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Versions: 00 01 draft-ietf-quic-transport

Network Working Group                                        R. Hamilton
Internet-Draft                                                J. Iyengar
Intended status: Informational                                  I. Swett
Expires: January 9, 2017                                         A. Wilk
                                                                  Google
                                                            July 8, 2016


           QUIC: A UDP-Based Multiplexed and Secure Transport
               draft-hamilton-quic-transport-protocol-00

Abstract

   QUIC (Quick UDP-based Internet Connection) 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
   TLS1.3 for key negotiation.

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 January 9, 2017.





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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
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   4
   3.  A QUIC Overview . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Low-Latency Version Negotiation . . . . . . . . . . . . .   5
     3.2.  Low-Latency Connection Establishment  . . . . . . . . . .   5
     3.3.  Stream Multiplexing . . . . . . . . . . . . . . . . . . .   5
     3.4.  Rich Signaling for Congestion Control and Loss Recovery .   5
     3.5.  Stream and Connection Flow Control  . . . . . . . . . . .   6
     3.6.  Authenticated and Encrypted Header and Payload  . . . . .   6
     3.7.  Resilience to NAT Rebinding . . . . . . . . . . . . . . .   6
   4.  Connection Establishment  . . . . . . . . . . . . . . . . . .   7
     4.1.  Version Negotiation . . . . . . . . . . . . . . . . . . .   7
     4.2.  Combined Crypto and Transport Handshake . . . . . . . . .   8
       4.2.1.  Transport Parameters and Options  . . . . . . . . . .   8
       4.2.2.  Proof of Source Address Ownership . . . . . . . . . .   9
       4.2.3.  Crypto Handshake Protocol Features  . . . . . . . . .   9
   5.  Streams: QUIC's Data Structuring Abstraction  . . . . . . . .  10
     5.1.  Life of a Stream  . . . . . . . . . . . . . . . . . . . .  11
       5.1.1.  idle  . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.1.2.  reserved  . . . . . . . . . . . . . . . . . . . . . .  13
       5.1.3.  open  . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.1.4.  half-closed (local) . . . . . . . . . . . . . . . . .  14
       5.1.5.  half-closed (remote)  . . . . . . . . . . . . . . . .  14
       5.1.6.  closed  . . . . . . . . . . . . . . . . . . . . . . .  15
     5.2.  Stream Identifiers  . . . . . . . . . . . . . . . . . . .  15
     5.3.  Stream Concurrency  . . . . . . . . . . . . . . . . . . .  16
     5.4.  Sending and Receiving Data  . . . . . . . . . . . . . . .  16
   6.  Packetization and Reliability . . . . . . . . . . . . . . . .  17
   7.  Flow Control  . . . . . . . . . . . . . . . . . . . . . . . .  18
     7.1.  Important considerations  . . . . . . . . . . . . . . . .  19
       7.1.1.  Mid-stream RST_STREAM . . . . . . . . . . . . . . . .  19



