PlantLinc
PLR5000 User’s Guide
P/N 161-09888-001
DATA-LINC
Group
18
Main Menu Option (5): Edit Multipoint Parameters
Figure 5: Multipoint Parameters
Shown below are example settings. Please refer to supplied configuration sheets for your modem’s
configuration.
In a multipoint network, it is critical to know how many radio modems are being used as Repeaters. Any
radio modem that is used as a Repeater essentially becomes a Master to the Remotes and other Repeaters to
which it is communicating. Therefore, the user must first identify how many Repeaters are connected to the
Master by assigning a value in parameter
(0) Number Repeaters
. This parameter must also be set for each
Repeater in the system (i.e., in the event that a Repeater is connected to one or more other Repeaters). This
parameter does need to be set for multipoint Remotes.
In point-to-point operation, the PLR5000 radio modems acknowledge every data packet transmitted. In a
multipoint network, the Remotes do not acknowledge transmissions from a Master to the Remotes. This is to
prevent system overload. If the Remotes acknowledged all data transmissions from the Master in a large
multipoint system, then all system capacity would be spent having the Master listen for acknowledgments
from the Remotes. Because the transmission is not acknowledged by the Remotes, 100% confidence does not
exist that every remote has received every message from the Master. To address this issue, the user may
modify option
(1) Master Packet Repeat
, assigning a value between 0 (the packet is transmitted once) to 9
(the packet is repeated 9 times). For networks with solid RF links, this parameter would be set at the lower
end of the scale (0-1). If the network has some weak or marginal links, it would be set toward the higher
values. If a Remote receives a packet from a Master more than once, it will discard the repeated packets.
While packets transmitted from the Master to the Remotes in a multipoint network are not acknowledged,
packets transmitted from Remotes to the Master are. However, it is possible that more than one remote will
attempt to transmit to the Master at the same time, and it is therefore important that a protocol exists to
resolve contention for the Master between Remotes.
This is addressed through parameters
(2) Max Remote Retry
and
(3) Retry Odds
. The Max Remote Retry
setting defines how many times (0 to 9) the Remote will attempt to retransmit a packet to the Master before