Microhard Systems P900 - Retransmissions; Network Synchronization

© Microhard Systems Inc. Confidential 65
4.0 Point to Point Configuration
4.2.3 Retransmissions
Packet Retransmissions can be used to ensure data reaches its intended destination by resending the
same packet over and over. In Point to Point system all data is acknowledged by the destination, result-
ing in retransmissions only being used if no acknowledgement is received. The overall impact on system
performance, while not as significant as it is in Mesh and Point to Multipoint networks, should still be
considered. 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 trans-
mission).
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.
4.2.4 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)
- Forward Error Correction (S158)
- Network Type (S133)
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.