User's Manual

Page 20 FRH-SD07TU/TB Manual
3.2 Pac ke t Transm ission 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 FRH-SD07TU/TB 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 FRH (series) modem configured as a repeater.
3.2.1 Pac ket Transm ission M ode 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
Data Transmission
ACK response
Figure 3–2: Packet Transmission and ACK response
Rev. 050415-01.1