Internet DRAFT - draft-tsvwg-quic-protocol
draft-tsvwg-quic-protocol
Network Working Group R. Hamilton
Internet-Draft J. Iyengar
Intended status: Informational I. Swett
Expires: July 16, 2016 A. Wilk
Google
January 13, 2016
QUIC: A UDP-Based Secure and Reliable Transport for HTTP/2
draft-tsvwg-quic-protocol-02
Abstract
QUIC (Quick UDP Internet Connection) is a new multiplexed and secure
transport atop UDP, designed from the ground up and optimized for
HTTP/2 semantics. While built with HTTP/2 as the primary application
protocol, QUIC builds on decades of transport and security
experience, and implements mechanisms that make it attractive as a
modern general-purpose transport. QUIC provides multiplexing and
flow control equivalent to HTTP/2, security equivalent to TLS, and
connection semantics, reliability, and congestion control equivalent
to TCP.
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/.
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 16, 2016.
Copyright Notice
Copyright (c) 2016 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
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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. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 3
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
5. A QUIC Overview . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Connection Establishment Latency . . . . . . . . . . . . 5
5.2. Flexible Congestion Control . . . . . . . . . . . . . . . 6
5.3. Stream and Connection Flow Control . . . . . . . . . . . 6
5.4. Multiplexing . . . . . . . . . . . . . . . . . . . . . . 7
5.5. Authenticated and Encrypted Header and Payload . . . . . 7
5.6. Forward Error Correction . . . . . . . . . . . . . . . . 7
5.7. Connection Migration . . . . . . . . . . . . . . . . . . 8
6. Packet Types and Formats . . . . . . . . . . . . . . . . . . 8
6.1. QUIC Public Packet Header . . . . . . . . . . . . . . . . 8
6.2. Special Packets . . . . . . . . . . . . . . . . . . . . . 12
6.2.1. Version Negotiation Packet . . . . . . . . . . . . . 12
6.2.2. Public Reset Packet . . . . . . . . . . . . . . . . . 13
6.3. Regular Packets . . . . . . . . . . . . . . . . . . . . . 13
6.3.1. Frame Packet . . . . . . . . . . . . . . . . . . . . 14
6.3.2. FEC Packet . . . . . . . . . . . . . . . . . . . . . 15
7. Life of a QUIC Connection . . . . . . . . . . . . . . . . . . 15
7.1. Connection Establishment . . . . . . . . . . . . . . . . 15
7.2. Data Transfer . . . . . . . . . . . . . . . . . . . . . . 16
7.2.1. Life of a QUIC Stream . . . . . . . . . . . . . . . . 16
7.3. Connection Termination . . . . . . . . . . . . . . . . . 18
8. Frame Types and Formats . . . . . . . . . . . . . . . . . . . 19
8.1. Frame Types . . . . . . . . . . . . . . . . . . . . . . . 19
8.2. STREAM Frame . . . . . . . . . . . . . . . . . . . . . . 19
8.3. ACK Frame . . . . . . . . . . . . . . . . . . . . . . . . 21
8.3.1. Entropy Accumulation . . . . . . . . . . . . . . . . 25
8.4. STOP_WAITING Frame . . . . . . . . . . . . . . . . . . . 25
8.5. WINDOW_UPDATE Frame . . . . . . . . . . . . . . . . . . . 26
8.6. BLOCKED Frame . . . . . . . . . . . . . . . . . . . . . . 27
8.7. CONGESTION_FEEDBACK Frame . . . . . . . . . . . . . . . . 27
8.8. PADDING Frame . . . . . . . . . . . . . . . . . . . . . . 27
8.9. RST_STREAM Frame . . . . . . . . . . . . . . . . . . . . 27
8.10. PING frame . . . . . . . . . . . . . . . . . . . . . . . 28
8.11. CONNECTION_CLOSE frame . . . . . . . . . . . . . . . . . 28
8.12. GOAWAY Frame . . . . . . . . . . . . . . . . . . . . . . 29
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9. QUIC Transport Parameters . . . . . . . . . . . . . . . . . . 30
9.1. Required Parameters . . . . . . . . . . . . . . . . . . . 30
9.2. Optional Parameters . . . . . . . . . . . . . . . . . . . 30
10. QuicErrorCodes . . . . . . . . . . . . . . . . . . . . . . . 30
11. Priority . . . . . . . . . . . . . . . . . . . . . . . . . . 32
12. HTTP/2 Layering over QUIC . . . . . . . . . . . . . . . . . . 32
12.1. Stream Management . . . . . . . . . . . . . . . . . . . 32
12.2. HTTP/2 Header Compression . . . . . . . . . . . . . . . 33
12.3. Parsing HTTP/2 Headers . . . . . . . . . . . . . . . . . 33
12.4. Persistent Connections . . . . . . . . . . . . . . . . . 33
12.5. QUIC Negotiation in HTTP . . . . . . . . . . . . . . . . 33
13. Handshake Protocol Requirements . . . . . . . . . . . . . . . 34
13.1. Connection Establishment in 0-RTT . . . . . . . . . . . 34
13.2. Source Address Spoofing Defense . . . . . . . . . . . . 34
13.3. Opaque Source Address Tokens . . . . . . . . . . . . . . 34
13.4. Transport Parameter Negotiation . . . . . . . . . . . . 35
13.5. Certificate Compression . . . . . . . . . . . . . . . . 35
13.6. Server Config Update . . . . . . . . . . . . . . . . . . 35
14. Recent Changes By Version . . . . . . . . . . . . . . . . . . 35
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
15.1. Normative References . . . . . . . . . . . . . . . . . . 36
15.2. Informative References . . . . . . . . . . . . . . . . . 36
15.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 37
1. Contributors
This protocol is the outcome of work by many engineers, not just the
authors of this document. The design and rationale behind QUIC draw
significantly from work by Jim Roskind [1]. In alphabetical order,
the contributors to the project are: Britt Cyr, Ryan Hamilton, Jana
Iyengar, Fedor Kouranov, Charles Krasic, Jo Kulik, Adam Langley, Jim
Roskind, Robbie Shade, Satyam Shekhar, Cherie Shi, Ian Swett, Raman
Tenneti, Antonio Vicente, Patrik Westin, Alyssa Wilk, Dale Worley,
Dan Zhang, Daniel Ziegler.
2. Acknowledgments
Special thanks are due to the following for helping shape QUIC and
its deployment: Chris Bentzel, Misha Efimov, Roberto Peon, Alistair
Riddoch, Siddharth Vijayakrishnan, and Assar Westerlund. QUIC has
also benefited immensely from discussions with folks in private
conversations and public ones on the proto-quic@chromium.org mailing
list.
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3. Introduction
QUIC (Quick UDP Internet Connection) is a new multiplexed and secure
transport atop UDP, designed from the ground up and optimized for
HTTP/2 semantics. While built with HTTP/2 as the primary application
protocol, QUIC builds on decades of transport and security
experience, and implements mechanisms that make it attractive as a
modern general-purpose transport. QUIC provides multiplexing and
flow control equivalent to HTTP/2, security equivalent to TLS, and
connection semantics, reliability, and congestion control equivalent
to TCP.
