https://github.com/quicwg/base-drafts
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draft-ietf-quic-transport.md
---
title: "QUIC: A UDP-Based Multiplexed and Secure Transport"
abbrev: QUIC Transport Protocol
docname: draft-ietf-quic-transport-latest
date: {DATE}
category: std
ipr: trust200902
area: Transport
workgroup: QUIC
stand_alone: yes
pi: [toc, sortrefs, symrefs, docmapping]
author:
-
ins: J. Iyengar
name: Jana Iyengar
org: Google
email: jri@google.com
role: editor
-
ins: M. Thomson
name: Martin Thomson
org: Mozilla
email: martin.thomson@gmail.com
role: editor
normative:
QUIC-RECOVERY:
title: "QUIC Loss Detection and Congestion Control"
date: {DATE}
author:
-
ins: J. Iyengar
name: Jana Iyengar
org: Google
role: editor
-
ins: I. Swett
name: Ian Swett
org: Google
role: editor
QUIC-TLS:
title: "Using Transport Layer Security (TLS) to Secure QUIC"
date: {DATE}
author:
-
ins: M. Thomson
name: Martin Thomson
org: Mozilla
role: editor
-
ins: S. Turner, Ed.
name: Sean Turner
org: sn3rd
role: editor
informative:
QUIC-HTTP:
title: "Hypertext Transfer Protocol (HTTP) over QUIC"
date: {DATE}
author:
-
ins: M. Bishop
name: Mike Bishop
org: Microsoft
role: editor
SST:
title: "Structured Streams: A New Transport Abstraction"
author:
- ins: B. Ford
date: 2007-08
seriesinfo:
ACM SIGCOMM 2007
QUICCrypto:
title: "QUIC Crypto"
author:
- ins: A. Langley
- ins: W. Chang
date: 2016-05-26
target: "http://goo.gl/OuVSxa"
EARLY-DESIGN:
title: "QUIC: Multiplexed Transport Over UDP"
author:
- ins: J. Roskind
date: 2013-12-02
target: "https://goo.gl/dMVtFi"
--- 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 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.
--- middle
# 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}}.
# 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:
* Client: The endpoint initiating a QUIC connection.
* Server: The endpoint accepting incoming QUIC connections.
* Endpoint: The client or server end of a connection.
* Stream: A logical, bi-directional channel of ordered bytes within
a QUIC connection.
* Connection: A conversation between two QUIC endpoints with a
single encryption context that multiplexes streams within it.
* Connection ID: The identifier for a QUIC connection.
* 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.
# A QUIC Overview
This section briefly describes QUIC's key mechanisms and benefits. Key
strengths of QUIC include:
* Low-latency Version Negotiation
* Low-latency connection establishment
* Multiplexing without head-of-line blocking
* Authenticated and encrypted header and payload
* Rich signaling for congestion control and loss recovery
* Stream and connection flow control
* Connection Migration and Resilience to NAT rebinding
## Low-Latency Version Negotiation
QUIC combines version negotiation with the rest of connection establishment to
avoid unnecessary roundtrip delays. A QUIC client proposes a version to use for
the connection, and encodes the rest of the handshake using the proposed
version. If the server does not speak the client-chosen version, it forces
version negotiation by sending back a Version Negotiation packet to the client,
causing a roundtrip of delay before connection establishment.
This mechanism eliminates roundtrip latency when the client's
optimistically-chosen version is spoken by the server, and incentivizes servers
to not lag behind clients in deployment of newer versions. Additionally, an
application may negotiate QUIC versions out-of-band to increase chances of
success in the first roundtrip and to obviate the additional roundtrip in the
case of version mismatch.
## 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}}.
## 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.
## 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.
## 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.
## 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.
## 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.
# Packet Types and Formats
We first describe QUIC's packet types and their formats, since some are
referenced in subsequent mechanisms. Note that unless otherwise noted, all
values specified in this document are in little-endian format and all field
sizes are in bits.
## Common Header
All QUIC packets begin with a QUIC Common header, as shown below.
~~~
+------------+---------------------------------+
| Flags(8) | Connection ID (64) (optional) |
+------------+---------------------------------+
~~~
The fields in the Common Header are the following:
* 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 XXX.)
