipment and enhancing the development efficiency, it has been required to utilize the low cost Ethernet of global standards, to use the Linux, an open source OS as a target OS and to enhance the modular construction by use of middleware.

The present work has made it possible to use the Ethernet for real time communications network by using an extended version of Linux for real time operation, and to use CORBA, a standard middleware on the Ethernet.

It is expected that the work results will be widely used in the fields of built-in equipment, such as robots, info-based electrical appliances and automobiles.