[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03

QUIC                                                         I. Lubashev
Internet-Draft                                       Akamai Technologies
Intended status: Informational                              May 29, 2018
Expires: November 30, 2018


              Partially Reliable Message Streams for QUIC
               draft-lubashev-quic-partial-reliability-03

Abstract

   This memo introduces a new EXPIRED_STREAM_DATA frame to enable
   partial reliability for QUIC streams.  The EXPIRED_STREAM_DATA frame
   allows a sender to give up on retransmitting older parts of a stream
   and to notify the receiver about this decision.  The content of this
   draft is intended for merging into QUIC transport, recovery, and
   applicability drafts as a negotiable extension and/or QUIC Version 2
   transport feature.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 30, 2018.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of



Lubashev                Expires November 30, 2018               [Page 1]


Internet-Draft                   quic-pr                        May 2018


   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Stream-per-Message Alternative  . . . . . . . . . . . . .   3
     2.2.  Partially Reliable Message Streams  . . . . . . . . . . .   3
     2.3.  Minimum retransmittable offset and smallest receive
           offset  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  EXPIRED_STREAM_DATA Frame . . . . . . . . . . . . . . . . . .   4
   4.  Sender Interface and Behavior . . . . . . . . . . . . . . . .   5
     4.1.  Communicating Message Boundary  . . . . . . . . . . . . .   5
     4.2.  Translating Application Offsets to QUIC Offsets . . . . .   5
     4.3.  Sender Behavior . . . . . . . . . . . . . . . . . . . . .   5
       4.3.1.  Coalescing Minimum Retransmittable Offset Updates . .   6
       4.3.2.  Example . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Receiver Interface and Behavior . . . . . . . . . . . . . . .   7
   6.  Retransmission of EXPIRED_STREAM_DATA . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Since version 00  . . . . . . . . . . . . . . . . . . . .   8
     9.2.  Since version 01  . . . . . . . . . . . . . . . . . . . .   8
     9.3.  Since version 02  . . . . . . . . . . . . . . . . . . . .   8
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  Introduction

   Some applications, especially applications with near real-time
   requirements, need transport that supports partially reliable streams
   - streams that deliver bytes in order but allow for applicaiton-
   controlled gaps.  These applications communicate using application-
   specific messages that are serialized over QUIC streams.
   Applications desire partially reliable streams when their messages
   expire and lose their usefulness due to later events (time passing,
   newer messages, etc).



Lubashev                Expires November 30, 2018               [Page 2]


Internet-Draft                   quic-pr                        May 2018


   Examples of applications that can benefit from partially reliable
   streams are real time video (all prior data is to be expired when a
   new key frame is available) and data replication (expire previous
   updates, when a new update overwrites the data).

   The content of this draft is intended for [I-D.ietf-quic-transport],
   [I-D.ietf-quic-recovery] and, [I-D.ietf-quic-applicability] as a QUIC
   extension and/or QUIC Version 2.

2.1.  Stream-per-Message Alternative

   It is possible to avoid the need for partially reliable streams by
   encoding one message per QUIC stream.  When a message expires, the
   sender can reset the stream, causing RST_STREAM frame to be
   transmitted, unless all data in the stream has already been fully
   acknowledged.  Likewise, the receiver can send STOP_SENDING frame to
   indicate its disinterest in the message.  The problem with this
   approach is that messages transmitted by the application typically
   belong to a message stream, and applications may need to support
   multiple concurrent message streams.  Hence, a message-per-stream
   approach requires each message to contain an extra header portion to
   associate the message with a logical application stream.  In case of
   short messages, this approach introduces a significant overhead due
   to STREAM frames and message headers.  It also places the burden on
   the application to reorder data arriving on multiple QUIC streams.
   Furthermore, splitting each application stream into multiple QUIC
   streams renders QUIC's per-stream flow control ineffective and
   requires an application to build its own.

2.2.  Partially Reliable Message Streams

   The proposed single-stream mechanism keeps aplication messages
   arriving in order on a single stream, while allowing the application
   to control message expiration.

   The key to partially reliabile message streams is notifying the
   receiver about data that will not be retransmitted and ensuring that
   the receiver can identify the beginning of each new message.

   It is important to note that the proposed protocol does not guarantee
   that data is read by the receiver application at the stream offsets
   written to by the sender application.

2.3.  Minimum retransmittable offset and smallest receive offset

   For fully reliable streams, the smallest unacknowledged data offset
   is treated by the sender to be the minimum retransmittable offset.
   Likewise, the smallest receive offset for a stream is the smallest



Lubashev                Expires November 30, 2018               [Page 3]


Internet-Draft                   quic-pr                        May 2018


   data offset that has not been received by the receiver.  Due to loss
   and reordering, the smallest receive offset may be smaller than the
   largest received offset.

   Partially reliable streams allow the sender to advance its minimum
   retransmittable offset and notify the receiver to advance its
   smallest receive offset.

3.  EXPIRED_STREAM_DATA Frame

   The EXPIRED_STREAM_DATA frame (type=0x??) is used by a sender to
   inform a receiver of the minimum retransmittable offset (Section 2.3)
   for a stream.

