Re: [TLS] Questions about ALPN

[Martin Thomson <[e-mail]>]

On 9 April 2014 12:40, Andrei Popov <[e-mail]> wrote:
> things like "HTTP/2 over TLS" and "HTTP/2 over TCP" aren't IDs of individual protocols because they describe entire stacks of protocols

A protocol that is layered on another protocol includes all the
properties of that protocol in the same way that I gain all the
advantages (and disadvantages) of a library when I link to it.  But
that protocol presents a new API that completely subsumes the included
protocol.  To the users of that protocol, they see HTTP/2 (over TCP,
over IP, over 1Gb Ethernet, over copper) and that is similar, but
necessarily different to HTTP/2 (over TLS, over TCP, etc...).
Therefore they can - and should - be identified differently.

It might be that we use a single identifier to refer to things that
are, in all the aspects we care about, identical.  That's called
generalization, and it might not always be appropriate.

The idea that X over Y and X over Z might be nice in theory, but it's
rare that this abstraction isn't leaky at some level.  There are cases
that we might not care to distinguish between, particularly below the
IP layer, but even there the effects can be visible.  We just pretend
really hard that we're properly insulated by all those layers.  Better
to call X over Y = X1 and X over Z = X2 and avoid the confusion issue.