* 0x02 = PUBLIC_RESET. Set to indicate that the packet is a Public Reset
packet.
* 0x04 = DIVERSIFICATION_NONCE. Set to indicate the presence of a 32-byte
diversification nonce in the header. (DISCUSS_AND_MODIFY: This flag should
be removed along with the Diversification Nonce bits, as discussed further
below.)
* 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.
* 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.
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
| flag set? |-------->| by server? |--------> Version Negotiation
+------------+ +-------------+ packet
| |
| NO | NO
V V
Regular packet with Regular packet with
no QUIC Version in header QUIC Version in header
~~~
{: #packet-types title="Types of QUIC Packets"}
## Regular Packets
Each Regular packet's header consists of a Common Header followed by fields
specific to Regular packets, as shown below:
~~~
+------------+---------------------------------+
| Flags(8) | Connection ID (64) (optional) | ->
+------------+---------------------------------+
+---------------------------------------+-------------------------------+
| Version (32) (client-only, optional) | Diversification Nonce (256) | ->
+---------------------------------------+-------------------------------+
+------------------------------------+
| Packet Number (8, 16, 32, or 48) | ->
+------------------------------------+
+------------+
| AEAD Data |
+------------+
Decrypted AEAD Data:
+------------+-----------+ +-----------+
| Frame 1 | Frame 2 | ... | Frame N |
+------------+-----------+ +-----------+
~~~
{: #regular-packet-format title="Regular Packet"}
The fields in a Regular packet past the Common Header are the following:
* 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 XXX.
* DISCUSS_AND_REPLACE: Diversification Nonce: A 32-byte nonce generated by the
server and used only in the Server->Client direction to ensure that the server
is able to generate unique keys per connection. Specifically, when using
QUIC's 0-RTT crypto handshake, a repeated CHLO with the exact same connection
ID and CHLO can lead to the same (intermediate) initial-encryption keys being
derived for the connection. A server-generated nonce disallows a client from
causing the same keys to be derived for two distinct connections. Once the
connection is forward-secure, this nonce is no longer present in packets.
This nonce can be removed from the packet header if a requirement can be added
for the crypto handshake to ensure key uniqueness. The expectation is that
TLS1.3 meets this requirement. Upon working group adoption of this document,
this requirement should be added to the crypto handshake requirements, and the
nonce should be removed from the packet format.
* 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.
* AEAD Data: A Regular packet's header, which includes the Common Header, and
the Version, Diversification Nonce, and Packet Number fields, is authenticated
but not encrypted. The rest of a Regular packet, starting with the first
frame, is both authenticated and encrypted. Immediately following the header,
Regular packets contain AEAD (Authenticated Encryption with Associated Data)
data. This data must be decrypted in order for the contents to be
interpreted. After decryption, the plaintext consists of a sequence of
frames, as shown (frames are described in Section XXX).
### 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 XXX.) 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,
* If a sender sets PACKET_NUMBER_SIZE bits to 11, it MUST NOT have more than
(2^46) packets in flight.
* If a sender sets PACKET_NUMBER_SIZE bits to 10, it MUST NOT have more than
(2^30) packets in flight.
* If a sender sets PACKET_NUMBER_SIZE bits to 01, it MUST NOT have more than
(2^14) packets in flight.
* 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?
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.)
### 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 type-dependent headers, and
variable-length data, as follows:
~~~
+-----------+---------------------------+-------------------------+
| Type (8) | Headers (type-dependent) | Data (type-dependent) |
+-----------+---------------------------+-------------------------+
~~~
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.
~~~
+------------------+--------------------+
| Type-field value | Frame type |
+------------------+--------------------+
| 1FDOOOSS | STREAM |
| 01NTLLMM | ACK |
| 00000000 (0x00) | PADDING |
| 00000001 (0x01) | RST_STREAM |
| 00000010 (0x02) | CONNECTION_CLOSE |
| 00000011 (0x03) | GOAWAY |
| 00000100 (0x04) | WINDOW_UPDATE |
| 00000101 (0x05) | BLOCKED |
| 00000110 (0x06) | STOP_WAITING |
| 00000111 (0x07) | PING |
+------------------+--------------------+
~~~
{: #frame-types title="Types of QUIC Frames"}
## 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 rest of the
Version Negotiation packet is a list of 4-byte versions which the server
supports, as shown below.
