Why QUIC Is the Future of Web Protocols: From HTTP/1.1 to HTTP/3

1. Introduction

自 2015 年以来，QUIC 协议开始在 IETF 进行标准化并被国内外各大厂商相继落地。鉴于 QUIC 具备“0RTT 建连”、“支持连接迁移”等诸多优势，即将成为下一代互联网协议。

After reading this article you will learn and understand:

History of the HTTP protocol

Problems of each HTTP version and how they were solved

Features of the QUIC protocol

How to confidently answer interview questions about HTTP

Approach: Starting from the widely used HTTP/1.1, we introduce the issues of each version and how newer versions address them.

2. History of HTTP

HTTP 0.9 (1991) only supports GET and has no headers.

HTTP 1.0 (1996) formed, supporting headers, rich text, status codes, caching, but connections cannot be reused.

HTTP 1.1 (1999) adds connection reuse, chunked transfer, and resume support.

HTTP 2.0 (2015) introduces binary framing, multiplexing, header compression, and server push.

HTTP 3.0 (2018) implements QUIC; in October 2018 the IETF mapped HTTP onto QUIC as "HTTP/3".

Problems of HTTP/1.1

1. Unidirectional request

Only the client can initiate a request; the server cannot push data proactively.

2. Large protocol overhead

Headers are bulky and cannot be compressed, increasing transmission cost. For example, every request repeats Cache-Control: no-cache, wasting bandwidth.

3. Head‑of‑line blocking

Subsequent requests must wait for the previous response, preventing full bandwidth utilization. Example: request A blocks request B until A finishes.

HTTP/2 Features and Issues

Features

1. Binary framing

HTTP/2 splits data into header frames and data frames, which are transmitted in independent streams.

2. Multiplexing

Multiple requests and responses can be sent concurrently over a single connection without waiting for each other.

3. Stream priority

Important resources can be prioritized to improve page rendering speed.

4. Header compression

Uses the HPACK algorithm to reduce redundant header data.

5. Server push

The server can proactively send resources required by the client, reducing latency.

Issues

1. Connection establishment latency

TCP’s three‑way handshake and TLS handshake add multiple RTTs; QUIC later addresses this.

2. Head‑of‑line blocking at the TCP layer

Multiplexing solves HTTP‑level blocking but TCP‑level blocking remains.

3. QUIC Protocol

What is QUIC?

QUIC (Quick UDP Internet Connection) is a Google‑designed transport protocol built on UDP that combines TCP‑like reliability, TLS security, and HTTP/2 performance features to reduce network latency.

QUIC Features

1. Based on UDP

Unlike TCP, UDP is connectionless, eliminating the time‑consuming TCP three‑way handshake.

2. Low connection latency

QUIC removes the multiple RTTs required by TCP/TLS handshakes and supports 0‑RTT data transmission after the first key exchange.

0‑RTT Connection

First connection uses 1‑RTT to exchange encryption keys; subsequent connections can send data immediately (0‑RTT) using previously exchanged keys via Diffie‑Hellman key exchange.

3. Connection migration

HTTP/2 identification

HTTP/2 identifies a connection by a four‑tuple (source IP, source port, destination IP, destination port). Changing any element forces a new connection.

QUIC identification

QUIC uses a 64‑bit random Connection ID, which remains constant across IP/port changes, enabling seamless migration without reconnecting.

4. Customizable congestion control

QUIC implements congestion control in user space, allowing algorithms such as BBR to be chosen per application, unlike TCP’s fixed Cubic.

5. No head‑of‑line blocking

QUIC moves stream IDs to the transport layer and uses packet numbers that allow out‑of‑order delivery, so loss of a packet does not stall other streams.

Conclusion

With modern bandwidth no longer the bottleneck, latency dominates performance. QUIC replaces TCP with UDP, adds 0‑RTT connections, smooth connection migration, eliminates head‑of‑line blocking, and offers flexible congestion control, making it a strong candidate for the next‑generation transport layer.

References

HTTP/3 From A To Z: Core Concepts

QUIC official website