[tcpm] (no subject)

[Jana Iyengar <[e-mail]>]

Mark,

Apologies for this late review. It's been a while since I read the draft,
and I have just a couple of comments.

I have one high-order point. The document limits itself to transports where
loss detection *and retransmission* occurs. Specifically, Section (S.2)
says: "The requirements in this document only apply to cases where loss
detected via a timer is repaired by a retransmission of the original data.
Other cases are certainly possible---e.g., replacing the lost data with an
updated version---but fall outside the scope of this document."

There are a couple of other places as well ("all timer-based retransmission
mechanisms", and also in requirement (3)). I would suggest that the draft
applies to loss detection, not to recovery or retransmission. Specifically,
QUIC detects loss using a Probe Timeout (equivalent to an RTO), but may not
retransmit lost data for a variety of reasons. Is there a reason to
preclude this behavior?

More generally, TCP conflates *what* to send with *when* to send it, and
whether to send something is presumed "yes". QUIC decouples these pieces,
and that may be true of other future protocols as well. (This is true of
SCTP using the partial-reliability extension as well, RFC 3758).

The requirements in the document already apply to these protocols, because
the principles apply to the loss detection function of the transport, not
the recovery function.

In terms of text changes, I think simply removing "and retransmission" from
most places is adequate to achieve this. Requirement (3) however relies on
the data getting acked, which can be generalized. The current text is:
"The backoff SHOULD be removed after the successful repair of the lost data
and subsequent transmission of non-retransmitted data."
This can be replaced by:
"The backoff SHOULD be removed after an acknowledgement is received for a
subsequently sent packet."
---

Editorial suggestions:
- remove para beginning with "This document is a bit "weird" ...", and also
drop the phrase "At this point, however" from the beginning of the next
para. This is unnecessary text, IMO.
- Take it or leave it: change title from "Requirements" to "Guidelines".

- jana