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Versions: (draft-hamilton-quic-transport-protocol) 00 01 02 03 04 05 06

QUIC                                                     J. Iyengar, Ed.
Internet-Draft                                                    Google
Intended status: Standards Track                         M. Thomson, Ed.
Expires: June 1, 2017                                            Mozilla
                                                       November 28, 2016


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

Abstract

   QUIC is a multiplexed and secure transport protocol that runs on top
   of UDP.  QUIC builds on past transport experience, and implements
   mechanisms that make it useful as a modern general-purpose transport
   protocol.  Using UDP as the basis of QUIC is intended to address
   compatibility issues with legacy clients and middleboxes.  QUIC
   authenticates all of its headers, preventing third parties from from
   changing them.  QUIC encrypts most of its headers, thereby limiting
   protocol evolution to QUIC endpoints only.  Therefore, middleboxes,
   in large part, are not required to be updated as new protocol
   versions are deployed.  This document describes the core QUIC
   protocol, including the conceptual design, wire format, and
   mechanisms of the QUIC protocol for connection establishment, stream
   multiplexing, stream and connection-level flow control, and data
   reliability.  Accompanying documents describe QUIC's loss recovery
   and congestion control, and the use of TLS 1.3 for key negotiation.

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 June 1, 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 .   6
     3.5.  Stream and Connection Flow Control  . . . . . . . . . . .   6
     3.6.  Authenticated and Encrypted Header and Payload  . . . . .   6
     3.7.  Connection Migration and Resilience to NAT Rebinding  . .   7
   4.  Packet Types and Formats  . . . . . . . . . . . . . . . . . .   7
     4.1.  Common Header . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Regular Packets . . . . . . . . . . . . . . . . . . . . .   9
       4.2.1.  Packet Number Compression and Reconstruction  . . . .  10
       4.2.2.  Frames and Frame Types  . . . . . . . . . . . . . . .  11
     4.3.  Version Negotiation Packet  . . . . . . . . . . . . . . .  12
     4.4.  Public Reset Packet . . . . . . . . . . . . . . . . . . .  12
   5.  Life of a Connection  . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Version Negotiation . . . . . . . . . . . . . . . . . . .  13
     5.2.  Crypto and Transport Handshake  . . . . . . . . . . . . .  15
       5.2.1.  Transport Parameters and Options  . . . . . . . . . .  15
       5.2.2.  Proof of Source Address Ownership . . . . . . . . . .  16
       5.2.3.  Crypto Handshake Protocol Features  . . . . . . . . .  16
     5.3.  Connection Migration  . . . . . . . . . . . . . . . . . .  17
     5.4.  Connection Termination  . . . . . . . . . . . . . . . . .  18
   6.  Frame Types and Formats . . . . . . . . . . . . . . . . . . .  19
     6.1.  STREAM Frame  . . . . . . . . . . . . . . . . . . . . . .  19
     6.2.  ACK Frame . . . . . . . . . . . . . . . . . . . . . . . .  20
       6.2.1.  Time Format . . . . . . . . . . . . . . . . . . . . .  23
     6.3.  STOP_WAITING Frame  . . . . . . . . . . . . . . . . . . .  23
     6.4.  WINDOW_UPDATE Frame . . . . . . . . . . . . . . . . . . .  24



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     6.5.  BLOCKED Frame . . . . . . . . . . . . . . . . . . . . . .  24
     6.6.  RST_STREAM Frame  . . . . . . . . . . . . . . . . . . . .  25
     6.7.  PADDING Frame . . . . . . . . . . . . . . . . . . . . . .  25
     6.8.  PING frame  . . . . . . . . . . . . . . . . . . . . . . .  26
     6.9.  CONNECTION_CLOSE frame  . . . . . . . . . . . . . . . . .  26
     6.10. GOAWAY Frame  . . . . . . . . . . . . . . . . . . . . . .  27
   7.  Packetization and Reliability . . . . . . . . . . . . . . . .  27
   8.  Streams: QUIC's Data Structuring Abstraction  . . . . . . . .  29
     8.1.  Life of a Stream  . . . . . . . . . . . . . . . . . . . .  29
       8.1.1.  idle  . . . . . . . . . . . . . . . . . . . . . . . .  31
       8.1.2.  reserved  . . . . . . . . . . . . . . . . . . . . . .  31
       8.1.3.  open  . . . . . . . . . . . . . . . . . . . . . . . .  32
       8.1.4.  half-closed (local) . . . . . . . . . . . . . . . . .  32
       8.1.5.  half-closed (remote)  . . . . . . . . . . . . . . . .  32
       8.1.6.  closed  . . . . . . . . . . . . . . . . . . . . . . .  33
     8.2.  Stream Identifiers  . . . . . . . . . . . . . . . . . . .  34
     8.3.  Stream Concurrency  . . . . . . . . . . . . . . . . . . .  34
     8.4.  Sending and Receiving Data  . . . . . . . . . . . . . . .  34
   9.  Flow Control  . . . . . . . . . . . . . . . . . . . . . . . .  35
     9.1.  Edge Cases and Other Considerations . . . . . . . . . . .  36
       9.1.1.  Mid-stream RST_STREAM . . . . . . . . . . . . . . . .  36
       9.1.2.  Response to a RST_STREAM  . . . . . . . . . . . . . .  37
       9.1.3.  Offset Increment  . . . . . . . . . . . . . . . . . .  37
       9.1.4.  BLOCKED frames  . . . . . . . . . . . . . . . . . . .  37
   10. Error Codes . . . . . . . . . . . . . . . . . . . . . . . . .  38
   11. Security and Privacy Considerations . . . . . . . . . . . . .  43
     11.1.  Spoofed Ack Attack . . . . . . . . . . . . . . . . . . .  43
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  44
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  44
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  44
     13.2.  Informative References . . . . . . . . . . . . . . . . .  44
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  45
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  45

1.  Introduction

   QUIC is a multiplexed and secure transport protocol that runs on top
   of UDP.  QUIC builds on past transport experience and implements
   mechanisms that make it useful as a modern general-purpose transport
   protocol.  Using UDP as the substrate, QUIC seeks to be compatible
   with legacy clients and middleboxes.  QUIC authenticates all of its
   headers, preventing middleboxes and other third parties from changing
   them, and encrypts most of its headers, limiting protocol evolution
   largely to QUIC endpoints only.

   This document describes the core QUIC protocol, including the
   conceptual design, wire format, and mechanisms of the QUIC protocol



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   for connection establishment, stream multiplexing, stream and
   connection-level flow control, and data reliability.  Accompanying
   documents describe QUIC's loss detection and congestion control
   [QUIC-RECOVERY], and the use of TLS 1.3 for key negotiation
   [QUIC-TLS].

2.  Conventions and Definitions

   The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
   document.  It's not shouting; when they are capitalized, they have
   the special meaning defined in [RFC2119].

   Definitions of terms that are used in this document:

   o  Client: The endpoint initiating a QUIC connection.

   o  Server: The endpoint accepting incoming QUIC connections.

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

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

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

   o  Connection ID: The identifier for a QUIC connection.

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

3.  A QUIC Overview

   This section briefly describes 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



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   o  Connection Migration and Resilience to NAT rebinding

3.1.  Low-Latency Version Negotiation

   QUIC combines version negotiation with the rest of connection
   establishment to avoid unnecessary roundtrip delays.  A QUIC client
   proposes a version to use for the connection, and encodes the rest of
   the handshake using the proposed version.  If the server does not
   speak the client-chosen version, it forces version negotiation by
   sending back a Version Negotiation packet to the client, causing a
   roundtrip of delay before connection establishment.

   This mechanism eliminates roundtrip latency when the client's
   optimistically-chosen version is spoken by the server, and
   incentivizes servers to not lag behind clients in deployment of newer
   versions.  Additionally, an application may negotiate QUIC versions
   out-of-band to increase chances of success in the first roundtrip and
   to obviate the additional roundtrip in the case of version mismatch.

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.  The format of the
   QUIC options and parameters used during negotiation are described in
   this document, but the handshake protocol that runs on Stream ID 1 is
   described in the accompanying crypto handshake draft [QUIC-TLS].

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.
   QUIC ensures that lost packets carrying data for an individual stream
   only impact that specific stream.  Data received on other streams can
   continue to be reassembled and delivered to the application.








