HTTP/2 vs. HTTP/3

HTTP/3 is the third major version of the HTTP (Hypertext Transfer Protocol) network protocol used to exchange data on the World Wide Web. It is based on a new transport protocol called QUIC (Quick UDP Internet Connections), a multiplexed and secure transport layer over UDP (User Datagram Protocol).

HTTP/2, on the other hand, is the second major version of HTTP and was designed to improve the performance of the Web by enabling the efficient use of network resources. It introduces several new features, including multiplexing (allowing multiple requests to be sent over the same connection), header compression, and server push (allowing the server to send data to the client proactively).

Some of the main differences between HTTP/2 and HTTP/3 are:

HTTP/3 is based on QUIC, a new transport protocol, while HTTP/2 is based on TCP (Transmission Control Protocol).
HTTP/3 has improved performance and security compared to HTTP/2 due to QUIC and its built-in encryption.
HTTP/3 introduces a new header compression algorithm called QPACK, which is more efficient than the header compression algorithm used in –HTTP/2 (HPACK).
HTTP/3 supports multiplexing and server push, similar to HTTP/2.
HTTP/3 is not backward compatible with HTTP/2, which means that a client that supports HTTP/3 can only communicate with a server that also supports HTTP/3.

QUIC

QUIC (Quick UDP Internet Connections) is a multiplexed and secure transport layer protocol over UDP (User Datagram Protocol) developed by Google. It is designed to improve the performance of the Web by reducing the latency and connection setup time of HTTP (Hypertext Transfer Protocol) requests.

QUIC is similar to TCP (Transmission Control Protocol) in many ways. Both are used to establish a reliable end-to-end connection between two devices and ensure that data is delivered correctly. However, there are some key differences between the two protocols:

TCP is a connection-oriented protocol that establishes a full end-to-end connection between two devices before data can be transferred. QUIC is also connection-oriented, but it can establish a connection more quickly due to its use of UDP.
TCP uses a three-way handshake to establish a connection, which adds additional latency to the connection setup process. QUIC uses a different connection establishment process that is faster and more efficient.
TCP is a stream-oriented protocol, which means that data is delivered as a continuous stream of bytes. QUIC is also stream-oriented, but it introduces the concept of streams, which allow multiple independent streams of data to be multiplexed over the same connection.
TCP uses sequence numbers to ensure that data is delivered in the correct order. QUIC uses packet numbering and an acknowledgment mechanism similar to TCP, but it also includes additional mechanisms to ensure that data is delivered correctly and efficiently.
TCP includes built-in congestion control mechanisms to prevent the network from becoming overloaded. QUIC also includes congestion control mechanisms, but they are more advanced and efficient than TCP ones.
QUIC includes built-in encryption, which makes it more secure than TCP.

QPACK Compression

QPACK (QUIC Protocol for HTTP/3 Header Compression) is a header compression algorithm designed for use with HTTP/3 (Hypertext Transfer Protocol version 3), which is based on the QUIC (Quick UDP Internet Connections) transport protocol. It is designed to reduce the size of HTTP header fields, which can be particularly large for certain types of Web traffic, such as Web APIs or Web push notifications.

HTTP headers contain metadata about a Web request or response, such as the type of content being transferred, the server software, the cookies, and other information. In HTTP/2 and earlier versions of HTTP, header compression was achieved using the HPACK (HTTP/2 Protocol for Header Compression) algorithm, which used a combination of static and dynamic tables to compress the headers.

QPACK is an improvement over HPACK in several ways:

QPACK is more efficient than HPACK, resulting in smaller header sizes and less network bandwidth usage.
QPACK is designed to work better with the multiplexing and server push features of HTTP/3, which allow multiple requests and responses to be sent over the same connection simultaneously.
QPACK is designed to be more resilient to attacks, such as header injection attacks, that can be used to exploit vulnerabilities in the header compression algorithm.
QPACK is designed to be more flexible and extensible, allowing it to be extended to support new types of headers or other features in the future.

Multiplexing

HTTP/3 multiplexing is a feature that allows multiple HTTP requests and responses to be sent over the same connection simultaneously. This is achieved using a new transport protocol called QUIC (Quick UDP Internet Connections), which is based on UDP (User Datagram Protocol) and includes a multiplexing layer that allows multiple streams of data to be multiplexed over the same connection.

Multiplexing allows a client to send multiple requests to the server concurrently rather than waiting for each request to complete before sending the next one. This can improve the performance of the Web by reducing the latency of requests and allowing the client to make more efficient use of network resources.

