超文本传输协议版本 2

IETF HTTP2草案(draft-ietf-httpbis-http2-13)

摘要

本规范描述了一种优化的超文本传输协议(HTTP)。HTTP/2通过引进报头字段压缩以及多路复用来更有效利用网络资源、减少感知延迟。另外还介绍了服务器推送规范。

本文档保持对HTTP/1.1的后向兼容，HTTP的现有的语义保持不变。

1 介绍

The Hypertext Transfer Protocol (HTTP) is a wildly successful protocol. However, the HTTP/1.1 message format ([RFC7230], Section 3) was designed to be implemented with the tools at hand in the 1990s, not modern Web application performance. As such it has several characteristics that have a negative overall effect on application performance today.

超文本传输协议（HTTP）是一个非常成功的协议。但是HTTP/1.1 是针对90年代的情况而不是现代web应用的性能而设计的，导致它的一些特点已经对现代应用程序的性能产生负面影响。

In particular, HTTP/1.0 only allows one request to be outstanding at a time on a given connection. HTTP/1.1 pipelining only partially addressed request concurrency and suffers from head-of-line blocking. Therefore, clients that need to make many requests typically use multiple connections to a server in order to reduce latency.

特别是，HTTP/1.0只允许在一个连接上建立一个当前未完成的请求。HTTP/1.1管道只部分处理了请求并发和报头阻塞的问题。因此客户端需要发起多次请求通过数次连接服务器来减少延迟。

Furthermore, HTTP/1.1 header fields are often repetitive and verbose, which, in addition to generating more or larger network packets, can cause the small initial TCP [TCP] congestion window to quickly fill. This can result in excessive latency when multiple requests are made on a single new TCP connection.

此外，HTTP/1.1的报头字段经常重复和冗长。在产生更多或更大的网络数据包时，可能导致小的初始TCP堵塞窗口被快速填充。这可能在多个请求建立在一个新的TCP连接时导致过度的延迟。

This specification addresses these issues by defining an optimized mapping of HTTP's semantics to an underlying connection. Specifically, it allows interleaving of request and response messages on the same connection and uses an efficient coding for HTTP header fields. It also allows prioritization of requests, letting more important requests complete more quickly, further improving performance.

本协议通过定义一个优化的基础连接的HTTP语义映射来解决这些问题。具体地，它允许在同一连接上交错地建立请求和响应消息，并使用高效率编码的HTTP报头字段。它还允许请求的优先级，让更多的重要的请求更快速的完成，进一步提升了性能。

The resulting protocol is designed to be more friendly to the network, because fewer TCP connections can be used in comparison to HTTP/1.x. This means less competition with other flows, and longer-lived connections, which in turn leads to better utilization of available network capacity.

最终协议设计为对网络更友好，因为它相对HTTP/1.x减少了TCP连接。这意味着与其他流更少的竞争以及更长时间的连接,

从而更有效地利用可用的网络容量。

Finally, this encapsulation also enables more efficient processing of messages through use of binary message framing.

最后，这种封装也通过使用二进制消息帧使信息处理更具扩展性。

2 HTTP / 2协议概述