Markdown Version | Session Recording

Session Date/Time: 22 Mar 2022 13:30

detnet

Summary

The DetNet Working Group at IETF 113 discussed various aspects of deterministic networking, covering charter updates, milestone revisions, and a range of technical drafts. Key discussions included expanding the charter to encompass new traffic treatments, an ITU-T liaison report, the framework for DetNet control planes, OAM mechanisms for MPLS and IP, a packet ordering function, IPv6 data plane enhancements using extension headers, requirements for large-scale DetNet deployments, and specific queuing/forwarding solutions like Time-Sensitive Cyclic Queuing and Forwarding (TCQF) and Deadline-based Forwarding. Additionally, discussions touched on one-way delay measurement without clock synchronization and PCE extensions for DetNet path computation. The chairs emphasized the contribution-driven nature of the WG and planned for adoption calls for requirements and solution documents in upcoming months.

Key Discussion Points

• Opening & Logistics: The session was held in a hybrid format, with a note on IETF policies, code of conduct, and tools (Meetecho for queue/blue sheets, Hedgedoc for notes). Two sessions were planned, one WG-specific and a joint session with PALS/MPLS.
• Charter Update:
  • Discussion focused on adding flexibility to the charter's traffic treatment clause, specifically for queuing and scheduling.
  • A proposal to add "for example" between "including" and "forwarding" was presented to allow for non-prescriptive listing of traffic treatments.
  • The AD (John Scudder) had no objection, noting it makes the intent clearer.
  • A question arose regarding coordination with SDOs like IEEE TSN for shared mechanisms; the chairs affirmed continued coordination while evaluating proposals based on specifics.
• Milestones Update:
  • Milestones were updated to reflect progress and an expanded scope, notably for OAM and data plane enhancements.
  • A correction was noted for the "first OAM document" entry, clarifying it's not specific to "IP OAM."
  • The "enhanced DetNet data plane requirements" milestone was clarified to cover requirements for new queuing mechanisms and solutions, stemming from discussions with the Transport Area AD.
  • The WG confirmed its contribution-driven approach, allowing for multiple requirements and solution documents if merited, rather than a single document per area.
• ITU-T SG13/Q6 Liaison Report (Scott Mansfield):
  • Reviewed liaison activity between IETF and ITU-T SG13/Q6 (QoS and QoE, large-scale networks, resource control).
  • Highlighted ITU-T's focus on "large-scale networks" and "inter-domain networks," looking at use cases, frameworks, and architectures for 2030 and beyond, often from a top-down perspective.
  • Emphasized the importance of terminology alignment between SDOs.
  • Mentioned key ITU-T documents related to functional architecture, jitter guarantee, and QoS requirements for IMT-2020 (5G) and beyond.
  • Encouraged IETF participation in ITU-T meetings as invited experts to identify gaps and foster collaboration.
• DetNet Controller Plane Framework (Shusang Li):
  • Document aims to consolidate DetNet control plane requirements and provide an overview of control architecture (fully distributed, fully centralized SDN-like, hybrid).
  • Covers considerations for various DetNet mechanisms (explicit paths, resource reservation, POF) and data plane solutions (MPLS, IP, SR).
  • Updates included refining management plan specifications and removing detailed protocol extension examples.
  • Discussion points: Integration with RAW architecture (Pascal Thubert, Carlos Pignataro suggested specific proposals on the mailing list); inclusion of TSN control plane protocols (Toerless Eckert suggested QCC reference).
  • Authors requested more WG input on flow aggregation and management plan scope (YANG, OAM).
• DetNet MPLS OAM (Greg Mirsky):
  • Presented updates to the DetNet ACH definition, differentiating it from pseudo-wire ACH with a new version number, sequence number, channel type, node ID, flags, and session identifier.
  • Coordination with PALS/MPLS OAM design team was confirmed.
  • Proposed an IANA registry for DetNet MPLS OAM flags.
  • Discussion on the encoding and mechanism of OAM packets; specific usage of fields like "session ID" needs further definition.
  • Concern raised that the document might not be ready for a Working Group Last Call (WGLC) due to unaddressed mechanism discussions.
• DetNet IP OAM (Greg Mirsky):
  • Document describes active OAM for DetNet IP using UDP encapsulation, mapping to monitor the DetNet flow.
  • For DetNet service sub-layer realization, it proposes using MPLS over UDP for OAM to ensure fate-sharing with the DetNet flow.
  • Lou Berger emphasized the need for a solution that works for native IP (6-tuple flows) without MPLS encapsulation, suggesting this document or another should cover it.
  • Pascal Thubert suggested using IPv6 extension headers (Hub-by-Hop, SRH, Destination Option) for native IP OAM, similar to MPLS encapsulation, to signal path and treatment independent of application flows.
• Packet Ordering Function (POF) (Janos Farkas):
  • Document describes algorithms for POF in the DetNet service sub-layer to address out-of-order packet delivery caused by replication and elimination.
  • The draft is stable, focusing on algorithms, with delay variation aspects considered out of scope for this document.
  • The authors are seeking WG adoption.
  • Toerless Eckert suggested the ultimate goal should be a normative YANG document for POF parameters and other service sub-layer functions.
• IP/IPv6 Data Plane Enhancements using Extension Headers (Pascal Thubert):
  • Proposal to use IPv6 extension headers (Hub-by-Hop, Destination Option, SRH) as a network construct to carry path and treatment information, independent of application flow 5-tuple.
  • This approach aims to enable transport of multiple flow types (data, OAM) and aggregated flows with shared fate, similar to MPLS.
  • Emphasized the advantage of Hub-by-Hop headers being processed close to the IPv6 header, potentially enabling hardware processing.
  • Discussion on the guarantee of HBH header processing in a limited domain (DetNet scope) vs. the global internet, and interworking with SRH.
• Large Scale DetNet Requirements (Fan Yang):
  • Document motivated by prototyping and trials of large-scale deterministic networks.
  • New requirements added: support for configuration of multiple queuing mechanisms and cross-domain mechanisms.
  • Overall technical requirements include time synchronization, propagation latency, high speed, numerous devices, massive traffic, and tolerance for failures/topology changes.
  • Potential data plane implications: IPv6 extension headers, redundancy/flow identification (e.g., for aggregation), and queue-related information.
  • The authors are requesting an adoption call for this document as the starting point for enhanced requirements.
• Time-Sensitive Cyclic Queuing and Forwarding (TCQF) (Toerless Eckert):
  • Highlighted limitations of existing bounded latency solutions (RFC 2212, TSN ATS, TSN cyclic queuing) for large-scale, high-speed networks.
  • Proposed TCQF as an enhanced cyclic queuing mechanism, carrying cycle identity in the packet, supporting arbitrary latency and high speeds (proven up to 100Gbps+).
  • The draft proposes standardizing TCQF with an MPLS forwarding plane using the traffic class field.
  • Adjacent work includes YANG models, ingress policing, and tagging for other data planes (e.g., DSCP, SRv6).
  • Question on adopting multiple data plane solutions vs. a generic one; the presenter advocated for multiple solutions based on deployment experience, suggesting TCQF is a good first candidate.
• Reference Delay-Based One-Way Delay (OWD) Measurement (Bin Yang):
  • Proposed a method for accurate end-to-end OWD measurement without clock synchronization, leveraging a deterministic path (from DetNet) as a reference.
  • Method uses a reference packet and a target packet, with timestamps recorded at both ends, and equations to derive the target delay.
  • Benefits include reduced deployment cost and no impact on intermediate devices.
  • Concern raised about timer instability and skew without clock synchronization.
• Deadline-based Forwarding (Xianfeng Li):
  • Proposed a solution for DetNet based on deadline attributes (Time-Dependent Delay Limit - TDL) for packet forwarding.
  • TDL attributes change with time, with TDL=0 having the highest priority.
  • Mechanism involves carrying TDL information in the packet and placing packets into queues based on TDL.
  • Benefits: No clock synchronization required, relative time operation, pragmatic enhancement of PQ, supports partial upgrades and scalability.
• PCE-based Path Computation for DetNet (Shuanglong Chen):
  • Document describes extensions to PCE for carrying bounded latency constraints and distributing deterministic paths.
  • Proposed PCE extensions include a metric object for end-to-end delay/jitter, an IOSP extended flag TLV for deterministic path capability, and ERO/SRERO extensions for distributing path computation (e.g., DetNet sub-TLV, cycle sub-TLV).
  • Suggested that this work could be done in DetNet or PCE WG, and comments are welcome.

