QUIC (pronounced "quick") is a general-purpose

transport layer In computer networking, the transport layer is a conceptual division of methods in the layered architecture of protocols in the network stack in the Internet protocol suite and the OSI model. The protocols of this layer provide end-to-e ...

network protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...

initially designed by

Jim Roskind Jim Roskind is an American software engineer best known for designing the QUIC protocol in 2012 while an employee of Google. As of 2018, QUIC was used in 8% of all internet traffic. Roskind co-founded Infoseek in 1994 with 7 other people, includ ...

Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...

, implemented, and deployed in 2012, announced publicly in 2013 as experimentation broadened, and described at an

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements an ...

meeting. QUIC is used by more than half of all connections from the

Chrome web browser Google Chrome is a cross-platform web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS ...

to Google's servers.

Microsoft Edge Microsoft Edge is a proprietary, cross-platform web browser created by Microsoft. It was first released in 2015 as part of Windows 10 and Xbox One and later ported to other platforms as a fork of Google's Chromium open-source project: Android ...

(a derivative of the open-source Chromium browser) and

Firefox Mozilla Firefox, or simply Firefox, is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. It uses the Gecko rendering engine to display web pages, which implements current ...

support it.

Safari A safari (; ) is an overland journey to observe wild animals, especially in eastern or southern Africa. The so-called "Big Five" game animals of Africa – lion, leopard, rhinoceros, elephant, and Cape buffalo – particularly form an impor ...

implements the protocol, however it is not enabled by default. Although its name was initially proposed as the acronym for "Quick UDP Internet Connections", IETF's use of the word QUIC is not an acronym; it is simply the name of the protocol. QUIC improves performance of connection-oriented

web application A web application (or web app) is application software that is accessed using a web browser. Web applications are delivered on the World Wide Web to users with an active network connection. History In earlier computing models like client-serv ...

s that are currently using TCP. It does this by establishing a number of

multiplexed In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...

connections between two endpoints using

User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) netwo ...

(UDP), and is designed to obsolete TCP at the transport layer for many applications, thus earning the protocol the occasional nickname "TCP/2". QUIC works hand-in-hand with HTTP/2's multiplexed connections, allowing multiple streams of data to reach all the endpoints independently, and hence independent of

packet loss Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion.Ku ...

es involving other streams. In contrast, HTTP/2 hosted on

Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...

(TCP) can suffer head-of-line-blocking delays of all multiplexed streams if any of the TCP packets are delayed or lost. QUIC's secondary goals include reduced connection and transport latency, and

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

estimation in each direction to avoid congestion. It also moves

congestion control Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...

algorithms into the

user space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

at both endpoints, rather than the

kernel space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

, which it is claimed will allow these algorithms to improve more rapidly. Additionally, the protocol can be extended with

forward error correction In computing, telecommunication, information theory, and coding theory, an error correction code, sometimes error correcting code, (ECC) is used for controlling errors in data over unreliable or noisy communication channels. The central idea i ...

(FEC) to further improve performance when errors are expected, and this is seen as the next step in the protocol's evolution. It has been designed to avoid

protocol ossification Protocol ossification is the loss of flexibility, extensibility and evolvability of network protocols. This is largely due to middleboxes that are sensitive to the wire image of the protocol, and which can interrupt or interfere with messages tha ...

so that it remains evolvable, unlike TCP which has suffered significant ossification. In June 2015, an

Internet Draft An Internet Draft (I-D) is a document published by the Internet Engineering Task Force (IETF) containing preliminary technical specifications, results of networking-related research, or other technical information. Often, Internet Drafts are int ...

of a specification for QUIC was submitted to the

for standardization. A QUIC working group was established in 2016. In October 2018, the IETF's HTTP and QUIC Working Groups jointly decided to call the HTTP mapping over QUIC "

HTTP/3 HTTP/3 is the third major version of the Hypertext Transfer Protocol used to exchange information on the World Wide Web, complementing the widely-deployed HTTP/1.1 and HTTP/2. Unlike previous versions which relied on the well-established TCP ...