~~~
+-----------------------------------+
| Flags(8) | Connection ID (64) | ->
+-----------------------------------+
+------------------------------+----------------------------------------+
| 1st Supported Version (32) | 2nd Supported Version (32) supported | ...
+------------------------------+----------------------------------------+
~~~
{: #version-negotiation-format title="Version Negotiation Packet"}
## Public Reset Packet
A Public Reset packet MUST have the PUBLIC_RESET flag set, and MUST include the
full 64-bit connection ID. The rest of the Public Reset packet is encoded as if
it were a crypto handshake message of the tag PRST, as shown below.
~~~
+-----------------------------------+
| Flags(8) | Connection ID (64) | ->
+-----------------------------------+
+-------------------------------------+
| Quic Tag (PRST) and tag value map |
+-------------------------------------+
~~~
{: #public-reset-format title="Public Reset Packet"}
The tag value map contains the following tag-values:
* RNON (public reset nonce proof) - a 64-bit unsigned integer.
* RSEQ (rejected packet number) - a 64-bit packet number.
* CADR (client address) - the observed client IP address and port number. This
is currently for debugging purposes only and hence is optional.
DISCUSS_AND_REPLACE: The crypto handshake message format is described in the
QUIC crypto document, and should be replaced with something simpler when this
document is adopted. The purpose of the tag-value map following the PRST tag is
to enable the receiver of the Public Reset packet to reasonably authenticate the
packet. This map is an extensible map format that allows specification of
various tags, which should again be replaced by something simpler.
# 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 XXX. 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 XXX. Finally a connection may be terminated by either endpoint, as
described in Section XXX.
## 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 XX, 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 for a
connection that has not yet been established, it compares the client's version
to the versions it supports.
* If the client's version is acceptable to the server, the server MUST use this
protocol version for the lifetime of the connection. All subsequent packets
sent by the server MUST have the version flag off.
* If the client's version is not acceptable to the server, the server MUST send
a Version Negotiation packet to the client. This packet will have the VERSION
flag set and will include the server's set of supported versions. On
subsequently received packets for the same connection ID with the unacceptable
version, the server MUST continue responding with a Version Negotiation
packet.
When the client receives a Version Negotiation packet from the server, it should
select an acceptable protocol version. If such a version is found, the client
MUST resend all packets using the new version, and 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 send its version on all packets until it receives a packet from
the server with the VERSION flag off. If version negotiation is successful, the
client should receive a packet from the server with the VERSION flag off
indicating the end of version negotiation. All subsequent packets the client
sends MUST have the version flag off.
Once the server receives a packet from the client with the VERSION flag off, it
MUST ignore the VERSION flag in subsequently received packets.
The Version Negotiation packet is unencrypted and exchanged without
authentication. To avoid a downgrade attack, the client needs to verify its
record of the server's version list in the Version Negotiation packet and the
server needs to verify its record of the client's originally proposed version.
Therefore, the client and server MUST include this information later in their
corresponding crypto handshake data.
## 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 XXX). 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.
### 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 and handed off to the crypto handshake
protocol to be transmitted to the peer.
#### 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.
#### Required Transport Parameters
* SFCW: Stream Flow Control Window. The stream level flow control
byte offset advertised by the sender of this parameter.
* CFCW: Connection Flow Control Window. The connection level flow
control byte offset advertised by the sender of this parameter.
* MSPC: Maximum number of incoming streams per connection.
#### Optional Transport Parameters
* 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.
* 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.)
### 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. 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.)
### 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.
* The crypto handshake MUST ensure that the final negotiated key is distinct for
every connection between two endpoints.
* 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.
* 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.
* Source Address Spoofing Defense: Since QUIC handles source address
verification, the crypto protocol SHOULD NOT impose a separate source address
verification mechanism.
* 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.
* 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.
