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Versions: (draft-hamilton-quic-transport-protocol)
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QUIC J. Iyengar, Ed.
Internet-Draft Google
Intended status: Standards Track M. Thomson, Ed.
Expires: July 18, 2017 Mozilla
January 14, 2017
QUIC: A UDP-Based Multiplexed and Secure Transport
draft-ietf-quic-transport-01
Abstract
QUIC is a multiplexed and secure transport protocol that runs on top
of UDP. QUIC builds on past transport experience, and implements
mechanisms that make it useful as a modern general-purpose transport
protocol. Using UDP as the basis of QUIC is intended to address
compatibility issues with legacy clients and middleboxes. QUIC
authenticates all of its headers, preventing third parties from
changing them. QUIC encrypts most of its headers, thereby limiting
protocol evolution to QUIC endpoints only. Therefore, middleboxes,
in large part, are not required to be updated as new protocol
versions are deployed. This document describes the core QUIC
protocol, including the conceptual design, wire format, and
mechanisms of the QUIC protocol for connection establishment, stream
multiplexing, stream and connection-level flow control, and data
reliability. Accompanying documents describe QUIC's loss recovery
and congestion control, and the use of TLS 1.3 for key negotiation.
Note to Readers
Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/search/?email_list=quic .
Working Group information can be found at https://github.com/quicwg ;
source code and issues list for this draft can be found at
https://github.com/quicwg/base-drafts/labels/transport .
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 http://datatracker.ietf.org/drafts/current/.
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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 July 18, 2017.
Copyright Notice
Copyright (c) 2017 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
(http://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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
2.1. Notational Conventions . . . . . . . . . . . . . . . . . 5
3. A QUIC Overview . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Low-Latency Connection Establishment . . . . . . . . . . 5
3.2. Stream Multiplexing . . . . . . . . . . . . . . . . . . . 6
3.3. Rich Signaling for Congestion Control and Loss Recovery . 6
3.4. Stream and Connection Flow Control . . . . . . . . . . . 6
3.5. Authenticated and Encrypted Header and Payload . . . . . 7
3.6. Connection Migration and Resilience to NAT Rebinding . . 7
3.7. Version Negotiation . . . . . . . . . . . . . . . . . . . 7
4. Versions . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Packet Types and Formats . . . . . . . . . . . . . . . . . . 8
5.1. Common Header . . . . . . . . . . . . . . . . . . . . . . 8
5.1.1. Identifying Packet Types . . . . . . . . . . . . . . 10
5.1.2. Handling Packets from Different Versions . . . . . . 10
5.2. Regular Packets . . . . . . . . . . . . . . . . . . . . . 11
5.2.1. Packet Number Compression and Reconstruction . . . . 12
5.2.2. Frames and Frame Types . . . . . . . . . . . . . . . 13
5.3. Version Negotiation Packet . . . . . . . . . . . . . . . 14
5.4. Public Reset Packet . . . . . . . . . . . . . . . . . . . 15
6. Life of a Connection . . . . . . . . . . . . . . . . . . . . 15
6.1. Version Negotiation . . . . . . . . . . . . . . . . . . . 15
6.2. Crypto and Transport Handshake . . . . . . . . . . . . . 16
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6.2.1. Transport Parameters and Options . . . . . . . . . . 16
6.2.2. Proof of Source Address Ownership . . . . . . . . . . 17
6.2.3. Crypto Handshake Protocol Features . . . . . . . . . 18
6.2.4. Version Negotiation Validation . . . . . . . . . . . 19
6.3. Connection Migration . . . . . . . . . . . . . . . . . . 19
6.4. Connection Termination . . . . . . . . . . . . . . . . . 19
7. Frame Types and Formats . . . . . . . . . . . . . . . . . . . 20
7.1. STREAM Frame . . . . . . . . . . . . . . . . . . . . . . 21
7.2. ACK Frame . . . . . . . . . . . . . . . . . . . . . . . . 22
7.2.1. Ack Block Section . . . . . . . . . . . . . . . . . . 24
7.2.2. Timestamp Section . . . . . . . . . . . . . . . . . . 25
7.3. STOP_WAITING Frame . . . . . . . . . . . . . . . . . . . 26
7.4. WINDOW_UPDATE Frame . . . . . . . . . . . . . . . . . . . 27
7.5. BLOCKED Frame . . . . . . . . . . . . . . . . . . . . . . 27
7.6. RST_STREAM Frame . . . . . . . . . . . . . . . . . . . . 28
7.7. PADDING Frame . . . . . . . . . . . . . . . . . . . . . . 28
7.8. PING frame . . . . . . . . . . . . . . . . . . . . . . . 29
7.9. CONNECTION_CLOSE frame . . . . . . . . . . . . . . . . . 29
7.10. GOAWAY Frame . . . . . . . . . . . . . . . . . . . . . . 29
8. Packetization and Reliability . . . . . . . . . . . . . . . . 30
9. Streams: QUIC's Data Structuring Abstraction . . . . . . . . 32
9.1. Life of a Stream . . . . . . . . . . . . . . . . . . . . 32
9.1.1. idle . . . . . . . . . . . . . . . . . . . . . . . . 34
9.1.2. reserved . . . . . . . . . . . . . . . . . . . . . . 34
9.1.3. open . . . . . . . . . . . . . . . . . . . . . . . . 35
9.1.4. half-closed (local) . . . . . . . . . . . . . . . . . 35
9.1.5. half-closed (remote) . . . . . . . . . . . . . . . . 35
9.1.6. closed . . . . . . . . . . . . . . . . . . . . . . . 36
9.2. Stream Identifiers . . . . . . . . . . . . . . . . . . . 37
9.3. Stream Concurrency . . . . . . . . . . . . . . . . . . . 37
9.4. Sending and Receiving Data . . . . . . . . . . . . . . . 37
10. Flow Control . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Edge Cases and Other Considerations . . . . . . . . . . 39
10.1.1. Mid-stream RST_STREAM . . . . . . . . . . . . . . . 39
10.1.2. Response to a RST_STREAM . . . . . . . . . . . . . . 40
10.1.3. Offset Increment . . . . . . . . . . . . . . . . . . 40
10.1.4. BLOCKED frames . . . . . . . . . . . . . . . . . . . 40
11. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . 41
12. Security and Privacy Considerations . . . . . . . . . . . . . 44
12.1. Spoofed Ack Attack . . . . . . . . . . . . . . . . . . . 44
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
14.1. Normative References . . . . . . . . . . . . . . . . . . 45
14.2. Informative References . . . . . . . . . . . . . . . . . 45
14.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 46
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 46
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 46
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C.1. Since draft-ietf-quic-transport-00: . . . . . . . . . . . 47
C.2. Since draft-hamilton-quic-transport-protocol-01: . . . . 47
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
1. Introduction
QUIC is a multiplexed and secure transport protocol that runs on top
of UDP. QUIC builds on past transport experience and implements
mechanisms that make it useful as a modern general-purpose transport
protocol. Using UDP as the substrate, QUIC seeks to be compatible
with legacy clients and middleboxes. QUIC authenticates all of its
headers, preventing middleboxes and other third parties from changing
them, and encrypts most of its headers, limiting protocol evolution
largely to QUIC endpoints only.
This document describes the core QUIC protocol, including the
conceptual design, wire format, and mechanisms of the QUIC protocol
for connection establishment, stream multiplexing, stream and
connection-level flow control, and data reliability. Accompanying
documents describe QUIC's loss detection and congestion control
[QUIC-RECOVERY], and the use of TLS 1.3 for key negotiation
[QUIC-TLS].
2. Conventions and Definitions
The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
document. It's not shouting; when they are capitalized, they have
the special meaning defined in [RFC2119].
Definitions of terms that are used in this document:
o Client: The endpoint initiating a QUIC connection.
o Server: The endpoint accepting incoming QUIC connections.
o Endpoint: The client or server end of a connection.
o Stream: A logical, bi-directional channel of ordered bytes within
a QUIC connection.
o Connection: A conversation between two QUIC endpoints with a
single encryption context that multiplexes streams within it.
o Connection ID: The identifier for a QUIC connection.
o QUIC packet: A well-formed UDP payload that can be parsed by a
QUIC receiver. QUIC packet size in this document refers to the
UDP payload size.
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2.1. Notational Conventions
Packet and frame diagrams use the format described in [RFC2360]
Section 3.1, with the following additional conventions:
[x] Indicates that x is optional
{x} Indicates that x is encrypted
x (*) ... Indicates that x is variable-length
x (A/B/C) ... Indicates that x is one of A, B, or C bits long
3. A QUIC Overview
This section briefly describes QUIC's key mechanisms and benefits.
Key strengths of QUIC include:
o Low-latency connection establishment
o Multiplexing without head-of-line blocking
o Authenticated and encrypted header and payload
o Rich signaling for congestion control and loss recovery
o Stream and connection flow control
o Connection migration and resilience to NAT rebinding
o Version negotiation
3.1. Low-Latency Connection Establishment
QUIC relies on a combined crypto and transport handshake for setting
up a secure transport connection. QUIC connections are expected to
commonly use 0-RTT handshakes, meaning that for most QUIC
connections, data can be sent immediately following the client
handshake packet, without waiting for a reply from the server. QUIC
provides a dedicated stream (Stream ID 1) to be used for performing
the crypto handshake and QUIC options negotiation. The format of the
QUIC options and parameters used during negotiation are described in
this document, but the handshake protocol that runs on Stream ID 1 is
described in the accompanying crypto handshake draft [QUIC-TLS].