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       7.1.2.  Response to a RST_STREAM  . . . . . . . . . . . . . .  20
       7.1.3.  Offset Increment  . . . . . . . . . . . . . . . . . .  20
       7.1.4.  BLOCKED frames  . . . . . . . . . . . . . . . . . . .  20
   8.  Connection Termination  . . . . . . . . . . . . . . . . . . .  20
   9.  Packet Types and Formats  . . . . . . . . . . . . . . . . . .  21
     9.1.  Public Packet Header  . . . . . . . . . . . . . . . . . .  21
     9.2.  Special Packets . . . . . . . . . . . . . . . . . . . . .  25
       9.2.1.  Version Negotiation Packet  . . . . . . . . . . . . .  25
       9.2.2.  Public Reset Packet . . . . . . . . . . . . . . . . .  25
     9.3.  Regular Packets . . . . . . . . . . . . . . . . . . . . .  26
   10. Frame Types and Formats . . . . . . . . . . . . . . . . . . .  26
     10.1.  Frames . . . . . . . . . . . . . . . . . . . . . . . . .  27
     10.2.  Frame Types  . . . . . . . . . . . . . . . . . . . . . .  27
     10.3.  STREAM Frame . . . . . . . . . . . . . . . . . . . . . .  27
     10.4.  ACK Frame  . . . . . . . . . . . . . . . . . . . . . . .  29
     10.5.  STOP_WAITING Frame . . . . . . . . . . . . . . . . . . .  32
     10.6.  WINDOW_UPDATE Frame  . . . . . . . . . . . . . . . . . .  33
     10.7.  BLOCKED Frame  . . . . . . . . . . . . . . . . . . . . .  34
     10.8.  PADDING Frame  . . . . . . . . . . . . . . . . . . . . .  34
     10.9.  RST_STREAM Frame . . . . . . . . . . . . . . . . . . . .  34
     10.10. PING frame . . . . . . . . . . . . . . . . . . . . . . .  35
     10.11. CONNECTION_CLOSE frame . . . . . . . . . . . . . . . . .  35
     10.12. GOAWAY Frame . . . . . . . . . . . . . . . . . . . . . .  36
   11. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . .  36
   12. Security and Privacy Considerations . . . . . . . . . . . . .  38
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  38
   14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  38
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  39
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  39
     15.2.  Informative References . . . . . . . . . . . . . . . . .  39
     15.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  39

1.  Introduction

   QUIC (Quick UDP-based Internet Connection) 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



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   for connection establishment, stream multiplexing, stream and
   connection-level flow control, and data reliability.  Accompanying
   documents describe QUIC's loss recovery and congestion control
   [draft-iyengar-quic-loss-recovery], and the use of TLS1.3 for key
   negotiation [draft-thomson-quic-tls].

2.  Conventions and Definitions

   Definitions of terms that are used in this document:

   o  "Client": The endpoint initiating a QUIC connection.

   o  "Server": The endpoint accepting incoming QUIC connections.

   o  "Endpoint": The client or server end of a connection.

   o  "Stream": A logical, bi-directional channel of ordered bytes
      within a QUIC connection.

   o  "Connection": A conversation between two QUIC endpoints with a
      single encryption context that multiplexes streams within it.

   o  "Connection ID": The identifier for a QUIC connection.

   o  "QUIC Packet": A well-formed UDP payload that can be parsed by a
      QUIC receiver.  QUIC packet size in this document refers to the
      UDP payload size.

3.  A QUIC Overview

   We now briefly describe QUIC's key mechanisms and benefits.  Key
   strengths of QUIC include:

   o  Low-latency Version Negotiation

   o  Low-latency connection establishment

   o  Multiplexing without head-of-line blocking

   o  Authenticated and encrypted header and payload

   o  Rich signaling for congestion control and loss recovery

   o  Stream and connection flow control

   o  Resilience to NAT rebinding





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3.1.  Low-Latency Version Negotiation

   (TODO: add text here)

3.2.  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.  Theformat 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 [draft-thomson-
   quic-tls].

3.3.  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.

   Because it is designed from the ground up for multiplexed operation,
   QUIC ensures that 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.

3.4.  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, both original and retransmitted, carries a new
   packet number.  This allows a QUIC sender to distinguish ACKs for
   retransmissions from ACKs for original transmissions, thus 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 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



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   reordering or loss.  A QUIC endpoint has an accurate picture of which
   packets the peer has received.

3.5.  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, QUIC's
   stream-level flow control works as follows.  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 per-stream 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
   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.

3.6.  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 active attacks,
   others are mechanisms used by middleboxes to improve TCP performance.
   However, even "performance-enhancing" middleboxes 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.

   Caveat: PUBLIC_RESET packets that reset a connection are currently
   not authenticated.

3.7.  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/or port, such
   as those caused by NAT rebindings.  QUIC also provides automatic
   cryptographic verification of a rebound client, since the client




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   continues to use the same session key for encrypting and decrypting
   packets.