QUIC operates entirely in userspace, and is currently shipped to
users as a part of the Chromium browser, enabling rapid deployment
and experimentation. As a userspace transport atop UDP, QUIC allows
innovations which have proven difficult to deploy with existing
protocols as they are hampered by legacy clients and middleboxes, or
by prolonged Operating System development and deployment cycles.
An important goal for QUIC is to inform better transport design
through rapid experimentation. As a result, we hope to inform and
where possible migrate distilled changes into TCP and TLS, which tend
to have much longer iteration cycles.
This document describes the conceptual design and the wire
specification of the QUIC protocol. Accompanying documents describe
the combined crypto and transport handshake [QUIC-CRYPTO], and loss
recovery and congestion control [draft-quic-loss-recovery].
Additional resources, including a more detailed rationale document,
are available on the Chromium QUIC webpage [2].
4. Conventions and Definitions
All integer values used in QUIC, including length, version, and type,
are in little-endian byte order, and not in network byte order. QUIC
does not enforce alignment of types in dynamically sized frames.
A few terms that are used throughout this document are defined below.
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 bi-directional flow of bytes across a logical channel
within a QUIC connection.
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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.
5. A QUIC Overview
We now briefly describe QUIC's key mechanisms and benefits. QUIC is
functionally equivalent to TCP+TLS+HTTP/2, but implemented on top of
UDP. Key advantages of QUIC over TCP+TLS+HTTP/2 include:
o Connection establishment latency
o Flexible congestion control
o Multiplexing without head-of-line blocking
o Authenticated and encrypted header and payload
o Stream and connection flow control
o Forward error correction
o Connection migration
5.1. Connection Establishment Latency
QUIC combines the crypto and transport handshakes, reducing the
number of roundtrips required for setting up a secure connection.
QUIC connections are commonly 0-RTT, meaning that on most QUIC
connections, data can be sent immediately without waiting for a reply
from the server, as compared to the 1-3 roundtrips required for
TCP+TLS before application data can be sent.
QUIC provides a dedicated stream (Stream ID 1) to be used for
performing the handshake, but the details of this handshake protocol
are out of this document's scope. For a complete description of the
current handshake protocol, please see the QUIC Crypto Handshake
[3]document. QUIC current handshake will be replaced by TLS 1.3 in
the future.
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5.2. Flexible Congestion Control
QUIC has pluggable congestion control and richer signaling than TCP,
which enables QUIC to provide richer information to congestion
control algorithms than TCP. Currently, the default congestion
control is a reimplementation of TCP Cubic; we are currently
experimenting with alternative approaches.
One example of richer information is that each packet, both original
and retransmitted, carries a new packet sequence number. This allows
a QUIC sender to distinguish ACKs for retransmissions from ACKs for
original transmissions, thus avoiding TCP's retransmission ambiguity
problem. QUIC ACKs also explicitly carry 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 roundtrip-time (RTT) calculation.
Finally, QUIC's ACK frames support up to 256 NACK ranges, so QUIC is
more resilient to reordering than TCP (with SACK), as well as able to
keep more bytes on the wire when there is reordering or loss. Both
client and server have a more accurate picture of which packets the
peer has received.
5.3. Stream and Connection Flow Control
QUIC implements stream- and connection-level flow control, closely
following HTTP/2's flow control. QUIC's stream-level flow control
works as follows. A QUIC receiver advertises the absolute byte
offset within each stream upto 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 per-stream flow control, QUIC implements connection-
level flow control to limit the aggregate buffer that a QUIC receiver
is willing to allocate to a connection. Connection flow control
works in the same way as stream flow control, but the bytes delivered
and highest received offset are all aggregates across all streams.
Similar to TCP's receive-window autotuning, QUIC implements
autotuning of flow control credits for both stream and connection
flow controllers. QUIC's autotuning increases the size of the
credits sent per WINDOW_UPDATE frame if it appears to be limiting the
sender's rate, and throttles the sender when the receiving
application is slow.
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5.4. Multiplexing
HTTP/2 on TCP suffers from head-of-line blocking in TCP. Since
HTTP/2 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 HTTP/2 stream that is encapsulated in subsequent segments.
Because QUIC is designed from the ground up for multiplexed
operation, lost packets carrying data for an individual stream
generally only impact that specific stream. Each stream frame can be
immediately dispatched to that stream on arrival, so streams without
loss can continue to be reassembled and make forward progress in the
application.
Caveat: QUIC currently compresses HTTP headers via HTTP/2 HPACK
header compression, which imposes head-of-line blocking for header
frames only.
5.5. Authenticated and Encrypted Header and Payload
TCP headers appear in plaintext on the wire and 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 active attacks, others are
mechanisms used by middleboxes in the network sometimes in an attempt
to transparently improve TCP performance. However, even
"performance-enhancing" middleboxes still effectively limit the
evolvability of the transport protocol, as has been observed in the
design of MPTCP and in its subsequent deployability issues.
QUIC packets are always authenticated and typically the payload is
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. QUIC protects
connections from witting or unwitting middlebox manipulation of end-
to-end communication.
Caveat: PUBLIC_RESET packets that reset a connection are currently
not authenticated.
5.6. Forward Error Correction
In order to recover lost packets without waiting for a
retransmission, QUIC currently employs a simple XOR-based FEC scheme.
An FEC packet contains parity of the packets in the FEC group. If
one of the packets in the group is lost, the contents of that packet
can be recovered from the FEC packet and the remaining packets in the
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group. The sender may decide whether to send FEC packets to optimize
specific scenarios (e.g., beginning and end of a request).
5.7. Connection Migration
TCP connections are identified by a 4-tuple of source address, source
port, destination address and destination port. A well-known problem
with TCP is that connections do not survive IP address changes (for
example, by switching from WiFi to cellular) or port number changes
(when a client's NAT binding expires causing a change in the port
number seen at the server). While MPTCP addresses the connection
migration problem for TCP, it is still plagued by lack of middlebox
support and lack of OS deployment.
QUIC connections are identified by a 64-bit Connection ID, randomly
generated by the client. QUIC can survive IP address changes and NAT
re-bindings since the Connection ID remains the same across these
migrations. QUIC also provides automatic cryptographic verification
of a migrating client, since a migrating client continues to use the
same session key for encrypting and decrypting packets.
6. Packet Types and Formats
QUIC has Special Packets and Regular Packets. There are two types of
Special Packets: Version Negotiation Packets and Public Reset
Packets, and two types of Regular Packets: Frame Packets, and FEC
Packets. All QUIC packets should be sized to fit within the path's
MTU to avoid IP fragmentation. Path MTU discovery is a work in
progress, and the current QUIC implementation uses a 1350-byte
maximum QUIC packet size for IPv6, 1370 for IPv4.
