Subject: HTTP/2.0 negotiation latency Re: Mandatory encryption

From: Brian Pane <[email-masked]>
Date: Wed, 18 Jul 2012 10:52:40 -0700

On Wednesday, July 18, 2012, Roberto Peon wrote:

> #1 isn't obvious one way or another. For the first request TLS potentially
> harms latency as compared to http/1.1. For subsequent requests it comes out
> as better (given application protocol changes). More interestingly,
> negotiating http/2 over port 80 will require a round trip, which is the
> same latency penalty one will pay for using TLS at a site that you have
> recently visited assuming we use false-start.
>

This is a point that I think is worth highlighting: if browsers use the
presence of the NPN extension in the ServerHello to determine whether the
server can handle false start, the result is that the latency for
TCP+TLS+NPN is no greater than that of TCP+HTTP Upgrade.

I believe that's what the latest version of Chrome does.

I think it would be useful for the NPN spec to say something like, "If a
server does not support False Start, it MUST NOT send the NPN protocol list
extension." That would elevate Chrome's current heuristic to a standard.

-Brian