4.  Connection Establishment

   QUIC's connection establishment intertwines version negotiation with
   the crypto and transport handshakes to reduce connection
   establishment latency.  We first describe version negotiation, since
   the subsequent crypto and transport handshakes rely on successful
   version negotiation.

4.1.  Version Negotiation

   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 a 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 MUST compare the client's version to the versions it
   supports.

   o  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.

   o  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.  In this case, a 1-RTT delay
      is incurred before the server can process client data.

   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 packet with the
   version flag off from the server indicating the end of version
   negotiation, and the client now sends all subsequent packets with the
   version flag off.

   In order to avoid downgrade attacks, the client and server must
   include their supported versions in their corresponding crypto
   handshake data.  The client needs to verify that the server's version



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   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.

   During connection establishment, the handshake must negotiate various
   transport parameters.  The currently defined transport parameters are
   described later in the document.

4.2.  Combined 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.  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 a Stream Frame on the crypto stream.

4.2.1.  Transport Parameters and Options

   The transport component of the handshake is responsible for
   exchanging and/or 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.

4.2.1.1.  Encoding

   (TODO: Describe format with example)

   QUIC encodes the transport parameters and options as tag-value pairs,
   all as 7-bit ASCII strings.  QUIC parameter tags are listed below.

4.2.1.2.  Required Transport Parameters

   o  SFCW: Stream Flow Control Window.  The stream level flow control
      byte offset advertised by the sender of this parameter.

   o  CFCW: Connection Flow Control Window.  The connection level flow
      control byte offset advertised by the sender of this parameter.

   o  MSPC: Maximum number of incoming streams per connection.







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4.2.1.3.  Optional Transport Parameters

   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 the
      common case when an ephemeral UDP port is used for a single QUIC
      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.  (TODO:
      List connection options.)

4.2.2.  Proof of Source Address Ownership

   Transport protocols commonly use a roundtrip time to verify a
   client's address ownership for protection from malicious clients that
   spoof their source address.  QUIC uses a cookie, called the Source
   Address Token (STK), to mostly eliminate this roundtrip of delay.
   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.)

4.2.3.  Crypto Handshake Protocol Features

   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 [draft-mthomson-quic-tls].  An application that maps



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   to QUIC MAY however specify an alternative crypto handshake protocol
   to be used.

   The following list of requirements and recommendations documents
   properties of the current prototype handshake which should be
   provided by any handshake protocol.

   o  Transport Negotiation: The crypto handshake MUST provide a
      mechanism for the transport component to exchange transport
      parameters and Source Address Tokens.

   o  Connection Establishment in 0-RTT: Since low-latency connection
      establishment is a critical feature of QUIC, the QUIC handshake
      protocol SHOULD attempt to achieve 0-RTT connection establishment
      latency for repeated connections between the same endpoints.

   o  Source Address Spoofing Defense: Since QUIC handles source address
      verification, the crypto protocol SHOULD NOT impose a separate
      source address verification mechanism.

   o  Server Config Update: A QUIC server may refresh the source-address
      token (STK) mid-connection, to update the information stored in
      the STK at the client and to extend the period over which 0-RTT
      connections can be established by the client.  A crypto protocol

   o  Certificate Compression: Early QUIC experience demonstrated that
      compressing certificates exchanged during a handshake is valuable
      in reducing latency.  This additionally helps to reduce the
      amplification attack footprint when a server sends a large set of
      certificates, which is not uncommon with TLS.  The crypto protocol
      SHOULD compress certificates and any other information to minimize
      the number of packets sent during a handshake.

5.  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. (TODO: Perhaps define HTTP/2-like
   priority scheme, including a PRIORITY frame for QUIC stream
   priorities.)  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,



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   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
   [cite SST], which may be a more appealing description for some
   applications.

5.1.  Life of a Stream

   The semantics of QUIC streams is based on HTTP/2 streams, and the
   lifecycle of a QUIC stream therefore closely follows that of an
   HTTP/2 stream [RFC7540], with some differences to accommodate the
   possibility of out-of-order delivery in QUIC.  The lifecycle of a
   QUIC stream is shown in the following figure and described below.


