" in advance of making it a worldwide standard. In May 2021, the IETF standardized QUIC in , supported by , and .

Background

, or TCP, aims to provide an interface for sending streams of data between two endpoints. Data is handed to the TCP system, which ensures the data makes it to the other end in exactly the same form, or the connection will indicate that an error condition exists. To do this, TCP breaks up the data into

network packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control inform ...

s and adds small amounts of data to each packet. This additional data includes a sequence number that is used to detect packets that are lost or arrive out of order, and a

checksum A checksum is a small-sized block of data derived from another block of digital data for the purpose of detecting errors that may have been introduced during its transmission or storage. By themselves, checksums are often used to verify data ...

that allows the errors within packet data to be detected. When either problem occurs, TCP uses

automatic repeat request Automatic repeat request (ARQ), also known as automatic repeat query, is an error-control method for data transmission that uses acknowledgements (messages sent by the receiver indicating that it has correctly received a packet) and timeouts ...

(ARQ) to tell the sender to re-send the lost or damaged packet. In most implementations, TCP will see any error on a connection as a blocking operation, stopping further transfers until the error is resolved or the connection is considered failed. If a single connection is being used to send multiple streams of data, as is the case in the HTTP/2 protocol, all of these streams are blocked although only one of them might have a problem. For instance, if a single error occurs while downloading a GIF image used for a

favicon A favicon (; short for favorite icon), also known as a shortcut icon, website icon, tab icon, URL icon, or bookmark icon, is a file containing one or more small icons, associated with a particular website or web page. A web designer can create ...

, the entire rest of the page will wait while that problem is resolved. This phenomenon is known as

head-of-line blocking Head-of-line blocking (HOL blocking) in computer networking is a performance-limiting phenomenon that occurs when a line of packets is held up in a queue by a first packet. Examples include input buffered network switches, out-of-order delivery a ...

. As the TCP system is designed to look like a "data pipe", or stream, it deliberately contains little understanding of the data it transmits. If that data has additional requirements, like

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can d ...

using

TLS TLS may refer to: Computing * Transport Layer Security, a cryptographic protocol for secure computer network communication * Thread level speculation, an optimisation on multiprocessor CPUs * Thread-local storage, a mechanism for allocating vari ...

, this must be set up by systems running on top of TCP, using TCP to communicate with similar software on the other end of the connection. Each of these sorts of setup tasks requires its own

handshake A handshake is a globally widespread, brief greeting or parting tradition in which two people grasp one of each other's like hands, in most cases accompanied by a brief up-and-down movement of the grasped hands. Customs surrounding handshakes a ...

process. This often requires several round-trips of requests and responses until the connection is established. Due to the inherent latency of long-distance communications, this can add significant overhead to the overall transmission. TCP has suffered from

, due to its wire image being in

cleartext In cryptography, plaintext usually means unencrypted information pending input into cryptographic algorithms, usually encryption algorithms. This usually refers to data that is transmitted or stored unencrypted. Overview With the advent of co ...

and hence visible to and malleable by

middlebox A middlebox is a computer networking device that transforms, inspects, filters, and manipulates traffic for purposes other than packet forwarding. Examples of middleboxes include firewalls, network address translators (NATs), load balancers, and ...

es. One measurement found that a third of paths across the Internet encounter at least one intermediary that modifies TCP metadata, and 6.5% of paths encounter harmful ossifying effects from intermediaries. Extensions to TCP have been affected: the design of

MPTCP Multipath TCP (MPTCP) is an ongoing effort of the Internet Engineering Task Force's (IETF) Multipath TCP working group, that aims at allowing a Transmission Control Protocol (TCP) connection to use multiple paths to maximize throughput and inc ...

was constrained by middlebox behaviour, and the deployment of TCP Fast Open has been likewise hindered.

