| 摘要 |
A central station 101 continuously transmits a slot of predetermined time length which comprises a polling frame Pxx and a downward data frame Ixx. After receiving the upward data frame Dxx, it sequentially and repeatedly carries out an individual polling of upwardly communicating terminal stations 102 and 103 at a time interval which is more than the predetermined time interval for the polling frame Pxx. Unspecified polling is carried out of unspecified terminal stations by a polling frame Po which does not carry out this individual polling. Independently of the polling frame Pxx, the downward data frame Ixx is repeatedly transmitted to downwardly communicating terminal stations 104 and 105. The polling frame Pxx and the downward data frame Ixx which are included within the same slot are transmitted to a terminal station 106 which is in the upward and downward duplex communication mode at a time interval longer than the predetermined time interval. The terminal stations 102 through 106 transmit a polling request Rxx or an upward data frame Dxx to the polling frame Pxx from the central station 101 at a time interval longer than the predetermined time interval.
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