Start fleshing out voip module

specification/1-client_server_api.rst

@@ -427,6 +427,8 @@ the complete dataset is provided in "chunk".
 Events
 ------
 
+.. _sect:events:
+
 Overview
 ~~~~~~~~
 

specification/modules/voip_events.rst

@@ -1,17 +1,18 @@
 Voice over IP
--------------
-Matrix can also be used to set up VoIP calls. This is part of the core
-specification, although is at a relatively early stage. Voice (and video) over
-Matrix is built on the WebRTC 1.0 standard. Call events are sent to a room, like
-any other event. This means that clients must only send call events to rooms
-with exactly two participants as currently the WebRTC standard is based around
-two-party communication.
+=============
 
-{{voip_events}}
+This module outlines how two users in a room can set up a Voice over IP (VoIP)
+call to each other. Voice and video calls are built upon the WebRTC 1.0 standard.
+Call signalling is achieved by sending `message events`_ to the room. As a result,
+this means that clients MUST only send call events to rooms with exactly two
+participants as currently the WebRTC standard is based around two-party
+communication.
+
+.. _message events: `sect:events`_
 
 Message Exchange
-~~~~~~~~~~~~~~~~
-A call is set up with messages exchanged as follows:
+----------------
+A call is set up with message events exchanged as follows:
 
 ::
 
@@ -38,28 +39,57 @@ Or a rejected call:
 
 Calls are negotiated according to the WebRTC specification.
 
+Events
+------
+
+{{voip_events}}
+
+Client behaviour
+----------------
 
 Glare
 ~~~~~
-This specification aims to address the problem of two users calling each other
-at roughly the same time and their invites crossing on the wire. It is a far
-better experience for the users if their calls are connected if it is clear
-that their intention is to set up a call with one another. In Matrix, calls are
-to rooms rather than users (even if those rooms may only contain one other user)
-so we consider calls which are to the same room. The rules for dealing with such
-a situation are as follows:
 
- - If an invite to a room is received whilst the client is preparing to send an
-   invite to the same room, the client should cancel its outgoing call and
-   instead automatically accept the incoming call on behalf of the user.
- - If an invite to a room is received after the client has sent an invite to
-   the same room and is waiting for a response, the client should perform a
-   lexicographical comparison of the call IDs of the two calls and use the
-   lesser of the two calls, aborting the greater. If the incoming call is the
-   lesser, the client should accept this call on behalf of the user.
+"Glare" is a problem which occurs when two users call each other at roughly the
+same time. This results in the call failing to set up as there already is an
+incoming/outgoing call. A glare resolution algorithm can be used to determine
+which call to hangup and which call to answer. If both clients implement the
+same algorithm then they will both select the same call and the call will be
+successfully connected.
+
+
+As calls are "placed" to rooms rather than users, the glare resolution algorithm
+outlined below is only considered for calls which are to the same room. The
+algorithm is as follows:
+
+ - If an invite to a room is received whilst the client is **preparing to send**
+   an invite to the same room:
+
+    * the client should cancel its outgoing call and instead
+      automatically accept the incoming call on behalf of the user.
+
+ - If an invite to a room is received **after the client has sent** an invite to
+   the same room and is waiting for a response:
+
+    * the client should perform a lexicographical comparison of the call IDs of
+      the two calls and use the **lesser** of the two calls, aborting the
+      greater. If the incoming call is the lesser, the client should accept
+      this call on behalf of the user.
+
 
 The call setup should appear seamless to the user as if they had simply placed
-a call and the other party had accepted. Thusly, any media stream that had been
+a call and the other party had accepted. This means any media stream that had been
 setup for use on a call should be transferred and used for the call that
 replaces it.
 
+Server behaviour
+----------------
+
+TURN Servers
+~~~~~~~~~~~~
+
+Security considerations
+-----------------------
+
+
+