Here are some key differences between HTTP/2 Multiplexing and HTTP/3 Multiplexing:

HTTP/2 Multiplexing:

Uses a traditional TCP connection
Can improve performance by allowing multiple requests to be sent over a single connection in parallel
May still suffer from head-of-line blocking, where the processing of one request blocks the processing of subsequent requests on the same connection

HTTP/3 Multiplexing:

Uses the QUIC protocol, which provides multiplexing and security similar to TLS
Can improve performance by allowing multiple requests to be sent over a single connection in parallel, with reduced connection establishment time
Can provide better performance in high latency or frequently interrupted connections
It may not be supported by all servers and clients yet, as it is a relatively new protocol.

Server Push

HTTP/3 server push is a feature that allows the server to proactively send data to the client without waiting for a request. This can reduce the number of round-trips required to load a webpage by allowing the server to send resources that the client will likely need preemptively.

For example, when a client requests a webpage, the server can use server push to send the HTML, CSS, and JavaScript resources that the client will need to render the page rather than waiting for the client to request each resource individually. This can reduce the time it takes to load the page and improve the user experience.

Server push is similar to HTTP/2 server push, but it is more efficient due to the multiplexing and header compression features of HTTP/3.

The server can push multiple resources to the client in a single push
The client can choose to accept or reject pushed resources
Pushed resources are associated with a specific request and are automatically discarded if the associated request is canceled or terminated
Pushed resources are cached by the client and can be used to satisfy subsequent requests without having to send additional requests to the server
HTTP/3 Server Push can improve performance by reducing the number of round trips between the client and server and by allowing the client to start downloading resources before it knows it needs them proactively

Encryption

HTTP/3 (Hypertext Transfer Protocol version 3) includes built-in encryption using a new transport protocol called QUIC (Quick UDP Internet Connections). Some of the main features of HTTP/3 encryption are:

Strong encryption: HTTP/3 uses the same encryption algorithms as TLS (Transport Layer Security), the standard encryption protocol for secure Web communication. The specific encryption algorithms and cipher suites used by HTTP/3 can be negotiated during the connection setup process.
Negotiable encryption: HTTP/3 supports a variety of encryption algorithms and cipher suites, allowing the client and server to negotiate the most appropriate encryption scheme for their needs. This allows HTTP/3 to be used in various environments and use cases.
Resilient to attacks: HTTP/3 is designed to resist attacks that can compromise the connection’s security, such as man-in-the-middle attacks and attacks on the encryption algorithms themselves.
Efficient: HTTP/3 is designed to be fast and efficient, with minimal overhead and impact on performance. Encryption is an important part of this design to provide strong encryption without sacrificing performance.
Flexible: HTTP/3 is designed to be flexible and extensible, allowing it to be easily extended to support new encryption algorithms or other security features in the future.
Compatible with TLS: HTTP/3 is compatible with TLS (Transport Layer Security), which means that it can be used with existing Web infrastructure and applications that use TLS for encryption.

How will HTTP/3 Evolve

It is difficult to predict exactly how HTTP/3 will evolve, as the development of the protocol is driven by the needs of the Web community and the technical capabilities of the underlying transport protocols and infrastructure. However, HTTP/3 will likely continue to evolve and improve as the protocol matures and more experience is gained with its use.

Some of the areas where HTTP/3 is likely to evolve include:

Performance: HTTP/3 is already designed to be faster and more efficient than HTTP/2, but there is always room for improvement. Future versions of HTTP/3 may introduce additional features and enhancements to improve performance further and reduce latency.
Security: HTTP/3 includes built-in encryption using the same algorithms as TLS (Transport Layer Security), but security is an ongoing concern on the Web. Future versions of HTTP/3 may introduce additional security features or improvements to the encryption algorithms to make the protocol more secure.
Compatibility: HTTP/3 is not backward compatible with HTTP/2, which means that a client supporting HTTP/3 can only communicate with a server supporting HTTP/3. However, HTTP/3 is compatible with TLS, which means it can be used with existing Web infrastructure and applications that use TLS for encryption. Future versions of HTTP/3 may introduce additional compatibility features to make using the protocol with a wider range of Web applications and services easier.
New use cases: HTTP/3 is designed to support a wide range of Web traffic and use cases, but there may be new types of Web traffic or applications that emerge in the future that require additional features or capabilities. Future versions of HTTP/3 may introduce new features or enhancements to support these use cases.

It is not yet clear what the next major HTTP version will be after HTTP/3. It is possible that HTTP/3 will become the standard protocol for the Web and that no further major versions will be necessary. Alternatively, there may be a need for a new version of HTTP to address new requirements or challenges that arise on the Web.