User's Manual

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