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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 carries a new packet number, including those
   carrying retransmitted data.  This obviates the need for a separate
   mechanism to distinguish acks for retransmissions from those for
   original transmissions, avoiding TCP's retransmission ambiguity
   problem.  QUIC acknowledgments also explicitly encode the delay
   between the receipt of a packet and its acknowledgment being sent,
   and together with the monotonically-increasing packet numbers, this
   allows for precise network roundtrip-time (RTT) calculation.  QUIC's
   ACK frames support up to 256 ack blocks, so QUIC is more resilient to
   reordering than TCP with SACK support, as well as able to keep more
   bytes on the wire when there is reordering or loss.

3.5.  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, a QUIC
   receiver advertises the absolute byte offset within each stream up to
   which the receiver is willing to receive data.  As data is sent,
   received, and delivered on a particular stream, the receiver sends
   WINDOW_UPDATE frames that increase the advertised offset limit for
   that stream, allowing the peer to send more data on that stream.  In
   addition to this stream-level flow control, QUIC implements
   connection-level flow control to limit the aggregate buffer that a
   QUIC receiver is willing to allocate to all streams on a connection.
   Connection-level flow control works in the same way as stream-level
   flow control, but the bytes delivered and highest received offset are
   all aggregates across all streams.

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 mechanisms used
   by middleboxes to improve TCP performance, others are active attacks.
   Even "performance-enhancing" middleboxes that routinely interpose on
   the transport state machine end up limiting the evolvability of the
   transport protocol, as has been observed in the design of MPTCP and
   in its subsequent deployability issues.

   Generally, QUIC packets are always authenticated and the payload is
   typically fully encrypted.  The parts of the packet header which are
   not encrypted are still authenticated by the receiver, so as to
   thwart any packet injection or manipulation by third parties.  Some



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   early handshake packets, such as the Version Negotiation packet, are
   not encrypted, but information sent in these unencrypted handshake
   packets is later verified under crypto cover.

   PUBLIC_RESET packets that reset a connection are currently not
   authenticated.

3.7.  Connection Migration and Resilience to NAT Rebinding

   QUIC connections are identified by a 64-bit Connection ID, randomly
   generated by the client.  QUIC's consistent connection ID allows
   connections to survive changes to the client's IP and port, such as
   those caused by NAT rebindings or by the client changing network
   connectivity to a new address.  QUIC provides automatic cryptographic
   verification of a rebound client, since the client continues to use
   the same session key for encrypting and decrypting packets.  The
   consistent connection ID can be used to allow migration of the
   connection to a new server IP address as well, since the Connection
   ID remains consistent across changes in the client's and the server's
   network addresses.

4.  Packet Types and Formats

   We first describe QUIC's packet types and their formats, since some
   are referenced in subsequent mechanisms.  Note that unless otherwise
   noted, all values specified in this document are in little-endian
   format and all field sizes are in bits.

4.1.  Common Header

   All QUIC packets begin with a QUIC Common header, as shown below.

      +------------+---------------------------------+
      |  Flags(8)  |  Connection ID (64) (optional)  |
      +------------+---------------------------------+

   The fields in the Common Header are the following:

   o  Flags:

      *  0x01 = VERSION.  The semantics of this flag depends on whether
         the packet is sent by the server or the client.  A client MAY
         set this flag and include exactly one proposed version.  A
         server may set this flag when the client-proposed version was
         unsupported, and may then provide a list (0 or more) of
         acceptable versions as a part of version negotiation (described
         in Section XXX.)




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

      *  0x04 = DIVERSIFICATION_NONCE.  Set to indicate the presence of
         a 32-byte diversification nonce in the header.
         (DISCUSS_AND_MODIFY: This flag should be removed along with the
         Diversification Nonce bits, as discussed further below.)

      *  0x08 = CONNECTION_ID.  Indicates the Connection ID is present
         in the packet.  This must be set in all packets until
         negotiated to a different value for a given direction.  For
         instance, if a client indicates that the 5-tuple fully
         identifies the connection at the client, the connection ID is
         optional in the server-to-client direction.

      *  0x30 = PACKET_NUMBER_SIZE.  These two bits indicate the number
         of low-order-bytes of the packet number that are present in
         each packet.

         +  11 indicates that 6 bytes of the packet number are present

         +  10 indicates that 4 bytes of the packet number are present

         +  01 indicates that 2 bytes of the packet number are present

         +  00 indicates that 1 byte of the packet number is present

      *  0x40 = MULTIPATH.  This bit is reserved for multipath use.

      *  0x80 is currently unused, and must be set to 0.

   o  Connection ID: An unsigned 64-bit random number chosen by the
      client, used as the identifier of the connection.  Connection ID
      is tied to a QUIC connection, and remains consistent across client
      and/or server IP and port changes.

   While all QUIC packets have the same common header, there are three
   types of packets: Regular packets, Version Negotiation packets, and
   Public Reset packets.  The flowchart below shows how a packet is
   classified into one of these three packet types:











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Check the flags in the common header
                 |
                 |
                 V
           +--------------+
           | PUBLIC_RESET |  YES
           | flag set?    |-------> Public Reset packet
           +--------------+
                 |
                 | NO
                 V
           +------------+         +-------------+
           | VERSION    |  YES    | Packet sent |  YES
           | flag set?  |-------->| by server?  |--------> Version Negotiation
           +------------+         +-------------+               packet
                 |                       |
                 | NO                    | NO
                 V                       V
         Regular packet with       Regular packet with
     no QUIC Version in header    QUIC Version in header

                      Figure 1: Types of QUIC Packets

4.2.  Regular Packets

   Each Regular packet's header consists of a Common Header followed by
   fields specific to Regular packets, as shown below:

+------------+---------------------------------+
|  Flags(8)  |  Connection ID (64) (optional)  | ->
+------------+---------------------------------+
+---------------------------------------+-------------------------------+
|  Version (32) (client-only, optional) |  Diversification Nonce (256)  | ->
+---------------------------------------+-------------------------------+
+------------------------------------+
|  Packet Number (8, 16, 32, or 48)  | ->
+------------------------------------+
+------------+
|  AEAD Data |
+------------+

Decrypted AEAD Data:
+------------+-----------+     +-----------+
|   Frame 1  |  Frame 2  | ... |  Frame N  |
+------------+-----------+     +-----------+

                         Figure 2: Regular Packet




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   The fields in a Regular packet past the Common Header are the
   following:

   o  QUIC Version: A 32-bit opaque tag that represents the version of
      the QUIC protocol.  Only present in the client-to-server
      direction, and if the VERSION flag is set.  Version Negotiation is
      described in Section XXX.

   o  DISCUSS_AND_REPLACE: Diversification Nonce: A 32-byte nonce
      generated by the server and used only in the Server->Client
      direction to ensure that the server is able to generate unique
      keys per connection.  Specifically, when using QUIC's 0-RTT crypto
      handshake, a repeated CHLO with the exact same connection ID and
      CHLO can lead to the same (intermediate) initial-encryption keys
      being derived for the connection.  A server-generated nonce
      disallows a client from causing the same keys to be derived for
      two distinct connections.  Once the connection is forward-secure,
      this nonce is no longer present in packets.  This nonce can be
      removed from the packet header if a requirement can be added for
      the crypto handshake to ensure key uniqueness.  The expectation is
      that TLS1.3 meets this requirement.  Upon working group adoption
      of this document, this requirement should be added to the crypto
      handshake requirements, and the nonce should be removed from the
      packet format.

   o  Packet Number: The lower 8, 16, 32, or 48 bits of the packet
      number, based on the PACKET_NUMBER_SIZE flag.  Each Regular packet
      is assigned a packet number by the sender.  The first packet sent
      by an endpoint MUST have a packet number of 1.

   o  AEAD Data: A Regular packet's header, which includes the Common
      Header, and the Version, Diversification Nonce, and Packet Number
      fields, is authenticated but not encrypted.  The rest of a Regular
      packet, starting with the first frame, is both authenticated and
      encrypted.  Immediately following the header, Regular packets
      contain AEAD (Authenticated Encryption with Associated Data) data.
      This data must be decrypted in order for the contents to be
      interpreted.  After decryption, the plaintext consists of a
      sequence of frames, as shown (frames are described in
      Section XXX).

