© Microhard Systems Inc. Confidential 49
3.0 Mesh Configuration
3.2.5 Retransmissions
Packet Retransmissions can be used to ensure data reaches its intended destination by resending the
same packet over and over unless acknowledged by the recipient. While this is an effective tool to add
system robustness, it has large impact on the performance of the system in broadcast mode. 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).
S113 = 5 - Packet Retransmissions (0-254)
While retransmissions can provide some correction for data collisions, it is not advisable as adding re-
transmission may actually amplify the number of collisions. Retransmissions are typically used in noisy
environments to combat interference and low signal strength, ensuring data is received at the intended
destination.
3.2.6 Network Synchronization
Network Synchronization is what allows all units to hop from frequency to frequency at the same time.
Each Mesh Frame contains a configurable number of sync slots, that the coordinators can use to send
synchronization data. Sync data does not need to be sent during each frame, and is therefore configur-
able using register S216
S216 = 3 - Mesh Duty Cycle (1-100)
Register S216 defines how often the coordinator transmits sync packets (1-100). After each sync packet
transmission the coordinator picks a random number from 1 to the value in S216 and transmits the next
packet in this slot.
If the network is busy with traffic it is not necessary to send the sync packet very often, as the sync data
is also embedded into the data stream. For idle systems, an increased number of sync packets allows
for faster synchronization of new units. However, the higher the value of S216, the longer it will take for
new units to find and synchronize with a coordinator.
In large systems with many coordinators, it may be necessary to adjust the number of available sync
slots per Mesh frame to allow adequate slots for each coordinator to transmit sync data. This can be
adjusted using S215.
S215 = 1 - Number of Mesh Sync Slots (1-10)
Adding an unnecessary number of sync slots adds to the length of the Mesh Frame, which in turn cre-
ates a longer hop interval (number of sync slots + number of aloha slots = hop interval), increasing over-
head and reducing system performance.
For units to synchronize with the network, each unit must have the same:
- Network ID (S104), Network Type (S133), Forward Error Correction (S158) and
- the same number of Aloha Slots (S214), number of Sync Slots (S215).
In Mesh without roaming, Hop Pattern (S106) and Hop Zone (S180) must also match.
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