RE: Partially Reliable Message Stream

[Mike Bishop <[e-mail]>]

I find the one octet gap a bit confusing, but as I think about it, I see why you need it.  If all the stream data arrived successfully (but hadn't been acknowledged yet due to loss of the ACK, delay, etc.) and the EXPIRED_STREAM_DATA gets lost, the receiver can only retroactively realize there was a jump.  Having an octet that is never transmitted ensures the receiver actually sees a gap, which means that an in-order API will not proceed until it has received either the missing octet or an EXPIRED_STREAM_DATA informing it the octet will never arrive.

This simplification (versus -02) comes at a price:  If an API were exposing stream data out-of-order, then in your example, the receiver knows that a message always begins on a ten-byte boundary.  A receiver can no longer find ten-byte boundaries, because the offset on the read side doesn't match the offset on the send side.  I agree with you that this seems like a reasonable trade-off for the simpler flow control.

One conflict I see in the doc:

*         Section 3 says:  Receipt of an EXPIRED_STREAM_DATA does not advance the largest received offset for the stream.

  *   Section 5 says:  A receiver SHOULD discard any stream data received for an offset smaller than the new smallest receive offset, possibly advancing the largest received offset for the stream.

Other minor nits are better done via PR.
From: QUIC <[e-mail]> On Behalf Of Lubashev, Igor
Sent: Wednesday, May 30, 2018 9:45 AM
To: QUIC WG <[e-mail]>
Subject: Partially Reliable Message Stream

I've just uploaded a new draft for partially reliable QUIC streams.  Note: this feature is likely not in scope for V1, but it can be an extension for V1 and/or a part of V2.

The new version 03 (https://tools.ietf.org/html/draft-lubashev-quic-partial-reliability-03) no longer needs complex flow control changes and removes the need to transmit multiple frames in the same packet.


  *   Igor

P.S.
  There is also a new version 02, which includes a more complex algorithm with more features and different trade-offs.  But I think version 03 is a better match for the needs so far.