Decisions and Action Items

Decisions:

• The Area Director (John Scudder) approved the proposed charter update to add "for example" to the traffic treatment clause, making it non-prescriptive and allowing for new mechanisms like queuing and scheduling.

Action Items:

• DetNet Controller Plane Framework: Authors to consider adding flow aggregation and incorporating RAW integration proposals (from Pascal Thubert, Carlos Pignataro) and TSN protocol references (from Toerless Eckert) based on mailing list discussions.
• DetNet MPLS OAM: Continue discussion on the mailing list regarding specific usage of "session ID" and other fields, and readiness for a Working Group Last Call.
• DetNet IP OAM: Greg Mirsky to provide comments on supporting native IP 6-tuple flows in the document and explore the use of IP extension headers for DetNet OAM. Mailing list discussion to continue.
• Packet Ordering Function (POF): Mailing list discussion requested on the feasibility and scope of a YANG model for POF configuration parameters.
• IP/IPv6 Data Plane Enhancements: Continue discussion on the mailing list and socialize the idea in SixMan WG.
• Large Scale DetNet Requirements: Chairs will poll the working group for adoption of this document as the enhanced requirements document, potentially as soon as next month, following further mailing list discussion.
• Time-Sensitive Cyclic Queuing and Forwarding (TCQF): Continue mailing list discussions, with a view towards potential adoption of solutions documents around the next IETF, allowing time for other contributions.
• Reference Delay-Based OWD Measurement: Further discussion on the mailing list regarding the impact of timer instability without clock synchronization.
• Deadline-based Forwarding: Continue mailing list discussions.
• PCE-based Path Computation for DetNet: Authors to bring this work to the PCE WG for discussion and coordinate with PCE chairs regarding which WG will own the work, pending DetNet WG interest.

Next Steps

• Continue active engagement and technical discussions on the DetNet mailing list for all presented drafts.
• The chairs plan to initiate a Working Group adoption poll for the "Large Scale DetNet Requirements" document in the near future.
• For solution documents related to traffic treatment enhancements (e.g., TCQF, Deadline-based Forwarding), the chairs plan to consider adoption calls around the next IETF (IETF 114) to allow time for additional contributions and discussions.
• Further coordination with other WGs (e.g., PCE, SixMan) is encouraged for relevant drafts.