4.2.1.  Packet Number Compression and Reconstruction

   The complete packet number is a 64-bit unsigned number and is used as
   part of a cryptographic nonce for packet encryption.  To reduce the
   number of bits required to represent the packet number over the wire,
   at most 48 bits of the packet number are transmitted over the wire.
   A QUIC endpoint MUST NOT reuse a complete packet number within the



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   same connection (that is, under the same cryptographic keys).  If the
   total number of packets transmitted in this connection reaches 2^64 -
   1, the sender MUST close the connection by sending a CONNECTION_CLOSE
   frame with the error code QUIC_SEQUENCE_NUMBER_LIMIT_REACHED
   (connection termination is described in Section XXX.)  For
   unambiguous reconstruction of the complete packet number by a
   receiver from the lower-order bits, a QUIC sender MUST NOT have more
   than 2^(packet_number_size - 2) in flight at any point in the
   connection.  In other words,

   o  If a sender sets PACKET_NUMBER_SIZE bits to 11, it MUST NOT have
      more than (2^46) packets in flight.

   o  If a sender sets PACKET_NUMBER_SIZE bits to 10, it MUST NOT have
      more than (2^30) packets in flight.

   o  If a sender sets PACKET_NUMBER_SIZE bits to 01, it MUST NOT have
      more than (2^14) packets in flight.

   o  If a sender sets PACKET_NUMBER_SIZE bits to 00, it MUST NOT have
      more than (2^6) packets in flight.

      DISCUSS: Should the receiver be required to enforce this rule that
      the sender MUST NOT exceed the inflight limit?  Specifically,
      should the receiver drop packets that are received outside this
      window?

      Any truncated packet number received from a peer MUST be
      reconstructed as the value closest to the next expected packet
      number from that peer.

   (TODO: Clarify how packet number size can change mid-connection.)

4.2.2.  Frames and Frame Types

   A Regular packet MUST contain at least one frame, and MAY contain
   multiple frames and multiple frame types.  Frames MUST fit within a
   single QUIC packet and MUST NOT span a QUIC packet boundary.  Each
   frame begins with a Frame Type byte, indicating its type, followed by
   type-dependent headers, and variable-length data, as follows:

     +-----------+---------------------------+-------------------------+
     |  Type (8) |  Headers (type-dependent) |  Data (type-dependent)  |
     +-----------+---------------------------+-------------------------+

   The following table lists currently defined frame types.  Note that
   the Frame Type byte in STREAM and ACK frames is used to carry other
   frame-specific flags.  For all other frames, the Frame Type byte



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   simply identifies the frame.  These frames are explained in more
   detail as they are referenced later in the document.

         +------------------+--------------------+
         | Type-field value |     Frame type     |
         +------------------+--------------------+
         | 1FDOOOSS         |  STREAM            |
         | 01NTLLMM         |  ACK               |
         | 00000000 (0x00)  |  PADDING           |
         | 00000001 (0x01)  |  RST_STREAM        |
         | 00000010 (0x02)  |  CONNECTION_CLOSE  |
         | 00000011 (0x03)  |  GOAWAY            |
         | 00000100 (0x04)  |  WINDOW_UPDATE     |
         | 00000101 (0x05)  |  BLOCKED           |
         | 00000110 (0x06)  |  STOP_WAITING      |
         | 00000111 (0x07)  |  PING              |
         +------------------+--------------------+

                      Figure 3: Types of QUIC Frames

4.3.  Version Negotiation Packet

   A Version Negotiation packet is only sent by the server, MUST have
   the VERSION flag set, and MUST include the full 64-bit Connection ID.
   The rest of the Version Negotiation packet is a list of 4-byte
   versions which the server supports, as shown below.

+-----------------------------------+
|  Flags(8)  |  Connection ID (64)  | ->
+-----------------------------------+
+------------------------------+----------------------------------------+
|  1st Supported Version (32)  |  2nd Supported Version (32) supported  | ...
+------------------------------+----------------------------------------+

                   Figure 4: Version Negotiation Packet

4.4.  Public Reset Packet

   A Public Reset packet MUST have the PUBLIC_RESET flag set, and MUST
   include the full 64-bit connection ID.  The rest of the Public Reset
   packet is encoded as if it were a crypto handshake message of the tag
   PRST, as shown below.









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      +-----------------------------------+
      |  Flags(8)  |  Connection ID (64)  | ->
      +-----------------------------------+
      +-------------------------------------+
      |  Quic Tag (PRST) and tag value map  |
      +-------------------------------------+

                       Figure 5: Public Reset Packet

   The tag value map contains the following tag-values:

   o  RNON (public reset nonce proof) - a 64-bit unsigned integer.

   o  RSEQ (rejected packet number) - a 64-bit packet number.

   o  CADR (client address) - the observed client IP address and port
      number.  This is currently for debugging purposes only and hence
      is optional.

   DISCUSS_AND_REPLACE: The crypto handshake message format is described
   in the QUIC crypto document, and should be replaced with something
   simpler when this document is adopted.  The purpose of the tag-value
   map following the PRST tag is to enable the receiver of the Public
   Reset packet to reasonably authenticate the packet.  This map is an
   extensible map format that allows specification of various tags,
   which should again be replaced by something simpler.

5.  Life of a Connection

   A QUIC connection is a single conversation between two QUIC
   endpoints.  QUIC's connection establishment intertwines version
   negotiation with the crypto and transport handshakes to reduce
   connection establishment latency, as described in Section XXX.  Once
   established, a connection may migrate to a different IP or port at
   either endpoint, due to NAT rebinding or mobility, as described in
   Section XXX.  Finally a connection may be terminated by either
   endpoint, as described in Section XXX.

5.1.  Version Negotiation

   QUIC's connection establishment begins with version negotiation,
   since all communication between the endpoints, including packet and
   frame formats, relies on the two endpoints agreeing on a version.

   A QUIC connection begins with a client sending a handshake packet.
   The details of the handshake mechanisms are described in Section XX,
   but all of the initial packets sent from the client to the server




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   MUST have the VERSION flag set, and MUST specify the version of the
   protocol being used.

   When the server receives a packet from a client with the VERSION flag
   set for a connection that has not yet been established, it compares
   the client's version to the versions it supports.

   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.  On subsequently received
      packets for the same connection ID with the unacceptable version,
      the server MUST continue responding with a Version Negotiation
      packet.

   When the client receives a Version Negotiation packet from the
   server, it should select an acceptable protocol version.  If such a
   version is found, the client MUST resend all packets using the new
   version, and the resent packets MUST use new packet numbers.  These
   packets MUST continue to have the VERSION flag set and MUST include
   the new negotiated protocol version.

   The client MUST send its version on all packets until it receives a
   packet from the server with the VERSION flag off.  If version
   negotiation is successful, the client should receive a packet from
   the server with the VERSION flag off indicating the end of version
   negotiation.  All subsequent packets the client sends MUST have the
   version flag off.

   Once the server receives a packet from the client with the VERSION
   flag off, it MUST ignore the VERSION flag in subsequently received
   packets.

   The Version Negotiation packet is unencrypted and exchanged without
   authentication.  To avoid a downgrade attack, the client needs to
   verify its record of the server's version list in the Version
   Negotiation packet and the server needs to verify its record of the
   client's originally proposed version.  Therefore, the client and
   server MUST include this information later in their corresponding
   crypto handshake data.






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5.2.  Crypto and Transport Handshake

   QUIC relies on a combined crypto and transport handshake to minimize
   connection establishment latency.  QUIC provides a dedicated stream
   (Stream ID 1) to be used for performing a combined connection and
   security handshake (streams are described in detail in Section XXX).
   The crypto handshake protocol encapsulates and delivers QUIC's
   transport handshake to the peer on the crypto stream.  The first QUIC
   packet from the client to the server MUST carry handshake information
   as data on Stream ID 1.

5.2.1.  Transport Parameters and Options

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

   The transport component of the handshake is responsible for
   exchanging and negotiating the following parameters for a QUIC
   connection.  Not all parameters are negotiated, some are parameters
   sent in just one direction.  These parameters and options are encoded
   and handed off to the crypto handshake protocol to be transmitted to
   the peer.

5.2.1.1.  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.

5.2.1.2.  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.

5.2.1.3.  Optional Transport Parameters

   o  TCID: Indicates support for truncated Connection IDs.  If sent by
      a peer, indicates that connection IDs sent to the peer should be
      truncated to 0 bytes.  This is expected to commonly be used by an
      endpoint where the 5-tuple is sufficient to identify a connection.
      For instance, if the 5-tuple is unique at the client, the client



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      MAY send a TCID parameter to the server.  When a TCID parameter is
      received, an endpoint MAY choose to not send the connection ID on
      subsequent packets.

   o  COPT: Connection Options are a repeated tag field.  The field
      contains any connection options being requested by the client or
      server.  These are typically used for experimentation and will
      evolve over time.  Example use cases include changing congestion
      control algorithms and parameters such as initial window.  (TODO:
      List connection options.)

