What is QUIC ?
Quick protocol is somewhere in between TCP and UDP.Upto HTTP/2 TCP is used as underlying transport protocol. One of the benefits of HTTP/2 over HTTP 1.1 is multiplexing of http request streams over Single TCP connection. Using single connection improves efficiency and better utilization of bandwidth.In HTTP/1.1 browser creates multiple connections, means multiple times initial handshake process takes place, which is nothing but waste of bandwidth and increases the latency.Creating new connections is slow because of initial handshake. Single TCP connection gives better efficiency of resources and bandwidth.
Since TCP provides reliable, ordered, and error-checked delivery of a stream of octets (bytes), it also suffers from Head of line blocking issue. In HTTP 2 all HTTP requests are serviced by single connection via multiplexing technique and if error occurs in any of chunk all the streams got blocked.This is serious issue because it blocks everything.Until that chunk is not corrected, all the chunks behind that error got blocked. This issue is more prevalent in error prone links. Blocking is proportional to health of the link.
QUIC uses single connection end to end between client and server, so it saves handshake cost etc.Internally it uses multiplexing and there is one to one mapping between HTTP request stream and UDP connection.This is the main different between HTTP/2 and QUIC.So if error occurs in one Stream other streams are not affected by this. Error recovery and Re-transmission is taken care by QUIC layer.