QMux
draft-opik-quic-qmux-00
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Kazuho Oku , Lucas Pardue , Jana Iyengar , Eric Kinnear | ||
| Last updated | 2025-07-23 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
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draft-opik-quic-qmux-00
QUIC K. Oku
Internet-Draft Fastly
Intended status: Standards Track L. Pardue
Expires: 24 January 2026 Cloudflare
J. Iyengar
Netflix
E. Kinnear
Apple
23 July 2025
QMux
draft-opik-quic-qmux-00
Abstract
This document specifies a polyfill of QUIC version 1 that runs on top
of bi-directional streams such as TLS.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the QUIC Working Group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/quic/.
Source for this draft and an issue tracker can be found at
https://github.com/kazuho/draft-opik-quic-qmux.
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 24 January 2026.
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Copyright Notice
Copyright (c) 2025 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 Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. The Protocol . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Properties of Underlying Transport . . . . . . . . . . . 4
4. QUIC Frames . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. STREAM Frames . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. STREAM Frames without the Length Field . . . . . . . 6
4.1.2. Ordering of STREAM frames . . . . . . . . . . . . . . 6
4.2. QX_TRANSPORT_PARAMETERS Frames . . . . . . . . . . . . . 7
4.3. QX_PING Frames . . . . . . . . . . . . . . . . . . . . . 8
5. Transport Parameters . . . . . . . . . . . . . . . . . . . . 8
5.1. Permitted and Forbidden Transport Parameters . . . . . . 8
5.2. max_frame_size Transport Parameter . . . . . . . . . . . 9
6. Closing the Connection . . . . . . . . . . . . . . . . . . . 10
7. Using 0-RTT . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Unreliable Datagram Extension . . . . . . . . . . . . . . 10
9. Version Agility . . . . . . . . . . . . . . . . . . . . . . . 11
10. Implementation Considerations . . . . . . . . . . . . . . . . 11
11. Security Considerations . . . . . . . . . . . . . . . . . . . 11
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . 12
13.2. Informative References . . . . . . . . . . . . . . . . . 12
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
QUIC version 1 [QUIC] is a bi-directional, authenticated transport-
layer protocol built on top of UDP [UDP]. The protocol provides
multiplexed flow-controlled streams without head-of-line blocking as
a core service. It also offers low-latency connection establishment
and efficient loss recovery.
However, there are downsides to QUIC.
One downside is that QUIC, being based on UDP, is not as universally
accessible as TCP [TCP], due to occasionally being blocked by
middleboxes.
Another downside is that QUIC is computationally more expensive
compared to TLS [TLS13] over TCP. This increased cost is partly
because QUIC encrypts each packet, which is smaller than the
encryption unit of TLS, leading to more overhead, and partly because
UDP is less optimized within computing infrastructures.
Due to these limitations, applications are often served using both
QUIC and TCP. QUIC is employed to provide the optimal user
experience, while TCP acts as a fallback for ensuring network
reachability and computational efficiency as needed.
One such example is HTTP, which has different bindings for QUIC
(HTTP/3 [HTTP3]) and TCP (HTTP/2 [HTTP2]). Recently, security
concerns have prompted proposals to revise HTTP/2
([h2-stream-limits]), which has sparked discussions about the costs
of maintaining multiple HTTP versions.
Another example is WebTransport, a superset of HTTP. Because HTTP
has different bindings for QUIC and TCP, WebTransport defines its own
extensions for the two HTTP variants ([webtrans-h3], [webtrans-h2]).
To reduce or eliminate the costs associated with duplicated efforts
in providing services on top of both transport protocols, this
document specifies a polyfill that allows application protocols built
on QUIC to run on transport protocols that provide single bi-
directional, byte-oriented stream such as TCP or TLS.
The specified polyfill provides a compatibility layer for the set of
operations (i.e., API) required by QUIC, as specified in Section 2.4
and Section 5.3 of [QUIC].
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2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. The Protocol
QMux can be used on any transport that provides a bi-directional,
byte-oriented stream that is ordered and reliable; for details, see
Section 3.1.
QUIC frames are sent directly on top of the transport.
The frames are not encrypted. It is the task of the transport (e.g.,
TLS) to provide confidentially and integrity.
QUIC packet headers are not used.
For exchanging the Transport Parameters, a new frame called
QX_TRANSPORT_PARAMETERS frame is defined.