5.2.2.  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.)

5.2.3.  Crypto Handshake Protocol Features

   QUIC's current crypto handshake mechanism is documented in
   [QUICCrypto].  QUIC does not restrict itself to using a specific
   handshake protocol, so the details of a specific handshake protocol
   are out of this document's scope.  If not explicitly specified in the
   application mapping, TLS is assumed to be the default crypto
   handshake protocol, as described in [QUIC-TLS].  An application that
   maps to QUIC MAY however specify an alternative crypto handshake
   protocol to be used.




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

   o  The crypto handshake MUST ensure that the final negotiated key is
      distinct for every connection between two endpoints.

   o  Transport Negotiation: The crypto handshake MUST provide a
      mechanism for the transport component to exchange transport
      parameters and Source Address Tokens.  To avoid downgrade attacks,
      the transport parameters sent and received MUST be verified before
      the handshake completes successfully.

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

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

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

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

   The following information used during the QUIC handshake MUST be
   cryptographically verified by the crypto handshake protocol:

   o  Client's originally proposed version in its first packet.

   o  Server's version list in it's Version Negotiation packet, if one
      was sent.

5.3.  Connection Migration

   QUIC connections are identified by their 64-bit Connection ID.
   QUIC's consistent connection ID allows connections to survive changes
   to the client's IP and/or port, such as those caused by client or



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   server migrating to a new network.  QUIC also provides automatic
   cryptographic verification of a rebound client, since the client
   continues to use the same session key for encrypting and decrypting
   packets.

   DISCUSS: Simultaneous migration.  Is this reasonable?

   TODO: Perhaps move mitigation techniques from Security Considerations
   here.

5.4.  Connection Termination

   Connections should remain open until they become idle for a pre-
   negotiated period of time.  A QUIC connection, once established, can
   be terminated in one of three ways:

   1.  Explicit Shutdown: An endpoint sends a CONNECTION_CLOSE frame to
       the peer initiating a connection termination.  An endpoint may
       send a GOAWAY frame to the peer prior to a CONNECTION_CLOSE to
       indicate that the connection will soon be terminated.  A GOAWAY
       frame signals to the peer that any active streams will continue
       to be processed, but the sender of the GOAWAY will not initiate
       any additional streams and will not accept any new incoming
       streams.  On termination of the active streams, a
       CONNECTION_CLOSE may be sent.  If an endpoint sends a
       CONNECTION_CLOSE frame while unterminated streams are active (no
       FIN bit or RST_STREAM frames have been sent or received for one
       or more streams), then the peer must assume that the streams were
       incomplete and were abnormally terminated.

   2.  Implicit Shutdown: The default idle timeout for a QUIC connection
       is 30 seconds, and is a required parameter (ICSL) in connection
       negotiation.  The maximum is 10 minutes.  If there is no network
       activity for the duration of the idle timeout, the connection is
       closed.  By default a CONNECTION_CLOSE frame will be sent.  A
       silent close option can be enabled when it is expensive to send
       an explicit close, such as mobile networks that must wake up the
       radio.

   3.  Abrupt Shutdown: An endpoint may send a Public Reset packet at
       any time during the connection to abruptly terminate an active
       connection.  A Public Reset packet SHOULD only be used as a final
       recourse.  Commonly, a public reset is expected to be sent when a
       packet on an established connection is received by an endpoint
       that is unable decrypt the packet.  For instance, if a server
       reboots mid-connection and loses any cryptographic state
       associated with open connections, and then receives a packet on
       an open connection, it should send a Public Reset packet in



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       return.  (TODO: articulate rules around when a public reset
       should be sent.)

   TODO: Connections that are terminated are added to a TIME_WAIT list
   at the server, so as to absorb any straggler packets in the network.
   Discuss TIME_WAIT list.

6.  Frame Types and Formats

   As described in Section XXX, Regular packets contain one or more
   frames.  We now describe the various QUIC frame types that can be
   present in a Regular packet.  The use of these frames and various
   frame header bits are described in subsequent sections.

6.1.  STREAM Frame

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

      +------------+--------------------------------+
      |  Type (8)  |  Stream ID (8, 16, 24, or 32)  |
      +------------+--------------------------------+
      +---------------------------------------------+
      |  Offset (0, 16, 24, 32, 40, 48, 56, or 64)  |
      +---------------------------------------------+
      +-------------------------+---------------------------------+
      |  Data length (0 or 16)  |  Stream Data (per data length)  |
      +-------------------------+---------------------------------+

   The STREAM frame header fields are as follows:

   o  Frame Type: The Frame Type byte is an 8-bit value containing
      various flags, and is formatted as the following 8 bits: 1FDOOOSS.

      *  The leftmost bit must be set to 1 indicating that this is a
         STREAM frame.

      *  'F' is the FIN bit, which is used for stream termination.

      *  The 'D' bit indicates whether a Data Length field is present in
         the STREAM header.  When set to 0, this field indicates that
         the Stream Data field extends to the end of the packet.  When
         set to 1, this field indicates that Data Length field contains
         the length (in bytes) of the Stream Data field.  The option to
         omit the length should only be used when the packet is a "full-
         sized" packet, to avoid the risk of corruption via padding.





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      *  The 'OOO' bits encode the length of the Offset header field as
         0, 16, 24, 32, 40, 48, 56, or 64 bits long.

      *  The 'SS' bits encode the length of the Stream ID header field
         as 8, 16, 24, or 32 bits.  (DISCUSS: Consider making this 8,
         16, 32, 64.)

   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 the data in this STREAM frame.  The first
      byte in the stream has an offset of 0.

   o  Data Length: An optional 16-bit unsigned number specifying the
      length of the Stream Data field in this STREAM frame.

   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.

6.2.  ACK Frame

   Receivers send ACK frames to inform senders which packets they have
   received, as well as which packets are considered missing.  The ACK
   frame contains between 1 and 256 ack blocks.  Ack blocks are ranges
   of acknowledged packets.

   To limit the ACK blocks to the ones that haven't yet been received by
   the sender, the sender periodically sends STOP_WAITING frames that
   signal the receiver to stop acking packets below a specified sequence
   number, raising the "least unacked" packet number at the receiver.  A
   sender of an ACK frame thus reports only those ACK blocks between the
   received least unacked and the reported largest observed packet
   numbers.  It is recommended for the sender to send the most recent




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   largest acked packet it has received in an ack as the STOP_WAITING
   frame's least unacked value.

   Unlike TCP SACKs, QUIC ACK blocks are irrevocable.  Once a packet is
   acked, even if it does not appear in a future ack frame, it is
   assumed to be acked.

   A sender MAY intentionally skip packet numbers to introduce entropy
   into the connection, to avoid opportunistic ack attacks.  The sender
   MUST close the connection if an unsent packet number is acked.  The
   format of the ACK frame is efficient at expressing blocks of missing
   packets; skipping packet numbers between 1 and 255 effectively
   provides up to 8 bits of efficient entropy on demand, which should be
   adequate protection against most opportunistic ack attacks.

+--------------------------------------------------------------+
| Type (8) | Largest Acked (8, 16, 32, or 48) | Ack Delay (16) |
+--------------------------------------------------------------+

Ack Block Section:
+-------------------------------------------------------------------------+
| Number Blocks (8) (opt) | First Ack Block Length (8, 16, 32 or 48 bits) |
+-------------------------------------------------------------------------+
+-----------------------------------------------------------------+
| Gap To Next Block (8) | Ack Block Length (8, 16, 32, or 48 bits | <-- optional,
+-----------------------------------------------------------------+     repeats

Timestamp Section:
+--------------------+
| Num Timestamps (8) |
+--------------------+
+---------------------------------------------------------+
| Delta Largest Acked (8) | Time Since Largest Acked (32) | <-- optional
+---------------------------------------------------------+
+---------------------------------------------------------------+
| Delta Largest Acked (8) | Time Since Previous Timestamp  (16) | <-- optional,
+---------------------------------------------------------------+     repeats

   The fields in the ACK frame are as follows:

   o  Frame Type: The Frame Type byte is an 8-bit value containing
      various flags.  This byte is formatted as the following 8 bits:
      01NULLMM.

      *  The first two bits must be set to 01 indicating that this is an
         ACK frame.





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      *  The 'N' bit indicates whether the frame has more than 1 ack
         range.

      *  The 'U' bit is unused.