The following information used during the QUIC handshake MUST be
cryptographically verified by the crypto handshake protocol:
* Client's originally proposed version in its first packet.
* Server's version list in it's Version Negotiation packet, if one was sent.
## 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.
## 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:
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.
# Frame Types and Formats
As described in Section XXX, 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.
## STREAM Frame
STREAM frames implicitly create a stream and carry stream data. A STREAM frame
is shown below.
~~~
+------------+--------------------------------+
| Type (8) | Stream ID (8, 16, 24, or 32) |
+------------+--------------------------------+
+---------------------------------------------+
| Offset (0, 16, 24, 32, 40, 48, 56, or 64) |
+---------------------------------------------+
+-------------------------+---------------------------------+
| Data length (0 or 16) | Stream Data (per data length) |
+-------------------------+---------------------------------+
~~~
The STREAM frame header fields are as follows:
* Frame Type: The Frame Type byte is an 8-bit value containing various flags,
and is formatted as the following 8 bits: 1FDOOOSS.
* The leftmost bit must be set to 1 indicating that this is a STREAM frame.
* 'F' is the FIN bit, which is used for stream termination.
* 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.
* The 'OOO' bits encode the length of the Offset header field as 0, 16, 24,
32, 40, 48, 56, or 64 bits long.
* 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.)
* Stream ID: A variable-sized unsigned ID unique to this stream.
* 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.
* Data Length: An optional 16-bit unsigned number specifying the length of the
Stream Data field in this STREAM frame.
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.
## 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. It is recommended for the sender to
send the most recent largest acked packet it has received in an ack as the
STOP_WAITING frame's least unacked value.
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.
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.
~~~
+--------------------------------------------------------------+
| Type (8) | Largest Acked (8, 16, 32, or 48) | Ack Delay (16) |
+--------------------------------------------------------------+
Ack Block Section:
+-------------------------------------------------------------------------+
| Number Blocks (8) (opt) | First Ack Block Length (8, 16, 32 or 48 bits) |
+-------------------------------------------------------------------------+
+-----------------------------------------------------------------+
| Gap To Next Block (8) | Ack Block Length (8, 16, 32, or 48 bits | <-- optional,
+-----------------------------------------------------------------+ repeats
Timestamp Section:
+--------------------+
| Num Timestamps (8) |
+--------------------+
+---------------------------------------------------------+
| Delta Largest Acked (8) | Time Since Largest Acked (32) | <-- optional
+---------------------------------------------------------+
+---------------------------------------------------------------+
| Delta Largest Acked (8) | Time Since Previous Timestamp (16) | <-- optional,
+---------------------------------------------------------------+ repeats
~~~
The fields in the ACK frame are as follows:
* Frame Type: The Frame Type byte is an 8-bit value containing various flags.
This byte is formatted as the following 8 bits: 01NULLMM.
* The first two bits must be set to 01 indicating that this is an ACK frame.
* The 'N' bit indicates whether the frame has more than 1 ack range.
* The 'U' bit is unused.
* The two 'LL' bits encode the length of the Largest Acked field as 1, 2, 4,
or 6 bytes long.
* The two 'MM' bits encode the length of the Ack Block Length fields as 1, 2,
4, or 6 bytes long.
* 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.)
* 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.
* Ack Block Section:
* 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.
* First Ack Block Length: An unsigned packet number delta that indicates the
number of contiguous additional packets being acked starting at the Largest
Acked.
* 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.
* 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.
* Timestamp Section:
* Num Timestamps: An unsigned 8-bit number specifying the total number of
<packet number, timestamp> pairs following, including the First Timestamp.
* 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.)
* 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 this packet.
* Delta Largest Observed (opt, repeated): (Same as above.)
* Time Since Previous Timestamp (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.
### 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.
## STOP_WAITING Frame
The STOP_WAITING frame 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:
~~~
+---------------------------------------------------+
| Type (8) | Least unacked delta (8, 16, 32, or 48) |
+---------------------------------------------------+
~~~
The fields in the STOP_WAITING frame are as follows:
* Frame Type: The Frame Type byte is an 8-bit value that must be set to 0x06
indicating that this is a STOP_WAITING frame.
