User's Manual

TS4000 Radio Modem User’s Manual AirNet Packet Protocol 56
Packet Transmit Time = Packet Length / Channel Rate
Packet Length = (Data Bits + Overhead Bits)
x Framing Overhead x Coding Overhead
= (Data Bits + 112) x 1.1 { x 1.5 }
Overhead Bits = 14 bytes x 8 bits per byte = 112 bits
Framing Overhead = 1.1
Coding Overhead (optional) = 1.5
Packet Timeout = Decay Time + Attack Time + ACK Packet Transmit Time
Where:
Decay Time = Tx Decay Time + Additional Transmit Attack Time
Attack Time = Tx Attack Time + Additional Transmit Attack Time
ACK Packet Transmit Time = ACK Packet Length / Channel Rate
ACK Packet Length -Uncoded = 16 bytes x 8 bits per byte = 128 bits
-Coded = 128 bits x 1.5 = 192 bits
The following is a summary of the suggested settings for a system that has one
or more store and forward repeaters. Note that more detail on the parameters
and equations can be found later in this section.
Slot Time = Attack Time + Maximum Carrier Detect Time Variation
= 1.5 x Attack Time
Where:
Attack Time = Radio Attack Time + Additional Transmit Attack Time
Tx Decay Time and Tx Attack Time are fixed values that are preset
for the radio in the TS4000. These values can be read out of the
TS4000 using the Retrieve Radio Hardware menu or button. The
Additional Transmit Attack Time is the value set on the radio tab of
the modem configuration.
Min Idle Slots - ACK Packets = 0
Min Idle Slots - Relay Packets (Relay #1) = 1
Min Idle Slots - Relay Packets (Relay #2) = 2
...
...
Min Idle Slots - Relay Packets (Relay #Z) = Z
Min Idle Slots - Data Packets = Highest Relay # + 1 = Z + 1
Tx Index - ACK Packets = 1
Tx Index - Relay Packets = 1
Tx Index - Data Packets = Estimated Backlogged Nodes / Attempt Rate
Where:
Estimated Backlogged Nodes (number of nodes that simultaneously
want to transmit) = the greater of
A) Average Number of Backlogged Nodes or
B) 1/4 Maximum Possible Number of Backlogged Nodes
Attempt Rate = (Packet Detection Ratio)
1/2
Packet Detection Ratio = Slot Time / Total Packet Time
Packet Timeout
System with
Repeaters - Setup
Summary
Slot Time
Min Idle Slots
Tx Index