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                        app     +--------+
                 reserve_stream |        |
                 ,--------------|  idle  |
                /               |        |
               /                +--------+
              V                      |
        +----------+ send data/      |
        |          | recv data       | send data/
    ,---| reserved |------------.    | recv data
    |   |          |             \   |
    |   +----------+              v  v
    |               recv FIN/   +--------+ send FIN/
    |            app read_close |        | app write_close
    |                 ,---------|  open  |-----------.
    |                /          |        |            \
    |               v           +--------+             v
    |        +----------+            |             +----------+
    |        |   half   |            |             |   half   |
    |        |  closed  |            | send RST/   |  closed  |
    |        | (remote) |            | recv RST    | (local)  |
    |        +----------+            |             +----------+
    |            |                   |                    |
    |            | recv FIN/         |          send FIN/ |
    |            | app write_close/  |    app read_close/ |
    |            | send RST/         v          send RST/ |
    |            | recv RST     +--------+      recv RST  |
    | send RST/  `------------->|        |<---------------'
    | recv RST                  | closed |
    `-------------------------->|        |
                                +--------+

       send:   endpoint sends this frame
       recv:   endpoint receives this frame

       data: application data in a STREAM frame
       FIN: FIN flag in a STREAM frame
       RST: RST_STREAM frame

       app: application API signals to QUIC
       reserve_stream: causes a StreamID to be reserved for later use
       read_close: causes stream to be half-closed without receiving a FIN
       write_close: causes stream to be half-closed without sending a FIN

   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



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   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:

5.1.1.  idle

   All streams start in the "idle" state.

   The following transitions are valid from this state:

   Sending or receiving a STREAM frame causes the stream to become
   "open".  The stream identifier is selected as described in
   Section 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.

5.1.2.  reserved

   A stream in this state has been reserved for later use by the
   application.  In this state only the following transitions are
   possible:

   o  Sending or receiving a STREAM frame causes the stream to become
      "open".

   o  Sending or receiving a RST_STREAM frame causes the stream to
      become "closed".

5.1.3.  open

   A stream in the "open" state may be used by both peers to send frames
   of any type.  In this state, a sending peer must observe the flow-
   control limit advertised by its receiving peer (Section XX).




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   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".

5.1.4.  half-closed (local)

   A stream that is in the "half-closed (local)" state MUST NOT be used
   for sending STREAM frames; WINDOW_UPDATE and RST_STREAM MAY be sent
   in this state.

   A stream transitions from this state to "closed" when a frame that
   contains an FIN flag is received or when either peer sends a
   RST_STREAM frame.

   An endpoint can receive any type of frame in this state.  Providing
   flow-control credit using WINDOW_UPDATE frames is necessary to
   continue receiving flow-controlled frames.  In this state, a receiver
   MAY ignore WINDOW_UPDATE frames for this stream, which might arrive
   for a short period after a frame bearing the FIN flag is sent.

5.1.5.  half-closed (remote)

   A stream that is "half-closed (remote)" is no longer being used by
   the peer to send any data.  In this state, a sender is no longer
   obligated to maintain a receiver stream-level flow-control window.

   If an endpoint receives any STREAM frames for a stream that is in
   this state, it MUST close the connection with a
   QUIC_STREAM_DATA_AFTER_TERMINATION error (Section 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.






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5.1.6.  closed

   The "closed" state is the terminal state.

   A final offset is present in both a frame bearing a FIN flag and in a
   RST_STREAM frame.  Upon sending either of these frames for a stream,
   the endpoint MUST NOT send a STREAM frame carrying data beyond the
   final offset.

   An endpoint that receives any frame for this stream after receiving
   either a FIN flag and all stream data preceding it, or a RST_STREAM
   frame, MUST quietly discard the frame, with one exception.  If a
   STREAM frame carrying data beyond the received final offset is
   received, the endpoint MUST close the connection with a
   QUIC_STREAM_DATA_AFTER_TERMINATION error (Section 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.)