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3.2. Stream Multiplexing
When application messages are transported over TCP, independent
application messages can suffer from head-of-line blocking. When an
application multiplexes many streams atop TCP's single-bytestream
abstraction, a loss of a TCP segment results in blocking of all
subsequent segments until a retransmission arrives, irrespective of
the application streams that are encapsulated in subsequent segments.
QUIC ensures that lost packets carrying data for an individual stream
only impact that specific stream. Data received on other streams can
continue to be reassembled and delivered to the application.
3.3. Rich Signaling for Congestion Control and Loss Recovery
QUIC's packet framing and acknowledgments carry rich information that
help both congestion control and loss recovery in fundamental ways.
Each QUIC packet carries a new packet number, including those
carrying retransmitted data. This obviates the need for a separate
mechanism to distinguish acks for retransmissions from those for
original transmissions, avoiding TCP's retransmission ambiguity
problem. QUIC acknowledgments also explicitly encode the delay
between the receipt of a packet and its acknowledgment being sent,
and together with the monotonically-increasing packet numbers, this
allows for precise network roundtrip-time (RTT) calculation. QUIC's
ACK frames support up to 256 ack blocks, so QUIC is more resilient to
reordering than TCP with SACK support, as well as able to keep more
bytes on the wire when there is reordering or loss.
3.4. Stream and Connection Flow Control
QUIC implements stream- and connection-level flow control, closely
following HTTP/2's flow control mechanisms. At a high level, a QUIC
receiver advertises the absolute byte offset within each stream up to
which the receiver is willing to receive data. As data is sent,
received, and delivered on a particular stream, the receiver sends
WINDOW_UPDATE frames that increase the advertised offset limit for
that stream, allowing the peer to send more data on that stream. In
addition to this stream-level flow control, QUIC implements
connection-level flow control to limit the aggregate buffer that a
QUIC receiver is willing to allocate to all streams on a connection.
Connection-level flow control works in the same way as stream-level
flow control, but the bytes delivered and highest received offset are
all aggregates across all streams.
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3.5. Authenticated and Encrypted Header and Payload
TCP headers appear in plaintext on the wire and are not
authenticated, causing a plethora of injection and header
manipulation issues for TCP, such as receive-window manipulation and
sequence-number overwriting. While some of these are mechanisms used
by middleboxes to improve TCP performance, others are active attacks.
Even "performance-enhancing" middleboxes that routinely interpose on
the transport state machine end up limiting the evolvability of the
transport protocol, as has been observed in the design of MPTCP and
in its subsequent deployability issues.
Generally, QUIC packets are always authenticated and the payload is
typically fully encrypted. The parts of the packet header which are
not encrypted are still authenticated by the receiver, so as to
thwart any packet injection or manipulation by third parties. Some
early handshake packets, such as the Version Negotiation packet, are
not encrypted, but information sent in these unencrypted handshake
packets is later verified under crypto cover.
PUBLIC_RESET packets that reset a connection are currently not
authenticated.
3.6. Connection Migration and Resilience to NAT Rebinding
QUIC connections are identified by a 64-bit Connection ID, randomly
generated by the client. QUIC's consistent connection ID allows
connections to survive changes to the client's IP and port, such as
those caused by NAT rebindings or by the client changing network
connectivity to a new address. QUIC provides automatic cryptographic
verification of a rebound client, since the client continues to use
the same session key for encrypting and decrypting packets. The
consistent connection ID can be used to allow migration of the
connection to a new server IP address as well, since the Connection
ID remains consistent across changes in the client's and the server's
network addresses.
3.7. Version Negotiation
QUIC version negotiation allows for multiple versions of the protocol
to be deployed and used concurrently. Version negotiation is
described in Section 6.1.
4. Versions
QUIC versions are identified using a 32-bit value.
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The version 0x00000000 is reserved to represent an invalid version.
This version of the specification is identified by the number
0x00000001.
Versions with the most significant 16 bits of the version number
cleared are reserved for use in future IETF consensus documents.
[[RFC editor: please remove the remainder of this section before
publication.]]
The version number for the final version of this specification
(0x00000001), is reserved for the version of the protocol that is
published as an RFC.
Version numbers used to identify IETF drafts are created by adding
the draft number to 0xff000000. For example, draft-ietf-quic-
transport-13 would be identified as 0xff00000D.
Versions of QUIC that are used for experimentation are coordinated on
the github wiki [4].
5. Packet Types and Formats
We first describe QUIC's packet types and their formats, since some
are referenced in subsequent mechanisms.
All numeric values are encoded in network byte order (that is, big-
endian) and all field sizes are in bits. When discussing individual
bits of fields, the least significant bit is referred to as bit 0.
Hexadecimal notation is used for describing the value of fields.
5.1. Common Header
All QUIC packets begin with a QUIC Common header, as shown below.
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
+-+-+-+-+-+-+-+-+
| Flags (8) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ [Connection ID (64)] +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type-Dependent Fields (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in the Common Header are the following:
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o Flags:
* 0x01 = VERSION. The semantics of this flag depends on whether
the packet is sent by the server or the client. A client MAY
set this flag and include exactly one proposed version. A
server may set this flag when the client-proposed version was
unsupported, and may then provide a list (0 or more) of
acceptable versions as a part of version negotiation (described
in Section 6.1.)
* 0x02 = PUBLIC_RESET. Set to indicate that the packet is a
Public Reset packet.
* 0x04 = KEY_PHASE. This is used by the QUIC packet protection
to identify the correct packet protection keys, see [QUIC-TLS].
* 0x08 = CONNECTION_ID. Indicates the Connection ID is present
in the packet. This must be set in all packets until
negotiated to a different value for a given direction. For
instance, if a client indicates that the 5-tuple fully
identifies the connection at the client, the connection ID is
optional in the server-to-client direction.
* 0x30 = PACKET_NUMBER_SIZE. These two bits indicate the number
of low-order-bytes of the packet number that are present in
each packet.
+ 11 indicates that 6 bytes of the packet number are present
+ 10 indicates that 4 bytes of the packet number are present
+ 01 indicates that 2 bytes of the packet number are present
+ 00 indicates that 1 byte of the packet number is present
* 0x40 = MULTIPATH. This bit is reserved for multipath use.
* 0x80 is currently unused, and must be set to 0.
o Connection ID: An unsigned 64-bit random number chosen by the
client, used as the identifier of the connection. Connection ID
is tied to a QUIC connection, and remains consistent across client
and/or server IP and port changes.
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5.1.1. Identifying Packet Types
While all QUIC packets have the same common header, there are three
types of packets: Regular packets, Version Negotiation packets, and
Public Reset packets. The flowchart below shows how a packet is
classified into one of these three packet types:
Check the flags in the common header
|
|
V
+--------------+
| PUBLIC_RESET | YES
| flag set? |-------> Public Reset packet
+--------------+
|
| NO
V
+------------+ +-------------+
| VERSION | YES | Packet sent | YES Version
| flag set? |-------->| by server? |--------> Negotiation
+------------+ +-------------+ packet
| |
| NO | NO
V V
Regular packet with Regular packet with
no QUIC Version in header QUIC Version in header
Figure 1: Types of QUIC Packets
5.1.2. Handling Packets from Different Versions
Version negotiation (Section 6.1) is performed using packets that
have the VERSION bit set. This bit is always set on packets that are
sent prior to connection establishment. When receiving a packet that
is not associated with an existing connection, packets without a
VERSION bit MUST be discarded.
Implementations MUST assume that an unsupported version uses an
unknown packet format.
Between different versions the following things are guaranteed to
remain constant are:
o the location and size of the Flags field,
o the location and value of the VERSION bit in the Flags field,
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o the location and size of the Connection ID field, and
o the Version (or Supported Versions, Section 5.3) field.
All other values MUST be ignored when processing a packet that
contains an unsupported version.
5.2. Regular Packets
Each Regular packet contains additional header fields followed by an
encrypted payload, as shown below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Version (32)] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Number (8/16/32/48) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| {Encrypted Payload (*)} ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Regular Packet
The fields in a Regular packet past the Common Header are the
following:
o QUIC Version: A 32-bit opaque tag that represents the version of
the QUIC protocol. Only present in the client-to-server
direction, and if the VERSION flag is set. Version Negotiation is
described in Section 6.1.
o Packet Number: The lower 8, 16, 32, or 48 bits of the packet
number, based on the PACKET_NUMBER_SIZE flag. Each Regular packet
is assigned a packet number by the sender. The first packet sent
by an endpoint MUST have a packet number of 1.
o Encrypted Payload: The remainder of a Regular packet is both
authenticated and encrypted once packet protection keys are
available. [QUIC-TLS] describes packet protection in detail.
After decryption, the plaintext consists of a sequence of frames,
as shown in Figure 3. Frames are described in Section 5.2.2.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame 1 (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame 2 (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame N (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Contents of Encrypted Payload
5.2.1. Packet Number Compression and Reconstruction
The complete packet number is a 64-bit unsigned number and is used as
part of a cryptographic nonce for packet encryption. To reduce the
number of bits required to represent the packet number over the wire,
at most 48 bits of the packet number are transmitted over the wire.