   An endpoint that receives an EXPIRED_STREAM_DATA frame for a send-
   only stream MUST terminate the connection with error
   PROTOCOL_VIOLATION.

   The frame is as follows:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Stream ID (i)                        ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Minimum Stream Offset (i)                  ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields in the EXPIRED_STREAM_DATA frame are as follows:

   Stream ID:  The stream ID of the stream that is affected encoded as a
      variable-length integer.

   Minimum Stream Offset:  A variable-length integer indicating the
      minimum offset of the stream data that will sent (or re-
      transmitted) on the identified stream, in units of octets.

   Since Stream 0 MUST be reliable, Stream ID MUST NOT be 0.

   Upon receipt of an EXPIRED_STREAM_DATA frame, the receiver advances
   the smallest receive offset for the stream (Section 2.3) to be the
   Minimum Stream Offset value.

   The sender MUST NOT reduce the minimum retransmittable offset for a
   stream, but loss and reordering can cause EXPIRED_STREAM_DATA frames
   to be received out of order.  EXPIRED_STREAM_DATA frames that do not
   advance the smallest receive offset for the stream MUST be ignored.




Lubashev                Expires November 30, 2018               [Page 4]


Internet-Draft                   quic-pr                        May 2018


   It is possible for the smallest receive offset to become larger than
   the largest received offset a the stream.  Receipt of an
   EXPIRED_STREAM_DATA does not advance the largest received offset for
   the stream.

4.  Sender Interface and Behavior

   QUIC library interface needs provide a way for a sender to expire
   data previously written to the transport by updating the minimum
   retransmittable offset (Section 2.3) for a stream.  A typical sender
   would call this API function whenever data previously enqueued for
   transmission expires, per application semantics.  The sender would
   keep track of the message boundaries and request expiration of data
   on a message boundary.

4.1.  Communicating Message Boundary

   To allow a sender application to expire stream data written to the
   transport but never sent to the receiver, the sender transport needs
   to create a gap between data previously sent on the stream and data
   to be sent after the expiration point.  The gap ensures that the
   receiver does not deliver subsequent octets to the application until
   the receipt of the EXPIRED_STREAM_DATA frame, in case packets
   containing the EXPIRED_STREAM_DATA frame and subsequent STREAM frame
   are reordered.

   To avoid complicated connection flow control accounting (see version
   02 of this draft [1]), a single octet gap is used for communicating
   the message boundary.  Sender's EXPIRED_STREAM_DATA frame extends the
   minimum stream offset past that gap.  Upon receipt of the
   EXPIRED_STREAM_DATA frame, the receiver is able to notify the
   application of a gap, which allows the application to identify the
   beginning of a new message.

4.2.  Translating Application Offsets to QUIC Offsets

   Since the QUIC library and the application need to communicate data
   offsets (for example, for the purpose of updating the minimum
   retransmittable stream offset), the QUIC library needs to translate
   appliction offsets to QUIC offsets.  Depending on the richness of the
   APIs exposed to the application, keeping a single difference between
   the current application and QUIC offsets is likely to be sufficient.

4.3.  Sender Behavior

   This section discusses sender behavior in terms of QUIC offsets, and
   the translation from applicatoin offsets (see Section 4.2) is
   implicit.



Lubashev                Expires November 30, 2018               [Page 5]


Internet-Draft                   quic-pr                        May 2018


   When an application instructs its QUIC transport to advance the
   minimum retransmittable offset for a stream, and there is any
   unacknowledged data (including unsent data) at an offset smaller than
   the new minimum retransmittable offset, the sender SHOULD transmit an
   EXPIRED_STREAM_DATA frame (Section 3), except as provided for in
   Section 4.3.1.

   -  When the new minimum retransmittable offset is less than or equal
      to the current send offset, the Minimum Stream Offset field in the
      EXPIRED_STREAM_DATA frame is set to the new minimum
      retransmittable offset.

   -  When the new minimum retransmittable offset is larger the current
      send offset, the Minimum Stream Offset field in the
      EXPIRED_STREAM_DATA frame is set to the current send offset plus
      1, and stream data starting at the new minimum retransmittable
      offset is henceforth sent starting at the current send offset plus
      1 (which becomes the new minimum retransmittable offset).  Hence,
      it may be possible for a minimum retransmittable offset to become
      larger than the current send offset for a stream.

4.3.1.  Coalescing Minimum Retransmittable Offset Updates

   When an application instructs its QUIC transport to advance the
   minimum retransmittable offset for a stream, but the current send
   offset is not larger than the minimum retransmittable offset
   specified in the _previous_ call to this API function, the current
   stream offset is not advanced and an EXPIRED_STREAM_DATA frame is not
   sent.  Stream data starting at the requested minimum retransmittable
   offset is henceforth sent starting at the previous minimum
   retransmittable offset (which remains the minimum retransmittable
   offset for the stream).

   Note that the coalescing rule does not apply (the EXPIRED_STREAM_DATA
   frame _is_ sent) if the very first message has expired before any of
   its octets have been transmitted.  This allows the receiver to always
   ascertain the location of any gaps in messages it is receiving.

