Version and Extension Negotiation (#295)

Fixes #265

Author: ianswett

draft-ietf-moq-transport.md

@@ -350,6 +350,30 @@ PATH parameter ({{path}}) which is sent in the SETUP message at the
 start of the session.  The ALPN value {{!RFC7301}} used by the protocol
 is `moq-00`.
 
+## Version and Extension Negotiation {#version-negotiation}
+
+Endpoints use the exchange of SETUP messages to negotiate the MOQT version and
+any extensions to use.
+
+The client indicates the MOQT versions it supports in its SETUP message (see
+{{message-setup}}). It also includes the union of all Setup Parameters
+{{setup-params}} required for a handshake by any of those versions.
+
+Within any MOQT version, clients request the use of extensions by adding SETUP
+parameters corresponding to that extension. No extensions are defined in this
+document.
+
+The server replies with a SETUP message that indicates the chosen version,
+includes all parameters required for a handshake in that version, and parameters
+for every extension requested by the client that it supports.
+
+New versions of MOQT MUST specify which existing extensions can be used with
+that version. New extensions MUST specify the existing versions with which they
+can be used.
+
+If a given parameter carries the same information in multiple versions,
+but might have different optimal values in those versions, there SHOULD be
+separate SETUP parameters for that information in each version.
 
 ## Session initialization {#session-init}