COMMUNICATION APPARATUS

In a communication system comprising a network unit and a plurality of subscriber units connected to the network unit, the network unit generates a message in which validity of transmission grant information is set for the subscriber units, and suspends a transmission of polling information to allocate a transmission grant to the subscriber units by using the transmission grant information for a fixed time in consideration of a processing time of the subscriber units from a time when the message has been completely transmitted. Also, when a disconnection state of an inputted cell from the subscriber units is detected, the network unit may suspend an input disconnection detecting operation for a fixed time from a time when the message and the polling information have been completely transmitted. Furthermore, a switchover of an input disconnection detection/transmission grant information may be suspended by mutually exchanging messages.