Telechat Review of draft-ietf-tsvwg-usr-exp-12
review-ietf-tsvwg-usr-exp-12-iotdir-telechat-bhandari-2025-09-14-00

I am the assigned IoT Directorate reviewer for this draft. The Directorate aims
to review IETF documents related with IoT (Internet of Things). Please treat
these comments just like any other last call comments. For more information,
please see https://datatracker.ietf.org/group/iotdir/about/

This document provides a clear and valuable mechanism for using common ports
for multiple experiments through the use of PExID. The problem statement is
well-defined, and the proposed solution addresses the resource constraints on
transport ports effectively.

My comments, which should be treated like any other last-call comments, focus
on the implications for constrained devices and IoT application design.

Implications of PExID in the Payload: The document's recommendation for the
application to carry the PExID in its payload and perform demultiplexing is a
concern. While acknowledging the limited header space or consistent options
availability in all the transport protocols, this approach introduces
complexity for constrained IoT devices. This model forces application
developers to handle logic that is typically part of the transport layer,
leading to increased application complexity, a larger code footprint, and
potential for implementation errors. This is particularly relevant for widely
used IoT protocols like CoAP, where the PExID would constitute a overhead on a
message's already compact header and payload structure.

Alignment with Other Reviews: The concerns raised about the operational model
for PExID share similarities with feedback from other directorates. The GENART
review, for instance, raised issues about scalability and firewall containment,
which are directly related to a protocol's ability to be easily managed and
filtered at the network edge. Similarly, the Opsdir review highlighted the need
for a clear transition path from an experimental phase to a permanent
allocation, this is also a requirement for long-lived IoT deployments.