9XTendNEMA™
RS
‐
232/485
RF
Modem
–
Product
Manual
v2.x4x
[2007.01.04]
©
2007
MaxStream,
Inc.,
Confidential
&
Proprietary
‐
All
Rights
Reserved
55
Repeater Network Configuration
A network may consist of End Nodes (EN), End/Repeater Nodes (ERN) and a Base Node (BN). The
base node initiates all communications.
A repeater network can be configured to operate using Basic Broadcast or Basic Addressed com-
munications. The addressing capabilities of the modem allow integrators to send a packet as a glo-
bal packet (DT = 0xFFFF) and shift out of every modem in the network (Basic Broadcast).
Alternatively, the packet can be sent with a specific DT (Destination Address) parameter so that it
is only accepted by a specific remote node (Basic Addressed).
Configuration Instruction (Basic Broadcast Communications)
The configuration instructions above reflect configuration for a Basic Broadcast Repeater system.
To configure a Basic Addressed Repeater system, use the DT (Destination Address) parameter to
assign unique addresses to each modem in the network.
Algorithm Details
• Packet ID (PID) is composed of TX (transmitting) modem MY address and packet sequence
number.
• Incoming packets with a PID already found in the PID buffer will be ignored.
• Each modem maintains a PID buffer 4 deep of previously received packets (managed as
FIFO).
Packets may be shifted out the serial port and/or repeated depending on the DT parameter con-
tained in the RF packet.
Repeat Delay Based on RSSI
A transmitted packet may be received by more that one repeater at the same time. In order to
reduce the probability that the repeaters will transmit at the same instant, resulting in a collision
and possible data loss; an algorithm has been developed that will allow a variable back-off prior to
retransmission of the packet by a repeater. The algorithm allows radios that receive the packet
with a stronger RF signal (RSSI) to have the first opportunity to retransmit the packet.
The RN (Delay Slots) parameter is used to configure this delay. Set RN=0 (no delays) for small
networks with few repeaters or repeaters that are not within range of each other. Set RN=1 for
systems with 2 to 5 repeaters that may be within range of each other.
The actual length of the delay is computed by the formula:
Delay (ms) = L * DS
DS = (-41-RSSI)/10*RN)+RandomInt(0,RN)
Where L is the length of the transmitted packet in milliseconds, DS is the number of delay slots to
wait, RSSI is the received signal strength in dBm, RN is the value of the RN register and Random-
Int(A,B) is a function that returns a random integer from A to B-0
Assign each modem a unique MY (source) address. (The AM (Auto-set MY) command will con-
figure a unique source address that is based on modem serial number.)
Enable Basic Broadcast Communications (DT = 0xFFFF) or Addressed Broadcast Communica-
tions (DT specifies a specific destination)
Configure PK, RO and RB to ensure that RF packet aligns with protocol packet. (ex. PK=0x100,
RB=0x100, RO depends on baud rate).
Configure one or more repeaters in the system (MD = 5).
Configure remote nodes as destinations (MD = 6). This will ensure that the remote node waits
for the repeater traffic to subside before it transmits a response.
Table
5
‐
02. DT
(Destination
Address)
parameter
truth
table
Address Match
Send out serial port?
Repeat?
Global
Yes
Yes
Local
Yes
No
None
No
Yes
