SCHC

Summary

The SCHC Interim meeting on May 7, 2024, focused on status updates for active working group documents and a detailed presentation on the advancement of the SCHC Architecture. The primary technical discussion centered on refining architectural definitions (Endpoint, Instance, Stratum, Session) and addressing the challenge of routing SCHC datagrams to specific instances when underlying network discriminators are absent.

Key Discussion Points

1. Working Group Document Status

Alexander Pelov provided updates on the following documents based on the Chair Slides:

draft-ietf-schc-protocol-numbers: Quentin Lampin is assigned as the document shepherd.
draft-ietf-schc-8824-update: Alexander Pelov is the shepherd. The shepherd review is ongoing and expected to conclude by the next meeting, with a goal to start the Working Group Last Call (WGLC) then.
draft-ietf-schc-over-networks-prone-to-disruptions: Alejandro (not present) will provide news on Forward Error Correction (FEC) performance evaluation at the next session.

2. SCHC Architecture Advancement

Quentin Lampin and Marion Dumay presented the latest design team progress regarding the architecture, referencing the SCHC Architecture Advancement slides.

Architectural Definitions

The team introduced and refined several core concepts:

Endpoint: A logical entity providing SCHC functionality, distinct from supporting hardware.
Instance: A logical component within an endpoint performing SCHC operations independently with its own context.
Stratum: A portion of the network protocol stack targeted by SCHC.
Context/Instance Configuration: Definitions include rules, metadata (data models/parsers), and instance-specific settings (e.g., uplink/downlink roles).
Session: A communication session between instances sharing a common context.
Datagram: The unit of exchange (packets or fragments) including Rule ID and payload.

Technical Discussion on Definitions

Stratum and Adjacency: Marco Tiloca queried whether a stratum must consist of adjacent layers. He proposed a case where SCHC might compress UDP and L2 but skip an intervening IP layer. Quentin Lampin and Alexander Pelov clarified that in such a case, the layers are still considered contiguous in the stack, but the rule would simply specify "value-sent" or "ignore" for the fields of the skipped layer. Alternatively, this could be represented as two separate strata. The consensus was that a single stratum generally covers contiguous and adjacent layers.
Session Scope: Marco Tiloca noted that the definition of "Session" should support group communication. Quentin Lampin agreed to update the definition from "between two instances" to "two or more instances."
Identification: Marco Tiloca asked about canonical IDs for endpoints and instances. Marion Dumay and Quentin Lampin noted that session IDs and instance IDs are necessary for management and routing, particularly in multi-tenant gateway scenarios.

3. Routing Datagrams to Instances

The group discussed how a "Dispatcher" within an endpoint routes incoming datagrams to the correct "Instance" when no external discriminator (like a VLAN ID or UDP port) is available.

Potential Solutions Discussed:

SCHC Control Header: A dedicated header prepended to the datagram to provide a discriminator.
Existing Protocols: Reusing standards like UDP-Lite or MPLS labels.
The "Container" Approach: Alexander Pelov suggested the architecture define a "container" or placeholder (potentially using the draft-ietf-schc-schclet framework) that can hold metadata, checksums, or instance IDs. This would allow specific deployments (e.g., SCHC over Ethernet) to define the container's format in separate documents.

Decisions and Action Items

Shepherd Assignment: Quentin Lampin is officially the shepherd for draft-ietf-schc-protocol-numbers.
Shepherd Assignment: Alexander Pelov is officially the shepherd for draft-ietf-schc-8824-update.
Data Tracker Update: Alexander Pelov to update the Datatracker with these shepherd assignments.
Architecture Refinement: The design team will update the "Session" definition to include multi-party communication and refine the "Stratum" definition regarding layer adjacency.

Next Steps

The design team will continue discussing the format and requirements of the "SCHC Control Header" or "Container" on the mailing list.
A more advanced version of the architecture document is expected before IETF 120.
The next interim meeting will include a performance evaluation of FEC for draft-ietf-schc-over-networks-prone-to-disruptions.

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