The packet communications service is a high speed, high quality digital data transmission service. The DDX-P service started in May 1980 (Showa 55). The service is a packet communications service that links terminals directly to an exchange using a dedicated digital line. Its high reliability makes it suitable for host lines and important lines. A feature of the service is that it is charged on an as-used basis, with charges based on the quantity of data rather than on time or distance.