6.1. QUIC Public Packet Header
All QUIC packets on the wire begin with a public header sized between
2 and 19 bytes. The wire format for the public header is as follows:
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0 1 2 3 4 8
+--------+--------+--------+--------+--------+--- ---+
| Public | Connection ID (0, 8, 32, or 64) ... | ->
|Flags(8)| (variable length) |
+--------+--------+--------+--------+--------+--- ---+
9 10 11 12
+--------+--------+--------+--------+
| QUIC Version (32) | ->
| (optional) |
+--------+--------+--------+--------+
13 14 15 16 17 18
+--------+--------+--------+--------+--------+--------+
| Packet Number (8, 16, 32, or 48) |
| (variable length) |
+--------+--------+--------+--------+--------+--------+
The payload may include various type-dependent header bytes as
described below.
The fields in the public header are the following:
o Public Flags:
* 0x01 = PUBLIC_FLAG_VERSION. Interpretation of this flag
depends on whether the packet is sent by the server or the
client. When sent by the client, setting it indicates that the
header contains a QUIC Version (see below). This bit must be
set by a client in all packets until confirmation from the
server arrives agreeing to the proposed version is received by
the client. A server indicates agreement on a version by
sending packets without setting this bit. When this bit is set
by the server, the packet is a Version Negotiation Packet.
Version Negotiation is described in more detail later.
* 0x02 = PUBLIC_FLAG_RESET. Set to indicate that the packet is a
Public Reset packet.
* Two bits at 0x0C indicate the size of the Connection ID that is
present in the packet. These bits must be set to 0x0C in all
packets until negotiated to a different value for a given
direction (e.g., client may request fewer bytes of the
Connection ID be presented).
+ 0x0C indicates an 8-byte Connection ID is present
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+ 0x08 indicates that a 4-byte Connection ID is present
+ 0x04 indicates that a 1-byte Connection ID is used
+ 0x00 indicates that the Connection ID is omitted
* Two bits at 0x30 indicate the number of low-order-bytes of the
packet number that are present in each packet. The bits are
only used for Frame Packets. For Public Reset and Version
Negotiation Packets (sent by the server) which don't have a
packet number, these bits are not used and must be set to 0.
Within this 2 bit mask:
+ 0x30 indicates that 6 bytes of the packet number is present
+ 0x20 indicates that 4 bytes of the packet number is present
+ 0x10 indicates that 2 bytes of the packet number is present
+ 0x00 indicates that 1 byte of the packet number is present
* 0x40 is reserved for multipath use.
* 0x80 is currently unused, and must be set to 0.
o Connection ID: This is an unsigned 64 bit statistically random
number selected by the client that is the identifier of the
connection. Because QUIC connections are designed to remain
established even if the client roams, the IP 4-tuple (source IP,
source port, destination IP, destination port) may be insufficient
to identify the connection. For each transmission direction, when
less uniqueness is sufficient to identify the connection, a
truncated transmitted Connection ID length is negotiable.
o QUIC Version: A 32 bit opaque tag that represents the version of
the QUIC protocol. Only present if the public flags contain
FLAG_VERSION (i.e public_flags & FLAG_VERSION !=0). A client may
set this flag, and include EXACTLY one proposed version, as well
as including arbitrary data (conforming to that 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, but MUST not include any data after the version(s).
Examples of version values in recent experimental versions include
"Q025" which corresponds to byte 9 containing 'Q", byte 10
containing '0", etc. [See list of changes in various versions
listed at the end of this document.]
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o Packet Number: The lower 8, 16, 32, or 48 bits of the packet
number, based on which FLAG_?BYTE_SEQUENCE_NUMBER flag is set in
the public flags. Each Regular Packet (as opposed to the Special
public reset and version negotiation packets) is assigned a packet
number by the sender. The first packet sent by an endpoint shall
have a packet number of 1, and each subsequent packet shall have a
packet number one larger than that of the previous packet. The
lower 64 bits of the packet number is used as part of a
cryptographic nonce; therefore, a QUIC endpoint must not send a
packet with a packet number that cannot be represented in 64 bits.
If a QUIC endpoint transmits a packet with a packet number of
(2^64-1), that packet must include a CONNECTION_CLOSE frame with
an error code of QUIC_SEQUENCE_NUMBER_LIMIT_REACHED, and the
endpoint must not transmit any additional packets. At most the
lower 48 bits of a packet number are transmitted. To enable
unambiguous reconstruction of the packet number by the receiver, a
QUIC endpoint must not transmit a packet whose packet number is
larger by (2^(bitlength-2)) than the largest packet number for
which an acknowledgement is known to have been transmitted by the
receiver. Therefore, there must never be more than (2^46) packets
in flight. Any truncated packet number shall be inferred to have
the value closest to the one more than the largest known packet
number of the endpoint which transmitted the packet that
originally contained the truncated packet number. The transmitted
portion of the packet number matches the lowest bits of the
inferred value.
A Public Flags processing flowchart follows:
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Check the public flags in public 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 Regular Packet with
QUIC Version present in header
6.2. Special Packets
6.2.1. Version Negotiation Packet
A version negotiation packet is only sent by the server. Version
Negotiation packets begin with an 8-bit public flags and 64-bit
Connection ID. The public flags must set PUBLIC_FLAG_VERSION and
indicate the 64-bit Connection ID. The rest of the Version
Negotiation packet is a list of 4-byte versions which the server
supports:
0 1 2 3 4 5 6 7 8
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
| Public | Connection ID (64) | ->
|Flags(8)| |
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
9 10 11 12 13 14 15 16 17
+--------+--------+--------+--------+--------+--------+--------+--------+---...--+
| 1st QUIC version supported | 2nd QUIC version supported | ...
| by server (32) | by server (32) |
+--------+--------+--------+--------+--------+--------+--------+--------+---...--+
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6.2.2. Public Reset Packet
A Public Reset packet begins with an 8-bit public flags and 64-bit
Connection ID. The public flags must set PUBLIC_FLAG_RESET and
indicate the 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 (see [QUIC-CRYPTO]):
0 1 2 3 4 8
+--------+--------+--------+--------+--------+-- --+
| Public | Connection ID (64) ... | ->
|Flags(8)| |
+--------+--------+--------+--------+--------+-- --+
9 10 11 12 13 14
+--------+--------+--------+--------+--------+--------+---
| Quic Tag (32) | Tag value map ... ->
| (PRST) | (variable length)
+--------+--------+--------+--------+--------+--------+---
Tag value map: The tag value map contains the following tag-values:
o RNON (public reset nonce proof) - a 64-bit unsigned integer.
Mandatory.
o RSEQ (rejected packet number) - a 64-bit packet number.
Mandatory.
o CADR (client address) - the observed client IP address and port
number. This is currently for debugging purposes only and hence
is optional.
(TODO: Public Reset packet should include authenticated (destination)
server IP/port.)
6.3. Regular Packets
Regular Packets are authenticated and encrypted. The Public Header
is authenticated but not encrypted, and the rest of the packet
starting with the Private Flags field is encrypted. Immediately
following the Public Header, Regular Packets contain AEAD
(authenticated encryption and associated data) data. This data must
be decrypted in order for the contents to be interpreted. After
decryption, the plaintext starts with a Private Header.