3.1. Properties of Underlying Transport
QMux is designed to work on top of transport layer protocols that
provide the following capabilities:
In-order delivery of bytes in both direction: Underlying transport
provides a byte-oriented and bi-directional stream that deliver
the bytes in order; i.e., bytes that were sent in one order become
available to the receiving side in the same order.
Guaranteed delivery: If the transport runs on top of a lossy
network, that transport recovers the bytes lost; e.g., by
retransmitting them. This requires buffering and reassembly, in
order to achieve the first bullet point (in-order delivery).
Congestion control: When used on a shared network, the transport is
congestion controlled. Implementations of QMux simply write
outgoing frames to the transport when that transport permits.
Confidentially and Integrity: Unless used upon endpoints between
which tampering or monitoring is a non-concern, the transport
provides confidentially and integrity protection.
TLS over TCP provides all these capabilities.
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UNIX sockets are an example that provides only the first two.
Congestion control is not employed, as UNIX sockets do not face a
shared bottleneck. Confidentiality and integrity protection are
deemed unnecessary in environments where the operating system is
trusted.
4. QUIC Frames
In QMux, the following QUIC frames can be used, as if they were sent
or received in the application packet number space:
* PADDING
* RESET_STREAM
* STOP_SENDING
* STREAM
* MAX_DATA
* MAX_STREAM_DATA
* MAX_STREAMS
* DATA_BLOCKED
* STREAM_DATA_BLOCKED
* STREAMS_BLOCKED
* CONNECTION_CLOSE
The frame formats are identical to those in QUIC version 1.
Likewise, the meaning and requirements for the use of these frames
are consistent with QUIC version 1, with the exception to the
specific changes made to the STREAM frames, as detailed in
Section 4.1.
Use of other frames defined in QUIC version 1 is prohibited for
various reasons. ACK frames are not used because the underlying
transport guarantees delivery. Frames related to the cryptographic
handshake are not used because an underlying security layer can
provide equivalent features. Use of frames that communicate
Connection IDs and those related to path migration is forbidden.
The full list of prohibited frames is:
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* PING
* ACK
* CRYPTO
* NEW_TOKEN
* NEW_CONNECTION_ID
* RETIRE_CONNECTION_ID
* PATH_CHALLENGE
* PATH_REPONSE
* HANDSHAKE_DONE
Endpoints MUST NOT send prohibited frames. If an endpoint receives
one it MUST close the connection with an error of type
FRAME_ENCODING_ERROR.
4.1. STREAM Frames
While the frame format remains unchanged, there are two differences
in the handling of STREAM frames between QUIC version 1 and QMux.
4.1.1. STREAM Frames without the Length Field
In QMux, when a STREAM frame that omits the Length field is used, the
size of that STREAM frame is determined by the maximum frame size, as
regulated by the max_frame_size Transport Parameter (Section 5.2).
This behavior contrasts with that of QUIC version 1, where the
absence of the Length field implies that the STREAM frame extends to
the end of the QUIC packet payload.
This variation arises due to the characteristics of the underlying
transports of QMux, which may not have, or provide visibility into,
the packet boundaries.
4.1.2. Ordering of STREAM frames
For each stream being sent, senders MUST send stream payload in
order.
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When receiving a STREAM frame that carries a payload not immediately
following the payload of the previous STREAM frame for the same
Stream ID, receivers MUST close connection with an error of type
PROTOCOL_VIOLATION_ERROR.
This change from QUIC version 1 eliminates the need for
implementations to buffer and reassemble the stream payload. As a
result, the payload being received can be directly passed to the
application as it is read from the transport. This efficiency is due
to the underlying transport's guarantee of in-order delivery.
These changes do not impact the senders' capability to interleave
STREAM frames from multiple streams.
4.2. QX_TRANSPORT_PARAMETERS Frames
In QMux, Transport Parameters are exchanged as frames.
QX_TRANSPORT_PARAMETERS frames are formatted as shown in Figure 1.
QX_TRANSPORT_PARAMETERS Frame {
Type (i) = 0x3f5153300d0a0d0a,
Length (i),
Transport Parameters (..),
}
Figure 1: QX_TRANSPORT_PARAMETERS Frame Format
QX_TRANSPORT_PARAMETERS frames contain the following fields:
Length: A variable-length integer specifying the length of the
Transport Parameters field in this QX_TRANSPORT_PARAMETERS frame.
Transport Parameters: The Transport Parameters. The encoding of the
payload is as defined in Section 18 of [QUIC].