* 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 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.
## WINDOW_UPDATE Frame
The WINDOW_UPDATE frame informs the peer of an increase in an endpoint's flow
control receive window. The StreamID 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:
~~~
+---------------------------------------------------+
| Type(8) | Stream ID (32) | Byte offset (64) |
+---------------------------------------------------+
~~~
The fields in the WINDOW_UPDATE frame are as follows:
* Frame Type: The Frame Type byte is an 8-bit value that must be set to 0x04
indicating that this is a WINDOW_UPDATE frame.
* Stream ID: ID of the stream whose flow control windows is being updated, or 0
to specify the connection-level flow control window.
* 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.
## BLOCKED Frame
A sender sends a BLOCKED frame 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:
~~~
+------------------------------+
| Type(8) | Stream ID (32) |
+------------------------------+
~~~
The fields in the BLOCKED frame are as follows:
* Frame Type: The Frame Type byte is an 8-bit value that must be set to 0x05
indicating that this is a BLOCKED frame.
* 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.
## RST_STREAM Frame
An endpoint may use a RST_STREAM frame to abruptly terminate a stream. The
frame is as follows:
~~~
+----------------------------------------------------------------------+
| Type(8) | StreamID (32) | Byte offset (64) | Error code (32) |
+----------------------------------------------------------------------+
~~~
The fields are:
* Frame type: The Frame Type is an 8-bit value that must be set to 0x01
specifying that this is a RST_STREAM frame.
* Stream ID: The 32-bit Stream ID of the stream being terminated.
* 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.
* Error code: A 32-bit error code which indicates why the stream is being
closed.
## PADDING Frame
The PADDING frame 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
only has a Frame Type field, and must have the 8-bit Frame Type field set to
0x00. The PADDING frame is as follows:
~~~
+--------+
| 0x00 |
+--------+
~~~
## PING frame
Endpoints can use PING frames to verify that their peers are still alive or to
check reachability to the peer. The PING frame contains no payload. 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 only has a Frame Type field, and must have the 8-bit Frame Type field set
to 0x07. The PING frame is as follows:
~~~
+--------+
| 0x07 |
+--------+
~~~
## CONNECTION_CLOSE frame
An endpoint sends a CONNECTION_CLOSE frame 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:
~~~
+-----------------------------------------------------------------------+
| Type(8) | Error code (32) | Reason phrase length (16) | Reason phrase |
+-----------------------------------------------------------------------+
~~~
The fields of a CONNECTION_CLOSE frame are as follows:
* Frame Type: An 8-bit value that must be set to 0x02 specifying that this is a
CONNECTION_CLOSE frame.
* Error Code: A 32-bit error code which indicates the reason for closing this
connection.
* 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 QuicErrorCode.
* Reason Phrase: An optional human-readable explanation for why the connection
was closed.
## GOAWAY Frame
An endpoint may use a GOAWAY frame to notify its peer that the connection should
stop being used, and will likely be aborted 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:
~~~
+-----------------------------------------------------------+
| Type (8) | Error code (32) | Last Good Stream ID (32) |
+-----------------------------------------------------------+
+----------------------------------------------+
| Reason phrase length (16) | Reason phrase |
+----------------------------------------------+
~~~
The fields of a GOAWAY frame are as follows:
* Frame type: An 8-bit value that must be set to 0x03 specifying that this is a
GOAWAY frame.
* Error Code: A 32-bit field error code which indicates the reason for closing
this connection.
* 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.
* 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.
* Reason Phrase: An optional human-readable explanation for why the connection
was closed.
# 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 XX). 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.
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 SHOULD only
resend frames that require retransmission.
* 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.
* ACK, STOP_WAITING, and PADDING frames MUST NOT be retransmitted. New frames
of these types may however be bundled with any outgoing packet.
* 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}}.
# 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.
## 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.
~~~
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
~~~
{: #stream-lifecycle title="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 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:
### 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 XX. 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 XX) of type YYYY.
### reserved
A stream in this state has been reserved for later use by the application. In
this state only the following transitions are possible:
* Sending or receiving a STREAM frame causes the stream to become "open".