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0 1
+--------+--------+
|Private | FEC (8)|
|Flags(8)| (opt) |
+--------+--------+
The fields in the private header are the following:
o Private Flags:
* 0x01 = FLAG_ENTROPY - for data packets, signifies that this
packet contains the 1 bit of entropy, for fec packets, contains
the xor of the entropy of protected packets.
* 0x02 = FLAG_FEC_GROUP - indicates whether the fec byte is
present.
* 0x04 = FLAG_FEC - signifies that this packet represents an FEC
packet.
o FEC (FEC Group Number Offset): An FEC Group Number is the Packet
Number of the first packet in the FEC group. The FEC Group Number
Offset is an 8 bit unsigned value which should be subtracted from
the current packet's Packet Number to yield the FEC Group Number
for this packet. This is only present if the private flags
contain FLAG_FEC_GROUP. All packets within a single FEC group
must have Packet Numbers encoded into an identical number of bytes
(i.e., the Packet Number coding must not change during a group)
(TODO: Document the inputs to encryption and decryption and describe
trial decryption.)
6.3.1. Frame Packet
Beyond the Private Header, Frame Packets have a payload that is a
series of type-prefixed frames. The format of frame types is defined
later in this document, but the general format of a Frame Packet is
as follows:
+--------+---...---+--------+---...---+
| Type | Payload | Type | Payload |
+--------+---...---+--------+---...---+
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6.3.2. FEC Packet
FEC packets (those packets with FLAG_FEC set) have a payload that
simply contains an XOR of the null-padded payload of each Data Packet
in the FEC group. FEC packets must also have FLAG_FEC_GROUP set.
+-----...----+
| Redundancy |
+-----...----+
7. Life of a QUIC Connection
7.1. Connection Establishment
A QUIC client is the endpoint that initiates a connection. QUIC's
connection establishment intertwines version negotiation with the
crypto and transport handshakes to reduce connection establishment
latency. We first describe version negotiation below.
Each of the initial packets sent from the client to the server must
set the version flag, and must specify the version of the protocol
being used. Every packet sent by the client must have the version
flag on, until it receives a packet from the server with the version
flag off. After the server receives the first packet from the client
with the version flag off, it must ignore any (possibly delayed)
packets with the version flag on.
When the server receives a packet with a Connection ID for a new
connection, it will compare the client's version to the versions it
supports. If the client's version is acceptable to the server, the
server will use this protocol version for the lifetime of the
connection. In this case, all packets sent by the server will have
the version flag off.
If the client's version is not acceptable to the server, a 1-RTT
delay will be incurred. The server will 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.
When the client receives a Version Negotiation Packet from the
server, it will select an acceptable protocol version and resend all
packets using this version. These packet must continue to have the
version flag set and must include the new negotiated protocol
version. Eventually, the client receives the first Regular Packet
(i.e. not a Version Negotiation Packet) from the server indicating
the end of version negotiation, and the client now sends all
subsequent packets with the version flag off.
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In order to avoid downgrade attacks, the version of the protocol that
the client specified in the first packet and the set of versions
supported by the server must be included in the crypto handshake
data. The client needs to verify that the server's version list from
the handshake matches the list of versions in the Version Negotiation
Packet. The server needs to verify that the client's version from
the handshake represents a version of the protocol that it does not
actually support.
The rest of the connection establishment is described in the
handshake document [QUIC-CRYPTO]. The crypto handshake is performed
over the dedicated crypto stream (Stream ID 1).
During connection establishment, the handshake must negotiate various
transport parameters. The currently defined transport parameters are
described later in the document.
7.2. Data Transfer
QUIC implements connection reliability, congestion control, and flow
control. QUIC flow control closely follows HTTP/2's flow control.
QUIC reliability and congestion control are described in an
accompanying document. A QUIC connection uses a single packet
sequence number space for shared congestion control and loss recovery
across the connection.
All data transferred in a QUIC connection, including the crypto
handshake, is sent as data inside streams, but the ACKs acknowledge
QUIC Packets.
This section conceptually describes the use of streams for data
transfer within a QUIC connection. The various frames that are
mentioned in this section are described in the section on Frame Types
and Formats.
7.2.1. Life of a QUIC Stream
Streams are independent sequences of bi-directional data cut into
stream frames. 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]. (HTTP/2's usage of QUIC streams is
described in more detail later in the document.)
Stream creation is done implicitly, by sending a STREAM frame for a
given stream. To avoid stream ID collision, the Stream-ID must be
even if the server initiates the stream, and odd if the client
initiates the stream. 0 is not a valid Stream-ID. Stream 1 is
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reserved for the crypto handshake, which should be the first client-
initiated stream. When using HTTP/2 over QUIC, Stream 3 is reserved
for transmitting compressed headers for all other streams, ensuring
reliable in-order delivery and processing of headers.
Stream-IDs from each side of the connection must increase
monotonically as new streams are created. E.g. Stream 2 may be
created after stream 3, but stream 7 must not be created after stream
9. The peer may receive streams out of order. For example, if a
server receives packet 10 including frames for stream 9 before it
receives packet 9 including frames for stream 7, it should handle
this gracefully.
If the endpoint receiving a STREAM frame does not want to accept the
stream, it can immediately respond with a RST_STREAM frame (described
below). Note, however, that the initiating endpoint may have already
sent data on the stream as well; this data must be ignored.
Once a stream is created, it can be used to send and receive data.
This means that a series of stream frames can be sent by a QUIC
endpoint on a stream until the stream is terminated in that
direction.
Either QUIC endpoint can terminate a stream normally. There are
three ways that streams can be terminated:
1. Normal termination: Since streams are bidirectional, streams can
be "half-closed" or "closed". When one side of the stream sends
a frame with the FIN bit set to true, the stream is considered to
be "half-closed" in that direction. A FIN indicates that no
further data will be sent from the sender of the FIN on this
stream. When a QUIC endpoint has both sent and received a FIN,
the endpoint considers the stream to be "closed". While the FIN
should be sent with the last user data for a stream, the FIN bit
can be sent on an empty stream frame following the last data on
the stream.
2. Abrupt termination: Either the client or server can send a
RST_STREAM frame for a stream at any time. A RST_STREAM frame
contains an error code to indicate the reason for failure (error
codes are listed later in the document.) When a RST_STREAM frame
is sent from the stream originator, it indicates a failure to
complete the stream and that no further data will be sent on the
stream. When a RST_STREAM frame is sent from the stream
receiver, the sender, upon receipt, should stop sending any data
on the stream. The stream receiver should be aware that there is
a race between data already in transit from the sender and the
time the RST_STREAM frame is received. In order to ensure that
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the connection-level flow control is correctly accounted, even if
a RST_STREAM frame is received, a sender needs to ensure that
either: the FIN and all bytes in the stream are received by the
peer or a RST_STREAM frame is received by the peer. This also
means that the sender of a RST_STREAM frame needs to continue
responding to incoming STREAM_FRAMEs on this stream with the
appropriate WINDOW_UPDATEs to ensure that the sender does not get
flow control blocked attempting to delivery the FIN.
