Thanks Karl.
Agree that the arbitration phase is slow in CAN and adds to the overhead, not a good comparison. The way CAN-XL was updated to support 20 Mbps and keeping backward compatibility is nice.
Thx,
Arvind.
From: Budweiser Karl, EL-442 <Karl.Budweiser@xxxxxx>
Sent: Wednesday, October 28, 2026 3:17 AM
To: Subramaniam Aravindhan <arvind@xxxxxxxxxxxx>; STDS-802-3-EPLCA@xxxxxxxxxxxxxxxxx
Subject: AW: [802.3_EPLCA] Updated minutes for 10/22 and deadline to request a presentation
Dear Arvind,
please note that you cannot count the header bytes on CAN and compare them 1:1 to the Ethernet header! On CAN the header is partially part of the arbitration which is typically running at a lower speed than
the rest of the frame (data phase), so you need to weight the header bits accordingly. With a 5Mbit/s CAN-FD that uses 500kbit/s in the arbitration phase, for example, the equivalent header length would be:
(29bits*5Mbit/s)/500kbit/s + 27bits = 317bits ~ 40byte
This is, the CAN header looks short but takes quite the same time to transmit an 80byte “Ethernet header” on a 10BASE-T1S network…
The main difference between CAN and 10BASE-T1S is therefore not the protocol efficiency but the QoS-scheme. CAN will give precedence to the most important message of all peers, while 10BASE-T1S picks the most
important message of the next peer first…
Kind regards,
Karl
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Sent from outside the BMW organization - be CAUTIOUS, particularly with links and attachments.
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Absender außerhalb der BMW Organisation - Bitte VORSICHT beim Öffnen von Links und Anhängen.
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Hi Natalie and all,
Few more thoughts on the 4B/5B change proposal in the PCS layer:
>>A participant asked if the presenter was proposing to change the MAC data rate to 12.5 Mb/s. The presenter answered in the affirmative.
>>Ms. Wienckowski stated that changes considering changes to the MAC data rate were beyond the scope of the CFI and the Study Group’s charter.
- The 10BASET1S is already using 12.5Mbps transceivers and we are not making any changes to the medium, or transceiver, or multidrop method.
- In a shared medium multi-drop protocol, for example whether a node gets 1Mbps or 1.25Mbps bandwidth is transparent and does not affect upper layer protocol; only helps.
- The changes are localized to PCS layer and there are no changes in MAC. In the MAC MII interface definition, the clock is input to MAC and controlled by PCS/PLCA.
- We are still backward compatible, and this capability would be enabled only in the context of EPLCA when all the nodes are of EPLCA type in a zone.
- 25% improvement with a limited changes to PCS layer is still a good performance improvement. Especially the bandwidth requirements of the new zonal applications are only going to keep
increasing. The layer-3 and above protocol overheads are also increasing in automotive applications due to timestamping requirements and other header overheads. Compared to CAN, the Layer-2 and above layers overhead in ethernet is much higher which already
reduces usable bandwidth. For example, with a 64-byte payload we are already at ~64-byte of overhead due to Layer-2, and Layer-3; which is 50% usable bandwidth.
On the PAR, don’t we have to follow the following template? Where does the “PLCA Enhancement SG Objectives” slides fit in the PAR?
PAR.pptx
Thx,
Arvind
Dear Colleagues,
I have updated the minutes for October 22nd to add the following to the notes on Enhanced
PLCA (EPLCA) –Technical Feasibility Study For Predictable Max Latency –Study3
A participant asked if the presenter was proposing to change the MAC data rate to 12.5 Mb/s. The presenter answered in the affirmative.
Ms. Wienckowski stated that changes considering changes to the MAC data rate were beyond the scope of the CFI and the Study Group’s charter.
Please keep in mind the scope of the CFI and the Study Group's charter as you prepare presentations for the upcoming Plenary. If you plan to attend and have not yet done so, please
register for the meeting and pay the required meeting fee. While you do not have to be a WG voter to vote in the Study Group, you are still required to pay all necessary meeting fees to participate.
Here is a reminder of the deadline to request time to present:
November
9-12, 2026 (Plenary) (Requests due AOE October 29, Presentations due AOE November 3)
Priorities during the meeting:
-
Respond to comments from other 802 groups on our PAR and CSD submissions
-
Discussion and approval of Objectives
-
Other presentations
Thanks,
Natalie Wienckowski
In-Vehicle Networking Solutions LLC
IEEE P802.3dm Chair and Chief Editor
IEEE P802.3 EPLCA SG Chair Pro Tem
natalie@xxxxxxxxxxxxxxxxxxx
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