Subject: [LOOPS] Narrowing the scope: (4) Reconstruction (FEC) or retransmission

From: Carsten Bormann <[email-masked]>
Date: Tue, 26 May 2020 01:15:44 +0200

In tomorrow’s LOOPS side meeting, we want to discuss whether we can narrow the initial scope of the WG sufficiently that the resulting charter looks more tractable (we can then recharter after delivering on the initial scope).

LOOPS recovery has been discussed as a potential combination of reconstruction (FEC) and retransmission mechanisms.

To simplify the initial protocol, we could choose to do only one of these.

Reconstruction (FEC) is its own area of knowledge, but then we can tap existing proposals in NWCRG and TSVWG — we would coordinate closely with both groups.
Due to the CPU requirements, deployment of FEC might require specific platforms, limiting the use cases that can be addressed.

Retransmission is reasonably well understood (with recent advances such as RACK still waiting for their global try-out).  More than reconstruction, retransmission leads to reordering visible to the end-to-end protocols (or needs the LOOPS egress to do resequencing ➔ latency!).
Retransmission being well-understood, it does require taking on more protocol design work ((N)ACK structure etc. — still probably coordinating with TSVWG on some of the details).
Deployment requires a couple bandwidth-delay products (of the LOOPS segment) of buffer space, but less CPU than for reconstruction.

So can we limit ourselves to one of these for the initial charter?  Which one?

Comments are welcome on the list and/or in the meeting in ~16 hours.

Grüße, Carsten