The QX_TRANSPORT_PARAMETERS frame is the first frame sent by
endpoints. Endpoints MUST send the QX_TRANSPORT_PARAMETERS frame as
soon as the underlying transport becomes available. Note neither
endpoint needs to wait for the peer's Transport Parameters before
sending its own, as Transport Parameters are a unilateral declaration
of an endpoint's capabilities (Section 7.4 of [QUIC]).
If the first frame being received by an endpoint is not a
QX_TRANSPORT_PARAMETERS frame, the endpoint MUST close the connection
with an error of type TRANSPORT_PARAMETER_ERROR.
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The frame type (0x3f5153300d0a0d0a; "\xffQMX\r\n\r\n" on wire) has
been chosen so that it can be used to disambiguate QMux from HTTP/1.1
[HTTP1] and HTTP/2.
4.3. QX_PING Frames
In QMux, QX_PING frames allow endpoints to test peer reachability
above the underlying transport.
QX_PING frames are formatted as shown in Figure 2.
QX_PING Frame {
Type (i) = 0xTBD..0xTBD+1,
Sequence Number (i),
}
Figure 2: QX_PING Frame Format
Type 0xTBD is used for sending a ping (i.e., request the peer to
respond). Type 0xTBD+1 is used in response.
QX_PING frames contain the following fields:
Sequence Number: A variable-length integer used to identify the
ping.
When sending QX_PING frames of type 0xTBD, endpoints MUST send
monotonically increasing values in the Sequence Number field, since
that allows the endpoints to identify to which ping the peer has
responded.
When sending QX_PING frames of type 0xTBD+1 in response, endpoints
MUST echo the Sequence Number that they received.
When receiving multiple QX_PING frames of type 0xTBD before having
the chance to respond, an endpoint MAY only respond with one QX_PING
frame of type 0xTBD+1 carrying the largest Sequence Number that the
endpoint has received.
5. Transport Parameters
QMux uses a subset of Transport Parameters defined in QUIC version 1.
Also, one new Transport Parameter specific to QMux is defined.
5.1. Permitted and Forbidden Transport Parameters
In QMux, use of the following Transport Parameters is allowed.
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* max_idle_timeout
* initial_max_data
* initial_max_stream_data_bidi_local
* initial_max_stream_data_bidi_remote
* initial_max_stream_data_uni
* initial_max_streams_bidi
* initial_max_streams_uni
The definition of these Transport Parameters are unchanged.
Use of other Transport Parameters defined in QUIC version 1 is
prohibited. When an endpoint receives one of the prohibited
Transport Parameters, the endpoint MUST close the connection with an
error of type TRANSPORT_PARAMETER_ERROR.
Endpoints MUST NOT send Transport Parameters that extend QUIC version
1, unless they are specified to be compatible with QMux.
When receiving Transport Parameters not defined in QUIC version 1,
receivers MUST ignore them unless they are specified to be usable on
QMux.
5.2. max_frame_size Transport Parameter
The max_frame_size Transport Parameter (0xTBD) is a variable-length
integer specifying the maximum size of the QUIC frame that the peer
can send, in the unit of bytes.
The initial value of the max_frame_size Transport Parameter is 16384.
By sending the Transport Parameter, the maximum frame size can only
be increased. When receiving a value below the initial value,
receivers MUST close the connection with an error of type
TRANSPORT_PARAMETER_ERROR.
Endpoints MUST NOT send QUIC frames that exceed the maximum declared
by the peer.
When receiving QUIC frames that exceed the declared maximum,
receivers MUST close the connection with an error of type
FRAME_ENCODING_ERROR.
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6. Closing the Connection
As is with QUIC version 1, a connection can be closed either by a
CONNECTION_CLOSE frame or by an idle timeout.
Unlike QUIC version 1, there is no draining period; once an endpoint
sends or receives the CONNECTION_CLOSE frame or reaches the idle
timeout, all the resources allocated for the Service are freed and
the underlying transport is closed immediately.
7. Using 0-RTT
TLS 1.3 introduced the concept of early data (also knows as 0-RTT
data).
When using QMux on top of TLS that supports early data, clients MAY
use early data when resuming a connection, by reusing certain
Transport Parameters as defined in Section 7.4.1 of [QUIC].
Similarly, when accepting early data, the servers MUST send Transport
Parameters that obey to the restrictions defined in Section 7.4.1 of
[QUIC].
8. Extensions
Not all the extensions of QUIC version 1 can be used. Each extension
have to define its mapping for QMux, or explicitly allow the use; see
Section 5.1.