      *  The two 'LL' bits encode the length of the Largest Acked field
         as 1, 2, 4, or 6 bytes long.

      *  The two 'MM' bits encode the length of the Ack Block Length
         fields as 1, 2, 4, or 6 bytes long.

   o  Largest Acked: A variable-sized unsigned value representing the
      largest packet number the peer is acking in this packet (typically
      the largest that the peer has seen thus far.)

   o  Ack Delay: Time from when the largest acked, as indicated in the
      Largest Acked field, was received by this peer to when this ack
      was sent.

   o  Ack Block Section:

      *  Num Blocks (opt): An optional 8-bit unsigned value specifying
         the number of additional ack blocks (besides the required First
         Ack Block) in this ACK frame.  Only present if the 'N' flag bit
         is 1.

      *  First Ack Block Length: An unsigned packet number delta that
         indicates the number of contiguous additional packets being
         acked starting at the Largest Acked.

      *  Gap To Next Block (opt, repeated): An unsigned number
         specifying the number of contiguous missing packets from the
         end of the previous ack block to the start of the next.

      *  Ack Block Length (opt, repeated): An unsigned packet number
         delta that indicates the number of contiguous packets being
         acked starting after the end of the previous gap.  Along with
         the previous field, this field is repeated "Num Blocks" times.

   o  Timestamp Section:

      *  Num Timestamps: An unsigned 8-bit number specifying the total
         number of <packet number, timestamp> pairs following, including
         the First Timestamp.

      *  Delta Largest Acked (opt): An optional 8-bit unsigned packet
         number delta specifying the delta between the largest acked and
         the first packet whose timestamp is being reported.  In other



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         words, this first packet number may be computed as (Largest
         Acked - Delta Largest Acked.)

      *  First Timestamp (opt): An optional 32-bit unsigned value
         specifying the time delta in microseconds, from the beginning
         of the connection to the arrival of this packet.

      *  Delta Largest Observed (opt, repeated): (Same as above.)

      *  Time Since Previous Timestamp (opt, repeated): An optional
         16-bit unsigned value specifying time delta from the previous
         reported timestamp.  It is encoded in the same format as the
         Ack Delay.  Along with the previous field, this field is
         repeated "Num Timestamps" times.

6.2.1.  Time Format

   DISCUSS_AND_REPLACE: Perhaps make this format simpler.

   The time format used in the ACK frame above is a 16-bit unsigned
   float with 11 explicit bits of mantissa and 5 bits of explicit
   exponent, specifying time in microseconds.  The bit format is loosely
   modeled after IEEE 754.  For example, 1 microsecond is represented as
   0x1, which has an exponent of zero, presented in the 5 high order
   bits, and mantissa of 1, presented in the 11 low order bits.  When
   the explicit exponent is greater than zero, an implicit high-order
   12th bit of 1 is assumed in the mantissa.  For example, a floating
   value of 0x800 has an explicit exponent of 1, as well as an explicit
   mantissa of 0, but then has an effective mantissa of 4096 (12th bit
   is assumed to be 1).  Additionally, the actual exponent is one-less
   than the explicit exponent, and the value represents 4096
   microseconds.  Any values larger than the representable range are
   clamped to 0xFFFF.

6.3.  STOP_WAITING Frame

   The STOP_WAITING frame is sent to inform the peer that it should not
   continue to wait for packets with packet numbers lower than a
   specified value.  The packet number is encoded in 1, 2, 4 or 6 bytes,
   using the same coding length as is specified for the packet number
   for the enclosing packet's header (specified in the QUIC Frame
   packet's Flags field.)  The frame is as follows:

      +---------------------------------------------------+
      | Type (8) | Least unacked delta (8, 16, 32, or 48) |
      +---------------------------------------------------+

   The fields in the STOP_WAITING frame are as follows:



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   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 complete packet number of the enclosing packet to
      determine the least unacked packet number.  The resulting least
      unacked packet number is the earliest packet for which the sender
      is still awaiting an ack.  If the receiver is missing any packets
      earlier than this packet, the receiver SHOULD consider those
      packets to be irrecoverably lost and MUST NOT report those packets
      as missing in subsequent acks.

6.4.  WINDOW_UPDATE Frame

   The WINDOW_UPDATE frame informs the peer of an increase in an
   endpoint's flow control receive window.  The StreamID can be zero,
   indicating this WINDOW_UPDATE applies to the connection level flow
   control window, or non-zero, indicating that the specified stream
   should increase its flow control window.  The frame is as follows:

      +---------------------------------------------------+
      |  Type(8)  |  Stream ID (32)  |  Byte offset (64)  |
      +---------------------------------------------------+

   The fields in the WINDOW_UPDATE frame are as follows:

   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.

6.5.  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:





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      +------------------------------+
      |  Type(8)  |  Stream ID (32)  |
      +------------------------------+

   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.

6.6.  RST_STREAM Frame

   An endpoint may use a RST_STREAM frame to abruptly terminate a
   stream.  The frame is as follows:

+----------------------------------------------------------------------+
|  Type(8)  |  StreamID (32)  |  Byte offset (64)  |  Error code (32)  |
+----------------------------------------------------------------------+

   The fields are:

   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 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.

6.7.  PADDING Frame

   The PADDING frame pads a packet with 0x00 bytes.  When this frame is
   encountered, the rest of the packet is expected to be padding bytes.
   The frame contains 0x00 bytes and extends to the end of the QUIC
   packet.  A PADDING frame only has a Frame Type field, and must have
   the 8-bit Frame Type field set to 0x00.  The PADDING frame is as
   follows:






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      +--------+
      |  0x00  |
      +--------+

6.8.  PING frame

   Endpoints can use PING frames to verify that their peers are still
   alive or to check reachability to the peer.  The PING frame contains
   no payload.  The receiver of a PING frame simply needs to ACK the
   packet containing this frame.  The PING frame SHOULD be used to keep
   a connection alive when a stream is open.  The default is to send a
   PING frame after 15 seconds of quiescence.  A PING frame only has a
   Frame Type field, and must have the 8-bit Frame Type field set to
   0x07.  The PING frame is as follows:

      +--------+
      |  0x07  |
      +--------+

6.9.  CONNECTION_CLOSE frame

   An endpoint sends a CONNECTION_CLOSE frame to notify its peer that
   the connection is being closed.  If there are open streams that
   haven't been explicitly closed, they are implicitly closed when the
   connection is closed.  (Ideally, a GOAWAY frame would be sent with
   enough time that all streams are torn down.)  The frame is as
   follows:

+-----------------------------------------------------------------------+
| Type(8) | Error code (32) | Reason phrase length (16) | Reason phrase |
+-----------------------------------------------------------------------+

   The fields of a CONNECTION_CLOSE frame are as follows:

   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.

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





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6.10.  GOAWAY Frame

   An endpoint may use a GOAWAY frame to notify its peer that the
   connection should stop being used, and will likely be aborted in the
   future.  The endpoints will continue using any active streams, but
   the sender of the GOAWAY will not initiate any additional streams,
   and will not accept any new streams.  The frame is as follows:

      +-----------------------------------------------------------+
      |  Type (8) |  Error code (32) |  Last Good Stream ID (32)  |
      +-----------------------------------------------------------+
      +----------------------------------------------+
      | Reason phrase length (16)  |  Reason phrase  |
      +----------------------------------------------+

   The fields of a GOAWAY frame are as follows:

   o  Frame type: An 8-bit value that must be set to 0x03 specifying
      that this is a GOAWAY frame.

   o  Error Code: A 32-bit field error code which indicates the reason
      for closing this connection.

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

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

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

7.  Packetization and Reliability

   The maximum packet size for QUIC is the maximum size of the encrypted
   payload of the resulting UDP datagram.  All QUIC packets SHOULD be
   sized to fit within the path's MTU to avoid IP fragmentation.  The
   recommended default maximum packet size is 1350 bytes for IPv6 and
   1370 bytes for IPv4.  To optimize better, endpoints MAY use PLPMTUD
   [RFC4821] for detecting the path's MTU and setting the maximum packet
   size appropriately.

   A sender bundles one or more frames in a Regular QUIC packet.  A
   sender MAY bundle any set of frames in a packet.  All QUIC packets
   MUST contain a packet number and MAY contain one or more frames
   (Section XX).  Packet numbers MUST be unique within a connection and



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   MUST NOT be reused within the same connection.  Packet numbers MUST
   be assigned to packets in a strictly monotonically increasing order.
   The initial packet number used, at both the client and the server,
   MUST be 0.  That is, the first packet in both directions of the
   connection MUST have a packet number of 0.