3. Streams are also terminated when the connection is terminated, as
described in the next section.
7.3. Connection Termination
Connections should remain open until they become idle for a pre-
negotiated period of time. When a server decides to terminate an
idle connection, it should not notify the client to avoid waking up
the radio on mobile devices. A QUIC connection, once established,
can be terminated in one of two 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 when sent 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.
An endpoint may also send a PUBLIC_RESET packet at any time during
the connection to abruptly terminate an active connection. A
PUBLIC_RESET is the QUIC equivalent of a TCP RST.
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8. Frame Types and Formats
QUIC Frame Packets are populated by frames. which have a Frame Type
byte, which itself has a type-dependent interpretation, followed by
type-dependent frame header fields. All frames are contained within
single QUIC Packets and no frame can span across a QUIC Packet
boundary.
8.1. Frame Types
There are two interpretations for the Frame Type byte, resulting in
two frame types: Special Frame Types, and Regular Frame Types.
Special Frame Types encode both a Frame Type and corresponding flags
all in the Frame Type byte, while Regular Frame Types use the Frame
Type byte simply.
Currently defined Special Frame Types are:
+------------------+-----------------------------+
| Type-field value | Control Frame-type |
+------------------+-----------------------------+
| 1fdooossB | STREAM |
| 01ntllmmB | ACK |
| 001xxxxxB | CONGESTION_FEEDBACK |
+------------------+-----------------------------+
Currently defined Regular Frame Types are:
+------------------+-----------------------------+
| Type-field value | Control Frame-type |
+------------------+-----------------------------+
| 00000000B (0x00) | PADDING |
| 00000001B (0x01) | RST_STREAM |
| 00000010B (0x02) | CONNECTION_CLOSE |
| 00000011B (0x03) | GOAWAY |
| 00000100B (0x04) | WINDOW_UPDATE |
| 00000101B (0x05) | BLOCKED |
| 00000110B (0x06) | STOP_WAITING |
| 00000111B (0x07) | PING |
+------------------+-----------------------------+
8.2. STREAM Frame
The STREAM frame is used to both implicitly create a stream and to
send data on it, and is as follows:
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0 1 ... SLEN
+--------+--------+--------+--------+--------+
|Type (8)| Stream ID (8, 16, 24, or 32 bits) |
| | (Variable length SLEN bytes) |
+--------+--------+--------+--------+--------+
SLEN+1 SLEN+2 ... SLEN+OLEN
+--------+--------+--------+--------+--------+--------+--------+--------+
| Offset (0, 16, 24, 32, 40, 48, 56, or 64 bits) (variable length) |
| (Variable length: OLEN bytes) |
+--------+--------+--------+--------+--------+--------+--------+--------+
SLEN+OLEN+1 SLEN+OLEN+2
+-------------+-------------+
| Data length (0 or 16 bits)|
| Optional(maybe 0 bytes) |
+------------+--------------+
The fields in the STREAM frame header are as follows:
o Frame Type: The Frame Type byte is an 8-bit value containing
various flags (1fdooossB):
* The leftmost bit must be set to 1 indicating that this is a
STREAM frame.
* The 'f' bit is the FIN bit. When set to 1, this bit indicates
the sender is done sending on this stream and wishes to "half-
close" (described in more detail later.)
* which is described in more detail later in this document.
* The 'd' bit indicates whether a Data Length is present in the
STREAM header. When set to 0, this field indicates that the
STREAM frame extends to the end of the Packet.
* The next three 'ooo' bits encode the length of the Offset
header field as 0, 16, 24, 32, 40, 48, 56, or 64 bits long.
* The next two 'ss' bits encode the length of the Stream ID
header field as 8, 16, 24, or 32 bits long.
o Stream ID: A variable-sized unsigned ID unique to this stream.
o Offset: A variable-sized unsigned number specifying the byte
offset in the stream for this block of data.
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o Data length: An optional 16-bit unsigned number specifying the
length of the data in this stream frame. 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.
A stream frame must always have either non-zero data length or the
FIN bit set.
8.3. ACK Frame
The ACK frame is sent to inform the peer which packets have been
received, as well as which packets are still considered missing by
the receiver (the contents of missing packets may need to be resent).
The design of QUIC's ACK frame is different from TCP's and SCTP's
SACK representations in that QUIC ACKs indicate the largest packet
number observed thus far followed by a list of missing packet, or
NACK, ranges indicating gaps in packets received below this packet
number. To limit the NACK ranges to the ones that haven't yet been
communicated to the peer, the peer periodically sends STOP_WAITING
frames that signal the receiver to stop waiting for 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
NACK ranges between the received least unacked and the reported
largest observed packet numbers. The frame is as follows:
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0 1 N
+--------+--------+---------------------------------------------------+
| Type |Received| Largest Observed |
| (8) |Entropy | (8, 16, 32, or 48 bits) |
+--------+--------+---------------------------------------------------+
N+1 N+2 N+3 N+4 N+8
+--------+--------+---------+--------+--------------------------------+
| Ack Delay | Num | Delta | First Timestamp |
| Time (16) |Timestamp|Largest | (32 bits) |
| | (8) |Observed| |
+--------+--------+---------+--------+--------------------------------+
N+9 N+11 - X
+--------+-------------------+
| Delta | Time Since |
|Largest | Previous Timestamp| <-- Repeat (NumTimestamp - 1) times
|Observed| (16 bits) |
+--------+-------------------+
X X+1 - Y Y+1
+--------+-------------------------------------------------+--------+
| Number | Missing Packet Sequence Number Delta | Range |
| Ranges | (8, 16, 32, or 48 bits) | Length |
| (opt) | (repeats Number Ranges times) |(Repeat)|
+--------+-------------------------------------------------+--------+
Y+2 Y+3 - Z
+--------+-----------------------------------------------------+
| Number | Revived Packet Number |
| Revived| (8, 16, 32, or 48 bits, same as Largest Observed) |
| (opt) | (repeats Number Revived times) |
+--------+-----------------------------------------------------+
The fields in the ACK frame are as follows:
o Frame Type: The Frame Type byte is an 8-bit value containing
various flags (01ntllmmB).
* The first two bits must be set to 01 indicating that this is an
ACK frame.
* The 'n' bit indicates whether the frame has any NACK ranges.
* The 't' bit indicates whether the ACK frame has been truncated.
Truncation can happen when the complete ACK frame does not fit
within a single QUIC Packet, or when the number of NACK ranges
exceeds the maximum number of reportable NACK ranges (255).
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When truncated, the ACK frame limits the largest observed
packet number to the largest that can be reported, even though
the receiver may have received packets with packet numbers
larger than the largest observed.
* The two 'll' bits encode the length of the Largest Observed
field as 1, 2, 4, or 6 bytes long.
