| 摘要 |
A private branch exchange which accommodates a plurality of extension terminals and which is arranged to effect line exchanges by specifying a destination terminal from among the extension terminals on the basis of a called-subaddress information element contained in incoming information. When the incoming information containing the called-subaddress information element is received, it is determined whether the called-subaddress information element is contained in the incoming information. If there is no called-subaddress information element, the call is refused. It is also determined whether connection with an extension terminal is possible or impossible, on the basis of the received incoming information. If the connection is impossible, information to that effect is transmitted to a calling party.
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