A QUIC endpoint MUST NOT reuse a complete packet number within the
same connection (that is, under the same cryptographic keys). If the
total number of packets transmitted in this connection reaches 2^64 -
1, the sender MUST close the connection by sending a CONNECTION_CLOSE
frame with the error code QUIC_SEQUENCE_NUMBER_LIMIT_REACHED
(connection termination is described in Section 6.4.) For
unambiguous reconstruction of the complete packet number by a
receiver from the lower-order bits, a QUIC sender MUST NOT have more
than 2^(packet_number_size - 2) in flight at any point in the
connection. In other words,
o If a sender sets PACKET_NUMBER_SIZE bits to 11, it MUST NOT have
more than (2^46) packets in flight.
o If a sender sets PACKET_NUMBER_SIZE bits to 10, it MUST NOT have
more than (2^30) packets in flight.
o If a sender sets PACKET_NUMBER_SIZE bits to 01, it MUST NOT have
more than (2^14) packets in flight.
o If a sender sets PACKET_NUMBER_SIZE bits to 00, it MUST NOT have
more than (2^6) packets in flight.
DISCUSS: Should the receiver be required to enforce this rule that
the sender MUST NOT exceed the inflight limit? Specifically,
should the receiver drop packets that are received outside this
window?
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Any truncated packet number received from a peer MUST be
reconstructed as the value closest to the next expected packet
number from that peer.
(TODO: Clarify how packet number size can change mid-connection.)
5.2.2. Frames and Frame Types
A Regular packet MUST contain at least one frame, and MAY contain
multiple frames and multiple frame types. Frames MUST fit within a
single QUIC packet and MUST NOT span a QUIC packet boundary. Each
frame begins with a Frame Type byte, indicating its type, followed by
additional type-dependent fields:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (8) | Type-Dependent Fields (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Generic Frame Layout
The following table lists currently defined frame types. Note that
the Frame Type byte in STREAM and ACK frames is used to carry other
frame-specific flags. For all other frames, the Frame Type byte
simply identifies the frame. These frames are explained in more
detail as they are referenced later in the document.
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+---+------------------+------------------+--------------+
| | Type-field value | Frame type | Definition |
+---+------------------+------------------+--------------+
| | "1FDOOOSS" | STREAM | Section 7.1 |
| | | | |
| | "01NULLMM" | ACK | Section 7.2 |
| | | | |
| | 00000000 (0x00) | PADDING | Section 7.7 |
| | | | |
| | 00000001 (0x01) | RST_STREAM | Section 7.6 |
| | | | |
| | 00000010 (0x02) | CONNECTION_CLOSE | Section 7.9 |
| | | | |
| | 00000011 (0x03) | GOAWAY | Section 7.10 |
| | | | |
| | 00000100 (0x04) | WINDOW_UPDATE | Section 7.4 |
| | | | |
| | 00000101 (0x05) | BLOCKED | Section 7.5 |
| | | | |
| | 00000110 (0x06) | STOP_WAITING | Section 7.3 |
| | | | |
| | 00000111 (0x07) | PING | Section 7.8 |
+---+------------------+------------------+--------------+
5.3. Version Negotiation Packet
A Version Negotiation packet is only sent by the server, MUST have
the VERSION flag set, and MUST include the full 64-bit Connection ID.
The remainder of the Version Negotiation packet is a list of 32-bit
versions which the server supports, as shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Supported Version 1 (32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Supported Version 2 (32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Supported Version N (32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Version Negotiation Packet
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5.4. Public Reset Packet
A Public Reset packet MUST have the PUBLIC_RESET flag set, and MUST
include the full 64-bit connection ID. The content of the Public
Reset packet is TBD.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Public Reset Fields (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Public Reset Packet
6. Life of a Connection
A QUIC connection is a single conversation between two QUIC
endpoints. QUIC's connection establishment intertwines version
negotiation with the crypto and transport handshakes to reduce
connection establishment latency, as described in Section 6.2. Once
established, a connection may migrate to a different IP or port at
either endpoint, due to NAT rebinding or mobility, as described in
Section 6.3. Finally a connection may be terminated by either
endpoint, as described in Section 6.4.
6.1. Version Negotiation
QUIC's connection establishment begins with version negotiation,
since all communication between the endpoints, including packet and
frame formats, relies on the two endpoints agreeing on a version.
A QUIC connection begins with a client sending a handshake packet.
The details of the handshake mechanisms are described in Section 6.2,
but all of the initial packets sent from the client to the server
MUST have the VERSION flag set, and MUST specify the version of the
protocol being used.
When the server receives a packet from a client with the VERSION flag
set, it compares the client's version to the versions it supports.
If the version selected by the client is not acceptable to the
server, the server discards the incoming packet and responds with a
version negotiation packet (Section 5.3). This includes the VERSION
flag and a list of versions that the server will accept. A server
MUST send a version negotiation packet for every packet that it
receives with an unacceptable version.
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If the packet contains a version that is acceptable to the server,
the server proceeds with the handshake (Section 6.2). All subsequent
packets sent by the server MUST have the VERSION flag unset. This
commits the server to the version that the client selected.
When the client receives a Version Negotiation packet from the
server, it should select an acceptable protocol version. If the
server lists an acceptable version, the client selects that version
and resends all packets using that version. The resent packets MUST
use new packet numbers. These packets MUST continue to have the
VERSION flag set and MUST include the new negotiated protocol
version.
The client MUST set the VERSION flag on all packets until version
negotiation concludes. Version negotiation successfully concludes
when the client receives a packet from the server with the VERSION
flag unset. All subsequent packets sent by the client SHOULD have
the VERSION flag unset.
Once the server receives a packet from the client with the VERSION
flag unset, it MUST ignore the flag in subsequently received packets.
Version negotiation uses unprotected data. The result of the
negotiation MUST be revalidated once the cryptographic handshake has
completed (see Section 6.2.4).
6.2. Crypto and Transport Handshake
QUIC relies on a combined crypto and transport handshake to minimize
connection establishment latency. QUIC provides a dedicated stream
(Stream ID 1) to be used for performing a combined connection and
security handshake (streams are described in detail in Section 9).
The crypto handshake protocol encapsulates and delivers QUIC's
transport handshake to the peer on the crypto stream. The first QUIC
packet from the client to the server MUST carry handshake information
as data on Stream ID 1.
6.2.1. Transport Parameters and Options
During connection establishment, the handshake must negotiate various
transport parameters. The currently defined transport parameters are
described later in the document.
The transport component of the handshake is responsible for
exchanging and negotiating the following parameters for a QUIC
connection. Not all parameters are negotiated, some are parameters
sent in just one direction. These parameters and options are encoded
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and handed off to the crypto handshake protocol to be transmitted to
the peer.
6.2.1.1. Encoding
(TODO: Describe format with example)
QUIC encodes the transport parameters and options as tag-value pairs,
all as 7-bit ASCII strings. QUIC parameter tags are listed below.
6.2.1.2. Required Transport Parameters
o SFCW: Stream Flow Control Window. The stream level flow control
byte offset advertised by the sender of this parameter.
o CFCW: Connection Flow Control Window. The connection level flow
control byte offset advertised by the sender of this parameter.
o MSPC: Maximum number of incoming streams per connection.
o ICSL: Idle timeout in seconds. The maximum value is 600 seconds
(10 minutes).
6.2.1.3. Optional Transport Parameters
o TCID: Indicates support for truncated Connection IDs. If sent by
a peer, indicates that connection IDs sent to the peer should be
truncated to 0 bytes. This is expected to commonly be used by an
endpoint where the 5-tuple is sufficient to identify a connection.
For instance, if the 5-tuple is unique at the client, the client
MAY send a TCID parameter to the server. When a TCID parameter is
received, an endpoint MAY choose to not send the connection ID on
subsequent packets.
o COPT: Connection Options are a repeated tag field. The field
contains any connection options being requested by the client or
server. These are typically used for experimentation and will
evolve over time. Example use cases include changing congestion
control algorithms and parameters such as initial window. (TODO:
List connection options.)
6.2.2. Proof of Source Address Ownership
Transport protocols commonly use a roundtrip time to verify a
client's address ownership for protection from malicious clients that
spoof their source address. QUIC uses a cookie, called the Source
Address Token (STK), to mostly eliminate this roundtrip of delay.
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This technique is similar to TCP Fast Open's use of a cookie to avoid
a roundtrip of delay in TCP connection establishment.
On a new connection, a QUIC server sends an STK, which is opaque to
and stored by the client. On a subsequent connection, the client
echoes it in the transport handshake as proof of IP ownership.
A QUIC server also uses the STK to store server-designated connection
IDs for Stateless Rejects, to verify that an incoming connection
contains the correct connection ID.
A QUIC server MAY additionally store other data in a the STK, such as
measured bandwidth and measured minimum RTT to the client that may
help the server better bootstrap a subsequent connection from the
same client. A server MAY send an updated STK message mid-connection
to update server state that is stored at the client in the STK.
(TODO: Describe server and client actions on STK, encoding,
recommendations for what to put in an STK. Describe SCUP messages.)
6.2.3. Crypto Handshake Protocol Features
QUIC's current crypto handshake mechanism is documented in
[QUICCrypto]. QUIC does not restrict itself to using a specific
handshake protocol, so the details of a specific handshake protocol
are out of this document's scope. If not explicitly specified in the
application mapping, TLS is assumed to be the default crypto
handshake protocol, as described in [QUIC-TLS]. An application that
maps to QUIC MAY however specify an alternative crypto handshake
protocol to be used.