* The two 'mm' bits encode the length of the Missing Packet
Sequence Number Delta field as 1, 2, 4, or 6 bytes long.
o Received Entropy: An 8 bit unsigned value specifying the
cumulative hash of entropy in all received packets up to the
largest observed packet. Entropy accumulation is described later
in this section.
o Largest Observed: A variable-sized unsigned value representing the
largest packet number the peer has observed. When an ACK frame is
truncated, it indicates a packet number greater than the specified
largest observed has been received, but information about those
additional receptions can't fit into this frame (typically due to
packet size restrictions).
o Ack Delay Time: A 16-bit unsigned float with 11 explicit bits of
mantissa and 5 bits of explicit exponent, specifying the time
elapsed in microseconds from when largest observed was received
until this Ack frame was sent. 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.
o Timestamp Section:
* Num Timestamp: An 8-bit unsigned value specifying the number of
timestamps that are included in this ack frame. There will be
this many pairs of <packet number, timestamp> following in the
timestamps.
* Delta Largest Observed: An 8-bit unsigned value specifying the
packet number delta from the first timestamp to the largest
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observed. Therefore, the packet number is the largest observed
minus the delta largest observed.
* First Timestamp: A 32-bit unsigned value specifying the time
delta in microseconds, from the beginning of the connection of
the arrival of the packet specified by Largest Observed minus
Delta Largest Observed.
* Delta Largest Observed (Repeated): (Same as above.)
* Time Since Previous Timestamp (Repeated): A 16-bit unsigned
value specifying delta from the previous timestamp. It is
encoded in the same format as the Ack Delay Time.
o Missing Packet Section:
* Num Ranges: An optional 8-bit unsigned value specifying the
number of missing packet ranges between largest observed and
least unacked. Only present if the 'n' flag bit is 1.
* Missing Packet Sequence Number Delta: A variable-sized packet
number delta. For the first missing packet range, it is a
delta from the largest observed. For subsequent nack ranges,
it is the number of packets received between ranges. In the
case of the first nack range, a value of 0 specifies that the
packet reported as the largest observed is missing. In the
case of the later nack ranges, a value of 0 indicates the
missing packet ranges are contiguous (used only when more than
256 packets in a row were lost).
* Range Length: An 8-bit unsigned value specifying one less than
the number of sequential nacks in the range.
o Revived Packet Section:
* Num Revived: An 8-bit unsigned value specifying the number of
revived packets, recovered via FEC. Just like the Num Ranges
field, this field is only present if the 'n' flag bit is 1.
* Revived Packet Sequence Number: A variable-sized unsigned value
representing a packet the peer has revived via FEC. Its length
is the same as the length of the Largest Observed field. All
packet numbers in this list are sorted in ascending order
(smallest first) and must also be present in the list of NACK
ranges.
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8.3.1. Entropy Accumulation
The entropy bits for a subset of packets (known to a receiver or
sender) are accumulated into an 8 bit unsigned value, and similarly
presented in both a STOP_WAITING frame and an ACK frame. If we
defined E(k) to be the FLAG_ENTROPY bit present in packet number k,
then the k'th packet's contribution C(k) is defined to be E(k) left
shifted by k mod 8 bits. The accumulated entropy is then the
bitwise-XOR sum of the contributions C(k), for all packets in the
desired subset.
8.4. 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 Public Flags field.) The frame is as follows:
0 1 2 3 4 5 6 7
+--------+--------+--------+--------+--------+--------+-------+-------+
|Type (8)|Sent | Least unacked delta (8, 16, 32, or 48 bits) |
| |Entropy | (variable length) |
+--------+--------+--------+--------+--------+--------+-------+-------+
The fields in the STOP_WAITING frame are as follows:
o 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.
o Sent Entropy: An 8-bit unsigned value specifying the cumulative
hash of entropy in all sent packets up to the packet with packet
number one less than the least unacked packet. [See "Entropy
Accumulation" section in the ACK frame section for details of this
calculation.]
o Least Unacked Delta: A variable length packet number delta with
the same length as the packet header's packet number. In the case
of an FEC revived packet, the same length as the other packets in
the FEC group. Subtract it from the header's packet number to
determine the least unacked. The resulting least unacked is the
smallest packet number of any packet for which the sender is still
awaiting an ack. If the receiver is missing any packets smaller
than this value, the receiver should consider those packets to be
irrecoverably lost.
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8.5. WINDOW_UPDATE Frame
The WINDOW_UPDATE frame is used to inform the peer of an increase in
an endpoint's flow control receive window. The stream ID can be 0,
indicating this WINDOW_UPDATE applies to the connection level flow
control window, or > 0 indicating that the specified stream should
increase its flow control window. The frame is as follows:
An absolute byte offset is specified, and the receiver of a
WINDOW_UPDATE frame may only send up to that number of bytes on the
specified stream. Violating flow control by sending further bytes
will result in the receiving endpoint closing the connection.
On receipt of multiple WINDOW_UPDATE frames for a specific stream ID,
it is only necessary to keep track of the maximum byte offset.
Both stream and session windows start with a default value of 16 KB,
but this is typically increased during the handshake. To do this, an
endpoint should negotiate the SFCW (Stream Flow Control Window) and
CFCW (Connection/Session Flow Control Window) parameters in the
handshake. The value associated with each tag should be the number
of bytes for initial stream window and initial connection window
respectively.
The frame is as follows:
0 1 4 5 12
+--------+--------+-- ... --+-------+--------+-- ... --+-------+
|Type(8) | Stream ID (32 bits) | Byte offset (64 bits) |
+--------+--------+-- ... --+-------+--------+-- ... --+-------+
The fields in the WINDOW_UPDATE frame are as follows:
o 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.
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.
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8.6. BLOCKED Frame
The BLOCKED frame is used to indicate to the remote endpoint that
this endpoint is ready to send data (and has data to send), but is
currently flow control blocked. This is a purely informational
frame, which is 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:
0 1 2 3 4
+--------+--------+--------+--------+--------+
|Type(8) | Stream ID (32 bits) |
+--------+--------+--------+--------+--------+
The fields in the BLOCKED frame are as follows:
o Frame Type: The Frame Type byte is an 8-bit value that must be set
to 0x05 indicating that this is a BLOCKED frame.
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 at the
connection level.
8.7. CONGESTION_FEEDBACK Frame
The CONGESTION_FEEDBACK frame is an experimental frame currently not
used. It is intended to provide extra congestion feedback
information outside the scope of the standard ack frame. A
CONGESTION_FEEDBACK frame must have the first three bits of the Frame
Type set to 001. The last 5 bits of the Frame Type field are
reserved for future use.
8.8. 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.
8.9. RST_STREAM Frame
The RST_STREAM frame allows for abnormal termination of a stream.
When sent by the creator of a stream, it indicates the creator wishes
to cancel the stream. When sent by the receiver of a stream, it
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indicates an error or that the receiver did not want to accept the
stream, so the stream should be closed. The frame is as follows:
0 1 4 5 12 8 16
+-------+--------+-- ... ----+--------+-- ... ------+-------+-- ... ------+
|Type(8)| StreamID (32 bits) | Byte offset (64 bits)| Error code (32 bits)|
+-------+--------+-- ... ----+--------+-- ... ------+-------+-- ... ------+
The fields in a RST_STREAM frame are as follows:
o Frame type: The Frame Type is an 8-bit value that must be set to
0x01 specifying that this is a RST_STREAM frame.
