What problems have HTTP/1, HTTP/2, and HTTP/3 solved?

What problem does each generation of HTTP solve? The following diagram illustrates the main features.

HTTP/1HTTP 1.0 was finalized and fully documented in 1996. Each request to the same server required a separate TCP connection.HTTP 1.1 was released in 1997.

TCP connections can be kept open for reuse (persistent connections), but this does not solve the problem of HOL (Head of Line) blocking.HOL blocking - when the number of parallel requests allowed by the browser runs out, subsequent requests have to wait for the previous request to complete.HTTP/2HTTP 2.0 was released in 2015. It solved the HOL problem through request multiplexing, eliminating HOL blocking at the application layer, but HOL still exists at the transport (TCP) layer.As shown in the figure, HTTP 2.0 introduced the concept of HTTP “streams”: an abstraction that allows multiplexing of different HTTP exchanges over the same TCP connection.

Each stream does not need to be sent sequentially. Application Scenario: Large Web Sites: The multiplexing feature of HTTP/2 allows multiple requests to share a single connection, avoiding the queue header blocking problem of HTTP/1.1. This is ideal for complex web pages that need to load a large number of resources (e.g., images, scripts, stylesheets, etc.).

CDN: HTTP/2's header compression and binary format significantly reduces the amount of data and improves data transfer efficiency. More efficient connection reuse gives CDNs better performance when transferring large files or streaming content. Mobile applications: HTTP/2 significantly reduces network latency on mobile devices, making it suitable for mobile applications and API requests that require fast responses.HTTP/3The first draft of HTTP 3.0 was released in 2020.

It is the successor to HTTP 2.0. It uses QUIC as the underlying transport protocol instead of TCP, thus eliminating HOL blocking in the transport layer.QUIC is based on UDP.

It introduces streams as first-class citizens to the transport layer.QUIC streams share the same QUIC connection, so there is no need for additional handshaking and slow starts to create new QUIC streams, but QUIC streams are transport-independent, so a packet loss that affects one stream won't affect other streams in most cases.QUIC is the first version of HTTP 2.0 to use TCP as the underlying transport protocol, thus eliminating HOL blocking in the transport layer.

Application Scenarios: Real-time Applications and Gaming: HTTP/3's fast handshake and low latency make it ideal for applications that require real-time data transfer, such as online gaming, video conferencing, and real-time streaming media. Today's web applications: Because HTTP/3 offers more efficient connection management and a better user experience, it is a better choice for modern web applications and service providers, such as those using SPAs (Single Page Applications) and frequent small data requests. Services with high security requirements: The QUIC protocol comes with encryption and simplifies the TLS handshake, making HTTP/3 a good fit for services that require fast, secure connection establishment.