   A sender SHOULD minimize per-packet bandwidth and computational costs
   by bundling as many frames as possible within a QUIC packet.  A
   sender MAY wait for a short period of time to bundle multiple frames
   before sending a packet that is not maximally packed, to avoid
   sending out large numbers of small packets.  An implementation may
   use heuristics about expected application sending behavior to
   determine whether and for how long to wait.  This waiting period is
   an implementation decision, and an implementation should be careful
   to delay conservatively, since any delay is likely to increase
   application-visible latency.

   Regular QUIC packets are "containers" of frames; a packet is never
   retransmitted whole, but frames in a lost packet may be rebundled and
   transmitted in a subsequent packet as necessary.

   A packet may contain frames and/or application data, only some of
   which may require reliability.  When a packet is detected as lost,
   the sender SHOULD only resend frames that require retransmission.

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

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

   o  All other frames MUST be retransmitted.

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

   A receiver acknowledges receipt of a received packet by sending one
   or more ACK frames containing the packet number of the received
   packet.  To avoid perpetual acking between endpoints, a receiver MUST
   NOT generate an ack in response to every packet containing only ACK
   frames.  However, since it is possible that an endpoint sends only
   packets containing ACK frame (or other non-retransmittable frames),




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   the receiving peer MAY send an ACK frame after a reasonable number
   (currently 20) of such packets have been received.

   Strategies and implications of the frequency of generating
   acknowledgments are discussed in more detail in [QUIC-RECOVERY].

8.  Streams: QUIC's Data Structuring Abstraction

   Streams in QUIC provide a lightweight, ordered, and bidirectional
   byte-stream abstraction.  Streams can be created either by the client
   or the server, can concurrently send data interleaved with other
   streams, and can be cancelled.  QUIC's stream lifetime is modeled
   closely after HTTP/2's [RFC7540].  Streams are independent of each
   other in delivery order.  That is, data that is received on a stream
   is delivered in order within that stream, but there is no particular
   delivery order across streams.  Transmit ordering among streams is
   left to the implementation.  QUIC streams are considered lightweight
   in that the creation and destruction of streams are expected to have
   minimal bandwidth and computational cost.  A single STREAM frame may
   create, carry data for, and terminate a stream, or a stream may last
   the entire duration of a connection.  Implementations are therefore
   advised to keep these extremes in mind and to implement stream
   creation and destruction to be as lightweight as possible.

   An alternative view of QUIC streams is as an elastic "message"
   abstraction, similar to the way ephemeral streams are used in SST
   [SST], which may be a more appealing description for some
   applications.

8.1.  Life of a Stream

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














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

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

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

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

                      Figure 6: Lifecycle of a stream

   Note that this diagram shows stream state transitions and the frames
   and flags that affect those transitions only.  For the purpose of
   state transitions, the FIN flag is processed as a separate event to



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   the frame that bears it; a STREAM frame with the FIN flag set can
   cause two state transitions.  When the FIN bit is sent on an empty
   STREAM frame, the offset in the STREAM frame MUST be one greater than
   the last data byte sent on this stream.

   Both endpoints have a subjective view of the state of a stream that
   could be different when frames are in transit.  Endpoints do not
   coordinate the creation of streams; they are created unilaterally by
   either endpoint.  The negative consequences of a mismatch in states
   are limited to the "closed" state after sending RST_STREAM, where
   frames might be received for some time after closing.

   Streams have the following states:

8.1.1.  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.

8.1.2.  reserved

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

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

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








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8.1.3.  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).

   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".

8.1.4.  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.

8.1.5.  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).




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   A stream can transition from this state to "closed" by sending a
   frame that contains a FIN flag or when either peer sends a RST_STREAM
   frame.

8.1.6.  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.)





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8.2.  Stream Identifiers

   Streams are identified by an unsigned 32-bit integer, referred to as
   the StreamID.  To avoid StreamID collision, clients MUST initiate
   streams usinge odd-numbered StreamIDs; streams initiated by the
   server MUST use even-numbered StreamIDs.

   A StreamID of zero (0x0) is reserved and used for connection-level
   flow control frames (Section XX); the StreamID of zero cannot be used
   to establish a new stream.

   StreamID 1 (0x1) is reserved for the crypto handshake.  StreamID 1
   MUST NOT be used for application data, and MUST be the first client-
   initiated stream.

   Streams MUST be created or reserved in sequential order, but MAY be
   used in arbitrary order.  A QUIC endpoint MUST NOT reuse a StreamID
   on a given connection.

8.3.  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).

8.4.  Sending and Receiving Data

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



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   When new data is to be sent on a stream, a sender MUST set the
   encapsulating STREAM frame's offset field to the stream offset of the
   first byte of this new data.  The first byte of data that is sent on
   a stream has the stream offset 0.  A receiver MUST ensure that
   received stream data is delivered to the application as an ordered
   byte-stream.  Data received out of order MUST be buffered for later
   delivery, as long as it is not in violation of the receiver's flow
   control limits.

   An endpoint MUST NOT send any stream data without consulting the
   congestion controller and the flow controller, with the following two
   exceptions.

   o  The crypto handshake stream, Stream 1, MUST NOT be subject to
      congestion control or connection-level flow control, but MUST be
      subject to stream-level flow control.

   o  An application MAY exclude specific stream IDs from connection-
      level flow control.  If so, these streams MUST NOT be subject to
      connection-level flow control.

   Flow control is described in detail in Section XX, and congestion
   control is described in the companion document [QUIC-RECOVERY].

9.  Flow Control

   It is necessary to limit the amount of data that a sender may have
   outstanding at any time, so as to prevent a fast sender from
   overwhelming a slow receiver, or to prevent a malicious sender from
   consuming significant resources at a receiver.  This section
   describes QUIC's flow-control mechanisms.

   QUIC employs a credit-based flow-control scheme similar to HTTP/2's
   flow control [RFC7540].  A receiver advertises the number of octets
   it is prepared to receive on a given stream and for the entire
   connection.  This leads to two levels of flow control in QUIC: (i)
   Connection flow control, which prevents senders from exceeding a
   receiver's buffer capacity for the connection, and (ii) Stream flow
   control, which prevents a single stream from consuming the entire
   receive buffer for a connection.

   A receiver sends WINDOW_UPDATE frames to the sender to advertise
   additional credit, for both connection and stream flow control.  A
   receiver advertises the maximum absolute byte offset in the stream or
   in the connection which the receiver is willing to receive.

   The initial flow control credit is 65536 bytes for both the stream
   and connection flow controllers.



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   A receiver MAY advertise a larger offset at any point in the
   connection by sending a WINDOW_UPDATE frame.  A receiver MUST NOT
   renege on an advertisement; that is, once a receiver advertises an
   offset via a WINDOW_UPDATE frame, it MUST NOT subsequently advertise
   a smaller offset.  A sender may receive WINDOW_UPDATE frames out of
   order; a sender MUST therefore ignore any reductions in flow control
   credit.

   A sender MUST send BLOCKED frames to indicate it has data to write
   but is blocked by lack of connection or stream flow control credit.
   BLOCKED frames are expected to be sent infrequently in common cases,
   but they are considered useful for debugging and monitoring purposes.

   A receiver advertises credit for a stream by sending a WINDOW_UPDATE
   frame with the StreamID set appropriately.  A receiver may simply use
   the current received offset to determine the flow control offset to
   be advertised.

   Connection flow control is a limit to the total bytes of stream data
   sent in STREAM frames.  A receiver advertises credit for a connection
   by sending a WINDOW_UPDATE frame with the StreamID set to zero
   (0x00).  A receiver may maintain a cumulative sum of bytes received
   cumulatively on all streams to determine the value of the connection
   flow control offset to be advertised in WINDOW_UPDATE frames.  A
   sender may maintain a cumulative sum of stream data bytes sent to
   impose the connection flow control limit.

9.1.  Edge Cases and Other Considerations

   There are some edge cases which must be considered when dealing with
   stream and connection level flow control.  Given enough time, both
   endpoints must agree on flow control state.  If one end believes it
   can send more than the other end is willing to receive, the
   connection will be torn down when too much data arrives.  Conversely
   if a sender believes it is blocked, while endpoint B expects more
   data can be received, then the connection can be in a deadlock, with
   the sender waiting for a WINDOW_UPDATE which will never come.

