FUTABA FDL01TU, Instruction Manual

Page: 27 / 83

13
3.2
Packet Transmission Mode
Packet transmission mode
operates as half-duplex communication and requires explicit
commands to control the modem transmissions. Because this mode allows the addressing of
different
destination
receiver modems by embedding the address in the data packets, it is
best suited for 1:n and n:m topology applications.
In
packet transmission mode , the FDL01TU modem normally waits in a ready-to-
receive state .
When a transmission command is issued to the sender modem from its terminal equipment,
the modem searches for a clear frequency channel and, when found, transmits the message
to the intended
destination receiver modem.
Packet transmission mode also allows expansion of the effective wireless
communication range by using an additional FDL01TU modem configured as a
repeater
.
3.2.1 Packet Transmission Mode Protocol
In
packet transmission mode
, after a data packet is transmitted from the sender modem
(station) to a destination station , the destination station acknowledges successful
communication by returning an
acknowledgement (ACK) packet
to the sender modem.
The sender modem waits for the ACK packet and when it is received, indicates that the
transmission was successful. If it does not receive an
ACK packet
, it will continue to
retransmit the data packet until it does receive an ACK packet or until the retransmission
count
(
REG11
or
RNO command
setting) reaches the preset limit. If the sender modem
receives an ACK packet anytime during the retransmission attempts, it returns a
“
successive completion response”
(P0) code to its terminal equipment. If the modem
does not receive an
ACK packet
, it returns a “
transmission failed
” (N1) code to its
terminal equipment.
Sender Modem Destination Modem
Figure 3–2: Packet Transmission and ACK response
3.2.2 Broadcast Transmission Protocol
Broadcast transmission (sending the same data to multiple modems simultaneously) is
possible in
packet transmission mode
by setting 255 as the
destination address
( REG02 ). However, because ACK packet are not returned when executing the broadcast
transmission
, the sender modem does not receive confirmation of the “ successful
reception ” of the transmitted data from any of the receiver modems.
In
broadcast transmission , the sender modem transmit the data packet the number of
times equal to the preset
retransmission count
(
REG11
or
RNO command
setting) plus
Data Transmission
ACK response