The following list of requirements and recommendations documents
properties of the current prototype handshake which should be
provided by any handshake protocol.
o The crypto handshake MUST ensure that the final negotiated key is
distinct for every connection between two endpoints.
o Transport Negotiation: The crypto handshake MUST provide a
mechanism for the transport component to exchange transport
parameters and Source Address Tokens. To avoid downgrade attacks,
the transport parameters sent and received MUST be verified before
the handshake completes successfully.
o Connection Establishment in 0-RTT: Since low-latency connection
establishment is a critical feature of QUIC, the QUIC handshake
protocol SHOULD attempt to achieve 0-RTT connection establishment
latency for repeated connections between the same endpoints.
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o Source Address Spoofing Defense: Since QUIC handles source address
verification, the crypto protocol SHOULD NOT impose a separate
source address verification mechanism.
o Server Config Update: A QUIC server may refresh the source-address
token (STK) mid-connection, to update the information stored in
the STK at the client and to extend the period over which 0-RTT
connections can be established by the client.
o Certificate Compression: Early QUIC experience demonstrated that
compressing certificates exchanged during a handshake is valuable
in reducing latency. This additionally helps to reduce the
amplification attack footprint when a server sends a large set of
certificates, which is not uncommon with TLS. The crypto protocol
SHOULD compress certificates and any other information to minimize
the number of packets sent during a handshake.
6.2.4. Version Negotiation Validation
The following information used during the QUIC handshake MUST be
cryptographically verified by the crypto handshake protocol:
o Client's originally proposed version in its first packet.
o Server's version list in it's Version Negotiation packet, if one
was sent.
6.3. Connection Migration
QUIC connections are identified by their 64-bit Connection ID.
QUIC's consistent connection ID allows connections to survive changes
to the client's IP and/or port, such as those caused by client or
server migrating to a new network. QUIC also provides automatic
cryptographic verification of a rebound client, since the client
continues to use the same session key for encrypting and decrypting
packets.
DISCUSS: Simultaneous migration. Is this reasonable?
TODO: Perhaps move mitigation techniques from Security Considerations
here.
6.4. Connection Termination
Connections should remain open until they become idle for a pre-
negotiated period of time. A QUIC connection, once established, can
be terminated in one of three ways:
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1. Explicit Shutdown: An endpoint sends a CONNECTION_CLOSE frame to
the peer initiating a connection termination. An endpoint may
send a GOAWAY frame to the peer prior to a CONNECTION_CLOSE to
indicate that the connection will soon be terminated. A GOAWAY
frame signals to the peer that any active streams will continue
to be processed, but the sender of the GOAWAY will not initiate
any additional streams and will not accept any new incoming
streams. On termination of the active streams, a
CONNECTION_CLOSE may be sent. If an endpoint sends a
CONNECTION_CLOSE frame while unterminated streams are active (no
FIN bit or RST_STREAM frames have been sent or received for one
or more streams), then the peer must assume that the streams were
incomplete and were abnormally terminated.
2. Implicit Shutdown: The default idle timeout for a QUIC connection
is 30 seconds, and is a required parameter (ICSL) in connection
negotiation. The maximum is 10 minutes. If there is no network
activity for the duration of the idle timeout, the connection is
closed. By default a CONNECTION_CLOSE frame will be sent. A
silent close option can be enabled when it is expensive to send
an explicit close, such as mobile networks that must wake up the
radio.
3. Abrupt Shutdown: An endpoint may send a Public Reset packet at
any time during the connection to abruptly terminate an active
connection. A Public Reset packet SHOULD only be used as a final
recourse. Commonly, a public reset is expected to be sent when a
packet on an established connection is received by an endpoint
that is unable decrypt the packet. For instance, if a server
reboots mid-connection and loses any cryptographic state
associated with open connections, and then receives a packet on
an open connection, it should send a Public Reset packet in
return. (TODO: articulate rules around when a public reset
should be sent.)
TODO: Connections that are terminated are added to a TIME_WAIT list
at the server, so as to absorb any straggler packets in the network.
Discuss TIME_WAIT list.
7. Frame Types and Formats
As described in Section 8, Regular packets contain one or more
frames. We now describe the various QUIC frame types that can be
present in a Regular packet. The use of these frames and various
frame header bits are described in subsequent sections.
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7.1. STREAM Frame
STREAM frames implicitly create a stream and carry stream data. The
type byte for a STREAM frame contains embedded flags, and is
formatted as "1FDOOOSS". These bits are parsed as follows:
o The leftmost bit must be set to 1, indicating that this is a
STREAM frame.
o "F" is the FIN bit, which is used for stream termination.
o The "D" bit indicates whether a Data Length field is present in
the STREAM header. When set to 0, this field indicates that the
Stream Data field extends to the end of the packet. When set to
1, this field indicates that Data Length field contains the length
(in bytes) of the Stream Data field. The option to omit the
length should only be used when the packet is a "full-sized"
packet, to avoid the risk of corruption via padding.
o The "OOO" bits encode the length of the Offset header field as 0,
16, 24, 32, 40, 48, 56, or 64 bits long.
o The "SS" bits encode the length of the Stream ID header field as
8, 16, 24, or 32 bits. (DISCUSS: Consider making this 8, 16, 32,
64.)
A STREAM frame is shown below.
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 (8/16/24/32) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Offset (0/16/24/32/40/48/56/64) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Data Length (16)] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Data (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: STREAM Frame Format
The STREAM frame contains the following fields:
o Stream ID: A variable-sized unsigned ID unique to this stream,
whose size is determined by the "SS" bits in the type byte.
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o Offset: A variable-sized unsigned number specifying the byte
offset in the stream for the data in this STREAM frame. The first
byte in the stream has an offset of 0.
o Data Length: An optional 16-bit unsigned number specifying the
length of the Stream Data field in this STREAM frame.
o Stream Data: The bytes from the designated stream to be delivered.
A STREAM frame MUST have either non-zero data length or the FIN bit
set.
Stream multiplexing is achieved by interleaving STREAM frames from
multiple streams into one or more QUIC packets. A single QUIC packet
MAY bundle STREAM frames from multiple streams.
Implementation note: One of the benefits of QUIC is avoidance of
head-of-line blocking across multiple streams. When a packet loss
occurs, only streams with data in that packet are blocked waiting for
a retransmission to be received, while other streams can continue
making progress. Note that when data from multiple streams is
bundled into a single QUIC packet, loss of that packet blocks all
those streams from making progress. An implementation is therefore
advised to bundle as few streams as necessary in outgoing packets
without losing transmission efficiency to underfilled packets.
7.2. ACK Frame
Receivers send ACK frames to inform senders which packets they have
received, as well as which packets are considered missing. The ACK
frame contains between 1 and 256 ack blocks. Ack blocks are ranges
of acknowledged packets.
To limit the ACK blocks to the ones that haven't yet been received by
the sender, the sender periodically sends STOP_WAITING frames that
signal the receiver to stop acking packets below a specified sequence
number, raising the "least unacked" packet number at the receiver. A
sender of an ACK frame thus reports only those ACK blocks between the
received least unacked and the reported largest observed packet
numbers. An endpoint SHOULD use the "Largest Acked" packet number it
received to calculate the "Least Unacked Delta" value in any
STOP_WAITING frame it might send.
Unlike TCP SACKs, QUIC ACK blocks are irrevocable. Once a packet is
acked, even if it does not appear in a future ACK frame, it is
assumed to be acked.
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A sender MAY intentionally skip packet numbers to introduce entropy
into the connection, to avoid opportunistic ack attacks. The sender
MUST close the connection if an unsent packet number is acked. The
format of the ACK frame is efficient at expressing blocks of missing
packets; skipping packet numbers between 1 and 255 effectively
provides up to 8 bits of efficient entropy on demand, which should be
adequate protection against most opportunistic ack attacks.
The type byte for a ACK frame contains embedded flags, and is
formatted as "01NULLMM". These bits are parsed as follows:
o The first two bits must be set to 01 indicating that this is an
ACK frame.
o The "N" bit indicates whether the frame has more than 1 ack range
(i.e., whether the Ack Block Section contains a Num Blocks field).
o The "U" bit is unused and MUST be set to zero.
o The two "LL" bits encode the length of the Largest Acked field as
1, 2, 4, or 6 bytes long.
o The two "MM" bits encode the length of the Ack Block Length fields
as 1, 2, 4, or 6 bytes long.
An ACK frame is shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Largest Acked (8/16/32/48) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ack Delay (16) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[Num Blocks(8)]| Ack Block Section (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NumTS (8) | Timestamp Section (*) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: ACK Frame Format
The fields in the ACK frame are as follows:
o Largest Acked: A variable-sized unsigned value representing the
largest packet number the peer is acking in this packet (typically
the largest that the peer has seen thus far.)
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o Ack Delay: Time from when the largest acked, as indicated in the
Largest Acked field, was received by this peer to when this ack
was sent.
o Num Blocks (opt): An optional 8-bit unsigned value specifying the
number of additional ack blocks (besides the required First Ack
Block) in this ACK frame. Only present if the 'N' flag bit is 1.
o Ack Block Section: Contains one or more blocks of packet numbers
which have been successfully received. See Section 7.2.1.
o Num Timestamps: An unsigned 8-bit number specifying the total
number of <packet number, timestamp> pairs in the Timestamp
Section.
o Timestamp Section: Contains zero or more timestamps reporting
transit delay of received packets. See Section 7.2.2.