5.2.  Stream Identifiers

   Streams are identified by an unsigned 32-bit integer, referred to as
   the StreamID.  To avoid StreamID collision, clients MUST initiate




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   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 MAY be created in arbitrary order.  A QUIC endpoint MUST NOT
   reuse a StreamID on a given connection.

5.3.  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).

5.4.  Sending and Receiving Data

   Once a stream is created, endpoints may use the stream to send and
   receive data.  Each endpoint may send a series of STREAM frames
   encapsulating data on a stream until the stream is terminated in that
   direction.  Streams are an ordered byte-stream abstraction, and they
   have no other structure within them.  STREAM frame boundaries are not
   expected to be preserved in retransmissions from the sender or during
   delivery to the application at the receiver.

   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.  A receiver MUST ensure that received
   stream data is delivered to the application as an ordered byte-



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   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 windows, with one exception in the
   case of connection-level flow control, as described in Section XX.
   The congestion controller is described in the companion document
   [draft-loss-recovery].

6.  Packetization and Reliability

   The maximum packet size for QUIC is the maximum size of the encrypted
   payload of the resulting UDP datagram.  A default maximum packet size
   of 1350 bytes is recommended.  Endpoints SHOULD use PLPMTUD [RFC4821]
   for detecting the path's MTU and setting the maximum packet size
   appropriately.

   A sender bundles one or more frames to send in a Regular QUIC Packet.
   A sender MAY bundle any set of frames in a packet.  All QUIC Packets
   MUST contain a Packet Sequence Number (PSN) and MAY contain one or
   more frames (Section XX).  PSNs MUST be unique within a connection
   and MUST NOT be reused within the same connection.  PSNs MUST be
   assigned to packets in a strictly monotonically increasing order.

   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.

   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 rebundle frames and application data that
   require retransmission.

   o  All application data sent in STREAM frames MUST be retransmitted,
      with one exception.  When an endpoint sends a RST_STREAM frame,
      data outstanding on that stream SHOULD NOT be retransmitted, since
      subsequent data on this stream is expected to not be delivered by
      the receiver.






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   o  ACK, STOP_WAITING, and PADDING frames MUST NOT be retransmitted.
      New frames of these types may however be bundled with any outgoing
      packet.

   o  All other frames MUST be retransmitted.

   Upon detecting losses, a sender MUST take appropriate congestion
   control action.  The details of loss detection and congestion control
   are described in [draft-loss-recovery].

   A receiver acknowledges receipt of a received packet by sending one
   or more ACK frames containing the PSN 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 (TODO: Describe acking acks.)  Strategies and implications of
   the frequency of generating acknowledgments are discussed in more
   detail in [draft-loss-recovery].

7.  Flow Control

   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 advertisesadvertise 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.



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   BLOCKED frames are expected to be sent infrequently in common cases,
   but they MAY be 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.

7.1.  Important 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.

7.1.1.  Mid-stream RST_STREAM

   On receipt of an RST_STREAM frame, an endpoint will tear down state
   for the matching stream and ignore further data arriving on that
   stream.  This could result in the endpoints getting out of sync,
   since the RST_STREAM frame may have arrived out of order and there
   may be further bytes in flight.  The data sender would have counted
   the data against its connection level flow control budget, but a
   receiver that has not received these bytes would not know to include
   them as well.  The receiver must learn of the number of bytes that
   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.




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7.1.2.  Response to a RST_STREAM

   Since streams are bidirectional, a sender of a RST_STREAM needs to
   know how many bytes the peer has sent on the stream.  If an endpoint
   receives a RST_STREAM frame and has sent neither a FIN nor a
   RST_STREAM, it MUST send a RST_STREAM in response, bearing the offset
   of the last byte sent on this stream as the final offset.

7.1.3.  Offset Increment

   This document leaves when and how many bytes to advertise in a
   WINDOW_UPDATE to the implementation, but offers a few considerations.
   WINDOW_UPDATE frames constitute overhead, and therefore, sending a
   WINDOW_UPDATE with small offset increments is undesirable.  At the
   same time, sending WINDOW_UPDATES with large offset increments
   requires the sender to commit to that amount of buffer.
   Implementations must find the correct tradeoff between these sides to
   determine how large an offset increment to send in a WINDOW_UPDATE.

