Network Working Group A. Pelov
Internet-Draft IMT Atlantique
Intended status: Informational 4 February 2025
Expires: 8 August 2025
SCHC Rule Format for Message Aggregation in Delay Tolerant Networks
draft-pelov-schc-aggregation-rule-format-01
Abstract
This document defines a new Rule Format for Message Aggregation
(referred to as Aggregation) within the SCHC framework. By bundling
multiple SCHC-compressed packets into a single Aggregation Data Unit
(ADU), the mechanism reduces the number of transmissions required in
delay-tolerant networks. The Aggregation process is triggered by
conditions such as reaching the L2 Maximum Transmission Unit (MTU),
exceeding a maximum delay, or meeting a minimum packet rate
threshold. This new rule type is backward compatible with existing
SCHC operations and offers an efficient solution for energy-sensitive
and asymmetric communication scenarios.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Aggregation Overview . . . . . . . . . . . . . . . . . . . . 2
3. SCHC Aggregation Rule Specification . . . . . . . . . . . . . 3
3.1. Aggregation Triggers . . . . . . . . . . . . . . . . . . 3
4. Operational Considerations . . . . . . . . . . . . . . . . . 4
5. Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Examples and Use Cases . . . . . . . . . . . . . . . . . . . 5
8.1. Example: Periodic Sensor Data Aggregation . . . . . . . . 5
8.1.1. Example: MTU-Triggered Aggregation . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Low-power, delay-tolerant networks benefit significantly from
minimizing the number of transmissions to conserve energy. The
Static Context Header Compression (SCHC) framework, as described in
RFC8724 (https://www.rfc-editor.org/rfc/rfc8724.html), already
provides mechanisms for compressing and fragmenting IPv6/UDP packets
for LPWANs. This document introduces an additional SCHC Rule
Type鈥擜ggregation鈥攚hich enables the bundling of multiple SCHC-
compressed packets into a single Aggregation Data Unit (ADU). The
Aggregation mechanism is particularly beneficial when latency is
acceptable in exchange for reduced network traffic and improved
energy efficiency.
2. Aggregation Overview
In the proposed architecture, an application packet is first
processed by the SCHC Compression module. The compressed packet is
then passed to the Aggregation module, which appends an Aggregation
RuleID and a size field to the compressed payload. Multiple such
packets are concatenated into one ADU. The ADU is transmitted to the
lower layers based on one or more of the following triggers:
* MTU Threshold: When the cumulative size of aggregated data reaches
the L2 Maximum Transmission Unit.
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* Maximum Delay: When the waiting time in the aggregation buffer
exceeds a configured maximum delay.
* Minimum Packet Rate: When a periodic condition (e.g., a
transmission scheduled once per day) is met in low-traffic
scenarios.
3. SCHC Aggregation Rule Specification
The Aggregation Rule defines the packet format and processing steps
for bundling SCHC-compressed packets. The following figure
illustrates the structure of an Aggregation packet:
|------ SCHC Aggregation Header -------------|-- SCHC Compressed Payload ---|
|------- RuleID -------|-- Size Field -------|
+---------+------------+---------------------+------------------------------+~~~~~~~~~~~~~~~~~~~~~~~~+
| Aggregation RuleID | Size Field (N bits) | Compressed Packet Payload | (Optional additional segments)
+---------+------------+---------------------+------------------------------+~~~~~~~~~~~~~~~~~~~~~~~~+
Figure 1: SCHC Aggregation Packet Format
Each aggregated segment contains:
* Aggregation RuleID: A unique identifier indicating that the packet
has undergone aggregation.
* Size Field: An N-bit field (with N defined in the SCHC Context)
specifying the length in bytes of the compressed payload.
* Compressed Payload: The output from the SCHC Compression process.
Additional SCHC-compressed packets are concatenated using the same
"Size Field + Compressed Payload" structure. Note that there is no
need fo Aggregation RuleID for the subsequent packets in one ADU.
3.1. Aggregation Triggers
The Aggregation module maintains a buffer of compressed packets and
transmits the ADU when one or more of the following conditions is
met:
* MTU Threshold: The total size of the ADU equals or exceeds a
threshold, e.g. equal to the L2 MTU.
* Maximum Delay: The time a packet remains in the aggregation buffer
exceeds a preconfigured maximum delay.
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* Minimum Packet Rate: A periodic trigger (e.g., transmitting at
least once per day) ensures that packets are not delayed
indefinitely in low-traffic conditions.
4. Operational Considerations
The Aggregation mechanism offers significant energy savings by
reducing the number of transmissions; however, it introduces several
trade-offs:
* Delay versus Efficiency: While aggregation reduces transmissions,
it inherently introduces additional delay. This is acceptable in
delay-tolerant networks but must be carefully tuned to meet
application requirements.
* Error Recovery: Loss or corruption of an ADU can affect multiple
SCHC packets simultaneously. Implementations must include
strategies for error detection and potential recovery of
aggregated data.
* Buffer Management: Efficient management of the aggregation buffer
is crucial to ensure that packets are aggregated and transmitted
in a timely manner, especially under fluctuating network
conditions.
5. Flow Diagram
The following diagram illustrates the data flow from SCHC Compression
to Aggregation and subsequent transmission:
+-----------------+ +---------------------+ +-----------------------+
| Application | ----> | SCHC Compression | ----> | SCHC Aggregation |
| Data Packet | | (Compressed Data) | | (Aggregation Buffer) |
+-----------------+ +---------------------+ +-----------+-----------+
|
v
+-----------------------+
| Lower Layers (L2) |
| Transmission of ADU |
+-----------------------+
Figure 2: Data Flow for SCHC Aggregation
Note that the PDU of the SCHC Aggregation can be sent to other SCHC
processes.
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6. Security Considerations
Aggregating multiple SCHC-compressed packets into a single ADU can
increase the impact of packet interception or corruption. To
mitigate these risks, the integrity mechanisms employed during SCHC
Compression must be extended to cover the entire ADU. In addition,
implementations should:
* Apply end-to-end integrity checks on the aggregated data.
* Consider mechanisms to detect and recover from partial data loss
in an ADU.
7. IANA Considerations
No IANA Considerations.
8. Examples and Use Cases
8.1. Example: Periodic Sensor Data Aggregation
In a sensor network, individual sensor readings are first compressed
using SCHC Compression. The Aggregation module then collects these
compressed packets over a period (e.g., one day) and bundles them
into an ADU. This reduces the number of uplink transmissions,
thereby conserving energy while accommodating delay-tolerant
reporting.
8.1.1. Example: MTU-Triggered Aggregation
In scenarios with higher traffic, multiple SCHC-compressed packets
are buffered until their combined size approaches the L2 MTU. The
ADU is then transmitted immediately, optimizing channel usage and
reducing overhead.
9. References
The following documents are referenced in this draft:
* RFC8724 (https://www.rfc-editor.org/rfc/rfc8724.html): SCHC:
Framework for Compression and Fragmentation of IPv6/UDP Packets
for LPWANs.
10. Normative References
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[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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