10BASE-T1S PLCA Bandwidth Calculator

16.06.2026

This tool estimates 10BASE-T1S PLCA bandwidth from Linux ethtool --set-plca-cfg parameters.

PLCA assigns transmit opportunities, not fixed bandwidth. A node only consumes significant bus time when it actually transmits.

Basic PLCA Parameters

node-cnt Number of configured PLCA transmit opportunities. to-tmr [BT] Transmit opportunity timer in bit times. burst-cnt Additional frames allowed after the first frame. burst-tmr [BT] Timer used for burst operation.

Advanced Parameters

Frame size [bytes] Ethernet payload / MTU size used for the bandwidth calculation. Payload size [bytes] Useful payload size used for effective payload bandwidth. Beacon overhead [BT] Not an ethtool parameter. Used only as calculator assumption for PLCA cycle overhead. Line rate [Mbit/s] 10BASE-T1S uses 10 Mbit/s. At 10 Mbit/s, 1 BT = 100 ns. Preamble + SFD [bytes] Simplified Ethernet wire-time model. IFG [bytes] Simplified inter-frame gap handling. Include VLAN tag in wire size Adds 4 bytes to the calculated wire size. This does not configure VLAN. Start delay model Calculation assumption. Default custom value follows to-tmr / 2 until edited manually. Custom start delay [BT] Burst gap model Calculation assumption. Default custom value follows burst-tmr / 2 until edited manually. Custom burst gap [BT]

Size model:
Frame size = Ethernet payload / MTU
Payload size = useful data for effective bandwidth
Wire size = preamble + SFD + Ethernet header + optional VLAN + frame size + FCS + IFG

Configuration Summary

Static Bandwidth Table

Per-Node Table

Realistic packet transmission scenario

This table shows the assumed packet distribution for the realistic PLCA scenario. At least one transmit opportunity is unused and only waits for the TO timer.

PLCA Cycle Overview

Selected TO / selected node Selects the TO / node highlighted in the PLCA Cycle Overview. This does not change the bandwidth calculation.

Selected TO Usage

Selected Node Realistic Bandwidth

Realistic distribution for the selected TO

Simplified view.
For more details about PLCA symbols and commands, see: Microchip Knowledge Base – PLCA Symbols and Commands, Inter Frame Gap in 10BASE-T1S

Generated ethtool Command

Interface name Linux network interface used for the generated ethtool command. Enable PLCA enable setting used by ethtool.

node-id: uses the current Selected TO / selected node value from the PLCA Cycle Overview.

References and Assumptions

Normative reference

IEEE 802.3cg, 10BASE-T1S PLCA specification.

Implementation / explanation references

Linux ethtool PLCA parameters: enable, node-id, node-cnt, to-tmr, burst-cnt, burst-tmr.
Microchip Knowledge Base – PLCA Symbols and Commands, Inter Frame Gap in 10BASE-T1S . This reference is used for explanation only, not as the normative calculation source.

Tool-specific assumptions

10BASE-T1S line rate is 10 Mbit/s.
1 BT at 10 Mbit/s is 100 ns.
Beacon overhead is not configurable through ethtool. This tool uses 20 BT by default.
Frame size means Ethernet payload / MTU size.
Payload size means useful user payload used for effective bandwidth.
Wire size is calculated as preamble + SFD + Ethernet header + optional VLAN + frame size + FCS + IFG.
TX start delay and burst gap are calculation assumptions, not additional ethtool parameters.
0 frames means no transmission. The TO consumes only the TO timer / timeout.
The Ethernet timing model is simplified and intended for engineering estimation.
The diagrams do not show the full PLCA / PCS symbol sequence.
The calculation is not a bit-exact PHY simulation.