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 for this stream.
o Error code: A 32-bit QuicErrorCode which indicates why the stream
is being closed. QuicErrorCodes are listed later in this
document.
8.10. PING frame
The PING frame can be used by an endpoint to verify that a peer is
still alive. 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 do this after 15 seconds of quiescence,
which is much shorter than most NATs time out. A PING frame only has
a Frame Type field, and must have the 8-bit Frame Type field set to
0x07.
8.11. CONNECTION_CLOSE frame
The CONNECTION_CLOSE frame allows for notification that the
connection is being closed. If there are streams in flight, those
streams are all 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 4 5 6 7
+--------+--------+-- ... -----+--------+--------+--------+----- ...
|Type(8) | Error code (32 bits)| Reason phrase | Reason phrase
| | | length (16 bits)|(variable length)
+--------+--------+-- ... -----+--------+--------+--------+----- ...
The fields of a CONNECTION_CLOSE frame are as follows:
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o Frame Type: An 8-bit value that must be set to 0x02 specifying
that this is a CONNECTION_CLOSE frame.
o Error Code: A 32-bit field containing the QuicErrorCode 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 QuicErrorCode.
o Reason Phrase: An optional human-readable explanation for why the
connection was closed.
8.12. GOAWAY Frame
The GOAWAY frame allows for notification that the connection should
stop being used, and will likely be aborted in the future. 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 streams. The frame is as follows:
0 1 4 5 6 7 8
+--------+--------+-- ... -----+-------+-------+-------+------+
|Type(8) | Error code (32 bits)| Last Good Stream ID (32 bits)| ->
+--------+--------+-- ... -----+-------+-------+-------+------+
9 10 11
+--------+--------+--------+----- ...
| Reason phrase | Reason phrase
| length (16 bits)|(variable length)
+--------+--------+--------+----- ...
The fields of a GOAWAY frame are as follows:
o Frame type: An 8-bit value that must be set to 0x06 specifying
that this is a GOAWAY frame.
o Error Code: A 32-bit field containing the QuicErrorCode 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.
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o Reason Phrase: An optional human-readable explanation for why the
connection was closed.
9. QUIC Transport Parameters
The handshake is responsible for negotiating a variety of transport
parameters for a QUIC connection.
9.1. Required Parameters
o SFCW - Stream Flow Control Window. The size in bytes of the
stream level flow control window.
o CFCW - Connection Flow Control Window. The size in bytes of the
connection level flow control window.
9.2. Optional Parameters
o SRBF - Socket receive buffer size in bytes. The peer may want to
limit their max CWND to something similar to the socket receive
buffer if they fear the peer may sometimes be delayed in reading
packets from kernel's socket buffer. Defaults to 256kbytes and
has a minimum value of 16kbytes.
o TCID - Connection ID truncation. Indicates support for truncated
Connection IDs. If sent by a peer, indicates the connection IDs
sent to the peer should be truncated to 0 bytes. Useful for cases
when a client ephemeral port is only used for a single connection.
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.
10. QuicErrorCodes
The number to code mappings for QuicErrorCodes are currently defined
in the Chromium source code in src/net/quic/quic_protocol.h. (TODO:
hardcode numbers and add them here)
o QUIC_NO_ERROR: There was no error. This is not valid for
RST_STREAM frames or CONNECTION_CLOSE frames
o QUIC_STREAM_DATA_AFTER_TERMINATION: There were data frames after
the a fin or reset.
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o QUIC_SERVER_ERROR_PROCESSING_STREAM: There was some server error
which halted stream processing.
o QUIC_MULTIPLE_TERMINATION_OFFSETS: The sender received two
mismatching fin or reset offsets for a single stream.
o QUIC_BAD_APPLICATION_PAYLOAD: The sender received bad application
data.
o QUIC_INVALID_PACKET_HEADER: The sender received a malformed packet
header.
o QUIC_INVALID_FRAME_DATA: The sender received an frame data. The
more detailed error codes below are prefered where possible.
o QUIC_INVALID_FEC_DATA: FEC data is malformed.
o QUIC_INVALID_RST_STREAM_DATA: Stream rst data is malformed
o QUIC_INVALID_CONNECTION_CLOSE_DATA: Connection close data is
malformed.
o QUIC_INVALID_ACK_DATA: Ack data is malformed.
o QUIC_DECRYPTION_FAILURE: There was an error decrypting.
o QUIC_ENCRYPTION_FAILURE: There was an error encrypting.
o QUIC_PACKET_TOO_LARGE: The packet exceeded MaxPacketSize.
o QUIC_PACKET_FOR_NONEXISTENT_STREAM: Data was sent for a stream
which did not exist.
o QUIC_CLIENT_GOING_AWAY: The client is going away (browser close,
etc.)
o QUIC_SERVER_GOING_AWAY: The server is going away (restart etc.)
o QUIC_INVALID_STREAM_ID: A stream ID was invalid.
o QUIC_TOO_MANY_OPEN_STREAMS: Too many streams already open.
o QUIC_CONNECTION_TIMED_OUT: We hit our pre-negotiated (or default)
timeout
o QUIC_CRYPTO_TAGS_OUT_OF_ORDER: Handshake message contained out of
order tags.
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o QUIC_CRYPTO_TOO_MANY_ENTRIES: Handshake message contained too many
entries.
o QUIC_CRYPTO_INVALID_VALUE_LENGTH: Handshake message contained an
invalid value length.
o QUIC_CRYPTO_MESSAGE_AFTER_HANDSHAKE_COMPLETE: A crypto message was
received after the handshake was complete.
o QUIC_INVALID_CRYPTO_MESSAGE_TYPE: A crypto message was received
with an illegal message tag.
o QUIC_SEQUENCE_NUMBER_LIMIT_REACHED: Transmitting an additional
packet would cause a packet number to be reused.
11. Priority
(TODO: implement)
QUIC will use the HTTP/2 prioritization mechanism. Roughly, a stream
may be dependent on another stream. In this situation, the "parent"
stream should effectively starve the "child" stream. In addition,
parent streams have an explicit priority. Parent streams should not
starve other parent streams, but should make progress proportional to
their relative priority.
12. HTTP/2 Layering over QUIC
Since QUIC integrates various HTTP/2 mechanisms with transport
mechanisms, QUIC implements a number of features that are also
specified in HTTP/2. As a result, QUIC allows HTTP/2 mechanisms to
be replaced by QUIC's implementation, reducing complexity in the
HTTP/2 protocol. This section briefly describes how HTTP/2 semantics
can be offered over a QUIC implementation.