7.2.1. Ack Block Section
The Ack Block Section contains between one and 256 blocks of packet
numbers which have been successfully received. If the Num Blocks
field is absent, only the First Ack Block length is present in this
section. Otherwise, the Num Blocks field indicates how many
additional blocks follow the First Ack Block Length field.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| First Ack Block Length (8/16/32/48) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Gap 1 (8)] | [Ack Block 1 Length (8/16/32/48)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Gap 2 (8)] | [Ack Block 2 Length (8/16/32/48)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [Gap N (8)] | [Ack Block N Length (8/16/32/48)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Ack Block Section
The fields in the Ack Block Section are:
o First Ack Block Length: An unsigned packet number delta that
indicates the number of contiguous additional packets being acked
starting at the Largest Acked.
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o Gap To Next Block (opt, repeated): An unsigned number specifying
the number of contiguous missing packets from the end of the
previous ack block to the start of the next.
o Ack Block Length (opt, repeated): An unsigned packet number delta
that indicates the number of contiguous packets being acked
starting after the end of the previous gap. Along with the
previous field, this field is repeated "Num Blocks" times.
7.2.2. Timestamp Section
The Timestamp Section contains between zero and 255 measurements of
packet receive times relative to the beginning of the connection.
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
+-+-+-+-+-+-+-+-+
| [Delta LA (8)]|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| [First Timestamp (32)] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[Delta LA 1(8)]| [Time Since Previous 1 (16)] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[Delta LA 2(8)]| [Time Since Previous 2 (16)] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|[Delta LA N(8)]| [Time Since Previous N (16)] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Timestamp Section
The fields in the Timestamp Section are:
o Delta Largest Acked (opt): An optional 8-bit unsigned packet
number delta specifying the delta between the largest acked and
the first packet whose timestamp is being reported. In other
words, this first packet number may be computed as (Largest Acked
- Delta Largest Acked.)
o First Timestamp (opt): An optional 32-bit unsigned value
specifying the time delta in microseconds, from the beginning of
the connection to the arrival of the packet indicated by Delta
Largest Acked.
o Delta Largest Acked 1..N (opt, repeated): (Same as above.)
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o Time Since Previous Timestamp 1..N(opt, repeated): An optional
16-bit unsigned value specifying time delta from the previous
reported timestamp. It is encoded in the same format as the Ack
Delay. Along with the previous field, this field is repeated "Num
Timestamps" times.
7.2.2.1. Time Format
DISCUSS_AND_REPLACE: Perhaps make this format simpler.
The time format used in the ACK frame above is a 16-bit unsigned
float with 11 explicit bits of mantissa and 5 bits of explicit
exponent, specifying time in microseconds. The bit format is loosely
modeled after IEEE 754. For example, 1 microsecond is represented as
0x1, which has an exponent of zero, presented in the 5 high order
bits, and mantissa of 1, presented in the 11 low order bits. When
the explicit exponent is greater than zero, an implicit high-order
12th bit of 1 is assumed in the mantissa. For example, a floating
value of 0x800 has an explicit exponent of 1, as well as an explicit
mantissa of 0, but then has an effective mantissa of 4096 (12th bit
is assumed to be 1). Additionally, the actual exponent is one-less
than the explicit exponent, and the value represents 4096
microseconds. Any values larger than the representable range are
clamped to 0xFFFF.
7.3. STOP_WAITING Frame
The STOP_WAITING frame (type=0x06) is sent to inform the peer that it
should not continue to wait for packets with packet numbers lower
than a specified value. The packet number is encoded in 1, 2, 4 or 6
bytes, using the same coding length as is specified for the packet
number for the enclosing packet's header (specified in the QUIC Frame
packet's Flags field.) 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Least Unacked Delta (8/16/32/48) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: STOP_WAITING Frame Format
The STOP_WAITING frame contains a single field:
o Least Unacked Delta: A variable-length packet number delta with
the same length as the packet header's packet number. Subtract it
from the complete packet number of the enclosing packet to
determine the least unacked packet number. The resulting least
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unacked packet number is the earliest packet for which the sender
is still awaiting an ack. If the receiver is missing any packets
earlier than this packet, the receiver SHOULD consider those
packets to be irrecoverably lost and MUST NOT report those packets
as missing in subsequent acks.
7.4. WINDOW_UPDATE Frame
The WINDOW_UPDATE frame (type=0x04) informs the peer of an increase
in an endpoint's flow control receive window. The Stream ID can be
zero, indicating this WINDOW_UPDATE applies to the connection level
flow control window, or non-zero, indicating that the specified
stream should increase its flow control window. 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 (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Byte Offset (64) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields in the WINDOW_UPDATE frame are as follows:
o Stream ID: ID of the stream whose flow control windows is being
updated, or 0 to specify the connection-level flow control window.
o Byte offset: A 64-bit unsigned integer indicating the absolute
byte offset of data which can be sent on the given stream. In the
case of connection level flow control, the cumulative number of
bytes which can be sent on all currently open streams.
7.5. BLOCKED Frame
A sender sends a BLOCKED frame (type=0x05) when it is ready to send
data (and has data to send), but is currently flow control blocked.
BLOCKED frames are purely informational frames, but extremely useful
for debugging purposes. A receiver of a BLOCKED frame should simply
discard it (after possibly printing a helpful log message). The
frame is as follows:
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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 (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The BLOCKED frame contains a single field:
o Stream ID: A 32-bit unsigned number indicating the stream which is
flow control blocked. A non-zero Stream ID field specifies the
stream that is flow control blocked. When zero, the Stream ID
field indicates that the connection is flow control blocked.
7.6. RST_STREAM Frame
An endpoint may use a RST_STREAM frame (type=0x01) to abruptly
terminate a stream. 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 (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Byte Offset (64) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields are:
o Stream ID: The 32-bit Stream ID of the stream being terminated.
o Byte offset: A 64-bit unsigned integer indicating the absolute
byte offset of the end of data written on this stream by the
RST_STREAM sender.
o Error code: A 32-bit error code which indicates why the stream is
being closed.
7.7. PADDING Frame
The PADDING frame (type=0x00) pads a packet with 0x00 bytes. When
this frame is encountered, the rest of the packet is expected to be
padding bytes. The frame contains 0x00 bytes and extends to the end
of the QUIC packet. A PADDING frame has no additional fields.
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7.8. PING frame
Endpoints can use PING frames (type=0x07) to verify that their peers
are still alive or to check reachability to the peer. The PING frame
contains no additional fields. The receiver of a PING frame simply
needs to ACK the packet containing this frame. The PING frame SHOULD
be used to keep a connection alive when a stream is open. The
default is to send a PING frame after 15 seconds of quiescence. A
PING frame has no additional fields.
7.9. CONNECTION_CLOSE frame
An endpoint sends a CONNECTION_CLOSE frame (type=0x02) to notify its
peer that the connection is being closed. If there are open streams
that haven't been explicitly closed, they are implicitly closed when
the connection is closed. (Ideally, a GOAWAY frame would be sent
with enough time that all streams are torn down.) 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason Phrase Length (16) | [Reason Phrase (*)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields of a CONNECTION_CLOSE frame are as follows:
o Error Code: A 32-bit error code which indicates the reason for
closing this connection.
o Reason Phrase Length: A 16-bit unsigned number specifying the
length of the reason phrase. This may be zero if the sender
chooses to not give details beyond the Error Code.
o Reason Phrase: An optional human-readable explanation for why the
connection was closed.
7.10. GOAWAY Frame
An endpoint may use a GOAWAY frame (type=0x03) to notify its peer
that the connection should stop being used, and will likely be closed
in the future. The endpoints will continue using any active streams,
but the sender of the GOAWAY will not initiate any additional
streams, and will not accept any new streams. The frame is as
follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Last Good Stream ID (32) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason Phrase Length (16) | [Reason Phrase (*)] ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The fields of a GOAWAY frame are as follows:
o Frame type: An 8-bit value that must be set to 0x03 specifying
that this is a GOAWAY frame.
o Error Code: A 32-bit field error code which indicates the reason
for closing this connection.
o Last Good Stream ID: The last Stream ID which was accepted by the
sender of the GOAWAY message. If no streams were replied to, this
value must be set to 0.
o Reason Phrase Length: A 16-bit unsigned number specifying the
length of the reason phrase. This may be zero if the sender
chooses to not give details beyond the error code.
o Reason Phrase: An optional human-readable explanation for why the
connection was closed.
8. Packetization and Reliability
The maximum packet size for QUIC is the maximum size of the encrypted
payload of the resulting UDP datagram. All QUIC packets SHOULD be
sized to fit within the path's MTU to avoid IP fragmentation. The
recommended default maximum packet size is 1350 bytes for IPv6 and
1370 bytes for IPv4. To optimize better, endpoints MAY use PLPMTUD
[RFC4821] for detecting the path's MTU and setting the maximum packet
size appropriately.
A sender bundles one or more frames in a Regular QUIC packet. A
sender MAY bundle any set of frames in a packet. All QUIC packets
MUST contain a packet number and MAY contain one or more frames
(Section 5.2.2). Packet numbers MUST be unique within a connection
and MUST NOT be reused within the same connection. Packet numbers
MUST be assigned to packets in a strictly monotonically increasing
order. The initial packet number used, at both the client and the
server, MUST be 0. That is, the first packet in both directions of
the connection MUST have a packet number of 0.