* Sending or receiving a RST_STREAM frame causes the stream to become "closed".
### 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 XX).
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".
### 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.
### 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 XX).
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 XX).
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.
### 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 XX).
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 XX).
Frames of unknown types are ignored.
(TODO: QUIC_STREAM_NO_ERROR is a special case. Write it up.)
## 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 XX); 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.
## Stream Concurrency
An endpoint can limit the number of concurrently active incoming streams by
setting the MSPC parameter (see Section XX) 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 XX).
## 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.
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.
* 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.
* 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 XX, and congestion control is
described in the companion document {{QUIC-RECOVERY}}.
# 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.
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.
## 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.
### 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 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.
### 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.
### 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.
### 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.
# Error Codes
This section lists all the QUIC error codes that may be used in a
CONNECTION_CLOSE frame. TODO: Trim list and group errors for readabiity.
* 0x01: QUIC_INTERNAL_ERROR. (Connection has reached an invalid state.)
* 0x02: QUIC_STREAM_DATA_AFTER_TERMINATION. (There were data frames after the a
fin or reset.)
* 0x03: QUIC_INVALID_PACKET_HEADER. (Control frame is malformed.)
* 0x04: QUIC_INVALID_FRAME_DATA. (Frame data is malformed.)
* 0x30: QUIC_MISSING_PAYLOAD. (The packet contained no payload.)
* 0x2e: QUIC_INVALID_STREAM_DATA. (STREAM frame data is malformed.)
* 0x57: QUIC_OVERLAPPING_STREAM_DATA. (STREAM frame data overlaps with buffered
data.)
* 0x3d: QUIC_UNENCRYPTED_STREAM_DATA. (Received STREAM frame data is not
encrypted.)
* 0x58: QUIC_ATTEMPT_TO_SEND_UNENCRYPTED_STREAM_DATA. (Attempt to send
unencrypted STREAM frame. Not sent on the wire, used for local logging.)
* 0x59: QUIC_MAYBE_CORRUPTED_MEMORY. (Received a frame which is likely the
result of memory corruption.)
* 0x06: QUIC_INVALID_RST_STREAM_DATA. (RST_STREAM frame data is malformed.)
* 0x07: QUIC_INVALID_CONNECTION_CLOSE_DATA. (CONNECTION_CLOSE frame data is
malformed.)
* 0x08: QUIC_INVALID_GOAWAY_DATA. (GOAWAY frame data is malformed.)
* 0x39: QUIC_INVALID_WINDOW_UPDATE_DATA. (WINDOW_UPDATE frame data is
malformed.)
* 0x3a: QUIC_INVALID_BLOCKED_DATA. (BLOCKED frame data is malformed.)
* 0x3c: QUIC_INVALID_STOP_WAITING_DATA. (STOP_WAITING frame data is malformed.)
* 0x4e: QUIC_INVALID_PATH_CLOSE_DATA. (PATH_CLOSE frame data is malformed.)
* 0x09: QUIC_INVALID_ACK_DATA. (ACK frame data is malformed.)
* 0x0a: QUIC_INVALID_VERSION_NEGOTIATION_PACKET. (Version negotiation packet is
malformed.)
* 0x0b: QUIC_INVALID_PUBLIC_RST_PACKET. (Public RST packet is malformed.)
* 0x0c: QUIC_DECRYPTION_FAILURE. (There was an error decrypting.)
* 0x0d: QUIC_ENCRYPTION_FAILURE. (There was an error encrypting.)
* 0x0e: QUIC_PACKET_TOO_LARGE. (The packet exceeded kMaxPacketSize.)
* 0x10: QUIC_PEER_GOING_AWAY. (The peer is going away. May be a client or
server.)
* 0x11: QUIC_INVALID_STREAM_ID. (A stream ID was invalid.)
* 0x31: QUIC_INVALID_PRIORITY. (A priority was invalid.)
* 0x12: QUIC_TOO_MANY_OPEN_STREAMS. (Too many streams already open.)
* 0x4c: QUIC_TOO_MANY_AVAILABLE_STREAMS. (The peer created too many available
streams.)
