AbstractFor the OSI message exchange protocol, the MHS (message handling system) was recommended in 1984 by CCITT. The implementation of this protocol is being considered by network service enterprises and computer manufacturers in various countries. MHS is constructed as an application of OSI common application protocol. ROS (remote operations service) and RTS (reliable transfer service), specified by MHS, and performing the acknowledgement of send/receive of application data and the interruption/recovery, can also be used in common with other applications of OSI. This paper presents an analysis and evaluation of ROS and RTS from the viewpoint of the number of transmitted/received packets and the transfer time. The relation between the window size and the transfer efficiency in RTS is derived. For the system combining ROS and RTS, the method for controlling the window size corresponding to the response time, as well as the method for setting the session data length corresponding to the interruption rate, are presented. As to the method of combining ROS and RTS, it is shown that a large amount of application data can be transferred in a stable way, even if the interruption rate is large, by applying RTS to ROS.