4.3.2.  Example

   For example, an application wrote four 10-octet messages (A, B, C, D)
   to the transport, and the current send offset (the next offset to be
   sent) is 12.  In this example, the upper-case indicates bytes to be
   sent, while the lower-case indicates bytes already sent.







Lubashev                Expires November 30, 2018               [Page 6]


Internet-Draft                   quic-pr                        May 2018


    0                   1   s               2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |a a a a a a a a a a b b B B B B B B B B C C C C C C C C C C D D ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   When the application desires to expire messages A and B, it requests
   the minimum retransmittable offset to be 20.  The transport then
   sends an EXPIRED_STREAM_DATA frame with Minimum Stream Offset field
   set to 13, and the subsequent STREAM frame would send message C
   starting at stream offset 13.

    0                   1   s m             2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |a a a a a a a a a a b b   C C C C C C C C C C D D D D D D D D D D
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   However, if the application requestes to expire octets corresponding
   to message C before any subsequent STREAM frames could be sent, no
   new EXPIRED_STREAM_DATA frame is sent, and the subsequent STREAM
   frame would send message D starting at stream offset 13.

    0                   1   s m             2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |a a a a a a a a a a b b   D D D D D D D D D D
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.  Receiver Interface and Behavior

   Upon receipt of an EXPIRED_STREAM_DATA frame (Section 3), the
   receiver SHOULD assume that none of the data before the new smallest
   receive offset (Section 2.3) will be retransmitted.  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.  Discarding such data ensures that
   when the application observes a gap in the data stream, what follows
   the gap is a beginning of a new message.

   It is recommended that a QUIC library API provides a way for the
   receiver application to learn of the presence of a gap in the data
   stream, indicating that the data that follows the gap is a beginning
   of a new message.







Lubashev                Expires November 30, 2018               [Page 7]


Internet-Draft                   quic-pr                        May 2018


6.  Retransmission of EXPIRED_STREAM_DATA

   The most recent EXPIRED_STREAM_DATA frame (Section 3) for a stream
   MUST be retransmitted if it is declared lost, until the sender is
   certain that the receiver is not expecting retransmission of any
   expired data.  I.e. the frame MUST be retransmitted until the stream
   enters "half-closed (local)" state, or all data between the largest
   Minimum Stream Offset field in an acknowledged EXPIRED_STREAM_DATA
   frame and the current minimum retransmittable offset (Section 2.3)
   has been acknowledged.

7.  IANA Considerations

   This document has no actions for IANA.

8.  Security Considerations

   This document has no new security considerations.

9.  Change Log

9.1.  Since version 00

   -  Fixed flow control to disallow other streams to use connection
      credits designated for skipping expired bytes.

9.2.  Since version 01

   -  Added an ability by the receiver as well as the sender to control
      partial reliability of QUIC streams.

   -  Added Exempt Stream Bytes value and updated connection flow
      control calculation to use Exempt Stream Bytes value.

   -  Replaced the Min Stream Offset value with the existing values:
      "min retransmittable offset" (for sender) and "smallest receive
      offset" (for receiver).  (Section 2.3)

   -  Changed MIN_STREAM_DATA frame to be a receiver-transmitted frame.

   -  Added sender-transmitted EXPIRED_STREAM_DATA frame.  (Section 3)

9.3.  Since version 02

   -  Significantly simplifed the proposal by treating the stream as a
      message stream, allowing for data offsets not to be preserved
      between the sender and the receiver.




Lubashev                Expires November 30, 2018               [Page 8]


Internet-Draft                   quic-pr                        May 2018


   -  Reverted to sender-only transport-level control of message
      expiration.

   -  Removed the need for Exempt Stream Bytes and changes to connection
      flow control accounting.

   -  Removed MIN_STREAM_DATA frame.

10.  Acknowledgments

   Many thanks to Mike Bishop, Ian Swett, and Subodh Iyengar for their
   reviews, feedback, and ideas.  Thus draft would not happen without
   their input.  Kudos to the QUIC working group for a mountain of
   feedback on this draft and for diligently plowing through hard
   problems, making thousands of big and small decisions, to make the
   Internet better for everyone.

11.  References

11.1.  Normative References

   [I-D.ietf-quic-applicability]
              Kuehlewind, M. and B. Trammell, "Applicability of the QUIC
              Transport Protocol", draft-ietf-quic-applicability-01
              (work in progress), October 2017.

   [I-D.ietf-quic-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Detection and
              Congestion Control", draft-ietf-quic-recovery-12 (work in
              progress), May 2018.

   [I-D.ietf-quic-transport]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-12 (work
              in progress), May 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

11.2.  URIs

   [1] https://tools.ietf.org/html/draft-lubashev-quic-partial-
       reliability-02






Lubashev                Expires November 30, 2018               [Page 9]


Internet-Draft                   quic-pr                        May 2018


Author's Address

   Igor Lubashev
   Akamai Technologies

   EMail: igorlord@alum.mit.edu













































Lubashev                Expires November 30, 2018              [Page 10]


Html markup produced by rfcmarkup 1.127, available from https://tools.ietf.org/tools/rfcmarkup/