Session Date/Time: 10 May 2023 00:00

DETNET

Summary

The DETNET working group met to discuss the status of the requirements draft and to delve into the evaluation of existing Time-Sensitive Networking (TSN) mechanisms against DETNET requirements. A significant portion of the meeting was dedicated to a presentation and discussion of the draft-liu-detnet-sr-based-cyclic-queuing-forwarding (CSQF) solution, focusing on its queuing mechanisms, jitter handling, centralized control, and scalability in Segment Routing (SR) networks.

Key Discussion Points

Requirements Draft Revision:
- Peng shared that a revision to the requirements draft is underway, incorporating comments from co-authors.
- The chair requested that proposed changes be sent to the mailing list for discussion before posting a new version.
Evaluation of TSN Mechanisms against DETNET Requirements:
- A lengthy discussion ensued regarding how to evaluate existing TSN (IEEE 802.1Q) queuing and scheduling mechanisms against the DETNET requirements.
- Need for a Separate Document: A suggestion was made for a separate document to evaluate the gap between existing TSN mechanisms and DETNET requirements.
- Concerns about "All or Nothing" Conclusion: A concern was raised that a single document might wrongly imply that all TSN mechanisms are unsuitable for any DETNET requirement. It was emphasized that DETNET requirements are often case-by-case, and some TSN mechanisms might satisfy certain requirements, but not all or for all scaling scenarios.
- Case-by-Case Evaluation: There was general agreement that evaluating existing TSN mechanisms against DETNET requirements should be done on a "case-by-case" basis, identifying which mechanisms meet which requirements, rather than a blanket statement.
- Role of Solution Authors: It was suggested that proponents of new DETNET solutions are best placed to evaluate how their proposed mechanisms (especially if extensions of existing TSN mechanisms like CQF) address the scaling requirements. This evaluation could take the form of an explanation or a table mapping solutions to requirements.
- Pilot Evaluation for Learning: The chair expressed a desire to take at least one "classic" TSN mechanism (e.g., CQF) through an evaluation process against the scaling requirements draft. This would serve as a learning exercise for the working group and inform potential revisions to the requirements document. Shusong Liu offered to adapt existing work on CQF analysis to fulfill this.
CSQF (Cyclic Specified Queuing and Forwarding) Presentation:
- Core Mechanism: Shusong Liu presented the CSQF mechanism, which uses multiple queues (output, target input, burst tolerant) with cycle numbers to provide bounded latency and jitter.
- Jitter Handling: Jitter from processing delay is absorbed by dynamic queuing delay, using burst-tolerant queues.
- Centralized Control: A key aspect is the use of a centralized controller for path calculation, time slot scheduling, and resource reservation. The controller ensures no congestion or conflictions by reserving time slots for each flow.
- SR Encapsulation: SR labels (MPLS or SRv6 SIDs) are used to carry information, including the cycle number, for each hop. This allows the cycle number for a packet to differ at different nodes along the path, offering flexibility.
- Scalability: Intermediate nodes only need to read the label, not maintain per-flow state, enhancing scalability.
- Controller Algorithms: The presentation touched upon offline/online planning and algorithms (e.g., column generation, greedy) for joint routing and scheduling.
- Q&A Highlights:
  - Cycle Number Encoding: Confirmed that SR labels encode both the output port and the cycle number, potentially using a range of SIDs for different cycles on the same port.
  - Conflict Resolution: The controller proactively prevents conflicts by checking resource availability (e.g., time slot capacity) during scheduling. If resources are insufficient, new flow requests might be rejected or rescheduled.
  - Synchronization: The system requires frequency synchronization across nodes, and the controller needs to know the exact start time of cycles for each node.
  - Cycle Duration: Cycle duration is not directly tied to individual flow specifications but is a network-wide planning parameter.
  - Traffic Specification: Resource reservation is based on provided traffic specifications (max packet size, traffic pattern, burst). If actual traffic deviates, it's considered a flow's problem, not a network issue.
  - Flexibility: The ability to update the label stack allows the controller to adjust time slots dynamically based on network status.
  - Standardization Path: The work is currently seeking DETNET WG consensus on its utility before proposing SR extensions to the SPRING WG.
IPR Reminder: The chair reminded the presenter to check and file an IPR disclosure if patent application numbers shown on one of the slides (slide 18) are relevant to the proposed draft. The "Huawei confidential" footer also needs to be removed from the slides before posting.

Decisions and Action Items

AI: Peng to send proposed revisions to the DETNET requirements draft to the mailing list for discussion prior to posting a new version.
AI: Shusong Liu (and Ego) to adapt existing analysis of CQF against DETNET requirements and share it (e.g., on the Wiki or mailing list) as a learning exercise for the WG on how to perform such evaluations.
Decision: Authors of DETNET solution drafts are expected to include sections evaluating how their proposed mechanisms address the DETNET scaling requirements. This could take the form of an explanatory text or a table mapping the solution to specific requirements.
AI: Shusong Liu to remove "Huawei confidential" footers and check IPR disclosure requirements for any patent application numbers mentioned in the CSQF presentation slides before sending them for posting.

Next Steps

Continue discussion on the requirements draft revisions on the mailing list.
DETNET solution authors to prepare or update their drafts to include sections evaluating how their solutions meet the DETNET scaling requirements.
Further discussion on the CSQF draft (draft-liu-detnet-sr-based-cyclic-queuing-forwarding) on the mailing list.
The tcqf draft is planned for presentation at a future meeting.