DISTRIBUTED ELECTRONIC MAILBOX SYSTEM

摘要

A distributed electronic mailbox system comprises a plurality of terminals (12) on a common telephone line (10) to which each terminal can be intermittently connected. One of the terminals (12), if no terminal is found acting as a network control terminal (12), assumes that function. The network control terminal (12) interrogates each terminal (12) in turn to see if it has a message to send. Each interrogated terminal (12) sends a confirmatory message on to the telephone line (10) if it has a message to send and commences sending blocks of text message alternating with repeat confirmatory messages which suppress the polling activity of the network control terminal (12). If a terminal detects in a text message its own identifier address it knows the text message is destined to be received by itself and sends out a return message on to the telephone line (10). If the message originating terminal (12) does not receive the return message after it has provided the destination terminal identifier address in the text message it knows the destination terminal is not at that moment connected to the telephone line (10) and abandons its attempt to send the text message. Destination terminals receiving a text message check the received text message blocks by comparing two identically sent data words in the text message block. If the data words are not the same as one another the error detecting terminal (12) provides an error message on the telephone line (10) to which the message sending terminal (12) responds by re-sending the last provided text message block.