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DNT2400 - 08/18/09
In point-to-point operation, by default a remote will send the data in its transmit buffer on each hop, up to
the limit controlled by its RemoteSlotSize parameter. If desired, the MinPacketLength and TxTimeout
parameters can be set above their default values, which configures the remote to wait until the specified
amount of data is available or the specified delay has expired before transmitting. In transparent mode, if
the remote is buffering more data than can be sent on one hop, it will send the remaining data in subse-
quent hops. The remote adds its own address, a packet sequence number and error checking bytes to
the data when it is transmitted. These additional bytes are not output at the base if the base is in trans-
parent mode. When a transmission is received by the base, it will be acknowledged if it checks error free.
If no acknowledgment is received, the remote will retransmit the same data on the next hop.
2.7.2 Point-to-Multipoint Network Operation
In a point-to-multipoint network, the base is usually configured for protocol formatting, unless the applica-
tions running on each remote can determine the data’s destination from the data itself. Protocol formatting
adds addressing and other overhead bytes to the user data. If the addressed remote is using transparent
formatting, the source (originator) address and the other overhead bytes are removed. If the remote is
using protocol formatting, the source address and the other overhead bytes are output with the user data.
A remote can operate in a point-to-multipoint network using either transparent or protocol formatting, as
the base is the destination by default. In transparent operation, a remote DNT2400 automatically adds
addressing, a packet sequence number and error checking bytes as in a point-to-point network. When the
base receives the transmission, it will format the data to its host according to its formatting configuration.
A remote running in transparent mode in a point-to-multipoint network can have the MinPacketLength and
TxTimeout parameters set to their default values to reduce latency, or above their default values to re-
duce the volume of small packet transmissions.
2.7.3 Peer-to-Peer Network Operation
After a remote has joined the network, it can communicate with another remote through peer-to-peer
messaging, where the base acts as an automatic message relay. In protocol mode, if a remote specifies a
destination address other than the base address, peer-to-peer messaging is enabled. In transparent
mode, the RmtTransDestAddr parameter sets the destination address. Changing RmtTransDestAddr from
the default base address to the address of another remote enables peer-to-peer messaging. The broad-
cast address can also be used as a peer-to-peer destination address. In this case, the message will be
unicast from the remote to the base (using ARQ) and then broadcast by the base (no ARQ). For peer-to-
peer broadcasts, no acknowledgement is sent and no TxDataReply packet is reported to the host.
2.8 Full-Duplex Serial Data Communications
From a host application’s perspective, DNT2400 serial communications appear full duplex. Both the base
host application and each remote host application can send and receive serial data at the same time. At
the radio level, the base and remotes do not actually transmit at the same time. If they did, the transmis-
sions would collide. As discussed earlier, the base transmits a beacon with a synchronization signal at the
beginning of each hop, followed by its user data. After the base transmission, the remotes can transmit.
Each base and remote transmission may contain all or part of a complete message from its host applica-
tion. From an application’s perspective, the radios are communicating in full duplex since the base can
receive data from a remote before it completes the transmission of a message to the remote and vice-
versa.
