Microhard Systems P900 - Page 54

© Microhard Systems Inc. Confidential 54
3.0 Mesh Configuration
Actual cost of RSSI used by Microhard to determine route cost is listed in the table below:
The cost of a hop can be modified by the user by setting register S245. Setting this register influences
the relationship between the number of hops and the signal strength of the path.
S245 = 100 - Cost of one hop in Mesh (0-255)
Setting the value of S245 low, in relation to the cost of RSSI would result in a path that is not concerned
with the number of hops, so long as the signal between hops was strong. Setting the value of S245 to a
high cost value would indicate that using the shortest path possible is the most important, resulting in
low latency and increased throughput, even at the risk of the path being weak, resulting in lost packets
and retransmissions.
The illustration shows how different paths are calculated, and how the best path is determined before
being added to the routing table.
Cost of RSSI RSSI (dBm) Cost of RSSI RSSI (dBm) Cost of RSSI RSSI (dBm)
0 Less than 55 10 79 26 92
1 55 - 59 11 80 28 93
2 60 - 64 12 81 32 94
3 65 - 67 13 82 35 95
4 68 - 69 14 83 38 96
5 70 - 71 16 84 40 97
6 72 - 73 18 85 44 98
7 74 - 75 19 86 49 99
8 76 - 77 20 87 50 100
9 78 21 88 - 91 50 100+
Table 3-2: Cost of RSSI
Drawing 3-8: Routing Path Cost
R1
R2
R3
A
B
-52dBm
(0)*
-72dBm
(6)*
-54dBm
(0)*
-67dBm
(3)*
-91Bm
(21)*
Path 1
Path 2
Path 3
Shows the path cost from Modem A to Modem B.
Path Path Cost (Cost of hop =100) # Hops
1 (2x100) + 3 + 21 = 224 2
2 (2x100) + 0 +40 = 240 2
3 (3x100) + 0 + 6 + 0 = 306 3
*Cost of RSSI
-97dBm
(40)*
Path Path Cost (Cost of hop =10) # Hops
1 (2x10) + 3 + 21 = 44 2
2 (2x10) + 0 +40 = 60 2
3 (3x10) + 0 + 6 + 0 = 36 3