QUIC

QUIC (pronounced 'quick') is a general-purpose transport layer network protocol initially designed by Jim Roskind at Google, implemented, and deployed in 2012, announced publicly in 2013 as experimentation broadened, and described to the IETF. While still an Internet Draft, QUIC is used by more than half of all connections from the Chrome web browser to Google's servers. Most other web browsers do not support the protocol. QUIC (pronounced 'quick') is a general-purpose transport layer network protocol initially designed by Jim Roskind at Google, implemented, and deployed in 2012, announced publicly in 2013 as experimentation broadened, and described to the IETF. While still an Internet Draft, QUIC is used by more than half of all connections from the Chrome web browser to Google's servers. Most other web browsers do not support the protocol. 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. Among other applications, QUIC improves performance of connection-oriented web applications that are currently using TCP. It does this by establishing a number of multiplexed connections between two endpoints over User Datagram Protocol (UDP). This 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 losses involving other streams. In contrast, HTTP/2 hosted on Transmission Control Protocol (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 estimation in each direction to avoid congestion. It also moves congestion control algorithms into the user space at both endpoints, rather than the kernel space, which it is claimed will allow these algorithms to improve more rapidly. Additionally, the protocol can be extended with forward error correction (FEC) to further improve performance when errors are expected, and this is seen as the next step in the protocol's evolution. In June 2015, an Internet Draft of a specification for QUIC was submitted to the IETF 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' in advance of making it a worldwide standard. Transmission Control Protocol, 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 packets 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 transmitted out of order, and a checksum that allows the errors within packet data to be detected. When either problem occurs, TCP uses automatic repeat request (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, the entire rest of the page will wait while that problem is resolved. 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 using TLS, 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 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.