Characteristics

QUIC aims to be nearly equivalent to a TCP connection but with much-reduced latency. It does this primarily through two changes that rely on the understanding of the behaviour of

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide We ...

traffic. The first change is to greatly reduce overhead during connection setup. As most HTTP connections will demand

, QUIC makes the exchange of setup keys and supported protocols part of the initial handshake process. When a client opens a connection, the response packet includes the data needed for future packets to use encryption. This eliminates the need to set up the TCP connection and then negotiate the security protocol via additional packets. Other protocols can be serviced in the same way, combining together multiple steps into a single request-response. This data can then be used both for following requests in the initial setup, as well as future requests that would otherwise be negotiated as separate connections. The second change is to use UDP rather than TCP as its basis, which does not include

loss Loss may refer to: Arts, entertainment, and media Music * ''Loss'' (Bass Communion album) (2006) * ''Loss'' (Mull Historical Society album) (2001) *"Loss", a song by God Is an Astronaut from their self-titled album (2008) * Losses "(Lil Tjay son ...

recovery. Instead, each QUIC stream is separately flow controlled and lost data is retransmitted at the level of QUIC, not UDP. This means that if an error occurs in one stream, like the favicon example above, the

protocol stack The protocol stack or network stack is an implementation of a computer networking protocol suite or protocol family. Some of these terms are used interchangeably but strictly speaking, the ''suite'' is the definition of the communication protoco ...

can continue servicing other streams independently. This can be very useful in improving performance on error-prone links, as in most cases considerable additional data may be received before TCP notices a packet is missing or broken, and all of this data is blocked or even flushed while the error is corrected. In QUIC, this data is free to be processed while the single multiplexed stream is repaired. QUIC also includes a number of other more mundane changes that also improve overall latency and throughput. For instance, the packets are encrypted individually, so that they do not result in the encrypted data waiting for partial packets. This is not generally possible under TCP, where the encryption records are in a

bytestream A bitstream (or bit stream), also known as binary sequence, is a sequence of bits. A bytestream is a sequence of bytes. Typically, each byte is an 8-bit quantity, and so the term octet stream is sometimes used interchangeably. An octet may ...

and the protocol stack is unaware of higher-layer boundaries within this stream. These can be negotiated by the layers running on top, but QUIC aims to do all of this in a single handshake process. Another goal of the QUIC system was to improve performance during network-switch events, like what happens when a user of a mobile device moves from a local

WiFi hotspot A hotspot is a physical location where people can obtain Internet access, typically using Wi-Fi technology, via a wireless local-area network (WLAN) using a router connected to an Internet service provider. Public hotspots may be created by ...

to a mobile network. When this occurs on TCP, a lengthy process starts where every existing connection times out one-by-one and is then re-established on demand. To solve this problem, QUIC includes a connection identifier which uniquely identifies the connection to the server regardless of source. This allows the connection to be re-established simply by sending a packet, which always contains this ID, as the original connection ID will still be valid even if the user's

IP address An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...

changes. QUIC can be implemented in the application-space, as opposed to being in the

operating system kernel The kernel is a computer program at the core of a computer's operating system and generally has complete control over everything in the system. It is the portion of the operating system code that is always resident in memory and facilitates ...

. This generally invokes additional overhead due to

context switch In computing, a context switch is the process of storing the state of a process or thread, so that it can be restored and resume execution at a later point, and then restoring a different, previously saved, state. This allows multiple processe ...

es as data is moved between applications. However, in the case of QUIC, the protocol stack is intended to be used by a single application, with each application using QUIC having its own connections hosted on UDP. Ultimately the difference could be very small because much of the overall HTTP/2 stack is already in the applications (or their libraries, more commonly). Placing the remaining parts in those libraries, essentially the error correction, has little effect on the HTTP/2 stack's size or overall complexity. This organization allows future changes to be made more easily as it does not require changes to the

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learn ...

for updates. One of QUIC's longer-term goals is to add new systems for

(FEC) and improved congestion control. One concern about the move from TCP to UDP is that TCP is widely adopted and many of the "

es" in the internet infrastructure are tuned for TCP and rate-limit or even block UDP. Google carried out a number of exploratory experiments to characterize this and found that only a small number of connections were blocked in this manner. This led to the use of a rapid fallback-to-TCP system;

Chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

's network stack opens both a QUIC and traditional TCP connection at the same time, which allows it to fall back with negligible latency. QUIC has been specifically designed to be deployable, evolvable and to have anti-ossification properties; it is the first

transport protocol to deliberately minimise its wire image for these ends. Beyond encrypted headers, it is 'greased' and it has protocol invariants explicitly specified.

