Session Date/Time: 22 Aug 2023 12:00

DETNET

Summary

This meeting focused on the initial evaluation of existing Time-Sensitive Networking (TSN) queuing mechanisms, specifically ECQF (Enhanced Cyclic Queuing and Forwarding) from IEEE 802.1, against the DETNET Working Group's requirements draft. The presentation of ECQF detailed its functionalities, including phase offset detection (CPAP protocol), time-based and counter-based bin assignments, and stream aggregation/disaggregation. A preliminary scorecard highlighted that existing mechanisms, including ECQF, struggle with scalability to a large number of flows and hops with complex topologies, suggesting these are critical areas for new DETNET solutions. Discussions also touched upon the relationship between ECQF and other IETF-proposed mechanisms like CSQF/TCQF, and the need to clarify evaluation criteria within the requirements draft.

Key Discussion Points

ECQF (Enhanced Cyclic Queuing and Forwarding) Presentation:
- An in-depth introduction to ECQF, a new development in IEEE 802.1, was provided. Key features include:
  - No time synchronization, but frequency synchronized nodes. Cycles do not begin at the same absolute time but use a common cycle duration.
  - CPAP Protocol: A new protocol leveraging hardware-based timestamping to detect and align cycle phase offsets between adjacent nodes.
  - Time-based and Counter-based Bin Assignment: Mechanisms for assigning frames to output bins based on arrival time or byte count.
  - Stream Aggregation and Disaggregation: Methods to change between slower and faster cycle levels to manage flows efficiently, with counter-based assignment favored for its robustness.
  - Multiple Cycle Levels: Support for various traffic classes with different priorities and cycle durations on the same output port, where faster levels are integer multiples of slower ones.
- Discussion on CPAP protocol issues included field usage, message binding, and potential for single-message phase offset detection.
- The presentation clarified that ECQF is designed for point-to-point links and relies on hardware timestamping, contrasting it with IETF's TCQF which considers more complex topologies and clock drifts, thus often requiring explicit tagging.
- While ECQF aims for determinism, its performance is heavily dependent on accurate phase offset detection.
Evaluation Against DETNET Requirements Draft:
- An initial evaluation of both CQF and ECQF against DETNET requirements was presented.
- ECQF showed improvement over CQF in "Deliver in time" and "Synchronous" requirements (moving from 'No' to 'Yes' or 'Partial').
- However, both CQF and ECQF still received 'Partial' or 'No' for requirements related to scalability to a large number of flows and scalability to a large number of hops with complex topology.
- This highlights these two scalability requirements as crucial gaps in existing mechanisms that new DETNET proposals need to address.
Discussion on ATS Evaluation:
- A participant suggested that ATS (Asynchronous Time-Sensitive) could achieve a 'Yes' for "Scalable to large number of hops with complex topology" (requirement 3.7), arguing that its end-to-end latency scales linearly with hop count, similar to other solutions.
- Another participant countered that while ATS provides worst-case bounds, these might be too large for some services, hence retaining a 'Partial' evaluation for certain low-latency requirements.
- The discussion underscored the ambiguity in what constitutes "acceptable" scaling for this requirement.
Clarification of Requirements and "Partial" Evaluations:
- A participant suggested refining the requirements draft to clarify what defines a 'Yes', 'No', or 'Partial' evaluation, especially for scalability.
- It was proposed that certain fundamental network capability requirements (e.g., 3.6, 3.8) might need to be 'Yes', while flow/traffic scheduling requirements (e.g., 3.4, 3.5, 3.7) could potentially be 'Partial' under certain conditions.

Decisions and Action Items

New Proposal Presentations: One-slide summaries for new mechanisms (initially planned for this meeting) will be deferred to the next open meeting to allow presenters sufficient time to prepare and to include supporting material.
Mailing List Discussion on Requirement 3.7: Jianing will start a discussion on the mailing list to clarify the text for requirement 3.7 ("Scalable to large number of hops with complex topology") and the definition of 'Yes' vs. 'Partial' for such scaling.

Next Steps

Guidelines for Next Meeting Presentations: The Chair will send guidelines to the mailing list this week for presentations at the next meeting. These will likely include:
- A summary evaluation slide (similar to the scorecard presented).
- A small number of supporting slides to explain the evaluation details, particularly for scalability requirements (3.6 and 3.7).
- Time limits for each presentation (suggested 10-15 minutes).
Next Meeting Focus: The next meeting will focus on reviewing the single-slide/short deck evaluations of new DETNET queuing and scheduling mechanisms against the requirements draft.