FR, FR + FRF.12, and MLPoFR L2 overhead
I've always followed the SRND in terms of calculating the L2 overhead for the LLQ policy-map values.
Copied from the QoS SRND (pg 33, Chapter 1-15)
A more accurate method for provisioning VoIP is to include the Layer 2 overhead, which includes
preambles, headers, flags, cyclic redundancy checks (CRCs), and ATM cell-padding. The amount of
overhead per VoIP call depends on the Layer 2 technology used:
• 802.1Q Ethernet adds (up to) 32 bytes of Layer 2 overhead.
• Point-to-point protocol (PPP) adds 12 bytes of Layer 2 overhead.
• Multilink PPP (MLP) adds 13 bytes of Layer 2 overhead.
• Frame Relay adds 4 bytes of Layer 2 overhead; Frame Relay with FRF.12 adds 8 bytes.
• ATM adds varying amounts of overhead, depending on the cell padding requirements.
For a g711 call, I understood the frame size would be-
FR = 160B + 40B + 4B
FR + FRF.12 = 160B + 40B + 8B
MLPoFR = 160B + 40B + 13B (MLPoFR)
This thread from an online forum seems to also follow this calculation;
But then I came upon Petr's post on "Computing VoIP traffic bandwidth consumption"
FR = 160B + 40B + 7B
FRF.12 = 160B + 40B + 7B
MLPoFR = 160B + 40B + 9B
This blog makes complete sense on how voice packets are not fragmented so there should be no additional FRF.12/MLP overhead for voice packets.
But for the lab should we be following the SRND L2 overhead values, Petr's post, others? What if the question states to refer to the SRND?