* 0x13: QUIC_PUBLIC_RESET. (Received public reset for this connection.)
* 0x14: QUIC_INVALID_VERSION. (Invalid protocol version.)
* 0x16: QUIC_INVALID_HEADER_ID. (The Header ID for a stream was too far from
the previous.)
* 0x17: QUIC_INVALID_NEGOTIATED_VALUE. (Negotiable parameter received during
handshake had invalid value.)
* 0x18: QUIC_DECOMPRESSION_FAILURE. (There was an error decompressing data.)
* 0x19: QUIC_NETWORK_IDLE_TIMEOUT. (The connection timed out due to no network
activity.)
* 0x43: QUIC_HANDSHAKE_TIMEOUT. (The connection timed out waiting for the
handshake to complete.)
* 0x1a: QUIC_ERROR_MIGRATING_ADDRESS. (There was an error encountered migrating
addresses.)
* 0x56: QUIC_ERROR_MIGRATING_PORT. (There was an error encountered migrating
port only.)
* 0x1b: QUIC_PACKET_WRITE_ERROR. (There was an error while writing to the
socket.)
* 0x33: QUIC_PACKET_READ_ERROR. (There was an error while reading from the
socket.)
* 0x32: QUIC_EMPTY_STREAM_FRAME_NO_FIN. (We received a STREAM_FRAME with no
data and no fin flag set.)
* 0x38: QUIC_INVALID_HEADERS_STREAM_DATA. (We received invalid data on the
headers stream.)
* 0x3b: QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA. (The peer received too much
data, violating flow control.)
* 0x3f: QUIC_FLOW_CONTROL_SENT_TOO_MUCH_DATA. (The peer sent too much data,
violating flow control.)
* 0x40: QUIC_FLOW_CONTROL_INVALID_WINDOW. (The peer received an invalid flow
control window.)
* 0x3e: QUIC_CONNECTION_IP_POOLED. (The connection has been IP pooled into an
existing connection.)
* 0x44: QUIC_TOO_MANY_OUTSTANDING_SENT_PACKETS. (The connection has too many
outstanding sent packets.)
* 0x45: QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS. (The connection has too
many outstanding received packets.)
* 0x46: QUIC_CONNECTION_CANCELLED. (The quic connection has been cancelled.)
* 0x47: QUIC_BAD_PACKET_LOSS_RATE. (Disabled QUIC because of high packet loss
rate.)
* 0x49: QUIC_PUBLIC_RESETS_POST_HANDSHAKE. (Disabled QUIC because of too many
PUBLIC_RESETs post handshake.)
* 0x4a: QUIC_TIMEOUTS_WITH_OPEN_STREAMS. (Disabled QUIC because of too many
timeouts with streams open.)
* 0x4b: QUIC_FAILED_TO_SERIALIZE_PACKET. (Closed because we failed to serialize
a packet.)
* 0x55: QUIC_TOO_MANY_RTOS. (QUIC timed out after too many RTOs.) x1c:
QUIC_HANDSHAKE_FAILED. (Crypto errors.Hanshake failed.)
* 0x1d: QUIC_CRYPTO_TAGS_OUT_OF_ORDER. (Handshake message contained out of
order tags.)
* 0x1e: QUIC_CRYPTO_TOO_MANY_ENTRIES. (Handshake message contained too many
entries.)
* 0x1f: QUIC_CRYPTO_INVALID_VALUE_LENGTH. (Handshake message contained an
invalid value length.)
* 0x20: QUIC_CRYPTO_MESSAGE_AFTER_HANDSHAKE_COMPLETE. (A crypto message was
received after the handshake was complete.)
* 0x21: QUIC_INVALID_CRYPTO_MESSAGE_TYPE. (A crypto message was received with
an illegal message tag.)
* 0x22: QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER. (A crypto message was received
with an illegal parameter.)
* 0x34: QUIC_INVALID_CHANNEL_ID_SIGNATURE. (An invalid channel id signature was
supplied.)
* 0x23: QUIC_CRYPTO_MESSAGE_PARAMETER_NOT_FOUND. (A crypto message was received
with a mandatory parameter missing.)