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A sender SHOULD minimize per-packet bandwidth and computational costs
by bundling as many frames as possible within a QUIC packet. A
sender MAY wait for a short period of time to bundle multiple frames
before sending a packet that is not maximally packed, to avoid
sending out large numbers of small packets. An implementation may
use heuristics about expected application sending behavior to
determine whether and for how long to wait. This waiting period is
an implementation decision, and an implementation should be careful
to delay conservatively, since any delay is likely to increase
application-visible latency.
Regular QUIC packets are "containers" of frames; a packet is never
retransmitted whole, but frames in a lost packet may be rebundled and
transmitted in a subsequent packet as necessary.
A packet may contain frames and/or application data, only some of
which may require reliability. When a packet is detected as lost,
the sender re-sends any frames as necessary:
o All application data sent in STREAM frames MUST be retransmitted,
with one exception. When an endpoint sends a RST_STREAM frame,
data outstanding on that stream SHOULD NOT be retransmitted, since
subsequent data on this stream is expected to not be delivered by
the receiver.
o ACK, STOP_WAITING, and PADDING frames MUST NOT be retransmitted.
New frames of these types may however be bundled with any outgoing
packet.
o All other frames MUST be retransmitted.
Upon detecting losses, a sender MUST take appropriate congestion
control action. The details of loss detection and congestion control
are described in [QUIC-RECOVERY].
A receiver acknowledges receipt of a received packet by sending one
or more ACK frames containing the packet number of the received
packet. To avoid perpetual acking between endpoints, a receiver MUST
NOT generate an ack in response to every packet containing only ACK
frames. However, since it is possible that an endpoint sends only
packets containing ACK frame (or other non-retransmittable frames),
the receiving peer MAY send an ACK frame after a reasonable number
(currently 20) of such packets have been received.
Strategies and implications of the frequency of generating
acknowledgments are discussed in more detail in [QUIC-RECOVERY].
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9. Streams: QUIC's Data Structuring Abstraction
Streams in QUIC provide a lightweight, ordered, and bidirectional
byte-stream abstraction. Streams can be created either by the client
or the server, can concurrently send data interleaved with other
streams, and can be cancelled. QUIC's stream lifetime is modeled
closely after HTTP/2's [RFC7540]. Streams are independent of each
other in delivery order. That is, data that is received on a stream
is delivered in order within that stream, but there is no particular
delivery order across streams. Transmit ordering among streams is
left to the implementation. QUIC streams are considered lightweight
in that the creation and destruction of streams are expected to have
minimal bandwidth and computational cost. A single STREAM frame may
create, carry data for, and terminate a stream, or a stream may last
the entire duration of a connection. Implementations are therefore
advised to keep these extremes in mind and to implement stream
creation and destruction to be as lightweight as possible.
An alternative view of QUIC streams is as an elastic "message"
abstraction, similar to the way ephemeral streams are used in SST
[SST], which may be a more appealing description for some
applications.
9.1. Life of a Stream
The semantics of QUIC streams is based on HTTP/2 streams, and the
lifecycle of a QUIC stream therefore closely follows that of an
HTTP/2 stream [RFC7540], with some differences to accommodate the
possibility of out-of-order delivery due to the use of multiple
streams in QUIC. The lifecycle of a QUIC stream is shown in the
following figure and described below.
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app +--------+
reserve_stream | |
,--------------| idle |
/ | |
/ +--------+
V |
+----------+ send data/ |
| | recv data | send data/
,---| reserved |------------. | recv data
| | | \ |
| +----------+ v v
| recv FIN/ +--------+ send FIN/
| app read_close | | app write_close
| ,---------| open |-----------.
| / | | \
| v +--------+ v
| +----------+ | +----------+
| | half | | | half |
| | closed | | send RST/ | closed |
| | (remote) | | recv RST | (local) |
| +----------+ | +----------+
| | | |
| | recv FIN/ | send FIN/ |
| | app write_close/ | app read_close/ |
| | send RST/ v send RST/ |
| | recv RST +--------+ recv RST |
| send RST/ `------------->| |<---------------'
| recv RST | closed |
`-------------------------->| |
+--------+
send: endpoint sends this frame
recv: endpoint receives this frame
data: application data in a STREAM frame
FIN: FIN flag in a STREAM frame
RST: RST_STREAM frame
app: application API signals to QUIC
reserve_stream: causes a StreamID to be reserved for later use
read_close: causes stream to be half-closed without receiving a FIN
write_close: causes stream to be half-closed without sending a FIN
Figure 12: Lifecycle of a stream
Note that this diagram shows stream state transitions and the frames
and flags that affect those transitions only. For the purpose of
state transitions, the FIN flag is processed as a separate event to
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the frame that bears it; a STREAM frame with the FIN flag set can
cause two state transitions. When the FIN bit is sent on an empty
STREAM frame, the offset in the STREAM frame MUST be one greater than
the last data byte sent on this stream.
Both endpoints have a subjective view of the state of a stream that
could be different when frames are in transit. Endpoints do not
coordinate the creation of streams; they are created unilaterally by
either endpoint. The negative consequences of a mismatch in states
are limited to the "closed" state after sending RST_STREAM, where
frames might be received for some time after closing.
Streams have the following states:
9.1.1. idle
All streams start in the "idle" state.
The following transitions are valid from this state:
Sending or receiving a STREAM frame causes the stream to become
"open". The stream identifier is selected as described in
Section 9.2. The same STREAM frame can also cause a stream to
immediately become "half-closed".
An application can reserve an idle stream for later use. The stream
state for the reserved stream transitions to "reserved".
Receiving any frame other than STREAM or RST_STREAM on a stream in
this state MUST be treated as a connection error (Section 11) of type
YYYY.
9.1.2. reserved
A stream in this state has been reserved for later use by the
application. In this state only the following transitions are
possible:
o Sending or receiving a STREAM frame causes the stream to become
"open".
o Sending or receiving a RST_STREAM frame causes the stream to
become "closed".
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9.1.3. open
A stream in the "open" state may be used by both peers to send frames
of any type. In this state, a sending peer must observe the flow-
control limit advertised by its receiving peer (Section 10).
From this state, either endpoint can send a frame with the FIN flag
set, which causes the stream to transition into one of the "half-
closed" states. An endpoint sending an FIN flag causes the stream
state to become "half-closed (local)". An endpoint receiving a FIN
flag causes the stream state to become "half-closed (remote)"; the
receiving endpoint MUST NOT process the FIN flag until all preceding
data on the stream has been received.
Either endpoint can send a RST_STREAM frame from this state, causing
it to transition immediately to "closed".
9.1.4. half-closed (local)
A stream that is in the "half-closed (local)" state MUST NOT be used
for sending STREAM frames; WINDOW_UPDATE and RST_STREAM MAY be sent
in this state.
A stream transitions from this state to "closed" when a frame that
contains an FIN flag is received or when either peer sends a
RST_STREAM frame.
An endpoint can receive any type of frame in this state. Providing
flow-control credit using WINDOW_UPDATE frames is necessary to
continue receiving flow-controlled frames. In this state, a receiver
MAY ignore WINDOW_UPDATE frames for this stream, which might arrive
for a short period after a frame bearing the FIN flag is sent.
9.1.5. half-closed (remote)
A stream that is "half-closed (remote)" is no longer being used by
the peer to send any data. In this state, a sender is no longer
obligated to maintain a receiver stream-level flow-control window.
If an endpoint receives any STREAM frames for a stream that is in
this state, it MUST close the connection with a
QUIC_STREAM_DATA_AFTER_TERMINATION error (Section 11).
A stream in this state can be used by the endpoint to send frames of
any type. In this state, the endpoint continues to observe
advertised stream-level and connection-level flow-control limits
(Section 10).
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A stream can transition from this state to "closed" by sending a
frame that contains a FIN flag or when either peer sends a RST_STREAM
frame.
9.1.6. closed
The "closed" state is the terminal state.
A final offset is present in both a frame bearing a FIN flag and in a
RST_STREAM frame. Upon sending either of these frames for a stream,
the endpoint MUST NOT send a STREAM frame carrying data beyond the
final offset.
An endpoint that receives any frame for this stream after receiving
either a FIN flag and all stream data preceding it, or a RST_STREAM
frame, MUST quietly discard the frame, with one exception. If a
STREAM frame carrying data beyond the received final offset is
received, the endpoint MUST close the connection with a
QUIC_STREAM_DATA_AFTER_TERMINATION error (Section 11).
An endpoint that receives a RST_STREAM frame (and which has not sent
a FIN or a RST_STREAM) MUST immediately respond with a RST_STREAM
frame, and MUST NOT send any more data on the stream. This endpoint
may continue receiving frames for the stream on which a RST_STREAM is
received.
If this state is reached as a result of sending a RST_STREAM frame,
the peer that receives the RST_STREAM might have already sent - or
enqueued for sending - frames on the stream that cannot be withdrawn.
An endpoint MUST ignore frames that it receives on closed streams
after it has sent a RST_STREAM frame. An endpoint MAY choose to
limit the period over which it ignores frames and treat frames that
arrive after this time as being in error.
STREAM frames received after sending RST_STREAM are counted toward
the connection and stream flow-control windows. Even though these
frames might be ignored, because they are sent before their sender
receives the RST_STREAM, the sender will consider the frames to count
against its flow-control windows.
In the absence of more specific guidance elsewhere in this document,
implementations SHOULD treat the receipt of a frame that is not
expressly permitted in the description of a state as a connection
error (Section 11). Frames of unknown types are ignored.
(TODO: QUIC_STREAM_NO_ERROR is a special case. Write it up.)
