Connections

A QUIC connection is a single conversation between two QUIC endpoints. QUIC’sconnection establishment combines version negotiation with the cryptographicand transport handshakes to reduce connection establishment latency.

To actually send data over such a connection, one or more streams have to becreated and used.

Connection ID

Each connection possesses a set of connection identifiers, or connection IDs,each of which can be used to identify the connection. Connection IDs areindependently selected by endpoints; each endpoint selects the connection IDsthat its peer uses.

The primary function of these connection IDs is to ensure that changes inaddressing at lower protocol layers (UDP, IP, and below) do not cause packetsfor a QUIC connection to be delivered to the wrong endpoint.

By taking advantage of the connection ID, connections can thus migrate betweenIP addresses and network interfaces in ways TCP never could. For instance,migration allows an in-progress download to move from a cellular network connectionto a faster wifi connection when the user moves their device into a locationoffering wifi. Similarly, the download can proceed over the cellular connectionif wifi becomes unavailable.

Port numbers

QUIC is built atop UDP, so a 16 bit port number field is used to differentiateincoming connections.

Version negotiation

An QUIC connection request originating from a client will tell the serverwhich QUIC protocol version it wants to speak, and the server will respondwith a list of supported versions for the client to select from.