   A receiver MAY use an autotuning mechanism to tune the size of the
   offset increment to advertise based on a roundtrip time estimate and
   the rate at which the receiving application consumes data, similar to
   common TCP implementations.

7.1.4.  BLOCKED frames

   If a sender does not receive a WINDOW_UPDATE frame when it has run
   out of flow control credit, the sender will be blocked and may send a
   BLOCKED frame.  A receiver should not wait for a BLOCKED frame before
   responding with a WINDOW_UPDATE, since doing so will cause at least
   one roundtrip of quiescence.  Further, if blocked, a sender will go
   into quiescence, which may result in poor performance of the
   congestion controller.  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
   reasonably accounting for the possibiity of loss, a receiver should
   send a WINDOW_UPDATE frame at least two roundtrip times before the
   sender gets blocked.

8.  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 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



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       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.

   An endpoint may also send a PUBLIC_RESET packet at any time during
   the connection to abruptly terminate an active connection.

9.  Packet Types and Formats

   QUIC has two types of packets: Regular Packets containing frames, and
   Special Packets.  There are two types of Special Packets: Version
   Negotiation Packets and Public Reset 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.  Both sizes are without IP and UDP overhead.

9.1.  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       5            8
+--------+--------+--------+--------+--------+--------+---    ---+
|Flags(8)|  Connection ID (64) (optional)   ...     | ->
+--------+--------+--------+--------+--------+--------+--    ---+

     9       10       11        12
+--------+--------+--------+--------+
|      QUIC Version (32)            | ->
|         (optional)                |
+--------+--------+--------+--------+


    13       14       15        16      17       18       19       20
+--------+--------+--------+--------+--------+--------+--------+--------+
|                        Diversification Nonce                          | ->
|                              (optional)                               |
+--------+--------+--------+--------+--------+--------+--------+--------+

    21       22       23        24      25       26       27       28
+--------+--------+--------+--------+--------+--------+--------+--------+
|                   Diversification Nonce Continued                     | ->
|                              (optional)                               |
+--------+--------+--------+--------+--------+--------+--------+--------+

    29       30       31        32      33       34       35       36
+--------+--------+--------+--------+--------+--------+--------+--------+
|                   Diversification Nonce Continued                     | ->
|                              (optional)                               |
+--------+--------+--------+--------+--------+--------+--------+--------+

    37       38       39        40      41       42       43       44
+--------+--------+--------+--------+--------+--------+--------+--------+
|                   Diversification Nonce Continued                     | ->
|                              (optional)                               |
+--------+--------+--------+--------+--------+--------+--------+--------+


    45      46       47        48       49       50
+--------+--------+--------+--------+--------+--------+
|           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:



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   o  Flags:

      *  0x01 = FLAG_VERSION.  The semantics of this flag depends on
         whether the packet is sent by the server or the client.  A
         client sets this flag to indicate that the header contains a
         QUIC version (see below).  A client MUST set this bit in all
         packets until confirmation from the server arrives agreeing to
         the proposed version.  A server indicates agreement on a
         version by sending packets without setting this bit.  When the
         server sets this bit, the packet is a Version Negotiation
         Packet.  Version Negotiation is described in more detail later.

      *  0x02 = FLAG_PUBLIC_RESET.  Set to indicate that the packet is a
         Public Reset packet.

      *  0x04 = Indicates the presence of a 32 byte diversification
         nonce in the header.

      *  0x08 = 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 (e.g., client indicates the 5-tuple
         fully identifies the connection, so connection is is optional).

      *  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



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      the 4-tuple is sufficient to identify the connection, the
      connection ID may be omitted.

   o  QUIC Version: A 32 bit opaque tag that represents the version of
      the QUIC protocol.  Only present if the flags contain FLAG_VERSION
      (i.e 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.]

