© Microhard Systems Inc. Confidential 77
5.0 Point to Multipoint Configuration
5.2.3 Unit Addressing
In a Point to Multipoint Network each unit must have a unique unit address, which can be configured
using register S105. Duplicate addresses may result in unpredictable problems in the network. In a PMP
Network data flow is such that data from the Master is sent to all units by setting the destination address
(S140) to 65535, meaning data is broadcast to all units.
5.2.4 Retransmissions
Packet Retransmissions can be used to ensure data reaches its intended destination by resending the
same packet over and over. In Point to Multipoint system data from the master is not acknowledged by
the destination, meaning data will be transmitted an additional number of times specified by S113, re-
sulting in a significant impact on system performance. The more times a modem retransmits data, the
more the overall throughput of the system is reduced. To adjust the retransmission rate, use register
S113, the default value is 5 (+ the initial transmission). Although, this number should be as low as possi-
ble to keep as much bandwidth in the system as possible.
S113 = 5 - Packet Retransmissions (0-254)
Retransmissions are typically used in noisy environments to combat interference and low signal
strength, ensuring data is received at the intended destination.
5.2.5 Network Synchronization
Network Synchronization is what allows all units to hop from frequency to frequency at the same time.
For units to synchronize with the network, each unit must have the same:
- Network ID (S104)
- Network Type (S133)
- Forward Error Correction (S158)
Sync Timeout
Once synchronized to the network the unit does not need to receive sync data often to keep track of
where the system is supposed to be (in time and frequency). The sync Timeout defines the number of
hops where no sync data is received from a Master and/or Repeater before losing sync. In other words,
how long a unit will remain synchronized with the network without receiving any sync packets before it
gives up and loses sync.
S248 = 512 Sync Timeout (4-65534)
Setting a value too low will cause the unit to lose sync easily and time will be wasted trying to re-sync to
the network. Several hops can go by without receiving a sync packet, and this is completely normal. If
this value is set too high, the unit will assume for a long time that the network is still out there, when
especially in mobile applications it may not be.
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