Teledesign Systems Inc TS4000EH Manuel D’Utilisation
TS4000 Radio Modem User’s Manual
AirNet Packet Protocol
62
Data Packet Transmit Time = Data Packet Length / Channel Rate
Data Packet Length = (Data Bits + Overhead Bits)
x Framing Overhead x Coding Overhead
Overhead Bits = 14 bytes x 8 bits per byte = 112 bits
Framing
Overhead
=
1.1
Coding Overhead (optional) = 1.5
The ACK packet delay at the destination node is the amount of time it takes for
the destination node to send the ACK packet.
ACK Packet Delay at Destination Node = Decay Time
+ Attack Time
+ ACK Packet Transmit Time
After the ACK packet is transmitted by the destination node, it must be re-
transmitted by the various repeaters in the system. This is the sum of the time it
takes each relay to transmit the ACK packet.
Relay Delays for ACK Packet = Relay #1ACK Packet Delay
+ Relay #2 ACK Packet Delay
...
...
...
+ Relay #Y ACK Packet Delay
Relay #Y ACK Packet Delay = Decay Time
+ (Y x Slot Time)
+ Attack Time
+ ACK Packet Transmit 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
Decay Time = Tx Decay Time + Additional Transmit Attack Time
Attack Time = Tx Attack Time + Additional Transmit Attack Time
The average delay is the average amount of time from when a packet is ready
for transmission to when the packet is actually transmitted. This number is for a
single attempt and does not include the time for any retries due to corrupted
transmissions. Note that the average delay varies based on the number of
backlogged nodes in the system at a given time. Also note that the average
delay varies substantially even with constant conditions due to the random
nature of events.
For ease of notation we shall rename some of the parameters.
Tslot = Slot Time
PDR = Packet Detection Ratio
TI = Transmission Index
N = Backlogged Nodes
PR = (TI - 1)/TI
Average Delay = Tslot x (1 + PDR - PRN)
PDR x ln(1/PR)
Data Packet Delay
Average Delay