   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 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 received from a peer shall be inferred
      to have the value closest to the one more than the largest known
      packet number received from that peer.  The transmitted portion of
      the packet number matches the lowest bits of the inferred value.

   A Flags processing flowchart follows:









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Check the 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

9.2.  Special Packets

9.2.1.  Version Negotiation Packet

   A Version Negotiation packet is only sent by the server.  Version
   Negotiation packets begin with an 8-bit flags and 64-bit Connection
   ID.  The flags must set 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
+--------+--------+--------+--------+--------+--------+--------+--------+--------+
|Flags(8)|    Connection ID (64)                                                 | ->
+--------+--------+--------+--------+--------+--------+--------+--------+--------+

     9       10       11        12       13      14       15       16       17
+--------+--------+--------+--------+--------+--------+--------+--------+---...--+
|      1st QUIC version supported   |     2nd QUIC version supported    |   ...
|      by server (32)               |     by server (32)                |
+--------+--------+--------+--------+--------+--------+--------+--------+---...--+


9.2.2.  Public Reset Packet

   A Public Reset packet begins with an 8-bit flags and 64-bit
   Connection ID.  The PUBLIC_FLAG_RESET flag MUST be set and the header
   MUST indicate the entire 64-bit Connection ID.  The rest of the



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   Public Reset packet is encoded as if it were a crypto handshake
   message of the tag PRST ():

        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.

9.3.  Regular Packets

   Each Regular Packet consists of a Public Header followed by a series
   of data frames.  The Public Header is authenticated but not
   encrypted, and the rest of the packet starting with the first frame
   both authenticated and 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 consists
   of a sequence of frames, as described in the following section.

   (TODO: Document the inputs to encryption and decryption and describe
   trial decryption.)

10.  Frame Types and Formats

   A single Regular Packet 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 header fields,
   and variable-length data.



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10.1.  Frames

   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 |
   +--------+---...---+--------+---...---+

10.2.  Frame Types

   There are two types of Frames: 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                        |
      +------------------+-----------------------------+

   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                       |
      +------------------+-----------------------------+

10.3.  STREAM Frame

   STREAM frames implicitly create a stream and carry stream data.  A
   STREAM frame is shown below.






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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 STREAM frame header fields 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.  The first byte in
      the stream has an offset of 0.




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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 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.

10.4.  ACK Frame

   Receivers send ACK frames to inform senders which packets they have
   received, as well as which packets it still considers missing.  The
   ack frame contains between 1 and 256 ack blocks.  Ack blocks are
   ranges of acknowledged packets, similar to TCP's SACK blocks, but
   QUIC has no equivalent of TCP's cumulative ack point, because packets
   are retransmitted with new sequence numbers.

   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



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   format of the ACK frame is efficient at expressing blocks of missing
   packets; skipping packet sequence 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.

   Section Offsets

   0: Start of the ack frame.

   T: Byte offset of the start of the timestamp section.

   A: Byte offset of the start of the ack block section.

   N: Length in bytes of the largest acked.

     0                            1  => N                     N+1 => A(aka N + 3)
+---------+-------------------------------------------------+--------+--------+
|   Type  |                   Largest Acked                 |  Largest Acked  |
|   (8)   |    (8, 16, 32, or 48 bits, determined by ll)    | Delta Time (16) |
|01nullmm |                                                 |                 |
+---------+-------------------------------------------------+--------+--------+


     A             A + 1  ==>  A + N
+--------+----------------------------------------+
| Number |             First Ack                  |
|Blocks-1|           Block Length                 |
| (opt)  |(8, 16, 32 or 48 bits, determined by mm)|
+--------+----------------------------------------+

  A + N + 1                A + N + 2  ==>  T(aka A + 2N + 1)
+------------+-------------------------------------------------+
| Gap to next|              Ack Block Length                   |
| Block (8)  |   (8, 16, 32, or 48 bits, determined by mm)     |
| (Repeats)  |       (repeats Number Ranges times)             |
+------------+-------------------------------------------------+
     T        T+1             T+2                 (Repeated Num Timestamps)
+----------+--------+---------------------+ ...  --------+------------------+
|   Num    | Delta  |     Time Since      |     | Delta  |       Time       |
|Timestamps|Largest |    Largest Acked    |     |Largest |  Since Previous  |
|   (8)    | Acked  |      (32 bits)      |     | Acked  |Timestamp(16 bits)|
+----------+--------+---------------------+     +--------+------------------+

   The fields in the ACK frame are as follows:

   o  Frame Type: The Frame Type byte is an 8-bit value containing
      various flags (01nullmmB).



