Deciphering the third transport protocol's four RFCs is a task to rival the proverbial blind man trying to understand an elephant. //

Streams are the primary mechanism making QUIC a better fit for request/response operations. When HTTP runs over TCP, the only way to allow one request to proceed independently of another is to open multiple parallel TCP connections.

With each connection running its own congestion control loop, the experience of congestion on one connection is not apparent to the other connections; each connection tries to figure out the appropriate amount of bandwidth to consume on its own, while competing with the others. And if HTTP runs over a single TCP connection, a single dropped packet blocks the entire progress of any requests in flight until that lost packet is retransmitted.

So QUIC allows for many streams within a single connection, and each stream can make progress independently from the others. A single packet loss only impacts the stream (or streams) whose data was in that packet. At the same time, QUIC can use that one packet loss to respond appropriately to congestion. //

Larry Peterson and Bruce Davie are the authors behind Computer Networks: A Systems Approach and the related Systems Approach series of books. All their content is open source and available for free on GitHub. https://github.com/SystemsApproach