As is the case with QUIC version 1, use of extension frames have to
be negotiated before use; see Section 19.21 of [QUIC].
This specification defines the mapping of the Unreliable Datagram
Extension.
8.1. Unreliable Datagram Extension
The use of the Unreliable Datagram Extension [QUIC_DATAGRAM] is
permitted, with one modification:
Similar to STREAM frames, when employing DATAGRAM frames of type 0x30
(i.e., DATAGRAM frames without the Length field), their size is
determined by the max_frame_size Transport Parameter (Section 5.2).
Apart from this, the encoding and semantics of the Unreliable
Datagram Extension remain unchanged. The use of the extension is
negotiated via the Transport Parameters.
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As discussed in Section 5 of [QUIC_DATAGRAM], senders can drop
DATAGRAM frames if the transport is blocked by flow or congestion
control.
9. Version Agility
Unlike QUIC, QMux does not define a mechanism for version
negotiation.
In large-scale deployments requiring service and protocol version
discovery, QMux can and is likely to be implemented over TLS. The
Application-Layer Protocol Negotiation Extension of TLS [ALPN] is the
favored mechanism to negotiate between an application protocol based
on this specification and others.
When ALPN is unavailable, first 8 bytes exchanged on the transport
(i.e., the type field of the QX_TRANSPORT_PARAMETERS frame in the
encoded form) can be used to identify if QMux is in use.
10. Implementation Considerations
Similar to HTTP/3 with Extensible Priorities [HTTP_PRIORITY],
application protocols using QUIC may employ stream multiplexing along
with a system to tune the delivery sequence of QUIC streams.
To alternate between QUIC streams of varying priorities in a timely
manner, it is advisable for QMux implementations to avoid creating
deep buffers holding QUIC frames. Instead, endpoints should wait for
the transport layer to be ready for writing. Upon becoming writable,
they should write QUIC frames according to the latest prioritization
signals.
Additionally, implementations may consider monitoring or adjusting
the flow and congestion control parameters of the underlying
transport. This approach aims to minimize data buffering within the
transport layer before transmission. However, improper adjustment of
these parameters could potentially lead to lower throughput.
11. Security Considerations
TODO Security
12. IANA Considerations
TODO
13. References
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13.1. Normative References
[QUIC] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[QUIC_DATAGRAM]
Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
Datagram Extension to QUIC", RFC 9221,
DOI 10.17487/RFC9221, March 2022,
<https://www.rfc-editor.org/rfc/rfc9221>.
[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/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
13.2. Informative References
[ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[h2-stream-limits]
Thomson, M. and L. Pardue, "Using HTTP/3 Stream Limits in
HTTP/2", Work in Progress, Internet-Draft, draft-thomson-
httpbis-h2-stream-limits-00, 6 November 2023,
<https://datatracker.ietf.org/doc/html/draft-thomson-
httpbis-h2-stream-limits-00>.
[HTTP1] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.
[HTTP2] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>.
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[HTTP3] Bishop, M., Ed., "HTTP/3", RFC 9114, DOI 10.17487/RFC9114,
June 2022, <https://www.rfc-editor.org/rfc/rfc9114>.
[HTTP_PRIORITY]
Oku, K. and L. Pardue, "Extensible Prioritization Scheme
for HTTP", RFC 9218, DOI 10.17487/RFC9218, June 2022,
<https://www.rfc-editor.org/rfc/rfc9218>.
[TCP] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
<https://www.rfc-editor.org/rfc/rfc9293>.
[UDP] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/rfc/rfc768>.
[webtrans-h2]
Frindell, A., Kinnear, E., Pauly, T., Thomson, M.,
Vasiliev, V., and G. Xie, "WebTransport over HTTP/2", Work
in Progress, Internet-Draft, draft-ietf-webtrans-http2-12,
7 July 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-webtrans-http2-12>.
[webtrans-h3]
Frindell, A., Kinnear, E., and V. Vasiliev, "WebTransport
over HTTP/3", Work in Progress, Internet-Draft, draft-
ietf-webtrans-http3-13, 7 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-
webtrans-http3-13>.
Acknowledgments
TODO acknowledge.
Authors' Addresses
Kazuho Oku
Fastly
Email: kazuhooku@gmail.com
Lucas Pardue
Cloudflare
Email: lucas@lucaspardue.com
Jana Iyengar
Netflix
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Email: jri.ietf@gmail.com
Eric Kinnear
Apple
Email: ekinnear@apple.com
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