User's Manual

TS4000 Radio Modem User’s Manual AirNet Packet Protocol 38
The time it takes each relay to send the packet is basically the packet transmit
time. Added to this must be the number of idle slots between the last
transmission and when the current relay decides to transmit.
Relay #Y Data Packet Delay = Decay Time
+ (Y x Slot Time)
+ Attack Time
+ Data Packet Transmit Time
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 relays 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.
Data Packet Delay
Average Delay