Google QUIC (gQUIC)

The protocol that was created by Google and taken to the IETF under the name QUIC (already in 2012 around QUIC version 20) is quite different from the QUIC that has continued to evolve and be refined within the IETF. The original Google QUIC was designed to be a general purpose protocol, though it was initially deployed as a protocol to support HTTP(S) in Chromium. The current evolution of the IETF QUIC protocol is a general purpose transport protocol. Chromium developers continued to track the evolution of IETF QUIC's standardization efforts to adopt and fully comply with the most recent internet standards for QUIC in Chromium.

Adoption

Browser support

The QUIC code was experimentally developed in

Google Chrome Google Chrome is a cross-platform web browser developed by Google. It was first released in 2008 for Microsoft Windows, built with free software components from Apple WebKit and Mozilla Firefox. Versions were later released for Linux, macOS, ...

starting in 2012, and was announced as part of Chromium version 29 (released on August 20, 2013). It is currently enabled by default in Chromium and Chrome. Support in

arrived in May 2021.

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ancest ...

added experimental support in the WebKit engine through the Safari Technology Preview 104 in April 2020. Official support was added in

14, included in

macOS Big Sur macOS Big Sur (version 11) is the seventeenth major release of macOS, Apple Inc.'s operating system for Macintosh computers. It was announced at Apple's Worldwide Developers Conference (WWDC) on June 22, 2020, and was released to the publi ...

and

iOS 14 iOS 14 is the fourteenth major release of the iOS mobile operating system developed by Apple Inc. for their iPhone and iPod Touch lines. Announced at the company's Worldwide Developers Conference on June 22, 2020 as the successor to iOS 13 ...

, but the feature must be turned on manually.

Client support

The cronet library for QUIC and other protocols is available to Android applications as a module loadable via

Google Play Services Google Play Services is a proprietary software package produced by Google for installation on Android devices. It consists of background services and libraries for use by mobile apps running on the device When it was introduced in 2012, it pro ...

cURL cURL (pronounced like "curl", UK: , US: ) is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various network protocols. The name stands for "Client URL". History cURL was ...

7.66, released 11 September 2019, supports HTTP/3 (and thus QUIC). In October 2020, Facebook announced that it has successfully migrated its apps, including

Instagram Instagram is a photo and video sharing social networking service owned by American company Meta Platforms. The app allows users to upload media that can be edited with filters and organized by hashtags and geographical tagging. Posts can ...

, and server infrastructure to QUIC, with already 75% of its Internet traffic using QUIC. All mobile apps from Google support QUIC, including

YouTube YouTube is a global online video sharing and social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by Google, and is the second mo ...

and

Gmail Gmail is a free email service provided by Google. As of 2019, it had 1.5 billion active users worldwide. A user typically accesses Gmail in a web browser or the official mobile app. Google also supports the use of email clients via the POP and ...

Uber Uber Technologies, Inc. (Uber), based in San Francisco, provides mobility as a service, ride-hailing (allowing users to book a car and driver to transport them in a way similar to a taxi), food delivery ( Uber Eats and Postmates), pa ...

's mobile app also uses QUIC.

Server support

, there are several actively maintained implementations. Google servers support QUIC and Google has published a prototype server.

Akamai Technologies Akamai Technologies, Inc. is an American content delivery networkJ. Dilley, B. Maggs, J. Parikh, H. Prokop, R. Sitaraman, and B. Weihl. (CDN), cybersecurity, and cloud service company, providing web and Internet security services. Akamai's Inte ...

has been supporting QUIC since July 2016. A Go implementation called quic-go is also available, and powers experimental QUIC support in the Caddy server. On July 11, 2017, LiteSpeed Technologies officially began supporting QUIC in their load balancer (WebADC) and

LiteSpeed Web Server LiteSpeed Web Server (LSWS) is proprietary web server software. It is the 4th most popular web server, estimated to be used by 10% of websites as of July 2021. LSWS is developed by privately held LiteSpeed Technologies. The software uses the s ...

products. , 88.6% of QUIC websites used LiteSpeed and 10.8% used

Nginx Nginx (pronounced "engine x" ) is a web server that can also be used as a reverse proxy, load balancer, mail proxy and HTTP cache. The software was created by Igor Sysoev and publicly released in 2004. Nginx is free and open-source softw ...