* 0x24: QUIC_CRYPTO_MESSAGE_PARAMETER_NO_OVERLAP. (A crypto message was
received with a parameter that has no overlapwith the local parameter.)
* 0x25: QUIC_CRYPTO_MESSAGE_INDEX_NOT_FOUND. (A crypto message was received
that contained a parameter with too fewvalues.)
* 0x5e: QUIC_UNSUPPORTED_PROOF_DEMAND. (A demand for an unsupport proof type
was received.)
* 0x26: QUIC_CRYPTO_INTERNAL_ERROR. (An internal error occured in crypto
processing.)
* 0x27: QUIC_CRYPTO_VERSION_NOT_SUPPORTED. (A crypto handshake message
specified an unsupported version.)
* 0x48: QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT. (A crypto handshake message
resulted in a stateless reject.)
* 0x28: QUIC_CRYPTO_NO_SUPPORT. (There was no intersection between the crypto
primitives supported by thepeer and ourselves.)
* 0x29: QUIC_CRYPTO_TOO_MANY_REJECTS. (The server rejected our client hello
messages too many times.)
* 0x2a: QUIC_PROOF_INVALID. (The client rejected the server's certificate chain
or signature.)
* 0x2b: QUIC_CRYPTO_DUPLICATE_TAG. (A crypto message was received with a
duplicate tag.)
* 0x2c: QUIC_CRYPTO_ENCRYPTION_LEVEL_INCORRECT. (A crypto message was received
with the wrong encryption level (i.e. itshould have been encrypted but was
not.))
* 0x2d: QUIC_CRYPTO_SERVER_CONFIG_EXPIRED. (The server config for a server has
expired.)
* 0x35: QUIC_CRYPTO_SYMMETRIC_KEY_SETUP_FAILED. (We failed to setup the
symmetric keys for a connection.)
* 0x36: QUIC_CRYPTO_MESSAGE_WHILE_VALIDATING_CLIENT_HELLO. (A handshake message
arrived, but we are still validating theprevious handshake message.)
* 0x41: QUIC_CRYPTO_UPDATE_BEFORE_HANDSHAKE_COMPLETE. (A server config update
arrived before the handshake is complete.)
* 0x5a: QUIC_CRYPTO_CHLO_TOO_LARGE. (CHLO cannot fit in one packet.)
* 0x37: QUIC_VERSION_NEGOTIATION_MISMATCH. (This connection involved a version
negotiation which appears to have beentampered with.)
* 0x50: QUIC_IP_ADDRESS_CHANGED. (IP address changed causing connection close.)
* 0x51: QUIC_CONNECTION_MIGRATION_NO_MIGRATABLE_STREAMS. (Connection migration
errors.Network changed, but connection had no migratable streams.)
* 0x52: QUIC_CONNECTION_MIGRATION_TOO_MANY_CHANGES. (Connection changed
networks too many times.)
* 0x53: QUIC_CONNECTION_MIGRATION_NO_NEW_NETWORK. (Connection migration was
attempted, but there was no new network tomigrate to.)
* 0x54: QUIC_CONNECTION_MIGRATION_NON_MIGRATABLE_STREAM. (Network changed, but
connection had one or more non-migratable streams.)
* 0x5d: QUIC_TOO_MANY_FRAME_GAPS. (Stream frames arrived too discontiguously so
that stream sequencer buffermaintains too many gaps.)
* 0x5f: QUIC_STREAM_SEQUENCER_INVALID_STATE. (Sequencer buffer get into weird
state where continuing read/write will leadto crash.)
* 0x60: QUIC_TOO_MANY_SESSIONS_ON_SERVER. (Connection closed because of server
hits max number of sessions allowed.
# Security and Privacy Considerations
## Spoofed Ack Attack
An attacker receives an STK from the server and then releases the IP address on
which it received the STK. The attacked may in the future, spoof this same
address (which now presumably addresses a different endpoint), and initiates a
0-RTT connection with a server on the victim's behalf. The attacker then spoofs
ack packets 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.
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.
# IANA Considerations
This document has no IANA actions yet.
--- back
# 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.
# 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.
