Bus line traffic control adapter apparatus

The invention provides a bus line traffic control adapter apparatus which can secure a communications throughput of a data terminal which is already in a communicating condition even where there is a limitation in transfer capacity on a bus line. A first packet controller extracts throughput information in call user data in a call request packet. A traffic controller subtracts a current throughput value read out from a total throughput control section from allowable throughput information on a bus line, compares a value obtained by the subtraction with the throughput information notified from the first packet controller, and permits or rejects origination of a call in accordance with a result of the comparison. When a notification of rejection of origination of a call is received, the first packet controller cancels the received call request packet then and notifies a clear indication packet to the data terminal by way of a second ISDN control section.