. Although at first only Google servers supported HTTP-over-QUIC connections,

Facebook Facebook is an online social media and social networking service owned by American company Meta Platforms. Founded in 2004 by Mark Zuckerberg with fellow Harvard College students and roommates Eduardo Saverin, Andrew McCollum, Dust ...

also launched the technology in 2018, and

Cloudflare Cloudflare, Inc. is an American content delivery network and DDoS mitigation company, founded in 2009. It primarily acts as a reverse proxy between a website's visitor and the Cloudflare customer's hosting provider. Its headquarters are in Sa ...

has been offering QUIC support on a beta basis since 2018. , 5.0% of all websites use QUIC. Microsoft Windows Server 2022 supports both HTTP/3 and SMB over QUIC protocols via MsQuic. The Application Delivery Controller of

Citrix Citrix Systems, Inc. is an American multinational cloud computing and virtualization technology company that provides server, application and desktop virtualization, networking, software as a service (SaaS), and cloud computing technologi ...

(Citrix ADC, NetScaler) can function as a QUIC proxy since version 13. In addition, there are several stale community projects: libquic was created by extracting the Chromium implementation of QUIC and modifying it to minimize dependency requirements, and goquic provides Go bindings of libquic. Finally, quic-reverse-proxy is a Docker image that acts as a

reverse proxy In computer networks, a reverse proxy is the application that sits in front of back-end applications and forwards client (e.g. browser) requests to those applications. Reverse proxies help increase scalability, performance, resilience and securi ...

server, translating QUIC requests into plain HTTP that can be understood by the origin server.

.NET 5 The domain name net is a generic top-level domain (gTLD) used in the Domain Name System of the Internet. The name is derived from the word ''network'', indicating it was originally intended for organizations involved in networking technologies ...

introduces experimental support for QUIC using the MsQuic library.

Source code

References

Bibliography

* * * * * * * * * *

External links

* * * – Version-Independent Properties of QUIC * – QUIC: A UDP-Based Multiplexed and Secure Transport * – Using TLS to Secure QUIC * – QUIC Loss Detection and Congestion Control *

QUIC, a multiplexed stream transport over UDP

QUIC: Design Document and Specification Rationale
Jim Roskind's original document (2012/2013) *

Daniel Stenberg Magnus Daniel Stenberg is a Swedish developer, recipient of the Polhem Prize 2017 for his work on cURL. He was born and raised in Huddinge, a suburb south of Sweden's capital Stockholm. He created a utility which, after various name and license ...

HTTP/3 explained
*

Linux Weekly News LWN.net is a computing webzine with an emphasis on free software and software for Linux and other Unix-like operating systems. It consists of a weekly issue, separate stories which are published most days, and threaded discussion attached to ...

Connecting on the QUIC
(2013)
QUIC:
IETF-88 TSV Area Presentation (2013-11-07) * Chromium Blog

(2013)
QUIC: next generation multiplexed transport over UDP
(Google Developers, 2014)
HTTP over UDP: an Experimental Investigation of QUIC

Multipath QUIC
(extension to QUIC)
Innovating Transport with QUIC: Design Approaches and Research Challenges
(2017)
EPIQ 2018 Keynote
– ''Facebook's IETF QUIC deployment,'' Subodh Iyengar on YouTube
EPIQ 2021 Keynote
– ''QUIC at Microsoft'', Nick Bankson on YouTube * * {{youTube, nP1yzxHcgeM, QUIC at Apple (2021) - Tommy Pauly, link=no
qvis: QUIC and HTTP/3 visualization suite.

The Illustrated QUIC Connection
Transport layer protocols Internet protocols Computer networking