Murata Electronics North America CCT24 Manual Do Utilizador
Page 13 of 90
CCT24
Figure 2.10.1
2.10.1 Polling Mode
Polling channel access is used for point-to-point and point-to-multipoint systems where only one remote
will attempt to transmit data at a time, usually in response to a command from the base.
will attempt to transmit data at a time, usually in response to a command from the base.
Polling (mode 0) is a special case of CSMA mode 1. The user can set the BaseSlotSize and CSMA_
RemtSlotSize parameters when using this mode. Since only one remote will attempt to transmit at a time,
to minimize latency, the CSMA_Predelay and CSMA_Backoff parameters are not used. Lease renewals
are also not used, again to minimize latency. Thus, when the base is operated in protocol mode with
Announce messages enabled, only join messages are generated. This mode provides high throughput as
there is no contention between remotes and the entire portion of the hop frame following the base trans-
mission is available for a remote to transmit. Applications where more than one remote may attempt to
transmit at a time, where event and/or periodic I/O reporting are enabled, and/or tree-routing operation is
required should not use this mode.
RemtSlotSize parameters when using this mode. Since only one remote will attempt to transmit at a time,
to minimize latency, the CSMA_Predelay and CSMA_Backoff parameters are not used. Lease renewals
are also not used, again to minimize latency. Thus, when the base is operated in protocol mode with
Announce messages enabled, only join messages are generated. This mode provides high throughput as
there is no contention between remotes and the entire portion of the hop frame following the base trans-
mission is available for a remote to transmit. Applications where more than one remote may attempt to
transmit at a time, where event and/or periodic I/O reporting are enabled, and/or tree-routing operation is
required should not use this mode.
2.10.2 CSMA Mode
When using CSMA channel access, each remote/router with data to send listens to see if the channel is
clear and then transmits. If the channel is not clear, a radio will wait a random period of time and listen
again. CSMA works best when a large or variable number of radios transmit infrequent bursts of data.
There is no absolute upper limit on the number of radios that can be supported in this mode - it depends
on message density. A maximum of 126 radios can be supported if base-managed join/leave tracking is
required, or an unlimited number of remotes if base join-leave tracking is not required or will be handled
by the host application.
clear and then transmits. If the channel is not clear, a radio will wait a random period of time and listen
again. CSMA works best when a large or variable number of radios transmit infrequent bursts of data.
There is no absolute upper limit on the number of radios that can be supported in this mode - it depends
on message density. A maximum of 126 radios can be supported if base-managed join/leave tracking is
required, or an unlimited number of remotes if base join-leave tracking is not required or will be handled
by the host application.
There are two important parameters related to CSMA operation. The CSMA_Backoff parameter defines
the initial time that a radio will wait when it determines the channel is busy before again checking to see if
the channel is clear (back-off interval). If, after finding the channel busy and backing off, the radio finds
the initial time that a radio will wait when it determines the channel is busy before again checking to see if
the channel is clear (back-off interval). If, after finding the channel busy and backing off, the radio finds