Network Working Group A. Pelov
Internet-Draft IMT Atlantique
Intended status: Informational 4 February 2025
Expires: 8 August 2025

SCHC Architecture for Process Stacking and Routing in Constrained
Networks
draft-pelov-schc-process-stacking-routing-00

Abstract

This document specifies architectural guidelines for dynamically
stacking and routing SCHC processes in constrained networks. It
details how independent SCHC modules can be composed into processing
chains that adapt to PDU attributes. For instance, SCHC Compression
may trigger SCHC Fragmentation when the compressed PDU exceeds the L2
MTU, or alternatively, trigger SCHC Aggregation. For traffic that is
not delay tolerant, a direct routing from SCHC Compression to SCHC
Reliability Fragmentation is provided. Subsequent processing by SCHC
FEC Fragmentation modules ensures robust error correction. This
modular approach promotes scalability and flexibility within the SCHC
framework.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 2
3. Process Stacking and Routing Recommendation . . . . . . . . . 3
4. Schemas . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Process Stacking Overview . . . . . . . . . . . . . . . . 4
4.2. Detailed Routing Logic Schema . . . . . . . . . . . . . . 4
5. Operational Considerations . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Examples and Use Cases . . . . . . . . . . . . . . . . . . . 5
8.1. Example 1: Compression and Fragmentation . . . . . . . . 5
8.2. Example 2: Compression and Aggregation . . . . . . . . . 5
8.3. Example 3: Direct Path for Non-Delay-Tolerant Traffic . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6

1. Introduction

RFC8724 defines the SCHC framework for compressing and fragmenting
IPv6/UDP packets in low-power, constrained networks. While the
specification addresses individual processes, many deployment
scenarios require multiple SCHC processes to be chained based on the
properties of the PDU. This document presents architectural
guidelines to dynamically stack and route SCHC processes, enabling
optimal handling of PDUs through configurable processing chains.

2. Architectural Overview

The proposed architecture is built upon two core principles:

* Modular Composition: Each SCHC process (e.g., Compression,
Fragmentation, Aggregation) is an independent module with clearly
defined interfaces for exchanging metadata such as PDU size, delay
sensitivity, and error correction parameters.

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* Dynamic Routing: A central Process Router evaluates incoming PDUs
against operational criteria (e.g., PDU size relative to the L2
MTU, aggregation requirements, delay tolerance) and directs them
through the appropriate processing chain.

This design ensures that the SCHC framework can be adapted in real
time to diverse network conditions and application requirements.

3. Process Stacking and Routing Recommendation

Operators may configure SCHC processes in various sequences. Typical
chains include:

* Compression and Fragmentation Chain:

1. SCHC Compression reduces header overhead.

2. If the compressed PDU exceeds the L2 MTU, the Process Router
directs it to SCHC Fragmentation.

3. Each fragment is then passed to SCHC FEC Fragmentation for
error correction.

* Compression and Aggregation Chain:

1. SCHC Compression is applied.

2. If multiple small PDUs can be combined, the Process Router
forwards the compressed output to SCHC Aggregation.

3. SCHC Reliability Fragmentation is invoked to ensure reliable
delivery.

4. Finally, SCHC FEC Fragmentation is applied to the resulting
fragments.

* Direct Reliability Chain for Non-Delay-Tolerant Traffic:

1. SCHC Compression is executed on the PDU.

2. For traffic that is not delay tolerant, the Process Router
bypasses intermediate processing steps and directs the
compressed PDU directly to SCHC Reliability Fragmentation.

3. SCHC FEC Fragmentation is then applied to incorporate error
correction.
This streamlined path minimizes processing delay, catering to
applications where latency is a critical parameter.

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4. Schemas

4.1. Process Stacking Overview

+---------------------+
| SCHC Compression |
+---------------------+
|
v
+---------------+
| Decision Node | <-- Evaluates PDU size, delay tolerance, and aggregation requirement
+---------------+
/ | \
/ | \
(PDU > MTU) (Aggregation) (Non-Delay Tolerant)
/ | \
v v v
+---------------------+ +------------------+ +--------------------------------+
| SCHC Fragmentation | | SCHC Aggregation | | SCHC Reliability Fragmentation|
+---------------------+ +------------------+ +--------------------------------+
| | |
v v v
+---------------------+ +------------------------------+ +-----------------------------+
| SCHC FEC | | SCHC Reliability Fragmentation| | SCHC FEC Fragmentation |
| Fragmentation | +------------------------------+ +-----------------------------+
+---------------------+ |
v
+-----------------------+
| SCHC FEC Fragmentation|
+-----------------------+

Figure 1: Overview of SCHC Process Stacking and Routing

4.2. Detailed Routing Logic Schema

5. Operational Considerations

The architecture ensures:

* Interface Consistency: Standardized metadata exchange between
modules (e.g., PDU size, delay tolerance, error correction
parameters) ensures seamless handovers.

* Dynamic Adaptation: The Process Router can adjust routing
decisions based on real-time network conditions, including MTU
constraints and delay sensitivity.

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* Scalability: The modular design allows additional SCHC processes
to be integrated with minimal impact on existing chains.

6. Security Considerations

The modifications introduced by dynamic process stacking do not alter
the fundamental security mechanisms of SCHC as defined in RFC8724.
Implementations must protect the metadata exchanged between modules
and ensure that the decision logic within the Process Router is
resilient against unauthorized manipulation.

7. IANA Considerations

No IANA Considerations.

8. Examples and Use Cases

8.1. Example 1: Compression and Fragmentation

A compressed PDU that exceeds the L2 MTU is routed to SCHC
Fragmentation. Each fragment is then processed by SCHC FEC
Fragmentation to add error correction, ensuring reliable delivery
despite potential losses.

8.2. Example 2: Compression and Aggregation

For scenarios requiring the combination of multiple small PDUs, SCHC
Compression is followed by SCHC Aggregation. The aggregated output
is then forwarded to SCHC Reliability Fragmentation to provide
recovery capabilities, with SCHC FEC Fragmentation applied
subsequently.

8.3. Example 3: Direct Path for Non-Delay-Tolerant Traffic

In applications with strict delay constraints, the processing chain
is streamlined. After SCHC Compression, the Process Router directs
non-delay-tolerant PDUs directly to SCHC Reliability Fragmentation,
bypassing the aggregation and conventional fragmentation steps. SCHC
FEC Fragmentation is then applied to incorporate error correction
with minimal latency overhead.

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+---------------------+
| SCHC Compression |
+---------------------+
|
v
+--------------------------------+
| SCHC Reliability Fragmentation |
+--------------------------------+
|
v
+-----------------------------+
| SCHC FEC Fragmentation |
+-----------------------------+

Figure 2: Direct Routing for Non-Delay-Tolerant Traffic

9. Normative References

[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>.

Author's Address

Alexander Pelov
IMT Atlantique
2bis rue de la Chataigneraie
35536 Cesson-S茅vign茅
France
Email: alexander.pelov@imt-atlantique.fr

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