9.1.1.  Mid-stream RST_STREAM

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



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   were sent on the stream to make the same adjustment in its connection
   flow controller.

   To avoid this de-synchronization, a RST_STREAM sender MUST include
   the final byte offset sent on the stream in the RST_STREAM frame.  On
   receiving a RST_STREAM frame, a receiver definitively knows how many
   bytes were sent on that stream before the RST_STREAM frame, and the
   receiver MUST use the final offset to account for all bytes sent on
   the stream in its connection level flow controller.

9.1.2.  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.

9.1.3.  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.

9.1.4.  BLOCKED frames

   If a sender does not receive a WINDOW_UPDATE frame when it has run
   out of flow control credit, the sender will be blocked and MUST send
   a BLOCKED frame.  A BLOCKED frame is expected to be useful for
   debugging at the receiver.  A receiver SHOULD NOT wait for a BLOCKED
   frame before sending with a WINDOW_UPDATE, since doing so will cause
   at least one roundtrip of quiescence.  For smooth operation of the
   congestion controller, it is generally considered best to not let the
   sender go into quiescence if avoidable.  To avoid blocking a sender,
   and to reasonably account for the possibiity of loss, a receiver
   should send a WINDOW_UPDATE frame at least two roundtrips before it
   expects the sender to get blocked.




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10.  Error Codes

   This section lists all the QUIC error codes that may be used in a
   CONNECTION_CLOSE frame.  TODO: Trim list and group errors for
   readabiity.

   o  0x01: QUIC_INTERNAL_ERROR.  (Connection has reached an invalid
      state.)

   o  0x02: QUIC_STREAM_DATA_AFTER_TERMINATION.  (There were data frames
      after the a fin or reset.)

   o  0x03: QUIC_INVALID_PACKET_HEADER.  (Control frame is malformed.)

   o  0x04: QUIC_INVALID_FRAME_DATA.  (Frame data is malformed.)

   o  0x30: QUIC_MISSING_PAYLOAD.  (The packet contained no payload.)

   o  0x2e: QUIC_INVALID_STREAM_DATA.  (STREAM frame data is malformed.)

   o  0x57: QUIC_OVERLAPPING_STREAM_DATA.  (STREAM frame data overlaps
      with buffered data.)

   o  0x3d: QUIC_UNENCRYPTED_STREAM_DATA.  (Received STREAM frame data
      is not encrypted.)

   o  0x58: QUIC_ATTEMPT_TO_SEND_UNENCRYPTED_STREAM_DATA.  (Attempt to
      send unencrypted STREAM frame.  Not sent on the wire, used for
      local logging.)

   o  0x59: QUIC_MAYBE_CORRUPTED_MEMORY.  (Received a frame which is
      likely the result of memory corruption.)

   o  0x06: QUIC_INVALID_RST_STREAM_DATA.  (RST_STREAM frame data is
      malformed.)

   o  0x07: QUIC_INVALID_CONNECTION_CLOSE_DATA.  (CONNECTION_CLOSE frame
      data is malformed.)

   o  0x08: QUIC_INVALID_GOAWAY_DATA.  (GOAWAY frame data is malformed.)

   o  0x39: QUIC_INVALID_WINDOW_UPDATE_DATA.  (WINDOW_UPDATE frame data
      is malformed.)

   o  0x3a: QUIC_INVALID_BLOCKED_DATA.  (BLOCKED frame data is
      malformed.)





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   o  0x3c: QUIC_INVALID_STOP_WAITING_DATA.  (STOP_WAITING frame data is
      malformed.)

   o  0x4e: QUIC_INVALID_PATH_CLOSE_DATA.  (PATH_CLOSE frame data is
      malformed.)

   o  0x09: QUIC_INVALID_ACK_DATA.  (ACK frame data is malformed.)

   o  0x0a: QUIC_INVALID_VERSION_NEGOTIATION_PACKET.  (Version
      negotiation packet is malformed.)

   o  0x0b: QUIC_INVALID_PUBLIC_RST_PACKET.  (Public RST packet is
      malformed.)

   o  0x0c: QUIC_DECRYPTION_FAILURE.  (There was an error decrypting.)

   o  0x0d: QUIC_ENCRYPTION_FAILURE.  (There was an error encrypting.)

   o  0x0e: QUIC_PACKET_TOO_LARGE.  (The packet exceeded
      kMaxPacketSize.)

   o  0x10: QUIC_PEER_GOING_AWAY.  (The peer is going away.  May be a
      client or server.)

   o  0x11: QUIC_INVALID_STREAM_ID.  (A stream ID was invalid.)

   o  0x31: QUIC_INVALID_PRIORITY.  (A priority was invalid.)

   o  0x12: QUIC_TOO_MANY_OPEN_STREAMS.  (Too many streams already
      open.)

   o  0x4c: QUIC_TOO_MANY_AVAILABLE_STREAMS.  (The peer created too many
      available streams.)

   o  0x13: QUIC_PUBLIC_RESET.  (Received public reset for this
      connection.)

   o  0x14: QUIC_INVALID_VERSION.  (Invalid protocol version.)

   o  0x16: QUIC_INVALID_HEADER_ID.  (The Header ID for a stream was too
      far from the previous.)

   o  0x17: QUIC_INVALID_NEGOTIATED_VALUE.  (Negotiable parameter
      received during handshake had invalid value.)

   o  0x18: QUIC_DECOMPRESSION_FAILURE.  (There was an error
      decompressing data.)




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   o  0x19: QUIC_NETWORK_IDLE_TIMEOUT.  (The connection timed out due to
      no network activity.)

   o  0x43: QUIC_HANDSHAKE_TIMEOUT.  (The connection timed out waiting
      for the handshake to complete.)

   o  0x1a: QUIC_ERROR_MIGRATING_ADDRESS.  (There was an error
      encountered migrating addresses.)

   o  0x56: QUIC_ERROR_MIGRATING_PORT.  (There was an error encountered
      migrating port only.)

   o  0x1b: QUIC_PACKET_WRITE_ERROR.  (There was an error while writing
      to the socket.)

   o  0x33: QUIC_PACKET_READ_ERROR.  (There was an error while reading
      from the socket.)

   o  0x32: QUIC_EMPTY_STREAM_FRAME_NO_FIN.  (We received a STREAM_FRAME
      with no data and no fin flag set.)

   o  0x38: QUIC_INVALID_HEADERS_STREAM_DATA.  (We received invalid data
      on the headers stream.)

   o  0x3b: QUIC_FLOW_CONTROL_RECEIVED_TOO_MUCH_DATA.  (The peer
      received too much data, violating flow control.)

   o  0x3f: QUIC_FLOW_CONTROL_SENT_TOO_MUCH_DATA.  (The peer sent too
      much data, violating flow control.)

   o  0x40: QUIC_FLOW_CONTROL_INVALID_WINDOW.  (The peer received an
      invalid flow control window.)

   o  0x3e: QUIC_CONNECTION_IP_POOLED.  (The connection has been IP
      pooled into an existing connection.)

   o  0x44: QUIC_TOO_MANY_OUTSTANDING_SENT_PACKETS.  (The connection has
      too many outstanding sent packets.)

   o  0x45: QUIC_TOO_MANY_OUTSTANDING_RECEIVED_PACKETS.  (The connection
      has too many outstanding received packets.)

   o  0x46: QUIC_CONNECTION_CANCELLED.  (The quic connection has been
      cancelled.)

   o  0x47: QUIC_BAD_PACKET_LOSS_RATE.  (Disabled QUIC because of high
      packet loss rate.)