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9.2. Stream Identifiers
Streams are identified by an unsigned 32-bit integer, referred to as
the StreamID. To avoid StreamID collision, clients MUST initiate
streams usinge odd-numbered StreamIDs; streams initiated by the
server MUST use even-numbered StreamIDs.
A StreamID of zero (0x0) is reserved and used for connection-level
flow control frames (Section 10); the StreamID of zero cannot be used
to establish a new stream.
StreamID 1 (0x1) is reserved for the crypto handshake. StreamID 1
MUST NOT be used for application data, and MUST be the first client-
initiated stream.
Streams MUST be created or reserved in sequential order, but MAY be
used in arbitrary order. A QUIC endpoint MUST NOT reuse a StreamID
on a given connection.
9.3. Stream Concurrency
An endpoint can limit the number of concurrently active incoming
streams by setting the MSPC parameter (see Section 6.2.1.2) in the
transport parameters. The maximum concurrent streams setting is
specific to each endpoint and applies only to the peer that receives
the setting. That is, clients specify the maximum number of
concurrent streams the server can initiate, and servers specify the
maximum number of concurrent streams the client can initiate.
Streams that are in the "open" state or in either of the "half-
closed" states count toward the maximum number of streams that an
endpoint is permitted to open. Streams in any of these three states
count toward the limit advertised in the MSPC setting.
Endpoints MUST NOT exceed the limit set by their peer. An endpoint
that receives a STREAM frame that causes its advertised concurrent
stream limit to be exceeded MUST treat this as a stream error of type
QUIC_TOO_MANY_OPEN_STREAMS (Section 11).
9.4. Sending and Receiving Data
Once a stream is created, endpoints may use the stream to send and
receive data. Each endpoint may send a series of STREAM frames
encapsulating data on a stream until the stream is terminated in that
direction. Streams are an ordered byte-stream abstraction, and they
have no other structure within them. STREAM frame boundaries are not
expected to be preserved in retransmissions from the sender or during
delivery to the application at the receiver.
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When new data is to be sent on a stream, a sender MUST set the
encapsulating STREAM frame's offset field to the stream offset of the
first byte of this new data. The first byte of data that is sent on
a stream has the stream offset 0. A receiver MUST ensure that
received stream data is delivered to the application as an ordered
byte-stream. Data received out of order MUST be buffered for later
delivery, as long as it is not in violation of the receiver's flow
control limits.
An endpoint MUST NOT send any stream data without consulting the
congestion controller and the flow controller, with the following two
exceptions.
o The crypto handshake stream, Stream 1, MUST NOT be subject to
congestion control or connection-level flow control, but MUST be
subject to stream-level flow control.
o An application MAY exclude specific stream IDs from connection-
level flow control. If so, these streams MUST NOT be subject to
connection-level flow control.
Flow control is described in detail in Section 10, and congestion
control is described in the companion document [QUIC-RECOVERY].
10. Flow Control
It is necessary to limit the amount of data that a sender may have
outstanding at any time, so as to prevent a fast sender from
overwhelming a slow receiver, or to prevent a malicious sender from
consuming significant resources at a receiver. This section
describes QUIC's flow-control mechanisms.
QUIC employs a credit-based flow-control scheme similar to HTTP/2's
flow control [RFC7540]. A receiver advertises the number of octets
it is prepared to receive on a given stream and for the entire
connection. This leads to two levels of flow control in QUIC: (i)
Connection flow control, which prevents senders from exceeding a
receiver's buffer capacity for the connection, and (ii) Stream flow
control, which prevents a single stream from consuming the entire
receive buffer for a connection.
A receiver sends WINDOW_UPDATE frames to the sender to advertise
additional credit, for both connection and stream flow control. A
receiver advertises the maximum absolute byte offset in the stream or
in the connection which the receiver is willing to receive.
The initial flow control credit is 65536 bytes for both the stream
and connection flow controllers.
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A receiver MAY advertise a larger offset at any point in the
connection by sending a WINDOW_UPDATE frame. A receiver MUST NOT
renege on an advertisement; that is, once a receiver advertises an
offset via a WINDOW_UPDATE frame, it MUST NOT subsequently advertise
a smaller offset. A sender may receive WINDOW_UPDATE frames out of
order; a sender MUST therefore ignore any reductions in flow control
credit.
A sender MUST send BLOCKED frames to indicate it has data to write
but is blocked by lack of connection or stream flow control credit.
BLOCKED frames are expected to be sent infrequently in common cases,
but they are considered useful for debugging and monitoring purposes.
A receiver advertises credit for a stream by sending a WINDOW_UPDATE
frame with the StreamID set appropriately. A receiver may simply use
the current received offset to determine the flow control offset to
be advertised.
Connection flow control is a limit to the total bytes of stream data
sent in STREAM frames. A receiver advertises credit for a connection
by sending a WINDOW_UPDATE frame with the StreamID set to zero
(0x00). A receiver may maintain a cumulative sum of bytes received
cumulatively on all streams to determine the value of the connection
flow control offset to be advertised in WINDOW_UPDATE frames. A
sender may maintain a cumulative sum of stream data bytes sent to
impose the connection flow control limit.
10.1. Edge Cases and Other Considerations
There are some edge cases which must be considered when dealing with
stream and connection level flow control. Given enough time, both
endpoints must agree on flow control state. If one end believes it
can send more than the other end is willing to receive, the
connection will be torn down when too much data arrives. Conversely
if a sender believes it is blocked, while endpoint B expects more
data can be received, then the connection can be in a deadlock, with
the sender waiting for a WINDOW_UPDATE which will never come.
10.1.1. Mid-stream RST_STREAM
On receipt of an RST_STREAM frame, an endpoint will tear down state
for the matching stream and ignore further data arriving on that
stream. This could result in the endpoints getting out of sync,
since the RST_STREAM frame may have arrived out of order and there
may be further bytes in flight. The data sender would have counted
the data against its connection level flow control budget, but a
receiver that has not received these bytes would not know to include
them as well. The receiver must learn of the number of bytes that
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were sent on the stream to make the same adjustment in its connection
flow controller.
To avoid this de-synchronization, a RST_STREAM sender MUST include
the final byte offset sent on the stream in the RST_STREAM frame. On
receiving a RST_STREAM frame, a receiver definitively knows how many
bytes were sent on that stream before the RST_STREAM frame, and the
receiver MUST use the final offset to account for all bytes sent on
the stream in its connection level flow controller.
10.1.2. Response to a RST_STREAM
Since streams are bidirectional, a sender of a RST_STREAM needs to
know how many bytes the peer has sent on the stream. If an endpoint
receives a RST_STREAM frame and has sent neither a FIN nor a
RST_STREAM, it MUST send a RST_STREAM in response, bearing the offset
of the last byte sent on this stream as the final offset.
10.1.3. Offset Increment
This document leaves when and how many bytes to advertise in a
WINDOW_UPDATE to the implementation, but offers a few considerations.
WINDOW_UPDATE frames constitute overhead, and therefore, sending a
WINDOW_UPDATE with small offset increments is undesirable. At the
same time, sending WINDOW_UPDATES with large offset increments
requires the sender to commit to that amount of buffer.
Implementations must find the correct tradeoff between these sides to
determine how large an offset increment to send in a WINDOW_UPDATE.
A receiver MAY use an autotuning mechanism to tune the size of the
offset increment to advertise based on a roundtrip time estimate and
the rate at which the receiving application consumes data, similar to
common TCP implementations.
10.1.4. BLOCKED frames
If a sender does not receive a WINDOW_UPDATE frame when it has run
out of flow control credit, the sender will be blocked and MUST send
a BLOCKED frame. A BLOCKED frame is expected to be useful for
debugging at the receiver. A receiver SHOULD NOT wait for a BLOCKED
frame before sending with a WINDOW_UPDATE, since doing so will cause
at least one roundtrip of quiescence. For smooth operation of the
congestion controller, it is generally considered best to not let the
sender go into quiescence if avoidable. To avoid blocking a sender,
and to reasonably account for the possibiity of loss, a receiver
should send a WINDOW_UPDATE frame at least two roundtrips before it
expects the sender to get blocked.
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11. Error Codes
Error codes are 32 bits long, with the first two bits indicating the
source of the error code:
0x0000-0x3FFF: Application-specific error codes. Defined by each
application-layer protocol.
0x4000-0x7FFF: Reserved for host-local error codes. These codes
MUST NOT be sent to a peer, but MAY be used in API return codes
and logs.
0x8000-0xAFFF: QUIC transport error codes, including packet
protection errors. Applicable to all uses of QUIC.
0xB000-0xFFFF: Cryptographic error codes. Defined by the crypto
handshake protocol in use.
This section lists the defined QUIC transport error codes that may be
used in a CONNECTION_CLOSE or RST_STREAM frame. Error codes share a
common code space. Some error codes apply only to either streams or
the entire connection and have no defined semantics in the other
context.
QUIC_INTERNAL_ERROR (0x8001): Connection has reached an invalid
state.
QUIC_STREAM_DATA_AFTER_TERMINATION (0x8002): There were data frames
after the a fin or reset.
QUIC_INVALID_PACKET_HEADER (0x8003): Control frame is malformed.
QUIC_INVALID_FRAME_DATA (0x8004): Frame data is malformed.
QUIC_MISSING_PAYLOAD (0x8030): The packet contained no payload.
QUIC_INVALID_STREAM_DATA (0x802e): STREAM frame data is malformed.