12.1. Stream Management
When HTTP/2 headers and data are sent over QUIC, the QUIC layer
handles most of the stream management. HTTP/2 Stream IDs are
replaced by QUIC Stream IDs. HTTP/2 does not need to do any explicit
stream framing when using QUIC---data sent over a QUIC stream simply
consists of HTTP/2 headers or body. Requests and responses are
considered complete when the QUIC stream is closed in the
corresponding direction.
Stream flow control is handled by QUIC, and does not need to be re-
implemented in HTTP/2. QUIC's flow controller replaces the two
levels of poorly matched flow controllers in current HTTP/2
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deployments---one at the HTTP/2 level, and the other at the TCP
level.
12.2. HTTP/2 Header Compression
QUIC implements HPACK header compression [4] for HTTP/2, which
unfortunately introduces some Head-of-Line blocking since HTTP/2
header blocks must be decompressed in the order they were compressed.
Since streams may be processed in arbitrary order at a receiver,
strict ordering across headers is enforced by sending all headers on
a dedicated headers stream, with Stream ID 3. An HTTP/2 receiver
using QUIC would thus process data from a stream only after receiving
the corresponding header on the headers stream.
Future work will tweak the compressor and decompressor in QUIC so
that the compressed output does not depend on unacked previous
compressed state. This could be done, perhaps, by creating
"checkpoints" of HPACK state which are updated when headers have been
acked. When compressing headers QUIC would only compress relative to
the previous "checkpoint".
12.3. Parsing HTTP/2 Headers
Bytes sent on the dedicated headers stream are simply HTTP/2 HEADERS
frames. The exact layout of these frames is described in RFC 7540
[5].
12.4. Persistent Connections
Unlike when using TCP, the underlying connection for QUIC is
guaranteed to be persistent. The HTTP "Connection" header is
therefore does not apply. For best performance, it is expected that
clients will not close a QUIC connection until the user navigates
away from all web pages using that connection, or until the server
closes the connection.
12.5. QUIC Negotiation in HTTP
The Alternate-Protocol header is used to negotiate use of QUIC on
future HTTP requests. To specify QUIC as an alternate protocol
available on port 123, a server uses:
"Alternate-Protocol: 123:quic"
When a client receives a Alternate-Protocol header advertising QUIC,
it can then attempt to use QUIC for future secure connections on that
domain. Since middleboxes and/or firewalls can block QUIC and/or UDP
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communication, a client should implement a graceful fallback to TCP
when QUIC reachability is broken.
Note that the server may reply with multiple field values or a comma-
separated field value for Alternate-Protocol to indicate the various
transports it supports.
A server can also send a header to notify that QUIC should not be
used on this domain. If it sends the alternate-protocol-required
header, the client should remember to not use QUIC on that domain in
future, and not do any UDP probing to see if QUIC is available.
13. Handshake Protocol Requirements
QUIC provides a dedicated stream (Stream ID 1) to be used for
performing a combined connection and security handshake, but the
details of this handshake protocol are out of this document's scope.
However, QUIC does impose a number of requirements on any such
handshake protocol. The following list of requirements documents
properties of the current prototype handshake which should be
provided by any future handshake protocol.
13.1. Connection Establishment in 0-RTT
The QUIC handshake protocol manages to successfully achieve 0-RTT for
most connections, and is critical to QUIC's latency improvements.
13.2. Source Address Spoofing Defense
TCP verifies the client's address by burning a round trip on the SYN,
SYN_ACK exchange. QUIC uses a source address token delivered by the
server in a previous connection.
13.3. Opaque Source Address Tokens
QUIC servers store a number of pieces of data in the source address
token, for use on a subsequent connection from the same client. This
includes recently used source addresses, measured bandwidth to the
client, and server-designated connection IDs (for Stateless REJs).
An alternative handshake protocol's analog of a source address token
needs to be (i) opaque at the client, and (ii) large enough to permit
these bits of information to be stored. Alternatively, the handshake
protocol should have a different method to store this information at
the client.
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13.4. Transport Parameter Negotiation
In addition to negotiating crypto parameters, the QUIC handshake also
negotiates QUIC and HTTP/2 level parameters, including max open QUIC
streams and other QUIC connection options.
13.5. Certificate Compression
The QUIC handshake compresses certificates so that an REJ, including
the common Google certificate chain, is able to fit into two 1350
byte packets. This helps to reduce the amplification attack
footprint of QUIC without reducing 0-RTT rate.
13.6. Server Config Update
QUIC uses a Server Config Update (SCUP) message to refresh the
source-address token (STK) and server config mid-connection,
extending the period over which 0-RTT connections can be established
by the client.
14. Recent Changes By Version
o Q009: added priority as the first 4 bytes on spdy streams.
o Q010: renumber the various frame types
o Q011: shrunk the fnv128 hash on NULL encrypted packets from 16
bytes to 12 bytes.
o Q012: optimize the ack frame format to reduce the size and better
handle ranges of nacks, which should make truncated acks virtually
impossible. Also adding an explicit flag for truncated acks and
moving the ack outside of the connection close frame.
o Q013: Compressed headers for *all* data streams are serialized
into a reserved stream. This ensures serialized handling of
headers, independent of stream cancellation notification.
o Q014: Added WINDOW_UPDATE and BLOCKED frames, no behavioral
change.
o Q015: Removes the accumulated_number_of_lost_packets field from
the TCP and inter arrival congestion feedback frames and adds an
explicit list of recovered packets to the ack frame.
o Q016: Breaks out the sent_info field from the ACK frame into a new
STOP_WAITING frame.
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o Changed GUID to Connection ID
o Q017: Adds stream level flow control
o Q018: Added a PING frame
o Q019: Adds session/connection level flow control
o Q020: Allow endpoints to set different stream/session flow control
windows
o Q021: Crypto and headers streams are flow controlled (at stream
level)
o Q023: Ack frames include packet timestamps
o Q024: HTTP/2-style header compression
o Q025: HTTP/2-style header keys. Removal of error_details from the
RST_STREAM frame.
o Q026: Token binding, adds expected leaf cert (XLCT) tag to client
hello
o Q027: Adds a nonce to the server hello
o Q029: Server and client honor QUIC_STREAM_NO_ERROR on early
response
.
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key Words for use in RFCs to Indicate
Requirement Levels", March 1997.
15.2. Informative References
[RFC7540] Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
Protocol Version 2 (HTTP/2)", May 2015.
[QUIC-CRYPTO]
Langley, A. and W. Chang, "QUIC Crypto", June 2015.
[QUIC-CC] Iyengar, J. and I. Swett, "QUIC Loss Recovery and
Congestion Control", December 2015.
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15.3. URIs
[1] https://goo.gl/dMVtFi
[2] https://www.chromium.org/quic
[3] http://goo.gl/jOvOQ5
[4] http://http2.github.io/http2-spec/compression.html
[5] https://httpwg.github.io/specs/rfc7540.html#HEADERS
Authors' Addresses
Ryan Hamilton
Google
Email: rch@google.com
Janardhan Iyengar
Google
Email: jri@google.com
Ian Swett
Google
Email: ianswett@google.com
Alyssa Wilk
Google
Email: alyssar@google.com
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