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   o  0x49: QUIC_PUBLIC_RESETS_POST_HANDSHAKE.  (Disabled QUIC because
      of too many PUBLIC_RESETs post handshake.)

   o  0x4a: QUIC_TIMEOUTS_WITH_OPEN_STREAMS.  (Disabled QUIC because of
      too many timeouts with streams open.)

   o  0x4b: QUIC_FAILED_TO_SERIALIZE_PACKET.  (Closed because we failed
      to serialize a packet.)

   o  0x55: QUIC_TOO_MANY_RTOS.  (QUIC timed out after too many RTOs.)
      x1c: QUIC_HANDSHAKE_FAILED.  (Crypto errors.Hanshake failed.)

   o  0x1d: QUIC_CRYPTO_TAGS_OUT_OF_ORDER.  (Handshake message contained
      out of order tags.)

   o  0x1e: QUIC_CRYPTO_TOO_MANY_ENTRIES.  (Handshake message contained
      too many entries.)

   o  0x1f: QUIC_CRYPTO_INVALID_VALUE_LENGTH.  (Handshake message
      contained an invalid value length.)

   o  0x20: QUIC_CRYPTO_MESSAGE_AFTER_HANDSHAKE_COMPLETE.  (A crypto
      message was received after the handshake was complete.)

   o  0x21: QUIC_INVALID_CRYPTO_MESSAGE_TYPE.  (A crypto message was
      received with an illegal message tag.)

   o  0x22: QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER.  (A crypto message
      was received with an illegal parameter.)

   o  0x34: QUIC_INVALID_CHANNEL_ID_SIGNATURE.  (An invalid channel id
      signature was supplied.)

   o  0x23: QUIC_CRYPTO_MESSAGE_PARAMETER_NOT_FOUND.  (A crypto message
      was received with a mandatory parameter missing.)

   o  0x24: QUIC_CRYPTO_MESSAGE_PARAMETER_NO_OVERLAP.  (A crypto message
      was received with a parameter that has no overlapwith the local
      parameter.)

   o  0x25: QUIC_CRYPTO_MESSAGE_INDEX_NOT_FOUND.  (A crypto message was
      received that contained a parameter with too fewvalues.)

   o  0x5e: QUIC_UNSUPPORTED_PROOF_DEMAND.  (A demand for an unsupport
      proof type was received.)

   o  0x26: QUIC_CRYPTO_INTERNAL_ERROR.  (An internal error occured in
      crypto processing.)



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   o  0x27: QUIC_CRYPTO_VERSION_NOT_SUPPORTED.  (A crypto handshake
      message specified an unsupported version.)

   o  0x48: QUIC_CRYPTO_HANDSHAKE_STATELESS_REJECT.  (A crypto handshake
      message resulted in a stateless reject.)

   o  0x28: QUIC_CRYPTO_NO_SUPPORT.  (There was no intersection between
      the crypto primitives supported by thepeer and ourselves.)

   o  0x29: QUIC_CRYPTO_TOO_MANY_REJECTS.  (The server rejected our
      client hello messages too many times.)

   o  0x2a: QUIC_PROOF_INVALID.  (The client rejected the server's
      certificate chain or signature.)

   o  0x2b: QUIC_CRYPTO_DUPLICATE_TAG.  (A crypto message was received
      with a duplicate tag.)

   o  0x2c: QUIC_CRYPTO_ENCRYPTION_LEVEL_INCORRECT.  (A crypto message
      was received with the wrong encryption level (i.e. itshould have
      been encrypted but was not.))

   o  0x2d: QUIC_CRYPTO_SERVER_CONFIG_EXPIRED.  (The server config for a
      server has expired.)

   o  0x35: QUIC_CRYPTO_SYMMETRIC_KEY_SETUP_FAILED.  (We failed to setup
      the symmetric keys for a connection.)

   o  0x36: QUIC_CRYPTO_MESSAGE_WHILE_VALIDATING_CLIENT_HELLO.  (A
      handshake message arrived, but we are still validating theprevious
      handshake message.)

   o  0x41: QUIC_CRYPTO_UPDATE_BEFORE_HANDSHAKE_COMPLETE.  (A server
      config update arrived before the handshake is complete.)

   o  0x5a: QUIC_CRYPTO_CHLO_TOO_LARGE.  (CHLO cannot fit in one
      packet.)

   o  0x37: QUIC_VERSION_NEGOTIATION_MISMATCH.  (This connection
      involved a version negotiation which appears to have beentampered
      with.)

   o  0x50: QUIC_IP_ADDRESS_CHANGED.  (IP address changed causing
      connection close.)

   o  0x51: QUIC_CONNECTION_MIGRATION_NO_MIGRATABLE_STREAMS.
      (Connection migration errors.Network changed, but connection had
      no migratable streams.)



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   o  0x52: QUIC_CONNECTION_MIGRATION_TOO_MANY_CHANGES.  (Connection
      changed networks too many times.)

   o  0x53: QUIC_CONNECTION_MIGRATION_NO_NEW_NETWORK.  (Connection
      migration was attempted, but there was no new network tomigrate
      to.)

   o  0x54: QUIC_CONNECTION_MIGRATION_NON_MIGRATABLE_STREAM.  (Network
      changed, but connection had one or more non-migratable streams.)

   o  0x5d: QUIC_TOO_MANY_FRAME_GAPS.  (Stream frames arrived too
      discontiguously so that stream sequencer buffermaintains too many
      gaps.)

   o  0x5f: QUIC_STREAM_SEQUENCER_INVALID_STATE.  (Sequencer buffer get
      into weird state where continuing read/write will leadto crash.)

   o  0x60: QUIC_TOO_MANY_SESSIONS_ON_SERVER.  (Connection closed
      because of server hits max number of sessions allowed.

11.  Security and Privacy Considerations

11.1.  Spoofed Ack Attack

   An attacker receives an STK from the server and then releases the IP
   address on which it received the STK.  The attacked may in the
   future, spoof this same address (which now presumably addresses a
   different endpoint), and initiates a 0-RTT connection with a server
   on the victim's behalf.  The attacker then spoofs ack packets to the
   server which cause the server to potentially drown the victim in
   data.

   There are two possible mitigations to this attack.  The simplest one
   is that a server can unilaterally create a gap in packet-number
   space.  In the non-attack scenario, the client will send an ack with
   a larger largest acked.  In the attack scenario, the attacker may ack
   a packet in the gap.  If the server sees an ack for a packet that was
   never sent, the connection can be aborted.

   The second mitigation is that the server can require that acks for
   sent packets match the encryption level of the sent packet.  This
   mitigation is useful if the connection has an ephemeral forward-
   secure key that is generated and used for every new connection.  If a
   packet sent is encrypted with a forward-secure key, then any acks
   that are received for them must also be forward-secure encrypted.
   Since the attacker will not have the forward secure key, the attacker
   will not be able to generate forward-secure encrypted ack packets.




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12.  IANA Considerations

   This document has no IANA actions yet.

13.  References

13.1.  Normative References

   [QUIC-RECOVERY]
              Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection
              and Congestion Control", November 2016.

   [QUIC-TLS]
              Thomson, M., Ed. and S. Turner, Ed, Ed., "Using Transport
              Layer Security (TLS) to Secure QUIC", November 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
              Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
              <http://www.rfc-editor.org/info/rfc4821>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <http://www.rfc-editor.org/info/rfc7540>.

13.2.  Informative References

   [EARLY-DESIGN]
              Roskind, J., "QUIC: Multiplexed Transport Over UDP",
              December 2013, <https://goo.gl/dMVtFi>.

   [QUIC-HTTP]
              Bishop, M., Ed., "Hypertext Transfer Protocol (HTTP) over
              QUIC", November 2016.

   [QUICCrypto]
              Langley, A. and W. Chang, "QUIC Crypto", May 2016,
              <http://goo.gl/OuVSxa>.

   [SST]      Ford, B., "Structured Streams: A New Transport
              Abstraction", ACM SIGCOMM 2007 , August 2007.





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Appendix A.  Contributors

   The original authors of this specification were Ryan Hamilton, Jana
   Iyengar, Ian Swett, and Alyssa Wilk.

   The original design and rationale behind this protocol draw
   significantly from work by Jim Roskind [EARLY-DESIGN].  In
   alphabetical order, the contributors to the pre-IETF QUIC project at
   Google are: Britt Cyr, Jeremy Dorfman, Ryan Hamilton, Jana Iyengar,
   Fedor Kouranov, Charles Krasic, Jo Kulik, Adam Langley, Jim Roskind,
   Robbie Shade, Satyam Shekhar, Cherie Shi, Ian Swett, Raman Tenneti,
   Victor Vasiliev, Antonio Vicente, Patrik Westin, Alyssa Wilk, Dale
   Worley, Fan Yang, Dan Zhang, Daniel Ziegler.

Appendix B.  Acknowledgments

   Special thanks are due to the following for helping shape pre-IETF
   QUIC and its deployment: Chris Bentzel, Misha Efimov, Roberto Peon,
   Alistair Riddoch, Siddharth Vijayakrishnan, and Assar Westerlund.

   This document has benefited immensely from various private
   discussions and public ones on the quic@ietf.org and proto-
   quic@chromium.org mailing lists.  Our thanks to all.

Authors' Addresses

   Jana Iyengar (editor)
   Google

   Email: jri@google.com


   Martin Thomson (editor)
   Mozilla

   Email: martin.thomson@gmail.com















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