Murata Electronics North America DNT500FP 사용자 설명서
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©2008 by RF Monolithics, Inc.
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DNT900 - 11/05/08
serial data to transmit at a time, or where periodic reporting and/or event reporting are enabled should not
use this mode.
use this mode.
CSMA Contention (Mode 1)
- provides classical CSMA channel access, and gives the user control over
both the CSMA_MaxBackoff and CSMA_Predelay parameters. This mode is well-suited for large num-
bers of uncoordinated remotes, and/or where periodic/event reporting is used. In addition to CSMA_
MaxBackoff
bers of uncoordinated remotes, and/or where periodic/event reporting is used. In addition to CSMA_
MaxBackoff
and CSMA_Predelay, the user can set the BaseSlotSize and RemoteSlotSize parameters
when using this mode. The following guidelines are suggested for setting CSMA_Predelay:
•
For lightly loaded CSMA contention networks, decrease CSMA_Predelay
to 0x20 or less to reduce latency.
•
For heavily loaded CSMA contention networks, increase CSMA_Predelay
to 0x80 or more for better throughput.
As an option, the CSMA modes allow the base station to directly track remotes entering and leaving the
network for up to 254 remotes. The base station is operated in protocol mode and is configured to gener-
ate a CONNECT message for its host when a remote registers, and a DISCONNECT message when the
remote’s registration lease expires.
network for up to 254 remotes. The base station is operated in protocol mode and is configured to gener-
ate a CONNECT message for its host when a remote registers, and a DISCONNECT message when the
remote’s registration lease expires.
The base station in a CSMA network can generate CONNECT messages for more than 254 remotes.
This allows the host application to track remotes entering and leaving a large CSMA network by creating
a table of MAC addresses and periodically sending a GetRemoteRegister command to each remote in
the table. Failure to answer a GetRemoteRegister command indicates the remote is no longer active in
the network.
This allows the host application to track remotes entering and leaving a large CSMA network by creating
a table of MAC addresses and periodically sending a GetRemoteRegister command to each remote in
the table. Failure to answer a GetRemoteRegister command indicates the remote is no longer active in
the network.
CSMA modes work well in many applications, but CSMA has some limitations, as summarized below:
•
Bandwidth is not guaranteed to any remote.
•
Marginal RF links to some remotes can create a relatively high chance of
collisions in heavily loaded networks.
2.7.2 TDMA Modes
The TDMA modes provide guaranteed bandwidth to some or all of the remotes in the network. Remotes
that register with the base station receive several special parameters, including ranging information and a
specific channel access slot assignment. TDMA registrations are always leased and must be renewed
every 250 hops. The DNT500 provides three different modes of TDMA access, as discussed below.
that register with the base station receive several special parameters, including ranging information and a
specific channel access slot assignment. TDMA registrations are always leased and must be renewed
every 250 hops. The DNT500 provides three different modes of TDMA access, as discussed below.
TDMA Dynamic Slots (Mode 2)
- is used for general-purpose TDMA applications where scaling the
capacity per slot to the number of active remotes is automatic. Each remote that registers with the base
receives an equal time slice. As new remotes join, the size of the TDMA slots shrink accordingly. The
number of slots, individual slot start times, and the RemoteSlotSize are computed automatically by the
DNT500 network in this mode. The user should note that the bandwidth to each remote will change
immediately as remotes join and leave the network. When running in protocol mode, care must be taken
not to format packets too long to be sent in a single hop due to automatic RemoteSlotSize reduction.
receives an equal time slice. As new remotes join, the size of the TDMA slots shrink accordingly. The
number of slots, individual slot start times, and the RemoteSlotSize are computed automatically by the
DNT500 network in this mode. The user should note that the bandwidth to each remote will change
immediately as remotes join and leave the network. When running in protocol mode, care must be taken
not to format packets too long to be sent in a single hop due to automatic RemoteSlotSize reduction.
TDMA Fixed Slots (Mode 3)
- is used for applications that have fixed data throughput requirements, such
as isochronous voice or streaming telemetry. The slot start time and the RemoteSlotSize are computed
automatically by the DNT500 network in this mode. The user must set the number of slots.
automatically by the DNT500 network in this mode. The user must set the number of slots.