FAQ: Total Packet Length Estimates (Framing Utility)

The AX-Radiolab configuration utility allows to estimate the Total Packet Length in ms when using the Framing Utility. The estimated time to process packet comes from the following equation :

Tx Completion = FULL TX PACKET LENGTH (bits) / PHY RATE (bps)

FULL TX PACKET LENGTH = A + B + (C * D)
FULL TX PACKET LENGTH = Preamble (bits) + Framing Mode Flags (bits) + [ (Packet Length + CRC Length) X Framing Mode Insertion

A: Preamble (bits)
B: Framing Mode Flags (bits)
• HoldC : 2*8 (2 HDLC flags at the beginning and end) = 16 bits
• Raw Pattern Match : Length of the selected sync word, usually 16 or 32 bits
• PN9 Compatibility : length of the selected sync word, typically 11, 16, 24, or 32 bits

C: [ (Packet Length + CRC Length) X Framing Mode Insertion if any
Framing Mode Insertion (if any)
• HoldC : 6/5 comes from the HDLC protocol having to insert a 0 bit after 5 consecutive 1 bits
• Raw Pattern Match : factor is always 1, no bits need to be inserted
• PN9 Compatibility : factor is always 1, no bits need to be inserted

Example :

A= Preamble
B= 2*8 (2 HDLC flags at the beginning and end)
C= (packet length in bits + 16 (CRC length)) * HoldC
HoldC : HDLC protocol having to insert a 0 bit after 5 consecutive 1 bits
PHY RATE = Phy Rate in bps

A= 24 bits
B = 8 + 16 = 24 bits
C = (8 + 16) * 6/5 = 24 * 1.2 = 28.8 bits
PHY Rate = 9800 bps

TOTAL = 76.8 bits
PHY Rate = 9800 bps

TIME = 7.8 ms = ~ 8 ms

The Framing Utility converts the result to the upper decimal value.

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