PURPOSE: To estimate a cell abort rate with high accuracy by allowing a call connection controller to accept a call connection request when a cell abort rate from an abort rate estimate device is less than a prescribed permissible rate, applying post processing via an outgoing line buffer and outputting the result.

CONSTITUTION: An abort rate estimate device 206 of an exchange 201 calculates a cell abort rate from a received call connection request condition 11 and outputs a cell abort rate data 12 being the result of calculation to a call connection controller 205. Upon the receipt of the data 12, the controller 205 outputs a control signal 13 to a preprocessing section to accept a call connection request when the received cell abort rate is a predetermined permissible rate or below, and to reject the request 10 when not. A cell relating to the connection request is fed to a switch 202 while a header representing an outgoing line is added thereto and sent to a post processing section 204 from a buffer for the relevant outgoing line by a switch 204. Then the post-processing such as delete of a header is implemented by the post processing section 204 and the result is sent to an output communication line.