QUIC 协议

Abstract

QUIC protocol

Authors

Walter Fan

Status

WIP as draft

Updated

2024-08-21

简介

QUIC provides applications with flow-controlled streams for structured communication, low-latency connection establishment, and network path migration.

QUIC includes security measures that ensure confidentiality, integrity, and availability in a range of deployment circumstances.

Accompanying documents describe the integration of TLS for key negotiation, loss detection, and an exemplary congestion control algorithm.

Background

Just like with HTTP/2, an advancement which was spearheaded by Google’s SPDY or speedy, HTTP/3 will again build on these achievements.

While HTTP/2 did give us multiplexing, and mitigate head-of-line-blocking, it is constrained by TCP. You can use a single TCP connection for multiple streams multiplexed together to transfer data, but when one of those streams suffers a packet loss, the whole connection (and all its streams) are held hostage, so to say, until TCP does its thing (retransmits the lost packet).

This means that all the packets, even if they are already transmitted and waiting, in the buffer of the destination node, are being blocked until the lost packet is retransmitted. Daniel Stenberg in his book on http/3 calls this a “TCP-based head of line block.” He claims that, with 2% packet loss, users will do better with HTTP/1, with six connections to hedge this risk.

QUIC is not constrained by this. With QUIC building on the on connectionless UDP protocol, the concept of connection does not carry the limitations of TCP and failures of one stream do not have to influence the rest.

While QUIC does away with TCP reliability features, it makes up for it above the UDP layer, providing retransmitting of packets, ordering and so on. Google Cloud Platform introduced QUIC support for their load balancers in 2018 and saw an improvement in mean page load time by 8% globally, and up to 13% in regions where latency is higher.

协议文档结构

Streams are the basic service abstraction that QUIC provides.

  • Section 2 describes core concepts related to streams,

  • Section 3 provides a reference model for stream states, and

  • Section 4 outlines the operation of flow control.

Connections are the context in which QUIC endpoints communicate.

  • Section 5 describes core concepts related to connections,

  • Section 6 describes version negotiation,

  • Section 7 details the process for establishing connections,

  • Section 8 describes address validation and critical denial-of-service mitigations,

  • Section 9 describes how endpoints migrate a connection to a new network path,

  • Section 10 lists the options for terminating an open connection, and

  • Section 11 provides guidance for stream and connection error handling.

Packets and frames are the basic unit used by QUIC to communicate.

  • Section 12 describes concepts related to packets and frames,

  • Section 13 defines models for the transmission, retransmission, and acknowledgment of data, and

  • Section 14 specifies rules for managing the size of datagrams carrying QUIC packets.

Finally, encoding details of QUIC protocol elements are described in:

  • Section 15 (versions),

  • Section 16 (integer encoding),

  • Section 17 (packet headers),

  • Section 18 (transport parameters),

  • Section 19 (frames), and

  • Section 20 (errors).

Reference