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      *  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 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  Largest Acked: A variable-sized unsigned value representing the
      largest packet number the peer has observed.

   o  Largest Acked Delta 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 acked 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  Ack Block Section:

      *  Num Blocks: An optional 8-bit unsigned value specifying one
         less than the number of ack blocks.  Only present if the 'n'
         flag bit is 1.

      *  Ack block length: A variable-sized packet number delta.  For
         the first missing packet range, the ack block starts at largest
         acked.  For the first ack block, the length of the ack block is
         1 + this value.  For subsequent ack blocks, it is the length of
         the ack block.  For non-first blocks, a value of 0 indicates
         more than 256 packets in a row were lost.

      *  Gap to next block: An 8-bit unsigned value specifying the
         number of packets between ack blocks.



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   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
         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.

10.5.  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:

        0        1        2        3         4       5       6
   +--------+--------+--------+--------+--------+-------+-------+
   |Type (8)|   Least unacked delta (8, 16, 32, or 48 bits)     |
   |        |                       (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  Least Unacked Delta: A variable length packet number delta with
      the same length as the packet header's packet number.  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



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      receiver is missing any packets smaller than this value, the
      receiver should consider those packets to be irrecoverably lost.

10.6.  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:

       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.

   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.







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10.7.  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:

        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.

10.8.  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.

10.9.  RST_STREAM Frame

   An endpoint may use a RST_STREAM frame to abruptly terminate a
   stream.  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 are:

   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.




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   o  Stream ID: The 32-bit Stream ID of the stream being terminated.

   o  Byte offset: A 64-bit unsigned integer indicating the absolute
      byte offset of the end of data written on this stream by the
      RST_STREAM sender.

   o  Error code: A 32-bit error code which indicates why the stream is
      being closed.

10.10.  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.

10.11.  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:

        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:

   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 error code which indicates the reason for
      closing this connection.

   o  Reason Phrase Length: A 16-bit unsigned number specifying the
      length of the reason phrase.  This may be zero if the sender
      chooses to not give details beyond the QuicErrorCode.





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   o  Reason Phrase: An optional human-readable explanation for why the
      connection was closed.

10.12.  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:

        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 error code which indicates the reason
      for closing this connection.

   o  Last Good Stream ID: The last Stream ID which was accepted by the
      sender of the GOAWAY message.  If no streams were replied to, this
      value must be set to 0.

   o  Reason Phrase Length: A 16-bit unsigned number specifying the
      length of the reason phrase.  This may be zero if the sender
      chooses to not give details beyond the error code.

   o  Reason Phrase: An optional human-readable explanation for why the
      connection was closed.

11.  Error Codes

   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)





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   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.

   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_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



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   o  QUIC_CRYPTO_TAGS_OUT_OF_ORDER: Handshake message contained out of
      order tags.

   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.

12.  Security and Privacy Considerations

   (TODO: List considerations)

13.  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, 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.

14.  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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15.  References

15.1.  Normative References

   [RFC2119]  Bradner, S., "Key Words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [draft-thomson-quic-tls]
              Thomson, M. and R. Hamilton, "Porting QUIC to TLS", March
              2016.

   [draft-iyengar-quic-loss-recovery]
              Iyengar, J. and I. Swett, "QUIC Loss Recovery and
              Congestion Control", July 2016.

15.2.  Informative References

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, "Hypertext Transfer
              Protocol Version 2 (HTTP/2)", May 2015.

15.3.  URIs

   [1] https://goo.gl/dMVtFi

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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