QUIC_OVERLAPPING_STREAM_DATA (0x8057): STREAM frame data overlaps
with buffered data.
QUIC_UNENCRYPTED_STREAM_DATA (0x803d): Received STREAM frame data is
not encrypted.
QUIC_MAYBE_CORRUPTED_MEMORY (0x8059): Received a frame which is
likely the result of memory corruption.
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QUIC_INVALID_RST_STREAM_DATA (0x8006): RST_STREAM frame data is
malformed.
QUIC_INVALID_CONNECTION_CLOSE_DATA (0x8007): CONNECTION_CLOSE frame
data is malformed.
QUIC_INVALID_GOAWAY_DATA (0x8008): GOAWAY frame data is malformed.
QUIC_INVALID_WINDOW_UPDATE_DATA (0x8039): WINDOW_UPDATE frame data
is malformed.
QUIC_INVALID_BLOCKED_DATA (0x803a): BLOCKED frame data is malformed.
QUIC_INVALID_STOP_WAITING_DATA (0x803c): STOP_WAITING frame data is
malformed.
QUIC_INVALID_PATH_CLOSE_DATA (0x804e): PATH_CLOSE frame data is
malformed.
QUIC_INVALID_ACK_DATA (0x8009): ACK frame data is malformed.
QUIC_INVALID_VERSION_NEGOTIATION_PACKET (0x800a): Version
negotiation packet is malformed.
QUIC_INVALID_PUBLIC_RST_PACKET (0x800b): Public RST packet is
malformed.
QUIC_DECRYPTION_FAILURE (0x800c): There was an error decrypting.
QUIC_ENCRYPTION_FAILURE (0x800d): There was an error encrypting.
QUIC_PACKET_TOO_LARGE (0x800e): The packet exceeded kMaxPacketSize.
QUIC_PEER_GOING_AWAY (0x8010): The peer is going away. May be a
client or server.
QUIC_INVALID_STREAM_ID (0x8011): A stream ID was invalid.
QUIC_INVALID_PRIORITY (0x8031): A priority was invalid.
QUIC_TOO_MANY_OPEN_STREAMS (0x8012): Too many streams already open.
QUIC_TOO_MANY_AVAILABLE_STREAMS (0x804c): The peer created too many
available streams.
QUIC_PUBLIC_RESET (0x8013): Received public reset for this
connection.
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QUIC_INVALID_VERSION (0x8014): Invalid protocol version.
QUIC_INVALID_HEADER_ID (0x8016): The Header ID for a stream was too
far from the previous.
QUIC_INVALID_NEGOTIATED_VALUE (0x8017): Negotiable parameter
received during handshake had invalid value.
QUIC_DECOMPRESSION_FAILURE (0x8018): There was an error
decompressing data.
QUIC_NETWORK_IDLE_TIMEOUT (0x8019): The connection timed out due to
no network activity.
QUIC_HANDSHAKE_TIMEOUT (0x8043): The connection timed out waiting
for the handshake to complete.
QUIC_ERROR_MIGRATING_ADDRESS (0x801a): There was an error
encountered migrating addresses.
QUIC_ERROR_MIGRATING_PORT (0x8056): There was an error encountered
migrating port only.
QUIC_EMPTY_STREAM_FRAME_NO_FIN (0x8032): We received a STREAM_FRAME
with no data and no fin flag set.
QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA (0x803b): The peer received
too much data, violating flow control.
QUIC_FLOW_CONTROL_SENT_TOO_MUCH_DATA (0x803f): The peer sent too
much data, violating flow control.
QUIC_FLOW_CONTROL_INVALID_WINDOW (0x8040): The peer received an
invalid flow control window.
QUIC_CONNECTION_IP_POOLED (0x803e): The connection has been IP
pooled into an existing connection.
QUIC_TOO_MANY_OUTSTANDING_SENT_PACKETS (0x8044): The connection has
too many outstanding sent packets.
QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS (0x8045): The connection
has too many outstanding received packets.
QUIC_CONNECTION_CANCELLED (0x8046): The QUIC connection has been
cancelled.
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QUIC_BAD_PACKET_LOSS_RATE (0x8047): Disabled QUIC because of high
packet loss rate.
QUIC_PUBLIC_RESETS_POST_HANDSHAKE (0x8049): Disabled QUIC because of
too many PUBLIC_RESETs post handshake.
QUIC_TIMEOUTS_WITH_OPEN_STREAMS (0x804a): Disabled QUIC because of
too many timeouts with streams open.
QUIC_TOO_MANY_RTOS (0x8055): QUIC timed out after too many RTOs.
QUIC_ENCRYPTION_LEVEL_INCORRECT (0x802c): A packet was received with
the wrong encryption level (i.e. it should have been encrypted but
was not.)
QUIC_VERSION_NEGOTIATION_MISMATCH (0x8037): This connection involved
a version negotiation which appears to have been tampered with.
QUIC_IP_ADDRESS_CHANGED (0x8050): IP address changed causing
connection close.
QUIC_TOO_MANY_FRAME_GAPS (0x805d): Stream frames arrived too
discontiguously so that stream sequencer buffer maintains too many
gaps.
QUIC_TOO_MANY_SESSIONS_ON_SERVER (0x8060): Connection closed because
server hit max number of sessions allowed.
12. Security and Privacy Considerations
12.1. Spoofed Ack Attack
An attacker receives an STK from the server and then releases the IP
address on which it received the STK. The attacker may, in the
future, spoof this same address (which now presumably addresses a
different endpoint), and initiate a 0-RTT connection with a server on
the victim's behalf. The attacker then spoofs ACK frames to the
server which cause the server to potentially drown the victim in
data.
There are two possible mitigations to this attack. The simplest one
is that a server can unilaterally create a gap in packet-number
space. In the non-attack scenario, the client will send an ack with
a larger largest acked. In the attack scenario, the attacker may ack
a packet in the gap. If the server sees an ack for a packet that was
never sent, the connection can be aborted.
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The second mitigation is that the server can require that acks for
sent packets match the encryption level of the sent packet. This
mitigation is useful if the connection has an ephemeral forward-
secure key that is generated and used for every new connection. If a
packet sent is encrypted with a forward-secure key, then any acks
that are received for them must also be forward-secure encrypted.
Since the attacker will not have the forward secure key, the attacker
will not be able to generate forward-secure encrypted ack packets.
13. IANA Considerations
This document has no IANA actions yet.
14. References
14.1. Normative References
[QUIC-RECOVERY]
Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
and Congestion Control".
[QUIC-TLS]
Thomson, M., Ed. and S. Turner, Ed, Ed., "Using Transport
Layer Security (TLS) to Secure QUIC".
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<http://www.rfc-editor.org/info/rfc4821>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<http://www.rfc-editor.org/info/rfc7540>.
14.2. Informative References
[EARLY-DESIGN]
Roskind, J., "QUIC: Multiplexed Transport Over UDP",
December 2013, <https://goo.gl/dMVtFi>.
[QUIC-HTTP]
Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
QUIC".
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[QUICCrypto]
Langley, A. and W. Chang, "QUIC Crypto", May 2016,
<http://goo.gl/OuVSxa>.
[RFC2360] Scott, G., "Guide for Internet Standards Writers", BCP 22,
RFC 2360, DOI 10.17487/RFC2360, June 1998,
<http://www.rfc-editor.org/info/rfc2360>.
[SST] Ford, B., "Structured Streams: A New Transport
Abstraction", ACM SIGCOMM 2007 , August 2007.
14.3. URIs
[1] https://github.com/quicwg/base-drafts/wiki/QUIC-Versions
Appendix A. Contributors
The original authors of this specification were Ryan Hamilton, Jana
Iyengar, Ian Swett, and Alyssa Wilk.
The original design and rationale behind this protocol draw
significantly from work by Jim Roskind [EARLY-DESIGN]. In
alphabetical order, the contributors to the pre-IETF QUIC project at
Google are: Britt Cyr, Jeremy Dorfman, Ryan Hamilton, Jana Iyengar,
Fedor Kouranov, Charles Krasic, Jo Kulik, Adam Langley, Jim Roskind,
Robbie Shade, Satyam Shekhar, Cherie Shi, Ian Swett, Raman Tenneti,
Victor Vasiliev, Antonio Vicente, Patrik Westin, Alyssa Wilk, Dale
Worley, Fan Yang, Dan Zhang, Daniel Ziegler.
Appendix B. Acknowledgments
Special thanks are due to the following for helping shape pre-IETF
QUIC and its deployment: Chris Bentzel, Misha Efimov, Roberto Peon,
Alistair Riddoch, Siddharth Vijayakrishnan, and Assar Westerlund.
This document has benefited immensely from various private
discussions and public ones on the quic@ietf.org and proto-
quic@chromium.org mailing lists. Our thanks to all.
Appendix C. Change Log
*RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document.
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C.1. Since draft-ietf-quic-transport-00:
o Replaced DIVERSIFICATION_NONCE flag with KEY_PHASE flag
o Defined versioning
o Reworked description of packet and frame layout
o Error code space is divided into regions for each component
C.2. Since draft-hamilton-quic-transport-protocol-01:
o Adopted as base for draft-ietf-quic-tls.
o Updated authors/editors list.
o Added IANA Considerations section.
o Moved Contributors and Acknowledgments to appendices.
Authors' Addresses
Jana Iyengar (editor)
Google
Email: jri@google.com
Martin Thomson (editor)
Mozilla
Email: martin.thomson@gmail.com
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